Ground source heat pumps can be linked together in a cascaded system

A cascaded ground source heat pump system allows heat pump units to work together to adjust to meet a property’s peak heat demand. It can be used to meet a high heat load, adjust to seasonal variations, maximise efficiencies of multiple temperature zones, add redundancy, and reduce overheating. When the demand for heat is low in the summertime, a unit in the system can operate in isolation to optimise efficiency and reduce running costs.

Refrigeration engineers might understand a cascaded ground source heat pump to mean a unit containing multi-stage compressors designed to take low-grade heat energy and convert this to a much higher temperature. A cascaded ground source heat pump system, however, can be defined in various ways.

Cascaded ground source heat pump systems feature a central ground array infrastructure, typically made up of either slinkies or boreholes. This infrastructure is sized to deal with a building’s entire peak and annual heat demand. Typically a cascaded system will see the ground arrays connected to numerous large ground source heat pumps. These are then linked together in one central plant room.

Most commercial heating and plumbing contractors will be familiar with cascaded boiler systems. They are generally used in projects with large heat loads, or critical applications where a degree of redundancy is required within the heating system.

With a cascaded boiler system, the usual approach is to set up the boilers to operate at the temperature needed by the circuit requiring the highest temperature. Mixing or blending valves are then used to reduce the temperature down to what is needed by other circuits. Boilers are often set up to run at temperatures well above the maximum required.

In order to enjoy the many benefits of ground source heat pumps and efficiently deliver the heating and hot water demands of commercial projects, Kensa’s cascaded system is a much more elegant and efficient solution. If the same approach was taken with ground source heat pumps as boilers, the system would function, but it would be inefficient and result in significantly higher running costs for the client. Kensa would not recommend this approach.

Cascaded heat pump systems are particularly useful in commercial applications. Not only do they efficiently meet fluctuating heat demands, but each unit can have its own use. For example, one could be dedicated to providing heating while another is providing hot water. This avoids any delay in demand, making the set-up ideal for businesses.

Many commercial buildings have multiple temperature requirements across different heating distribution systems.

An office building requires Kensa’s heat pumps to produce three different temperatures: 35°C for the underfloor heating in the new extension, 65°C for the domestic hot water system, and 50°C for the old radiator system.

In this building, the radiator load is small, accounting for around 30% of the total heat requirement. It made no sense to run all the heating at 50°C and ignore the higher efficiencies possible on the underfloor heating circuit. In this case, each unit could share the same ground array, but separate ground source heat pumps could be installed and optimised for each circuit.

The key difference between this example and a typical cascaded ground source heat pump installation is that on the load side, the heat pumps won’t all be feeding into a common distribution system. Instead, the heat pumps are feeding two or three dedicated circuits with differing temperature requirements. If there is a greater demand for heat in the future, multiple heat pumps can be cascaded for heat on one or more circuits, effectively forming a series of cascaded systems in one system.