Water heater efficiency

Refrigerators declined in efficiency following World War II due, apparently, to the substitution of lower-cost, lower-efficiency motors with improved thermal insulation to protect them from waste heat generation, and there is some evidence that water heater efficiency declined between the end of World War II and 1975, and that industrial dry-type transformers declined in efficiency between 1970 and 1993. 

Eventually, the cathodic protection may fail and consequently, the inner steel surface corrodes. One particular case is shown in Figure 8.23 for an old gas water heater and its pertinent sediment. The lifetime of the anode depends on the water temperature, the glass coating quality, and the water chemistry. Therefore, inspection of the anode must be done according to the manufacturer recommendations or experience in order to avoid corrosion in the interior of the vessel Apparently, a 5-year period after anode installation may be a good practice, but it depends on the water heater efficiency. If a water heater operates very efficiently, then the anode can last 10 or more years. 

Nonuniform corrosion or pitting corrosion frequently occurs on steel structures in seawater and in soil. Nonuniform and pitting corrosion easily lead to damage in tanks, pipelines, water heaters, ships, buoys and pontoons, because these structures lose their functional efficiency when their walls are perforated (see Chapter 4). 

But an ideological shift in Congress disrupted this process. In the 104th Congress, industrial opponents of appliance efficiency standards found sympathetic support, and passed a one-year moratorium on appliance efficiency standards in 1995. The moratorium held back DOE efforts on appliance standards for nearly two years. The refrigerator standard that was to be issued early in 1995 was delayed until 1997, and the effectiveness date set hack three years until 2001. Progress toward new standards on ballasts, water heaters, air conditioners, clothes washers, and other products was delayed. 

Furnaces and boilers sold today must by law have annual fuel utilization efficiency of at least 78 to 80 percent. Gas water heaters operating this way as space heaters are equivalent to the efficiency of pre-1992 furnaces and boilers which had space heating efficiencies typically in the mid-60 percent range. However, the combined efficiency for space and... 

The U.S. Department ofEnergy develops test procedures for efficiency measurements and sets minimum efficiency standards for furnaces, boilers, and water heaters. Information on energy efficiency of buildings and equipment is available from the DOE. 

Summary of Typical Water Heater Costs and Efficiencies... 

The first instantaneous water heaters which started appearing in the 1890s when gas or liquid fuels started becoming available, were un-pressurized. The first models had no automatic controls and vei"y limited safety features. Some early models were more efficient than standard modern gas-fired water heaters. 

The tank is typically about sixteen inches in diameter and about four to five feet tall. The top of the tank is domed upward and the bottom of the tank is also domed upward in a concave manner. The outside of the tank is insulated with a polyurethane foam insulation that is squirted into the gap between the tank and a thinner sheet metal jacket. The polyurethane is made of two different components that react and harden when mixed. Included in the mixture is a blowing agent that causes the polyurethane to expand in a foam-like manner. Prior to about 1980, water heaters were insulated with fiberglass insulation. The foam insulation process was developed to allow automation and increased manufacturing speed and reduced costs. A side benefit was improved insulating ability leading to a slight increase in efficiency. 

Average efficiency of new gas-fired water heaters has increased from an estimated 47 percent in the mid-1970s to about 56 percent in 1999. Over the same period the efficiency of electric water heaters has risen from about 75 percent to 86 percent. Revised efficiency standards were expected to be adopted during 2000. 

Energy factor is a measure of average service efficiency at a specified condition and hot water draw pattern. It includes the effects of both standby losses and rccnvei y efficiency of the water heater. Currently, water heaters are shipped from the manufacturers with thermostats set at 120°F (48.9°C) to reduce the risk of scalding. This is a drop from values of 140°F (60°C) that were reported from the early 1970s. 

Efficient models of water heaters have thicker insulation, up to three inches thick, on some of the most efficient electric water heaters. Another means to increase efficiency is installing heat traps, or anti—convection devices, on the inlet and outlet pipes. Standard heat traps consist of short pipe nipple containing a small plastic ball. On the inlet side the ball is lighter than water and floats up to seal the inlet pipe. On the outlet side the ball is heavier than water and sinks against the seal. This prevents the heated... 

