Technology guide

Heat recovery

A guide to key systems and applications Contents

Introduction 3 Heat recovery applications: Check the heat recovery application ventilation 29 charts for your type of heat recovery Balancing the increased need for ventilation with energy savings measures Heat recovery: the basics 8 How to identify waste heat, discover Heat recovery applications: where it is coming from and measure its use industrial processes 42 An initial guide to identifying waste transfer techniques Heat recovery applications: boilers 12 Next steps 55 Types of boilers, how they work and how How to take your heat recovery plans further you can capture wasted energy

Heat recovery applications: refrigeration 22 How to rearrange your refrigeration circuits to recover lost heat

Technology guide 3

Introduction This guide can provide you with an appreciation of heat recovery and how it can be applied to the various systems and processes carried out in your building.

Menu This guide is intended for anyone who has How to use this guide The application of heat responsibility for the efficient and cost-effective This guide will help you understand the recovery techniques operation of buildings, or those who use an basic principles of heat recovery as well industrial process where heat might be can significantly reduce as some of the common terminology. unnecessarily wasted. energy consumption, running The main part of this guide is divided into The application of heat recovery techniques sections which reflect the key applications costs and carbon emissions can significantly reduce energy consumption, for heat recovery in buildings. running costs and carbon emissions. These techniques can be applied in isolation, but You‘ll find some useful tables on the next few would be better as part of an overall strategy pages to help you decide which types of heat to reduce energy, cost and carbon. recovery application might be of interest to you. It may also be useful for you to complete the heat recovery checklist alongside this guide so that you can focus on the areas that are most specific to you. Technology guide 4

Heat recovery application chart by building type

Use this chart to determine which technologies and applications are most applicable to you, either by the type of building you have or the systems you have installed.

Building type Waste heat source and applications for heat recovery

Systems installed Boilers (steam or hot Refrigeration Ventilation systems Industrial Menu water) (cooling plant) processes

late heat late ow-grade heat heat ow-grade exchanger or recuperator Run around coil Flue economisers Pre-heat combustion air Blowdown on steam boilers High-grade heat recovery using a de-superheater L wheelThermal P pumps Heat Heat pipes Low- temperature processes High- temperature processes recovery from condenserthe

Page 14 17 19 25 27 32 34 38 35 39 45 50

Airport ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆

Courts ◆ ◆ ◆ ◆ ◆ ◆

Food and drink ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆

Distribution – warehouses ◆ ◆ ◆

Dwellings ◆

Education ◆ ◆ ◆ ◆ ◆

Emergency services ◆ ◆ ◆ ◆

Hospital/healthcare ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆

Hospitality – hotel ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ Technology guide 5

Building type Waste heat source and applications for heat recovery

Systems installed Boilers (steam or hot Refrigeration Ventilation systems Industrial water) (cooling plant) processes

late heat late Menu heat ow-grade exchanger or recuperator Run around coil Flue economisers Pre-heat combustion air Blowdown on steam boilers High-grade heat recovery using a de-superheater L wheelThermal P pumps Heat Heat pipes Low- temperature processes High- temperature processes recovery from condenserthe

Page 14 17 19 25 27 32 34 38 35 39 45 50

Hospitality – catering ◆ ◆ ◆ ◆ ◆ ◆

Industrial manufacturing ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆

Laboratory ◆ ◆ ◆ ◆ ◆ ◆ ◆

Laundry ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆

Sport and leisure ◆ ◆ ◆ ◆ ◆ ◆ ◆

Library/museum ◆ ◆ ◆ ◆ ◆

Office ◆ ◆ ◆ ◆ ◆ ◆ ◆

Pharmaceutical ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ manufacturing

Retail ◆ ◆ ◆ ◆ ◆ ◆

Swimming pool ◆ ◆ ◆ ◆ ◆ ◆ ◆

Textiles ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆

Waste ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ ◆ Technology guide 6

Heat recovery application chart by process type

Use this chart to inform discussions about which technologies and applications might be appropriate to you, either by the type of processes you undertake or the systems you have installed.

Processes on the site Potential heat recovery approaches

Potential heat recovery approaches

Menu

Page se of steam from condensers from Air-to-air exchanger Liquid-to-liquid exchanger of hot air U blowdown captured Heat during phase change Heat recovery Gas vapour) (or -to-liquid heat exchanger Direct ducting Boilers used for space heating 15 & 17 ◆ ◆

Boilers used for domestic water heating 15 & 17 ◆ ◆

Cold rooms 25 & 27 ◆ ◆

Chilled water systems 25 & 27 ◆ ◆

Space or process refrigeration 25 & 27 ◆ ◆

Supply and extract ventilation systems 32 & 51 ◆

Air compressors 45 ◆ ◆

Distillation processes 45 ◆

Drying processes 45 ◆ ◆ Technology guide 7

Processes on the site Potential heat recovery approaches

Potential heat recovery approaches

Page se of steam Gas vapour) (or -to-liquid heat exchanger Direct ducting of hot air U blowdown captured Heat during phase change Heat recovery condensers from Air-to-air exchanger Liquid-to-liquid exchanger

Menu Dyeing and finishing processes 46 ◆

Evaporation to create concentrates 47 ◆ ◆

Systems creating mechanical energy 47 ◆ ◆ ◆ ◆

Industrial scale ovens for food processing 48 ◆ ◆

Dairy pasteurisation and sterilisation 49 ◆

Cooling of primary processes 49 ◆ ◆ ◆ ◆

Large-scale laundering or other washing 49 ◆ ◆

Use of furnaces 50 ◆ ◆ ◆ Technology guide 8

Heat recovery: the basics Heat recovery is a method of reducing the overall energy consumption of your site and therefore reducing the running costs. Recovered heat can help you reduce energy consumption or provide useful heat for other purposes.

Menu Definition of heat recovery Glossary HVAC Heating, ventilation and air conditioning systems as found in buildings. Heat recovery in the context of buildings and Air handling unit or AHU A mechanical their services can be defined as the collection device typically used to supply or extract Latent heat The heat released or absorbed by and re-use of heat arising from a process that air from a space within a building. a substance during a change of state (or phase) would otherwise be lost. that occurs without a change in temperature. CHP A combined heat and power machine In most processes, some of the energy used will where waste heat from the process of Liquid One of the three basic states of matter. be lost as heat. Sometimes, the loss of this heat generating electricity is used for some other The density of a liquid is relatively stable and is intentional, such as in air conditioning, where purpose (such as raising steam) within the is close to that of a solid and much higher than the purpose of the system in cooling mode is same machine. a gas. Due to its closeness in density to solids, to remove heat from a space. In other instances, both are known as condensed matter. Fluid Any substance in either a liquid or the loss is either incidental, such as the heat lost gas state. LPG A fossil fuel – liquid petroleum gas. by a compressed air system, or accidental, such as heat lost through the fabric of the building. Heat recovery The collection and re-use of heat LTHW Low-temperature hot water. from a process that would otherwise be lost. Most buildings using energy for heating, cooling, MTHW Medium-temperature hot water. ventilation or any sort of industrial process have Heat sink A process where waste heat from Phase or state change Where a substance the potential to benefit from the application of a heat source can be usefully put to work. changes from a solid to a liquid or a liquid to a heat recovery devices and systems. Heat source The place or the environment gas (or vice versa) usually through the application from where heat is obtained. or withdrawal of heat and/or pressure. Technology guide 9

Recuperator A device for waste heat recovery The basic concept of Air in the office will continue to heat up due to that works by counter-flowing hot gases and heat recovery the warming effects of the people in the space cold air through a heat exchanger. as well as the equipment being used (such as Without heat recovery computers, photocopiers or printers). The levels Regenerator A cyclic heat storage device of carbon dioxide will also increase as people which continuously stores and releases energy. In this example building without heat recovery, breathe the air. energy is used to heat incoming air which would Sensible heat The energy exchanged during otherwise be too cold to supply directly to an The hot, stale air is removed from the space by a process that has as its sole effect a change office. The heat is typically supplied by the boiler an extract ventilation system, which discharges Menu of temperature. via a heating coil in the air handling unit. it directly outside along with the heat it contains. Vapour or gas One of the three basic states of matter. Gases fill the entire volume of Figure 1 Typical office ventilation system without heat recovery wherever they are contained and, like liquids, have the ability to flow. Both liquids and gases are therefore known as fluid matter. Bolier Waste heat Heat which is a by-product of a process or operation which is not captured or recovered and is therefore not re-used in a secondary system. Supply Cool air in

Heat added to incoming air

Extract Hot air out (heat wasted) Technology guide 10

With heat recovery heat needs to be added by the boiler before The recovery efficiency the air is supplied to the space. In our example building a cross flow heat of this type of system exchanger has been added to the system. The recovery efficiency of this type of system is typically between When the cool fresh air is drawn into the is typically between 55% and 65%. Some heat system it passes over a series of pipes which recovery devices can be much more efficient 55% and 65% contain the hot outgoing exhaust air. Some of depending on the temperature and nature of the heat from the exhaust air is transferred to the waste heat. the cool incoming air, which means that less Menu

Figure 2 Typical office ventilation system with a plate heat exchanger added for heat recovery Bolier

Heat recovered from exhaust air

Supply Warm air out (less heat wasted)

Less heat added to incoming air

Extract Cool air in Technology guide 11

Sources of waste heat Uses for recovered heat

You’re likely to have sources of ‘waste’ heat The most cost-effective use of waste heat in your building, for example, from the heating is to improve the energy efficiency of the heat or ventilation systems in an office, or the generating process itself. Common uses industrial drying process or compressed air (or ‘sinks’) for recovered heat include: system in a factory. • pre-heating of combustion air for boilers, The following common sources of waste heat ovens, furnaces, and so on Menu often present opportunities for cost-effective • preheating fresh air used to ventilate the heat recovery: building • ventilation system extracts • hot water generation, including pre-heating • boiler flue gases of boiler feed water

• boiler blowdown • space heating

• air compressors • drying

• refrigeration plant • other industrial process heating/pre-heating

• high-temperature exhaust gas streams • power generation. from furnaces, kilns, ovens and dryers

• hot liquid effluents

• power generation plant

• process plant cooling systems. Technology guide 12

Heat recovery applications: boilers A boiler is a device that converts the chemical energy of a fuel into a useful heat output, such as steam or hot water.

