ABSTRACT
Post occupancy evaluation (POE) helps us complete the feedback loop in our design, as it gives us comprehensive information about the design and on lessons learnt for future designs. POE can take several forms as follows:
• One-off tests • co-heating • air tightness testing • thermal imaging • observation of building envelope
• Instrumental monitoring • Experimental measurement of physical parameters of buildings • Energy performance analysis • Troubleshooting of building operation and performance • Calibration of dynamic simulation models • Occupant comfort and behaviour studies
ONE-OFF TESTS
Co-heating tests Co-heating tests are designed to measure the overall conductive and ventilation heat loss. They are carried out in unoccupied buildings in which a sufficient temperature difference between the inside and the outside is maintained with thermostat controlled portable electric heaters over a period of between one to three weeks (Figure 201). As the building enters into a steady state after a few days of heating, the overall fabric and ventilation heat loss becomes proportional to the heat loss coefficient and inversely proportional to the temperature difference. The heat loss coefficient is calculated by rearranging the heat loss equation:
Q = UA × ∆T (51)
and solving it for UA as follows:
UA = Q
∆T (52)
where:
UA – overall heat loss coefficient (W/K) Q – heat input (W) ΔT – temperature difference between inside and outside (K)
The co-heating test needs to be carried out in winter when a sufficient temperature difference between inside and outside of minimum 10 degrees can be maintained. Fluctuation of external temperature and solar radiation can make the results of the co-heating test unusable. The co-heating test is therefore best conducted during overcast weather conditions with relatively stable outside temperature. In order to minimise fluctuations of temperature differences, the results of co-heating tests are analysed using daily average values of heat input Q and temperature difference ΔT. When the former is plotted against the latter and a regression line fitted to the plotted points, the slope of the line will represent the heat loss coefficient UA (Figure 202). In this particular case related to the building in Figure 212, and unrelated to the specific test in Figure 201, the slope of the line and therefore the overall heat loss coefficient is UA = 249.6 W/K.
