PhD Thesis - Energy Systems Research Unit - University of Strathclyde

The second aspect is that the internal heat gains emitted can be considered to be afactor of the electrical power demand of the appliance. It is important to note that theaverage power demand is different from the nameplate value found on mostappliances, as the latter can only be considered as an upper bound to the actual powerdemand [57]. The electrical power demand in this case refers to the measuredelectrical demand. Given that typically all electrical consumption is eventuallydegraded to heat, this measured demand is therefore the same as the total heatemission (both sensible and latent) from the appliance. This also implies thatimprovements in energy-efficiency will correspond to changes in both the electricaldemand and the heat gains emitted by a particular appliance.In real life the difference in internal heat gains emitted due to technology changes formost household appliances is too small to be actually perceived and the main thermalloads will remain the heat loss or gain due to the heat transfer through the buildingfabric and ventilation [11]. Brunner et al. in [61] provide evidence, using natural gasbilling data, that a changeover from incandescent bulbs to CFL did not result in ahigher consumption of natural gas for use as space heating fuel, suggesting that thetwo are not correlated. In future zero or very low energy buildings this changeover intechnology may result in a situation where the internal conditions are much moresensitive and a change in heat gain emitted is actually perceivable. In the context ofthis thesis however, preliminary simulations showed that the change in internal heatgains due to the appliance energy-efficiency improvements assumed had such a smalleffect on the internal conditions of the building, it could be neglected.2.5.3.2 Non-electrical appliancesThe final part of the methodology concerns the modelling of heat gains which areemitted from non-electrical appliances. In a household typically these are limitedmainly to cooking gas hobs [11]. This is an important heat emitting activity whichcannot be associated with any electrical demand. In order to model such an event,research done by Stokes in [27] is used. Stokes in [27] reports on work done byMansouri et al. [62] on energy consumption in UK households whereby, based on75