Menu Principles of operation The shell type, where the hot combustion gases Where is heat wasted? pass down a tube and into subsequent bundles In the UK, the most common fuel for boilers is The operational efficiency of a boiler is of tubes immersed below water level where heat natural gas. However, where there is no mains measured by the percentage of the fuel input is transferred. Most steam and hot water boilers gas network, or the network infrastructure is energy that is eventually delivered as useful in the UK are derivatives of the shell type, which poor, oil, LPG and, in some cases, coal-fired heat output. Not all of the heat released when are also referred to as ‘fire tubes’. boilers are used. There is also a relatively small the fuel is combusted can be used; some number of biofuel-fired (biomass, biogas, and The water tube type, where the water is potential heat is never released due to so on) boilers in operation where there is good contained in tubes and the hot combustion gases incomplete combustion and some is lost. availability of fuel, and these continue to pass around them to transfer heat to the water. Major sources of heat loss from steam boilers increase in popularity. In either case, the heat must transfer across are through the flue gas, blowdown and radiation Inside a boiler, the fuel is combusted by flames the surface of the tubes containing the water to the boiler’s surroundings. For a shell type from burners. The resulting hot combustion or combustion gases. After use, the combustion steam boiler the losses are: gases transfer heat to water, which is fed into gases exit the boiler via a chimney known • Flue losses ~18% the boiler from an external source. as a flue. • Heat transfer gas and water side losses ~2% There are many different types of boiler design The output steam or hot water will be fed out and construction, but all boilers are derivatives of the boiler into a distribution system. This is • Insulated chamber radiation losses ~2% of two main types: a network of insulated pipes that transfer the • Water outlet blowdown losses ~3% steam or hot water to where it is used. Technology guide 13

This makes total losses of around 25%. Condensing boilers Tips for implementation The heat recovery options which follow can be used to reduce these total losses. Condensing boilers are highly efficient Installing boiler heat recovery systems because they already have a form of heat is a good way to reduce energy costs Where heat recovery is recovery built in. By capturing a large and carbon emissions. However, there appropriate proportion of the heat from hot flue are a few things you should look at before gases, they significantly reduce the you implement heat recovery. A qualified Boiler flue economisers are available for boiler amount of wasted heat. engineer will talk you through these Menu outputs as low as 100 kilowatts (kW) and in issues, but they will include: some cases even less. However, for boilers with This means that adding heat recovery an output rating of less than 150-200kW (the directly to a condensing boiler may not Controls Make sure the boiler controls are typical maximum size of packaged wall-hung be possible. However, it is likely that there set correctly. Running the boiler when it boilers) replacement with a fully condensing are other opportunities for heat recovery isn‘t needed or heating to overly high boiler should be considered before retro-fitting elsewhere in the system. temperatures are common problems a boiler flue economiser. leading to inefficiency.

Insulate Make sure the boiler, pipework Further references and any storage vessels are properly Low temperature hot water boilers insulated as this can be a major source technology overview (CTV008) of wasted heat.

Steam and high temperature hot water Maintain Ensure you have a regular boilers technology overview (CTV018) and thorough maintenance programme. If your equipment is running optimally How to implement blowdown heat recovery this will always help increase efficiency. (CTL020) Other energy saving techniques, such as the use of variable speed pumps, should also be investigated alongside heat recovery techniques. Technology guide 14

Figure 3 Boiler classification by temperature Heat recovery applications Type Temp °C Note Boiler flue economiser Page 14 Steam boiler >10 0 Water heated and allowed to vaporise Pre-heat combustion air using flue into steam gas heat or boiler house heat Page 17 High-temperature hot water >90 but <140 Water heated, pressurised and maintained Steam boiler blowdown Page 19 (HTHW) in liquid state

Menu Low-temperature hot water <90 Water heated and circulated at less than 90°C (LTHW)

Boiler flue economisers After the hot flue gas has passed through the Non-condensing boiler boiler it contains energy which can be used Gas-to-water heat exchange to pre-heat boiler Boiler flue economisers are a tried and tested to improve efficiency. To achieve this, the flue feed water to a steam boiler or to provide hot technology for recovering heat from flue gases. gas is passed through an economiser to capture water for other heating purposes. You can normally retro-fit an economiser to some of the heat. The captured heat can be most steam and high-temperature hot water Condensing boiler used in different ways to increase the efficiency boilers, and there are also opportunities to fit Gas-to-water heat exchange to pre-heat the of the boiler. The main applications are: economisers to conventional, non-condensing return water to a low temperature hot water heating boilers. heating boiler.

Non-condensing boiler Gas-to-air heat exchange to pre-heat the combustion air to a steam or hot water boiler.

Economisers are generally more financially viable when fitted to gas-fired boiler plant. Technology guide 15

Non-condensing gas-to-water excess of 100°C are possible – see page 20 for Condensing gas-to-water economiser some key tips on implementing heat recovery economiser on steam boilers.

Figure 4 Non-condensing gas-to-water The boiler water level controls should be of Figure 5 Condensing gas-to-water economiser fitted to boiler flue the ‘modulating’ type (ie not ‘on/off’) to ensure economiser fitted to boiler flue a continuous flow of feed water through the Heating Flue Flue heat exchanger. flow gases gases Menu Steam High-temperature hot water boilers Economiser Economiser Where an economiser is fitted to the flue of a high-temperature hot water boiler, the water Heating boiler circulated through the economiser can be used Fuel Steam for alternative heating purposes local to the Condense Boiler Fuel boiler boiler house such as space heating, domestic Heating feed return water hot water heating or pre-heating heavy fuel oil. In this type of economiser, the return water Benefits from the heating system is pumped through Steam boilers the heat exchanger tubes where it absorbs heat In steam boilers, the economiser is normally from the hot flue gases before being pumped Increase the net thermal efficiency a water jacket fitted around the flue stack. into the boiler, as shown in Figure 5. Less of your boiler by up to 5% by using The relatively cool boiler feed water is pumped energy is therefore required to heat the outgoing a non-condensing gas-to-water through the heat exchanger tubes, where it flow from the boiler. economiser or by up to 15% by using absorbs heat from the hot flue gas before being a condensing gas-to-water economiser. pumped into the boiler (see Figure 4). Less energy is therefore required to raise the steam. As the economiser is on the high-pressure side of the feed pump, feed water temperatures in Technology guide 16

Tips for implementation Case study A drinks manufacturer Consider these issues carefully when from the heating circuit is cool enough to implementing boiler flue economisers: gain the maximum benefit. For correct A global drinks manufacturer saved operation in hot water boilers this should • Ensure your economiser is the correct 4.1% on gas consumption due to installing be less than 50°C; for steam boilers this size. It is important to ensure that the flue a flue economiser when they upgraded will be closer to 90°C. gases are not condensed (changed from to a new steam boiler. The economiser Menu gas to liquid) and that the feed water does • The condensing type economiser is cost was 10.5% of the overall new budget not boil in the exchanger. normally installed at floor level, near and achieves payback in a little over to the boiler flue outlet. Therefore, you two years. • If you are installing an economiser which should consider how much floor space is designed to condense flue gases, you you will require in the boiler housing. should ensure that the water returning

Investment and payback

In an office with an annual energy spend If you’re replacing a boiler, consider buying on gas of around £15,000, an investment a condensing model as this already of £6,000 to £8,000 to retro-fit a boiler flue contains economiser technology, and the economiser could see a payback in four extra capital cost will pay back far more to five years. quickly than retrofitting. Technology guide 17

Pre-heating boiler combustion air The usual heat sources for heating combustion Boiler flue economiser air are: Boiler efficiencies can be improved by Ambient outside air is drawn through the boiler pre-heating the combustion air to the burner. • heat remaining in the flue gases flue economiser and ducted to the burner air You can do this by using a flue economiser or input. The burner-forced draught fan must be • higher temperature air drawn from the by making use of the warmer air from the top capable of overcoming the additional back top of the boiler house of the boiler house or around the boiler shell. pressure of the air ducting. • heat recovered by drawing air over or through In most boiler installations, the air required as the boiler casing to reduce shell losses. Menu part of the combustion process is generally Figure 6 Boiler flue economiser used taken from within the boiler room. In the case Energy saving potential of preheating to pre-heat boiler combustion air of a forced draught burner this is assisted by combustion air Flue a fan, but in a natural draught burner there is gases no assistance. This incoming combustion air Boiler efficiency can be increased by 1% by is at boiler room temperature, which is cooler raising the combustion air temperature by than boiler operating temperature. 20ºC, although the savings achieved will depend on the type of system installed. Boiler efficiency can be improved by pre-heating the incoming combustion air up to boiler operating temperature. This reduces the amount Benefits of boiler energy that becomes transferred to Burner the combustion air as it enters the system, You can increase boiler efficiency by Boiler Outside air and, as a result, provides a higher flame 1% by raising the combustion air Condense temperature from the burner. temperature by 20ºC. Ducting hot air Economiser down from the top of the boiler house into the boiler will typically provide savings of up to 1%, while drawing combustion air over or through the boiler casing can provide savings of up to 2%. Technology guide 18

