technologies

Water Source Heat Pumps

The Basic Principles & Benefits of a Water Source Heat Pump

From a very technical perspective, all heat pump systems are water source heat pumps. Water is an excellent conductor of heat, it conducts heat almost 20 times better than air. It is the water vapour in air that contains the heat extracted by air source heat pumps just as it is water which connects the pipes of a ground source heat pump system to the surrounding earth and allows it to conduct heat.

As well as being a great conductor of heat, water also has high density which means that it can store a lot of thermal energy.

All of the above means that water source heat pumps, if designed and installed properly, are the most efficient type. Involving a specialist heat pump contractor like us will ensure that your water source heat pump system runs efficiently and effectively.

Below are the key principles and benefits of a water source heat pump, but we’d love to hear from you and develop a proposal that meets your particular requirements.

What are the benefits of a water source heat pump?

Reduction of C02 emissions – unlike biomass, oil or LPG, WSHPs produce no carbon emissions on site.
Reduction of energy bills – WSHPs are one of the most efficient forms of energy supply. Running the systems requires a small level of electricity; however, a quality system will deliver an energy output of three to four times the input. This ratio is called Coefficient of Performance (COP).
Income generation – heat pump funding and grants such as the Renewable Heat Incentive (RHI) allow a significant return of investment for ground source heat pump installations.
Safety and convenience – the system requires little to no maintenance and has a life in excess of 25 years. It also removes any requirement for purchasing and storing any natural or combustible fuel components.

What is a water source heat pump system?

Any heat pump system which extracts heat directly from water is called a water source heat pump. A typical water source heat pump is able to extract up to five times more energy from the ground than the energy used by the heat pump and this makes water source heat pumps the most efficient option for providing heating and hot water.

What are the different heat source options for water source heat pumps?

There are two different methods for using water as your heat source:

Closed loop water source are the most cost effective and efficient system possible for heat pumps. They use either a series of metal heat exchangers or an array of pipe coils placed directly in the water source.
Open loop boreholes are most commonly used for large scale heat pump systems. They are comprised of at least one borehole which is drilled below the standing water table. A submersible pump is then installed in the borehole and this pumps water to the heat pumps which then extract heat from the water. Once the heat has been extracted the water is pumped into a second borehole (or boreholes) and discharged back into the ground.

How does a water source heat pump installation work?

A water source heat pump system pumps water into the heat pump heat exchanger either under open or closed pressure. Open pressure means that both ends of the pipe are open and so the water which is extracted is discharged back into the ground once the heat has been taken from it. Closed pressure means that a solution of water and glycol is circulated between a heat exchanger which is located in the water source and a second heat exchanger which is located in the heat pump. The pipe circuit is closed and has no open ends so it is called ‘closed’.

The density of water means that it holds lots of thermal energy and this provides a constant heat source throughout the year, even when the air temperature is very cold.

Water’s high thermal conductivity means that it is able to replenish the heat taken from it quickly from the surrounding earth and air.

Heat pump efficiency is a product of the difference between its heat source (the ground) and the heat use (the heating or hot water system). Closed water source heat pumps are the most efficient option because they are able to conduct heat from the air during the warmer months and then extract heat from the earth when the air temperature gets colder.

Closed loop water source heat pump systems are also the least expensive option as there is no cost for boreholes and the groundworks is usually minimal. However, you will need to have an adequate source of water within the vicinity of the heat use. We can advise on which water sources are suitable.

What can a water source heat pump be used for?

Water source heat pumps can provide all your space heating and hot water. They can also provide cheap cooling if you have a suitable distribution system installed.

Historically, heat pumps were not able to achieve high enough temperatures to meet all hot water demands and this meant that they often had to be topped up with a conventional system such as, direct electric or oil. However, modern heat pumps can achieve heating and hot water temperatures of 60℃+ and can provide 100% of your heating and hot water.

It has also been common for heat pump systems to only be recommended with underfloor heating. However, modern heat pumps can run efficiently with conventional radiators at efficiencies that make them much less expensive to run that oil or gas heating. In addition, there are also highly efficient radiators, such as Jaga Strada, which can be used with heat pumps and actually offer better efficiency than underfloor heating.

