Measurement of the heat loss from equipment in buildings is necessary in order to make accurate assessments of its impact on cooling loads. Advances in the design of buildings and improvement of the thermal characteristics of insulation materials and building envelope systems have significantly reduced the cooling load from external sources; however, the addition of various types of office equipment to buildings has become a major source of internal cooling load. Some equipment includes a nameplate rating showing total power consumption, while other equipment does not. Some manufacturers measure the equipment's maximum electric power consumption and list that as a power rating on the nameplate or in the equipment literature, while others list the equipment's maximum power capacity. Since the manufacturers' power ratings, if reported, are usually based on instantaneous measurement while the equipment is working at maximum capacity, use of equipment nameplate values for cooling load calculations may lead to oversizing of air-conditioning equipment, resulting in an extra initial cost as well as higher operating costs. On the other hand, underestimating the cooling load may result in insufficient cooling capacity. Another factor affecting calculation of cooling load is the split between the radiant and convective heat loads from the equipment. The convection portion of the heat transferred from the equipment to the surroundings is an instantaneous load, since it is added to room air by natural or forced convection without time delay, whereas the radiation portion is absorbed by the surfaces of the room and then dissipated over time. Accurate determination of cooling load is important in gauging the proper size of airconditioning equipment.

This article presents experimental results for the total heat gain and radiant/convective split from a sampling of the different types of equipment used in offices. The nameplate vs. measured values, operational vs. idle values, and radiant vs. convective values are compared and discussed.