CPD PROGRAMME
Professional development
The CIBSE Journal CPD Programme
Members of the Chartered Institution of Building Services Engineers (CIBSE) and other professional bodies are required to maintain their professional competence throughout their careers.
Continuing professional development (CPD) means the systematic maintenance, improvement and broadening of your knowledge and skills, and is therefore a long-term commitment to enhancing your competence. CPD is a requirement of both CIBSE and the Register of the Engineering Council (UK).
CIBSE Journal is pleased to offer this module in its CPD programme. The programme is free and can be used by any reader. This module will help you to meet CIBSE’s requirement for CPD. It will equally assist members of other institutions, who should record CPD activities in accordance with their institution’s guidance.
Simply study the module and complete the questionnaire on the final page, following the instructions for its submission. Modules will be available online at
www.cibsejournal.com/cpd while the information they contain remains current.
You can also complete the questionnaire online, and receive your results by return email.
Air source heat pumps
This module focuses on air source heat pumps and considers some of the current requirements and trends in this technology
If appropriately applied, the air source heat pump (ASHP) can be an effective means of providing heating energy for buildings in temperate climates, such as that of the UK. Although they do not currently attract any Renewable Heat Incentive (RHI) payments, the recent changes to the permitted development rights in England for ASHPs have eased the planning requirements for domestic installations (and some currently attract a one-off Renewable Heat Premium Payment1
). So they are increasingly likely
to come under consideration as a means of providing heating and hot water. This article considers some of the current requirements and trends in their application. Unlike other ‘renewable’ technologies,
the application of ASHPs will still use electricity or gas to fuel them, so may not be seen as the purest form of renewable heat but, with appropriate application, they can effectively draw on the practically inexhaustible and freely available source of heat stored in the air. Appropriate use of an electrically
powered heat pump can be cheaper than using an oil-fuelled or condensing-gas boiler, as well as reducing operational carbon emissions. Based on data collected in real applications by the Energy Savings Trust, properly installed and operated systems can provide typical savings2
in a
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three-bedroom semi-detached house of £380 per year (or 4,440 kg CO2
equivalent)
when replacing electric heating, and £80 (or 810 kg CO2
equivalent) per year when
supplanting oil heating (and, with the better performing systems, this can rise to £610 and £310, respectively, and can even save £130 when compared to gas).
Operational efficiency The efficiency, in terms of coefficient of performance (COP) (see CIBSE Journal October 2011, p51, for definition), is variable depending on the operating conditions and the refrigerant used, but can range from under 1 (when external temperatures are very low and the unit produces almost the same heat energy as the electricity it consumes) to COPs of 3 and above under spring/ autumn conditions when supplying low- temperature heating systems. The majority of heat pumps currently
in the marketplace are best suited for use with low temperature systems, such as underfloor heating at 30-45C, fan coils at 35-55C, and radiators sized to operate at 45-55C. Clearly, this is a temperature below that needed for the safe operation of domestic hot water where, to reduce risk from legionella, any hot water storage needs to be regularly heated to 60C3
. In
the case of a standalone heat pump system (known as a ‘monovalent’ system) that is being used to heat domestic hot water, this requires the use of a direct electric heater for brief periods to bring the stored water to an adequate temperature for legionella protection. ASHPs are recognised in the England
and Wales Building Regulations Approved Document Part L4
as being appropriate
for heating buildings when they have a COP of not less than 2.2 when being used for space heating, and not less than 2.0 when also being used for heating domestic hot water. These are based on measurements being made at standard external temperatures of 7C. This happens to be just below the average outdoor dry bulb temperature in southern England over the ‘heating season’ for housing, assuming that houses require some form of heating as outdoor temperatures fall below 15.5C (the base temperature used in the degree-day energy estimation method). With improved standards of construction, the point at which modern housing needs heating will be somewhat lower than this (probably nearer to an outdoor temperature of 11C). This means that the average temperature throughout the heating season will also be somewhat lower, at around 5C or 6C.
January 2012 CIBSE Journal 51
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