Use warm air from boiler house Tips for implementation

Figure 7 Warm air ducted to boiler burner There are some key things to remember so you should ensure that there is to pre-heat boiler combustion air when considering increasing combustion sufficient space to allow for safe access for Flue air temperatures. ongoing maintenance to the plant. gases

Most gas and oil burners can only tolerate Using the heat remaining in the flue a maximum increase in combustion air gases can be expensive, so you might Menu temperature of around 50ºC and increases Warm air only consider using an economiser in of more than this without changing the this way if other uses are impractical. burner in your boiler may cause damage. This technique also requires a stainless- However, there are modern burners steel heat exchanger to be fitted in the that can stand much higher temperatures boiler-flue system. It is also necessary and can normally be retro-fitted to Burner Boiler to fit bypass dampers when firing fuel Outside air existing boilers. oil instead of natural gas, which will Each of the techniques described will add to the cost of implementation and Warm air from the top of the boiler house require additional space in the plant room increase payback times. is ducted down to the burner air input. The burner-forced draught fan must be capable of overcoming the additional back pressure of the air ducting. Investment and payback

Alternatively, air can be drawn through the Adding simple ducting to bring hot air boiler casing but this may involve modifications from the top of the boiler house onto the to the manufacturers’ casing. burner using the existing fan in a typical office of around 250 people could cost as little as £1,000 and give a payback of around five years. Technology guide 19

Steam boiler blowdown Figure 8 Schematic of a steam boiler blowdown heat recovery system heat recovery

You can improve both energy and water treatment efficiency by recovering flash steam and residual heat from blowdown and achieve a payback of less than five years.

When water is converted to steam in a boiler it Menu leaves behind suspended solids and dissolved salts, or Total Dissolved Solids (TDS). Over time, the remaining water contains an increasing concentration of TDS and, if left unchecked, will eventually lead to crystallisation of the salts on the surfaces it comes into contact with. In turn, this will lead to the fouling of heat transfer surfaces and a general build-up of solids in the base of the boiler.

Controlling the quantity of TDS is an integral part of maintaining an efficient steam boiler system and is achieved by removing steam with high concentrations of TDS (blowdown) and replacing it with make-up water with lower Image courtesy of Spirax Sarvo Ltd TDS levels. This process reduces the TDS content in the boiler water and the likelihood of scaling. The blowdown process can be controlled manually or automatically and the regime can be intermittent or continuous, or a combination of both. Technology guide 20

Before discharging the blowdown water to Recovery of flash steam drain, it must be cooled to below 43ºC to comply Benefits Passing blowdown water through a flash with trade effluent consent conditions. This vessel generates low-pressure steam. The flash temperature reduction is achieved by diluting Heat recovery can reduce blowdown steam that separates as the pressure is reduced the blowdown water with cold water. energy losses by up to 50%, to give an downstream of the boiler blowdown valve can energy saving of 0.5% to 2.5% of heat The main disadvantage of blowdown is that then be collected and re-used for feed tank input in a boiler plant. Heat recovery from typically 1% to 5% of the energy input to the heating or other uses. This system of heat the remaining blowdown water can boiler is lost. However, up to 80% of the heat recovery is suitable for plants with continuous further reduce blowdown energy losses Menu in the boiler blowdown water can be recovered. blowdown systems. by up to 25%, providing a total energy Implementing heat recovery saves energy by saving of 0.75% to 3.75% of heat input. Energy saving potential from increasing the temperature of the feed water blowdown heat recovery to the boiler and reducing the amount of fuel consumed in the boiler. Blowdown heat recovery systems can potentially be used with any steam boiler, but Heat recovery can reduce are unlikely to be cost-effective on boilers below blowdown energy losses 1,000kW. As a guide, they work best when blowdown is carried out on a continuous basis, by up to 50% rather than intermittently. Continuous blowdown means you can install a much smaller heat recovery system for the same benefit. Technology guide 21

Tips for implementation Investment and payback

Before thinking about heat recovery ensure As a minimum, feed water should be Costs of implementing steam boiler heat you have a robust TDS regime in place. raised to temperatures over 85°C to recovery can range from £6,000 to If levels are too high, water carryover may minimise the oxygen content, but care £10,000, but in most situations would be result due to ‘priming’ and water may enter must be taken to avoid damage to pumps expected to pay back in around two years. the steam system, degrading the quality through cavitation. Cavitation is the of steam produced. formation and immediate implosion of Menu bubbles when water is subjected to a rapid Because there may be high levels of change in pressure in the pump. The TDS in the fluid passing through the heat continuous implosion of the bubbles on recovery equipment is it prudent to select pump surface can cause excessive wear equipment that can handle large quantities and in extreme cases failure of the pump. of contaminants to avoid fouling and similar issues. The Combustion Engineering Association (www.cea.org.uk) may be able to help you Heat can be recovered from both the steam find a steam boiler heat recovery specialist. and water stream, which is released from the system during continuous blowdown by using a two-stage process. Technology guide 22

Heat recovery applications: refrigeration Refrigeration is a process where heat is moved from one location to another.

Menu There are many applications for refrigeration, Principles of operation Where heat is wasted most commonly to provide cooling in refrigerators, The most common type of refrigeration system Refrigerant is circulated around the system freezers and cold stores. Refrigeration is also uses the vapour-compression refrigeration cycle, and is subjected to differing pressures and commonly used for cooling and heating in air which is sometimes referred to as a direct temperatures. At different times, the refrigerant conditioning systems. Large central systems expansion (DX) system. This type of system varies between vapour and liquid state, are used to provide cooling to a number of comprises the following essential components: depending on where it is in the cycle. appliances or pieces of equipment in commercial applications such as supermarkets and in • a compressor (with motor drive) The refrigerant enters the compressor as a industrial applications. vapour where it is then compressed, which • a condenser (heat exchanger) increases the pressure and temperature. The • an expansion device (usually an expansion vapour passes into the condenser, where heat valve) is rejected and the refrigerant cools. As it cools, it changes from a vapour to a liquid. • an evaporator (heat exchanger). The pressure of the refrigerant is reduced by These components are connected together with passing through an expansion device before pipework and arranged as indicated in Figure 9 it enters the evaporator. In the evaporator the on the next page. refrigerant evaporates (boils) to a vapour state, absorbing heat from the surroundings and therefore providing cooling. Technology guide 23

Figure 9 Refrigeration circuit – vapour compression system Heat recovery applications

Heat evaporation High-grade heat recovery using a de-superheater Page 25

Low-grade heat recovery Condenser from condensers Page 27

Menu Expansion valve

Evaporator

Compressor Cooling

About 20% of the heat rejection is due to Further references ‘de-superheating’ of the refrigerant prior to Refrigeration systems technology guide condensation and this heat has the potential (CTG046) to be recovered as ‘high-grade’ heat for other heating purposes. This is described on page 25.

The remainder of the heat rejection from the condenser can also be recovered and used as ‘low-grade’ heat as described on page 27. Technology guide 24

Tips for implementation Investment and payback

There are some general tips to consider room (such as a server room or cold store) By choosing to include de-superheater when implementing heat recovery on to units of more than 1,000kW used in large heat recovery (see page 26) on a refrigeration systems. food storage facilities such as chilled refrigeration system in a typical warehouses. new-build office for around 250 people Before implementing heat recovery, and using the recovered energy for space you should ensure the system is operating The amount of heat that can be recovered heating, it should be possible to reduce Menu as efficiently as possible. This will mean from a refrigeration system will be heavily overall gas consumption by 5% to 10%, looking at the time when the system influenced by the temperature required for saving around £1,000 from utility bills operates and the pressures and use. The higher the temperature (typically and giving paybacks in the region of temperatures that are being provided as up to a maximum of around 65°C), the lower two to three years. well as ensuring there are no refrigerant the amount of heat that can be recovered. leaks. Your contractor or engineer should Using a ‘full’ heat recovery system, If you are considering using recovered be able to help you with these issues. nearly 100% of the heat can be recovered, heat for space heating, be sure to factor but it will be at low grade (around If you require heat at a higher temperature in the cost of any ducting in your 40°C-45°C) and therefore less versatile than can be provided by the systems calculations as this can affect viability. in its application. shown in this section, you could consider Recovered low-grade heat is most suited to linking them with a heat pump to achieve providing space heating, so it’s important the temperature you need. that there is a constant requirement for Heat recovery can be applied to most sizes heating during the winter months to of plant, from small units used for a single make the most of any investment. Technology guide 25

High-grade heat recovery using • a process plant where demand for hot water is • buildings that need air conditioning and hot a de-superheater high, such as in steam boiler water pre-heating water, such as swimming pools and hospitals.

Most refrigeration systems have the potential • food processing plants where, for example, to incorporate heat recovery and one way you large amounts of hot water are needed for can do this is to install a de-superheater ahead washing down of the condenser in the circuit (see Figure 10).

Typically the heat of the refrigeration fluid, at Menu the discharge from the compressor (commonly known as the hot gas line), is between 60°C Figure 10 High-grade heat recovery using a de-superheater and 90°C but can be as high as 110°C. Out In A refrigerant-to-water heat exchanger can be installed in the hot gas pipeline to recover the superheat for alternative heating purposes Heat rejection near the refrigeration plant.

The heat exchanger provides recovered heat for use elsewhere and also de-superheats the Condenser refrigerant, which reduces the cooling duty of the condenser. High-grade heat recovered Heat exchanger from a de-superheater has wide applications, (de-superheater) including in: Expansion valve

Evaporator

Cooling Compressor Technology guide 26

The same principle can be used on large central Figure 11 De-superheater used on larger centralised system refrigeration systems with multiple compressors (see Figure 11). Hot water to HVAC & Domestic hot water The large amount of heat rejected by the Pump refrigeration system in a typical supermarket offers an attractive resource for use in store Rooftop space heating, with around 10% of rejected Heat exchanger Remote condenser heat being available at high grade. Much of Menu the remaining heat could also be recovered but as low grade.

