Match the technology to the application. You may be a good candidate for an HPWH if:
- Your business needs to replace an electric water heater
- You’re looking to add air conditioning to spaces where it would normally be cost-prohibitive
- Natural gas is not available in your area
- You require a large steady flow of hot water throughout the day
Because HPWHs produce cool, dry air as a by-product of heating water, the best applications are those that take advantage of both outputs simultaneously. Therefore, HPWHs are especially well-suited for commercial sector applications where demand for hot water is relatively constant and the need for cooling or dehumidification is continuous. Commercial laundries fit this description, as do many commercial kitchens and even fast-food restaurants, particularly in climates where space cooling is essential. The best applications tend to be buildings in hot and humid climates because cold, dry air is produced whenever there is a demand for water heating.
Pick the right size. Picking the right size HPWH system requires estimating daily hot water needs in gallons, just as you would size any other water heating system. However, for HPWH systems, an allowance must be made for high peaks in hot water demands. HPWH systems are quite efficient, but the heat production is slow and steady. A key factor to consider is the rate of hot water production, listed in product literature as the “recovery rate” and measured in gallons per hour. Recovery rates are typically half those of traditional electric water heaters, but the instantaneous power consumption (demand) is typically 40 to 70 percent less. Accordingly, electric demand savings with HPWH systems can be substantial, but only if the use of backup electric resistance heat is quite low.
If you’ll be using HPWH systems in applications that require considerable hot water over a short time, choose either a larger tank than a traditional hot water system has or an HPWH system with a high recovery rate. Either choice will help smooth over peak hot water loads.
Look for high energy efficiency. The Energy Star program establishes appliance efficiency specifications above the federal standards. Residential equipment that meets these specifications is awarded the Energy Star label, which helps consumers readily identify high-efficiency products. Check the Energy Star list of HPWHs to find the most efficient models (at this time, only integrated HPWHs qualify for the Energy Star label).
Perform a quick cost/benefit estimate. The cost-effectiveness of an HPWH is heavily weighted by utility rates and water use. Consistent water loads and a need for year-round cooling and dehumidification make HPWHs a more attractive option for many types of businesses. The initial cost of a commercial HPWH is much greater than an electric or gas-fired boiler, but the annual savings are large and paybacks typically range between two and three years. Water inlet and setpoint temperatures, HPWH location, air-conditioning and dehumidification loads, and water consumption rates are some of the parameters a commercial designer takes into account. Because estimating commercial HPWH economics is a complex process, it’s a good idea to contact a vendor or system designer to see if an HPWH is appropriate for your application.
If you have a smaller hot water load, it is possible to use a residential-size HPWH. However, for facilities that currently use electricity to heat water, the economics are typically attractive only if they consume at least 60 gallons of hot water per day. For facilities that currently use natural gas water heaters and have higher consumption levels, HPWHs can be cost-effective if the price of gas is high and the price of electricity is low. See Table 1 and Table 2 for cost estimates of a residential-size HPWH versus an electric water heater and a gas water heater.
Table 1: Cost-effectiveness of a residential-size HPWH versus an electric resistance water heater
Heat pump water heaters (HPWHs) produce significant energy savings compared to an electric resistance water heater. Those savings can yield short payback periods for the incremental retail cost in some cases.
Table 2: Cost-effectiveness of a residential-size HPWH versus a natural gas tank water heater
When natural gas prices are high and electricity prices are low, HPWHs can make economic sense when compared to gas water heaters.