The Illustrated Guide to Renewable Technologies

A BSRIA Guide www.bsria.co.uk

By Kevin Pennycook

BG 1/2008

BG 1-2008 (Renewables) cover (rev).p65 3 17/03/2008, 10:01

INTRODUCTION Welcome to a new BSRIA illustrated guide to low energy and renewable technologies. The publication is the ideal primer for understanding the wide variety of innovative systems that provide cleaner and less environmentally damaging ways of heating, cooling and powering buildings.

This guide covers the majority of technologies that derive all or some of their power from renewable sources of energy, such as wind and biofuel. However biomass boilers can be used in conjunction with combined heat and power (CHP) and absorption refrigeration. As it’s vital that clients and designers understand the relationships between conventional low energy systems and emerging renewable energy systems, the guide covers both types (although, for reasons of brevity, not all low energy systems were able to be included).

Renewable energy describes power obtained from sources that are essentially inexhaustible. This covers energy supplies such as wind power, geothermal power, biomass, and solar power including photovoltaics. Some renewable supplies can also be used to create secondary fuels, such as hydrogen for use in fuel cells.

Whether the motivation comes from tighter energy regulation, higher fuel prices, or greater corporate responsibility, clients and their design teams will be required to consider using such renewable forms of energy to partially or wholly offset the use of fossil fuels and mains electricity.

Some renewable energy sources are able to absorb naturally any carbon dioxide emitted as a consequence of their use or combustion. Biofuels, derived from plant crops, are a good example. The carbon dioxide emitted from burning wood chips or plant oils is absorbed very quickly by new growth. It stands to reason that burning oak is not as sustainable as burning coppiced wood, as the growth cycle is longer and the carbon dioxide emitted will hang around longer in the Earth’s atmospheric systems to play its role in increasing the greenhouse effect.

Other systems, such as wind turbines and solar panels, emit no carbon dioxide when generating electricity. However, a considerable amount of carbon dioxide will have been emitted during product manufacture.

The distinction is important for designers who take a whole-life costing approach to construction. Embodied energy should influence both the basis of a building’s design and the selection of products – including renewables. Photovoltaics, for example, contain precious materials that require considerable energy to manufacture and transport. Depending on their contribution to the building’s energy needs, it might take 20 years or more for the photovoltaics to redeem the energy used in their manufacture. This needs to be considered during the specification stage.

2 ILLUSTRATED GUIDE TO RENEWABLE TECHNOLOGIES © BSRIA BG 1/2008

There is also a mistaken belief that buildings will automatically benefit from improved efficiency and lower carbon-dioxide emissions by being kitted-out with renewables technologies. This is a fallacy. Few technologies are truly fit-and-forget and work in a low energy mode straight out of the box. Renewable technologies, by and large, require greater attention at design, and can be demanding to manage and maintain. So when clients are being asked to invest in renewables technology, they need to know under what conditions the systems will perform, and what levels of diligence and expertise will be required in their facilities management. Fine-tuning of the renewables systems after occupation is also vital to ensure sustainable performance over the long-term.

So while renewable energy systems are certainly desirable compared with conventional fossil-fuel energy sources, the starting point is not a supplier’s catalogue of gleaming solar panels or rooftop-mounted wind turbines.

The starting point is to reduce the loads in the building first, and then increase the efficiency of the heating, ventilating, cooling and lighting systems. This can be achieved by investing in passive design, building it properly, and through discerning product specification. The third step is to halve the carbon in the mains fuel supplies, perhaps by taking power from off-site wind turbines or district biomass-CHP. Community energy schemes using large- scale wind power, co or tri-generation and district heating make more environmental and economic sense than lots of separate, smaller renewable systems serving single buildings.

By following this process, designers can cut carbon-dioxide emissions to one-eighth of what they would otherwise be before need arises for specifying renewables technology.

As we head into a changing world where carbon neutrality will soon become a government objective, the mantra is this: keep it simple, do it well, finish things off properly, and only get clever with renewables where they are truly justified. And when you do, use this guide as your design primer.

Roderic Bunn BSRIA, March 2008

ILLUSTRATED GUIDE TO RENEWABLE TECHNOLOGIES 3 © BSRIA BG 1/2008

SUMMARY

Technology Characteristics Functionality Cost Reliability Maintenance CO2 saving Overall effectiveness requirement rating Absorption Requires no High. Waste Medium. More High. Few Low Medium – *** cooling mechanical heat from CHP expensive than moving parts high vapour source used to conventional compression. provide cooling chillers but Activated by source for air uses waste heat external heat conditioning source

Biomass Uses plant- High. Direct Medium. More High for direct Medium. Direct High ***** derived organic combustion expensive than combustion combustion material systems can conventional systems. systems are (relatively carbon replace gas/oil- boilers Anaerobic partially self neutral). Can fired boilers. digestion and cleaning produce heat or Requires large gasification biogas depending fuel storage systems can be on the type of facility problematic technology

