Building Design and Construction Handbook - Merritt - Ventech!

HEATING, VENTILATION, AND AIR CONDITIONING 13.47
TABLE 13.12 Air-Supply Distribution in Accordance with Heat Load
Space
Load,
Btu per hr % of load
Cfm
(% � 2,010)
Cellar 14,500 10.05 200
First-floor store 47,600 33.00 660
Vestibule 5,650 3.91 80
Office 4,900 3.39 70
Men’s room 2,800 1.94 40
Ladies’ room 1,590 1.10 25
Second-floor office No. 1 33,300 23.01 460
Office No. 2 16,650 11.51 230
Men’s room 2,820 1.95 40
Ladies’ room 2,080 1.44 30
Hall 12,585 8.70 175
144,475 100.00 2,010
q 160,000
�T � � � 73.6�F
1.08Q 1.08 � 2010
If we adjust the flame (oil or gas) so that the output was the capacity theoretically
required, the temperature rise would be
q 144,475
�T � � � 66.5�F
1.08Q 1.08 � 2010
In actual practice, we do not tamper with the flame adjustment in order to
maintain the manufacturer’s design balance. Instead, the amount of air supplied to
each room is in proportion to its load. (See Table 13.12 which is a continuation
of Table 13.11 in the design of a forced-air heating system.) Duct sizes can then
FIGURE 13.5 One-pipe hot-water heating
system.
be determined for the flow indicated in
the table (see Fig. 13.5). In this example,
minimum duct size for practical
purposes is 12 � 3 in. Other duct sizes
were obtained from Table 13.7, for a
friction loss per 100 ft of 0.15, and
equivalent rectangular sizes were obtained
from Table 13.6 and shown in
Fig. 13.5.
Humidification in Warm-Air Heating.
A warm-air heating system lends itself readily to humidification. Most warm-air
furnace manufacturers provide a humidifier that can be placed in the discharge
bonnet of the heater.
Theoretically, a building needs more moisture when the outside temperature
drops. During these colder periods, the heater runs more often, thus vaporizing
more water. During warmer periods less moisture is required and less moisture is
added because the heater runs less frequently.
Some manufacturers provide a woven asbestos-cloth frame placed in the pan to
materially increase the contact surface between air and water. These humidifiers
have no control.