Compressors

Cooled space Machine Evaporator room

Chilled display cases

Refrigerant pipework Technology guide 27

Low-grade heat recovery Figure 12 Low-grade heat recovery: Figure 13 Low-grade heat recovery: from the condenser air-cooled condenser water-cooled condenser

The condenser in your cooling system rejects heat, normally directly to atmosphere. If you Ventilation have a coincident cooling and heating demand, supply unit you could make good use of this heat despite Cooling water to it being low grade. Ducted warm air cooling tower or from heated space dry cooler Warm air supply Air cooled Menu Typically for refrigeration systems in the to heated space condenser Pump UK, the condensers will operate at ambient Ducted return air air temperatures of between 20°C and from heated space Condenser 400°C. The heat rejected could be used Expansion valve for alternative heating purposes, local to Expansion the refrigeration plant. valve Evaporator

Where air-cooled condensers are used (see Evaporator Compressor Figure 12), the simplest method of recovering Compressor Cooling the waste heat is to use the warm air discharge for space heating purposes. This can be achieved either by ducting the air from the condensers directly into the space that requires heating or potentially physically re-locating the condenser within the space that requires heating providing a direct supply. Technology guide 28

Ducting the heat from the condenser Server rooms Benefits will probably require the installation of a supplementary fan and, whichever method An increasing number of computers in In a supermarket, you could supply is adopted, it may be necessary to provide office spaces demands a proportional 75% to 90% of hot water demand from bypass ducting to discharge warm air to outside, increase in the number of servers. The heat recovered from refrigeration. when the space heating is not required. servers produce a significant amount of This could account for 2% to 3% of

Low-grade heat recovered from condensers can heat, which can affect their operation if the building’s total CO2 emissions. be upgraded to a higher grade through the use left unchecked. Therefore this results in Menu of heat pumps and then used for applications an increasing demand for 24-hour cooling such as space heating or pre-heating domestic in the server rooms in order to maintain hot water. their correct operation.

Where water-cooled condensers are used (see Where refrigerant cooling is used the Figure 13) the cooling water could, for example, resulting waste heat from the condensing be supplied to a warm air heater coil within units could be captured and used a ventilation system. elsewhere in the building for space or hot water heating. Technology guide 29

Heat recovery applications: ventilation In modern buildings you need to balance the requirements for ventilation systems to provide sufficient fresh air with efficient energy consumption. Heat recovery through the ventilation system, which would otherwise be lost, can reduce energy consumption.

Menu Principles Efficiency of heat recovery Heat recovery can potentially be applied to any HVAC system that uses ductwork to supply The ‘air tightness’ of spaces in buildings is The most effective way of recovering energy and extract ventilation air. You can commonly increasingly being targeted to improve building from ventilation and air-conditioning systems find opportunities in: efficiencies. is to make use of recirculated air. • offices This has resulted in contemporary ventilation systems being required to deliver more fresh Where ventilation heat recovery • lecture theatres air than before, usually to a greater occupancy can be applied • hospital wards and internal comfort level whilst ensuring There are many applications of heat recovery that energy is not being wasted and indoor • swimming pool halls technology in ventilating and air-conditioning air quality is at the correct levels. systems, but they are based on a few simple • manufacturing areas. The cost of installing a heating, ventilation techniques. The principal ones are thermal and air conditioning (HVAC) heat recovery wheels, plate heat exchangers, heat pipes system depends on the size and complexity and the run around system. of installation. In an average installation, without any huge complications and where plant operates continuously, you could recoup the cost within two years. For plant that runs for just 40 hours a week, the payback period would be around five years. Technology guide 30

It’s worth noting that installations in new Ventilation heat recovery – Ventilation heat recovery buildings where mechanical ventilation is being efficiencies applications provided are almost certain to contain some The efficiencies shown below are useful in form of heat recovery. This is because current Thermal wheel technology Page 32 comparing the range of technologies available building regulations demand a level of efficiency for heat recovery in ventilation systems: Plate heat exchanger which is very difficult to achieve without it and (recuperator) technology Page 34 such techniques are now commonly adopted. • Plate heat exchanger: typically 55%-65%, maximum 80% Heat pump technology Page 36 This section will be useful in informing the Menu debate about which sort of heat recovery to • Thermal wheel: typically 65%-75%, Run around coil (closed loop) include in new builds and should be particularly maximum 80% technology Page 41 useful to anyone wanting to retro-fit to an • Run around coil: typically 45%-50%, Heat pipe technology Page 40 existing system. maximum 55% A qualified engineer will be able to talk you • Heat pump: typically 35%-50%, through the various systems and advise on their maximum 60% specific requirements. As the efficiencies are so similar and the costs (particularly for new • Heat pipes: typically 50%-65%, build projects) not hugely varied, considerations maximum 75% such as space and maintenance may be just as important in your decision of which technology Further references to opt for as financial performance. How to implement heat recovery in heating, air conditioning and ventilation systems (CTL051)

Air to air energy recovery: A guide to equipment eligible for Enhanced Capital Allowances (ECA771)

How to implement de-stratification fans (CTL023) Technology guide 31

Tips for implementation

A key consideration when installing heat When installing heat recovery in an existing • damaged damper seals recovery in a ventilation system is to HVAC system, you need to consider the • seized damper actuators recognise that the introduction of the heat available space in the ductwork and recovery equipment will cause a pressure whether your fan power is adequate. • poorly calibrated controls drop on the supply and extract fans. Some Ideally, supply and extract AHUs and • recommissioning of systems fans may be able to cope, but it is essential Menu ductwork are usually stacked on top of one after alterations. that this is checked at design stage to another, but there are still opportunities ensure the overall performance of the It‘s worth noting that installations in new for heat recovery if they are not. However, system isn‘t compromised. buildings where mechanical ventilation is technologies like run around coils only being provided are almost certain to In general, heat recovery in ventilation tend to be economical if the ducts are in contain some form of heat recovery. This systems can’t be easily applied to the same plant room. is because current building regulations contaminated air streams, such as cooker Once installed, it‘s important that a demand a level of efficiency which is very hoods or some industrial extraction proper maintenance regime is undertaken. difficult to achieve without it and such systems, because the heat exchanger The regime should cover: techniques are now commonly adopted. can become fouled with particulates in the extract air stream. This is also • blocked filters This section will be useful in informing important where either smells or the debate about which sort of heat • dirty heat exchange surfaces substances which may be harmful to health recovery to include in new builds and could be present in the exhaust air stream. • dirty ductwork should be particularly useful to anyone wanting to retro-fit to an existing system. • blocked condensate drains Technology guide 32

Thermal wheel A thermal wheel typically comprises a circular wheel with a matrix or honeycomb material of Thermal wheel technology offers you the a large surface area through which air can pass. greatest percentage of heat recovery within The wheel sits with one half in the exhaust air an air system, and therefore the greatest stream and the other half in the supply air reduction in energy and carbon. However, there stream of the AHU. are limitations due to the physical size of the unit as well potential for cross-contamination of the As the thermal wheel rotates, energy from air streams. Additional heat recovery can be the exhaust air stream is captured within the Menu advantageous, especially where there is high honeycomb structure. The heat exchanger latent temperature in the return air. honeycomb rotates and the energy is transferred to the fresh air stream in the other half of the A thermal wheel, also known as a ‘rotary’ or AHU. Supply and exhaust air streams must ‘regenerative’ heat exchanger, is a system of Thermal wheel installed in an AHU (Image courtesy of be flowing in opposite directions to maximise heat transfer which involves a single rotating Nuaire Ltd) heat recovery and supply air temperature. wheel with high thermal capacity located within the supply and exhaust air streams of an air The rotary heat exchanger honeycomb is handling unit (AHU). Its rotation allows the normally manufactured from aluminium, which recovery of energy from air that would has good heat transfer properties, but it can also otherwise be lost to the atmosphere, and be manufactured from plastic or paper material. the energy to be used to pre-heat (or cool) The wheel is rotated by a small electric motor the incoming fresh air. Benefits and belt drive system.

The use of this technology will reduce the With the high efficiencies of thermal amount of energy needed to heat (or cool) the wheels, your investment could pay back supply air to the required temperature with a within two years. corresponding reduction in carbon emissions. Technology guide 33

Advantages and disadvantages Investment and payback Tips for implementation Thermal wheels are available to capture either When specifying new ventilation ‘sensible’ or ‘total heat’ (ie sensible and latent Remember these issues if considering equipment for an office building of heat) from the exhaust air stream and transfer a thermal wheel for your site: 2500m2, operating within normal office the captured energy into the supply air stream. • Using a thermal wheel in an AHU leads hours, a thermal wheel is likely to add The benefit of the total heat version is that it also to the supply and exhaust air streams around £7,000 to £9,000 to the capital cost captures latent heat (water vapour) and transfers mixing to a small degree. If this isn‘t but should pay back in around two years. this additional energy into the supply air stream Menu acceptable, because the exhaust air is If you were considering retro-fitting as well as sensible heat. contaminated in some way, you can a thermal wheel to existing equipment, The speed of rotation will determine the amount reduce the effect by using physical assuming you have the space and there of energy transferred between the two air seals and purge sections within the air are no significant complications, you streams; however, total heat thermal wheels handling unit. However, this may not should expect to pay more but still achieve can achieve efficiencies of up to 85%. stop the mixing completely. a payback in the region of three years. The thermal wheel has to be installed in the • In addition, air entering the wheel from AHU, so the size of the unit can be very large, either side must be filtered to prevent especially as air flow volume increases. You the wheel becoming fouled with The speed of rotation of the thermal wheel can should consider the space you have available, particulates in the air streams. be controlled with a variable speed motor for as this will increase the complexity of • You‘ll also need to ensure that good improved control of the temperature transfer. coordination of ductwork. access for maintenance is provided as If no heat (or cool) transfer is required, the motor part of the installation, and considering can be stopped and the air flow will pass straight the space requirements of a thermal through the honeycomb matrix without any wheel, this may be an important issue transfer of energy to the other compartment. in determining whether the project is feasible. Technology guide 34

