Handbook of air conditioning and refrigeration / Shan K

d. That is capable of being set back down to 55°F (12.8°C) and up to 90°F (32.2°C) during off
hours
10. HVAC&R piping, ducts, and plenums shall be insulated and meet the requirements listed in
Secs. 7.2, 17.2, and 17.4.
11. Duct systems shall be air balanced to within 10 percent of design airflow rates.
12. When separate heating and cooling equipment serve the same control zone, thermostats shall
be interlocked to prevent simultaneous heating and cooling
13. Exhausts with a volume flow rate over 300 cfm (140 L/s) that do not operate continuously
shall be equipped with gravity or motorized dampers that will automatically shut when the exhaust
systems are not in use.
14. Air systems with a design volume flow rate greater than 10,000 cfm (4720 L/s) shall have optimum
start controls.
29.5 VAV COOLING PACKAGED SYSTEMS
System Description
AC SYSTEMS: PACKAGED AND DESICCANT-BASED SYSTEMS 29.9
A VAV cooling packaged system is a multizone air conditioning system that provides conditioned
air without heating. It uses a packaged unit with DX cooling coils to condition the air and distribute
it to various control zones through VAV boxes, ducts, distributing devices, and controls. The zone
supply volume flow rate is modulated by the damper in the VAV box to match the variation of the
zone sensible load to maintain a preset zone temperature. A typical VAV cooling packaged system
with its system pressure characteristics is shown in Fig. 29.1. It consists of a packaged unit, many
FIGURE 29.1 A VAV cooling packaged system.