What are the stages of a closed loop water source heat pump installation?

A closed loop water source heat pump system will typically follow this process:

Desktop study – the first stage of a closed loop water source heat pump system is to ascertain whether the water source has the capacity to supply the required thermal energy. This will involve calculating the volumetric heat capacity of the water body and also the replenishment rate.
Design – once it is confirmed that the water source can supply the thermal energy for the proposed system, the design work starts. This will typically take 4-6 weeks and it is the most important step – mistakes during installation can usually be corrected but mistakes in the design of a system are much harder to resolve.
Site set up and planning – the third stage of installing a closed loop water source heat pump system is the site set up and planning which includes:
- Setting up welfare and health and safety provisions on site
- Setting out all trenches and groundworks accurately
- Double checking that you have sufficient capacity in your electrical supply for the heat pump system
- Having a plan to deal with the spoil from the trenching and for reinstating the areas affected by groundworks.
- Attain planning permission for the system. Not all heat pump systems require planning but Ofgem make it a requirement of the Renewable Heat Incentive scheme that you send evidence of planning approval, or that planning isn’t required.
- Ensure that all health and safety measures are taken care of. This includes: risk assessment and method statements, fencing off dangerous areas, providing welfare facilities as required, and making sure all operatives are suitably qualified and wearing the correct Personal Protective Equipment (PPE)
Install the heat exchangers in the water source – the next step is to install the heat exchangers which will extract the heat from the water source. Sizing the heat source correctly is the most important part of designing a heat pump system. If you undersize the heat collector then you won’t be able to get enough heat to keep the heat pumps operating and this will lead to recurring faults and inadequate heating. For closed loop water source heat pump systems there are two options for extracting the heat:
- An array of metal heat exchangers – these look like large radiators and are used most often in rivers and areas unsuitable for large arrays of pipework
- An array of pipe heat collectors – these are comprised of multiple coils of plastic pipe secured to a metal frame and then connected to a manifold next to the water source. These are most commonly used in lakes and large bodies of water.
Manifolding – Once the heat collectors are installed they need to be connected together to form a common flow and return. A manifold is used to bring all flow pipes together and all return pipes together. It is usually a good idea to also include flow regulators and isolation valves on the manifold too. Once the manifolding is complete, the main flow and return pipes are taken to the plant room ready for connection to the heat pumps.
Mechanical heat pump installation – The next step is to install the heat pump system. The mechanical installation happens first and includes all pipework, buffer vessel, valves, pumps, and the heat pumps themselves. This work is carried out by highly skilled and experienced engineers who will ensure that the installation is completed according to the design.
Electrical and controls installation – Once the mechanical installation is complete we can start the electrical and controls installation. One of the most common reasons for faults and under performing systems is not setting the control strategy correctly and not making sure that the heat pump system interfaces correctly with the rest of the heating/cooling/hot water system.
Commissioning and testing – The commissioning and testing process should include:
- Making sure the controls are set up correctly
- Checking that the whole system is successfully tested under pressure
- Flushing and filling the system thoroughly and properly
- Making sure that all air is removed from the system
- Making sure that the system controls are setting up as required by the owner and that the system is operating as it is meant to
- Gathering all the information required for the Renewable Heat Incentive application
Handover – this stage includes demonstrating the system to the client and showing them the various parts of the heat pump installation. It also includes handing over the operation and maintenance manual for the system.
Monitoring, servicing, and maintenance – the final stage is ongoing and involves:
- Remote monitoring: we use remote monitoring to log all the parameters of the system performance. This enables us to pick up any faults in the system quickly and to make sure our engineers have everything they need to fix the problem when they get to site. Our monitoring service also includes the periodic remote reading and submission of heat meter data to Ofgem for the Renewable Heat Incentive scheme.
- Servicing: All heat pump manufacturers require the heat pump system to be regularly and correctly serviced for the manufacturers warranty to remain valid. Regular servicing is also important to maximise the heat pump longevity. Correct and preemptive servicing can add years to the life of your heat pump system.
- Maintenance: There are two types of maintenance that people require: emergency, and non-emergency. It is important that you have a servicing and maintenance contract with a company which understands your system and has the resources to react quickly to any problems that arise.

