James R. Sand

Modelled performance of non-chlorinated substitutes for CFC11 and CFC12 in centrifugal chillers☆

Abstract A number of partially fluorinated alkanes and ethers were identified from earlier technical publications and from a joint Electric Power Research Institute/Environmental Protection Agency (EPRI/EPA) project as potential alternatives for chloroflurocarbon (CFC) and hydrogen-containing CFC refrigerants. These larger molecules, by virtue of their more elaborate structure, have larger vapour phase heat capacities ( C p s) and larger molecular weights than currently used refrigerants, which result in decreased volumetric capacities and greater flash gas losses in simple cycle applications. The compounds were fitted to the Lee-Kessler-Plocker and Carnahan-Starling-DeSantis equations of state, and refrigerant property routines based on these equations were used to simulate their performance in a single-stage centrifugal chiller as pure refrigerants and nearly azeotropic refrigerant mixtures. Consideration was given to the effects of acoustic velocity in the refrigerant, rotational mach numbers, the application of superheat prior to the compressor inlet to avoid ‘wet isentropic compression’, and liquid subcooling before isenthalpic expansion. Results indicate that several chlorine-free compounds give modelled chiller performance comparable to R11 and R123 and better than R12 and R134a. Blends of these refrigerants may be required to mitigate the inflammability of alternatives that show the best performance. Modifications to the basic chiller cycle — such as liquid subcooling and suction gas superheat — may offer unique advantages for more complicated, larger refrigerant molecules. An algorithm based on molecular bond energies and vapour phase C p s was used to estimate the flammability of these alternatives and of blends made from them. Depending on desirable and permissible deviations from the currently used chiller operating conditions and on the acceptability of flammable refrigerant combinations, ideal coefficients of performance comparable to R11 and 5–10% better than R12 are indicated.

Total Environmental Warming Impact (TEWI) Calculations for Alternative Automotive Air-Conditioning Systems

The Montreal Protocol phase-out of chlorofluorocarbons (CFCs) has required manufacturers to develop refrigeration and air-conditioning systems that use refrigerants that can not damage stratospheric ozone. Most refrigeration industries have adapted their designs to use hydrochlorofluorocarbon (HCFC) or hydrofluorocarbon (HFC) refrigerants; new automobile air- conditioning systems use HFC-134a. These industries are now being affected by scientific investigations of greenhouse warming and questions about the effects of refrigerants on global warming. Automobile air-conditioning has three separate impacts on global warming; (1) the effects of refrigerant inadvertently released to the atmosphere from accidents, servicing, and leakage; (2) the efficiency of the cooling equipment (due to the emission of C0{sub 2} from burning fuel to power the system); and (3) the emission of C0{sub 2} from burning fuel to transport the system. The Total Equivalent Warming Impact (TEWI) is an index that should be used to compare the global warming effects of alternative air-conditioning systems because it includes these contributions from the refrigerant, cooling efficiency, and weight. This paper compares the TEWI of current air-conditioning systems using HFC-134a with that of transcritical vapor compression system using carbon dioxide and systems using flammable refrigerants with secondary heat transfer loops. Results are found to depend on both climate and projected efficiency of C0{sub 2}systems. Performance data on manufacturing prototype systems are needed to verify the potential reductions in TEWI. Extensive field testing is also required to determine the performance, reliability, and ``serviceability`` of each alternative to HFC-134a to establish whether the potential reduction of TEWI can be achieved in a viable consumer product.

Carnahan-Starling-DeSantis and Lee-Kesler-Plöcker interaction coefficients for several binary mixtures of ozone-safe refrigerants

Abstract Interaction coefficients (ICs) which characterize the non-ideal behaviour of refrigerant mixtures are an important parameters for predicting or modelling the thermodynamic performance of these mixtures in air-conditioning and refrigeration cycles. Experimental data which permit calculation of these parameters for many combinations of the newer, more environmentally acceptable refrigerants are scarce. Saturated vapour pressure data for 70 known mixtures of 8 different refrigerants in 18 binary combinations were analysed to find the interaction coefficients from the best correlation between vapour pressures calculated from the Carnahan-Starling-DeSantis (CSD) and Lee-Kesler-Plocker (LKP) refrigerant property routines and experimental data. Nine of the experimentally measured ICs were not previously given for the CSD routines in the current version of refprop ® from the National Institute of Standards and Technology. Fifteen new LKP ICs are reported. Comparisons are made with both published values and those estimated using algorithms unique to each system of subroutines. Agreement between the ICs reported in this work and published or estimated values is reasonably good in most cases given the simplicity of the test apparatus and experimental procedures. Very good agreement was seen between the ICs calculated in this work and the literature values for R12/R152a, R134a/R134 and R22/F152a, but poor agreement was seen for R22/R142b. Comparisons of published to estimated ICs and reported to estimated ICs suggest that estimation techniques should be improved.

Potential impacts of CFC restrictions on refrigeration and space-conditioning equipment☆

Abstract Several organizations have recently surveyed alternatives to the use of CFC compounds in refrigeration and space-conditioning applications. ORNL has conducted a preliminary analysis of potential energy-use impacts and an industry survey of R & D needs in response to CFC restrictions. Of the restricted compounds, R11 and R12 will have the major impact due to their wide use in automotive air conditioning, domestic and commercial refrigeration, and centrifugal chillers. Alternative refrigerants available in the short term include R22, R500, R502, and certain blends, but these are not suitable substitutes for all applications. R134a and R123 are environmentally acceptable substitutes which appear promising for new equipment, but information on them is preliminary and they will not be commercially available for several years. Blends of previously unused compounds present additional possibilities. Provided that the new refrigerants prove to be fully acceptable substitutes, long-term adverse energy-use impacts on new equipment will be minor. Impacts will be severe if identified substitutes prove to be unacceptable or if R22 is also restricted in the future. However, significant penalties may be incurred by the use of substitute insulation materials in appliances and buildings. Substitute refrigerants for existing equipment may be a major problem. Generation of comprehensive and accurate information on the engineering properties and health effects of R134a and R123 is an urgent R & D need. Cooperative efforts are needed. The potential use of refrigerant mixtures needs to be explored as replacement substitutes and for efficiency and modulation benefits that can be derived by the use of non-azeotropic mixtures. Alternatives cycles need to be re-examined as back-up substitutes.

PERFORMANCE ANALYSIS OF INTEGRATED ACTIVE DESICCANT ROOFTOP AIR- CONDITIONING SYSTEM OPERATING IN HEATING MODE

This investigation describes the performance study of a novel Integrated Active Desiccant-Vapor Compression Hybrid Rooftop (IADR) at Oak Ridge National Laboratory (ORNL) in heating mode. The tests were performed at two different ratios of outdoor/return air. Analysis of performance characteristics under each operating mode, including heating capacity and energy efficiency ratio, are given. Results of defrost cycle are also presented. Comparison between the experimental performance of IADR unit and the calculated performance of other commercially available heat pump systems at comparable operating conditions has been conducted.Copyright