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Thread: Compressorless

  1. #1
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    Compressorless



    Hi Guys,

    Say if I have an AC system with a fixed speed compressor following it is a small hot water storage tank (assume constant 100DegC in the tank). The refrigerant passes though the compressor which goes into the superheated region and then passes though the hot water tank, which then beings up the pressure and temperature.

    Is it possible for the compressor to stop working (turn off) while the AC system continue to still function as per normal?

    Thanks



  2. #2
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    Re: Compressorless

    No, it isn't. For a start, if it were running with the compressor off, it wouldn't be running normally for a vapour compression system.
    Next, how's the refrigerant getting from the evaporator to the superheater (hot water tank)?
    And: what's your refrigerant?
    And: how do you control the flow?
    And: what stops the system reaching equilibrium (equalising out) in the compressorless operating mode?
    Why would you want to add more heat energy post compression anyway? It just reduces the efficiency of your condenser due to the high superheat. Or means you need a larger condenser.
    Last edited by FreezerGeezer; 12-05-2014 at 10:46 AM.

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    Re: Compressorless

    Quote Originally Posted by FreezerGeezer View Post
    No, it isn't. For a start, if it were running with the compressor off, it wouldn't be running normally for a vapour compression system.
    Next, how's the refrigerant getting from the evaporator to the superheater (hot water tank)?
    First the system is running under normal operating condition, i.e. running with the compressor on. Allowing some time to pass, the system is fully running, the superheat is just assumed to be 100DegC.

    Quote Originally Posted by FreezerGeezer View Post
    And: what's your refrigerant?
    Just assume to be R290

    Quote Originally Posted by FreezerGeezer View Post
    And: how do you control the flow?
    Are you talking about the flow from the evaporator to the condenser? Because it is assumed the control of flow would be limited to the capillary or the TX valve.

    Quote Originally Posted by FreezerGeezer View Post
    And: what stops the system reaching equilibrium (equalising out) in the compressorless operating mode?
    Well the superheater (assumed to be 100DegC) will slowly transfer heat into the refrigerant and will slowly reduce in temperature, at a certain stage, the compressor will kick back in as backup.

    Quote Originally Posted by FreezerGeezer View Post
    Why would you want to add more heat energy post compression anyway? It just reduces the efficiency of your condenser due to the high superheat. Or means you need a larger condenser.
    In this system I am working on will have a Heat recovery unit post superheat, thus reducing the size of the condenser, but this would also the refrigerant time to completely phase change back to liquid than aerated liquid before passing the capillary. This system would also allow for higher temperature operating conditions (i.e. places that reach 40+DegC)

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    Re: Compressorless

    how does the evap vapour enter the superheater. How does the liquid enter the evaporator

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    Re: Compressorless

    Quote Originally Posted by mad fridgie View Post
    how does the evap vapour enter the superheater. How does the liquid enter the evaporator
    Initially the evap vapour enters the superheater via the compressor, then when the compressor is off, I'm just assuming natural flow due to difference in temperature and pressure of the system.

    The liquid enters the evap via the capillary, is this what you mean... not too sure about that question.

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    Re: Compressorless

    That's what we're getting at about flow - how do you expect the superheated suction vapour to get through the compressor to the superheater?
    Refrigerant tends to migrate to the coldest point in the system. So why would the refrigerant flow to the superheater?
    And in the real world, the average split system seems to take just a few minutes - MAXIMUM - for system pressures to equalise. Ie the system reaches equilibrium in a very short time. Often less time that the anti recycle timer is set for.
    You say in a previous post that you fully understand the vapour compression refrigeration cycle. I'm afraid that I don't agree with that statement. While you may well have a better understanding of the theoretical performance than I do (it's a long time since my HNC), it appears that you haven't observed a system in operation.
    Can you please explain, in detail, what you are trying to achieve - what the idea is. Diagrams may help.
    If I understand correctly, you are using a calorifier between the compressor discharge & the condenser to perform the initial de-superheating, thus using the waste heat to provide hot water.
    But then you want to be able to turn the compressor off & use the calorifier in reverse to increase the refrigerant vapour pressure without compression & maintain enough pressure differential across the system to keep it running 'normally'?
    40*C ambient is no problem if the system is designed for it in the first place, by the way. So any new design that you're coming up with needs to have a practical benefit, like greatly enhanced efficiency, in order to be commercially successful.

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    Re: Compressorless

    I agree with FreezerGeezer 100%. The system design that you are describing is not going to work, at least from what I read so far...

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    Re: Compressorless

    So there is a non-return valve after the compressor, a liquid pressure zone is formed between the non-return valve and the capillary due to the more efficient condenser (due to the heat recovery or calorifier). Then the liquid which is backed up in the capillary phase changes into a vapour, which then passes into the low pressure zone in the accumulator.

    This is what I have understood, from someone else.... is it possible for the refrigerant to continue flowing or would the AC system only run until all the liquid backed up in the capillary has phase changed into vapour?

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    Re: Compressorless

    .

    In refrigeration we a very controlled by the relationship between the pressure and the temperature
    of the refrigerant in any one section of the refrigeration system.

    We move heat, that's all, but we can move it very efficiently if done correct but it
    relies on two fundamental principles.

    One is, we need a temperature difference to move heat. Heat only flows from high to low
    and we need at least a few degrees of difference (preferably ten degrees) to be able to move
    the heat.

    Second is, in normal vapour compression refrigeration systems, you need to create a pressure
    difference and that difference is created by a compressor, hence vapour compression.

    The pressure difference causes the temp difference and you need both to work.

    What you are talking about is the heat absorption method of refrigeration and that
    uses a completely different principle and very special refrigerant.

    Look up heat absorption refrigeration systems.

    Regards

    Rob

    .
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