BO-2362(RP 138) -- Development of an Improved Cooling Load Calculation Method ✓ Most Recent

Whenever cooling load calculations for equipment selection have been discussed by ASHRAE members, there have been generally two major suggestions made for revisions for procedures without the use of large-memory, high-speed computers. One has been to simplify the procedure and the other has been to develop consistency of the results regardiess of the procedure used. In response to these and other requests, TC 4.1 Load Calculation Data and Procedures funded RP-138 to investigate the possibilities for an improved procedure. This paper is a report of the results. obtained and it is hoped that continued feedback as a consequence of this formal report will make possible further improvements, all of which will produce a method more and more suitable for the needs. of ASHRAE members.

The major objective of this work was to simplify the method used without the necessity of having a digital computer available. For simplicity this method will be referred to as the manual method or the total equivalent temperature difference (TETD) method. The same simplifications developed for the manual method can be put into a computer program, if desired.

The plan for this work was to study each source of cooling load starting from the "fundamental driving potential with all of the possible variables for air conditioning loads. The effect of each of the variables was then studied for its sensitivity on the ultimate result. This, therefore, permits an evaluation to be made on the possible range of difference of the cooling load when simplifying assumptions are made. The results will be presented in this manner: each load source will be shown with the assumptions made and the expected deviations. The base reference for the cooling load in each case was the transfer function (TF) method which is described in Chapter 22 of the 1972 ASHRAE HANDBOOK OF FUNDAMENTALS (1) and related articles of the bibliography(2' 10). The TF method will not be described in this report except when variations from it are used.

It was assumed that all of the heat gains computed for each component of the load was converted to cooling load. Without knowing the specific configuration and details of the building' it is not;possible. to estimate the fraction of the input which is lost to the surroundings.