Electric Heat Pump Water Heaters

Electric Heat Pump Water Heaters

Electric Heat Pump Water Heaters use the surrounding air to heat water in a storage tank rather than generating heat directly. Because of this transfer of heat, these systems are extremely energy efficient, using only one-third to one-half as much of electricity normally needed for electric resistance heaters. Considering that water heating typically accounts for 15%-25% of your total home energy costs, investing in an efficient model will help you conserve natural resources while lowering your annual water-heating bill.

Quick Links:
How to buy?
What are my Options?
Energy Saving Tips
What do I ask a contractor?
How much can I save?

How to buy?

To size an electric heat pump water heater properly, you must determine its First Hour Rating (FHR). The FHR accounts for the effects of tank size and the speed at which cold water is heated.

To determine the projected size of the water heater, you should consider how much hot water is used during the busiest time of the day, the size of your house, and the size of your family. Below is a worksheet using the factors that will produce your FHR. By taking your specific FHR into account, you can select an appropriate sized system
 

Source: Gas Appliance Manufacturer's Association.
*The above worksheet assumes no water conservation measures.

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What are my Options?

Electric Heat Pump Water Heaters are available as integral units to be coupled with an existing electric resistance system or as one-piece systems with their own storage tanks. If you currently have an electric resistance heater, retrofitting your system will reduce the amount of electricity needed to generate hot water and thus lower your utility bills.

Ambient air heat pump water heaters take heat from the room and transfer it to the water in the storage tank. As the water is heated, cool air is released back into the room as a byproduct. These models are best suited to warmer climates.
Exhaust air heat pump water heaters capture heat from air that passes through a home's ventilation system.
Warm air from inside the home passes across the heat pump coil, where it transfers heat to the hot water. Cool air is exhausted to the outdoors as a byproduct. The exhaust fan can be reversed if cooling is preferred.

Exhaust air heat pump water heaters function best in homes that can benefit from additional ventilation.

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Energy Saving Tips

The efficiency of the model is measured by the Energy Factor (EF). The EF is an indicator of how much fuel was used in relation to the amount of hot water actually produced and used from the tap on a typical day. This figure is formulated based on:

Recovery efficiency: how efficiently the heat from the energy source is transferred to the water.
Standby losses: the percentage of heat loss per hour from the stored water compared to the heat content of the water (water heaters with storage tanks).
Cycling losses: the loss of heat as the water circulates through a water heater tank, and/or inlet and outlet pipes
Electric Heat Pump Water Heaters require significantly less electricity than standard electric water heaters, and can thus be up to three times more efficient. These systems usually have Energy Factors of 2.0-2.5.

Insulation:

Adding an insulating blanket will increase efficiency. A blanket ranges from only $10-20.
Insulating your water pipes will reduce the energy losses from the tank to the faucet. When installing, use plastic or rubber foam 3/4 inch coverings.

Lowering the Thermostat:

Use the lowest temperature setting that can provide your home with adequate hot water (generally 120°F or between the “low” and “medium” settings).
Lowering the setting by 10°F results in 3-5% saving in energy costs.
Thermostat dials can often read inaccurately. Adjust for the right temperature at the point of use.
If you are traveling, turn the thermostat to either the lowest setting or turn the heater off.

Heat traps:

These devices prevent the unintended hot water flow out of the tank, and will save you from $15-$30 annually on your water heating bill by stopping the convection of hot water out of the tank and into the supply piping. Many new systems have such trapping devices already installed.

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What do I ask a contractor?

These systems are generally easy to install, using the existing water and electrical connections.

Electric heat pump water heaters should be installed in a relatively open space so the system has access to ambient air. Approximately 1,000 cubic ft of air space is needed.
Installation locations should remain in the 40º–90ºF temperature range throughout the year.
When hiring a contractor, be sure to ask for references and cost estimates.
Maintenance.
Electric heat pump water heaters require slightly more maintenance than other electric models. Two hours of work per year is recommended to ensure that the system runs smoothly. This includes periodic cleaning of heat exchanger coils and evaporator filter.

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How much can I save?

Depending on size and energy factor, electric heat pump water heaters range in price from $600-$2,000. Heat pumps designed to draw heat from ambient air are generally less expensive.

Installation costs vary from about $300-$700 a unit. You will gain an immediate savings in energy costs: The payback period is usually only 2-5 years.

Payback Analysis

Source: http://www.aceee.org/consumerguide/waterheating.htm#lcc
1. Purchase costs include our best estimates of installation labor and do not include financial incentives.
2. Operating cost based on hot water needs for typical family of four and energy costs of 9.5¢/kWh for electricity, $1.40/therm for gas, $2.40/gallon for oil.
3. Future operating costs are neither discounted nor adjusted for inflation.
4. Estimates for tankless gas water heaters are based on the federal EF rating method, which may over-estimate the efficiency of tankless water heaters in houses.

Recent Developments and Newly Designed Models in the News
GE Hybrid Electric Water Heater. This unit will provide the same hot water homeowners are accustomed to, but requires only about half the energy to produce it. Based on the standard sized tank water heater, using about 4800 kWh per year, the new GE Hybrid Electric Water Heater is designed to use about 2300 kWh per year. This could mean savings of approximately $250 per year, and $2,500 over a 10-year period based on 10 cents per kWh.

It s expected to be available to purchase in 2009 for approximately $400 more than a standard 50-gallon tank electric water heater.

AirTap A7 Retrofit Water Heater from AirGenerate. Measuring 18" wide by 14" deep by 14" high, this system weighs only 48 pounds, and easily fits on top of a standard water heater. Other features include:

A list price of $499.
Output of 7,000 Btu/hour
First-hour rating of 42.5 gallons
Maximum water temperature of 135°F
Energy Factor of 2.11
With the release of this compact efficient system, Harvey Sachs, the buildings program director at the American Council for an Energy-Efficient Economy, said that consumers should be more receptive to electric heat-pump water heaters. “The economic savings potential is so much greater than before, with the run-up of energy prices,” said Sachs.

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