An introduction to heat pumps

    Heating

What is a heat pump?

Based on similar technology to air conditioners and freezers, heat pumps use the heat found in air, water or the ground and compress it using electricity. This compression causes the extracted warmth to heat up and then be released into the conditioned space through the use of water within a wet central heating system.

The history of the heat pump

Heat pumps have been used in a number of different areas for years. The first heat pump is said to have been built in 1856 and the first ground source heat pump in 1948. However, it is only within the last few years that popularity has soared, with heat pumps being used for heating both domestic and commercial properties.

Heat pumps provide heat energy from a variety of sources, depending on the model, to a heat sink. In order to work, they are required to shift thermal energy in the opposite direction to natural order. In other words, they take heat from a cooler environment and release it into a warmer one. Although classed as a renewable heating method, heat pumps tend to use around 1 unit of electricity for every 3-5 units of heat and so are not completely self-sufficient. Their conversion rate is, however, higher than that of radiators.

Seasonal performance factor

The seasonal performance factor of a heat pump is how much heat energy is generated using one unit of electricity over the course of a year. The higher the SPF, the more heat is generated for the same unit of electricity. Usually, air source heat pumps are around 3, water source heat pumps around 3.5 and ground source heat pumps around 4. The reason for the change is the difference in temperature witnessed in each heat source over the seasons. So the outside air temperature falls just when the air source heat pump needs to be providing the most heat, whereas the ground stays at much more of a constant temperature, meaning that the ground source heat pump doesn’t have to use as much electricity to reach the same temperature.

Important considerations for heat pumps

As heat pumps do not heat up water to the same extent as boilers within wet central heating systems, there are some important things to research before you install one. The first is radiator size. If you are replacing your wet central heating system with a heat pump, your current radiators may not be of an adequate size for the rooms. Secondly, as the heat is not of the same temperature as gas, oil and biomass boilers you would need to have a well-insulated house to ensure that the required temperature is reached. This is a recent/new build, an insulated solid wall property and cavity wall properties with cavity insulation.

Installing heat pumps

Are you thinking about getting a heat pump? We have scoured the country for the best tradespeople, so that we can make sure we only recommend those we really trust.

If you would like us to find you a local heat pump installer, just fill in the form below and we will be in touch shortly!


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      Air Source Heat Pumps

      Heating

    What are air source heat pumps ?

    Air source heat pumps convert heat energy from the air to provide heat and hot water for dwellings. They run on electricity, but are incredibly efficient (in some cases 300% or more), which means that for every one unit of electricity used, they produce 3 units of useful heat.

    If you compare that to a brand new boiler which is 90% efficient (1 unit of gas produces 0.9 units of useful heat), you can quickly see why these systems are so popular. In fact, if you don’t have access to mains gas, heat pumps are definitely the way to go to fulfil your heating and hot water requirements – provided you have a well insulated home, which is discussed later.

    Better still, if you decide to install an air source heat pump in your home, you can also benefit from the Renewable Heat Incentive, which pays you for each unit of hot water water you produce. In some cases, the funding will cover the cost of installing the heat pump, but it gets paid over 7 years on a quarterly basis, so you will still need to find the money upfront!

    How do air source heat pumps work in your house?

    The air source heat pump needs to be located outside in the open air, and uses a fan to draw air into it. This air then flows over a heat exchanger, which contains a refrigerant liquid. An evaporator uses the latent heat from the air to heat the refrigerant liquid sufficiently until it boils and turns to a gas. This gas is then compressed by a compressor, which causes it to significantly increase in temperature. An additional heat exchanger removes the heat from the refrigerant (turning it back to a liquid), which can then be used as useful heat. There are two types of air source heat pump:

    Air-to-water heat pumps

    Air to water heat pumps are by far the most popular. These take heat from air outside the property and transfer this to water, which can be used for space heating or as hot water for washing within the house.

    Air-to-air heat pumps

    These remove latent heat from the air outside the property which is then simply fed into the home through fans. This type of heat pump cannot be used to produce hot water.

    >>> The cost of heating your home with gas vs electricity <<<

    Air source heat pumps require electricity to run

    Since they include fans and compressors, air source heat pumps require electricity to operate, and bearing in mind the price of electricity is approximately 15p / kWh and gas is just 4p / kWh, on the face of it, you would expect heat pumps to be far more costly to run than gas boilers.

    This is not the case though – since for every kW of electricity used to run them, they provide approximately 2.5-3.5kW of equivalent useful energy (depending on the model and the temperature of the external air). This makes running costs comparable to a traditional gas boiler.

