Understanding the potential of air source heat pumps

(09/10/2009)

Fuel costs are continuing to rise year on year and in the UK, more people are suffering from fuel poverty, yet at the same time, we have to find sustainable ways of heating our houses to reduce our reliance on imported energy and lower our environmental impact. For the housing sector, this means adherence to the Code for Sustainable Homes, which sets strict targets for energy reduction.

“Many alternative technologies have claimed to be ‘low carbon’ but few have lived up to expectations so far, yet heat pumps can deliver affordable and sustainable heating for our social housing sector,” explains John Kellett, general manager of Mitsubishi Electric’s Heating Systems Department.

Many are aware of the efficiencies available with ground source heat pumps, yet few properties can afford the space or capital costs needed. Now the cheaper and easier to install sister technology – air source heat pumps (ASHP) – is available, with a host of manufacturers proclaiming the performance, viability and sustainability of their products. These include many traditional boiler manufacturers who have realised the potential for this technology.

ASHPs do offer a real hope of affordable, low carbon heating to Britain’s social housing sector but without countering the myths that exist and allowing people to make informed decisions, they could fail to live up to their potential.

“There are a number of myths around which have stopped people considering air source heat pumps and we want to highlight the Top Five to help people understand the potential of the technology,” adds Kellett.

1. ASHPs can’t work properly throughout the British winter – WRONG

Most manufacturers’ performance claims are based on factory data and perhaps some lab data. Mitsubishi Electric has extensive independent lab data carried out by the BRE (British Research Establishment), which confirms all its factory data.

More importantly, Mitsubishi Electric is the only manufacturer that has published the results of extensive live tests – undertaken over the last winter in the UK (with temperatures of -9ºC recorded). These demonstrate that the Ecodan® range can deliver the year-round performance needed and involved all three Ecodan models, retro-fitted to a small 3-bed terraced house, a 4-bed semi, and a large 5-bed detached home.

Ecodan delivered COP’s ranging from 3.0 to 3.33, showing that around 2.33kW of renewable energy is being harvested from the surrounding air for every 1kW of electricity used.

2. ASHPs can only work with underfloor heating – WRONG

Traditional ASHPs do work better and more efficiently at lower temperatures, but modern versions of the technology are more than capable of running traditional radiator systems. The important thing is to correctly size the heat emitter to suit both the individual rooms and the property as a whole.

3. ASHPs are noisy – WRONG

ASHPs have been available for decades, and the older fixed speed versions can be quite noisy. Modern systems have incorporated advanced, inverter-driven compressor technology from the commercial heating sector to produce very high efficiency levels at very low noise levels.

Ecodan is designed to be fitted to the outside wall of the property and uses its inverter-controlled compressor and fan to only run when required. This is part of what makes the unit so efficient, but also what helps to keep the noise level to a very quiet 49 dBA (at 1m in front of the unit).

4. ASHPs are difficult to install and only suitable for new build – WRONG

Mitsubishi Electric has deliberately chosen to market Ecodan through existing heating installers and it can be fitted by any qualified plumber who has been on the one-day training course. Some ASHPs do require specialist engineers qualified in F-Gas and refrigerant handling, but Ecodan incorporates a sealed refrigerant circuit – much like a domestic fridge – so it requires only an in / out water supply and single phase electricity.

With over 300 companies now listed as Approved Ecodan Installers, hundreds of households are starting to benefit from the low running costs and this includes a 200-year-old property near Marlborough, which has been running the system since last summer.

5. All ASHPs are the same – WRONG

There are essentially three types of ASHP currently available:

- Traditional technology. Widely used throughout Scandinavia and northern Europe, and now including numerous new entrants including those from traditional boiler manufacturers, these units are fixed speed, meaning they work at full power when on and are less efficient than modern, variable-speed systems. They are also much noisier and need sound-proofed or careful siting away from properties.

- Modern split system ASHPs from the air conditioning manufacturers. These involve a multi-part system with an outdoor unit, connected to a heat exchanger by copper refrigerant piping which then links to the water tank. These are very efficient systems having borrowed advanced heat pump technology from the air conditioning industry but they do require an additional F-Gas qualified engineer to install them.

- Modern sealed ASHPs. Ecodan from Mitsubishi Electric has a sealed refrigerant circuit making it easy to install by a qualified plumber. Being manufactured by the leading air conditioning manufacturer in the UK, it uses every available advanced component to deliver the highest levels of efficiency.

Ecodan can cut emissions by up to 50% over modern gas boilers and reduce running costs by over 30%. Even greater savings are possible in some retrofit applications and it can also help homes achieve Level 3 and 4 of the Code for sustainable homes.

Related categories:  Energy Conservation   Heat pumps   Residential applications