CHP Generates both High. Requires Medium. Medium. Medium. Medium. Can **** electricity and predictable and Requires full Proven Requires be improved heat using fossil relatively utilisation of technology regular planned if biomass fuel or renewable constant loads waste heat maintenance is used fuels for best performance Fuel cells Electrochemical High. Same as Low. Limited Medium. Long- Medium. Few Medium. ** device that CHP range of term reliability moving parts. Depends on produces commercially data not yet Fuel cell stack full utilisation electricity and available fuel available. has finite life of generated heat on-site cells, and Expected to be heat and fuel expensive reliable source

Greywater Reuses waste Medium. Low. Medium. Medium. Low ** recovery water (bathing, Requires match Installation and Pumps, filters, Requires washing, laundry) between waste on-going costs and sensors planned for toilet flushing, water source may not justify can present maintenance irrigation, and and use savings problems regime to other non- cover health potable uses risks

Ground Uses heat from High. Can pre- Medium. High. No Low. Providing Medium *** source the ground to cool air in Depends on moving parts steps are taken systems – air pre-condition the summer and cost of drilling to pre-filter air supply air to a pre-heat it in or excavation and avoid building winter to install pipes water ingress

Ground Makes use of High. Can be Medium. High. However, Low for closed- Medium *** source water from combined with Depends on open-loop loop systems systems – aquifers (either heat pump cost of systems are water directly or technology. boreholes susceptible to indirectly) to Heat source blockages and provide cooling in can pre-heat biological summer ventilation air fouling

Ground Takes up heat High. Systems Medium High. Relatively Low Medium. High **** source heat from ground and can be run in few moving COPs are pumps releases it at cooling mode parts. Proven dependant on higher technology relatively low temperatures. supply Heat can be used temperatures for space heating in heating and domestic hot mode water

4 ILLUSTRATED GUIDE TO RENEWABLE TECHNOLOGIES © BSRIA BG 1/2008

Technology Characteristics Functionality Cost Reliability Maintenance CO2 saving Overall effectiveness requirement rating Photovoltaics Converts sunlight Medium. Low. However, Medium. Low, but Low. Relative *** directly to DC Requires careful costs are Associated specialist to high cost electrical power. positioning for predicted to inverters can Requires inverter optimum improve cause problems to convert to AC performance. Wide range of installation options Rainwater Collects and Medium. Low. Medium. Medium. Low ** recovery stores rainwater Requires a Installation and Pumps, filters, Requires from roofs and balance on-going costs and sensors inclusion in a other catchment between may not justify can present planned areas for toilet collected water savings problems maintenance flushing and its use. regime Large storage tanks may be required Solar air Collects solar Medium. Medium. Solar High Low. System Low – *** heating energy to heat Relatively large collectors can cleaning medium. supply air. Can number of be an integral required, so Requires fan also heat re- techniques. part of the access can be power, circulated air Can also pre- building fabric an issue however this heat domestic could be hot water provided by photovoltaics Solar cooling Solar thermal Medium. Low. Relatively High Low. Low – * energy used to Requires high cost of Absorption medium drive absorption, matching of absorption chiller is low adsorption or solar collector chillers and maintenance desiccant cooling temperature solar collectors with chiller operating temperature. Solar water Solar energy used Medium. Medium Medium – high. Low Medium. **** heating to heat water, Proven Circulation Circulating usually for technology pump and pumps can be domestic hot with a range of valves are PV powered water purposes collectors for relatively different reliable operational requirements Surface Uses pumped Low. Relatively Low – medium. Medium – high. Low Medium. *** water water from the few buildings Depends on Filtration Depends on cooling sea, lakes or close to the length of required to the pumping rivers to provide suitable water piping required prevent heat power a cooling medium sources exchanger required fouling Water Range of devices Can be used in Medium. Generally Low – medium. Low **** conservation used to limit a wide range of Depends on reliable, but Waterless water applications device some devices urinals require consumption and building may be regular and types susceptible to correct hard water maintenance Wind Turbine/ Best Low. Depends Medium. Medium. Low – ** generator performance in greatly on Turbulent air Requires medium. converts wind open, non- available wind conditions regular Large sized energy to urban conditions. associated with maintenance. turbines in electrical power locations. Can Actual power urban locations Access may be non-urban or be installed on, output likely to may reduce an issue off-shore or integrated be much less lifespan of locations will into, a building than the rated components be more output effective

ILLUSTRATED GUIDE TO RENEWABLE TECHNOLOGIES 5 © BSRIA BG 1/2008

6 ILLUSTRATED GUIDE TO RENEWABLE TECHNOLOGIES © BSRIA BG 1/2008

CONTENTS Page

SUMMARY 4

ALPHABETICAL LIST OF SYSTEMS AND EQUIPMENT 8

ABSORPTION COOLING 9

BIOMASS 13

COMBINED HEAT AND POWER 20

FUEL CELLS 27

GREYWATER 32

GROUND SOURCE SYSTEMS 36 Ground source systems – air 36 Ground source systems – water 39 Ground source heat pumps 42 PHOTOVOLTAICS 47

