A properly designed air conditioning system, whether for residential or commercial application, must provide occupant comfort at minimal cost under a broad range of operating conditions. The interactions between a building, its occupants, heating-cooling and controls system, and the external environment are complex and constantly changing, and must be taken into consideration in any study of air conditioning system operation or building design, to properly analyze cost factors and system performance.

Several different study methods, each with its own advantages and disadvantages, are available. Mathematical analysis is perhaps the least satisfactory method for this type of study, because analytical solution of problems involving many variables is time-consuming and difficult. Field tests, since performed under actual conditions, can provide valuable information. However, they have certain important disadvantages: (1) some key factors - notably weather and occupancy -- are partially or wholly uncontrollable, (2) it is difficult and expensive to undertake tests which are subject to such factor variation as building construction, geographic location, and air conditioning system size and type. These problems add substantially to the difficulty of making valid comparisons. Finally, field tests besides being t1me consuming are, of course, not completely repeatable.

Many objections to field tests can be overcome, while still retaining most of their advantages, by simulating the complete building and its environment to an analog computer. Otherwise uncontrollable factors can thus be easily controlled. Each factor which might affect system operation can be varied independently while holding all other factors constant. Repeatability is assured and the time period required to run a complete study is reduced from months or years to just a few days.