Results 1 to 8 of 8
  1. #1
    Join Date
    Mar 2011
    Location
    England
    Age
    30
    Posts
    6
    Rep Power
    0

    Effect on vapour compression refrig cycle if indoor temp is increased?



    Hi guys, wondering if anyone can help me understand what will happen if the indoor environmental temperature were to increase from 30 to 35 C whilst the cooling indoor temp of 23 C remains constant. Assume that the work on compressor would increase, and efficiency would decrease ? Would any components likely to be damaged ? Will refrigerant leaving evaporator be at high temp/pressure causing expansion valve to open more and flow rate increase. Would this cause superheat to therefore decrease and again result in potential damage to the compressor and reduce efficiency. Any help is greatly appreciated.



  2. #2
    Join Date
    Oct 2006
    Location
    England
    Posts
    1,848
    Rep Power
    15

    Re: Effect on vapour compression refrig cycle if indoor temp is increased?

    .

    If you are talking about AC then if the system is inverter powered the

    Comp will ramp up to allow for the extra loadings (suction pressure rise)
    but as long as the AC is sized correctly it should have no real effect on
    the system as a whole.

    Think of your car driving up hill, the engin works harder than on a flat road
    but as long as there is enough power the engin will work fine under the increased load.

    The problems start if the AC is too small and therfore it will not cope with the extra
    duty. In this case the thing will run very inefficienty and it will have an undue effect
    on the system as a whole.

    Think car up hill towing a caravan, if the engin is 2ltr you could drive all day but
    if the engin is only a little 1.3ltr then it will slog its guts out and overheat / fail.

    Cheers

    taz

    .

  3. #3
    Join Date
    Mar 2011
    Location
    England
    Age
    30
    Posts
    6
    Rep Power
    0

    Re: Effect on vapour compression refrig cycle if indoor temp is increased?

    Thanks Taz,

    Ye hopefully the AC system can cope but if it cant is the theory surrounding the evaporator, expansion valve, superheat etc I listed correct ?


    Thanks.

  4. #4
    Join Date
    Oct 2006
    Location
    England
    Posts
    1,848
    Rep Power
    15

    Re: Effect on vapour compression refrig cycle if indoor temp is increased?

    Quote Originally Posted by mart434u View Post
    Hi guys, wondering if anyone can help me understand what will happen if the indoor environmental temperature were to increase from 30 to 35 C whilst the cooling indoor temp of 23 C remains constant. Assume that the work on compressor would increase, and efficiency would decrease ? Would any components likely to be damaged ? Will refrigerant leaving evaporator be at high temp/pressure causing expansion valve to open more and flow rate increase. Would this cause superheat to therefore decrease and again result in potential damage to the compressor and reduce efficiency. Any help is greatly appreciated.

    There will be a point when the system comp can't cope with the loading and then the suction pressure will rise.
    When that happens the expansion valve will be fully open but the air (heat) flowing over the evap will boil off the liquid.

    So the superheat value out of the evap will increase and then the comp will overheat because it relies on the
    reletively cool suction gas returning to cool it down.

    So in answer to your question.

    No the superheat will not decrease it will in fact increase and possibly cause problems for the comp due to overheating.

    Cheers

    taz

    .
    Last edited by taz24; 12-05-2011 at 02:42 PM.

  5. #5
    Join Date
    Oct 2003
    Location
    Belgium
    Age
    56
    Posts
    5,519
    Rep Power
    28

    Re: Effect on vapour compression refrig cycle if indoor temp is increased?

    Quote Originally Posted by mart434u View Post
    ...what will happen if the indoor environmental temperature were to increase from 30 to 35 C whilst the cooling indoor temp of 23 C remains constant. ...
    There must be something wrong in your explanation: twice indoor conditions.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  6. #6
    Join Date
    Mar 2011
    Location
    England
    Age
    30
    Posts
    6
    Rep Power
    0

    Re: Effect on vapour compression refrig cycle if indoor temp is increased?

    Probly just my poor english. I mean if the cycle is designed to cool room from 30 to 23C what would happen to the system components if you upped the temperature to 35 C. So now it must cool 35 to 23 C.

    Thanks,

  7. #7
    rahulsoniin's Avatar
    rahulsoniin Guest

    Re: Effect on vapour compression refrig cycle if indoor temp is increased?

    Quote Originally Posted by mart434u View Post
    Probly just my poor english. I mean if the cycle is designed to cool room from 30 to 23C what would happen to the system components if you upped the temperature to 35 C. So now it must cool 35 to 23 C.

    Thanks,

    Simple answer to this ? is that the total cooling capacity of same unit reduces coz of increase in discharge pressure. To make it simple, aassume that a car delivers 15kmpl while running under normal conditions or say on a flat road. The same car will deliver lower kmpl running uphill. Same applies with our air conditioners.

  8. #8
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    57
    Posts
    2,212
    Rep Power
    13

    Re: Effect on vapour compression refrig cycle if indoor temp is increased?

    If the system losses e.g. wall, roof, floor etc are less than the capacity of the a/c system, the room will eventually cool down to the desired set-point. It will, however, take a lot longer.

    ~ (35-23)/(30-23) = 12/7 = 1.71 times
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •