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.
EcoInnovation manufactures Eco-GFX (gravity film exchange) drainwater heat exchangers for commercial, industrial, and institutional applications; its residential model is called ThermoDrain. Warm drainwater flows through a section of copper drain pipe, around which is coiled smaller-diameter copper piping that carries cold water to the water heater or fixtures. The company claims to have improved efficiency of its Eco-GFX units by replacing air gaps between the copper pipes with conductive silver. These units can accommodate 1/2", 3/4", or 1" fresh water lines and 2", 3", or 4" drain lines. Eco-GFX comes in four types based on water flow needs from 4–7 gpm. Custom installations are available for large-scale commercial, industrial, and institutional applications.
Heat from domestic waste water, including residential and commercial washing machines, showers, dishwashers, and other appliances, can be recovered using a variety of heat exchangers. The most common, a gravity film heat exchanger (GFX), takes advantage of water’s surface tension. In these units, warm drainwater clings to the interior of a copper center pipe, around which a smaller-diameter copper pipe is coiled. Where the pipes meet, heat from the drainline warms the incoming water before it flows to the water heater.
These units can recover a significant amount of energy from homes but are particularly effective in commercial laundromats, restaurants, and other businesses that use a lot of hot water, as well as institutional facilities with concentrated showers.
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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