Commercial Water Heaters
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Introduction
Commercial water heaters are major energy consumers in many commercial facilities, accounting for about 11% of the total energy load on average. A hospitality facility may use up to 40% of its energy for heating water. In evaluating the water heating needs of your facility and the potential for improving energy efficiency, consider the facility's needs carefully, including time of use, amount of water, temperature range and flow rates.
Technology Options
Commercial water heaters are available in storage, instantaneous, indirect (unfired hot water storage tank), heat pump and tankless coil (heat recovery) configurations. Energy use varies by type: 75 to 500 kBtu/hr input for gas, 105 to 500 kBtu/hr for oil, and greater than 12 kW input for electric. Commercial water heaters include hot-water supply boilers as well. These are simply boilers configured to supply potable hot water rather than space heating.
Commercial facilities may require a complex distribution scheme using pumps and timers to deliver hot water to many users throughout a facility. Circulating pumps move heated water throughout an apartment complex or hotel so users can get instant hot water. Buildings with consistent water heating loads may use instantaneous water heaters while buildings with peak demands at specific times may use storage water heaters limiting their energy consumption.
The efficiency of an oil- or gas-fired commercial water heater is expressed as the thermal efficiency, stated as a percentage. A higher thermal efficiency indicates a more energy-efficient water heater. The thermal efficiency of a typical gas- or oil-fired unit is about 80%, but can range up to 95%.
Electric water heaters efficiencies do not vary significantly from 98% thermal efficiency. Another measure of energy efficiency for these units is the standby loss, expressed in percentage of loss per hour. Typical values range from 0.5% to 2.0%. The lower the value, the more efficient the electric water heater.
Heat-pump water heaters are a good option for electrical applications. Commercial heat pump water heaters are rated using a coefficient of performance (COP). COPs range from 1.5 to 3.5. The higher the COP, the better the energy performance.
Even though an electric water heater's thermal efficiency is high at 98%, gas- or oil-fired units may cost less to operate since fossil fuel prices are significantly lower than electricity prices. When considering water-heating equipment, analyze the cost-effectiveness of each possible solution to determine the best type of unit for your application.
Indirect water heaters may also be referred to as unfired hot water storage tanks. Since these devices are heated by an external source, their efficiency is determined by how well they are insulated. For the best efficiency, look for low heat-loss values. A typical maximum value is 6.5 Btu/h per square feet of tank area, or a minimum R-value of 12.5.
Efficiency Benefits
Perhaps the greatest energy efficiency opportunity lies in the design of the entire water heating system of a facility, not just the selection of the water heater. Large facilities may need to pump hot water throughout their buildings requiring pumps, valves and controls. Facilities with large peak loads may need a large storage system while facilities with consistent water heating loads may benefit form instantaneous water heaters. Facilities with large sources of waste heat, such as a large refrigeration condenser in a restaurant or hotel may benefit from an indirect system. Work at the system level to create an energy-efficient solution.
If using a gas-fired water heater, a more-efficient option is a gas-condensing water heater. This technology enables the fuel to transfer nearly all of its heat to the water, leading to 95% efficiencies or greater. Using gas-condensing water heaters may lead to energy savings up to 20%, depending upon the usage pattern.
Heat-pump water heaters may only use half the energy of electric resistance water heaters and provide a cooling/dehumidification benefit in some applications. Consider this water heating option if gas or oil is unavailable. If gas or oil is available, compare the relative operating costs of the heat pump to gas or oil equipment to find the best application for your facility.
Manufacturers
Numerous commercial water heater manufacturers make the products described above: American Water Heater Company, Bock Water Heaters, Bradford White Corporation, GSW Water Heating Company, Hamilton Engineering, Lennox Industries, Inc. and Lochinvar Water Heater Corporation.
For a downloadable directory of commercial water heaters, visit the Gas Appliance Manufacturers Association web site.
Purchasing Tips
Commercial water heating systems are complex and best left to professionals for design and application. When considering a new water heater, ask a professional to offer suggestions not only on the water heater, but also on the entire water heating system suitable for your facility's needs.
Emerging Technology
Condensing gas water heaters are increasingly popular, especially given the recent trend of rising gas prices. Commercial heat pump water heaters are making progress as well.