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HVAC Efficiency Should Be Part Of A Broad Strategy

Today's tip from Building Operating Management comes from Daniel H. Nall of Flack + Kurtz. For facility managers interested in efficiency, the HVAC system offers a significant opportunity. But the opportunity to boost HVAC efficiency should not be addressed in isolation. To be most effective, HVAC efficiency tactics should be part of a broad strategy to reduce energy use.

The pursuit of energy efficient buildings involves the integration of multiple strategies and systems. These systems include architectural enclosure, lighting, domestic water heating, vertical transportation and HVAC.

For HVAC systems, the loads come primarily from five sources: the building envelope (heating and cooling), lighting (cooling), occupancy (cooling), equipment for programmed use (cooling) and ventilation (heating and cooling).

Ventilation load is a function of either the number of persons occupying the space or of the mechanisms necessary to control contaminant concentration and introduction to the space. In most climates of the eastern and southwestern regions of the United States, minimization of outside airflow is an effective energy conservation strategy for some portion of the year, when the outside air is either warm and humid or very cold. Control of ventilation rate determined by occupancy, referred to as demand-control ventilation, is a common energy conservation strategy, especially for spaces with intermittent dense occupancy. Conventional practice would require continuous provision of the maximum calculated ventilation rate, allowing the peak occupancy to be averaged over several hours. Demand-control ventilation would provide the exact flow rate required for actual occupancy at a point, but would allow ventilation to be reduced to a minimum when the space is "in use," but unoccupied. Procedures for implementing demand-control ventilation are described in detail in ASHRAE Standard 62.1, the ventilation standard for acceptable indoor air quality.

With heating and cooling loads reduced to a minimum, utilizing a high-performance building envelope, high-performance lighting with daylight-responsive lighting controls and occupancy sensors, Energy Star office equipment and demand-controlled ventilation, the energy efficiency of the HVAC systems themselves can be addressed.


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