Environmental Engineering Reference
In-Depth Information
Figure 11.8
Simplified constant-volume HVAC system design. (From McNall, P.E.
and Persily, A.K., in
Ann. ACGIH: Evaluating Office Environmental Problems
, 10, 77,
ACGIH, Cincinnati, 1984. With permission.)
Figure 11.9
Simplified variable-volume HVAC system design. (From McNall, P.E.
and Persily, A.K., in
Ann. ACGIH: Evaluating Office Environmental Problems
, 10, 77,
ACGIH, Cincinnati, 1984. With permission.)
requirements (compared to CAV systems.) Variable-air-volume systems are
more complicated than CAV systems and, as a consequence, are more diffi-
cult to operate effectively. Not surprisingly, VAV system operation in many
buildings has been plagued with problems. One of the most common has
been the complete closing of VAV valves and cessation of air flow through
diffusers when a space's thermal requirements have been met. Under such
conditions, one or more spaces may receive little or no ventilation air.
ii. Air-water systems. Air-water systems differ from all-air ones in
that air can be reheated or cooled by passing over a fan coil before it enters
conditioned spaces. A terminal reheat system is illustrated in Figure 11.10 .
iii. All-water systems. In all-water, or hydronic systems, heating and
cooling occurs in terminal reheat units located in each space. The terminal
 
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