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CASCADED GSHP SYSTEMS A great solution for commercial projects


What is a ‘cascaded ground source heat pump system’?


Guy Cashmore, Technical Director at UK manufacturer, Kensa Heat Pumps, explains how a cascaded ground source heat pump system architecture can bring benefits to commercial projects where providing large volumes of heang and hot water is crical.


A cascaded ground source heat pump (GSHP) system, however, can be defined in various ways. Most commercial heating and plumbing contractors will be familiar with cascaded boiler systems. They are generally used in projects with large heat loads, and/or critical applications where a degree of diversification and redundancy is required within the heating system.


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GSHP systems can be cascaded in a similar manner, and feature a central ground array infrastructure, made up of either slinkies or boreholes, that is sized to deal with the entire heat demand (peak and annual). Typically a cascaded system will link this ground array with a number of large modular ground source heat pumps together all in one central plant room, therefore offering higher outputs. Projects utilising this type of cascaded ground source heat pump system design are eligible for the Government’s Non- Domestic Renewable Heat Incentive (RHI), which provides the system owner with a guaranteed quarterly income for 20 years based on the actual heat output of the system.


Why use a cascaded GSHP system architecture?


Cascaded GSHP systems can adjust between minimum and maximum heat demand as needed, which means that the system can take into account seasonal demand differences and optimally produce the required amount of heating. For example, in winter a project might need 100kW of heat to satisfy demand, however during the spring and summer the need for heat may be more like 40kW. In order to avoid inefficiencies, a cascaded GSHP system comprising two 50kW units might be installed. When a load greater than 50kW is needed, then both heat pumps will operate to fulfil demand, whilst only one need operate in the summer and shoulder seasons.


If the property requires heating and hot water, cascaded systems can also be designed with one or more heat pumps dedicated to the production of domestic hot water only, and the remaining units dedicated to satisfy the space heating load. Specialist high temperature GSHPs can be used to produce the domestic hot water, removing the reliance on immersion heaters.


One example of this is at Hornsea Garden Centre near Hull. The owners were looking to heat a new extension and upgrade the main building to underfloor heating. Kensa specified a cascaded GSHP system featuring two 45kW Plantroom units to cover the heating, and one 25kW High Temperature Plantroom unit to provide hot water.


efrigeration 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.


What are the benefits?


Using multiple GSHPs in a cascaded configuration has other advantages, too. Ground source technology gives the best efficiency when operated with long run cycles. Modulating GSHPs, either by frequent stop-start or by using inverters, invariably causes efficiency loss. Having a cascade of GSHPs means that the majority of the load will be supplied by units running almost continuously.


It also means that in the unlikely event of a heat pump breakdown, only a small per centage of the total capacity is lost, so the building isn't going to go completely cold whatever the weather. It also means that engineers can work on each individual heat pump separately, whilst the rest of the system remains operational. uMore information about cascaded ground source heat pump systems, including example project costs, schematic drawings and different ground array configurations, can be found at:


uCascaded Slinky System.


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Cascaded GSHP


www.kensaheatpumps.com/solution- centre/business/commercial-building/


Case study: Stakeford Depot N


orthumberland County Council utilised a cascaded ground source heat pump system to transform an energy inefficient depot that was in desperate need of heating upgrades.


At just under 3,000sq m the Stakeford Depot is the largest commercial premises to feature Kensa GSHPs to date. Consisting of a mixture of offices and workshops, the building remained occupied throughout the GSHP works.


The depot was heated by gas boilers that had been failing for a number of years. The problem was so bad that most offices had temporary electric heaters, while some even had permanent electric heaters installed. Consequently, running costs and carbon emissions were high, and occupant comfort was low.


Kensa had already successfully installed GSHP infrastructure at a number of sites across the county on behalf of Northumberland County Council. They specified five 75kW Kensa Plant Room units to provide heating and one 6kW Kensa Shoebox heat pump to provide hot water. The existing heating system was removed and replaced with a new wet heating system. Following detailed geological surveys and tests, 35 boreholes were drilled under nearby land to extract heat.


Northumberland County Council is committed to making its buildings more energy efficient as well as more environmentally friendly. They believe that ground source heat pumps will play an important role in helping them achieve their aims.


18 BUILDING SERVICES & ENVIRONMENTAL ENGINEER AUGUST 2018


Key facts: u3,000sq m council depot, workshops and offices;


u320,000kWh annual space heating demand;


u5 x 75kW Kensa Plant Room providing heating and 1 x 6kW Kensa Shoebox heat pump providing hot water;


uCascaded system architecture; uReplaced an ageing gas plantroom; u35 x boreholes.


Oakes Energy was appointed as a Kensa’s sub-contractor to handle the internal works. This included the installation of the GSHPs within the plant rooms, including new pipework, fittings, valves, pumps, and buffer vessels where required, new heat emitters (fan coil units and radiators), new wet heating distribution pipework, and of course the


uStakeford Depot heat pumps installed.


systems can adjust between minimum and maximum heat demand as needed, which means that the system can take into account seasonal demand dierences and opmally produce the required amount of heang.


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decommissioning and removal of the former heating system.


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