TABLE OF CONTENTS The primary purposes of computer modeling for cold-air distribution systems are to calculate design loads and to estimate the annual energy consumption of a given system. Many programs perform both design load and annual energy calculations from the same set of inputs.
The use of computer programs for HVAC load and energy calculations is discussed extensively in the following references:
1993 ASHRAE Handbook Fundamentals, chapter 28, "Energy Estimating Methods"
1995 ASHRAE Handbook HVAC Applications, chapter 36, "Computer Applications"
Air-Conditioning Systems Design Manual, section 2.5 (Lorsch et al. 1993).
Designers should use care when applying computer simulation programs to optimize cold-air distribution design decisions. Most available programs were developed to model conventional nonstorage cooling systems. These models may provide inaccurate results when applied with extreme supply air temperatures or with storage cooling plants.
The following sections discuss specific considerations for modeling cold-air distribution systems with common simulation programs.
Designers use computer calculations of design loads to size equipment such as fans, cooling coils, chillers, and other components. When calculating loads for cold-air distribution systems, users should consider the limitations of the program used.
The simplest load calculation programs calculate the space load and outside air ventilation load but do not consider effects of the distribution system on the equipment load. These programs may allow the user to specify distribution system gains, either as a percentage of the total load or as a supply air temperature increase.
More sophisticated programs simulate the distribution system performance.
