PO-86-01-3 -- Control of Supply Air Temperature and Outdoor Airflow and Its Effect on Energy Use in Variable Air Volume System ✓ Most Recent

A VAV system in a commercial office building in central New Jersey has been modeled, with DOE-2 and a variable-base bin method, to assess control strategies that lead to reduced HVAC costs with no decrease in comfort. The goal is to minimize the sum of fan and heating/cooling power while providing sufficient air to maintain desired office temperatures and air quality. With the 55 F (12.8 °C) supply air temperature specified by the HVAC designer, fan energy is kept low at the expense of the chillers. Raising the supply air temperature to 60 F (15.6 °C) makes more use of outdoor air in temperate weather and reduces the chiller energy consumption by a predicted 33 MWh/year while increasing fan power by only 4 MWh, for a net savings in combined fan and chiller power of 13%. An additional 9 MWh of net fan and chiller energy savings can be achieved by varying the supply air temperature with outdoor temperature. In winter, increasing the supply air temperature to 60 F (15.6 °C) reduces the need for terminal reheat and saves a predicted 22 MWh/year with fan energy increasing only 1 MWh, for a 10% net savings. Several supply air reset strategies yield nearly identical savings, with further reductions in heating matched by increases in fan energy.

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