How to link ground source heat pumps in a cascaded system to satisfy heat demand

Commercial premises typically need large volumes of heating and hot water. Paul Dennison – Sales Manager for Kensa Heat Pumps – explains how linking a number of ground source heat pumps together in a cascaded system architecture can satisfy this high heat demand – and qualify for the Non-Domestic RHI.
Many installers will have come across ground source heat pumps in domestic settings – such as single new-build or retrofit homes, for example. But they might not be aware that the technology can be especially effective in commercial scenarios, opening up a whole new and lucrative customer base.
Modular ground source heat pumps (such as Kensa’s Commercial Plant Room series that ranges between 25kW and 75kW) can be combined together in a central plant room to match the heat load of a building. The central ground array – whether coiled slinky pipe, boreholes or pond mats – is then sized to deal with the peak heat demand.
This type of ground source system architecture is becoming more common in commercial applications because it is so flexible and scalable. Installers need to realise that ground source heat pumps aren’t only suitable for domestic applications. By thinking outside of the box they can reach new markets and specify ground source heat pumps across a wide variety of scenarios.
Effective heat pump solutions
Cascaded systems feature multiple ground source heat pumps, which means that one or more units can take responsibility for producing the hot water, while the remaining units fulfil the space heating load. A high demand for hot water isn’t a problem for specialist high temperature ground source heat pumps, which removes the reliance on immersion heaters.Essentially this means any high heat load can be satisfied with this flexible and scalable solution. The set-up is also extremely efficient – the system can adjust between minimum and maximum heat demand as required, so it always produces the right amount of heating and hot water.
For example, in winter, a project might need 100kW of heat to satisfy demand whereas during the spring and summer the need for heat may be more like 40kW. In order to avoid inefficiencies, a cascaded ground source heat pump system comprising of two 50kW units might be installed. When a load greater than 50kW is needed, both heat pumps will operate to fulfil demand, while only one need operate in the summer.
Operational benefits and 20-year payback
There are other benefits too. Having more than one heat pump offers a degree of redundancy – in the unlikely event that one breaks down, the system will continue to operate. Although the full heat load cannot be met, a degree of heat can be maintained until the faulty unit can be replaced. It also means that engineers can work on each individual heat pump separately, while the rest of the system remains operational.
Commercial projects using a cascaded ground source heat pump system architecture are eligible for the Government’s Non-Domestic Renewable Heat Incentive (RHI), providing the system owners with a guaranteed quarterly income for 20 years based on the actual heat output of the system.
Case study: Hornsea Garden Centre
Hornsea Garden Centre near Hull is owned by brothers Charles and Robert Stubbs. It houses a large selection of plants, landscaping products, pet products, aquatics, furniture, home furnishings, clothing and tools.
The centre has recently undergone some development providing an extra 30,000 sq ft of retail space – plus an orangery, which is an improvement to the existing restaurant. The owners were looking to heat the new extension and upgrade the main building to underfloor heating to maximise available floor space.
Kensa specified a cascaded ground source heat pump system, featuring two 45kW Plant Room units to cover the heating and one 25kW High Temperature Plant Room unit to provide hot water.
The heat pumps are housed in a plant room based on a mezzanine level above the main site entrance. A large ground array consisting of 24 loops of 50m coiled slinky pipe is buried under a field across from the car park.
Lincoln-based installer Steve Robinson handled the job. He has experience in working with ground source heat pump technology in commercial scenarios.
“Maintaining a constant, controllable temperature in the garden centre was important for customer comfort, and also for the wellbeing of the plants and aquatic products too,” Steve explains. “With kitchen and customer toilet facilities in the restaurant, lots of hot water was also needed.
“A cascaded ground source heat pump system meant the building warms up very quickly to a cosy 22–23°C, and the temperature is easily controlled and adjusted.”
The system has been so successful that the owners are applying it again in a new garden centre that is currently being built in Durham.
Key facts
• New-build extension providing 30,000 sq ft of retail space
• Main building upgraded to underfloor heating
• Cascaded ground source heat pump system
• 2345kW Plant Room ground source heat pumps providing space heating
• 1325kW High Temperature Plant Room ground source heat pump providing hot water
• 24350m slinkies located under nearby field
• System contains 7,250 litres of water and 1,450 litres of antifreeze
More information on cascaded ground source heat pump systems, including example project costs, schematic drawings, and different ground array configurations can be found at

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