Building Design and Construction

Sizing an Air-Conditioning Plant

Consider the building shown in Fig. 13.3 (p. 13.43). Assume only the first and  second floors will be air conditioned. The design outdoor condition is assumed to be 95F DB (dry-bulb) and 75F WB (wet-bulb). The design indoor condition is 80F DB and 50% relative humidity.
The temperature gradient across an exposed wall will be 15F (95F  80F).
The temperature gradient between a conditioned and an interior nonconditioned space, such as the cellar ceiling, is assumed to be 10F.
Exterior walls are constructed of 4-in brick with 8-in cinder backup; interior finish is plaster on metal lath. Partitions consist of 2  4 studs, wire lath, and plaster. First floor has double flooring on top of joists; cellar ceiling is plaster on metal lath.

Lights may be assumed to average 4 W/ ft2. Assume 50 persons will be in the store, 2 in the first-floor office, 10 in the second-floor office No. 1, and 5 in secondfloor office No. 2.
Cooling Measured in Tons. Once we obtain the cooling load in Btu per hour, we
convert the load to tons of refrigeration by Eq. (13.15).
Cooling Requirements for First-Floor Store (Table 13.15a).

Load in tons = 86,951 / 12,000=7.25 tons

If supply air is provided at 18F differential, with fresh air entering the unit through an outside duct, the dehumidified air flow required for sensible heat is [from Eq. (13.30)]:

Cooling and supply-air requirements for the building are summarized in Table 13.16.


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