It is the essence of efficiency. But wait, there's more – through the use of controls, we add concepts of temperature anticipation, load shedding, ramping and coasting, and space zoning. With systems, we add in motor efficiency, static pressure efficiency, voltage frequency modulation, and zero leakage. Cool stuff.
Reducing heating and cooling loads is the first step in maximizing HVAC system energy performance. For example, more efficient lighting systems and office equipment, as well as better window and roof systems, can significantly reduce cooling loads. By carefully managing building loads, you can reduce the size and cost of the HVAC equipment. In addition, a more appropriately sized system HVAC system will provide improved thermal comfort and may achieve better ventilation. High-performance HVAC systems require commitment from the building owner and careful coordination of those involved in system design, specification, installation, and operation and maintenance. Facility managers need to appreciate the entire process. Increased attention to design at the outset of a project can result in systems that cost less to install and less to operate, and a regular maintenance routine can facilitate high performance throughout the life of the equipment.
A wide range of efficiencies is available in packaged equipment, chillers, boilers, and furnaces. In most cases, however, there are legal minimum energy efficiency standards. For example, the National Appliance Energy Conservation Act (NAECA) and the Energy Policy Act (EPAct) established minimum-efficiency standards for furnaces, boilers, and packaged equipment to which manufacturers must comply. In general, NAECA applies to smaller equipment and EPAct governs larger equipment. Many of the EPAct standards are based on those developed for the American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) Standard 90.1. The ASHRAE standard also includes efficiency requirements for many types of equipment not covered by EPAct, such as chillers. This standard has been adopted as the commercial building energy code in many states and localities.
Again, equipment efficiency must be considered in the context of the whole HVAC system. In a chilled-water system, for example, although the chiller is at the core of the system and typically is the single largest energy user, simply selecting a high-efficiency chiller does not guarantee high performance. Auxiliary equipment (such as fans and blowers) and design decisions (such as “approach temperatures”) can have substantial effects on efficiency. Thus, attention to overall system design and auxiliary components is critical to achieving optimal performance and comfort. In packaged air-conditioning systems, leaky ductwork, improper sizing, refrigerant charge, and air flow rates can considerably affect energy performance.
Finally, remember the importance of the economizer for “free” cooling-cooling by circulating outdoor air when conditions allow. The value of the economizer varies with climate, being greater where there are larger daily temperature swings and generally cooler temperatures. Where humidity at moderate temperatures may be very high (e.g., the Southeast), “enthalpy” controls prevent the introduction of relatively cool but humid air that will make the indoors uncomfortable.