An energy factor is a metric used in the

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to compare the

energy conversion efficiency Energy conversion efficiency (''η'') is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The input, as well as the useful output may be chemical, electric power, mechanical work, light (rad ...

of residential appliances and equipment. The energy factor is currently used for rating the efficiency of water heaters,

dishwasher A dishwasher is a machine that is used to clean dishware, cookware, and cutlery automatically. Unlike manual dishwashing, which relies heavily on physical scrubbing to remove soiling, the mechanical dishwasher cleans by spraying hot water, ty ...

s, clothes washers, and

clothes dryer A clothes dryer, also known as tumble dryer or simply dryer, is a powered household appliance that is used to remove moisture from a load of clothing, bedding and other textiles, usually shortly after they are washed in a washing machine. Many ...

s. The term is used by the

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to develop and enforce minimum energy conservation standards under the Energy Conservation Program. The higher the energy factor, the more efficient the appliance should be. Although the term energy factor is used to compare the relative efficiency of these appliances, the metric is defined differently for all four appliance categories. The energy factor is expressed in terms of site energy, which excludes losses through

energy conversion Energy transformation, also known as energy conversion, is the process of changing energy from one form to another. In physics, energy is a quantity that provides the capacity to perform work or moving, (e.g. Lifting an object) or provides heat ...

. All of these efficiency metrics are defined by Department of Energy test procedures.

Water heaters

The energy factor metric only applies to residential water heaters, which are currently defined by fuel, type, and input capacity. Generally, the EF number represents the thermal efficiency of the water heater as a percentage, since it is an average of the ratio of the theoretical heat required to raise the temperature of water drawn to the amount of energy actually consumed by the water heater.

Test procedure

The energy factor for residential water heaters is determined using the results from the 24-hour simulated use test. During the test 64.3±1.0 gallons of water are drawn from the water heater in six equally spaced draws that begin one hour apart. The hot water flow rate for each draw is 3.0±0.25 gallons per minute. After the beginning of the last draw a standby period of 18 hours follows. During the test, the test conditions must be operated at a specified value and accuracy.

Heat pump A heat pump is a device that can heat a building (or part of a building) by transferring thermal energy from the outside using a refrigeration cycle. Many heat pumps can also operate in the opposite direction, cooling the building by removing ...

water heaters (HPWHs) have different values specified for ambient air temperature and relative humidity. From the standard test procedure, the energy factor is defined as :

EF=\sum\limits_^6 \frac,

where

Q_

is the modified daily water heating energy consumption (Btu),

M_i

is the mass withdrawn from the ''i''^th draw (lb), and

C_

is the

specific heat In thermodynamics, the specific heat capacity (symbol ) of a substance is the heat capacity of a sample of the substance divided by the mass of the sample, also sometimes referred to as massic heat capacity. Informally, it is the amount of heat t ...

of the water of the ''i''^th draw Btu/lb°F, evaluated at the midpoint between 58°F and 135°F.

Uniform energy factor (UEF)

the Uniform Energy Factor (UEF) is newest measure of water heater overall efficiency according to the Department of Energy’s test method outlined in 10 CFR Part 430, Subpart B, Appendix E.

Energy conservation standards

Minimum federal energy conservation standards are defined by fuel, type, and rated storage volume. All standards are calculated as a function of the rated storage volume ''V'' in gallons. The current conservation standards are less efficient than the standards that go into effect in 2015.

Dishwashers

The energy factor for dishwashers is defined as "the number of cycles per kWh of input power."

Clothes washers

The energy factor for clothes washers, is defined as "the cubic foot capacity per kWh of input power per cycle."

Clothes dryers

The energy factor for clothes dryers is defined as "the number of pounds of clothes dried per kWh of power consumed."

References

{{Reflist Energy conversion