ers are available. The following options are available to install in new or to retrofit older homes: > Storage (tank) water heaters are signifi- cantly more efficient than they used to be (check the specific model/manufacturer, as efficiency may vary based on fuel type and technology), but they’re still less ef- ficient than most demand-based systems due to standby heat loss and energy use.
> Instantaneous (tankless) water heaters though improperly named, according to Klein, because the heater doesn’t (usually) instantaneously begin with hot water, eliminate standby losses and can signifi- cantly reduce energy use. These systems heat water only when there is a call for hot water from the system. It’s critical with tankless water heaters to consider required hot water flow rates, and to en- sure (as with any system) that distances from the heater to the fixtures aren’t too great (or if they are, they’re adequately addressed by recirculation or supplemen- tal heating).
> Solar (and solar assisted) water heat- ing systems heat water using the sun’s energy. They can reduce energy use by up to 90% in some areas but are useful even in cloudy and northern climates. Remem- ber that the sun has its own time frame for providing energy, and the occupant’s water use is on a different clock. You’re likely to need a supplemental heater with your solar system, because at a minimum, you’ll want hot water at night, and the system may not accommodate your needs on its own.
> Heat pump water heaters use electricity to move heat rather than generating heat themselves. Ground source heat pumps, for example, move warm ground tempera- tures into the home in the winter to pro- vide heating and move warm indoor air out of the home in the summer to provide cooling.
> Combination units provide both space heating and hot water in one system, eliminating the need for two separate systems. These systems use a blower (which blows air over a hot water coil and into the home’s ductwork) or a hydronic radiant heating system (which uses
water piping installed under floors or in baseboards). It’s especially useful for those with limited space for mechanical sys- tems, and provides improved efficiency.
> Drainwater heat recovery systems do just that: recover heat from hot water that’s traveling down the drain via a simple wa- ter pipe coil that is fed back to the water heater. This reduces the amount of work the heater must do to get hot water to temperature. Since a significant amount of hot water in homes is used for showers, that’s a great location for a heat recovery system. However, residential systems are challenged because of lesser water flow and the need for storage tanks, which aren’t needed in commercial applications.
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GreenBuilder October 2010
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