How to design a heating system

36 Pages·2006·0.565 MB·English

by  Carwardine, Helen, Race, Gay Lawrence

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
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 assessment29
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
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
● 23,500 commercial boilers
21 million domestic properties in the UK with gas-fired central heating, and a
● 9 million radiators
further 200,000 commercial properties with heating. The UK market for
● 22 million metres of underfloor
heating systems is substantial, with around 1.65 million new domestic boilers
heating pipe
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.
underfloor heating pipe (2005 figures)(1).
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 CO emissions, delivering almost half the CO emissions from
2 2
non-domestic buildings.
Given the current requirements to limit energy consumption and CO
2
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
There are many possible options to be considered, some of which are listed
Good design
in Table 1 below. These can give many permutations, from the simple use of
electric panel heating, using electricity both as the heat source and
Good design of heating systems is
essential to ensure that systems operate distribution medium, to a conventional gas boiler system distributing low
efficiently and safely and make effective
temperature water to a convector system. A more complex system would be
use of energy.
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 hea.ting
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
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
The design process Feedback/ 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. Both the RIBA Plan of Work Stages(5)and the ACE
Conditions of Engagement Agreements A(2) and B(2)(6), which are commonly
used for mechanical and electrical building services design, divide design into
the separate stages of outline design, scheme design and further/detail design.
In practice, therefore, the construction design process is invariably iterative,
with many design steps being revisited and revised as the design evolves and
develops, and this necessitates constant communication and clarification
between team members.
4 CIBSE Knowledge Series — How to design a heating system
Figure 3:
ACE Agreements A(2) &
RIBA plan of work (1999)
B(2) (2002) Construction process
AInception/Identification of C1 Appraisal stage n stages
g
client requirements si
C2 Strategic briefing e
d
B Strategic brief e-
r
P
COutline proposals C3 Outline proposals stage
DDetailed proposals C4 Detailed proposals stage
n
g
E Final proposals C5 Final proposals stage si
e
D
F Production information C6 Production information
stage
GTender documentation C7 Tender documentation and
tender action stage
HTender action
n
o
J Mobilisation/Project C8 Mobilisation, construction cti
planning and completion stage u
r
st
K Construction to practical n
o
completion C
L After practical completion
2.2 Heating design process
The problem with the standard design process is that it is both complex and
lacking in design task details. Although design is a clear part of the process,
detail of the design tasks involved is not given beyond global statements such
as ‘develop the design and prepare sufficient drawings…’.
Therefore, a simple straightforward design sequence for heating design has
been developed (see Figure 4 over the page) to both clarify the process and
allow detail of specific design tasks to be added. This gives a simplified linear
design sequence, from the pre-design stage through the various analysis,
decision and calculation steps through to the final solution, enabling design
tasks to be clearly linked to both preceding and succeeding actions. Although
some feedback loops are shown, in practice there are often feedback loops
between all tasks and even within specific tasks, reflecting the more iterative
nature of real-life design. Further detail on all of these steps is available in
section 3.
It is important to still set this in the context of the full design process. In practice
there are several design repetitions within the various stages, and overlaps from
one stage to another. For example, information on overall space requirements
and plant structural loadings is often required by other team membersat the
outline design stage. This degree of detail is unknown at this early stage
therefore often assumptions and approximations have to be made in order to
provide information. It is vital that these are checked as the design progresses.
CIBSE Knowledge Series — How to design a heating system 5
Figure 4:
Heating system design
process
Step no. Key design steps Design tasks
1 Pre-design Obtain design brief.
Identify client and building user needs and requirements.
Refer to feedback and lessons learned from previous projects

2 Gather design information Gather information about site, including utilities provision and fuel options.
Obtain information on use of building, occupancy hours and on possible building
form, fabric, etc

Establish and confirm key design requirements including Regulations and Codes of
Practice. Establish planning conditions for use of on-site renewables

3 Design data Establish the key design data and parameters that relate to the design of the
heating system, including building air tightness data, and potential use of renewables.
Develop room design data sheets

Check that design parameters comply with legislation, energy targets, etc

4 Building thermal performance Analyse building – establish fabric thermal performance and infiltration
analysis
Determine whether intermittent operation is likely and consider potential
pre-heat requirements

Estimate approximate building total heat loss to inform system selection process

5 Heating system option Consider zoning requirements. Consider alternative heat source (fuel) and heating
analysis and selection system options. Establish contribution from renewable sources

Consider operating and control strategies, and building usage and layout data.
Assess options against client requirements, performance, risk, energy use,
etc

