Post-Occupancy Monitoring

Any building is only as good as its performance; the architecture may be stunning and the technology employed may be cutting-edge but if the internal conditions for the occupants are poor, or it uses far more energy than intended, then the design has failed. To try and ensure a comfortable environment there are regulations governing temperature, CO2 levels, cold draughts and acoustics, and every new building must be modelled to prove that it will meet the relevant criteria. Likewise, there are regulations and guidelines covering energy use which all new buildings have to be shown to pass. In theory then, all new buildings should be pleasant places to live and work, with no surprising energy bills for the occupant.

Yet when studies look at the performance in use of buildings the results are not impressive. A report for the government by the BRE in 2006[1] looked at the ventilation performance of 8 schools built after 1995 and found that all of them had significant periods where the ventilation rate was less than the required 3l/s/person and on average, less than this flow rate was supplied for almost half the occupied hours. When comparisons are made between predicted and measured energy use there are sometimes discrepancies of over 100% [2] and CO2 emissions are sometimes also out by at least a factor of 2. Industry has a responsibility to address the often large differences between prediction and reality.

The only way to check if equipment and control strategies are working as intended and validate the modelling is with post-occupancy monitoring. How is the building performing when the occupants have been let loose in it, when it hasn’t been built quite to the standards assumed in the modelling? How robust is the system to reality?

From the foundation of Breathing Buildings and our earliest projects we have conducted post-occupancy monitoring to measure the performance of our systems. The data can be used to inform improvements both to the equipment and particularly to the control strategy. This is most important with a new system or strategy, where there isn’t the benefit of experience from previous installations and there may be unforeseen teething problems.

In the last year Breathing Buildings have monitored St. Raphael’s School in Uxbridge, one of the first projects with our NVHR systems installed. The data collected showed that the units were meeting the design criteria but also that there was room for improvement. Conclusions from analysis of the data were fed back to the product designers and control engineers and changes made, to the benefit of all future projects.

Another new strategy for Breathing Buildings was at Costa, Wrekin Retail Park, where our units are integrated with air conditioning and the heating system. We installed monitoring equipment in the space as soon as it became occupied in April and continue to collect data, looking for where the control strategy can be improved, both to the benefit of this and future installations.

Post-occupancy monitoring doesn’t compensate for poor modelling and design: it would be foolish to assume that an untried strategy will work perfectly first time. Collecting and analysing data in order to improve a strategy should be a natural part of the process. Only with the facts can we tackle the gap between prediction and reality so that buildings perform as intended.

Nick Wise

Consulting Engineer

References:

1. Ventilation and Indoor Air Quality in Schools – Guidance Report 202825, BRE, 2006.
2. Bridging the gap between predicted and actual energy performance in schools, Demanuele, Tweddell and Davies, 2010.