In order to decrease the use of petroleum and release of greenhouse gases such as carbon dioxide, the efficiency of transportation vehicles must be increased. One way to increase vehicle efficiency is by extending the electric-only operation of hybrid electric vehicles through the addition of batteries that can be charged using grid electricity. These plug-in hybrid electric vehicles (PHEVs) are currently being developed for introduction into the U.S. market. As with any consumer good, cost is an important design metric. This study optimizes a PHEV design for a mid-size, gasoline-powered passenger vehicle in terms of cost. Three types of batteries, Pb-acid, NiMH, and Li-ion, and three all-electric ranges of 10, 20, and 40 miles (16.1, 32.2, and 64.4 km) were examined. System modeling was performed using Powertrain Systems Analysis Toolkit (PSAT), an Argonne National Laboratory-developed tool. Performance constraints such as acceleration, sustained grade ability, and top speed were met by all systems. The societal impact of the least cost optimum system was quantified in terms of reduced carbon emissions and gasoline consumption. All of the cost optimal designs (one for each combination of all-electric distance and battery type) demonstrated more than a 60% reduction in gasoline consumption and 45% reduction in CO2 emissions, including the emissions generated from producing the electricity used to charge the battery pack, as compared with an average car in the current U.S. fleet. The least cost design for each all-electric range consisted of a Pb-acid design, including a necessary battery replacement of the battery pack twice during the 15 year assumed life. Due to the cost of the battery packs, the 10-mile all-electric range proved to be the least costly. Also, this system saved the most carbon dioxide emissions, a 53% reduction. The most fuel savings came from the PHEV40 system, yielding an 80% reduction in gasoline consumption.
Many of the refrigerants that have been examined as replacements for hydrochlorofluorocarbons (HCFCs) are zeotropic mixtures. The temperature of a zeotropic mixture does not remain constant throughout a heat exchanger, and zeotropes often exhibit a nonlinear temperature/enthalpy relationship. These factors contradict some assumptions that are made in deriving the Log Mean Temperature Difference (LMTD), a calculation that is used to compute the size of a heat exchanger (UA). Since the temperature is not an easily-determined function of enthalpy, in order to find a more accurate UA, the heat transfer process must be discretized and the properties determined at each point. An ammonia-water mixture and synthetic mixtures that are being studied as HCFC-22 replacements are analyzed. In each case, the actual UA is compared to the UA found using the LMTD. It is found that these errors can cause a heat exchanger to be undersized by as much as a factor of fifty.
The objective of this study is to evaluate the solid sorption technology for residential cooling applications. The solid sorption technology uses natural gas as the primary energy source for compressing and circulating the refrigerant in the air-conditioning system. The system delivered 6.7 kW of cooling at 35°C outdoor temperature. The cooling gas COP was 0.32 at 27.8°C outdoor temperature. An ammonia vapor compression system was established and tested by operating a steady state mechanical compressor in place of the cyclic thermal compressor to evaluate and verify the cyclic performance of the sorption system. The system’s thermal compressor efficiency was almost one-third that of the mechanical compressor based on the input power of the primary energy source for each compressor. The testing revealed that the cooling capacity at the air handler is about 1.75 kW less than that at the ammonia/glycol evaporator chiller due to parasitic power gains.
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