With energy-consuming equipment, such as water heaters and refrigerators, we have good data on energy consumption and can set clear standards accordingly. In some product categories—clothes washers, for example—Energy Star standards were adopted because those standards provide a high enough threshold to represent just the very top segment of the product market (less than 10%). In other product categories—e.g., refrigerators and dishwashers—we set a higher threshold than ENERGY STAR: for example, exceeding those standards by 10% or 20%. With lighting and lighting control equipment, certain generic products qualify, such as compact fluorescent lamps and occupancy/daylighting controls, while in other categories only a subset of products qualify. In some cases, products that meet the energy efficiency requirements are excluded, because of evidence of poor performance or durability. Microturbines are included here because of the potential for cogeneration (combined heat and power) that they offer.
The KC 1000 is a 1 M-Btu condensing, modulating water heater with efficiencies ranging from 93% to 99+%. Sealed combustion installation is an option. 20:1 modulation of the burner permits matching to load for energy savings. The system may be optionally equipped with a low NOx, SCAQM-certified burner (<30 ppm).
The most efficient fuel-fired water heaters include electronic-ignition gas-fired tankless (on-demand) models, direct-contact commercial water heaters, and advanced combination space- and water-heating systems.
Gas-fired condensing storage-tank type water heaters have fuel efficiencies greater than 90% and use a variety of types of insulation. Tankless water heaters have no standby losses, and some models have sealed combustion and no pilot lights. In combined or integrated systems, efficiencies are boosted by uniting space heating and/or cooling into a single system that includes water heating.
Other factors to consider include indoor air quality (in terms of combustion gases), particularly whether the system has sealed combustion with direct venting to the outdoors and/or enhanced combustion emissions controls (for NOx, particulates, etc.), and whether it is capable of continued operation in the event of a power outage. In almost every type of high-efficiency water heater there are issues of rate-of-use, climate, and maintenance that require consideration to make the appropriate selection for optimal results.
Commercial-sized water heaters listed here have thermal efficiency ratings of at least 96% for gas and 87% for oil, or have a high thermal efficiency along with additional environmental features such as sealed combustion. To date, neither CEE nor Energy Star has a commercial water heater standard.
Water heating accounts for about 17% of the energy consumed in homes, and some businesses—such as hotels and restaurants—have very high hot water demands. Providing energy-efficient hot water for these different uses can be accomplished using a variety of technologies. The most efficient fuel-fired water heaters include electronic-ignition gas-fired tankless or on-demand models, advanced combination space- and water-heating systems, and gas-fired condensing storage-tank type water heaters.
Tankless water heaters have no standby losses, and some models have sealed combustion and use condensing technology. Some models can be used as boilers for heating in very-low-energy buildings. In combined or integrated systems, efficiencies are boosted by uniting space heating and/or cooling into a single system that includes water heating, and some boilers provide domestic hot water.
A variety of heat exchangers are also used to heat water. Desuperheaters capture waste heat created by refrigeration and air-conditioning equipment in commercial, and some residential applications, but there have to be significant cooling loads for these products to be cost effective. And electric heat-pump water heaters pull heat from the air using compressors to evaporate and condense refrigerant in a closed loop, transferring that heat into water stored in an insulated tank. These units also cool and dehumidify surrounding air, so they need to be located appropriately. Heat can even be recovered from drain lines using gravity film heat exchanger (GFX) and other technologies.
Choice of water heater can depend on fuel, space, rate-of-use, climate, maintenance, and other factors. Note: combustion gases generated by some water heaters can impact indoor air quality, and refrigerants used in some heat pumps can impact the ozone. Electric-resistance water heaters are not included here because of the inefficiencies and fuel-source pollution inherent to electric power generation.
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