RAINWATER RECOVERY 53

SOLAR 59 Solar air heating 59 Solar cooling 63 Solar water heating 66 SURFACE WATER COOLING 73

WATER CONSERVATION 75

WIND POWER 80

ILLUSTRATED GUIDE TO RENEWABLE TECHNOLOGIES 7 © BSRIA BG 1/2008

ALPHABETICAL LIST OF SYSTEMS AND EQUIPMENT Absorption chillers 9-10, 12 Lithium bromide 10 Absorption cooling 63 Membrane filters 33 Adsorption cooling 64 Micro CHP 20, 22 Ammonia refrigeration 10 Open-loop systems 39, 41, 60-61, 68, 73 Anaerobic digestion 15 Perforated air-collectors 61 Back-pressure steam turbine systems 21 Photovoltaics 47, 52 Biofuel 13 Pitched roofs 48-49, 70 Biological treatment 33, 56 Plate heat-exchanger 21 Biomass CHP 22 Pressurised systems 68 Biomass storage 17 Rainwater 34-35, 53-56, 58 Biomass system 18 Reciprocating engine CHP 11 Building façade 48-49, 51, 59, 71, 82 Reed beds 33, 57 Cavity collector 60 Sand filters 33 Closed-loop collector 60 Seawater cooling system 74 Closed-loop systems 40 Shell and tube heat-exchanger 21 Collection tanks 55 Showers and baths 77 Combined heat and power 17, 18 Sloping roofs 48, 49, 70 Condenser 9-10, 12, 39 Soakaway 35, 58 Dehumidification 45 Solar air systems 59 Desiccant cooling 65 Solar collectors 60 Direct combustion 13, 18 Solar heating of ventilation air 59 Directly pumped systems 53 Solar shading devices 48, 50 Disinfection 57-58 Solar water heating systems 66, 70 Domestic hot water heating 45 Space cooling 23, 45 Drainback systems 69 Space heating 44 Dry air-coolers 12 Steam turbines 21 Evacuated-tube collectors 67 Surface water cooling 73 Evaporator 9-10, 42 Tri-generation 22 Flat roofs 48-49, 51 Unglazed plastic collectors 68 Flat-plate collectors 59 Urinals 75 Foul drainage 35, 58 Vapour-compression chiller 12 Fuel cells 27-31 Vertical-axis turbines 80 Gas turbines 11, 20-21 Water conservation 75, 79 Gasification 16 Water storage 34 Glazed flat-plate collectors 67 Water treatment 33 Gravity systems 53 Water-efficient WCs 76 Greywater systems 32 Waterless and vacuum toilets 77 Ground-coupled systems 36 Wet cooling towers 12 Ground source heat pumps 40, 42-46 Wind turbines 80-84 Heat exchangers 21, 39, 43-46, 60, 66-70, 73-74 Woodchip fuel 13

8 ILLUSTRATED GUIDE TO RENEWABLE TECHNOLOGIES © BSRIA BG 1/2008

Benefits Can make use of waste heat Refrigerants used have no global warming potential ABSORPTION COOLING Quiet and vibration-free System description Reliable Relatively low maintenance costs

Limitations Low efficiency, and low coefficient of performance compared to conventional chillers Relatively high cost compared to vapour compressors Larger heat-rejection plant than conventional chillers Slower to start up and slower to respond to changing loads

Schematic of absorption chiller. In a conventional vapour-compression chiller an electric motor is used to drive a compressor. In an absorption chiller a heat source drives the cooling process. Heat sources can include hot water, steam, hot air or hot products of combustion (exhaust gases) from the burning of fuel.

In a conventional mechanical vapour-compression chiller the refrigerant evaporates at a low pressure and produces a cooling effect. A compressor is then used to compress the vapour to a higher pressure where it condenses and releases heat. In an absorption chiller the compressor is replaced by a chemical absorber, generator and a pump. The pump consumes much less electricity than a comparable compressor (approximately nine percent of that for a vapour compression plant). The majority of the energy required to drive the cooling process is provided by the external supply of heat.

Absorption cycles use two fluids: the refrigerant and the absorbent. The most common fluids are water for the refrigerant and lithium bromide for the absorbent. These fluids are separated and re-combined in the absorption cycle. The low-pressure refrigerant vapour is absorbed into the absorbent releasing heat. The liquid refrigerant/absorbent solution is pumped to a generator with high operating pressure. Heat is then added at the high-pressure generator which causes the refrigerant to desorb from the absorbent and vaporise. The vapours flow to a condenser, where heat is rejected and condensed to a high-pressure liquid. The liquid is then throttled through an expansion valve to the lower pressure in the evaporator where it evaporates by absorbing heat. This absorbing of heat is used to provide a useful cooling effect. The remaining liquid absorbent in the generator passes through a valve where its pressure is reduced and is then re-combined with the low-pressure refrigerant vapours returning from the evaporator. The cycle is then repeated.

