How to design a heating system CIBSE Knowledge Series: KS8 Principal author Gay Lawrence Race Editors Helen Carwardine Ken Butcher CIBSE Knowledge Series — How to design a heating system Colin Campbell, [email protected], 3:16pm 03/09/2013, 1 Contents 1 Introduction . .1 1.1 Use of this guidance . .2 2 The heating design process . .4 2.1 The design process . .4 2.2 Heating system design process . .5 2.3 Key heating design calculation sequence . .8 2.4 Thermal comfort . .9 3 Key design steps . .10 3.1 Step 1: pre-design and design brief . .10 3.2 Step 2: gather design information . .11 3.3 Step 3: design data . .12 3.4 Step 4: building thermal performance analysis . .13 3.5 Step 5: heating system option analysis and selection . .15 3.6 Step 6: space heat losses and heat load . .20 3.7 Step 7: equipment sizing and selection . .23 3.8 Step 8: heating load analysis . .25 3.9 Step 9: plant sizing and selection . .27 3.10 Step 10: system analysis and control performance . .27 3.11 Step 11: Final value engineering and energy targets assessment 29 3.12 Step 12: design review . .29 4 Developing the design — key issues . .31 4.1 Design data . .31 4.2 Design margins . .31 4.3 Energy efficiency . .32 4.4 Quality control . .33 References . .34 Bibliography . .34 CIBSE Knowledge Series — How to design a heating system 1 Introduction In cooler climates the provision of heating is an essential part of creating Heating comfortable internal environments, and therefore heating system design is a fundamental part of building services design. In 2005: Heating is a major sector within mechanical building services. There are some ● 1.65 million new domestic boilers ● 21 million domestic properties in the UK with gas-fired central heating, and a 23,500 commercial boilers ● further 200,000 commercial properties with heating. The UK market for 9 million radiators ● 22 million metres of underfloor heating systems is substantial, with around 1.65 million new domestic boilers heating pipe Colin Campbell, [email protected], 3:16pm 03/09/2013, 1 installed per year and around 23,500 commercial boilers. There are around 9 million radiators installed per year with a further 22 million metres of were installed in the UK alone. (1) underfloor heating pipe (2005 figures) . Sources: BSRIA domestic boiler marketing report March 2006, BSRIA commercial boiler marketing report Heating is also a major consumer of energy within the UK, with space heating March 2006. accounting for over 40% of all non-transport energy use and over 60% of domestic energy use(2), rising to over 80% if hot water is included (see Figure 1). As major energy users, heating and hot water also generate a substantial proportion of CO2 emissions, delivering almost half the CO2 emissions from non-domestic buildings. Given the current requirements to limit energy consumption and CO2 production, good design of heating systems is essential to ensure that systems Figure 1: operate efficiently and safely and make effective use of energy. Historically UK non-transport energy there have been problems with oversizing of heating systems which can lead use (2002 figures) million to inefficient operation, particularly at part load operation, to control tonnes of oil equivalent problems and to a reduction in plant operating life(3). The energy consumption for oversized plant can be 50% more than necessary. 11·8 Although heating is often considered to be a simple, basic system, there are 2·4 4·4 many options and permutations to be considered. The majority of UK 41·4 buildings will require heating but different building types and locations will 15·0 have very different requirements and constraints — consider for example the choices possible for a small ground floor flat in a city centre development 9·7 against those for a holiday cottage in one of the National Parks, or the 12·9 3·3 choices for an urban industrial unit against those for a rural agricultural unit and farm shop. Space heating Water Cooking/catering The fundamental components of any heating system are: Lighting appliances Process use Motors/drivers — a means of generating heat, i.e. the heat source Drying/separation — a means of distributing the heat around the building or buildings, i.e. Other non-transport the distribution medium and network Source: DTI Energy consumption tables: overall energy consumption. URN No: — a means of delivering the heat into the space to be heated, i.e. the 05/2008 Table 1.2 Non-transport energy heat emitter. consumption by end use, 1990, 2000, 2001 and 2002 CIBSE Knowledge Series — How to design a heating system 1 Colin Campbell, [email protected], 3:16pm 03/09/2013, 1 Good design There are many possible options to be considered, some of which are listed in Table 1 below. These can give many permutations, from the simple use of Good design of heating systems is electric panel heating, using electricity both as the heat source and essential to