Residential air conditioning, thermal comfort and peak electricity demand management

About one in every two Australian households owns at least one air conditioner (AC) and that ratio is increasing rapidly due to the availability of low cost AC imports combined with electricity that is grossly underpriced. Rapid growth in residential AC ownership threatens to undermine national energy efficiency and greenhouse reduction targets. Furthermore residential AC is placing a strain on the national electricity system, especially during heat waves when electricity demand peaks. These AC-driven peak loads occur just occasionally each summer, and so increasing grid capacity to meet them represents a grossly inefficient use of capital. For example, at present 10% of New South Wales' generating capacity is needed for just 1 per cent of the time (less than 100 hours a year), and if residential AC penetration increases as expected, this will rise to 20% of generating capacity for use just 1% of the time by 2014. The alternative to continually expanding grid capacity to supply an ever increasing residential AC peak demand is to focus on managing that demand. The Demand Response (DR) approach can be defined as a change in an electrical product's normal mode of operation in response to an initiating signal originating from a remote agent, usually with the objective of reducing the product's power demand at times of peak load. Two broad demand response strategies have emerged to date. The first is based on real-time pricing for electricity. During heat waves the kW cost is increased to a level that is supposed to dissuade enough householders from switching on their AC units that aggregate peak load is kept within manageable limits. This approach relies on a clear price signal (Variable Pricing Regime - VPR), possibly orders of magnitude higher at peak demand times, to influence behaviour, but it lacks the certainty or firmness of response necessary for effective network management. The alternative DR strategy sees the utility company directly cycling off-and-on for short periods the individual householders' AC compressor during critical peak demand periods (Direct Load Control - DLC). This deprives householders of total control of their AC unit at the very same time they want it most, and so it requires a financial incentive for householders to consider participating. Because the utility is in control of the load shedding, firmness of response is assured. Both CPP and DLC approaches reduce to thermal comfort problems. The first finds out how much people are prepared to pay to shift their thermal sensation down a notch-or-two on the seven-point rating scale during heat-wave episodes. The second approach requires the utility to estimate how long the householder's AC compressor can be switched off before the house heats up to uncomfortable and unacceptable levels. This paper discusses various technical, economic, cultural and ethical issues relating to these emerging Demand Response thermal comfort questions.