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2.Select a trial size heater 2 / .
3.Subtract the hourly heater recovery from the demand.
4.The difference in gallons between demand and recovery must come from the tank.
5.Multiply the difference by the number of demand hours. The result is the “usable” number of gallons which must come from the tank.
6.Divide the “usable” tank gallons by .7 or .8 to obtain minimum tank size needed, see pages 7 thru 10.
7.Compare minimum calculated tank size with that of the “trial size” heater. If the heater tank is equal to or greater than calculated tank size the selection is satisfactory. If not, adjust recovery and storage as necessary, see page 10.
8.Divide the heater tank size by the heater recovery to be certain the tank will be recovered by the time of the next demand. If not, adjust recovery and storage as necessary, see page 10.
1* / The demand could be in minutes or seconds. In either case all references to hours in the procedure would revert to minutes or seconds. For example, a stationary rack type dishwasher may have a 12 second demand period and an 83 second recovery period.
2* / Review PROFILES OF OPERATION, Page 5, as an aid in determining whether to favor recovery or tank capacity in the selection of a “trial size” heater. Normally the hourly heater recovery of the heater selected should not exceed the hourly demand. In this way the hot water content of the tank will be put to use.
One temperature example
1.A two hour demand of 206 gph of 140°F water has been established. The lowest incoming water temperature is 40°F. The shortest time in any day in which the demand will be repeated is 8 hours.
2.A State
“Try” a Model SUF 100
3. | Needed: | 206 gph for 2 hours | |
| Subtract: | - 171 gph heater recovery at 100°F rise | |
| Equals: | 35 gallons needed from tank, first hour | |
| Multiplied by: | x 2 demand hours | |
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| Equals: | 70 usable gallons needed from tank | |
| Divide: | 70 ÷ .7 = 100. gallons minimum tank size | |
| Capacity | 100 gallon tank vs.100. gallon tank minimum | |
Compare tank size vs.recovery:
Used 70 gallon. 8 hours is available to recover tank.
(70 - 171 gph recovery = .41, .41 X 60 minutes = 24.6 minutes needed to recover 70 gallons.
Conclusion: The Model SUF 100
CAUTION: A two hour demand of 206 gph means that the 206 gph is spread throughout the entire hour. It does not mean that 206 gallons is dumped in 15 minutes and no additional hot is used in the remaining 45 minutes.
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