Water Heating Background

A wide range of water heater types may be encountered in office buildings. The following is a description of water heater types excerpted from a Guide to Water Heating, published by the American Council for an Energy-Efficient Economy (ACEEE):1

Storage tank water heaters are the most common type of water heater in the U.S. today. Ranging in size from 20 to 80 gallons (or larger) and fueled by electricity, natural gas, propane, or oil, storage water heaters heat water in an insulated tank. When you turn on the hot water tap, hot water is pulled out of the top of the water heater and cold water flows into the bottom. Without proper insulation, storage tank water heaters can be energy inefficient because heat is lost through the flue and the walls of the storage tank (this is called standby heat loss) even when no hot water is being used. New energy-efficient storage water heaters have higher levels of insulation around the tank and one-way valves where pipes connect to the tank, substantially reducing standby heat loss.

Demand water heaters, also known as instantaneous or tankless water heaters, eliminate the storage tank by heating water when hot water is needed. The energy consumption of these units is generally lower since standby losses are eliminated. Demand water heaters with enough capacity to meet household needs are gas or propane-fired. They have three significant drawbacks for some applications: Large simultaneous uses may challenge their capacity. They will not turn on unless the hot water flow is 0.5 to 0.75 gal/minute. Retrofit installation can be very expensive.

Heat pump water heaters are more efficient than electric water heaters because the electricity is used for moving heat from one place to another rather than for generating the heat directly. The heat source is outside air or air where the unit is located. Refrigerant fluid and compressors transfer heat into an insulated storage tank. Heat pump water heaters are available with built-in water tanks called integral units, or as add-ons to existing hot water tanks. A heat pump water heater uses one-third to one-half as much electricity as a conventional electric resistance water heater, and in warm climates they may do even better. Unfortunately, there are few sources for these products.

Indirect water heaters generally use the boiler as the heat source. In boiler systems, hot water from the boiler is circulated through a heat exchanger in a separate insulated tank. In the less common furnace-based systems, water in a heat exchanger coil circulates through the furnace to be heated, then through the water storage tank. Since hot water is stored in an insulated storage tank, the boiler or furnace does not have to turn on and off as frequently, improving its fuel economy. Indirect water heaters, when used in combination with new, high-efficiency boilers or furnaces, generally have the lowest operating costs among water heating technologies.

Solar water heaters use energy from the sun to heat water. Solar water heaters are designed to serve as preheaters for conventional storage or demand water heaters. While the initial cost of a solar water heater is high, it can save a lot of money over the long term. On a life-cycle cost basis, solar water heaters compete very well with electric and propane water heaters, though they are still usually more expensive than natural gas.”

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License