TABLE OF CONTENTS Following calculation of the cooling and heating loads, an analysis must be carried out to specify the various parameters for selection of equipment and design of the air distribution system. The psychrometric processes involved are rigorously discussed in Appendix D, where it is shown that the psychrometric chart is a useful tool in visualizing and solving problems.
The complete air-conditioning system may involve two or more of the processes considered in Appendix D. For example, in the conditioning of a space during the summer, the air supplied must have a sufficiently low temperature and moisture content to absorb the total cooling load of the space. Therefore, as the air flows through the space, it is heated and humidified. If the system is a closed loop, the air is then returned to the conditioning equipment, where it is cooled and dehumidified and supplied to the space again. Fresh outdoor air usually is required in the space; therefore, outdoor air (makeup air) must be mixed with the return air (recirculated air) before it goes to the cooling and dehumidifying equipment. During the winter months, the same general processes occur but in reverse. Notice that the psychrometric analysis generally requires consideration of the outdoor air required, the recirculated air, and the space load. Various systems will be considered that carry out these conditioning processes with some variations.
The most common design problem involves a system where outdoor air is mixed with recirculated air; the mixture is cooled and...
