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 7=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of water drawn during the sixth draw shall be increased or decreased as necessary such that the total volume of water withdrawn shall be equal to 64.3±1.0 gallons.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, r=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, Vmax 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

creased as necessary such that the total volume of water withdrawn shall be equal to 32.15 + 3*V4.5.6±1.0 gallons.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, Q.. Record the energy consumed prior to the fourth draw and at the end of the recovery period following the fourth draw, Qr. min.

max

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 de

Thr i=1

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

C, is the specific heat of water at the average temperature (T24 + T)/2, Btu/lbm 'F

T2 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 Tstby.1 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

Qur

Tt.stby - Ta.stby

where Tt.atby is the average storage tank temperature 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, °F

Tatby is the average ambient temperature 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, 'F

and UA is the standby heat loss coefficient of the storage tank,

BTU hr °F

6.1.5. Daily Water Heating Energy Consumption. The daily water heating energy consumption, Q. 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/lbm °F M is the mass of water within the storge tank, lbm

T2 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, 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 Qa is the adjusted daily water heating consumption, Btu

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

Tastby 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 Tatby.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

where M, is the mass withdrawn during the first draw, lbm

Cp is the specific heat of water at the average temperature (Tdel.1+T.1)/2, Btu/ lbm °F

Tdel. is the average delivery temperature for the first draw, 'F

Tin.1 is the average inlet temperature for the first draw, 'F

and Qr.max 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 light, Btu

The minimum recovery efficiency is computed as

where Qam is the daily water heating energy consumption as computed in accordance with section 6.2.3., Btu

M, is the mass associated with the ith draw, lbm

Cp is the specific heat of water computed at a temperature of (58 °F+135 °F)/2, Btu/ lbm °F

Tdel is the average delivery temperature for the ith draw, °F

and T. is the average inlet temperature for the ith draw, °F

6.2.5. Annual Energy Consumption. The annual energy consumption for instantaneous type water heaters is computed as— Eannual=Qdm* 365

where Qam is the modified daily energy consumption, Btu per day

and 365 is the number of days within a year, days.

7. Ratings for Untested Models

In order to relieve the test burden to manufacturers who offer water heaters which differ only in fuel type or power input, ratings for untested models may be established in accordance with the following procedures. In lieu of the following procedures a manufacturer may elect to test the unit for which a rating is sought.

7.1. Gas Water Heaters. Ratings obtained for gas water heaters using natural gas can be used for an identical water heater which utilizes propane gas if the input ratings are within 10 percent.

7.2. Electric Water Heaters

7.2.1. First Hour Rating. If an electric storage type water heater is available with more than one input rating, the manufacturer shall designate the standard input rating and the water heater need only be tested with heating elements at the designated standard input ratings. The first hour ratings for units having power input rating less than the designated standard input rating shall be assigned a first hour rating equivalent to the first draw of the first hour rating for the electric water heater with the standard input rating. For units having power inputs greater than the designated standard input rating, the first hour rating shall be equivalent to that measured for the water heater with the standard input rating.

7.2.2. Energy Factor. The energy factor for identical electric storage type water heaters, with the exception of heating element wattage, may use the energy factor obtained during testing of the water heater with the designated standard input rating.

[55 FR 42169, Oct. 17, 1990]

EFFECTIVE DATE NOTE: At 55 FR 42169, Oct. 17, 1990, part 430 was amended by revising appendix E to subpart B, effective April 15, 1991. For the convenience of the user, the superseded text appears below. APPENDIX E TO SUBPART B OF PART 430-UNIFORM TEST METHOD FOR MEASURING THE ENERGY CONSUMPTION OF WATER HEATERS

1. DEFINITIONS

1.1 "Cutout" means the moment in time when a water heater thermostat has acted to reduce the energy or fuel input to the heating elements or burners to a minimum.

1.2 "Design Power Rating" means the nominal power rating that a water heater manufacturer assigns to a particular design of water heater heating element, expressed in kilowatts.