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A thermoelectric power cycle (TPC) has the capability of converting a part of the Joule losses to utilizable electrical energy. The effect of this capability on the total efficiency of a TPC is examined by comparing it with conventional d.c. power cycle (DCPC). For reversible heat exchange and zero heat leakage, the total efficiency of the TPC is always greater than that of the DCPC. With heat...
The power output and thermal efficiency of a finite-time, optimized, extra-terrestrial, solar-radiant Stirling heat engine have been studied. The thermodynamic model adopted is a regenerative gas Stirling cycle coupled to a heat source and heat sink by radiant heat transfer. Both the heat source and sink are assumed to have infinite heat-capacity rates. Expressions are obtained for optimum power...
In Ontario, potential contributions of solar domestic hot-water (SDHW) heating to air-emission mitigation have been identified. The provincial utility Ontario Hydro does not include solar heating in its current demand-side management plans because of the capital cost barrier. We present results of life-cycle cost analyses for installing a typical solar system in single-family dwellings in Toronto...
We present a procedure for optimization of the first and second reheat pressures in thermal power plants. The analysis is based on the first-law efficiency and exergy-balance equations. For analysis, the plant is divided into two main units (the steam generator and the turbine cycle). The results indicate that a range of first and second reheat pressures satisfy different constraints. Improvement...
The automatic hot-gas by-pass technique is applied to reduce the capacity of refrigeration and air-conditioning systems when operating at part load. In this scheme, hot gas from the compressor is extracted and injected into the suction side of the compressor through a hot-gas by-pass valve. Thus, the refrigerant gas by-passes the evaporator and reduces the system capacity. In this paper, three hot-gas,...
Energy edge (EE) was a research-oriented demonstration project that began in 1985; 28 buildings were constructed to use 30% less electricity than a hypothetical simulated baseline building. Average energy savings for 18 buildings evaluated with post-occupancy tuned simulation models were less at 17%. Only six met the cost of conserved (CCE) energy of 5.6 /kWh for the total package of energy-efficiency...
We have considered the general case of a collector with four reflectors. An analytical model is developed for study of the effect of an individual reflector on the collector. Reflectors R-1, R-2, R-3, and R-4 face south, north, west, and east, respectively. For a collector with two reflectors R-1 and R-2 on the southern and northern sides, up to 44% enhancement is achieved in the solar gain for...
Criteria are described for working fluids in high-temperature heat pumps (HTHPs). Hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs) and hydrofluorinated ethers (HFEs) are being considered as working substances for HTHPs. Comparisons are made in terms of ecological and thermophysical properties for working fluids. Three HCFCs (R-123, R-235ca and R-244ca), two HFCs (R-152 and R-245ca) and...
The possibility of cooking during off-sunshine hours using phase change materials (PCMs) as storage media has been investigated experimentally. For this purpose, two concentric cylindrical vessels were constructed with 2-cm gaps. This gap was filled with stearic acid or magnesium nitrate hexahydrate as the PCMs. The cooker performance is evaluated in terms of charging and discharging times of the...
The designs of heating and cooling systems are typically based on heat transfer under steady-state conditions. In desert regions, however, there are large changes during a 24-hour period and the steady-state approach becomes inapplicable. An analysis of transient heat transfer through insulated walls is presented for three different cases. The results indicate that cooling loads for buildings are...
A method for setting up a reference year of reduced temperature data, proposed by Klein and Erbs, has been applied by us to 29 European locations for which an official test-reference year is available. This reference year of reduced temperatures may be utilized in computer programs for analysis of the thermal behaviour of buildings. The effectiveness of the method has been tested by calculating...
We analyze U.S. residential water use and water-heater energy use and apply this analysis to investigate water and energy savings associated with U.S. equipment efficiency standards currently in force.
In this paper, we introduce the combination of an energy-process model with the geometric distributed lag demand, called the energy-GDL process model, as well as its solution technique. In an energy-GDL process model, the demand is represented by a function of the prices not only in the current time period but also in previous time periods, based on the geometric, distributed lag structure. The...
Several years of measured data on global and diffuse radiation and sunshine duration for 40 widely spread locations in the latitude range 36° S to 60° N are used to develop and test models for estimating monthly-mean, daily, diffuse radiation on horizontal surfaces. Applicability of the clearness-index (K) and sunshine fraction (S) models for diffuse estimation and the effect of combining several...
Rapid growth in power electronic equipment (PEEs) implies that in about 10 years, more than 50% of electric utility output will be consumed by PEEs. While PEEs yield benefits of large energy savings and product reliability, they cause the problem of harmonics. Harmonics deteriorate power quality, produce metering errors, increase reactive power, and exacerbate line losses and heat in transmission...
A new mathematical model shows that a direct subsidy for an improved wood stove is not the best way to promote its use in rural India. The possibility of multiple uses of woodfuel and its sustainability are also discussed.
We have examined the thermodynamics of the carbothermic reduction of metal oxides in either nitrogen or argon atmospheres. The reaction, which is given generally by (where the M denotes metal) M x O y + C (+ N 2 ;) → {M x N y , M x C y , M} + CO, is highly endothermic and proceeds at temperatures from 1300 to 2350 K for the...
Electricity consumption in minor (or miscellaneous) appliances is growing rapidly in the domestic sector in the UK. Often minor appliances are substituting for major ones, as in the proliferation of small cooking devices. In this paper we compare ownership and consumption of minor appliances in the UK to that in the US, and conclude that minor appliances may deliver energy services more efficiently...
A generic approach is presented for estimating the energy-intensity of manufacturing processes. The major improvements in this technique over conventional methods of estimating energy-intensity in the manufacturing sector are the use of energy-intensity measures that are product-oriented and are based on physical measures of product output. The method is used to estimate electric intensities in...
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