13 Space heating and cooling

efficiency are determined for heat exchangers. New numerical results of fin efficiency for elliptical tubes are compared with published results for circular tubes. A relative fin efficiency gain of up to 18% is observed in the elliptical arrangement, as compared to the circular one. The efficiency gain, combined with the relative pressure drop reduction of up to 25% observed in previous studies show the elliptical arrangement has the potential for a considerably better overall performance than the conventional circular arrangement.

97103166 A comparative thermodynamic study of sorption systems-second law analysis Meunier, F. ef al. fnf. J. Refrig., July 1996, 19, (6), 414-421. Sorption systems appear to be potential candidates to replace vapour compression systems, in the light of the phasing out of CFCs. A study based on combined first and second law thermodynamic analysis of the different cycles has been conducted.

97103167 Continuous measurement of oil concentrations in refrigerating plants Ahnefeld, G. et ul. Ki Luft. Kultetech., December 1996, 32, (12), 545-54X. The author states that it is necessary to have precise knowledge of the quantities of lubricants in circulating refrigerants to ensure the correct functioning of a refrigerating installation. Some applications respond poorly to non-continuous methods of determining oil concentrations in refrigerants as set out in German standard DIN 8977. The paper reports that the amount of lubricant can be detected efficiently and reliably with the use of sonic speed sensors.

97103166 Correct freezing protection design Lubitz, R. Sonit. Heizi. Tech., Septemberl996, 61, (9), X7-88, 93-96. Advice is given for the design of pipes, fittings and heat exchangers in the circulation systems of heating and cooling plant to prcotect against freezing and corrosion. Charging, operation and monitoring, emptying and rinsing are all discussed.

97103169 The demise of the primary-secondary pumping paradigm for chilled water plant design Kirsner. W. Heal. Pip. Air Condit., November 1996, 68, (1 I), 73-78. In a two-year experiment with primary-secondary design of chilled water plants, the temperature difference of the chilled water returning to the campus plant is usually way below the design value for which the chillers and pumps were selected. Alternative design solutions are proposed for three problems outlined in the paper.

97103170 Desiccant assisted cooling-Coles supermarket Cheong. J. AfRAH .I., December 1996, 50, (12), 13-18. Hundreds of supermarkets in the USA have had desiccant dehumidification and cooling systems installed. The goal is to create a hybrid system combining desiccant technology in conjunction with an existing air conditioning unit to reduce energy consumption. A second objective was to model the energy consumption of the building using an energy modelling programme BUNYIP. The hybrid system has achieved lower humidity levels, but without any further cost reduction compared to conventional systems.

97103171 Desiccant cooling on the test stand Schiller. H. <‘lima Comm. Intemar., 11 November 1996, 30, (13), 31-36. (In German) Experimental investigations carried out in the Rud to investigate ways to make centralized air conditioning systems as energy efficient as possible, are investigated. The effect of the application of desiccant cooling (DEC) equipment has been studied by the Otto Meyer air conditioning laboratory, Hamburg.

97103172 Direct expansion cassettes Anon Clim Chuff Con., December 1996, (lo), 57-58. (In French) Details of direct expansion cassette air conditioners available on the French market.

97103173 Effect of reduced evaporator airflow on the high temperature performance of air conditioners Rodriguez, A. G. et al. Energy and Bldgs., October 1996, 24, (3), 195-201. Two residential-sized air conditioners in psychometric rooms at reduced evaporator airflows from 0 to 50% below that recommended by the manufacturer of each of the units are investigated. Performance of the units was quantified by the capacity, power coefficient of performance and sensible heat ratio.

97103174 Effectiveness of a thermal energy storage system using phase-change materials El-Dessouky, H. and Al-Juwayhel, F. Energy Convers. Mgmr, 1997, 38, (6), 601-617. Second law analysis is developed for a phase-change thermal energy storage system. A case study is presented to demonstrate the applicability of the model developed. The storage material considered was either paraffin wax or calcium chloride hexahydrate (CaC12, hH20), whereas the heat transfer fluid used was air or water.

