HEAT PUMPS
Cooling without the costs or carbon
The Royal College of General Practitioners has long warned that hotter summers linked to global warming, and increased air pollution could result in a summer crisis on a parallel with cold-related hospital admissions and excess winter deaths. These extreme weather conditions, combined with buildings become increasingly airtight and well insulated, means the need for cooling is paramount according this report from Kensa.
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sing some traditional cooling systems to combat overheating can be self- perpetuating. If the cooling system takes heat taken from a building and expels this into the surrounding air, this can raise the local air temperature, actually exacerbating the need for cooling. And, any systems that produce carbon emissions are ultimately unhelpful in the fight against climate change. Many multiple occupancy buildings, like flats, use
traditional district heating systems with a central plant, which can also contribute to the problem of overheating. In this system, hot water typically circulates at 65°C to 85°C through a network of pipes around the building. The system doesn’t know when each flat or office wants heating or hot water, so the high temperature circulating the pipework has to be maintained 24/7, raising the temperature within the building. In this article, leading UK manufacturer and
installation partner Kensa explains how ground source heat pump technology can reduce overheating in modern and efficient buildings without contributing to air pollution or climate change, by providing low cost and low carbon cooling, as well as heating.
How ground source heat pumps cool A ground source heat pump is an electrically powered heating device that works like a refrigerator in reverse. Pipework filled with a heat transfer fluid, known as a ground array, absorbs low-grade heat
22 June 2021
energy from a renewable source, such as the ground or water. The heat pump then compresses this heat energy to raise its temperature, transferring the additional heat to a home’s heating distribution system, where it can be used for space heating and domestic hot water. Passive or ‘free’ cooling with a ground source heat pump is a little-known benefit of the technology. Unlike the fluctuating air temperature, ground temperatures are stable all year round, and in the summer the ground is almost always more efficient for cooling than air. This is what gives ground source heat pumps the ability to provide ultra-low-cost cooling in the summer without the need for an additional ‘back-up’ appliance. By simply integrating or retrofitting a passive
cooling module or a separate plate heat exchanger to heat pump units manufactured by Kensa, the distribution system bypasses the ground source heat pump and utilises the cooler temperature of the ground (compared to internal building temperatures) to deliver a degree of passive cooling. The property is then simply cooled via a fan coil, passive beams or other potential systems, at an extremely low cost.
Shared arrays as a thermal energy supply grid Ground arrays can be installed on an individual or communal level, providing a sustainable and naturally replenished source of heat for either a single home or a whole street. Kensa has pioneered an innovative district heating infrastructure known as an ambient Shared Ground Loop Array system. Clusters of communal ground arrays, typically boreholes, act as the heat source for a loop of ambient temperature pipework which feeds heat to decentralised ground source heat pumps installed inside individual dwellings. As the residents have independent control over their own heating and hot water, the temperature within the buildings’ pipework is kept between -5°C to 20°C (ambient), only being upgraded when a heat pump calls for heating and hot water. This greatly minimises the problem of overheating within multiple occupancy buildings, reducing heat losses and therefore residents’ energy bills, and maximises the overall efficiency of the system. Another benefit of an ambient Shared Ground Loop Array system, is that it acts as a heating and
cooling thermal energy supply grid all year round. The by-product of extracting heat from the ground during the winter months is a large area of pre- chilled ground which is conveniently piped to the heat pump in each property and can provide passive cooling during the summer.
Even better, the heat that you take out of each property is reintroduced into the ground, recharging it and improving the heat pump heating efficiency the following winter. The savings on heating costs will normally offset the running cost of cooling in the summer, so the cost of cooling is neutral. As the ‘waste heat’ from cooling is being recycled, instead of released out into the atmosphere, this helps avoid further problems with overheating.
Balancing heating and cooling Larger ambient Shared Ground Loop Array systems connecting multiple buildings with a diverse mix of dwellings and commercial buildings creates further opportunities for efficiency improvements. For example, if you have a block of flats with retail space on the ground floor, such as a supermarket, then the annual heating load of the flats could be larger than the annual cooling load of the supermarket. In this scenario, the cold stored in the ground (created by extracting heat from the ground to heat the flats) can be enough to provide all, or much of, the annual cooling demand for the supermarket without the use of a heat pump at all! Now, in many modern commercial buildings, the demand for cooling is almost greater than the need for heating, especially for glazed offices or server rooms. For these buildings that need even more cooling, it is simple to reverse the heat pump hydraulic flows so that the heat pump actively cools the property. When operating in this reverse mode, ground source heat pumps can provide air conditioning, refrigeration or freezing. This active cooling is achieved by generating chilled water (typically at 6°C to 12°C) to cool the building, operating in a similar manner to a chiller. When connected to an ambient Shared Ground Loop Array, the waste heat can be sent into the ground, again giving you the benefit of recharging the ground array and improving heating system efficiency.
www.acr-news.com
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