Water Source Heat Pump

Summary: How Water Source heat pumps extract heat from a nearby water source which can be used to heat your hot water and your home.

Water Source heat pumps: The Basics

House showing installed Water Source Heating pipeworkWater source heat pumps work in essentially the same way as ground source heat pumps. The system transfers heat from a nearby water source such as a lake or river to your home through a heat exchanger attached to your house.

Closed or Open Loop:

A ground loop is a length of piping that is used to collect heat from the ground or the water source and take it to the heat pump. In a water source heat pump system the ground loop can be arranged in two different ways:

  • Closed configuration - this is arranged as it is in the ground source system where a loop of piping containing a mixture of water and antifreeze is immersed in a water source to collect ambient heat, rather than the earth. The ambient heat in the water is transferred to the fluid in the loop which takes this to the heat pump.
  • Open Configuration - in this case the source water itself is pumped into the system and then returned back to the water source once the heat has been extracted by the heat pump. It is generally thought that open systems are more efficient, but that they also need more maintenance.

Installing this system will lower the cost of heating your home, although as this is still not a very commonly installed system the savings that are achievable can vary. With the Renewable Heat Incentive subsidies there are also government-backed incentives which will increase your savings.

The Renewable Heat Premium Payments scheme allows you to claim a voucher for £1,250 towards the cost of installing a water source heat pump if your existing heating system uses oil, solid fuel or electricity, and from summer 2013 onwards the government plans to offer homeowners regular payments to generate renewable heat through the Renewable Heat Incentive scheme.

There is also a loan available for the cost of installation through the Green Deal scheme. The loan is repaid through payments on your energy bills, and as the payment shouldn't exceed the saving you've made this should mean that you pay no extra money to have a renewable technology in your home.

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How Water Source Heat Pumps work

You will need to have a large water source, such as a river or lake located near to your house. Installation may be expensive as you might need to hire divers or drain the water from the lake.

  • A mixture of antifreeze and water flows around the ground loop - which is immersed in the water source. This fluid absorbs the heat from the water.
  • The heated fluid in the ground loop is then pumped into a heat exchanger, where the heat is transferred to a refrigerant.
  • The refrigerant is then compressed using a compressor, which concentrates the heat so that it reaches a higher temperature. The heat is now sufficient to heat water for use in a central heating system or as hot water.
  • By this stage the ground loop fluid is cooled again and flows back through the piping in the water where it takes up more heat, repeating the process.

Your home's size and your requirement for heat will determine the length of the loop - longer loops are capable of extracting more heat from the water, but require a greater area of water.

Mitsubishi Air Source Heat Pump unitThere are different heat pump systems available and they work on a similar principle but instead take up heat from different sources:

  • Air Source heat pumps: These systems absorb heat from external air and are a sought after option as they are economic and simple to install and are especially suitable if you live in a city with little outside space.
  • Ground Source heat pumps: This system is similar to a water source pump except that the ground loop is buried in trenches in the ground in your garden.
  • MVHR (Mechanical Ventilation and Heat Recovery): This system reclaims the heat from warm air leaving your house. This system is ideally suited to more air-tight homes.

Installing a Water Source heat pump

If you are planning on installing a Water Source heat pump it is essential to get the correct planning and environmental permissions in place as you will be using a local water body. The Environment Agency will be able to assist you with this.

In order to be eligible for the Renewable Heat Incentive subsidies the system must be fitted by a MCS accredited installer.

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Water Source heat pump Installation Checklist

National Trust lakeYou will need to think about the following:

  • Planning permissions: Ensure you have the correct permissions in place before you start work.
  • Home insulation: It's important to insulate your home well to maximise the efficiency of your system. Water source heat pump systems generate a heat of a lower temperature than traditional boilers, and so poor insulation makes them much less efficient.
  • Your heating fuel: If you are currently using an electric, solid fuel or oil based heating system, a water source heat pump should deliver noticeable energy savings. If you are currently using a gas system it is likely you will see a smaller saving. This is why homes using a gas system do not currently qualify for payment from the Renewable Heat Premium Payment scheme; however homes on the gas grid may qualify for regular payments for heat generation through the Renewable Heat Incentive scheme which will be launched in summer 2013. Homes using a gas system also qualify for assistance through the Green Deal.
  • Which heating system? Under-floor heating, larger radiators or low temperature fan convectors are a more efficient choice than conventional radiator-based systems when used with the heat pump because of the lower water temperatures generated by the heat pump system.
  • Are you carrying out other building work? You can potentially reduce the cost of your pump installation by combining it with any other building work you have planned.

