this time (designated as,=0), the mean tank temperature (T.), and the oil, gas, and electrical energy measurements as appropriate. Begin the 24 hour simulated use test by drawing an amount of water out of the water heater equivalent to one-sixth of the daily hot water usage, 64.3 gallons. Record the average storage tank and ambient temperature every 15 minutes throughout the 24 hour simulated use test unless recovery or a draw is occurring. At elapsed time intervals of one, two, three, four and five hours from,=0), initiate additional draws removing an amount of water equivalent to one-sixth of 64.3 gallons, with the maximum allowable deviation for any single draw being ±0.5 gallons. The quantity of water drawn during the sixth draw shall be increased or decreased as necessary such that the total volume of water withdrawn shall be equal to 64.3±1.0 gallons.

All draws during the simulated use test are to be made at flow rates of 3.0±3.0 gallons per minute. Measurements of the inlet and outlet temperatures shall be made beginning 15 seconds after the draw is initiated and at every subsequent 5 second interval throughout the duration of each draw. The arithmetic mean of the hot water discharge temperature and the cold water inlet temperature shall be determined for each draw. Record the scale or meter reading, as appropriate, after each draw. At the end of the recovery period following the first draw, record the maximum mean tank temperature observed after cut-out, Tmax,, and the energy consumed, Q for oil, gas, and heat pump water heaters including auxiliary energy such as pilot lights, pumps, fans, etc. For heat pump water heaters Q., is the sum of the energy consumed by the heat pump and the electrical heating elements(s).

At the end of the recovery period following the sixth draw, record the total electric and/ or fuel energy consumption, Qu, and the scale reading or the meter reading, as appropriate. If a water scale is used, determine the net weight of the water withdrawn, MFHR in pounds. Record the maximum value of the mean tank temperature after cutout as T... Except as noted below, allow the water heater to remain in the standby mode until 24 hours have elapsed from the start of the test, F0. Prevent the water heater from beginning a recovery cycle during the last hour of the test by turning off the electric power to the electrical heating elements and heat pump, if present, or by turning down the fuel supply to the main burner at an elapsed time of 23 hours. If a recovery is taking place at an elapsed time of 23 hours, wait until the recovery is complete before reducing the electrical and/or fuel supply to the water heater. At 24 hours, record the mean tank temperature, T24 and the electric and/or fuel instrument readings. Determine the total energy consumption during the entire 24 hour simulated use test, Q. Record the time interval

between the time at which the maximum mean tank temperature is observed after the sixth draw and the end of the 24 hour test as atby.. Record the time during which water was not being withdrawn from the water heater during the entire 24 hour period as

Tatby.2.

5.2 Instantaneous Water Heaters

5.2.1. Setting the Outlet Discharge Temperature. Initiate normal operation of the water heater at the full input rating. Monitor the discharge water temperature and set to a value of 135°F ± 5°F in accordance with the manufacturer's instructions. If the water heater is not capable of providing 3.00 ± 0.25 gallons per minute then adjust the flow rate as necessary to achieve the specified discharge water temperature. Record the corresponding flow rate as Vmax. If the instantaneous water heater incorporates a controller which permits continous burner operation at a reduced input rate, adjust the flow rate as necessary to achieve a discharge water temperature of 135° ± 5°F while maintaining the minimum input rate. Record the corresponding flow rate, Vmin. If an outlet temperature of 135° ± 5°F cannot be achieved at the minimum allowable flow rate permitted by the instantaneous water heater, record the flow rate as Vmin and the outlet temperature as Tmin.

5.2.2. Power Input Determination. For oil and gas flow actuated water heaters, adjust the burners to the maximum firing rate value specified by the manufacturer.

5.2.3. First Hour Rating Test for Instantaneous Water Heaters. Establish normal heater operation at the maximum input rate with the discharge water temperature set in accordance with section 5.2.1. Record the time, oil, and/or gas meters as appropriate. Do not interrupt electrical or fuel to the water heater. Draw and collect water withdrawn from the water heater, while recording the inlet and outlet fluid temperatures beginning 15 seconds after the draw is initiated and at every subsequent 5 second interval throughout the duration of the draw in a suitable container for the purpose of determining its weight at the conclusion of the test. Alternatively, a water meter may be used to directly measure the value of water withdrawn. At the end of one hour terminate the draw. Determine the mass of water withdrawn, MFHR, in pounds, or the volume of water withdrawn, VFHR, in gallons with an error no greater than 2 percent.

5.2.4. 24 Hour Simulated Use Test

5.2.4.1. Fixed Input Instantaneous Water Heaters. Establish normal operation with the discharge water temperature and flow rate set to values of 135°F ± 5°F and Vmax, respectively. Record the oil, gas, and electrical energy measurements, as appropriate. Begin

the 24 hour simulated use test by drawing an amount of water out of the water heater equivalent to one-sixth of the daily not water usage, 64.3 gallons. At elapsed time intervals of one, two, three, four, and five hours from 1-0, initiate additional draws removing an amount of water equivalent to one-sixth of 64.3 gallons, with the maximum allowable deviation for any single draw being ± 0.5 gallons. The quantity of water drawn during the sixth draw shall be increased or decreased as necessary such that the total volume of water withdrawn shall be equal to 64.3+1.0 gallons. Measurements of the inlet and outlet water temperatures shall be made beginning 15 seconds after the draw is initiated and at every 5 second interval throughout the duration of the draw. The arithmetic mean of the hot water discharge temperature and the cold water inlet temperature shall be determined for each draw. Record the scale or meter reading, as appropriate, after each draw. At the end of the recovery period following the first draw, record the energy consumed, Q. Allow the water #heater to remain in the standby mode until exactly 24 hours have elapsed from the start of the test, 1-0. At 24 hours, record the electric and/or fuel instrument readings. Determine the energy consumption during the entire 24 hour simulated use test, Q.

