GSHP project exceeds the targets set for it
Carbon savings achieved by the ground-source heat-pump system that provide heating and cooling for the Oxford Earth Sciences Building are exceeding expectations. The system was provided by GI Energy, and CO2 emissions are 120 t a year lower than anticipated, despite the building behaving quite differently from what was expected at design stage. The saving is 23% more than expected.
The reality is that heating requirements are double what was expected and, at peak times, cooling demand is up to 10 times what was expected.
Performance data over an entire year showed COPs of 3.6 for heating and 4.7 for cooling.
Chris Davidson, director of development at GI Energy, comments, ‘The beauty of ground-source heat-pump systems is that they extract heat from, and return it to, the ground — making them many times more efficient than conventional heating or cooling.
The GSHP system is supported by gas boilers and conventional cooling, since the site is not large enough to meet peak heating and cooling loads, even with 63 boreholes sunk to a depth of 64 m into the ground to avoid hitting a high-pressure underground aquifer.
GI Energy’s brief was to provide as much heating and cooling as possible with a GSHP system, given the constraints of the site and using water at 45°C for heating and 6°C for cooling. GI Energy is responsible for deciding when to use the back-up boilers and air conditioners. The carbon savings are quoted across the whole of the heating and cooling system.
The computerised control system can switch each of the three ground-source heat pumps individually from heating to cooling and also control the back-up heating and cooling.
Monitoring throughout the year showed that the building required on average 100 MWh of heat, compared to the original estimate of 50 MWh, and that the cooling load average 25 to 35 MWh a week, much higher than the initial estimate of 5 to 10 MWh.
Steven Pearson of Oxford Earth Sciences says, ‘The system is providing much better savings than anticipated. While it is always reassuring to have a contract that delivers what is specified, there is a lot of value in GI Energy’s flexibility and ability to respond to changing demands.’