Coefficient of Performance (CoP) describes a heat pump's efficiency; it is the ratio of heat output to energy input and the larger the value the better. Heat pumps can generate up to 4 kilowatts of energy for each kilowatt of electricity they use. This means that heat pump systems can be very energy efficient. Another measure known as the System Efficiency Ratio (SER) describes the ratio of how many units of electricity the entire heating system uses to the number of units of heat the pump produces. Both the CoP and SER values range from 1 to around 4 - when choosing a system look for one with a value as high as possible.

Water Source heat pump Installation time

The installation time for a water source heat pump system varies with the size of the system being installed. By combining the water source heat pump installation with other building work you can potentially save money on your installation. This is particularly true if any changes to your heat distribution system are needed, such as fitting under floor heating.

Water Source heat pump Installers

You should always use an MCS accredited installer to install your heat pump system as this will allow the installation to qualify for the appropriate grants and subsidies. MCS accredited installers have the qualifications necessary to be able to sign off installations that comply with the government's Renewable Heat Incentive scheme. If you are getting the system installed through the Green Deal you will need a Green Deal installer to carry out the work.

Water Source heat pump Costs

House situated next to lakeAfter the initial installation cost, how much the system costs to run depends on a number of considerations - including the size of your home and how well insulated it is. If you choose an open-loop water source system the maintenance cost is normally higher, but this system is also likely to be more efficient.

As well as the savings you will make on your heating bills you could be eligible for a voucher for installation costs worth £1,250 from the Renewable Heat Premium Payments scheme as well as potentially being paid for the heat yours system generates through the Renewable Heat Incentive, due to be introduced in 2013. For more information on the Renewable Heat subsidies visit our RHI page.

Thanks to the recent launch of the Green Deal Scheme you could also qualify for financing worth part or all of your installation costs. The scheme pays for the installation on your behalf and then takes this money back through your energy bill using money you have saved by using the technology. This should mean that the installation does not represent any extra expense for you; though there is interest included in the payments which means that overall you will save more money by paying for the installation yourself. For further guidance on the Green Deal scheme take a look at our Green Deal page.

Heat pump systems need to use some electricity to pump the ground loop fluid around the system. However, the amount of thermal energy that they take up from the water source is higher than the amount of energy that is used to run them, meaning that they are energy efficient systems.

Heat pumps work in a different way to conventional boiler systems in that they generate lower temperature heat over much longer periods. This means that ideally you should leave the system running constantly during the winter to maximise efficiency. It's also best to install Low Surface Temperature (LST) radiators in place of your normal radiators for use with the pump. Their larger surface area makes up for the fact that the heat pump produces hot water at a lower temperature.

The benefits of Water Source heat pumps

Lake with reedsThe exact amount of money you will save will vary depending on your current heating system. You can also get a voucher for £1,250 (the Renewable Heat Premium Payment) and quarterly payments for the heat you generate (Renewable Heat Incentive) if the pump is installed by an MCS accredited installer. Heat pump systems also come with some additional benefits:

  • Reduce your environmental footprint: Heat pumps reduce your home's carbon emissions because they reduce the quantity of fuel that you need to burn to provide heating to your home.
  • No boiler necessary: If you install a heat pump you shouldn't need to use a boiler to top up your hot water.
  • No fuel deliveries: Your heat pump only needs electricity to run so there is no need to get fuel delivered to your home.

Water Source heat pumps - maximising your savings

The energy and money you save by installing the pump will depend on several things:

  • The way you distribute the heat produced: Under-floor heating is ideal for use with a heat pump system rather than using radiators because they are more efficient at distributing heat using lower temperature hot water.
  • Your existing system's efficiency: If your existing system is inefficient you are likely to see increased savings using a heat pump.
  • Will it provide hot water? Using a heat pump to generate hot water can lower its efficiency.
  • How it is used? Using a heat pump system it is likely that you will need to have the heating on for a longer period each day, but you may be able to turn the thermostat temperature down and still feel comfortable.

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