    Air Source Heat Pump

    The efficiency of air source heat pumps is measured by the Coefficient of Performance, which is simply how many units of useful energy produced from each unit of electricity are consumed to operate the system. For example, if at any moment the heat pump was producing 3kW of useful heat from each unit of electricity, the CoP would be 3.

    The CoP varies throughout the year, with lower figures achieved during the colder months (meaning they are running less efficiently), since there is less ambient heat available to remove from the air. This makes comparing the efficiency of different heat pump systems very difficult, so we use what is known as the Seasonal Performance Factor to compare like for like performance of models. This is the annualised CoP, taking into account the different performance throughout the year.

    Air source heat pumps don’t produce boiling water

    The air source heat pump does not produce the sort of hot water temperature you would associate with a gas, LPG or oil-powered boiler. With a boiler, you would expect the hot water to be heated to about 850c, while a heat pump produces water to about 550c. Trying to increase the water temperature from a heat pump beyond this requires the compressor to work harder, meaning more electricity – this in turn reduces its efficiency or coefficient of performance.

    As a result, it is very important to minimise heat loss from the property prior to installing a heat pump. This includes insulating the walls, loft and ideally the floor too. This means that even though the radiators won’t get as hot (using heat pumps), the house is still heated effectively and you are not straining the heat pump – which is expensive.

    When installing a heat pump, you may be required to increase the size of some of the radiators in certain rooms too. This is simply because the heat demand will not be met with the existing-sized radiators. If this is the case, you can expect to pay about £200 – £300 for each radiator that needs to be replaced (providing the pipework running to the existing radiator can be reused).

    Air source heat pumps and the Renewable Heat Incentive

    Heat pumps are part of the Renewable Heat Incentive scheme recently launched by the Government. It means that, if you install a renewable heating technology, you can get paid for each unit of heat you generate. RHI payment rates depend on lots of things, but you can see detailed information here.

    Occasionally, but not often, the RHI payments will be enough to cover the cost of the initial outlay of the air source heat pump.  Air source heat pumps normally cost between £7,000 – £10,000.In a standard property you can expect to receive a total of about £2-5,000. RHI payments are paid quarterly over 7 years, so you will need to stump up the money up front.

    Things to consider before investing in an air source heat pump

    Placement of air source heat pump – An air source heat pump requires plenty of space, either to mount on an external wall or to be placed on the ground. The unit needs good air flow, and foreign objects such as boxes, containers etc need to be kept well away.

    Cost of air source heat pump system vs system that is being replaced – Purchasing an air source heat pump on top of an existing heating system will prove to be an expensive option; therefore we recommend considering this when replacing an old electric or old oil-fuelled system. However an electric heater will convert 1kW of electrical energy to 1kW of heat energy and an air source heat pump will convert 1kW of electrical energy into 3.5kW (almost 4kW) of heat energy.

    Insulation – The air source heat pump emits low temperatures but on a consistent basis. To maximise effectiveness, ensure that your home is suitably energy efficient by installing wall insulation (either cavity or solid wall) and draught proofing. These are low cost measures that will make a big difference to your utility bills, therefore it is worth investing in them prior to replacing your heating system with an air source heat pump.

    Noise of air source heat pump – An air source heat pump does make some noise when operating, as both a fan and a compressor will be in motion. The noise is approximately 40-60 decibels (depending on the system) from a distance of one metre away. So please ensure if you invest in an air source heat pump, it is not placed directly outside your bedroom window!

    We have filmed an air source heat pump in motion, (don’t say we don’t treat you) so you can see for yourself how they operate.

    Efficiency of air source heat pumps – Despite air source heat pumps being able to operate at -250C, the efficiency decreases as the outside temperature drops; therefore if you live in a particularly cold place, you may well need to supplement the heat pump with an additional boiler to get the hot water you require. Try a CHP boiler if you can invest additional resources. The problem may be getting the two systems to work successfully in tandem; therefore a traditional boiler could be your only option.

    Local authority regulation for air source heat pump installation

    Generally there are fewer restrictions from local authorities in England and Scotland when looking to install an air source heat pump (noise being the main consideration), but please check with your council and installer before proceeding. In Wales and Northern Ireland, an air source heat pump installation requires planning permission.

    Benefits

    Limitations

    Cost

    Installing heat pumps

    Are you thinking about getting a heat pump? We have scoured the country for the best tradespeople, so that we can make sure we only recommend those we really trust.

    If you would like us to find you a local heat pump installer, just fill in the form below and we will be in touch shortly!


      Interested in heat pumps?