ILLUSTRATED GUIDE TO RENEWABLE TECHNOLOGIES 9 © BSRIA BG 1/2008

Absorption chillers have a number of advantages: Table 1: Absorption chiller range. Chiller type Heat source They are activated by heat Hot water Steam (3-9 Engine o No mechanical vapour-compression is required (80-130 C) bar) exhaust or steam gases (280- o The refrigerants used do not damage the atmosphere and have (0·2-1·0 800 C) no global warming potential (some refrigerants used in vapour bar) compression chillers have very high global-warming potential) Single-effect Require no lubricants Refrigerant Water - - Quiet and vibration free. Condenser type Water - - cooled System types Co-efficient of 0·7 - - Absorption chillers can be classified based on the type of heat source, performance the number of effects and the chemicals used in the absorption process. Indirect-fired absorption chillers use waste/rejected heat from another Double-effect process to drive the absorption process. Typical heat sources include Refrigerant steam, hot water or hot gases. Direct-fired chillers include an integral - Water Water burner, usually operating on natural gas. Condenser type - Water Water cooled cooled In a single-effect absorption chiller the heat released during the Co-efficient of - 1·2 1·1 chemical process of absorbing refrigerant vapour into the liquid stream performance is rejected as waste heat. In a double-effect absorption chiller some of this energy is used to generate high-pressure refrigerant vapour. Using Source: CIBSE Guide B4 this heat of absorption reduces the demand for heat and boosts the chiller system efficiency.

Double-effect chillers use two generators paired with a single condenser, absorber and evaporator. Although they operate with a greater efficiency they require a higher temperature heat input compared with a single-effect chiller. The minimum heat source temperature for a double-effect chiller is 140oC. Double-effect chillers are more expensive than single-effect chillers. Triple-effect chillers are under development.

Two absorbent-refrigerant mixtures are widely used. These are lithium bromide water mixture and ammonia refrigeration mixture. In a lithium bromide water mixture the lithium bromide (a salt) is the absorbent and the water is the refrigerant. Lithium bromide systems are the most commonly used absorption system, particularly for commercial cooling. In an ammonia system the water is the absorbent and the ammonia is the refrigerant. Ammonia systems are typically used when low temperature cooling or freezing is required.

Lithium bromide water systems are widely available as packaged units with capacities ranging from 100 kW to several thousands of kilowatts. A practical limitation associated with this type of system is that the minimum chilled water temperature that can be produced is approximately 5oC. Ammonia refrigeration systems are available in small (30-100 kW), medium (100-1000 kW) and large (>1000 kW) sizes. Cooling temperatures down to -60oC are possible.

Allied technologies

CHP Industrial processes producing waste heat Renewable sources producing heat.

10 ILLUSTRATED GUIDE TO RENEWABLE TECHNOLOGIES © BSRIA BG 1/2008

Where to use Absorption cooling can be considered as an alternative to traditional chillers if one of the following factors applies:

An existing combined heat and power (CHP) unit is present and not all of the waste heat is being used A new CHP installation is being considered Waste heat is available from a process Renewable fuel sources can be used such as landfill gas.

The available heat source will determine the type of absorption chiller that is suitable for a specific application. Typical sources of heat include:

Gas turbine CHP Reciprocating engine CHP Waste heat Hot water and steam.

With a gas turbine CHP, the exhaust gas from the gas turbine is used to raise steam in a waste heat boiler. The high-pressure steam available is suitable for supplying a double-effect absorption unit. The overall efficiency of the CHP can be enhanced if second stage heat recovery using the exhaust gases is used to heat water for domestic hot water and/or space heating uses.

Reciprocating engine CHP units typically provide hot water at 85-90oC. This can be used for a single-effect absorption chiller, although the performance of the chiller will have to be down-rated (single-effect absorption chillers normally work on a heat source at 102oC and above). Some CHP engines can produce water at higher temperatures, in which case the performance of the absorption chiller will be improved.

Waste heat from other sources such as industrial processes can also be used to drive absorption chillers. Low-pressure steam and water can be used with single-effect absorption chillers while higher pressure steam (7- 9 bar) can be used to drive double-effect chillers.

In instances where boilers provide space heating and are required to supply a small load in summer, or where a large ring-main is used to supply a few users, the efficiency of the boiler system can be improved by using the heated water/steam to drive an absorption chiller. In practice, however, it may be more efficient to reconsider the heating strategy and install a number of small local boilers.

Application considerations The factors that determine whether a heat source is suitable for an absorption cooling application are:

Temperature of the source heat-stream Flow rate of the recovered heat-stream Chemical composition of the source heat-stream Intermittency of the recovered heat stream temperature and flow.