ensure that systems operate distribution medium, to a conventional gas boiler system distributing low efficiently and safely and make effective use of energy. temperature water to a convector system. A more complex system would be one serving various buildings by using oil as the heat source to generate high temperature water for the main distribution, which is then reduced in temperature and pressure to low temperature water, via heat exchangers, to serve a radiator system. Table 1: Heat source gas CHP Heating systems LPG solar oil biomass coal off-peak electricity electricity wind air or water via heat pump ground via ground source heat pump Distribution medium water: low, medium or high temperature air steam electricity Factors to consider Emitter radiators ceiling panels forced convectors natural convectors Building type: panel heaters underfloor heating coils ● domestic ● school ● apartment building Whilst heating systems may seem relatively simple, in practice there are many ● retail factors to be considered during the design process, in order to achieve a ● hospital well-designed system that delivers both the required comfort conditions and ● factory level of control whilst still minimising energy consumption. This publication, ● office together with other CIBSE guidance, aims to assist the designer in achieving that aim. Location: ● city centre 1.1 Use of this guidance ● urban ● suburban This publication provides a clear, step-by-step overview of the whole heating ● rural design sequence: — section 2 maps the heating design process, with flowcharts illustrating the design steps sequence, and sets this in the context of the overall building process — section 3 outlines the key design procedures for each design step, and provides guidance on data requirements and sources, design outputs, key design issues and potential problem points 2 CIBSE Knowledge Series — How to design a heating system — section 4 addresses additional design issues that affect the design process. The publication links to the CIBSE Design Guides and also cross-references other key industry sources of design procedure guidance. Other relevant titles in the Knowledge Series are: — KS04 Understanding controls — KS06 Comfort — KS09 Energy efficient heating. Colin Campbell, [email protected], 3:16pm 03/09/2013, 1 This guidance is intended to enable and assist building services engineers involved in design, installation and commissioning to appreciate the key decisions and design steps involved in heating system design. It is likely to be of particular benefit to junior engineers and those whose main experience lies within other sectors of building services design. It can also be used by building services engineers to facilitate discussion on design requirements and design decisions with their clients. The publication answers the following questions, which can be used to help you find the most relevant sections to you: — What are the key stages in the heating design process? (Section 2.2) — What are the design criteria for thermal comfort? (Sections 2.4 and 3.3) — What should I consider when selecting a heating system? (Section 3.5) — How do I determine preheat requirements? (Section 3.6) — What should I consider to determine the required heating load? (Section 3.8) — When should I consider load diversity? (Section 3.8) — What else should I consider during design? (Section 4). Finally, a selected bibliography is provided for those who want further reading on the subject, subdivided to cover the main design steps and key topics such as design data, design calculations, design checks, heating plant and controls. Detailed technical information on heating system design and design data can be found in CIBSE Guide A (2006) and CIBSE Guide B (2001-2), chapter 1. CIBSE Knowledge Series — How to design a heating system 3 Colin Campbell, [email protected], 3:16pm 03/09/2013, 1 2 The heating design process 2.1 The design process Design involves translating ideas, proposals and statements of needs and requirements into precise descriptions of a specific product(4), which can then be delivered. (See Figure 2.) Two major features characterise the design process in general. Firstly, design tends to evolve through a series of stages during which the solution is increasingly designed at greater levels of detail, moving from broad outline through to fine detail. Secondly, design tends to contain iterative cycles of activities during which designs, or design components, are continually trialled, tested, evaluated and refined. Feedback is therefore an essential component of the design process, as shown in Figure 2. Figure 2: 1. Client Feedback/ The design process need Inform review Implement Design performance 4. Design 2. Design The design process delivery requirements Feedback/ review Select Develop 3. Design Within construction, design is a part of the larger construction process, as shown in Figure 3.