The flexibility in power consumption of heating, ventilation, and air-conditioning (HVAC) systems in buildings can be utilized to provide a battery-like service to the power grid. Recent work has reported that using HVAC systems in such a manner may lead to a net increase in energy consumption compared to normal operation, similar to a low round-trip efficiency (RTE) of a battery. In our previous work we showed that the low RTEs reported were due to the way the experiments/simulations were performed, and that using an HVAC system as a virtual battery repeatedly leads to an asymptotic RTE of one. In this work we show that when an additional constraint is imposed—that the mean temperature of the building must remain at its baseline value—the asymptotic RTE can be lower than one. We numerically investigate dependence on parameters such as building size and time period of charging/discharging.
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