ILLUSTRATED GUIDE TO RENEWABLE TECHNOLOGIES 11 © BSRIA BG 1/2008

Glossary Vapour-compression chiller A refrigeration device that uses mechanical The performance of an absorption chiller is dependent on the following: means (usually driven by an electric motor) to raise the pressure of a refrigerant A higher chilled water temperature gives a higher coefficient of Combined heat and power system performance (COP) and cooling capacity A system that simultaneously generates electricity and heat in a single integrated unit. A lower cooling water temperature gives a higher COP and The heat (usually in the form of heated water or cooling capacity steam) can be used for building services-related A higher temperature heat source gives a similar COP but processes. Also referred to as cogeneration increases cooling capacity. Dry-air coolers A device used to reject heat from a refrigeration Using a lower heat source temperature, higher condenser water system. Air is passed over a heat exchanger temperature or lower chiller water temperature will reduce the cooling (condenser) output. This means that a larger, more expensive machine will be Wet cooling towers required. A heat-rejection device that extracts heat from a refrigeration system to the atmosphere through The heat rejection from an absorption chiller will be greater than a the cooling of a water stream to a lower conventional chiller with the same cooling capacity. This will require temperature. Heat is lost through evaporation of larger heat rejection units (such as dry air-coolers or wet cooling towers) some of the water. Also referred to as an for absorption chillers. The associated space and weight constraints on evaporative cooling tower some sites may be an issue. Evaporator A part of a refrigeration system in which the Absorption chillers are slower to start-up than mechanical vapour refrigerant evaporates and in so doing takes up compression chillers. They are also slower to respond to changing loads. external heat in its vicinity For large systems a buffer tank may be required to increase the inertia for the chilled water circuit. The frequent starting and stopping of Condenser absorption chillers should be avoided. A part of a refrigeration system, which enables the refrigerant to condense, and in so doing gives

up heat Absorption chillers have few moving parts and have correspondingly lower maintenance requirements compared to conventional chillers. Maintenance costs can be lower than conventional chillers. Standards None identified An absorption chiller can be used to meet the base-load cooling demand in a building, while peak cooling loads can be met by a conventional References and further reading chiller. This approach can be advantageous because conventional chillers An Introduction to Absorption Cooling, Good usually cost less than the equivalent absorption chiller. Their use is Practice Guide 256, Energy Efficiency Best practice Programme 2001 therefore more cost-effective for limited running hours. Application Guide for Absorption Designers should consider the requirements for a standby heat source Cooling/Refrigeration using Recovered Heat, should the normal heat source (such as a CHP unit) not be available. ASHRAE 1995, ISBN 1 88341326 5 The requirement for standby capacity will depend on the criticality of ASHRAE Handbook – Refrigeration ASHRAE the business function associated with the building. Designers should also consider whether it is more appropriate to size the absorption chiller on Refrigeration and Heat Rejection, CIBSE Guide B4 the available heat source or on the building’s cooling demand. The Small-Scale Combined Heat and Power for Buildings, temperature of the heat source will determine whether a single or CIBSE AM12, 1999 double-effect chiller is appropriate.

An absorption chiller used in conjunction with a CHP unit will raise the viability and cost effectiveness of the CHP unit. Most CHP installations are sized on the basis of heat demand. This usually means that the building’s electrical base load is higher than the CHP’s electrical output. By using an absorption chiller the additional heat load allows increased running hours while reducing the electricity demand associated with conventional chillers.

12 ILLUSTRATED GUIDE TO RENEWABLE TECHNOLOGIES © BSRIA BG 1/2008

Benefits Biomass-fuels can be used to produce energy on a continuous basis (unlike renewables such as wind or solar energy) BIOMASS Biomass can be an economic alternative to fossil fuels System description Biomass is any plant-derived organic material that renews itself over a Biomass is a potential source of both heat short period. Biomass energy systems are based on either the direct or and electricity indirect combustion of fuels derived from those plant sources. Biomass technology is flexible and scaleable, from a single boiler to a power station The most common form of biomass is the direct combustion of wood in treated or untreated forms. Other possibilities include the production Limitations and subsequent combustion of biogas produced by either gasification or Biomass fuels have a lower energy density anaerobic digestion of plant materials. Liquid biofuels such as bioethanol compared to fossil fuels can also be used. The use of biomass is becoming increasingly common Biomass systems have particular design in some European countries (some countries such as Austria are heavily management and maintenance requirements dependant on biomass). The environmental benefits relate to the significantly lower amounts of energy used in biomass production and associated with sourcing, transportation and storage processing compared to the energy released when they are burnt. This can range from a four-fold return for biodiesel to an approximate 20-fold Biomass can be less convenient to operate energy return for woody biomass. than mains-supplied fuels such as natural gas Biomass systems are more management CHP systems and absorption chillers are discussed elsewhere in this guide. intensive and require expertise in facilities management Biomass system types Sources of biomass can fluctuate, so boilers should be specified to operate on a variety Direct combustion of fuels without risk of overheating or The direct combustion of wood-based fuel sources is likely to be the tripping out most practical use of biomass in building applications. Potential fuel sources are wide ranging and include solid wood, wood off-cuts, woodchips, pellets and briquettes. Typical examples of woody biomass include willow short-rotation coppice and miscanthus (perennial grass).

