RICHLAND, Wash. — Packaged air conditioners and heat pumps serve over 60 percent of the commercial building floor space in the nation, contributing to about 230 trillion Btu of energy consumption annually, according to the Pacific Northwest National Laboratory (PNNL). Therefore, even a small increase in operational efficiency of these units can lead to significant reductions in energy use. PNNL, with funding from the U.S. Department of Energy’s (DOE’s) Building Technologies Program, announced that it has evaluated a number of control strategies that can be implemented in a controller, which can be retrofitted into an existing unit, to substantially improve the operational efficiency of packaged equipment.

The results from detailed simulation analysis show significant energy (24 percent to 35 percent) and cost savings (38 percent) from fan, cooling and heating energy consumption when packaged units are retrofitted with advanced control packages. The major findings include:

• Retrofitting packaged HVAC units with the most energy-efficient package controls option considered (integrated differential enthalpy economizer, multi-speed supply fan, two-stage capacity control, and demand-controlled ventilation [DCV]) relative to a base case with no economizer and a constant speed supply fan, results in average HVAC energy savings (electricity for cooling and fan and gas for heating) across 16 locations in 15 climate zones of about 35 percent for three building types (small office, stand-alone retail, strip mall) and 24 percent for supermarkets.

• For the most energy efficient controls package considered, average HVAC cost savings are 46 percent, 43 percent, 35 percent, and 24 percent, respectively, for the small office, retail, strip mall, and supermarket buildings.

• Retrofitting packaged HVAC units with a modified (less aggressive) energy efficient controls package option (integrated differential dry-bulb economizer, multi-speed supply fan, single-stage capacity control and DCV) relative to modified base case with integrated differential dry-bulb economizer, constant speed supply fan and single-stage capacity control, results in average HVAC energy savings of about 28 percent for the small office building, 32 percent for the stand-alone retail and strip mall buildings, and 24 percent for the supermarket.

• For the modified packaged control option, average HVAC energy cost savings are 38 percent for all four building types.

• The maximum controller cost that will provide payback periods of no more than three years for all U.S. locations under current utility rates are $2,103 per controller for stand-alone retail, strip mall, and supermarket buildings and between $540 and $1,350 for small office buildings. The precise value depends on the number of square feet of floor space per controller (1,100 and 2,750 square feet, respectively, for the small office building costs given).

• Individual control strategies have different degrees of impact on energy and cost savings. The simulation results indicate that multi-speed fan control and DCV are the two control strategies contributing most of the savings. In many cases, multi-speed fan control dominates the impact in hot and mild climates (e.g., Miami and Los Angeles), while DCV dominates the impact in climates with significant heating and cooling loads (e.g., Baltimore) and cold climates (e.g., Seattle, Chicago, and Duluth).

PNNL noted that even if one-half of packaged HVAC units are retrofitted with the modified control package option, it will result in annual savings of approximately 55 trillion Btu (assuming the percent savings are 30 percent).

Publication date: 04/30/2012