Numerous studies in recent years on the matter of energy shortage lead one to believe that the U.S. demand for energy will shortly outstrip her power generating capacity and fossil fuel supply. According to a well quoted report of the Stanford Research Institute space heating and cooling for residential and commercial buildings amounts to approximately 20% of the total energy consumed in the U.S which was 60 trillion Btu per year in 1968. Moreover. frequent blackouts and brownouts in the east coast region of the U.S. are good indications that the electric power demand for summer air conditioning exceeds. for certain times, the capability of supply and distribution by the power companies.

It is under this context that accurate methodology for heating and cooling load calculations is most needed for the design of building which is to minimize the energy requirement. It is generally accepted that buildings can be designed to be energy-effective if their thermal insulation is increased; window size, air leakage, and lighting levels decreased; shading devices properly installed; heating and cooling systems adequately designed, installed, and maintained; and their heat storage capability most fully utilized. These energy saving features, however, must be considered with reference to numerous constraints, such as added costs for material, construction and maintenance, conformance to local building codes, occupancy life styles, aesthetics, construction practices, and availability of equipment.

In spite of these constraints, sufficient engineering information and technical basis exist today to warrant extensive studies on various design alternatives for heating and cooling the building to minimize the wasteful use of energy. Design and operation of heating and cooling systems based upon conventional steady-state calculations, for example, usually result in oversizing of equipment and overheating or cooling of the space to be controlled. An overdesigned system usually operates at lower efficiency and needs more material (consequently more energy) to produce it, thus creating a vicious cycle.

One effective way to design the heating and cooling systems which is optimum from the standpoint of energy consumption, peak power demand and many practical constraints mentioned above, is to study the building thermal performance by using accurate simulations. Because the use of computer simulations makes it possible to evaluate the sensitivity of various design alternatives on the net energy usage, they can be an effective tool in the design process. In order for such design studies to be conducted on the computer, however, the computer program to be used should be comprehensive and should indicate the proper response to the change of the many parameters which are pertinent to energy usage. The methodology recommended by the ASHRAE Task Group on Energy Requirements can meet these requirements, because it is designed to solve exact heat transfer relationships among the building structure, air in tne occupied space. occupants, lighting fixtures and other internal equipment as described hereafter.