Gas phase air cleaning effects on ventilation energy use and indicators for energy performance

Gas-phase air cleaners can be used to either reduce occupant dissatisfaction for the same outdoor air flow rate or to reduce the outdoor air flow rate for the same resulting occupant satisfaction based on its clean air delivery rate (CADR). The latter lowers the required ventilation rate for the same indoor air quality and can thus lead to a reduction in energy use for preheating/cooling and from transporting the outside air. However, there is no current method or metric for determining the energy benefit of installing a portable air cleaner. This study aimed to establish a framework and metric for assessing air cleaner efficiency in relation to energy use. The investigated gas-phase air cleaner (GPAC) represented a stand-alone (portable) unit equipped with an active carbon filter. In order to evaluate the proposed metric human subject experiments were conducted to investigate the effect of a gas-phase air cleaner on perceived air quality. The purpose of the experiment was to determine the CADR as a function of the percentage of subjects dissatisfied. The experiments were complemented by building energy simulations which were used to estimate the annual energy use for heating, cooling, and transporting the outside air (fan energy). A CADR of approximately 50% (12 L/s) was identified when the pollution source was only represented by building emissions and a CADR of approximately 30% (9 L/s) was found when both bio-effluents and building emissions represented the pollution source. The proposed indicator, clean air efficiency (CAE), can be used to compare different solutions used for providing clean air into the space. Based on the results shown for an air handling unit (AHU) and a stand-alone GPAC for Copenhagen, Denmark - dominated by a high heating load - the GPAC was a viable solution, i.e. higher CAE, only if the AHU was not equipped with a heat exchanger. The GPAC was also more efficient if both bio-effluents and building emissions were present as pollution sources.