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Facilities with high occupancy rates or elevated levels of indoor contaminants, such as schools, hospitals, nursing homes, and many offices, require large amounts of outdoor air. This presents a significant HVAC design challenge. This challenge is further exacerbated in hot and humid climates, due to the high humidity levels and large number of partial-load cooling hours. Maintaining relative humidities at levels recommended by the ASHRAE Standard 62 is difficult and costly if conventional HVAC approaches are used for such facilities.
Conventional packaged equipment is designed to accommodate approximately 15 to 20% outdoor air on an intermittent basis. If the equipment is applied to provide higher outdoor air quantities on a continuous basis, as called for by ASHRAE Standard 62, unacceptably high space humidities can result for extended periods of time.
At part load conditions, e.g., on days when the temperature is moderate but the humidity is high, a packaged HVAC unit will quickly bring the space to the desired set point temperature, then cycle off. Generally, no outdoor air is brought into a conditioned space as long as the thermostat does not call for cooling. Since there is no humidity control exercised, the indoor humidity increases until the sensible load in the space causes the thermostat to call for cooling. By this time, the mixed air condition supplied to the coil is elevated in humidity. This results in a high dew point temperature leaving the cooling coil.
The space temperature is maintained but humidity control is lost, resulting in elevated space humidity conditions, which promote microbial growth and other moisture related IAQ problems.
Given that all of the major building codes now require compliance with ASHRAE Standard 62, that data supporting the need for improved humidity control is available, and 80-90% of all HVAC sold in the U.S. each year are conventional packaged units, effective solutions that will allow packaged equipment to accommodate more outdoor air on a continuous basis are needed. The solution is the Pinnacle® Primary Ventilation System.