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Domestic Hot Water (DHW)

There are many different types of water heaters for houses. In addition to the efficiencies of individual water heating technologies, usage characteristics and hot water distribution play a large role in determining the total energy use due to hot water. Because DHW-related energy use is so occupant driven, for monitoring unoccupied houses it may become necessary to implement scheduled draw profiles.

Water Heaters

Domestic Hot Water (DHW) use accounts for about 12% of total household energy use in the United States, making it the third largest energy-use category, after heating and cooling. There are a wide variety of water heating technology options available to homeowners, but gas and electric tank-type water heaters are the most common. In addition to the common gas and electric water heaters, there are also tankless, or instant, water heaters in both gas and electric.

Hot Water Distribution

The hot water distribution system in a house introduces heat losses to the domestic hot water system as a whole, but the magnitude of those losses can vary significantly depending on the geometry and insulation added to the pipes. The total losses introduced by the distribution system can vary from 2% to 25%. Adding pipe insulation is an easy, inexpensive measure, but is not practical in retrofits. In fact, any efforts to improve the hot water distribution system in a house are truly only applicable to new construction.

There are two main geometry categories that are commonly used in homes; trunk and branch, and manifold or home-run systems.

Simulated Domestic Hot Water (DHW) Draw Profile

To evaluate advanced domestic hot water (DHW) systems performance, generating and implementing realistic domestic hot water draw profiles are many times required in unoccupied homes. There are different types of hot water draw profiles and controls mechanisms for testing different components of interest in the entire hot water system.