Ground source heat pumps
There are two types of heat pump available to the home-owner, air source and ground source heat pumps. Both use similar technology to a refrigerator; extracting heat from one area and moving it into another.
According to Peter Bartley from building services and sustainability consultants CHBS:
“Heat pumps use electricity, which is currently a carbon intensive fuel; however they have a very high efficiency, with a good system expected to provide, on average, three units of heat for every unit of electricity used. But the fact that electricity costs around three times more than gas means that running cost savings are small when compared to high efficiency condensing gas boilers, and carbon emissions can even be higher depending on the installed product efficiency. Heat pumps are now designed to provide both space heating and hot water, however they generate heat at lower temperatures than gas-boilers and will usually require underfloor heating or oversized radiators.”
As their names suggest air source heat pumps extract heat stored in the outdoor air and ground source heat pumps extract heat which is stored in the ground. Air source is not always feasible at lower temperatures, especially since the times when you’re most likely to need them, i.e. In the morning and evening, the air temperature will be at its lowest. A higher efficiency can generally be achieved from a ground source heat pump as the average temperature underground is higher than the average air temperature.
The Renewable Heat Incentive
Launched in March 2011, the Renewable Heat Incentive offers money towards installation costs as well as payments for heat generated. Peter Bartley from CHB Sustainability explains more.
The Renewable Heat Incentive is an initiative similar to the feed-in tariffs for electronic generation, which aims to encourage the installation of renewable heat equipment in the UK. Unlike the Feed in Tariff though, it will use a whole-house approach which integrates both energy-efficiency and heat generation, so as not to encourage excess production of heat.
It is open to everyone (including homeowners, landowners, businesses, schools hospitals and entire communities who have joined up to invest in these technologies), and applicable to several different technologies, including biomass, solar thermal, heat-pumps, on-site biogas, deep geothermal, energy from waste and injection of biomethane into the gas grid.
There are three steps involved:
Step One: you install in your property renewable heat systems such as solar thermal panels, heat pumps or a biomass boiler
Step Two: you measure how much heat your renewable energy systems produce
Step Three: you get paid a fixed amount based on that output, the type of technology and the size of the system.
It will be introduced in two phases:
1) Beginning in July 2011, this will include upfront one-off payments (the Renewable Heat Premium Payment) to homeowners to reduce the initial capital cost of investing in renewable heat technologies.
This will be similar to Feed in Tariffs for renewable electricity with an annual payment based on the amount of renewable energy generated.
2) The second phase will benefit those who have installed an eligible technology since 15th July 2009; therefore it is a great idea to take advantage of phase one to get an upfront grant as you will still be eligible for annual payments from October 2012 when phase two commences.
Details of the phase two payments are unknown at the moment but are expected to be of the scale to give simple payback on investment within 15 – 30 years.
When considering any renewable energy technologies it is essential to ensure that you have already exhausted all the straight-forward energy efficiency measures that you can, such as insulation, draught proofing and low energy lighting. There’s no point generating renewable energy just to waste it!
It is expected that Energy Performance Certificates will be used to judge whether homeowners have suitably well-insulated homes in order to be eligible for the financial incentives. Homeowners should also ensure that both the renewable heat technology products and installers are accredited by the Micro-generation Certification Scheme (MCS) (see Links) both to gain the financial benefits of the RHI, and ensure that the products and installers are reputable. Products certified under the Solar Keymark are also eligible for the RHI, but this certification doesn’t cover installers, so you’ll need to make sure your installer is certified under MCS.
Typical Annual Saving *
Typical Annual CO2 Saving *
Upfront RHI Grant **
Service by accredited installer every 3 – 5 years
|Ground Source Heat Pump
£9,000 - £17,000
Service by accredited installer every 3 – 5 years
£70 (300% efficient)
Regular cleaning but generally no servicing requirement
*Annual savings are based on comparison with a typical condensing gas boiler. Savings would be greater with more expensive and carbon intensive fuels such as oil or electricity. These savings do not include the benefits of the Renewable Heat Incentive.
**Phase 1 of the Renewable Heat Incentive is from July 2011 for the first 25,000 applicants (totalling £15m). These figures are based on the Government consultation and are not confirmed as yet.
The Hard Sell
There have recently been rumblings suggesting that installers in the renewable heating sector are making a name for themselves as the new double-glazing salesmen.
