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Worldwide scrutiny of the global warming impact of R-134a has presented the automotive industry with a pressing challenge to search for suitable alternative refrigerant(s). HFC-152a, referred to as R-152a in the air conditioning and refrigeration industry, is touted as an alternative [1, 2] to R-134a because of its lower global warming potential (GWP). R-152a is more environmentally benign than R-134a with GWP of 120 versus 1300. This paper is a follow up to the work on the potential applications of R-152a presented at the 2003 Vehicle Thermal Management Systems Conference (VTMS6) [3]. It documents continuing progress in applying R-152a to vehicle climate control systems. The paper compares R-152a cooling performance and energy performance to comparable R-134a system designs, including direct and indirect expansion systems. Also discussed are efforts to provide safe system operation with R-152a refrigerant.

As automotive power-train systems become more efficient, less waste heat is available for vehicle passenger cabin warming. As a result, alternative heating technologies are being investigated to alleviate this shortcoming. One alternative is to operate the existing A/C system in reverse (heat pump mode), thus providing supplemental heat. Recently, the environmental impact of refrigerant emissions has come under global scrutiny. The concern is their potential for global warming. Thus, the environmental characteristic of merit that makes for a more benign refrigerant in terms of emissions is lower Global Warming Potential (GWP). R-152a is a more environmentally benign refrigerant compared to R-134a with a GWP of 120 vs. 1,300 [1] and [2]. Both refrigerants are hydro-fluorocarbons - HFCs - (contain no chlorine) and hence, have zero ozone depletion potential. An environmentally benign refrigerant touted as a potential replacement for R-134a, is CO2.

In recent years, climate protection has become as important as ozone layer protection was in the late 1980's and early 1990s. Concerns about global warming and climate change have culminated in the Kyoto Protocol, a treaty requiring its signatories to limit their total emission of greenhouse gases to pre-1990 levels by 2008. The inclusion of hydrofluorocarbons (HFCs) as one of the controlled substances in the Kyoto Protocol has increased global scrutiny of the global warming impact of HFC-134a (called R-134a when used as a refrigerant), the current mobile air conditioning refrigerant. Industry's first response was to begin improving current R-134a systems to reduce leakage, reduce charge, and increase system energy efficiency, which in turn reduces tailpipe CO2 emissions. An additional option would be to replace the current R-134a with a refrigerant of lower global warming impact. This paper documents the use of another HFC, R-152a, in a mobile A/C system.

Concerns about global warming and climate change, combined with the inclusion of HFCs in the Kyoto Protocol as controlled gases, obligate the automotive air conditioning industry to assess the global warming impact of its HFC-134a emissions and develop cost effective mitigation strategies. One option would be replacing HFC-134a with a refrigerant with lower overall global warming impact. This paper demonstrates the feasibility of a secondary loop A/C system in automotive applications. The value of such a system is that it excludes refrigerant from the passenger compartment, thereby allowing the use of non-inert alternate refrigerants, such as hydrocarbons. It includes actual on-vehicle comparisons of A/C cooling performance and system energy requirements for secondary loop versus the current HFC-134a system. Also included is an assessment of the global warming impact advantage offered by a secondary loop A/C system.

In recent years, Global Warming Potential (GWP) has become as important as Ozone Depletion Potential (ODP) when evaluating a potential refrigerant. Increasing concern over GWP of HFC-134a and its effect on the environment have led international heating, ventilation and air conditioning, and refrigeration (HVAC & R) industries to look at other options. This study documents an assessment of some of the options. It describes simulated performance of R152a and hydrocarbon refrigerants and their potential as alternative refrigerants to HFC-134a in mobile air conditioning systems. In addition, a comparative assessment of the performance of a secondary loop system using these refrigerants is provided.