GROUND SOURCE HEAT PUMPS CASE STUDY
A CLIENT’S PERSPECTIVE
Our first major GSES has provided us with a series of valuable lessons in managing low-carbon technology, writes Steve Pearson, head of building services at the University of Oxford’s Estates Services. Thermal models are
fundamental to GSES design, but it is all too easy to trust the output of a model without understanding the assumptions on which they are built, and how they affect performance. It is all the more important for a GSES because the performance in any given period is heavily dependent on how the system was used in the preceding period.
There is a requirement for sensitivity analysis on our next project and a ‘sign off’ of the model assumptions.
Getting the control systems communicating effectively and the metering system accurate was a struggle.
It would be naive to think that all of this can be perfect before handover as the system cannot be optimised without in-use data.
Much has been talked of ‘soft landings’ but if ever there was a system that required attention post-PC it is GSES. We are fortunate that we were able to devote this attention to it and now have a GSES that is performing significantly better than the specification.
40 CIBSE Journal August 2013 Visualisation showing building with boreholes for ground-source energy system
Lessons learned By April 2012, all these issues appeared to be resolved. Some additional tweaks to the control software were also made to improve efficiency, but a further period of close monitoring was needed to ensure the problems had been rectified. Since this date, the system has operated without any significant fault, and has actually been shown to deliver greater carbon savings than originally predicted. While on the face of it this seems a positive result, in fact part of the reason for this is that the annual heating and cooling loads are significantly higher than predicted. This is, perhaps, unsurprising in a building with variable volume laboratory ventilation systems, the use of which is largely occupant-dependent and almost impossible to predict. It does however raise interesting questions about the specification of GSESs and the difficulty in establishing a criterion at design stage against which performance can be measured. The key lesson from the project is that
a significant amount of effort is necessary to ensure that the potential savings of LZC technologies are realised. At OUES, it was fortunate that the client and the design and construction team had a long-standing relationship and shared a commitment to proving the system’s reliability and performance. It is easy to imagine many buildings with LZC systems installed where there is not the will or the resources to resolve the issues and where, instead, the systems are turned off and forgotten. The carbon reduction performance of
LZC systems is, quite rightly, placed under the microscope. These systems should be made to justify the claims made on their behalf. Equally, it must be accepted that optimum performance is unlikely to be achieved without effort. If we are serious about closing the ‘performance gap’ we must allocate time and resources to fine- tuning during the early months and years of operation. CJ
KEITH HORSLEY is an associate at Hoare Lea
www.cibsejournal.com
Edmund Sumner
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