Plate heat exchanger or Figure 14 Principle of operation of other, but are separated by the parallel plates, recuperator a recuperator which allow energy to be transferred from the exhaust air to the incoming air supply. Recuperator technology is by far the most Hot common form of air-to-air heat recovery and Fresh air in extract air As the intake and exhaust air streams are is used in a variety of air handling units with physically separated and energy is transferred different air volumes. This technology can be through the plates, their material, thickness and linked with additional heating and cooling coils surface area affect the transfer efficiencies of to reduce the amount of energy required to the equipment. Manufacturers claim gross Menu maintain internal conditions. Cool air Warmed efficiencies between 50% and 80% depending exhaust fresh air on the specification of the unit. A plate heat exchanger (or recuperator) transfers heat between the supply and exhaust streams In traditional plate heat exchangers, sensible of an air handing unit. It recovers energy from heat (containing no moisture) will pass through extracted air that would otherwise be lost to the plates dividing the two air streams. Newer the atmosphere and uses it to pre-heat (or cool) plate heat exchangers, constructed from a the incoming fresh air. Figure 14 and the image semi-permeable membrane, will allow both below demonstrate the principle and structure sensible and latent heat to transfer between of the heat exchanger type. the two air streams, providing a greater energy saving. The use of a plate heat exchanger reduces the amount of energy needed to heat (or cool) the supply air to the required temperature with a Benefits corresponding reduction in carbon emissions. A 70% efficient plate heat exchanger in A plate heat exchanger is typically comprised a typical office could save you 38% of of a series of parallel plates of aluminium, plastic, your total gas consumption. stainless steel or synthetic fibre, which direct the intake (supply) air and exhaust (return) air. The A plate heat exchanger within an AHU (Image courtesy of Nuaire Ltd) supply and extract air streams cross over each Technology guide 35

Advantages and disadvantages Tips for implementation If heat recovery through the plate heat exchanger is not required, for example in Since the two streams are physically controlled to ensure that the air flow is summer conditions, and the exhaust air is at separated from each other there is a low above 0°C. Water freezing on the plates a higher temperature than the incoming supply risk of contamination transfer between can result in either loss of performance air, a mechanical bypass damper can divert the supply and exhaust air flows making or damage to the plates themselves. the air around the plate heat exchanger. This this application of this technology quite prevents unwanted heat being transferred If one of the air streams is cooler than the Menu flexible and broadly applicable to many to the supply air. dew point of the other air stream, there is a different industries. chance of condensation and therefore Depending upon the material of the plate condensate drains should be provided Investment and payback heat exchanger, the cold incoming air from to the ventilation unit.

outside may need to be temperature Plate heat exchangers are a relatively simple approach to heat recovery and, other than ongoing maintenance, are not a significant operative cost. For a typical As the plate heat exchanger must be installed ductwork through the building as four different office of 2,500m2 with normal working within the air handling unit, the physical size air paths must be coordinated within one area. hours, you should expect to pay around of the air handling unit can be large, especially an extra £6,000 to £8,000 for the inclusion as air flow volumes increase. Access for Heat pumps of a plate heat exchanger in a new build maintenance is also required, adding to project, which should pay back in well the overall plant space required. Heat pump coils remove heat or cool energy under two years. If you want to retro-fit from one location and direct it to another. They Due to the need to recover the exhaust air an exchanger to a similar sized system, are used to avoid cross-contamination of air or energy and pre-heat the incoming supply air, the cost is likely to be about £12,000 with when the systems can not be located within the the ductwork associated with the various air a payback period of around three years. same air handing unit. This system can be added paths must be co-ordinated within one area. retrospectively within an existing and separate Allowances must be made for routing of the air handling unit. Technology guide 36

A ventilation heat pump heat recovery system The cooled liquid is reduced in pressure by Figure 15 Heat pump in heating mode is built for efficient energy transfer from one air passing through an expansion device and enters stream to another where the two systems are the exhaust air coil (evaporator) located within Cooling coil physically independent from each other. Heat the exhaust air stream. In the evaporator the (evaporator) pumps can provide either heating or cooling refrigerant evaporates (boils) to a vapour state. Exhaust air energy to the coil located within the supply This is where the cooling takes place. The air stream. refrigerant re-enters the compressor and Expansion Compressor the cycle starts again. valve Heat pump systems operate on the same Menu principle as a basic refrigeration cycle. They use both coils within the air handling unit air Heat pump – cooling mode Supply air stream as either a condenser or an evaporator Figure 16 shows that when cooling is required for heating or cooling purposes. Refrigerant Heating coil the reverse occurs and heat energy is fed (condenser) pipework connects supply and extract coils directly from the compressor into the exhaust within the air streams of the separate air air coil (condenser) located within the exhaust handling units. A compressor and expansion Figure 16 Heat pump in cooling mode air stream of the AHU. device is located between the two coils. The cooled liquid is reduced in pressure after Heating coil (condenser) Heat pump – heating mode passing through an expansion device and enters the supply air coil (evaporator) located within Exhaust air Figure 15 shows that if the supply air requires the supply air stream. In the evaporator the heating, heat energy is fed directly from the refrigerant evaporates (boils) to a vapour state. Expansion Compressor compressor via the refrigerant pipework into This is where the cooling of the incoming supply valve the supply air coil (condenser) located within air takes place. The refrigerant then re-enters the supply air stream of the AHU. This heats the compressor and the refrigerant cycle the cooler incoming air and leaves the condenser starts again. Supply air as a cooled refrigerant liquid. Cooling coil (evaporator) Technology guide 37

Advantages and disadvantages Tips for implementation Investment and payback The heat pump efficiency, of up to 60%, is usually controlled by adjusting the speed of Don’t forget to consider these issues Heat pumps should save you a significant the compressor. when looking into heat pumps as your amount off your heating energy bill – in chosen heat recovery method: some cases as much as 60%. In a typical The major advantage of this system is that UK office of 250 people, that could be as it provides a means of heat recovery where • Although heat pumps provide a way much as £3,500 a year. two air streams are not close enough for of transferring energy between two Menu alternative and more efficient heat recovery separate air streams, overall efficiency methods. This can assist with the position will be reduced where long distances of the air handing units and reduction in the are involved. Benefits interconnecting ductwork within the air system. • The heat pump system can be a Due to the separation of the air streams via solution for retro-fit as well as new By using heat pumps with an efficiency of the coils and pipework, there is no risk of build where space constraints mean 50% to provide cooling as well as heating, cross-contamination within the air streams. other, more efficient methods can’t you could save up to 12% of total building

be used. CO2 in a typical office. Technology guide 38

Run around coil The possibility of exchanging heat between Figure 17 Run around coil system installed remote air streams is due to the coils being between supply and extract AHUs Run around coils are a process where heat or connected to each other by a pumped pipework cool energy is removed from one location and circuit. This pumping will use a small amount directed to another where the systems cannot of energy but this will be less than that being Exhaust air be located within the same air handing unit or saved by installing the system. to avoid cross-contamination of air. This system can be added retrospectively within existing The pipework is charged with a circulating fluid, and separate air handling units. normally water or glycol, which flows around Menu the circuit between the coils within the two A run around coil system is built to enable air streams. Hence the closed loop system or Supply air efficient energy transfer from one air system run around coil terminology (see Figure 17 ). to another, where the two systems are physically independent. Run around coil systems cannot transfer moisture from one air stream to another and This process involves a heat transfer coil in each therefore only sensible heat can be captured. of the supply and exhaust air streams, but, unlike Figure 18 The efficiencies of run around For the most cost-effective operation, with the thermal wheel and plate heat exchanger, a coils can be enhanced significantly by equal airflow rates and no condensation, typical run around coil system does not require the air connecting to a secondary heat source as effectiveness values range from 45% to 55%. streams to be located within the same AHU. shown below These coils recover energy from the extracted The fluid pipework distribution circuit connecting air that would otherwise be lost to atmosphere. the supply and exhaust coils, as well as Exhaust air This recovered energy can then be used to containing the circulating pump, requires pre-heat (or cool) the incoming fresh air stream. the following components: This reduces the amount of energy needed to • an expansion vessel heat (or cool) the supply air to the required temperature with a corresponding reduction • an automatic fill device to ensure the system in carbon emissions. remains charged Supply air Technology guide 39

• controls to bypass and shut down the system Tips for implementation Benefits when not required • various other safety devices and ancillaries. You could achieve up to an 8% reduction In very cold weather, ice may form on in electricity use in a general retail store the coils so you’ll need to ensure that your by installing a run around coil with specialist considers the use of Advantages and disadvantages 45% to 55% efficiency. frost protection in the system. • Provides heat recovery where air streams are You can use this approach as a retro-fit not close enough for alternative and more Menu option in existing separate supply and efficient methods. Using a run around system Heat pipes extract systems without significant can assist with positioning air handing units Heat pipes can only be used where the supply modification to the ductwork but and reduce the interconnecting ductwork. and extract air streams are contained in the remember that for it to be viable the • Additional energy efficiencies, up to 75%, same air handling unit. However, the energy distance between supply and extract can be introduced to the run around coil efficiency and lack of mechanical moving parts ducts shouldn‘t be too great. configuration if linked to a separate heat source. make them suitable for a majority of applications within new air handling units. • Glycol in the fluid system will reduce efficiency and increase pump power consumption. Heat pipes are simple, low maintenance Investment and payback devices that can transfer heat from one point to • The separation of the air streams means there another without having to use either an external is no risk of cross-contamination between power supply or moving parts (i.e. pumps or In a typical office building of around the air streams. compressors). In this context, a heat pipe heat 2,500m2, which operates on weekdays • Multiple air streams in a building can be used exchanger is used for efficient energy transfer and some early evenings, installation of a to further improve energy transfer. Exhaust from one air path to another. This process run around coil system might cost £5,000 heat recovery coils can be focused on involves sealed tubes, sometimes internally to £7,000 and give payback in the region high-energy areas where dedicated ventilation lined with a wick, charged with a refrigerant. In of two years. Retro-fitting run around services are provided (such as datacentres, heating, ventilation and air-conditioning systems, coils is unlikely to cost a significant kitchens and process ventilation) to maximise heat pipes are located within the supply and amount more than in new build. additional energy recovery. exhaust air streams of an air handling unit. Technology guide 40

The heat pipes are usually a continuous pipe, Figure 19 Heat pipes – principle of Run around coils versus which passes through both the supply and conversion heat pumps extract air streams.