Gas-Fired water heaters are also made more efficient by a variety of designs that increase the recov-ei y efficiency. These can be better flue baffles multiple, smaller-diameter flues submerged combustion chambers and improved combustion chamber geometry. All of these methods increase the heat transfer from the flame and flue gases to the water in the tank. Because natural draft systems rely on the buoyancy of combustion products, there is a limit to the recovery efficiency. If too much heat is removed from the flue gases, the water heater won t vent properly. Another problem, if the flue gases are too cool, is that the water vapor in the combustion products will condense in the venting system. This will lead to corrosion in the chimney and possible safety problems. 

Flue dampers that block the flue when the burner is not firing increase the efficiency of gas-fired water heaters. These can operate electrically or thermally. Because gas-fired water heaters lose so much heat up the flue during standby periods, this can provide significant savings. These are readily available on larger water heaters used in commercial settings but haven t been applied in the residential market because of their cost. 

First domestic gas water heater to work efficiently is developed. 

Where extraction turbines are employed, it is most efficient to operate at the lowest level of condensing possible (the highest level of extraction). This occurs when steam from the turbine is extracted and directed by various takeoffs, either to air or water heaters or to industrial processes requiring steam. This practice occurs because no heat is lost from the steam flowing from the throttle to the extraction takeoff (whence it can be delivered for beneficial use by the industrial process), whereas over two-thirds of the heat flowing from the throttle to the surface condenser is ultimately rejected, so efficiency suffers. 

Determine the efficiency and power output of a regenerative Rankine cycle using steam as the working fluid and a condenser pressure of 80 kPa. The boiler pressure is 3 MPa. The steam leaves the boiler at 400° C. The mass rate of steam flow is 1 kg/sec. The pump efficiency is 85% and the turbine efficiency is 88%. After expansion in the high-pressure turbine to 400 kPa, some of the steam is extracted from the turbine exit for the purpose of heating the feed-water in an open feed-water heater, the rest of the steam is reheated to 400°C and then expanded in the low-pressure turbine to the condenser. The water leaves the open feed-water heater at 400 kPa as saturated liquid. Determine the steam fraction extracted from the turbine exit, cycle efficiency, and net power output of the cycle. 

Plot the sensitivity diagram of cycle efficiency versus open feed-water heater temperature. 

Consider a steam power plant operating on the ideal regenerating Rankine cycle 1 kg/sec of steam flow enters the turbine at 15 MPa and 600°C and is condensed in the condenser at lOkPa. Some steam leaves the high-pressure turbine at 1.2 MPa and enters the open feed-water heater. If the steam at the exit of the open feed-water heater is saturated liquid, determine (1) the fraction of steam not extracted from the high-pressure turbine, (2) the rate of heat added to the boiler, (3) the rate of heat removed from the condenser, (4) the turbine power produced by the high-pressure turbine, (5) the turbine power produced by the low-pressure turbine, (6) the power required by the low-pressure pump, (7) the power required by the high-pressure pump, and (8) the thermal cycle efficiency. 

Determine the power required by the compressor, power required by pumps 1 and 2, power produced by turbines 1, 2, and 3, rate of heat added by the nuclear reactor, net power produced by the Brayton gas turbine plant, net power produced by the Rankine plant, rate of heat removed by coolers 1 and 2, rate of heat exchanged in the heat exchanger, rate of heat added in the gas burner, mass rate flow of helium in the Brayton cycle, mass rate flow of steam extracted to the feed-water heater (mixing chamber), cycle efficiency of the Brayton plant, cycle efficiency of the Rankine plant, and cycle efficiency of the combined Brayton-Rankine plant. 

Why do hot water heaters lose their efficiency quicker in households with hard water ... 

Swimming pool and rooftop water heaters can convert solar energy into heat with an efficiency of 50-70%. The efficiencies of electricity-generating solar collector systems are much lower. They operate at efficiencies from 5% to about 30%. 

The reformed gas leaves the furnace at a high temperature where high grade heat is recovered successively to a reformed gas boiler, steam superheater process feedstock heater and boiler, feedwater heater. The reformed gas then passes to the distillation area where low grade heat is efficiently recovered via column reboilers and a demineralized water heater. 

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