Operating instructions

Method C - Commercial Sizing Sample Calculation Example 2
This application is for a motel with 20 rooms. Each of these rooms has the following
fixtures: (1) Vanity, (1) Shower and (1) Bath
In addition, 5 rooms have an additional vanity. Also, there is a utility sink used by the staff
for cleaning and a laundry with two machines
Solution:
Use Table 5 and the fixture count to complete the example worksheet in figure 3 (on next
page). Note that we treated the vanities as "Private Lavatory Basins" and the utility tub as a
"Laundry Tub". From discussions with the washing machine manufacturer and the motel
owner, we find that 100 Gal/hr of 140°F water is used in the Laundry. This usage is recorded
on the "Laundry Line" at the bottom of Worksheet 2. The demand factor of 0.25 for a hotel is
from Table 6. The Probable Maximum Demand is 0.25 x 1978 = 494.5 GaVhr. To this, we add
the 100 GaVhr laundry usage for an Adjusted Probable maximum Demand of 594.5 Gal/hr.
From table 1, Select the most cost-effective combination of equal size Artesians that will
satisfy this requirement. In this case 2 model 340's, with 305 gph first hour rating at 140°F,
are selected. Combined first hour rating is 610 gph (2 x 305). The total gross boiler output
required is equal to the requirement for each model multiplied by the total number of water
heaters. In this case 2 x 220 = 440 MBH gross boiler output is required. Likewise, their total
boiler water flow through the water heater zone is equal to the requirement for each water
heater times the total number of water heaters. In this case (2 x 6.7) = 13.4 gal / min.
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