Source: Consortium for Energy Efficiency. 2002. "CEE High-Efficiency Commercial Air Conditioning and Heat Pump Initiative (HECAC)," p. 1. Boston, Mass.: Consortium for Energy Efficiency.

The table below gives recommendations from the same sources for unitary and applied heat pumps.

Recommended Efficiency Values for Unitary and Applied Heat Pumps
Equipment Type	Size Category	Sub-Category or Rating Condition	Required Efficiency
Air Cooled (Cooling Mode)	< 65,000 Btuh	Split System	13.0 SEER
		Single Package	13.0 SEER
	> 65,000 Btuh and < 135,000 Btuh	Split System and Single Package	11.0 EER 11.4 IPLV
	> 135,000 Btuh and <240,000 Btuh	Split System and Single Package	10.8 EER 11.2 IPLV
	> 240,000 Btuh	Split System and Single Package	10.0 EER 10.4 IPLV
Air Cooled (Heating Mode)	< 65,000 Btuh (Cooling Capacity)	Split System	8.0 HSPF
		Single Package	7.7 HSPF
	> 65,000 Btuh and < 135,000 Btuh (Cooling Capacity)	47oF db/43oF wb Outdoor Air	3.4 COP
		17oF db/15oF wb Outdoor Air	2.4 COP
	*135,000 Btuh (Cooling Capacity)	47oF db/43oF wb Outdoor Air	3.3 COP
		17oF db/15oF wb Outdoor Air	2.2 COP
Water Source (Cooling Mode)	< 135,000 Btuh (Cooling Capacity)	85oF Entering Water	14.0 EER
Water-Source (Heating Mode)	< 135,000 Btuh (Cooling Capacity)	70oF Entering Water	4.6 COP

Almost all commercial unitary equipment is air-cooled, but the exception, water-cooled heat pump systems, can even serve large multi-zone buildings. Small, packaged water-cooled air conditioners/heat pumps provide an easy way to get multiple temperature control zones in minimum space. Because most designs put all of the heat pumps on a single water "loop," these systems can efficiently serve where some zones require heating while others need cooling. Such cases are very common and include heat needed on the northern side while the southern exposure requires cooling or simultaneous core cooling and perimeter heating. The heat that some heat pumps reject in cooling mode is carried automatically to those needing to heat their zones. Ultimately, when the building is either predominantly in cooling or in heating mode, the water "loop" will drift out of pre-set temperature bounds, and heat pump efficiency will drop. To maintain loop temperature when the building wants more heat, a central boiler can be provided. When additional loop cooling is required, a cooling tower is employed (the chiller of customary central systems is replaced by the compressors of the heat pumps). Alternatively, ground water or a ground source heat exchanger can be used to support more constant loop temperature.

The primary disadvantage of this approach is that separate arrangements are required to meet ventilation requirements (see section on Ventilation Air and Energy Efficiency). These arrangements are often a supplemental duct system or a "dedicated outdoor air system" that brings in and exhausts conditioned air. These systems have limited or no ability to work as economizers. Instead, a "water-side" economizer can be employed, using a cooling tower to cool the loop temperature. The cooler the temperature, the more efficiently the heat pumps work in cooling mode. This allows overnight pre-cooling, for example.

Heating with Unitary Equipment

As suggested in the section on cooling with packaged systems, unitary equipment offers several options for heating. A gas or oil furnace is commonly integrated into the smaller, single-zone, constant volume, roof-top unit, making it a "year-round." When the thermostat calls for heat, the furnace is activated.

Packaged units are also available with electric heat. It is almost always cost-effective to use a heat pump as a first stage of heat and electric resistance as the second stage or back-up source. Before selecting electric heat, check your local utility rates. In most areas of the United States, electricity for heating costs two to three times more than natural gas. With typical gas and electric rates, heat pumps cost roughly the same as natural gas furnaces to operate. However, heat pumps do not function well at very low outdoor temperatures; therefore, in cold climates (e.g., New England & other Northern states), consider another source of heat.

Alternatively, most packaged units are also available with either hot water or steam coils as a source of heat. Roof-mounted coils and piping are subject to freezing and therefore not recommended. Some heating systems will locate hot water or electric coils in the ductwork downstream of the packaged unit. In other cases, heating is supplied by baseboard radiation. In these cases, the packaged air conditioning unit may not require any heat at all. If the minimum quantity of outdoor air for ventilation is low (usually 25 percent of the supply or less), no heat in the unit is required. Units that serve strictly interior zones also may not need a heating coil unless the ventilation load is high.

For smaller commercial buildings (such as apartment buildings and wings of schools), the use of "trains" of residential boilers is common, particularly when the boiler system provides service hot water by employing an indirect water heater. Residential-size units, up to 225,000 Btuh, are relatively inexpensive since they are made in relatively large quantities. For low-load conditions, if the "lead" boiler is a condensing unit, very high efficiencies are feasible. "Follower" units, dispatched in sequence as the load rises, need not be condensing units-if an appropriate control system is used. Such controls should always include an "outdoor reset" that reduces the output temperature when conditions outside are mild. Even though this increases circulating pump energy modestly, it improves overall efficiency.

Energy Efficiency of Packaged Equipment

In the cooling mode, packaged air conditioning and heat pump equipment is rated by its energy efficiency ratio (EER). This is the net cooling capacity (Btuh) divided by the electricity consumed (watts) at peak operating conditions. Another important measure of the cooling efficiency of this equipment is the integrated part-load value (IPLV), which is a single number based on the weighted average of EER for operation at various load levels. Manufacturers rate smaller equipment (less than 65,000 Btuh) on the basis of seasonal energy efficiency ratio (SEER), which is similar to EER except the rating takes into account the range of conditions during the cooling season. For these small units, the difference between listed "commercial" and "residential" units is that the former use three-phase equipment instead of single-phase.

In the heating mode, the rating depends on the type of heating equipment used. Small furnaces must be rated according to annual fuel utilization efficiency (AFUE) while larger furnaces are rated by either thermal efficiency or combustion efficiency (see section on Central Heating Plants: Boilers and Furnaces). Small packaged heat pumps must be rated according to heating season performance factor (HSPF) while larger heat pumps and hydronic systems are often compared by their coefficient of performance (COP, watts/watt), the ratio of their performance at high and low outside air (or entering water) temperatures. The higher the EER, IPLV, SEER, HSPF, or COP, the more energy efficient the equipment.