Clyde Brown, managing director of water heating specialist Elson, discusses how the Code for Sustainable Homes, level three and above can be met with an air source heat pump and thermal store.
When building new properties, house builders must comply with carbon emission targets. In accordance with Part L1A, each new property will have a TER (Target CO₂ Emission Rate) and, to be able to build, the DER (Dwelling CO₂ Emission Rate) must be the same or lower than the target.

But alongside Part L1A since April 2008 all new build social housing schemes have needed to meet level three of the Code for Sustainable Homes, which calls for a 25 per cent reduction on the Part L1A DER over the TER. And, as 20 per cent of any new housing development has to be dedicated to social housing, this doesn't just affect housing associations and local authorities.

In addition, even though house builders still have to comply with Part L1A rather than the Code for Sustainable Homes when building private new dwellings, it is thought the 2010 revisions to the Building Regulations will mirror level three of the code. And by 2013 all new build homes will have to comply with code level four (calling for a 44 per cent improvement), and by 2016 we might be looking at zero carbon housing.

Also since May 2008 all new homes, whether they be private or social housing, have needed a rating against the Code for Sustainable Homes, with a certificate being included in the Home Information Pack. So we imagine some house builders strive to meet the higher levels of the Code for Sustainable Homes for marketing purposes, as well as best practice.

Minimum carbon emissions

All of this means housing specifiers will be looking for heating and hot water products that produce minimum carbon emissions - and they need to be planning these into future projects. While the Code for Sustainable Homes is about more than just heating - as everything about the build and the dwelling must be considered and rated - specifying energy-efficient heating and hot water products results in major credits, so is going to give a house builder significant headway.

One solution is to opt for renewable or low-carbon heating technologies, such as air source heat pumps. Air source heat pumps extract heat from the outside air and, using electricity, upgrade it to a higher, more useful temperature via a heat exchanger. If designed and installed correctly, a heat pump can deliver between 3 kW and 4 kW of heat for every 1 kW of electrical energy used thereby reducing carbon emissions as well as fuel costs for the homeowner.

Various options

Air source heat pumps can be utilised for space heating, using underfloor heating or radiators with a large surface area, as well as water heating when coupled with a hot water storage cylinder.

For hot water storage, various options are available - but the thermal store is an advantageous choice, as this arrangement enables a house builder to reach level three of the Code for Sustainable Homes with ease*, and actually gets quite close to level four - which could be met if some other carbon saving measures were implemented*, for example improved fabric insulation, improved air tightness, accredited construction details and low energy lighting.

The thermal store offers a very similar end result to unvented water heating - namely powerful showers and fast filling baths - but utilises a traditional vented system. The principal of a thermal store is significantly different from a traditional domestic hot water storage system; whether vented or unvented.

Whereas in a traditional system the water that is stored in the cylinder is the same water that is emitted through the taps, in a thermal store the water within the tank remains static and is used as the energy source for heating the mains incoming water instantaneously, via a very efficient coil located within the thermal store.

When used in conjunction with an air source heat pump, the thermal store will be heated indirectly, using a primary coil connected to the heat pump. Where necessary, an immersion heater will boost the temperature of the hot water, for end user comfort and thermal disinfection. For added efficiency, a buffer tank can be used, where the energy is stored for later use.

Elson manufactures a variety of thermal stores which, with energy efficiency in mind, are well insulated and have low heat losses. We can design bespoke solutions for house builders, incorporating products from our parent group, Baxi. For example, we can provide a prefabricated, packaged solution that combines an Elson Coral Eco thermal store and a Baxi air source heat pump. We have the capability to design these packages in any size or configuration, and can adapt components in line with individual requirements.

Air source heat pumps offer an appropriate solution for house builders looking to meet the Code for Sustainable Homes. To offer water heating as well as space heating, air source heat pumps need to be coupled with a storage cylinder - and using a thermal store means codes three and possibly four can still be achieved with minor upgrades to other build elements

* Calculations based on a three bedroom semi-detached house, according to SAP 2005 (Standard Assessment Procedure)