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.

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.

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.

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.