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AM12 Combined heat and power for buildings (2013)
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AM12 Combined heat and power for buildings (2013)

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The UK faces three major challenges in its supply and use of energy:

  • First, the risks of climate change are now accepted and the need to reduce cumulative CO2 emissions has become a fundamental part of the energy policies of all countries with the Copenhagen Accord committing us to joint action.
  • Secondly, the UK has benefited from indigenous energy resources of coal, oil and natural gas for many years. We are now facing a new situation where we will be increasingly importing fossil fuels from a declining resource against a background of rising worldwide energy demand.
  • The third challenge is to maintain competitive energy prices to enable both industry and society to thrive. Many of the future low carbon energy strategies will increase the costs of energy supply.

In responding to these three challenges, energy strategies also need to minimise the impact on the wider environment, whether this is related to air quality in cities, visual impact in the countryside or at sea, or the safe disposal of waste products from energy systems.

Energy use in buildings is a major contributor to CO2 emissions and the supply of heat for space heating and hot water is associated with approximately 16% of total UK CO2 emissions (CCC, 2010). The role and responsibility of the building services engineer in meeting these challenges is therefore very significant.

Combined heat and power (chp) has been recognised as a technology that can reduce CO2 emissions. It can also be cost-effective to implement in many applications. The greater efficiency of fuel utilisation will also help improve energy security, chp thus has the potential to help meet all of the three challenges outlined above.

The energy efficiency benefits obtained with a chp system will still be needed even if the fuels used in the future are low carbon, as such fuels will be in short supply and will also have environmental impacts. Maximising the efficiency of utilisation of renewable fuel will remain an important part of the case for chp in the future.

CIBSE Applications Manual AM12: Small-scale chp for buildings was first published in 1999. With the growing concerns over global warming and the recognition of the role that chp can play in delivering low carbon buildings this revised and updated edition has been produced. A number of new sections have been added in this second edition, including:

  • a new chapter on district heating applications
  • more information on assessing environmental benefits
  • more detail on tri-generation and thermal storage.

 An addendum issued in August 2016 which is available to download here. This adds further guidance to page 50 in regard to 'The sizing of distribution pipework'. Future purchasers of the hard copy will receive the Addendum with the book.

1 Introduction

1.1 The energy challenges

1.2 What is chp?

1.3 Why chp should be considered

1.4 Scope of AM12

1.5 Purpose of AM12

Part 1: Technologies, applications and regulations

2 CHP and energy centres (fossil fuel)

2.1 Spark-ignition gas engines (50 kWe to 10 MWe)

2.2 Mini or small-scale chp (<50 kWe)

2.3 Micro gas turbine chp

2.4 Individual dwelling chp (<2 kWe)

2.5 Larger-scale chp

2.6 Fuel cells

2.7 Combined cooling, heating and power (tri-generation)

3 Renewable energy and chp

3.1 Biomass chp using combustion of solid biomass fuel

3.2 Biogas chp using gasification of solid biomass fuel

3.3 Liquid biofuel chp

3.4 Energy from waste

3.5 Biomethane injection

3.6 Integration of chp with renewable energy sources

3.7 Integration of chp with heat pumps

4 CHP for individual buildings

4.1 Introduction

4.2 Building heating, cooling and electrical demands

4.3 Fuel and electricity tariffs

4.4 Principles of chp sizing

4.5 Design of building heating systems to benefit chp operation

4.6 Building applications most suitable for chp

4.7 chp to improve security of electricity supply

5 Application of CHP to supply district heating

5.1 Principles of district heating

5.2 Typical applications of dh and chp

5.3 Selling electricity and private wire networks

5.4 Efficient design of dh systems to benefit chp operation

5.5 Use of thermal storage

5.6 District cooling

5.7 Large-scale district heating

6 Primary energy savings and environmental impact of chp

6.1 Primary energy savings

6.2 CO2 savings and impact of emission factors

6.3 CO2 benefits from tri-generation

6.4 Other emissions to air

6.5 Noise

6.6 Other environmental impacts

7 Legislation and regulations and impact on CHP viability

7.1 Planning

7.2 Building Regulations

7.3 Climate Change Act

7.4 Carbon trading: CRC Energy Efficiency Scheme and the EU Emissions Trading Scheme

7.5 CHP Quality Assurance Programme

7.6 Other financial mechanism

7.7 Parallel operation with DNO system

Part 2: Project implementation

8 Feasibility studies

8.1 Introduction

8.2 Data gathering of energy demands and system temperatures

8.3 chp performance, heat recovery options

8.4 Optimum sizing of chp

8.5 Thermal storage

8.6 Tri-generation (cchp)

8.7 Integration with other low carbon technologies

8.8 Typical capital and maintenance costs and efficiencies for gas-engine chp

8.9 Economic appraisal

8.10 Financing options

8.11 Feasibility report

9 Design

9.1 Allocation of responsibilities

9.2 Health and safety aspects

9.3 Energy balance for chp and heat recovery systems

9.4 System design: interfaces with heating circuit

9.5 System design: absorption chillers

9.6 System design: electrical interface

9.7 Fuel system

9.8 Combustion exhaust system

9.9 Combustion and ventilation air systems

9.10 Control systems

9.11 Maintenance facilities

9.12 Control of noise and vibration

9.13 Fire and gas detection and protection

9.14 Regulatory compliance and approvals

9.15 Specification: typical contents for chp package specification

9.16 Design of district heating

10 Procurement

10.1 Tendering

10.2 Assessment of tenders

11 Installation, commissioning and testing

11.1 Installation

11.2 Component testing, off-site testing

11.3 Commissioning

11.4 Client acceptance testing

12 Operation and maintenance

12.1 Operation

12.2 Operation and maintenance manuals

12.3 Maintenance and servicing

Part 3: Lessons learned

13 Lessons learned

13.1 Feasibility studies

13.2 Economic appraisals

13.3 Integration of chp into heating systems

13.4 District heating

13.5 Environmental impacts

13.6 Procurement

13.7 Detailed design and installation

13.8 Commissioning

13.9 Operation

13.10 Tri-generation and absorption chillers


Appendix A1: Conversion factors

Appendix A2: Glossary of terms

Principal author: Paul Woods (AECOM)

Steering Group: Phil Jones (Chair), Mark Anderson, Huw Blackwell, Lars Fabricius, Tony Gollogly, Dr Julian Packer, Dr Robin Wiltshire


Dr Jonathan Williams, Peter Pearson, Huw Blackwell, Dr Gregory Zdaniuk

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