5.2.4.2. Variable Input Instantaneous Water Heaters. If the instantaneous water heater incorporates a controller which permits continuous burner operation at a reduced input rate, the first three draws shall be conducted using the maximum flow rate, Vax, while removing an amount of water equivalent to one-sixth of 64.3 gallons, with the maximum allowable deviation for any one of the three draws being ± 0.5 gallons. The second three draws shall be conducted at Vmin. If an outlet temperature of 135° ± 5°F could not be achieved at the minimum flow rate permitted by the instantaneous water heater, the last three draws should be lengthened such that the volume removed is equivalent to

60 n

with the maximun allowable definition for any one of the three draws being ± 0.5 gallons. The quantity of water drawn during the sixth draw shall be increased or decreased as necessary such that the total volume of water withdrawn shall be equal to 32.15 + 3*V45.6±1.0 gallons. Measurements of the inlet and outlet water temperatures shall be made beginning 15 seconds after the draw is initiated and at every 5 second interval throughout the duration of the draw. Determine the arithmetic mean of the hot water discharge temperature and the cold water inlet temperature for each draw. Record the scale or meter reading, as appropriate, after each draw. At the end of the recovery period following the first draw, record the energy consumption, Qr. Record the energy consumed prior to the fourth draw and at the end of the recovery period following the fourth draw, Q. min.

max.

p(135°F-58°F)

VsepCp2(Tmax, 1 – İ。)

where M, is the mass withdrawn during the first draw, lbm

Cp is the specific heat of water at the average temperature (Tdel.+Tin,1)/2, btu/lbm °F Tel. 18 the average delivery temperature for the first draw, °F

Tin is the average inlet temperature for the first draw, :F

Va is the storage tank capacity, gal

p is the density of water at the average temperature (Tmax, 1+Ť.)/2, lbm/gal

Cp2 is the specific heat of water at the average temperature (Tmax.1+To)/2, Btu/lbm °F Tmax, is the maximum mean tank temperature recorded after cutout following the first draw, 'F

To is the maximum mean tank temperature recorded prior to the first draw, 'F and Q, is the total energy used by the water heater between cutout prior to the first draw and cutout following the first draw, including auxiliary energy such as pilot lights, pumps, fans, etc., Btu. (Electrical auxiliary energy shall be converted to

where Q is the hourly standby energy losses of the water heater, Btu/hr

Qby is the total energy consumer by the water heater between the time at which the maximum mean tank temperature is observed after the sixth draw and the end of the 24 hour test period, Btu

M is the mass of the water within the storage tank, lbm

Cp is the specific heat of water at the average temperature (T24 + Ï„No2, Btu/lbm °F T24 is the mean tank temperature at the end of the 24 hour test period, F

Tu is the maximum mean tank temperature observed after the sixth draw, 'F and Taby. is the elapsed time between the time at which the maximum mean tank temperature is observed after the sixth draw and the end of the 24 hour test period, hours

The standby heat loss coefficient for the tank is computed as—

where Q is the total energy used by the water heater during the 24 hours simulated use test including auxiliary energy such as pilot lights, pumps, fans, etc., Btu

C, is the specific heat of water at the average temperature (T2+T.)/2, Btu/bm °F

M is the mass of water within the storge tank, lbm

T24 is the average tank temperature at the conclusion of the 24 hours simulated use test, °F

T. is the average tank temperature at the beginning of the 24 hours simulated use test, recorded one minute before the first draw is initiated °F

and ʼn is the recovery efficiency of the hot water heater, dimensionless.

6.1.6. Adjusted Daily Water Heating Energy Consumption. The adjusted daily water heating energy consumption, Qda takes into account that the temperature difference between the storage tank and surrounding ambient temperature may not be the nominal value of 67.5°F (135°F - 67.5°F) due to the 10°F allowable variation in storage tank temperature, 135 ± 5°F, and the 5°F allowable variation in surrounding ambient temperature 65°F to 70°F. The adjusted daily water heating energy consumption is computed as

where Qda is the adjusted daily water heating consumption, Btu

Tby 18 the mean tank temperature during the total standby portion, Tatby.2, of the 24 hour test, F

Tasty is the average ambient temperature during the total standby portion, Tatby.2, of the 24 hour test, °F

UA is the standby heat loss coefficient for the storage tank, Btu/hr°F

and Taby.2 is the number of hours during the 24 hour simulated test when water was not being withdrawn from the water heater A modification is also needed to take into account that the temperature difference between the outlet water temperature and supply water temperature may not be equivalent to the nominal value of 77°F (135°F-58°F). The following equations adjust the experimental data to a nominal 77°F temperature rise.

The energy used to heat water, Btu per day, may be computed as

Qam