SE-99-01-4 (RP-1055) -- Experimental Results for Heat Gain and Radiant/Convective Split from Equipment in Buildings ✓ Most Recent

Measurement of the heat loss from equipment in buildings is necessary in order to make accurate assessments of its impact on cooling loads. Recent 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, laboratory, and hospital equipment to buildings has become a major source of internal cooling load. Unfortunately, accurate information on the total heat gain from equipment is lacking in current handbooks. Some equipment includes a nameplate rating showing total power consumption, while other equipment does not have this. Some manufacturers measure maximum electric power consumption by the equipment and list that as power ratings on the nameplate or in the equipment literature, while some others list the maximum power capacity of the system. Since the manufacturers' power ratings, if reported, are usually based on instantaneous measurement while 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 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 load 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 proper sizing of airconditioning equipment. This article presents experimental results for the total heat gain and radiant/convective split from equipment in offices, hospitals, and laboratories. The nameplate vs. measured values, peak vs. average values, operational vs. idle values, and radiant vs. convective values are compared and discussed. Furthermore, a brief guideline for use of the experimental results by practicing engineers for estimating equipment cooling load is presented.

Units: Dual