97103175 An empirical model for sizing capillary tubes Bansal, P. K. and Rupasinghe, A. S. 497-505.

Int. .I. Refrig., November 1996, 19, (8),

The development of an empirical model to size adiabatic and non-adiabatic capillary tubes for small vapour-compression refrigeration systems is reported. The model is validated with previous studies over a range of operating conditions. The paper finds reasonable correlation with the R134a experimental data.

97103176 Energy conservation and domestic hot water con- sumption with decentralised district heating connections for individual dwellinas Breuer, W. and Loose, P. Heiz. Luft. Haustech.. February 1997, 48, (2). 20-30. (In German1 Decentialized connections with compact stations for individual dwellings are becoming increasingly important in district heating technology. Circulation heat losses can be avoided by the decentralized supply of domestic hot water (DHW). Using a typical block of flats, it was found that around 30% of the energy requirements for heating DHW can be saved. The associated cost savings approximately compensate for the additional investment in equipment. Therefore, the paper concludes that compact stations are an economic alternative to central district heating building substations.

97103177 Evaluating the potential of vortex-enhanced eva- porator performance for refrigeration applications Gentry, M. et al. ASHRAE Trans.. 1996, 102, part 2, SA-96-2-1, 361-36. A preliminary assessment of vortex-induced air-side heat transfer enhance- ment for refrigeration applications was carried out and the results are reported in this paper. Based on the findings of this assessment, it is suggested that longitudinal vortices may significantly improve air-side thermal performance. Subsequently, this would lead to smaller heat exchangers for a fixed duty or to better thermal performance for a fixed heat exchanger envelope. Further research to evaluate the to-scale performance of vortex generators under frosting conditions is recom- mended.

97103176 Evaluation of the dynamic performance of a hot water tank with built-in heating coil Yang, L. et al. Int. J. Energy Res., 21, (3), 265-274. For the production and storage of domestic hot water (DHW). hot water tanks with a built-in water-heating coil are commonly used in district heating house stations in Denmark. In this study, an evaluation of the dynamic performance of a hot water tank with built-in heating coil is carried out by applying a dynamic simulation programme which has been made previously, based on a simple dynamic model developed by the authors. System evaluation of the way in which system parameters affect the domestic hot water capacity and the average district heating water cooling for a given hot water tank is presented and discussed in this paper. The measures indicated by the evaluation results to be necessary in order to operate the hot water tank in an efficient way and to achieve significant cooling of the district heating water.

97103179 Experimental and numerical results in closed annular space heat transfer at low temperature Chatain, D. and Vallcorba, R. Cryogenics, 1997, 37, (4), 187-193. The heat transfer between two coaxial cylinders whose annular space was filled with helium gas at low temperature (6 K<T<20 K) was investigated. A cryostat was constructed and many experiments on the conduction/ convection heat transfer transition in closed annular spaces were conducted. Gas convection was observed as soon as a temperature difference exists between the two cylinders, even at low pressures. The experimental results are compared to numerical simulations.

97103160 Experimental study on a double-orifice two-stage pulse tube refrigerator Chen, G. et al. Cryogenics, 1997, 37, (5), 271-273. The basic structure of a two-stage pulse tube refrigerator is detailed with the introduction of a novel phase shifter termed a double-orifice. The machine was driven by a valved compressor and the on-off timing was controlled by a computer and solenoids. The lowest temperature achieved was 3.1 K at the cold end of the second stage.

97103161 Find that leak. Part 1 Hawkins H. AIRAH J., November 1996, 50, (II), 48-49. The four techniques employed to detect refrigerant leaks are: (I) bubbles, (2) sniffers, (3) ultrasound, (4) dye.

97103162 Flexibility of ammonia systems Clarke R. AIRAH J., August 1996, 50, (8), 29-31. The design and selection of ammonia refrigerating systems offer great flexibility. The refrigerating plant installed at the Ammonia Refrigeration Training Centre, Werribee, Australia is used as an example. The major components of the plant are detailed. A plant with only two compressors, one condenser and one high pressure receiver provides a combination of three operating system temperatures and five production area tempera- tures. One system comprises three refrigerant evaporating methods and four liquid refrigerant supply methods.

Fuel and Energy Abstracts July 1997 259