THE ROLE OF THE

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HVAC System Overview and Refrigerant Design 133 TH ∫ 0 ax ( ) ∗ ⎡xt () ⎤ ⎣⎢ ⎦⎥ dt GWP( x) = TH ar () ∗ ⎡ ⎣⎢rt () ⎤ ⎦⎥ dt ∫ (9.1) The IPCC defines global warming potential as follows [6]: 0 The GWP has been defined as the ratio of the time-integrated radiative forcing from the instantaneous release of 1 kg of a trace substance relative to that of 1 kg of a reference gas (IPCC, l990): where TH is the time horizon over which the calculation is considered, a x is the radiative efficiency due to a unit increase in atmospheric abundance of the substance in question (i.e., Wm –2 kg –1 ), [x(t)] is the time-dependent decay in abundance of the instantaneous release of the substance, and the corresponding quantities for the reference gas are in the denominator. The GWP of any substance therefore expresses the integrated forcing of a pulse (of given small mass) of that substance relative to the integrated forcing of a pulse (of the same mass) of the reference gas over some time horizon. This value has supplanted Ozone Depletion Potential as far as concern over global effects on the environment. 9.6 total equIvalent warmIng ImPact (tewI) Total equivalent warming impact (TEWI) is the sum of direct as well as indirect contributions of global warming to the environment by greenhouse gases. For an automobile system, the refrigerant leaks directly into the system and energy is required to power the AC system. There is little opportunity to reduce the indirect emissions because the need to power the system from the automobile engine will always be present. An opportunity exists in the refrigerant choice—that is, replacing an R134a or similar system with a different refrigerant such as R152a, hydrocarbon, R744, etc. We can consider TEWI as having a “controllable” portion, which can be described as [7] TEWI (controllable) = (D R134a – D alternative) + (I R134 – I alternative) (9.2) Here, D is direct contribution and I is the indirect contribution to global warming. The direct portion of TEWI can be eliminated by replacement of R134a. Table 9.3 shows global warming impact in CO 2 per year for some refrigerants and the percentage of reduction by switching refrigerants. 9.7 ozone dePletIon PotentIal (odP) As can be seen from Table 9.2, ozone depletion values are zero for all compounds with the exception of R12. As stated earlier, the ozone depletion potential is the relative amount of damage that the particular chemical causes to the ozone relative to R-11 (Figure 9.2). Figure 9.3 shows the global warming impact of various refrigerant
134 The Role of the Chemist in Automotive Design table 9.3 global warming Impacta system r134a r152a r290 sec. loop w/r152a sec. loop w/r290 direct Indirect direct Indirect direct Indirect direct Indirect direct Indirect 100°F × 40% R.H. 125 262 20 240 2 255 20 316 2 313 (TEWI) 125 127 130 51 72 80°F × 50% R.H. 125 135 20 128 2 31 20 150 2 151 (TEWI) 125 112 126 90 106 Av. (TEWI) 125 119 128 70 89 Percent improvement of 0 95 100 56 71 “controllable” TEWI Source: Goodbane, M. SAE Paper 1999-01-084, 1999. With permission. a Kilograms of CO2 per year.
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THE ROLE OF THE CHEMIST IN AUTOMOTI
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CRC Press Taylor & Francis Group 60
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Contents Preface...................
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Contents ix 6.6 Thermal Properties
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Contents xi 11.4 Glass Microspheres
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The Author Herman Phlegm was born i
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2 The Role of the Chemist in Automo
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10 The Role of the Chemist in Autom
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3 3.1 IntroductIon Component Materi
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Component Materials in Automobiles
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6 6.1 IntroductIon Engineering Poly
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184 The Role of the Chemist in Auto
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190 Index Carbon dioxide emissions,
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192 Index heat exchanger designatio
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194 Index Power train, 95 Power tra
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THE ROLE OF THE

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