Commercial water-cooled central air conditioners (CACs) and heat pumps (HPs) reject heat to water. Evaporatively-cooled CACs and HPs spray water on the condenser to help remove heat from the condenser coils using the latent heat of evaporation. Commercial CACs and HPs can either be “single package” systems, where the evaporator coil and the condensing unit are combined into a single physical unit, or “split systems,” where the condensing unit is typically placed outdoors while the evaporator is indoors.
ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) Standard 90.1 is a commercial building energy code which all states must meet or exceed. ASHRAE Standard 90.1 includes minimum efficiency requirements for equipment, including commercial water- and evaporatively-cooled CACs and HPs. The Energy Policy and Conservation Act (EPCA) requires that if the equipment efficiency standards in ASHRAE Standard 90.1 are amended, DOE must either establish amended standards for the products at the levels specified in ASHRAE 90.1 or establish more stringent standards if they would result in significant additional energy savings and are technologically feasible and economically justified. Before 2011, national standards covered water- and evaporatively-cooled CACs and HPs with capacities up to 240,000 Btu/hr. In July 2009, DOE published a final rule establishing the first national standards for water- and evaporatively-cooled CACs and HPs with cooling capacities between 240,000 Btu/hr and 760,000 Btu/hr, which went into effect in January 2011. These national standards are equivalent to the standards in the 2007 version of ASHRAE 90.1. The 2010 version of ASHRAE 90.1, which was published in November 2010, raised the EER levels for commercial water- and evaporatively-cooled CACs and HPs. In 2012, DOE updated the standards to align with ASHRAE 90.1-2010.
The cooling efficiency of commercial water- and evaporatively-cooled CACs and HPs is measured by the energy efficiency ratio (EER), which is the cooling capacity (in Btu/hr) divided by the power input (in watts). The heating efficiency of HPs is measured by the coefficient of performance (COP), which is the heat delivered (in Btu) divided by the energy input (in Btu). The efficiency standards for commercial water- and evaporatively-cooled CACs and HPs vary by cooling capacity (in Btu/hr). Cooling capacity represents the amount of heat that an air conditioner or heat pump can remove from an enclosed space per hour.
Water- and evaporatively-cooled CACs and HPs are generally more efficient than air-cooled equipment. Water-cooled air conditioners can be used effectively in any type of environment, while evaporatively-cooled air conditioners are most effective in hot-dry climate regions.