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  1. #101
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    Re: My first self made EVAP



    Your SCT is 48.3C and water onto the cond is 49C, can not any better than that! (well that is actually impossible)



  2. #102
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    Re: My first self made EVAP

    I would say that you either a coil design problem or not enough airflow (my guess)
    What is your air onto the coil temp, not ambient

  3. #103
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    Re: My first self made EVAP

    Tomorrow I will put the digi-cools on and take a pic under the conditions. It is supposed to be 10C out tomorrow. I cannot decide if I need more gas or a bit less.
    I still don't like the elevated current draw. Not that efficient really...

    The defrost is really worrying me but it must just be an electrical setting.

  4. #104
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    Re: My first self made EVAP

    They are about equal, within .5 deg

  5. #105
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    Re: My first self made EVAP

    Quote Originally Posted by mad fridgie View Post
    Your SCT is 48.3C and water onto the cond is 49C, can not any better than that! (well that is actually impossible)
    He's condensing at 48.3C which should be equal to outlet temp. Subcooled temp would be lower. Closer to return temp. At the moment his condensing temp is equal to his return temp, which is too low.

    Check your super heat. Should be floating around 3-4K.

  6. #106
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    Re: My first self made EVAP

    The outlet temp can be higher than SCT, I would say there is a slight error in the readings.
    But there is nothing wrong with side.
    The low SST is the issue.
    With -10C suction temp. nothing wrong with charge.

  7. #107
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    Re: My first self made EVAP

    I can't get the bloody thing to defrost and I can't get to the entire coil to do it with hot water (design improvement #1 coming up). Luckly it will be 14C tomorrow. I can't ever remember having these temps at this time of the year.
    New reading shortly

  8. #108
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    Re: My first self made EVAP

    Here are a couple of pics that should tell a tale. EVAP Air on is 11.7C air off is 5.7. SH stayed steady around 7-8C, SC started off around -6-7C and by the end was around -17. The biggest issue is the Dt measured right at the discharge and 6cm from the suction, 55C by the time it reached limit. My 450L tank was to be heated from 20 to 39C. It took 50min...too long.

    yarmouth av 081a.jpgyarmouth av 080a.jpgyarmouth av 078a.jpg

    I was keeping a 2-3C differential on the liquid side of the condenser.
    Last edited by MikeHolm; 26-11-2011 at 01:37 PM.

  9. #109
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    Re: My first self made EVAP

    I was looking at the high subcooling, reasonable superheat and thought i might have a bit of a high charge (I thought there might be some backup into the condenser) but not too high. So I took a bit out, and i didn't have a scale but it was a couple of seconds on vapour side. Now my SC goes as high as 30 deg and SH is down to around 4 deg. The rest of the above conditions are roughly the same.

    Could I be looking at a liquid line restriction?

  10. #110
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    Re: My first self made EVAP

    Mike not enough info.
    Forget what you are using for just for a moment
    So what info do we need
    Water entering the condenser
    Water leaving the condenser
    Flow rate if possible
    Air temp entering the evap (not ambient)
    Air temp leaving the evap.
    saturated suction temperature ( SST) pressure/temp relationship
    refrigerant temp leaving the evap
    refrig temp entering the compressor
    Saturated discharge temperature (SCT) pressure/temp relationship (at the comp)
    Discharge Temperature (just after the comp outlet)
    Liquid temp leaving the condenser
    Liquid entering the TEV
    Liquid Pressure ( at the TEV inlet if possible)
    Current draw of the compressor

  11. #111
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    Re: My first self made EVAP

    This seems to be beyond me as i need to actually SEE this working to do any figuring. However if i may put my 2 cents worth in, could your evaporator have too closely spaced fins for those temperatures? Maybe the depth of your evaporator is allowing too much T.D. As we all know, once ice forms, it continues to grow and insulates evaporators, reducing performance and reducing air velocity.
    To the optimist, the glass is half full. To the pessimist, the glass is half empty.

  12. #112
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    Re: My first self made EVAP

    Quote Originally Posted by mad fridgie View Post
    Mike not enough info.
    Forget what you are using for just for a moment
    So what info do we need
    Water entering the condenser
    Water leaving the condenser
    Flow rate if possible
    Air temp entering the evap (not ambient)
    Air temp leaving the evap.
    saturated suction temperature ( SST) pressure/temp relationship
    refrigerant temp leaving the evap
    refrig temp entering the compressor
    Saturated discharge temperature (SCT) pressure/temp relationship (at the comp)
    Discharge Temperature (just after the comp outlet)
    Liquid temp leaving the condenser
    Liquid entering the TEV
    Liquid Pressure ( at the TEV inlet if possible)
    Current draw of the compressor
    Mad, I can get all that again with exception of the pressure at the EVAP( the pressure tap is within 1.5m of the tev). Excuse my ignorance but I assume SST or SCT includes the SH or SC. They should just record the suction temp and discharge temp separately.

    My biggest fear is causing damage to the comp in the short term with such a high pressure differential (20bar).
    Last edited by frank; 29-11-2011 at 01:19 PM.

  13. #113
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    Re: My first self made EVAP

    Quote Originally Posted by mikeref View Post
    This seems to be beyond me as i need to actually SEE this working to do any figuring. However if i may put my 2 cents worth in, could your evaporator have too closely spaced fins for those temperatures? Maybe the depth of your evaporator is allowing too much T.D. As we all know, once ice forms, it continues to grow and insulates evaporators, reducing performance and reducing air velocity.
    Mike, the coil designer has a lot of experience with heat pumps and long before I came to him for this coil, we talked a bit about how he designs his coils. He would rather have a larger spacing than have a tight package. There is a problem with defrost on this unit but I think it is electrical in nature. The coil is a 5 row and I will post a pic of the tube arrangement when I can find it.