      What kind of heat pump are you interested in?
      I would like to be contacted by local installers
      I would like to receive occasional news from TheGreenAge

        Ground Source Heat Pumps

        Heating

      What are ground source heat pumps?

      Ground source heat pumps use the earth as a heat source, taking advantage of the stable temperatures in the ground to provide heat and hot water for the home.

      Ground source heat pumps are not a new concept and have been around since the 19th century. This technology became very popular in Sweden in the 1970s and since then units have been sold worldwide.

      In the UK, there has been a sudden surge in demand in heat pumps since the launch of the Renewable Heat Incentive, which pays homeowners for each unit of hot water produced. Although rates are no longer as high as they were, they can still cover much of the initial install costs of the systems.

      How do ground source heat pumps work?

      A ground source heat pump system uses heat trapped beneath the ground and boosts it to a higher temperature using a heat pump. This heat is then used to provide home heating or hot water. The heat pump performs the same role as a boiler does in a central heating system, but uses ambient heat from the ground rather than burning fuel to generate heat.

      Initially, a heat transfer liquid (normally glycol) is pumped through pipes buried deep in the ground. As the liquid travels through the pipework it absorbs ambient heat from the ground and warms up, before returning back to the ground source heat pump unit. Once it returns, a heat exchanger removes the heat from the liquid and it then continues to travel round and round the pipework in a continuous cycle.

      The low-grade heat is transferred through the heat exchanger, then passes through a heat pump compressor which drives the temperature up to a level that is usable for heating and hot water.

      How much pipework does a GSHP require?

      The length of the ground loop depends on the size of your home and the amount of heat you need – longer loops can draw more heat from the ground, but need more space to be buried in.

      The pipework can either be laid horizontally or vertically. If laid horizontally, the pipework tends to be buried in trenches 2-3m deep, spread over a huge surface area to ensure the heat transfer liquid has the opportunity to increase to a sufficient temperature. If the pipework is installed vertically, boreholes get drilled in to ground (at a cost of £6,000 – £8,000 for each borehole!). These need to be drilled by professionals and will regularly exceed 100m in depth to ensure that the heat transfer liquid again has the opportunity to absorb enough heat.

      There are two types of ground source heat pump, and both have a few components in common – they consist of a ground heat exchanger, a heat pump and a heat distribution system (e.g. underfloor heating or radiators).

      Closed loop ground source heat pump

      The majority of ground source heat pumps installed today are closed loop heat pumps. As the name suggests, no outside liquid enters the loop of pipework at any point. In this set up, a sealed loop of high density polyethylene pipe is laid either vertically or horizontally in the ground. The heat transfer fluid is in a completely closed system travelling through the pipework and returning back to heat pump.

      Open loop ground source heat pump

      The open-loop ground source heat pump uses ground water to pump around the system; however the number of installations of this type are decreasing, mainly because you need a source of groundwater. Also an additional associated issue with the open loop ground source heat pump is that the quality of the groundwater can actually have a detrimental effect on the system.

      Ground source heat pumps require electricity

      The fact that ground source heat pumps run on electricity suggests that they are expensive to run (electricity is approximately 15p / kWh while gas is just 4p / kWh). However heat pumps are in fact incredibly efficient.

      In fact, ground source heat pumps are even more efficient than air source heat pumps, converting each unit of electricity (required to run the pump and compressor) into 3.5 – 4.5 units of useful heat. Compare this to a brand new energy efficient boiler, which converts each unit of gas into just 0.9 units of useful heat.

      The efficiency of air source heat pumps is measured by the Coefficient of Performance (CoP), which is simply how many units of useful energy are produced from each unit of electricity consumed to operate the system. With air source heat pumps, the coefficient of performance changes throughout the year. This is because since in the winter months, the unit needs to work harder (and hence uses more electricity) to drive the temperature up to an acceptable temperature.

      For ground source heat pumps the coefficient of performance is relatively consistent – this means that even in the middle of winter, when hot water and heating demand are at a maximum, the GSHP should be running equally as efficiently as it does on a red hot summer’s day. This is because the temperature underneath the ground remains relatively constant all year round – and this is one of the key advantages of GSHPs over air source heat pumps.

      Heat pumps do have some impact on the environment as they require electricity to run, but the heat they extract from the ground is constantly being renewed naturally, hence they are considered a renewable heating source.

      Installing a ground source heat pump

      The Energy Saving Trust (EST) recommends households considering a ground source heat pump to consult a Microgeneration Certification Scheme installer and only use a properly accredited professional to complete the work. During its trial, the EST found a variety of heat pumps incorrectly installed, which therefore didn’t perform as efficiently overall as they could have. It is essential to use an MCS-approved installer to qualify for the Renewable Heat Incentive.