Select proposed system

6 Design calculations Calculate space heat losses. Assess ventilation requirements and provision. Assess
Space heat losses and heat load HWS provision

Check system selection choice still appropriate.
Determine pre-heat requirements

7 Equipment selection and sizing Consider suitable emitter positions and connections.
Check distribution layout considering balancing and regulating requirements.
Consider circuit layouts and connections and pumping choices – variable or constant
volume.
Develop control requirements

Size and select emitters and distribution network and determine any distribution
losses

8 Design calculations Determine other loads such as HWS and process.
Heating load analysis Calculate main heating loads. Analyse load diversity and pre-heat requirement and
determine the total heating load
9 Plant sizing and selection Consider any standby requirement. Determine number of boilers /modules
required and size and select main plant. Finalise control requirements

Check layouts and services co-ordination for clashes and ease of commissioning
and maintenance

10 Design calculations Review system design and check predicted system performance.
System analysis Check part load performance
Control performance
Check that the selected controls are capable of achieving the required level of
control, response and energy efficiency, particularly at part load

11 Final value engineering and Check that final system and components meet client requirements for
energy targets assessment performance, quality, reliability, etc at acceptable cost; and also meet required
energy targets and comply with Regulations, such as meeting the seasonal efficiency
requirements

12 Review Design review
6 CIBSE Knowledge Series — How to design a heating system
As the design develops, these design steps are revisited and further detail
added with more accurate analysis as additional information becomes available.
The steps and amount of repetition involved will differ from design to design
but an example is illustrated in Figure 5. This uses the same design steps
Figure 5:
numbers as Figure 4 to show how the different steps are repeated and
Heating design process
revisited as the design develops. The detailed design tasks at each step have
mapped against the main
been omitted to keep the diagram to a manageable size.
design work stages
Design stage Step no. Key design steps Key outputs
Pre-design 1 Pre design: obtain client brief.
Refer to feedback and lessons learned from previous projects
Outline design 2 Gather design information and establish key design requirements. Design brief
Establish planning requirements Outline drawings
and schematics.
3 Establish key design data Provisional cost plan

4 Initial building thermal performance analysis.
Approximate heat loss
5 Heating system – consider options and fuel choices
7 Consider system requirements, potential layout, etc

9 Approximate total loads and plant size to arrive at cost plans, provide
space requirements and structural load information, etc.
Scheme / Detail design 2 Gather further necessary design information and establish key design Design drawings and
requirements schematics.
Cost plan
3 Establish key design data
4 Detailed building thermal performance analysis
5 Heating system choice and selection

6 Design calculations: space heat losses
7 Equipment selection and sizing – emitters and distribution network.
Control requirements

8 Design calculations: heating load analysis, possibly including thermal
modelling
9 Initial plant and control selection
11 Value engineering workshops
12 Interim design review
Design development/Final 4 Further building thermal performance analysis, to assist in modelling Design drawings and
proposals/Production dynamic building and system performance (if required) specification for tender
information purposes.
7 Final equipment selection and sizing Possibly co-ordination
drawings.
8 Final heating load calculation and analysis Final cost appraisal

9 Plant selection. Control requirements. Preparation of detailed design
drawings and specifications for plant and equipment
10 Design calculations.
System performance analysis, including part load performance and
predicted energy use. Possible final dynamic modelling of building and
system performance.
Control performance

11 Final value engineering exercise
12 Final design review
Post-occupancy review
CIBSE Knowledge Series — How to design a heating system 7
2.3 Key heating design calculation sequence
Within the overall heating design sequence there are some specific
calculations that will need to be carried out, and the sequence of these can
also be illustrated as shown in Figure 6. These mainly take place during steps
Figure 6:
4, 6 and 8 — building performance analysis, heat losses and load analysis;
Key steps for heating
continuing into system and equipment sizing in steps 7 and 9, and system
design calculation
analysis in step 10.
sequence
Building air- Internal and external Fabric
tightness details design conditions details
Condensation
'U' values
Site weather risk analysis
data
Infiltration Fabric heat
heat loss loss
Natural ventilation Space heat Internal gains (only Building thermal
load (if any) loss if both heating and response analysis
gains are continuous)
Emitter Space heating
sizing load Pre-heat
margin
Distribution system Infiltration load
sizing diversity Intermittent
operation
assessment
Distribution system Maximum simultaneous HWS
losses space heating load load
Load diversity Process
analysis load
Part load
performance
Total heating Central fresh air
load ventilation heating load
Boiler/heating Standby capacity
plant sizing (if required)
Final system and
control performance
analysis Flue Fuel supply
sizing system sizing
8 CIBSE Knowledge Series — How to design a heating system