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Increased building indoor air quality (IAQ) complaints due to reduced outdoor air ventilation rates led to ASHRAE Standard 62-1989. Even though the stipulated total outdoor ventilation flow rate may be drawn into the HV AC system, thermal imbalances in the various zones of the building can lead to certain zones being starved of the specified ventilation flow rate thereby creating localized IAQ problems. The objective of this paper is to compare the energy and IAQ implications of different practical outdoor air ventilation strategies all of which are identical in performance at design conditions but which differ under part-load operation. A simulation methodology and a computer program have been developed to predict the heating and cooling energy use of a two-zone terminal reheat variable air volume (TR VA V) system during partload operation specified by varying outdoor temperature and humidity conditions.
The trade-off between IAQ and energy use are studied for the following ventilation strategies for a typical 10,000 m2 commercial building: (i) constant outside air intake based on a value 20% higher than the ASHRAE minimum ventilation rate, (ii) constant ventilation air intake fraction, and (iii) ventilation air intake based on the unfavorable zone requirements (even though the other zone may be over-ventilated). Another issue which has been investigated is the manner in which the size of the building affects energy use and IAQ. Finally, we use bin data for Dallas, TX (a moderately hot and humid location) and Seattle, WA (a mild location) in order to determine the energy and IAQ implications of different ventilation strategies on building location. The effect of economizer cycles and of varying ventilation strategies depending upon diurnal building schedules have not been considered in this study. The results of this study will provide energy managers and HVAC designers insights into how to better operate/design TRVA V systems that will satisfy IAQ criteria while minimizing energy use.