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Pump it up

25 Sep 13 Heat pumps have been slow to catch on as a sustainable heating option. But that could soon change, reports Ewen Rose.

Growing demand for renewable heat; mandatory targets for cutting carbon underpinned by local authority planning requirements; Corporate Social Responsibility (CSR); financial incentives like the Renewable Heat Incentive (RHI) – all are good news for heat pumps. The domestic RHI comes into play next April with tariff levels set at 7.3p/kWh for air source heat pumps and 18.8p/kWh for ground source heat pumps, payable for seven years. Additional subsidies are also available if people opt for the most efficient type of installation.

These incentives, which will considerably shorten the payback period on the technology, along with the fact that homes and businesses are facing fuel bills forecast to rise by around 15% in the next two years, mean there is plenty of motivation to adopt this type of energy saving approach. The government has set an ambitious target of 6.8 million heat pump installations by 2030. This will require a huge leap to 600,000 installations a year and put a great strain on the resources of the sector. Currently just 20,000 are installed annually in the UK – there is concern that the industry simply won’t be able to cope with such a huge increase in activity.

Rapid market growth is often dangerous – think double glazing and solar panels. Reputable manufacturers and contractors are fearful of poorly trained installers jumping on the bandwagon and leaving a legacy of ham-fisted installations that set the market back again. There has already been plenty of negative publicity for the industry to contend with and the first round of Energy Saving Trust (EST) trials in 2010 were disappointing – to put it mildly. The poor performance was blamed on shoddy installation, commissioning and operation. The technology itself was given a clean bill of health, but that was no consolation to end- users struggling with under-performing systems – just 13% of those studied delivered the promised energy savings. Happily, round two of the EST field trials completed this summer produced much better results. It revealed that many of the problems encountered in 2010 were being addressed and that installers and users were getting to grips with the technology. It concluded that homes best suited for heat pump installations “could expect to earn savings and income of around £1,350 a year on air source heat pumps and around £3,000 a year on ground source heat pumps”.

About 80% of participants in the trial said they were satisfied with their heat pump’s performance, while 77% said they would recommend a heat pump to a friend. The EST said the new trial had built upon the first study, which “identified recommendations for the industry and end-users to achieve better performance from the technology”. Jaryn Bradford, the EST’s senior technical manager, explains: “From the study, it is clear that heat pumps are sensitive to design, commissioning and how the householder uses the system. However, the performance monitoring trials have provided early indications that the introduction of improved installation standards, amongst other things, will lead to improved performance.” This feedback has been greeted with a sigh of relief by hard-pressed heat pump manufacturers. A wave of negative press about disappointed owners with higher than expected electricity bills culminated last year in a poorly researched BBC Rip Off Britain programme that gave the technology a hammering. Subsequent investigation showed the technology itself was not to blame, but that there had been problems with how the systems featured on the programme had been sized and operated. However, once the bad news is out there it can be a long way back. “Misuse of heat pump technology is hugely damaging to the reputation of the renewable heating industry,” says Jeff House, marketing and applications manager at Baxi Commercial Division. “Although the industry can defend the technology against unfair attack; we cannot defend ourselves if a technology is inappropriately or inexpertly applied. It is clear that some heat pumps have been poorly selected; badly designed and installed – and, in many cases, they are simply inappropriate.”

“There is currently no financial or environmental logic behind using an electric heating system when gas is available. Perhaps some time in the future when the grid is decarbonised that will change, but for now electric heat pumps really only make sense when they are replacing oil-fired or less efficient forms of electric heating. B&ES Head of sustainability, David Frise

The first cardinal sin has been the use of electric systems in properties attached to the gas grid, according to David Frise, head of sustainability at the Building & Engineering Services Association (B&ES). “There is currently no financial or environmental logic behind using an electric heating system when gas is available. Perhaps some time in the future when the grid is decarbonised that will change, but for now electric heat pumps really only make sense when they are replacing oil-fired or less efficient forms of electric heating.