What are the stages of an open loop water source heat pump installation?

A open loop water source heat pump system will typically follow this process:

Desktop study – the first stage of an open loop water source heat pump system is to ascertain whether the site has suitable hydro-geology underneath it with enough water to supply the required thermal energy for the proposed heat pump system.
This typically involves an assessment of geological maps and borehole records..
Abstraction test – If the desktop study reveals a high chance of adequate water being available then the next step is to drill a water well and test the rate at which water can be sustainably abstracted. This will usually require an abstraction licence from the Environment Agency.
Discharge test – A second well is usually drilled at the same time as the abstraction well. The abstracted water is discharged into the discharge well and measurements are taken of the dissipation rate of the water. The discharge well should always be sited a suitable distance from the abstraction well so that the cooled or heated water is not recirculated.
Design – once we have the data from the abstraction and discharge wells we can calculate the number, diameter, and depth of the boreholes to provide the required thermal energy or cooling capacity. The design of the rest of the heat pump system will also be carried out during this time. This will typically take 4-6 weeks and it is the most important step – mistakes during installation can usually be corrected relatively easily but mistakes in the design of a system are much harder to resolve.
Site set up and planning – the third stage of installing an open loop water source heat pump system is the site set up and planning which includes:
- Setting up welfare and health and safety provisions on site
- Setting out all boreholes and trenches accurately
- Double checking that you have sufficient capacity in your electrical supply for the heat pump system
- Having a plan to deal with the spoil from the trenching, the waste water and drilling arisings, and for reinstating the areas affected by groundworks.
- Attain planning permission for the system. Not all heat pump systems require planning but Ofgem make it a requirement of the Renewable Heat Incentive scheme that you send evidence of planning approval, or that planning isn’t required.
- Ensure that all health and safety measures are taken care of. This includes: risk assessment and method statements, fencing off dangerous areas, providing welfare facilities as required, and making sure all operatives are suitably qualified and wearing the correct Personal Protective Equipment (PPE)
Drilling and well completion – the next step is to drill the water wells and install the well screen, submersible pump, telemetry and other associated parts. Once they are commissioned the wells are connected to a central manifold and taken to the plant room. An electrical supply is also run to the submersible pump and cables for the telemetry equipment.
Mechanical heat pump installation – The next step is to install the heat pump system. The mechanical installation happens first and includes all pipework, buffer vessel, valves, pumps, and the heat pumps themselves. This work is carried out by highly skilled and experienced engineers who will ensure that the installation is completed according to the design.
Electrical and controls installation – Once the mechanical installation is complete we can start the electrical and controls installation. One of the most common reasons for faults and under performing systems is not setting the control strategy correctly and not making sure that the heat pump system interfaces correctly with the rest of the heating/cooling/hot water system.
Commissioning and testing – The commissioning and testing process should include:
- Making sure the controls are set up correctly
- Checking that the whole system is successfully tested under pressure
- Flushing and filling the system thoroughly and properly
- Making sure that all air is removed from the system
- Making sure that the system controls are setting up as required by the owner and that the system is operating as it is meant to
- Gathering all the information required for the Renewable Heat Incentive application
Handover – this stage includes demonstrating the system to the client and showing them the various parts of the heat pump installation. It also includes handing over the operation and maintenance manual for the system.
Monitoring, servicing, and maintenance – The final stage is ongoing and involves:
- Remote monitoring: we use remote monitoring to log all the parameters of the system performance. This enables us to pick up any faults in the system quickly and to make sure our engineers have everything they need to fix the problem when they get to site. Our monitoring service also includes the periodic remote reading and submission of heat meter data to Ofgem for the Renewable Heat Incentive scheme.
- Servicing: All heat pump manufacturers require the heat pump system to be regularly and correctly serviced for the manufacturers warranty to remain valid. Regular servicing is also important to maximise the heat pump longevity. Correct and preemptive servicing can add years to the life of your heat pump system.
- Maintenance: There are two types of maintenance that people require: emergency, and non-emergency. It is important that you have a servicing and maintenance contract with a company which understands your system and has the resources to react quickly to any problems that arise.

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