TABLE OF CONTENTS Space load calculations for cold-air distribution systems are, in most respects, the same as for conventional designs. This subject is covered thoroughly in chapter 26 of the 1993 ASHRAE Handbook Fundamentals, in the Cooling and Heating Load Calculation Manual (McQuiston and Spitler 1992), and in ASHRAE's Air-Conditioning Systems Design Manual (Lorsch et al. 1993).
There are some load calculation considerations that require special attention for cold-air distribution systems. The designer should consider all heat gains to supply air, including heat gains from supply fans and mixing box fans, and heat gains to ductwork. These sensible heat gains are considered part of the space load, since they increase the required supply air volume. Fan heat is discussed in detail in section 4.4 and duct heat gain is covered in section 4.5.
The low relative humidity maintained in spaces served by cold-air distribution systems may provide the same comfort level at an increased dry-bulb setpoint, compared to a conventional design at a higher relative humidity. Chapter 3 addresses this issue in more detail. This increase in the space setpoint, which may be 2 F (1 C) or more, can result in a decrease in space-cooling loads. However, in most cases, designers should size cold-air distribution systems to maintain the same dry-bulb temperature as a conventional design. This conservative approach provides a safety factor for designers and still allows for energy savings by operating at a higher space setpoint.
The space load calculation should also account...
