Chapter hvac engineering Fundamentals: Part 1 Introduction

Equipment: Part 3
393
Figure 11.23
Psychrometric chart for chemical dehumidification.
Figure 11.24
Fixed-percentage outside air control.
Equipment: Part 3
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394
Chapter Eleven
Figure 11.25
One hundred percent outside air control.
Figure 11.26
Outside air control pressure.
ply-fan motor starter circuit, so the damper will be at least 50 percent
open before the fan starts. It is possible to control the outside and
return air quantities to match a varying exhaust (Fig. 11.26). The
space being exhausted is usually controlled at lower pressure than an
adjacent space. The real problem here is accurate sensing of the very
low-pressure differences used, while taking into account wind and
stack effects. One of the better methods presently used provides an
orifice in the wall between the two spaces where a velocity-measuring
device (hot-wire anemometer or fluidic sensor) is located. Exhaust and
makeup air quantities can then be adjusted to maintain a velocity
corresponding to the desired pressure difference.
Equipment: Part 3
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Any use is subject to the Terms of Use as given at the website.

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