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Appendix C: Indoor Chamber Energy Balance C.1 Determination of specific heat constants The data reduction programs determine the change in enthalpy of the glycol cooling loop based on the inlet and exit temperatures of the glycol and the integral of the linear relationship between temperature and specific heat, as given by: ∆Qglycol =m&glycol(A⋅(Tout−Tin)+B⋅(Tout2−Tin2)) (C.1) 2 The constants A and B for this equation are determined based on a linear fit of specific heat values calculated over an appropriate range of temperatures for a given concentration. The Fluidfile software from Dow Chemical (installed on the data acquisition PC in MEL 361) will calculate the concentration of a glycol solution given a temperature and density, and can calculate the specific heat of a solution given the concentration. The concentration of the glycol can be determined from either the density measured by the Micromotion flow meter and thermocouples in the loop or from a sample using a thermometer and hydrometer (both methods can be used in combination to ensure accuracy). With these values, the concentration of the solution can be calculated from Fluidfile. Once the concentration is known, a series of temperature and specific heat values can be generated using Fluidfile and a linear fit can be determined. C.2 Testing and results Table C.1 shows the results of chamber heat balance tests run to check the accuracy of the glycol energy balance results from the R410A baseline heat pump data taken during the last week of November, 1999. In that data, the chamber energy balance had a consistently higher capacity at the test points than the capacity calculated by other means. The mass flow rates and temperature ranges of the original data are included for comparison with the test points. The tests consisted of running just the glycol loop, blower and heater (to maintain a chamber temperature of 70oF—the same temperature as for the R410A data) and calculating the energy balance based on the heat input of the blower and heater and the heat removal by the glycol loop. The tests were conducted on three different days (11/30/99, 12/6/99 and 12/12/99) at three different flow rates and temperature inlets. In order to eliminate errors due to infiltration, for the first test on 12/12/99 the feed through for the instrumentation wires was blocked and for the second test, in addition to blocking the feed through, the edges of the removable door were taped. 64PDF Image | Comparison of R744 and R410A
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