State commercial tank type water heaters, hot water storage tanks and water heating systems using tanks have assigned tank efficiencies as follows:
Gas and Oil-Fired Tank Type Heaters
•Use 70% tank draw efficiency for all one and two temperature applications. For example, a gas fired Ultra Force®
•100 x .70 = 70.0 usable gallons of hot water available within 30°F temperature drop during the demand period.
•Conversely, if 70.0 gallons of usable hot water were needed from the tank over the demand period, the minimum purchased tank size would be:
70.0 ÷ .7 = 100 gallons
Note: Storing water below 140°F may require more storage capacity.
•If the input of the heater is satisfactory for recovery purposes but the tank size is not, an auxiliary hot water storage tank may be piped into the system to increase the amount of available hot water during the demand period. State instruction manuals show the details.
Electric Tank Type Heaters
•Use 70% tank draw efficiency for all two temperature applications. For example, a model CSB
-52 has a 52 gallon tank:
•52 x .70 = 36.4 usable gallons of hot water available within 30°F temperature drop during the demand period.
•Conversely, if 36.4 gallons of usable hot water were needed from the tank over the demand period, the minimum purchased tank size would be:
36.4÷ .7 = 52 gallons
•Use 80% tank draw efficiency for one temperature systems in the same manner as described for two temperature.
•As in the example of gas and
if necessary. However, it should be noted that State commercial electric water heaters are available in tank sizes to 120 gallons. Booster size heaters may also be connected to auxiliary tanks of any size. This would permit fuel conversion at a later date by heater substitution.
Auxiliary Tank (Unfired)
•As explained previously, auxiliary tanks are used to increase the hot water storage potential of gas and
.
• Use 70% tank draw efficiency for all two temperature. applications.
• Use 80% tank draw efficiency for all one temperature applications piped according to State instruction manuals.
Heater Recovery Plus Storage Tank Equals Demand
As previously explained, select maximum recovery and minimum storage if the hot water demand period is longer than 3 or 4 hours. Storage must be sufficient to handle any peaks within the demand period.
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