The indoor air quality of an actual variable air volume (VA V) heating, ventilation and air conditioning (HV AC) system in a building on the campus of the University of Missouri, Rolla has been analyzed, modified, and monitored. Components measured include temperature, relative humidity, C02, volatile organic matter (VOM), particulates, outside air flow rate, and building pressure. In addition to these parameters, the building is studied in normal operation, and for operation when the economizer damper was controlled to maintain minimum outside air.
Variable-air-volume systems utilize some of the latest technology available to control zone temperatures and save fan energy. In fact, the energy savings can be quite substantial. Then why do engineers and building managers have reservations about using this type of system? Probably the memory of past experiences. The chain of design, equipment selection, installation, and air balancing must be tailored to a building’s needs or conflicts will arise. There are many disciplines to consider when creating a VAV system, and if one link is weak, there can be trouble.
A field study investigated outside air delivery and thermal comfort in a normally operating variable-air-volume (VA V) system. In addition to finding that outside air delivery and thermal comfort are generally acceptable under a variety of operating conditions, a number of practical diagnostic techniques were used to more fully understand VA V system operation and design. It was concluded that unless a VAV system is well understood or continuously monitored, the likelihood of unexpected system behavior that can impact the outside air delivery and thermal comfort is high.
Modelling techniques were used to verify the success of a "minimal duct" ventilation system proposed for an underground carpark in a prestigious project in Singapore. The procedure to determine the various model scaling parameters, to select the appropriate fans to model the supply and exhaust fans, as well as the "dilution fans"; and to simulate the movement of air through the vehicle access ramps are presented. Measurements from the model were found to be reasonable when compared with results from numerical simulation. However, certain modifications were needed to improve the system.
Poor air quality in office buildings can result in loss of productivity, absenteeism and, in some cases, medical problems. The purpose of this Update is to provide guidelines for property managers and engineers for controlling indoor air quality using building ventilation systems.
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