Within the tube system, the sealed refrigerant These two types of heat recovery Fluid/condensate falling located at the bottom of the tube absorbs the system appear quite similar but in fact Supply air energy (heat) from the exhaust air stream. use different approaches to achieve As the refrigerant within the tube heats up, similar results. it changes from a liquid to a vapour. The high Cold air in Warm air out Menu Both systems can be used where supply temperature vapour rises vertically within the and exhaust air streams are not physically tube to the other end located within the cooler close by connecting the streams with incoming supply air stream. The energy (heat) pipework, but here the similarity ends. within the tube heats up the incoming air stream. As the temperature of the refrigerant Run around systems are simple: the within the tube decreases it changes back to a pump is the only mechanical part and Cold air out Warm air in liquid which falls back down the pipe walls to their efficiency is limited due to the the bottom of the tube in the exhaust air stream. heat transfer medium being used. Heat Then the cycle starts over again. Figure 19 pumps, on the other hand, operate like illustrates this operation. a refrigerant circuit and often use Exhaust air Vapour rising refrigerant fluid rather than a simple By using wicks within the heat pipe tubes, it is water/glycol mix. Using a compressor and possible to locate the tubes horizontally as the However, in this vertical configuration, the heat expansion valve provides greater control wick allows the migration of the liquid via the pipes are reliant on the arrangement of the AHU which, whilst increasing complexity, also wick rather than through buoyancy and gravity. sections (supply and exhaust). If the incoming increases efficiency. That said, greater efficiencies can be achieved supply air stream is to be heated by the warmer if the heat pipe tubes are mounted vertically, exhaust air (for example winter conditions) then allowing vapour to naturally migrate up and the AHU must be configured so that the warmer the cooler liquid to fall down via gravity. exhaust air is at the bottom and the cooler incoming air is at the top, thus allowing Technology guide 41

buoyancy and gravity to drive the movement Tips for implementation of air and the heat recovery process to occur.

If the incoming supply air stream is required Heat pipes have limited flexibility, so you As the heat pipe heat exchanger has to to be cooled from the cooler exhaust air need to bear these issues in mind if be installed within the air handling unit, then the AHU must be configured so that considering them for your site. the physical size of the AHU can be the cooler exhaust air is at the top and the more than would otherwise be the case, Due to the configuration of the heat pipe, warmer incoming air is at the bottom. especially as the air flow volume increases. they are unable to be controlled and Cool energy recovery can then occur. Good access for maintenance is also Menu isolated. So, if the heat recovery system required, again adding to the overall is not required, for example in summer plant space required. Advantages and disadvantages conditions, a mechanical bypass damper must be used to divert the air around the As the air streams are not mixed as part of the heat pipe coil. process of transferring heat via the heat pipes, there is no risk of cross-contamination provided there is a physical divide between the supply and exhaust air sections within the air handling unit.

The supply air can be further controlled by Investment and payback Benefits means of a main heating or cooling coil following

the heat transfer through the heat pipe heat In an office housing around 250 people Efficiencies of the heat pipe system can exchanger. working typical UK hours, heat pipes range from 50% to 55% on horizontal The heat pipe system requires the AHU and could potentially save up to 50% on gas pipes and up to 75% on vertical pipes. associated ductwork to be arranged in a specific bills, which could equate to well over way. Allowances should be made for routing £4,000 a year. ductwork through the building plant room. Technology guide 42

Heat recovery applications: industrial processes Process heating refers to types of heat transfer techniques such as drying, evaporating, separating, curing, heat treating, melting and controlling chemical reactions, used in a wide range of sectors, from laundries and food production to chemicals and foundries.

Menu Recovery of heat used in industrial processes The high-temperature range covers any process gas, a range of oils, LPG and coal. Various is frequently more complex than in other operating or discharging above 500°C, generally approaches are taken to transferring heat applications. You should use this section as associated with furnaces or kilns, in the metals, to the process, including: an initial guide to help you identify whether minerals, ceramics and glass sectors. • flue gases heated directly by combustion you should undertake the kinds of processes The most prevalent use of energy recovered where heat may be lost and the kinds of • hot water or steam generated in a boiler from processes occurs in the low temperature techniques which might be used to recover it. range and is in fact typically between ambient • through radiation from electrical heating and 200°C. Opportunities for heat recovery elements Energy use in industrial processes are based on operations which apply to many • in air heated indirectly from combustion industrial sites, such as boilers, refrigeration The use of energy for industrial processes gases via a heat exchanger. plant, air compressors and prime movers can be broadly classed into low and high (engines or turbines). Each application requires both fuel to generate temperature ranges. Low temperature covers the heat and a mechanism to deliver the processes that operate at or discharge at heat to the process. In combination, these temperatures up to 400°C-500°C. Typically, Process heating arrangements are known as ‘heat sources‘. you would find these processes in the Delivery of heat to industrial processes has two chemicals, food and drink, paper and board key aspects: the release of heat from a fuel and and textiles and laundering sectors. the transfer of heat to the process. A wide range of fuels are used, including electricity, natural Technology guide 43

Steam Hot water Indirect combustion/electrical heating Steam is the most widespread process heat Hot water can be produced by electricity or delivery medium. It is produced via combustion any fossil fuel. It can also be produced by heat This is where the combustion process is in boilers or as an output from a CHP plant. exchange with process fluids, as well as from separated from the material to be heated by The main advantages of steam are its high heat waste heat. Water has a large capacity for the structure of the furnace and many furnaces capacity and flexibility. The main disadvantage is retaining heat, which makes it more useful than operate on this principle. Burners fire into that it tends to be expensive to produce due to other media, such as air. However, unless it is a combustion chamber and heat is then inefficiencies in boiler and distribution systems. held under pressure, water will boil if heated transferred through the walls to the material Menu beyond 100°C. Although it is easy and safe to to be heated. This process is less efficient Warm air use, this limits the range of activities for which than direct heating, but prevents contamination water can be used as a heat-transfer medium. of the material. It can also be used where Warm air can be generated directly by electricity a product is flammable. or indirectly by fuel combustion. Warm air is Thermal oil generally used for the lower temperature ranges Direct electrical heating of process heating, such as drying activities, Thermal oil is usually used where temperatures where it supplies heat and acts as the carrier to higher than those which can be readily achieved There are various direct electrical heating remove water or other solvents from a product. with water are required. Systems must be techniques. Arc furnaces use electric current to robustly maintained to prevent the leak of hot heat metals directly. Induction furnaces are used oil and, therefore, problems are rare. to heat a range of materials, including metals and glasses. Very high temperatures of up to Direct combustion heat 300 to 400ºC can be achieved in inert atmospheres. Heating with microwaves (or radio Direct combustion heating, usually using natural frequency energy) is possible for some types of gas or fuel oil, is used in many medium and material. higher temperature process-heating applications such as rotary kilns. The main advantages of this form of heating are the efficiency of heat transfer and the rapidity of response to heat input changes. Technology guide 44

Specialist advice minimises both heat exchanger surface areas and costs. For certain processes it may not be possible to find a suitable use for the The application of these techniques will it‘s difficult to give general advice on the available waste heat because of a lack of often require a bespoke approach which level of investment required. However, the either an economic application or a viable fits with the specific context of the site, specialist with whom you engage should heat recovery technology. equipment and processes involved. provide examples of other projects they Further references have worked on, so you can make informed Heat recovery in industrial processes is Menu choices about the right solution for you. How to implement industrial heat recovery a specialised area and you will need equipment (CTL037) the services of a specialist. See page 55 for tips on finding a suitable organisation to help you with heat How to implement heat recovery in As the efficiency of heat recovery in recovery. compressed air (CTL166) industrial processes can vary so widely, Waste heat recovery in the process industries (GPG141) • the flow rate of the waste gas stream Process heating – where Heat recovery from air compressors heat is wasted • the temperature of the waste gases (GPG238)

• the composition of the waste gases. High-temperature gases Once these factors have been established, Loss of heat through hot waste gases is the means of heat recovery can be matched inevitable in all processes involving high to its end use. Costs for waste heat recovery temperatures. The energy efficiency of the and use must be also be assessed. process can be improved by recovering heat from the waste gas stream or the waste heat Heat transfer rates are highest at high can be used elsewhere to reduce primary temperature because of enhanced thermal energy use. However, several parameters conductivities and greater radiative heat transfer. must first be evaluated: Operating at high temperatures therefore Technology guide 45