Table 2: Typical properties. Fuel Energy density Energy density Bulk density Energy density Energy density by mass by mass by volume by volume GJ/tonne KWh/kg Kg/m3 MJ/m3 KWh/m3 Wood chips (very dependent on 7 – 15 2 – 4 175 – 350 2000 – 3600 600 – 1000 moisture content) Log wood (stacked – air dry 20% 15 4·2 300 – 550 4500 – 8300 1 300 – 2300 moisture content) Wood (solid oven dry) 18 – 21 5 – 5·8 450 – 800 8100 – 16 800 2300 – 4600 Wood pellets 18 5 600 – 700 10 800 – 12 600 3000 – 3500 Miscanthus (bail) 17 4·7 120 – 160 2000 – 2700 560 – 750

Table 3: An overview of biofuels, the feedstocks and processes used in their production. Biofuel type Specific name Biomass feedstock Production process Bioethanol Conventional bioethanol Sugar beets, grains Hydrolysis and fermentation Vegetable oil Pure vegetable oil Oil crops (such as rapeseed, Cold pressing and extraction sunflower seeds) Biodiesel Biodiesel from energy crops Oil crops (such as rapeseed, Cold pressing and extraction and Rapeseed methyl ester (RME), fatty sunflower seeds) transesterfication acid methyl/ethyl ester (FAME/FAEE) Biodiesel Biodiesel from waste (FAME/FAEE) Waste, cooking and frying oil Transesterfication Biogas Upgraded biogas (Wet) biomass Digestion Bio-ETBE Bioethanol Chemical synthesis

ILLUSTRATED GUIDE TO RENEWABLE TECHNOLOGIES 13 © BSRIA BG 1/2008

Biomass heaters range from small, simple wood-burning stoves to large fully automated boilers intended for large commercial/public buildings or community heating schemes. Features of a good large-scale boiler include the following:

Thermal efficiency greater than 85% Emissions at full load less than 250 mg/m3 CO, 150 mg/m3 dust and 300 mg/m3 NOx

Automatic cleaning of the boiler heat-exchanger and automatic Courtesy of Kohlbach Holding GmbH ash removal Remote monitoring of the boiler operating parameters.

An example of a 3D integrated biomass boiler and fuel delivery system. Table 4: Large-scale biomass boilers are available in a range of combustion types. Combustion Feed Fuel Power type Dual-chamber Mechanical Woodchips, 35 kW – 3 MW furnace bark Underfeed Mechanical Woodchips 20 kW – 2 MW furnace Stocker-fired Mechanical Woodchips From 200 kW furnace Cyclone furnace Pneumatic From 200 kW Fluidized-bed Mechanical Woodchips From 10 MW combustion Source: Planning and Installing Bioenergy Systems. A typical biomass boiler, installed in a UK primary school. The operational characteristics of biomass boilers differ significantly from traditional boilers (such as gas-fired boilers). Start-up times are longer and heat retention within the boiler means that heat is transferred to the heated medium for a considerable period after boiler shutdown. Although most biomass boilers are designed to allow modulation of the boiler output down to typically 30% of the maximum output, they are not best suited to frequent modulation. For efficient, low emission combustion, biomass needs to be burned rapidly and at a high temperature. One approach to achieving optimum performance is to incorporate a buffer tank into the system. A large volume of water is used as a thermal store between the boiler and the load side of the heating system. When the load decreases the temperature of the water in the tank rises and when the load subsequently increases there is a store of hot water to satisfy demand until the boiler output rises.

Another possible approach is to size the biomass boiler to meet the building’s base heating load and use a small conventional boiler to meet peak demands. This approach is also appropriate for dealing with seasonal variations in heating demand. However, care needs to be taken with the design and specification of the control system, which will be required to manage two boilers with very different operating characteristics.

Other considerations include types of biomass materials. Biomass boilers are available that are suitable for a wide range of woody fuel sources. Biomass should be selected for its local availability as well as for its combustion characteristics, as the environmental costs of transporting relatively bulky fuel over large distances will reduce the environmental benefits of biomass combustion. Alternative sources of supply are also very important. A 400 kW district-heating biomass boiler.

14 ILLUSTRATED GUIDE TO RENEWABLE TECHNOLOGIES © BSRIA BG 1/2008

BG 7-2009 heat pumps cover2.qxd 21/10/2009 08:56 Page 1

A BSRIA Guide www.bsria.co.uk

Heat Pumps

A guidance document for designers by Reginald Brown

BG 7/2009

ACKNOWLEDGEMENTS

This publication has been written by BSRIA’s Reginald Brown with additional information provided by David Bleicher and Mike Smith, and has been designed and produced by Ruth Radburn.

BSRIA would like to thank the following for their help and guidance in reviewing the document:

Heat Pump Association Strategy Committee Steve Pardy, Zisman Bowyer & Partners

This publication has been printed on Nine Lives Silk recycled paper.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means electronic or mechanical including photocopying, recording or otherwise without prior written permission of the publisher.

