Benefits of Geo-Exchange Technology Performance in Extremely High Temperatures
One of the main drawbacks of refrigeration technology is that efficiency drops off on hot days, when the ambient temperature exceeds design. This is particularly alarming when considering the unprecedented heatwave which the UK is currently experiencing.
When operating at design parameters, a condenser will remove energy from the required amount of refrigerant gas to match its design load, turning it into a liquid. As ambient temperatures increase, the corresponding pressure change within the refrigerant gas must be overcome by the compressor, causing it to draw more electrical energy. This drawback can, however, be overcome with the use of an appropriate heat sink.
Erda geo-exchange technology uses highly sophisticated controls techniques to allow us to maintain optimum temperature in our Erda | deep arrays. One such technique allows the rejection of energy from the Erda | deep array, lowering the flow temperature from the ground loop. Keeping the Erda | deep boreholes cooler allows for more efficient refrigeration within the store as the ground acts as a better heat sink at lower temperatures. In high temperatures like these, it is important to be able to provide efficient refrigeration, and so lower temperatures from the Erda | deep loop are essential.
Figure 1: Erda loop temperature vs external temperature for a supermarket located in the south of England
(12/07/22 – 19/07/22)
Figure 1 shows the external air temperature for an Erda system in the south of England compared to the temperature of flow leaving the ground loop. The temperature of the Erda | deep array is kept significantly lower than the air temperature during extremely hot periods, with the ambient temperature spiking at 36.1°C and the ground loop reaching a maximum of 25.9°C.
Figure 2: Ambient temperature compared with condenser outlet temperature and fridge pack return temperature.
Low ground loop temperatures like this allow our DDU refrigeration interfaces to more effectively provide refrigeration to the store, which is demonstrated by figure 2. The availability of a heat sink in the Erda | deep loop means that the refrigerant return from the refrigeration pack is cooler than the ambient temperature (figure 2). In the extreme temperatures experienced recently in the UK – and with even higher temperatures expected in the future – this is especially crucial as it allows the CO2 refrigerant to remain sub-critical (i.e. as a liquid), whereas at ambient temperatures it would be trans-critical (i.e. a gas) when reaching the refrigeration pack, which is healthier for the pack. This sub-critical refrigerant increases the system efficiency and decreases the compressor discharge pressure, saving electrical energy. The heat captured from refrigeration during warm periods such as this is then stored within the ground, and used to provide highly efficient heating during winter, making maximum use of the available thermal energy.
The extreme temperatures across the UK in recent days have further highlighted both the need for refrigeration systems which can run effectively under such conditions, and for low-carbon heating and cooling solutions which can help reduce CO2 emissions and aid in achieving our net-zero targets. Erda’s technology is capable of solving both problems simultaneously, providing highly efficient refrigeration and space cooling whilst helping to fight climate change.