BBC’s consumer rights TV series ‘Don’t Get Done Get Dom’ aired a programme at the end of April which fought the case of one consumer whose new heat pump caused his bills to go up instead of down. The programme went to the company’s managing director for a refund. It also warned viewers of the dangers of signing finance agreements without knowing their rights.
The ‘You and Yours’ series on Radio 4 also recently warned consumers to do their research before buying as performance could vary.
We spoke to Tobi Kellner, who works for the Centre for Alternative Technology (CAT) Information Service, which provides free and impartial advice on renewable energy technology.
Heat Pumps – COP
Tobi told us that he feels the door is wide open for intentional, and even unintentional mis-selling of heat pumps due to the nature of the technology. The performance of a heat pump is measured by the Coefficient of Performance (COP) (see below), and this is likely to be quoted in sales brochures. However, the actual performance depends on a number of variables.
The key factor is the difference in temperature between the source (the ground outside) and the target or ‘sink’ (your radiators or underfloor heating).
An installer may say that a heat pump has a COP of three or even four, but the small print of the heat pump data sheet might say this is specific to certain outdoor temperatures, where there’s perhaps a 40C difference between source and target temperatures. When thinking about the performance of your system, you should factor in lower COP when temperatures outside are low, meaning a bigger temperature difference between source and target. This grows further if your property uses traditional radiators, which require higher temperatures to deliver enough heat. In such conditions, your equipment’s COP could fall by one or two.
Tobi added that if your heat pump is used to produce domestic hot water for showers and baths, the target temperature is higher (since water is often heated to 60C or more to rule out Legionella problems), which also affects actual COP.
Another factor Tobi pointed out to us is that “the ‘free’ energy from heat pumps comes at the cost of very expensive electricity, which can actually make heat pumps an expensive form of heating.”
As electricity is about four times more costly than gas for each unit of heat, a heat pump with a COP of three will still be more expensive than using gas central heating. The same is true for CO2 emissions since electricity is ‘carbon heavy’. Basically, if you’re not on the gas grid, heat pumps could be a great option. If you’re already using gas and looking for a cost-effective heating option, look at the figures carefully before you buy.
Take your time
So it seems that it’s really a case of doing your research before you buy. Make sure you understand the jargon, so you can make sense of what the performance figures are really saying. And always use an MCS certified installer to ensure the job is done properly.
The Coefficient of Performance is the unit by which the performance of heat pumps is measured. Basically, it measures the amount of heat produced, as compared to the amount of electrical energy required to produce it. The less electricity required, the higher the COP, and the more efficient the heat pump.
So for example, at a COP of 3, you put in 1 unit of electricity and you get out 3 units of heat.
Refrigerant pollution issues
Peter Bartley from CHB Sustainability explains the risks associated with the refrigerants used in heat pumps.
Both air and ground source heat pumps use a refrigerant which is circulated within the system and transfers heat through a process of evaporation and condensation. Previously chlorofluorocarbon refrigerants (CFCs) or hydrogenated chlorofluorocarbon refrigerants (HCFCs) were commonly used, but these have been phased out due to the damage that they were shown to cause to the ozone layer. Most refrigerants used now are hydrogenated fluorocarbon refrigerants (HFCs) – these chemicals do not cause the same damage to the ozone layer as CFCs or HCFCs but are still potent global warming chemicals, up to 5,000 times the Global Warming Potential (GWP) of carbon dioxide based on a 100 year horizon. The most commonly found HFCs have a GWP of around 2,000.
Although they have a high GWP, the volume of HFCs released due to human activity is relatively low – it is estimated that HFC emissions account for around 1% of all greenhouse gas emissions (although this is expected to rise to 2-3%). Heat pumps are designed as tightly sealed systems in order to minimise leaks; however there is always a chance of a leak of a chemical which can pose a significant contributory factor towards climate change (around 20% of the climate change effect of refrigeration is due to refrigerant leaks and the other 80% due to the energy used).
There are now alternative refrigerants which have a much lower, or in some cases no contribution towards global warming. However, these chemicals can pose their own risks in terms of safety and environmental impact. Common low GWP alternatives are ammonia, hydrocarbons (petrochemicals such as propane, isobutane and butane) and CO2. However, ammonia is very toxic and flammable. Hydocarbons are highly flammable and can contribute to pollution, and so ironically CO2 looks to have a future as the ‘green’ refrigerant alternative to HFCs!
