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Water heating refers to the heating of water. This can be done using various methods.
Perhaps the simplest method is to use the same heating system as used for the heating of the house. The energy for the heating hence comes from gas or firewood. A heat exchanger is used to accomplish this.
Solar water heating can also be incorporated (often as a additional technology). Solar water heaters are widely useful because they can save large amounts of fuel. Also, small changes in lifestyle, such as doing laundry, dishes and bathing on sunny days, can greatly increase their efficiency. To further increase the efficiency of water heating, either with or without solar, hot water heat recycling units recover heat from drainlines thereby increasing water heating capacity and reducing the energy used to heat water.
The basic trick in a solar water heating system is to use a well-insulated holding tank. Some systems are vacuum- insulated, acting something like large thermos bottles. The tank is filled with hot water on sunny days, and made available at all times. Unlike a conventional tank water heater, the tank is filled only when there is sunlight.
Good storage makes a smaller, higher-technology collector feasible. Such collectors can use relatively exotic technologies, such as vacuum insulation, and reflective concentration of sunlight.
Current practical, comfortable water-heating systems combine the solar heating system with a thermostatic gas-powered flow-through heater, so that the temperature of the water is consistent, and the amount is unlimited. This again reduces life-style impacts at some cost in autonomy. Ideally, this would be a cogeneration system that produces other energy, and uses locally produced fuels.
Heat recycling, cogenereration and solar pre-heating can save 50-75% of the gas otherwise used. Also, some combinations provide redundant reliability by having several sources of heat.
- See Planet Mechanics documentary; episode "Heavy Metal House"