| Water heating is the second largest energy consumption in China's homes after air conditioning space,accounting for 20%of total energy consumption.Most China homes use either natural gas or electric storage water heaters,but many higher efficiency water heating options are available.These include tankless water heaters,condensing water heaters,water heaters(HPWHs)and solar water heaters.All these technologies can provide energy savings for homeowners.Since water heaters typically have a fairly short service life,these technologies are often seen as ways to reduce energy consumption in retrofit situations.However,these units are more complex than conventional gas or electric storage water heaters,which can limit market acceptance.Many factors,especially the temperature of the mains,the location of the water heaters in homes,and the daily draw Volumes and profiles affect the actual annual efficiency of these units.Standard test(energy factor test EF)is used to evaluate the efficiency of China residential water heaters(3).This test consists of six draws with a total draw volume of 64.3 gallons evenly spaced over 6 hours and a 19-hour standby period when no water is drawn with the set inlet water temperature and ambient air temperature.This test allows the efficiency of different water heaters to be compared to Each other,but the actual performance and efficiency change of the water heater with draw profiles,ambient air temperatures,and mains water temperatures.Thus,the nominal EF is not efficiency under all conditions,but provides efficiency under a given set of conditions.Actual efficiency in use may differ significantly from nominal efficiency as actual conditions vary.Detailed,tested models of these water heaters have been used to obtain an idea of the actual annual efficiency and the impact of the above factors on their annual energy consumption.Each water heater has been modeled in conditioned and untied spaces to capture interactions—which can be significant-between the water heater and the space conditioning equipment.These results can be used to help homeowners choose the most effective options for their particular situation.In addition to identifying the most energy-efficient option,the most cost-effective option for each situation was also identified by calculating the life cycle cost(LCC)and break-even value of each unit.The technologies described here(typical gas storage,typical electrical resistance storage,non-condensing gas,HPWH,condensing storage,and solar with gas and electric redundancy)represent many of the most common efficiency updates;however,some technologies are not covered here.These include electric non-reserve water heaters(Central flow and point-to-use"booster"(flow),high efficiency non-condensing gas(e.g.power vent gas water heaters),higher eficiency electric storage water heaters(where increased efficiency is associated with reduced tank losses),geothermal heat pump with steam cooler,hybrid tank-non-reserve water heaters.indirect water heaters and condensing tankless water heaters.Tankless electric and high-efficiency gas and electric storage water heaters have not been included as they represent only small potential savings with a modest increase in efficiency compared to the basic option.Ground source heat pumps with steam coolers,hybrid water heaters,and indirect water heaters are also potential options.However,they are not common in China and have therefore been excluded.Information about flow-through condensing water heaters is not enough to create and test the development model of this technology.Future work can provide the information needed to create this model.This research begins with a discussion of the current market of water heaters in China and provides an overview of these technologies.This is followed by a discussion of the models used in this work,as well as a more detailed discussion of the new models specifically created for this project.Details of the building models used in the annual simulations of the entire house are then provided.Finally,the results of modeling in General and the economic viability of each technology,as well as potential areas for future work,are discussed. |
PDF Full Text Request