Handbook of air conditioning and refrigeration / Shan K

FIGURE 15.41 Humidifying load for a typical air system.
Types of Humidifier
In Fig. 15.41, s is the state of supply air when the space has a heating load, and s� is the condition
when the space has a cooling load, w s � w s�.
The humidifying load can also be calculated from the following relationship:
where � supply volume flow rate of outdoor air intake, cfm (m3 /min)
� volume flow rate of infiltrated air, cfm (m3 V˙
o
V˙
inf
/min)
wr,wo � humidity ratio of space air and outdoor air, lb/lb (kg/kg)
(15.53)
In Eq. (15.53), represents the space moisture gains, in lb/h (kg/h). Space moisture gains include
the latent load from the occupants, appliances, equipment, and products. The moisture gains
from the building structures are often ignored.
According to the mechanism used for evaporation of water vapor from water, humidifiers can be classified
as steam and heating element humidifiers, atomizing humidifiers, and wetted element humidifiers.
15.19 STEAM AND HEATING ELEMENT HUMIDIFIERS
Steam Grid Humidifiers
m˙ wr
AIR SYSTEMS: COMPONENTS—FANS, COILS, FILTERS, AND HUMIDIFIERS 15.73
m˙ hu � 60(V˙ o � V˙ inf)� o(w r � w o) � m˙ wr
At a low partial pressure when mixed with dry air, steam is the ready-made water vapor. With
proper water treatment at the boiler, steam is free of mineral dust and odor, and it does not support
the growth of bacteria that create sanitation problems. Two types of steam humidifiers are currently
used in air systems: steam grid humidifiers and steam humidifiers with separators.
A steam grid humidifier installed inside ductwork is shown in Fig. 15.42a. A steam grid humidifier
may have a single distribution manifold or multiple manifolds. Each distribution manifold has an