Rooftop cooling and heating unit efficiencies are based on direct expansion air conditioning and furnace efficiencies. For added efficiency, install enthalpy-based economizers, heat recovery units-such as enthalpy wheels, or air-to-air heat exchangers. Occupancy control, dual-speed compressors, and NEMA Premium^TM ventilation fan motors will also increase efficiency. As another option, "demand-controlled ventilation" uses a carbon dioxide sensor to determine the occupancy of the conditioned space so that outlet dampers, inlet vanes, or variable speed drives can be used to reduce the amount of ventilation air provided to the space.

Direct expansion evaporator coils are incorporated into forced-air systems that can supply a mix of outdoor air and "return" air. These systems typically use furnaces to provide heating. Efficiency is measured in Energy Efficiency Ratio (EER) or Seasonal Energy Efficiency Ratio (SEER). Baseline systems often have a SEER of 10. High-efficiency units, available with SEERs of 16 and above, typically include higher efficiency compressors (i.e. scroll compressors) and condensing and evaporating fans, and increase the surface area of the condensing unit. Variable speed compressors and fans, as well as NEMA Premium^TM motors, also increase efficiencies.

Packaged Terminal AC (PTAC) cooling efficiencies are based on direct expansion air conditioning, but are typically limited to a Seasonal Energy Efficiency Ratio (SEER) of 12. Heating efficiencies rely on electrical resistance, heat pump, boiler, or furnace efficiencies. Heat pump PTACs are more efficient than electric resistance PTACs, but boiler or furnace PTACs will be less expensive to operate. Occupancy control can be used to reduce demand, either centrally or within each room.

Heat Pumps are typically incorporated into forced-air systems that supply a mix of outdoor air and "return" air. Baseline systems have a Seasonal Energy Efficiency Ratio (SEER) of 10 and a coefficient of performance of 2.5. Efficiency measures include high-efficiency units with SEERs of up to 18 (on water-based systems) with a COP of 4. Air-based systems can attain SEERs of up to 12.5 and COPs of 4. Water-based systems can employ variable speed circulation of condenser water, earth-coupled heat exchangers, and high efficiency boilers. Additional efficiencies can be obtained through the use of variable speed control of ventilation fans and NEMA Premium^TM fan motors.

Window unit efficiency is measured in Energy Efficiency Ratio (EER) or Seasonal Energy Efficiency Ratio (SEER). Baseline systems often have a SEER of 10. High-efficiency units are available with SEERs of 12 and above. Most high efficiency window air conditioners are ENERGY STAR qualified. To reduce building heat loss during the winter months, cover or remove the window unit.

To provide cooling, chilled water loops are installed in a coil and a mixture of outdoor and "return" air is blown across. (This system can also use hot water coils (from boilers) to provide heating.) The primary energy user in a chilled water system is the chiller's compressor bank. Baseline systems are often reciprocating compressors-while scroll, screw, or centrifugal compressors offer higher efficiency options, depending upon the size and application. You can also improve the efficiency of chilled water production by reducing condenser water temperature, raising chilled water temperature, varying chilled water flow and condenser fan speed, and installing water-side economizers on the cooling tower systems. Increased efficiencies can be obtained by using variable speed control on chilled water pumps and ventilation fans, and the use of NEMA Premium^TM fan motors.

Heating and cooling efficiencies are based upon boiler, chilled water, and direct expansion equipment efficiencies. The efficiency of the unit itself can be improved by installing a permanent-split capacitor fan motor (for single-phase power applications) or NEMA Premium^TM motors for higher horsepower and three-phase power applications. Occupancy sensors and/or programmable thermostats can be used to control fan operation.

Heating and cooling efficiencies are based upon either boiler or furnace and chilled water or direct expansion equipment efficiencies. Other efficiency measures include NEMA Premium^TM motors and variable frequency drives for fans, demand-controlled ventilation using carbon dioxide sensors, dual-enthalpy economizers, deck temperature reset controls, heat recovery units-such as enthalpy wheels or air-to-air heat exchangers and optimum start-stop strategies.

See central station air handling units for basic efficiency components and strategies. Additional measures include replacing inlet guide vane control with variable frequency drives and static pressure reset control with a direct digital control (DDC) system.

Furnaces are incorporated into forced-air systems that can supply a mix of outdoor air and "return" air. These systems can also use condensing units and evaporator coils to provide cooling. Efficiencies are measured by the Annual Fuel Utilization Efficiency (AFUE), with baseline furnace efficiencies of oil and gas (natural and propane) units typically around 80%. With high efficiency systems, this rises to 87% (oil) and 98% (gas). Energy efficiency measures in furnace systems include variable speed control of ventilation fans (tied to temperature, pressure, or carbon dioxide sensor output) and NEMA Premium^TM fan motors.

Boilers can be integrated into a range of systems, from radiant slab to hot water baseboard to ventilation fans blowing across hot water coils. Like furnaces, Annual Fuel Utilization Efficiencies (AFUEs) range from 80% to 87% for oil systems and from 80% to 98% for gas (natural and propane) systems. To attain efficiencies greater than 90%, you must use condensing gas boilers. Additional efficiency options include "low mass" (low water content) boilers, increased boiler insulation, control options to reset boiler water temperature based upon outdoor air temperatures, and variable speed control of the circulating pump operation and/or the ventilation fan operation. In all cases, NEMA Premium^TM motors improve overall system efficiencies.