Air compressors Case study Specialist advice Packaging Most of the electricity supplied to an air Low-temperature processes compressor (which can be up to 90%) is Packaging companies have saved converted to heat. It is possible to recover Distillation Page 45 20% of the energy consumption used anywhere from 50% to 90% of this thermal Drying Page 46 for the provision of compressed air by energy and use it to heat other air or water. Dyeing and finishing Page 46 upgrading their compressors and using Evaporation Page 47 Air-cooled and water-cooled packaged rotary a heat recovery system on exhausts. Prime movers Page 47 Menu screw compressors are typically enclosed in Ovens Page 48 cabinets and include heat exchangers and fans, Pasteurisation and sterilisation Page 49 but the waste heat discharged can be recovered. Process cooling Page 49 The next few pages provide an overview of the Process heating Page 49 common potential applications for heat recovery Distillation Washing Page 49 in relation to industrial processes. Distillation is conventionally carried out in High-temperature processes a column in which components of a liquid Low-temperature processes mixture are separated. By applying heat the Furnaces Page 50 component with the lower boiling point is Furnaces – recuperators Page 50 There are considerable opportunities and evaporated. The waste heat manifests itself potential for low-temperature waste heat Uses for high-temperature heat in the condenser, which is used for cooling recovery from the following typical plant recovery the volatile component being boiled off. and processes. Charge pre-heating Page 52 Steam generation Page 53 Electricity generation Page 53 Space heating Page 54 Technology guide 46

Drying Figure 21 A sketch of a typical finishing plant with heat recovery from the effluent discharge

Dryers are widely used in several industrial Mains sectors. Rotary dryers are the principal energy cold water Heat exchanger consumers, with spray and band dryers also Effluent being significant consumers. Heat is normally holding tank discharged as warm humid air (see Figure 20). Steam Dyeing and finishing To drain heater Menu Dyeing and finishing processes in the textile and fabric care sector provide good opportunities for Hot water Recycled hot tank water tank waste heat recovery (see Figure 21). Warm effluents can be a source for pre-heating incoming cold water and heat exchangers can be used on effluent containing fibres. Line of batch finishing machines

Figure 20 A sketch of a typical tunnel dryer with recirculation to direct exhaust gases back to the inlet of the process. Sump Sump

Exhaust Filter damper Fan Air Air heater Fan heater Rotating Three drainage channels brush filter Entrance Discharge below machines To drain Technology guide 47

Evaporation Figure 22 A sketch of a multiple effect Prime movers evaporator. The waste heat is cascaded in Evaporation is used to concentrate solutions of A prime mover is a component in a system temperature through a line of evaporator liquids (see Figure 23). Commonly this involves which converts other forms of energy into effects boiling off the water by the addition of heat. useful mechanical energy. Concentrating the vapour leaving the mixture is Many plants within industry use prime movers, the main source of heat loss, as in distillation. Reject vapour such as reciprocating gas or diesel engines, Evaporators are graded in terms of increasing Vapour gas turbines and steam turbines. The latter efficiency and hence effective use of heat, ie First effect Second effect Menu are sometimes used to recover thermal single effect, multiple effect and mechanical evaporator evaporator Flash energy, for example as pressure reduction units. recompression (MVR) evaporators. Feed Reciprocating engines can be useful sources of Steam heat at a variety of temperatures, ranging from moderate temperature exhaust gases to lower grade heat in the water cooling system and, in larger engines, the oil cooler. Gas turbine Trap Trap Hot well exhaust heat can be used for drying and can, via an absorption refrigeration system, Condensate provide cooling or refrigeration. Technology guide 48

Ovens recovered from the oven exhaust and used typically for other purposes, for example tray Ovens are commonly used in food ingredients washing, pre-heating boiler feed water, and and food derivatives industries. They can be so on (see Figure 23). either directly or indirectly fired. Heat can be

Figure 23 A sketch of heat recovery on a bakery oven. Heat recovered from the burner Figure 24 A sketch of plastics injection Menu exhaust is used for combustion air pre-heating and heat recovered from the oven exhaust is moulding machine cooling circuits with used to pre-heat hot water heat recovery used for space heating Water storage tank

Steam Mains Oven Oven water exhaust exhaust Oil cooling circuits for Fan coil Fan coil majority of machines HES HE3 HE4 unit unit Tray washer Oven exhaust Boiler feed Condensation Calorifiers Make-up plant Duty / standby Chiller unit Water pumps

Dough to Bread out prover Prover Oven of oven

Oil coolers on small machines Mould cooling circuit Gas Gas available at all machines supply supply Key HE1 HE2 HE1 Combustion air H/Ex 1 HE2 Combustion air H/Ex 2 HE3 Oven extract H/Ex 1 Burner Burner exhaust exhaust HE4 Oven extract H/Ex 2 Combustion Combustion HE5 Steam Calorifier air inlet air inlet Technology guide 49

Pasteurisation and sterilisation Figure 25 Typical heat recovery on a Case study galvanising plant. Liquid-to-liquid and In the dairy industry, pasteurisation is already Dairy industry gas-to-liquid heat exchangers are used highly efficient in terms of heat recovery; however to recover heat from the burner flue gases sterilisation, particularly bottle sterilisation, is Waste heat from a CHP unit in a dairy for pre-heating the pre-flux tanks energy intensive and provides more opportunity processing factory was initially used on

for waste heat recovery. Pre-flux Galvanising a spray drier. However, when the drier tanks bath closed a few years later, a new scheme 50-70ºC Process cooling was developed to use the heat for Menu Burner Burner process and space heating. Process cooling is widely employed for uses such as plastics injection moulding. Although Pump regarded as a ‘low grade’ heat source, it can Burner flue gases be viably used for space heating. Washing

In the fabric care industries, typically in Process heating Liquid-to-pre-flux Pump laundering, large amounts of heat are used for solution heat The largest consumer of energy in several Flue washing. The warm effluents that are normally exchanger gas-to-liquid industrial sectors is process heating (see heat drained can be a source of heat for pre-heating exchanger Figure 25). Heat input is normally via steam, incoming cold water. hot oil or direct firing. Process heating duties Fan include heating feed materials to reaction temperatures, pipe and storage vessel heating, calcining, kilning and so on. The heat is commonly available as hot gases, or in the solid product being processed. Technology guide 50

High-temperature processes Loss of heat through hot waste gases is Pre-heating combustion air inevitable and the energy efficiency of the Pre-heating of combustion air is one of the The opportunities for heat recovery from process can be improved by recovering heat most popular uses of waste heat from furnaces high-temperature processes are significant from the waste gas stream or the waste heat and kilns due to its high efficiency and reduction and mainly revolve around the use of can be used elsewhere to reduce primary in primary fuel use. For a long time, fuel gases furnace-based operations. energy use. Several parameters must first were only used for pre-heating combustion be evaluated: air for large boilers, metal-heating furnaces Furnaces and high-temperature kilns. But pre-heating • the flow rate of the waste gas stream Menu In any industrial furnace the combustion products using heat from flue gases is now also applied leave the furnace at a temperature higher than • the temperature or ‘quality’ of the to compact boilers and compact industrial the stock temperature (see Figure 26). waste gases furnaces.

• the composition of the waste gases. Equipment for combustion air pre-heating can Figure 26 Typical heat flows and losses be divided into recuperators and regenerators. Once these factors have been established, the in a furnace means of heat recovery can be matched to its A recuperator is a device for waste heat Heat input Heat in stock end use. Costs for waste heat recovery and recovery that works by counter-flowing hot use must also be assessed. gases and cold air through a heat exchanger. Furnace External versions are most common, but other Heat recovery applications techniques such as self-recuperative burners Waste heat in flue gases can be recovered are also used. A modern recuperator using

Moisture in fuel Hydrogen in fuel Opening in furnace Furnace surface/skin Other losses for the following: furnace exhaust gas of 1,000°C can preheat the Flue gas combustion air to over 500°C, which results in • preheating of combustion air energy savings of up to 30% compared with • charge pre-heating using cold combustion air.

• using waste heat as a heat source for other A regenerator is a cyclic heat storage device. processes. The choice of equipment depends on the efficiency of the device and where it is placed

in the furnace. It is recommended that, under Technology guide 51

circumstances where temperature profiles Increasing the temperature of combustion Heat recuperators – radiation type are critical within a furnace or kiln, both physical air also results in higher flame temperatures. The cold air and hot waste gases counter-flow and mathematical modelling of the furnace/ These are associated with higher nitrogen oxide along concentric tubes (see Figure 27 ). Heat burner geometry is undertaken to establish (NOx) emissions, which are subject to stringent transfer is by radiation. The hot air out is ducted optimum conditions. standards. High efficiency burners with low to the furnace burner combustion air inlet. NOx emissions have recently been developed. Most conventional gas/air burners are only capable of operating with pre-heated air up to Since the volume of combustion air increases Figure 27 A cross-section of a double shell 300°C. Above this temperature, purpose-built when it is preheated, it is necessary to consider Menu radiation recuperator burners must be used. While this adds to capital this when modifying air-duct diameters and costs, combustion efficiencies are improved blowers. It should be noted that pre-heating of and operating costs are therefore lower. combustion gases from high-density oils with a Cooler gases high sulphur content could cause clogging with out High-temperature burners, coupled with either dust or sulphides, corrosion or increases in NOx. recuperators or regenerators, are now common Hot air out in the UK metal, glass, pottery, refractory and chemical industries.

Combustion air pre-heating normally becomes attractive when furnaces or kilns operate above 500°C for an appreciable proportion of their cycle.

