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Today's tip from Building Operating Management comes from Daniel H. Nall of Flack + Kurtz. Facility managers looking for opportunities to reduce HVAC energy use should focus on airside and water side economizer strategies.
The first step to reducing HVAC energy consumption should be to make use of available environmental resources to help meet heating and cooling loads. These resources might include the outside air during portions of the year in many climates.
In the northeast, north central and in much of the west coast of the United States, the ambient outside air often has a lower enthalpy than does the interior room air. In such conditions, air returned from the occupied space can be dumped in preference for the lower enthalpy outside air, reducing the energy required to cool the supply air to the conditions necessary to maintain room temperature and humidity setpoints. This strategy is called airside economizer.
In buildings without sufficient architectural access to outside air, cooling towers can be used to make cold water when exterior conditions permit, providing chilled water without the energy penalty of refrigeration compressors. This process is called waterside economizer. Other resources that can be used to offset heating and cooling in the building can come from the building itself. Heat and moisture recovery from exhaust air can be used to temper incoming outside air, reducing the amount of energy required for heating when that outside air is very cold or cooling when that outside air is very hot or humid. Heat recovery can be a very effective strategy when high ventilation or exhaust rates are required, either because of occupancy or contaminant control.