      It is important to shop around and we always recommend getting several quotes before choosing the best option for you. Studies have shown that most suppliers tend to exaggerate the savings in energy costs this system will produce.

      Renewable Heat Incentive

      Heat pumps are part of the Government Renewable Heat Incentive (RHI) scheme. It means that you can get paid for every unit of renewable heat you generate. You can get a significant chunk of the cost of installation back over 7 years of payments – not to mention the savings to be made from the heat pump itself. Read more on that here.

      Benefits

      Limitations

      Cost

      Installing heat pumps

      Are you thinking about getting a heat pump? We have scoured the country for the best tradespeople, so that we can make sure we only recommend those we really trust.

      If you would like us to find you a local heat pump installer, just fill in the form below and we will be in touch shortly!


        Interested in heat pumps?

        What kind of heat pump are you interested in?
        I would like to be contacted by local installers
        I would like to receive occasional news from TheGreenAge

          Water Source Heat Pumps

          Heating

        What are water source heat pumps?

        Water source heat pumps work on a similar principle to both air source and ground source heat pumps. Instead of taking advantage of the heat in the air or the ground, they take advantage of the relatively consistent temperatures found in a body of water.

        A series of flexible pipework is submerged in a body of water, such as a lake, river or stream. A heat pump pushes working fluid through the network of piping, and this fluid absorbs the heat from the surrounding water as it goes.

        This working fluid is then compressed by an electric compressor, in a similar fashion to the other types of heat pump, which raises the temperature. A heat exchanger can then be used to remove the heat entirely from this working fluid, providing you with hot water that can be used for space heating (in radiators or under floor heating). It can even be plumbed into your hot water system, where a boiler can just provide the small amount of additional heat needed to bring it up to the required temperature, so it can be used for showers and baths.

        Once the heat has been removed from the working fluid via the heat exchanger, it is once again pumped back through the pipework, thereby completing a continuous cycle.

        The benefits of a water source heat pump

        The heat transfer rate from water is higher from the ground, making them more effective than ground source heat pumps. In addition, if using a water source heat pump with a moving body of water, the heat is constantly being replaced, as new warmer water replaces the cooler water that has had its heat extracted by the working fluid.

        For every 1kW of energy required to run a water source heat pump, 4-5kW of equivalent heat energy is produced which can be used to warm your home. This makes the technology more efficient than both air and ground source heat pumps.

        The supply of hot water is also pretty much constant, despite being cooler in the winter; the body of water will still possess sufficient heat to enable the water source heat pump to operate in the winter. An issue only arises if the body of water completely freezes.

        Unlike ground source heat pumps, where bore holes or trenches need to be dug on your plot for the piping, the pipework for a water source heat pump is relatively simple to install; it simply needs to be situated within a body of water, which should have little impact on your plot of land.

        Benefits

        Limitations

        Cost


          Interested in heat pumps?

          What kind of heat pump are you interested in?
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            Heat Pumps and Planning Permission

            Heating

          Do I need planning permission for a heat pump?

          Ground and water source heat pumps

          Usually, unless you live in a listed property or conservation area, ground and water source heat pumps are considered a permitted development. You shouldn’t need an application for planning permission. It is still worth checking with your local authority before starting installation, however.

          Air source heat pumps

          In England and Scotland you can install an air source heat pump (ASHP) as it forms part of permitted development. However in each region, the home owner needs to follow specific guidelines and not contravene them in order to proceed with the installation.

          Unfortunately if you live in Wales and Northern Ireland, you will have to speak to your local authority to get a planning application submitted and approved before proceeding with the installation.

          Air source heat pump permitted development criteria in England

          Since the end of 2011, if you live in England, all heat pumps (air, ground and water) are considered a permitted development, so no planning permission is required. This was legislated in parliament to make it easier for individuals to install renewable technologies for their homes. Different outcomes apply however if you live in a listed property, conservation area or a world heritage site. We would advise you to contact your local planning authority for further guidance.

          An air source heat pump is a permitted development provided numerous conditions are met:

          Additional guidance in England:

          Air source heat pump permitted development criteria in Scotland

          In Scotland it is considered permitted development, unless installing an ASHP contravenes the following points:

          You also need to make sure that the developer that is installing the ASHP speaks to the local authority and gets clearance for the size and type of unit being installed. Not all systems may necessarily comply with permitted development criteria.

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