©BSRIA BG 7/2009 October 2009 ISBN 978 0 86022 686 4 Printed by ImageData Ltd

HEAT PUMPS – A GUIDANCE DOCUMENT

CONTENTS

1 INTRODUCTION 1

2 HEAT PUMP FUNDAMENTALS 2 2.1 Heat pump technology and the economic carbon case 2 2.2 Refrigeration cycles and efficiency 3 2.3 Heat sources and sinks 4 2.4 Combined cycles 6 2.5 Integration of renewable energy 7 3 LEGISLATION 8 3.1 F-Gas Regulations 8 3.2 Handling of refrigerants 8 3.3 Pressure Systems Safety Regulations 9 3.4 Waste Electrical and Electronic Equipment Regulations 9 3.5 Building Regulations 9 3.6 Construction Design and Management Regulations 9 4 OUTLINE DESIGN 11 4.1 Sizing heat pump systems 11 4.2 Selection of heat source and sinks 14 4.3 Estimation of performance 15 5 DETAILED DESIGN OF HEATING AND COOLING SOURCE 16 5.1 Packaged units 16 5.2 Air source 17 5.3 Exhaust air source 20 5.4 Ground source 21 5.5 Ground water 28 5.6 Surface water 30 6 DETAILED DESIGN OF HEATING AND COOLING DISTRIBUTION 31 6.1 Principle 31 6.2 Air-to-air systems 31 6.3 Water (or brine) to air systems 36 6.4 Hydronic systems 36 6.5 Domestic hot water 40 6.6 Integration with conventional heat sources 42 6.7 Integration with renewable energy 44 7 SYSTEM CONTROLS 47

8 INSTALLATION 49 8.1 Delivery and positioning 49 8.2 Electrical installation 49 8.3 Internal pipework installation 50 8.4 Ground loops and boreholes 50

HEAT PUMPS – A GUIDANCE DOCUMENT

CONTENTS

9 COMMISSIONING AND TESTING 54 9.1 Electrical aspects 54 9.2 Refrigeration circuit 54 9.3 Heat source 54 9.4 Heating and cooling distribution 54 9.5 Handover 55 REFERENCES 71

BIBLIOGRAPHY 70

APPENDICES

APPENDIX A: HEAT PUMP THERMODYNAMICS 57

APPENDIX B: COMMISSIONING AND TESTING 64

APPENDIX C: F-GAS REGULATIONS 67

TABLES

Table 1: Heat sources and typical design assumptions 5 Table 2: Heat sinks and typical design assumptions 5 Table 3: Heat pump design factors for water-based heat distribution 11 Table 4: Practical selection issues for heat sources and sinks 14 Table 5: Maximum extraction rates for buried ground coils 21 Table 6: Recommended maximum length for different tube sizes 22 Table 7: Maximum extraction rates for close loop boreholes 23 Table 8: Absorption refrigeration 62 Table 9: Comparison of vapour compression refrigerants 65 Table 10: Absorption refrigerants 66 Table 11: Key dates for implementation of F-Gas requirements 68 Table 12: Common refrigerants subject to the F-Gas Regulations 68 Table 13: Obligations under the F-Gas Regulations 69 Table 14: Frequency of checks on heat pump systems required by F-Gas Regulations 69

HEAT PUMPS – A GUIDANCE DOCUMENT

FIGURES

Figure 1: Heat pump circuit 2 Figure 2: COP versus temperature lift 4 Figure 3: Gas engine heat pump 6 Figure 4: Example annual temperature profile corresponding space heating load 12 Figure 5: Possibilities to reduce noise from free standing external units 19 Figure 6: Buried ground coils 22 Figure 7: Proprietary manifold chamber 23 Figure 8: Preparation of an Energy Piles™ 24 Figure 9: Completed Energy Piles™ 25 Figure 10: Carbon dioxide heat-pipe 26 Figure 11: Schematic summary of air-to-air heat pumps 32 Figure 12: VRF with heat recovery 34 Figure 13: Use of a buffer vessel 38 Figure 14: Passive cooling from a ground loop 39 Figure 15: Tank-in-tank domestic hot water 40 Figure 16: Using a buffer vessel to pre-heat domestic hot water 41 Figure 17: Heat pump with a boiler 42 Figure 18: Solar contribution to ground source 45 Figure 19: Typical solar hot water integration 45 Figure 20: Typical small drilling rig used for heat pump boreholes 52 Figure 21: Components of a typical heat pump circuit 57 Figure 22: Heat pump cycle 58 Figure 23: Process efficiency and the pressure - enthalpy diagram 59 Figure 24: Temperature - entropy diagram 60 Figure 25: Vapour injection cycle 61 Figure 26: Reversible heat pump 62 Figure 27: Schematic of absorption chiller 63 Figure 28: Pressure enthalpy diagram for R134a 64

HEAT PUMPS – A GUIDANCE DOCUMENT

INTRODUCTIONINTRODUCTION 1

1 INTRODUCTION Heat pumps are increasingly being considered as an alternative to combustion-based heating plant as a means to reduce operating costs and carbon emissions. In some countries heat pumps have already taken a significant proportion of the market for heating appliances and this is likely to be a long-term trend throughout Europe. However, while it is true that space heating and hot water needs in housing and most other buildings can be fulfilled by heat pumps, it would be wrong to treat heat pumps simply as a drop-in replacement for conventional boilers. Heat pumps can replace boiler plant in existing houses, but this should not be done without a thorough review of the associated heat distribution system and rarely without system changes. Conversely, a hydronic heat distribution system, optimised for a heat pump should also work well with a condensing boiler.

