This measure can be claimed if electric heat pumps are used for delivering hot water and have an efficiency greater than the base case, as set out in the Key Assumptions for the Base Case in the Design section.
Note: The baseline assumes a standard instantaneous water heater which has a near 100% efficiency. So, an instantaneous electric water heater will not generate savings.
Providing hot water with high efficiency will reduce fuel consumption and related carbon emissions from water heating.
Heat pump water heaters (HPWH) use electricity to take the heat from surrounding air and transfer it to the water in an enclosed tank. This process is similar to the heat transfer process in a refrigerator but in reverse. Heat pump water heaters can be used with dual functionality in hotels for example to cool the kitchen, laundry, or ironing area and to generate hot water. Because they move heat rather than generate heat, heat pumps can provide efficiencies greater than 100%.
The efficiency of a heat pump is indicated by the Coefficient of Performance (COP). It is determined by dividing the energy output of the heat pump by the electrical energy needed to run the heat pump, at a specific temperature. The higher the COP, the more efficient the heat pump. Typical heat pump water heaters are two to three times more efficient than standard electric water heaters.
|Heat Pump Water Heaters||A low-pressure liquid refrigerant is vaporized in the heat pump's evaporator and passed into the compressor. As the pressure of the refrigerant increases, so does its temperature. The heated refrigerant runs through a condenser coil within the storage tank, transferring heat to the water stored there. As the refrigerant delivers its heat to the water, it cools and condenses, and then passes through an expansion valve where the pressure is reduced and the cycle starts over.|
|Air Source Heat Pumps||These systems are called "integrated" units because they integrate the heating of domestic water with a house space-conditioning system. They recover heat from the air by cooling and transferring heat to domestic hot water. Water heating can be provided with high efficiency with this method. Water heating energy can be reduced by 25% to 50%.|
|Ground Source Heat Pumps||
In some Ground-Source Heat Pumps, a heat exchanger, sometimes called a "desuperheater," removes heat from the hot refrigerant after it leaves the compressor. Water from the home’s water heater is pumped through a coil ahead of the condenser coil, in order that some of the heat that would have been dissipated at the condenser can be used to heat water. Excess heat is always available in the summer cooling mode, and is also available in the heating mode during mild weather when the heat pump is above the balance point and not working to full capacity. Other ground-source heat pumps provide domestic hot water (DHW) on demand: the whole machine switches to providing DHW when it is required.
Water heating is easier with ground-source heat pumps because the compressor is located indoors. They generally have many more hours of surplus heating capacity than required for space heating, because they have constant heating capacity.
Similar to air-source heat pumps, ground-source heat pumps can reduce water heating consumption by 25% to 50%, as some have a desuperheater that uses a portion of the heat collected to preheat hot water, and also can automatically switch over to heat hot water on demand.
Relationship to Other Measures
This measure directly reduces the energy consumption for hot water. Depending on the amount of hot water usage in the building, the impact of this measure on energy use may vary.
The base case COP assumed for the heat pumps is 1.0 and the default improved case is 1.5 for Homes and 3.0 for Hospitality.
To demonstrate compliance, the design team must provide the following documentation to support their claims.
|Design Stage||Post-Construction Stage|
At the design stage, the following must be used to demonstrate compliance:
At the post-construction stage, the following must be used to demonstrate compliance:
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