“Gas is cheaper and less carbon intensive so you would have to achieve an unusually high coefficient of performance (COP) with an electric system to beat gas,” he adds.

However, it is obvious that some developers are using electric heat pumps to achieve planning permission even when properties are attached to the gas grid. This really has to stop to prevent further damage to the technology’s reputation, according to Frise. It is also clear that the industry has to do a better job of explaining to end users how to operate heat pumps. A number of contractors have reported being recalled to installations to carry out repairs only to find that the heat pumps are performing perfectly well. The low temperature of the radiators can confuse users who expect them to feel hotter. Renewable systems operate at lower temperatures than conventional central heating, but this often comes as a surprise to end users. Heat pumps clearly can meet end-user expectations, but only if appropriately used and correctly installed and commissioned. Electric systems will perform perfectly well when replacing oil-fired or other electric systems and deliver excellent energy savings – elsewhere the experts suggest we should be considering gas-fired heat pumps.

Instead of using electricity as its primary fuel source, a gas absorption heat pump uses a gas burner to drive the induction motor that powers the refrigeration compressor. The refrigeration cycle is then supplemented by energy from the surrounding ambient air. Such a system is ideal for use with a low temperature radiator or underfloor heating system and will also produce domestic hot water at around 65°C via an indirect cylinder. Gas absorption heat pumps are primarily used in commercial or large residential schemes that would traditionally use boilers for space heating applications. As the heat pump is suitable for outdoor installation, the plant room size can be reduced, which is another potential benefit.

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Gas absorption can achieve much higher fuel efficiencies than traditional boiler systems, if used with lower flow temperatures, typically around 35°C, although fairly good performance can still be achieved up to 50°C. Operating costs are also said to be lower. Gas-fired systems are measured in terms of efficiency rather than COP and this makes it easier to achieve higher ratings under the BREEAM or LEED energy efficiency measurement schemes. The carbon intensity of gas is much lower than grid-supplied electricity – at 0.193kgCO2/kWh compared to 0.43kgCO2/kWh.

So there are plenty of options available to domestic and commercial users. Could this now relatively mature market, which seems to have experienced more than its fair share of teething problems, finally be about to demonstrate its full potential? The next couple of years, as energy prices continue to soar, will be crucial. Installation and commissioning problems will have to be overcome once and for all or users will start looking for alternatives.

What is Pump Heat?

Heat pumps make full use of heat naturally stored in the ground, water or the air to reduce the amount of fossil fuels we need to burn to heat or cool our buildings.

A heat pump works like a fridge in reverse. While a fridge takes heat out of the food stored inside and releases it into the room, the heat pump extracts heat from cold surroundings. It then brings this heat up to a temperature sufficient for central heating (between

55° and 60°C).

This works 24 hours a day in the summer as well as in the winter. As it is a low-temperature heat source – unlike conventional central heating, which operates at high temperatures – larger heating surfaces such as underfloor heating and low surface temperature radiators are the best way to extract maximum efficiency.

Ground source heat pumps extract heat from the ground using polyethylene pipes filled with a water and anti-freeze mixture laid either as ‘slinky’ loops buried a metre or two below the surface in horizontal trenches or in vertical boreholes drilled down to around 80m. The higher the temperature of the heat source, the more efficiently the heat pump will operate, but the key thing is having a constant temperature. The earth around UK buildings is on average a constant 10°C, which is ideal. The heat thus collected is around 50W per metre in a borehole or one kilowatt per 25m2 with the horizontal coils. This temperature is ideal as a pre-heated source of water for heating or as a cool water source for cooling in summer.

Air source heat pumps are not as efficient, but are easier to apply as they do not require any groundworks and can be used in properties without much surrounding land. They extract heat from the air and can be installed either inside or outside. Open loop water source heat pumps can be the most efficient of all as they use heat extracted from a body of water. In this case the water from the source itself is pumped directly through the system. This source water can also work for air conditioning systems and is particularly well suited for chilled ceiling systems providing, in theory, full building cooling.

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