Cooler air in

Hot gases in Technology guide 52

This kind of exchange is most influenced by Figure 28 Two-step heat exchanger in With furnace pre-heating, gases from the the temperature, so these recuperators are parallel flows furnace or kiln are directed to the incoming suitable when the temperature of the flue gases stock by means of ducting, or by extending is higher than 1000°C, or when the components the furnace. The economics of charge Air outlet of the flue gases are aggressive pre-heating depend heavily on the furnace, or contain a high percentage of particles. Cool gas out oven or kiln geometry. Initial capital expenditure in extending the Heat recuperators — convection type furnace or installing insulated ductwork may Menu In these recuperators the heat transfer between be high, but subsequent maintenance costs the primary and secondary fluids is done by Hot gas in should be minimal. At its most efficient, charge convection (see figure 28). The hot air out pre-heating rivals the pre-heating of combustion is ducted to the furnace burner combustion Air inlet air in economic viability. Charge pre-heating has air inlet. the advantage of low maintenance costs, while combustion air pre-heating normally has lower Their main feature is the full contact between Charge pre-heating capital costs. the gases and the tubes composing the When raw materials are pre-heated by exhaust recuperator, so that they are especially suitable Many furnaces, including blast furnaces and gases before being placed in a heating furnace, when: pottery tunnel kilns, incorporate charge the amount of fuel necessary to heat them in recuperation in the furnace design. In these • the working temperature is lower than 1000°C the furnace is reduced. As raw materials are cases, waste gases emitted after recuperation usually at room temperature, they can be • the gas streams are fairly clean (with no are at relatively low temperatures (typically heated sufficiently using high-temperature particles) and without especially corrosive less than 400°C). In certain industries, for flue gases, which noticeably reduce the fuel components. example aluminium and copper foundries, consumption rate. stock pre-heating has the additional advantage of removing the hazard of explosion caused by entrapped water vapour. Heat transfer efficiencies vary according to the geometry of the charge, its thermal conductivity, flow Technology guide 53

rates and temperatures. Estimates of the fuel Other processes (to generate steam or hot production and petrochemical refining, where savings possible with this technique vary water by a waste heat boiler) there is a demand for both electricity and low from 10%-30%. The temperature of furnace exhaust gas can pressure steam. be 400°C to 600°C, even after heat has been Power generation using waste heat requires: Steam generation recovered from it for pre-heating the charge or combustion air. One possibility is to install a • an almost continuous supply of waste heat: Waste heat boilers have been used for steam waste heat boiler to produce steam or hot water generation for many years in the UK chemical, • water pre-treatment from this heat, especially when large quantities copper, iron and steel industries. Steam Menu of steam or hot water are needed. • regular maintenance generation using waste heat is only economically viable if there is a continuous Sometimes exhaust gas heat can be used for • high-pressure boiler and condensing steam supply of heat and a definite requirement for heating purposes in other equipment, but only if turbine plant. process steam and paybacks on investments the heat quantity, temperature range, operation This last requirement results in high capital of around three years can be achieved. time and so on are suitable. Where this is the costs. Estimated payback periods are generally case, you could greatly reduce fuel consumption. Waste heat boilers are highly energy efficient three to six years and this use for waste heat One existing example is the use of exhaust gas (typically around 80%). In using waste heat has therefore not found favour in the UK. from a quenching furnace as a heat source in boilers, consideration should be given to the a tempering furnace. There is currently no example of a retro-fitted ease of installing the device and associated power generation system using high water treatment plant and the cost of regular Electricity generation temperature waste gas streams in the UK. maintenance. Use of waste heat boilers is The only exception is the use of gas turbine generally considered only at the plant design The generation of electricity using waste heat exhaust in waste heat boilers in a combined heat stage and not when considering retro-fit is well established in the UK chemical and and power (CHP) plant. For further information, opportunities. petrochemical industry, where it forms an see Department for Energy and Climate Change integral part of the chemical process stream. Waste heat boiler plant is normally purchased documents (www.decc.gov.uk). In this industry, processes are often uneconomic on the basis of process steam requirements or, without this heat recovery facility. Examples in a few cases, for a space heating requirement can be found in ethylene cracking, ammonia when a steam main is already employed. Technology guide 54

Uses for recovered heat from Space heating becomes more attractive when: Case study high-temperature processes • the source of waste heat is close to the area to Diamond Power Specialty Ltd Space heating be heated Although waste heat is frequently used Boiler cleaning and ash-handling systems • current heating systems are highly inefficient for space heating, this use is often not as producer Diamond Power paid back its cost-effective as others and payback periods • there is no other possible use for the waste heat recovery system in 3.3 years. The are typically three to five years. heat and the heat generating process has firm installed a simple mechanical been optimised ventilation system to remove the waste Menu Space heating has several disadvantages over heat from the compressor room. The other uses, such as combustion air pre-heating. • the heat exchange technology is simple to warm air contributes to the space heating If the source of the waste heat and the space to install and cheap to purchase and maintain in the workshop or is ducted outside in be heated are not adjacent, then long lengths of • the supply of waste heat is coincident with the warmer months. ducting combined with some form of air dilution the demand of the area to be heated. are often required. The high cost of transmitting the heat can thus offset any economic Most of these criteria should be met before advantage. Furthermore, if high temperature space heating is considered as a viable use for waste heat is used for space heating then, in hot waste gases. general, only a fraction of the heat available is Use of waste heat for space heating can, used. In the summer months, for example, all however, be economic when it displaces the waste heat is dumped. The economics are obsolete heating systems or is used to heat thus calculated for a heating season which lasts new buildings – that is, as an alternative to other about seven months. heating systems – and when some capital Space heating as an application for recovered investment would have been necessary anyway. waste heat should only be considered when other When space heating applications supplement options are shown not to be technically viable. existing heating plant, the economics are generally poor. Technology guide 55

Next steps By reading this overview guide, you should now have a good understanding of the types of processes that may be wasting heat unnecessarily in your business.

Menu There are a number of things you can do next Light manufacturing and For situations where the heat recovery system which will help you decide whether or not to warehousing heat recovery you are considering will be part of your building’s invest in the implementation of one or more webinar inherent systems (such as ventilation, heating heat recovery systems in your building. and so on), you should approach a building If your business is manufacturing on a smaller services engineer. If you don‘t have an existing scale or warehousing, there is a webinar that relationship with an engineering practice, Heat recovery checklist can help you. The webinar will show you how a good place to find a reputable company is you can reduce your energy bills by up to 30%, If you haven‘t already, you can use the Heat www.cibse.org, the website of the Chartered identify where heat is being wasted, where heat Recovery Checklist to help you ask the right Institution of Building Services Engineers, which recovery can be retro-fitted and how you could questions about the systems in your building. features a ‘Find an expert’ service. You could potentially offset the capital cost of heat This includes the important step of ensuring also contact the Combustion Engineering recovery against profits. your building services are already operating Association (www.cea.org.uk), which should efficiently before considering heat recovery. be able to help with certain technologies. Engage with a specialist The checklist covers practical issues and key If you are considering heat recovery to be things to look out for in your building. Once you’ve established that heat recovery incorporated into an industrial process, you‘ll is for you, you should engage a specialist to need to choose a specialist carefully and ensure advise you by carrying out a more detailed they have particular experience in the field. feasibility study and providing an estimate of One way to do this is to make contact with the work required. equipment manufacturers. Technology guide 56

Finally, heat recovery systems should always Further reading Waste heat recovery in the process be installed by experienced and reputable industries (GPG141) There are a number of other publications contractors. If you don‘t have an existing available through the Carbon Trust which might How to implement industrial heat recovery relationship with a contractor you can contact be of interest: equipment (CTL037) the Heating and Ventilation Contractors’ Association (www.hvca.org.uk). Heat recovery from air compressors Air-to-air heat recovery: a guide to (GPG238) equipment eligible for ECAs (ECA771)

Energy efficient operation of boiler plant Find products which qualify for Enhanced Menu (GPG369) Capital Allowances

Low temperature hot water boilers – Introducing energy saving opportunities for business (CTV008)

How to recover heat from a compressed air system (CTL051) Technology guide 57

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Menu  Access the best knowledge  Carbon Reduction Label  Carbon Trust Standard We provide expert practical advice designed This is managed by the Carbon Trust Focused on reduction, it is awarded to to help SMEs define a tailored energy saving Footprinting Company, which was set up organisations that measure, manage and programme. Visit the advice pages on by the Carbon Trust in 2007. Any product reduce their carbon footprint. It is managed our website to find introductory help for that has had its carbon footprint calculated by the Carbon Trust Standard Company, organisations in your sector and more and verified by an accredited verifier can which was set up by the Carbon Trust detailed information on specific topics have the label on its packaging or marketing in June 2008. Find out more at such as lighting and heating. Find out more material. It shows the total greenhouse gas www.carbontruststandard.com at www.carbontrust.co.uk/ emissions arising from every stage of the carbonsavingadvice product’s life cycle, including production, transportation, preparation, use and disposal.  Call us on 0800 085 2005 Find out more at www.carbon-label.com Our experts offer independent, authoritative  Publications advice. Lines open 8.30am-5.30pm, We have many other free downloadable Monday to Friday. publications, factsheets, case studies, how to guides, technical publications and DVDs to help businesses manage their energy use more effectively. Find out more at www.carbontrust.co.uk/ publications The Carbon Trust is a not-for-profit company with the mission to accelerate the move to a low carbon economy. CTG057 We provide specialist support to business and the public sector to help cut carbon emissions, save energy and commercialise low carbon technologies. By stimulating low carbon action we contribute to key UK goals of lower carbon emissions, the development of low carbon businesses, increased energy security and associated jobs.

We help to cut carbon emissions now by: • providing specialist advice and finance to help organisations cut carbon • setting standards for carbon reduction.

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Published in the UK: August 2011. © Carbon Trust