Methods for Testing and Rating the Performance of Heating and Air Conditioning Systems

EPCA required NBS to develop test procedures for each product for the determination of estimated annual operating cost and at least one other useful measure of energy consumption likely to assist consumers in making purchasing decisions. An additional requirement of the law was that “any test procedures prescribed be reasonably designed to produce test results which reflect energy efficiency, energy use, or estimated annual operating cost during a representative average use cycle and not be unduly burdensome to conduct.” Beginning in 1975, NBS staff reviewed the test procedures already in use within the appliance and heating and cooling industry. By the early 1980s, test procedures were in place for all covered products. Throughout the development, NBS staff worked closely with industry representatives experienced in testing the equipment to obtain their review and recommendations, particularly on energy conservation innovations that were being considered for future products. This review found many test procedures that could be used with minor modifications and recommended them for adoption. The industry procedures that required little change were primarily for “white” appliances, those used for cooking, cleaning, refrigerating food, etc. For them, the performance and annual cost of operation were primarily dependent on the use schedule. Therefore, NBS adopted steady-state tests plus a calculation procedure assuming a specific daily operating schedule. In the case of residential heating and cooling systems, however, entirely new procedures had to be developed, as described in these publications [1,2]. At the time, steady-state tests were used in the industry for central heating and cooling equipment. However, the equipment cycled on and off frequently throughout most days. During the start-up and shut-down periods, most of the equipment experienced non-trivial energy losses or inefficiencies associated with warm-up, cool-down, and/or migration of refrigerant. In addition, the performance of this equipment was almost independent of the user (except for thermostat setting) and primarily dependent on the weather conditions. As a result, NBS staff developed new procedures for this type of equipment that included steady-state and cycling tests coupled with a calculation procedure that accounted for the changing weather conditions throughout the heating and cooling seasons. Kelly and Chi published the initial procedure for central furnaces and boilers in 1978 [1]. The testing required was simple, but the estimation of yearly performance was done through an elaborate calculation procedure. They found that the performance of furnaces and boilers under part-load, on-off operation could be described by a simple “time-constant” model, and that data required to determine the time-constant could be obtained during “warm-up” and “cool-down” periods before and after a steady-state test without extensive cycling tests. Based on the test data, five major loss terms were calculated and subtracted from 100 to obtain the value of the seasonal efficiency.