Many small commercial operations have a limited need for hot water, so they have a small industrial water heater. Electric heaters cannot always be replaced at an economical cost with gas-fired equipment in such circumstances, to take advantage of the high cost of electricity with respect to natural gas heating. The electrical equipment is often less expensive for builders to install and may have been chosen when electricity was less expensive.
Also, with the 20-year life expectancy of a water heater, the equipment may not yet have been replaced with a more efficient device. Hence, as much as the small business person may want to convert to gas heating, the cost can be prohibitive, even when electricity demand savings are factored into the payback analysis.
An alternative worth considering is to use the existing water heater tank as a storage vessel and to circulate the tank volume through a small gas-fired boiler. Packaged units are available with the necessary controls, safety features, and circulating pump integral to the system. For a retrofit, this option is cheaper than installing an entirely new water heater and makes the advantages of gas heating available right away. The cost of gas is not only lower but system recovery (e.g., the time needed to replenish the hot-water supply after it is all used up) can be up to three times faster. In many instances, the storage capacity can even be reduced, with the associated reduction in standby losses.
Another option is to tap the tank for water to the facility air-handler coils, replacing electric resistance heating there as well. (Large buildings circulate hot and cold water in piping to air handler units and/or radiators.) An advantage of this arrangement is that having the spare capacity of the water storage tank available means the hydronic system has the ability to warm up a large volume of air very quickly first thing in the morning when peak electricity use by the HVAC equipment occurs in the winter. The peak use for domestic hot water occurs later in the day, giving the system time to generate the necessary volume of hot water in the storage vessel.
Future Tech!
How can these ideas be applied to residential systems? In the summer, the AC rejects heat to the air at the outside condensing unit. Why not reject some or all of that heat to water, via auxiliary coils and a small circulating pump ~ storing the thermal energy in the hot water tank? There are many heat pump water heaters available, and some AC manufacturers (Daikin) also offer a hybrid system to heat water, too, using the house heat pump.
Hot Spot has an add-on system, a heat recovery unit, that extracts heat from the refrigerant coils of your AC system, and uses that heat to heat the domestic water supply ~ or even the swimming pool water.
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Excerpted from Going Green, available as an eBook at this list of eBook retailers online.
