Chapter hvac engineering Fundamentals: Part 1 Introduction

364
Chapter Ten
Figure 10.40
Enclosed grid humidifier.
Then for air from 62.4 to 85
⬚
F,
Sensible heat
⫽
(85
⫺
62.4) lb / lb
w
a
3
3
⫻
10,000 ft / min
⫻
1.08 Btu / [h
䡠
(ft / min)
䡠
⬚
F]
⫽
244,080 Btu / h
Water required for humidification is
3
(0.0060
⫺
0.0054) lb / lb
⫻
10,000 ft / min
w
a
3
⫻
0.075 lb / ft
⫻
60 mm / h
⫽
270 lb / h water
a
The heating required to evaporate the water is
270 lb / h
⫻
1045 Btu / lb
⫽
282,150 Btu / h
w
10.19.3
Steam humidifiers
Steam humidifiers are used extensively nowadays because of their
simplicity and ease of control. The basic system consists of a modu-
lating control valve and a perforated pipe, or grid, mounted in an air
duct (Fig. 10.40). An enclosure around the grid is needed to remove
condensate, especially at start-up, when the system is cold. The steam-
jacketed grid is provided with an enclosure which is continuously
heated so that only dry steam is delivered into the airstream. Control
is provided by modulating the steam valve. A high-limit duct humid-
istat is recommended, as shown in Fig. 10.41, to avoid supersaturation
conditions in the duct, with resulting condensation. Steam pressures
should be 5 to 15 lb / in
2
gauge. Only clean steam should be used. Suf-
Equipment: Part 2
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