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Air Cond. capacity versus engine speed?

Discussion in 'Technical Q&A' started by jselevan, May 15, 2004.

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  1. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,879
    #1 jselevan, May 15, 2004
    Has anyone information concerning BTU capacity of an automobile A/C as a function of engine RPM?

    Question arises from desire to improve cooling in Boxer. System works well, not great. What are the limiting factors: evaporator volume? Surface area? Condenser volume? Surface area? System volume? Compressor capacity?

    I believe that the system produces colder air when the engine revolutions are higher. Not necessarily when traveling faster (coasting downhill in neutral does not produce air as cold as when coasting downhill in gear). Is there a linear (or non-linear) relationship between compressor RPM and cooling capacity, or does the system saturate at some RPM, above which there is no additional cooling?

    Sorry for all the questions. I understand the Carnot Cycle and the thermodynamics perfectly, including adiabatic expansion/compression, but have not designed a system around these principles. Help is appreciated.

    Jim S.
     
  2. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
    4,367
    NY
    #2 Steve King, May 15, 2004
    Its the size of the evaporator. Very simple , even if you go to a compressor conversion to one of the new sanyo's or etc. you still have an area problem. I think that the condensor is large enough but the evap. in the car is to small to produce large volumes of cold air.
     
  3. mikewestrick

    mikewestrick Rookie

    Apr 21, 2004
    21
    Fort Wayne, IN
    #3 mikewestrick, May 16, 2004
    There is some RPM at which the compressor no longer increases the volume of the freon being pumped. Pressure differential is what achieves the heat transfer (or lack of heat (cooling)). Evaporator, compressor and exchangers are all part of the equation. Even bigger factor is how well sealed is the passenger compartment? Adding insulation to the unseen passenger side of the firewall as well as black or clear silicon sealer around holes should help considerably
     
  4. jselevan

    jselevan Formula 3

    Nov 2, 2003
    1,879
    #4 jselevan, May 16, 2004
    Steve - your response suggests that increasing the size of the evaporator will increase cooling capacity. Makes sense.

    Mike, pressure differential relates to flow. If one could produce greater coolant flow (cubic feet per minute), would that lead to better cooling, or might the limited ability to condense and evaporate within the time allowed still represent a limiting factor?

    Thanks.

    Jim S.
     
  5. Mark 328

    Mark 328 Formula Junior

    Nov 6, 2003
    510
    Orange, Ca
    Full Name:
    Mark Foley
    #5 Mark 328, May 17, 2004
    Increasing the refrigerant flow in an evaporator can cause icing problems. The condenser should not be colder then about 40 Deg F--if so, the likelyhood of it icing-up (and sealing-off) is greater.
    Have "toyed" with the idea of putting another evaporator, or two, where the heater boxes are. One additional evaporator would probably be a better choice and use the other ducts to provide inlet air (for recirculation).
    Mark
     

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