  14. #114
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    Re: My first self made EVAP

    "SST and SCT" are in other words "Te & Tc", or the gauge pressure converted into a temperature. They are not subcooling or superheat
    Example R410a 20Barg = 35C, if this was the discharge pressure then SCT would be 35C, not to be confused with discharge temperature, or liquid pressure or liquid temperature.

  15. #115
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    Re: My first self made EVAP

    What size tube are using in the evap coil and how many circuits are there?

  16. #116
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    Re: My first self made EVAP

    Hi Mad,
    Here is a pic of a similar coil. The liquid line should be in front of the discharge line facing in the same direction (up). All tubing is 0.5" od and there are 4 circuits coming to a common 1.375" manifold which you can see in the pic. The overall coil size is 30" by 48" long. The tube rows are 1" apart and the U bends are 1.25' on centre.

    According the the pic I posted above, what the digi-cools show is the SST (0C) and SCT (46C). I'm still getting used to everything.

    Jens coil1.jpg
    Disregard the ends that you can see at the corners. It is not quite the same coil
    Last edited by MikeHolm; 29-11-2011 at 09:28 PM.

  17. #117
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    Re: My first self made EVAP

    Well, my issues with defrost were all down to an improperly grounded RV wire from the defrost control. whenever the control wanted to go into defrost, that wire went to ground and the valve didn't move. All seems well now.

  18. #118
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    Re: My first self made EVAP

    Thats a weight off your mind. Not sorry to put that to bed I'm sure

  19. #119
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    Re: My first self made EVAP

    Yes, well...on to the next thing which is programming a control that will do everything needed in one product. I am being pushed by Jens (the old Dane HP builder) to use the TAC Xenta controller and control all pumps, mixing valves and fans. I don't know if there is a difference between this type of controller and and equivalent PLC from Siemens or Allen Bradley. Any idea? As we have seen with most of the package North American stuff, it still uses 30 year old control technology and it can be improved on.

  20. #120
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    Re: My first self made EVAP

    Whats wrong with the Lodam? Have you hooked it up to your own unit yet?
    Better interface and more complete solution for your purpose than the other products I think

  21. #121
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    Re: My first self made EVAP

    The problem with the Lodam is that it is not capable of controlling many different loads other than the Heat pump itself. For example, I would like to be able to have a back up electric element which i can schedule based on off peak power rates. i also would like to be able to program the HP cycling and motorized mixing valve positions to blend water from a storage tank or solar to the evap. I don't think most of this is available with the Lodam.

    I haven't installed it on a HP yet but I will over the winter. I have 5 Viessmann boilers and a number of solar systems to install first. .... where does the time go?

  22. #122
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    Re: My first self made EVAP

    Hi Mike H.
    have you concidered a small micro PLC they are realtively cheap these days, come with analogue and digital inputs/outputs. Then set up the whole lot to what you want

  23. #123
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    Re: My first self made EVAP

    Howdy Mr Magoo,
    I have thought of that and before I decide I was told that the TAC Xenta was different than a standard PLC and there are cost savings as some of the output output relays are included BUT I haven't been able to find a good comparison guide between the different products. Once I get a system going, I 'd like to stick with it.

  24. #124
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    Re: My first self made EVAP

    The bugger went off on a LOW pressure lock out. I wasn't there to see it but that is the fault code. First thing I will do is to get a low pressure timer so the switch has to stay open for a period of time before the lockout occurs. Odd thing is that it hasn't been very cold the last few weeks (-3 to +6) so I don't think it is weather related.

    I will also get a receiver for it. It has about 5.5kg of refrigerant in so I should get a receiver to hold that charge, is this correct? Also, any idea what time is reasonable for LP switch timer 1m, 2m ,5m?

  25. #125
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    Re: My first self made EVAP

    I wouldn't hold out the LP switch for more than 20secs. If it staying in low pressure for longer than that its there for a reason. How high or low is the switch set. About 3-3.5 bar would be about right on a 410a system.

  26. #126
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    Re: My first self made EVAP

    I'm not sure what the rating is for the LP switch but the control allows 4 soft lockouts (of 5 sec each)then makes a hard lockout which needs to be manually reset. This appears to be what happened.

  27. #127
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    Re: My first self made EVAP

    A couple of months have gone by now Mike. Any more interesting experiences with the system to share?

  28. #128
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    Re: My first self made EVAP

    Well, now that you have mentioned it....a lot has happened. I decided to use the stock York board for archery target practice and get the TAC control put in. It seems the lockouts I had were partally due to the board not accepting one or the other stage turning off without the other one. Seems I cannot make it work so out it comes and in with the new control. Stay tuned.

  29. #129
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    Re: My first self made EVAP

    Long day yesterday. FINALLY got a control on my ASHP and charged up the system, but it is only for cooling right now. It is TAC because we had a few 301s and the old man knows them well enough. The problem is, he always had someone to do the programming and it seems the changes since Schneider bought them, results in no access t the proprietary cable for downloading the programming so the one we put in will now do cooling only as there is no defrost function fitted (it was meant for GSHP). Still looking for the right control. Lodam is a nice control but has its limitations, defo better for replacement or standard setups rather than original designs tho.

    Anyway, It is running very nicely but our evap is a bit big for this system (we dropped the comp to 8kw from 10kw) but should do quite well in heat mode.

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