So when considering a domestic heat pump it is worth considering whether a CO2 refrigerant product is available to reduce the risks of leaking high GWP refrigerants.
Beware lurking Legionella...
Legionella is a bacteria found in water which causes Legionnaires disease, a potentially fatal form of pneumonia which can affect anybody, but which principally affects those who are susceptible because of age, illness, immunosuppression, smoking etc. In order to prevent the bacteria from thriving, water for showering or bathing needs to be kept at temperatures above 60 degrees C, according to the Health and Safety Executive.
With a heat pump or solar thermal heating system, you would need to use a secondary heat source (e.g. electric immersion coil) to ensure that water in the hot water cylinder is heated to above 60C on a regular basis. The heat pump itself is not very efficient at heating water to these temperatures.
Ground source heat pumps tried and tested
"It is now five years since Ulrike had ‘earth heating’ installed in her farm in Germany. They dug one mile of plastic coils into the ground (her partner and son did this work, borrowing machinery from a friend). The liquid in the coils transports the ‘heat’ from under ground to the family’s big 800 litre water tank. A pump keeps the liquid flowing and the ‘heat’ from the transport liquid is passed into the water that goes into the house (for the central heating).
The water tank also takes the heat from the solar cells on the roof. The family had already installed the tank when they built a solar thermal heating system 15 years ago together with a wind generator (which has recently broken down due to a storm).
Ulrike says she’s found that the the pump which keeps the liquid flowing is the most expensive aspect of ground source heating. It takes 24 kw of energy, which costs about 300 Euro a month, making it quite uneconomical. This is despite it providing heating and hot water for the three households that reside on Ulrike’s farm.
Overall their ground source heating system cost 30,000 Euros, and that was without the costs of installation. Plus, the family already had some equipment because they’d previously had the solar thermal system installed.
This winter and the one before were problematic as temperatures where Ulrike lives in Germany reached -15C, and the equipment struggled. Factoring in the costs and hiccups with the equipment, Ulrike said she would be undecided if asked whether she would install this technology again."
"In September 2009, Peter Griffiths had a ground source heat pump installed at his rural home in Shropshire. The decision to invest in a ground source heat pump was made when his oil boiler needed replacing.
At first Pete considered a bio-mass boiler, however, concerns over the reliability and sourcing of fuel lead to the decision to install a ground source heat pump instead.
Pete went with a recommended provider which used their own certified installers and engineers. While everything from the initial decision on investing in a heat pump to the actual installation of the heat pump went smoothly, Pete explained that the work was very disruptive and, as with all building projects, took twice as long as expected and cost more then expected.
The heat pump which was installed used a ‘horizontal closed loop field’, which meant that roughly half an acre had to be dug up. In Pete’s case, this involved going into the next door neighbour’s land. Given the amount of land needed for a horizontal heat pump it may not be very practical for people living in urban areas.
Overall Pete had a very positive experience with the installation of the heat pump. Despite the disruption and under-budgeting, he felt that the pay back on it and the efficiency of the heat pump made up for it. Pete estimated that £10,000 had been paid for the installation of the heat pump, which included some work on his central heating system. In terms of energy bills, Pete thought £500 per year was being saved, however, his electricity usage had been increased. As the life span was estimated at 20 years, he was happy he would make back his money.
The investment has been further boosted by the fact that Pete will qualify (retrospectively) for the Renewable Heat Initiative (RHI) through which he will receive just over £1000 per year in grants. This is more than enough to pay for his energy bills per year."
There’s not much to distinguish between the companies on this table. All were disappointing as far as environmental policies and supply chain management strategies were concerned, with not one company scoring above a worst rating for supply chain management, and only Kensa Engineering and MasterTherm getting a best for environmental reporting.
Viessmann receives negative marks in our climate change category for operating in a high climate impact sector because it owns an airfield in Germany along with a fleet of private jets. It has subsidiaries in two tax havens and operations in four oppressive regimes.
According to the Senate Office of Public Records, Danfoss spent $167,343 on lobbying related to Clean Air & Water and Energy & Nuclear Power. In 2010. It also has subsidiaries in three tax havens and operations in five oppressive regimes.
DeLonghi picks up marks in the Anti-social Finance column for tax avoidance – its holding company is based in one tax haven, Luxembourg, and it has subsidiaries in three others.