This guide explains the design of heat-pump based heating and cooling systems to maximise the benefits of reduced operating costs and carbon emissions while avoiding excessive capital costs for plant and infrastructure. The guide’s emphasis is on the application of packaged heat pump plant for residential and small commercial buildings. Some guidance is provided for component-based plant that may be used for larger scale applications.

The information contained in this guide is drawn from a variety of sources including:

• Heat Pump Installer Manual. BSRIA • Heating Systems in Buildings – Design of Heat Pump Heating Systems. BS EN 15450:2007 • Ground Source Heat Pumps, BSRIA TN 18/99, 1999 • Guide to Good Practice - Heat Pumps, HVCA TR30 2007

Other published material is identified in the text, and a full list of bibliographies and references can be found on pages 70 – 71.

HEAT PUMPS – A GUIDANCE DOCUMENT 1

2 HEAT HEAT PUMPPUMP FUNDAMENTALS FUNDAMENTALS

2 HEAT PUMP FUNDAMENTALS 2.1 HEAT PUMP A heat pump is a device for transferring heat from a lower temperature TECHNOLOGY heat source to a higher temperature heat sink. This is opposite to the AND THE ECONOMIC natural flow of heat from a hot source to a cold sink, but is made CARBON CASE possible by the application of an external energy source to drive a thermodynamic refrigeration cycle. The important characteristic of a heat pump is that the amount of heat that can be transferred is greater than the energy needed to drive the cycle.

Figure 1: Heat pump circuit.

The ratio between the heat provided to the sink and the energy required is known as the coefficient of performance (COP). Electrically driven heat pumps used for space heating applications in moderate climates usually have a COP of a least 3·5 at design conditions. This means that 3·5 kWh of heat is output for 1 kWh electricity used to drive the process.

The COP is the determinant of whether the heat pump will be more economic to use than an alternative heating appliance and whether the carbon emissions with will less than an alternative heating appliance.

2 HEAT PUMPS – A GUIDANCE DOCUMENT

HEAT PUMP FUNDAMENTALS 2

For example, consider a space heating load of 100 kWh per week that can be served by a typical electric heat pump operating at an average COP of 3·5 or condensing gas boiler operating with a thermal efficiency of 100 percent (net calorific value basis):

Heat pump energy consumption = Load/COP = 100/3·5 = 28·6 kWh Boiler energy consumption = Load/Efficiency = 100/100% = 100 kWh

In simple terms, such a heat pump will be cheaper to operate provided that the electricity price is no more than 3·5 times the price of an alternative fuel. There are other factors that come into a more detailed analysis of the benefits, such as maintenance costs and equipment life, but the fuel price ratio is the key. This is also the main reason why the heat pump markets in some other countries have developed much more quickly than the UK where, historically, electricity has been more than 3·5 times the cost of natural gas. However, the long-term trend is for gas prices to increase faster than electricity prices, while heat pump COP gradually improves to provide a clear operating cost advantage for heat pumps. Heat pumps are already cheaper to operate than oil and LPG, and much cheaper to operate than direct electric heating.

While the operating costs for heat pumps and condensing boilers are rather similar at current fuel prices, the case for heat pumps as a low carbon technology is more conclusive.

In 2009, the current UK generator mix emitted carbon dioxide (CO2) at a

rate of approximately 0·43 kgCO2/kWh of electricity used (DEFRA 2007 data for greenhouse gas emissions reporting ). The corresponding figure

for natural gas is 0·194 CO2/kWh. Using the example given above for an electric heat pump with a COP of 3·5 and a condensing boiler operating with an efficiency of 100 percent (net calorific value basis), the carbon dioxide emissions are:

Heat pump CO2 emissions = 28·6 x 0·43 = 12·3 kg CO2

Boiler CO2 emissions = 100 x 0·194 = 19·4 kg CO2

The heat pump therefore emits 35 percent less CO2 than the condensing boiler.

2.2 REFRIGERATION Although a detailed knowledge of thermodynamics is not required for CYCLES AND the practical application of heat pumps, a basic understanding of the EFFICIENCY factors that influence efficiency is important for all heating systems designers, whether using packaged plant or component-based solutions.

A brief review of the thermodynamic refrigeration cycle is given in Appendix A – Page 57 and the properties of common refrigerants in Appendix B – Page 64.

HEAT PUMPS – A GUIDANCE DOCUMENT 3