MIL-HDBK-1003/1
The mixing equation may also be used to evaluate the required size of SWH storage tanks as Ts varies. Higher storage temperatures allow smaller tank sizes to deliver equal water to fixtures.
Add "506.4 Revisions to ASHRAE Chapter 48, Table 9, Row 9, Showers. Table 9, Row 9, Showers, indicates 225 gallons per hour (gph) per fixture for hot water flow in Gymnasiums, Industrial Plants, Schools, and YMCA's. Assume this represents continuous flow of shower fixture, what is the design fixture flow rate? Since 225 gph/60 min. per hour =
3.75 gpm of hot water flow = Qs, calculate the fixture flow Qf
from the mixing equation, using Tf = 110 degrees F, Ts = 140
degrees F, and Tc = 50 degrees F. Observe that Qf = Qs + Qc,
therefore Qc = Qf - Qs. Substituting:
Qf x Tf = (Qs x Ts) + (Qc x Tc)
Qf x Tf = (Qs x Ts) + ((Qf-Qs) x Tc)
Qf x Tf = (Qs x Ts) + (Qf x Tc) - (Qs x Tc)
(Qf x Tf) - (Qf x Tc) = (Qs x Ts) - (Qs x Tc)
Qf x (Tf-Tc) = Qs x (Ts-Tc)
Qf = Qs x [(Ts-Tc)/(Tf-Tc)]
Qf = 3.75 x [(140-50)/(110-50)]
Qf = 5.625 gpm
Therefore, the proper correction factor (CF) for Chapter 48, Table 9, Row 9 is equal to 2.5 gpm per fixture (per PL 102-486) divided by 5.625 gpm (calculated above), which results in CF = 0.444 for Tc of 50 degrees F. This may also be calculated as Qs = 1.667 divided by Qs = 3.75 equals CF = 0.444.
Thus, the gymnasium shower at 225 gph x CF corrects to 225 gph x 0.444 = 100 gph for Tc of 50 degrees F.
Add "SECTION 506.5 Life Cycle Cost Analysis. Executive Order
13123 requires life cycle cost analysis (LCCA) of alternatives and maximum utilization of energy conserving methods and equipment. Evaluate alternative energy source options, such
as electric, steam, oil-fired, and gas-fired service water heater units of similar first hour draw (FHD) or first hour rating (FHR) capacity, say plus or minus 5 percent.
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