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Thread: TXV SIZING ?

  1. #1
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    TXV SIZING ?

    if you have a 100 ton compressor dx airside.
    dual circuit
    50 tons each. circuit
    compressor unloads to about 20 tons.
    would you use 2 0ve 50'S?
    i am sure not! would you use 2 ove 20's????????????????????????????????
    the circuits are even.
    you must wet the top and bottom coil together.
    i would assume you could put a solenoid on one and control it separately.
    even then one txv would still only be 20 tons or 10 for each ?circuit??????
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  2. #2
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    You normally size TXV's based on 100 psi drop across the valve to get its rated tonnage. If you're on a dx coil with a distributor, you have to take into account the pressure drop thru the distributor, also. On the majority of dx chillers, all you have is a perforated distribution plate, so the pressure at the valve outlet (for all practical purposes) is your evap pressure. In the case of the latter, you can downsize rated tonnage and still get correct system capacity. On the former, you can jockey it around some, but generally need to stay close to the nominal system tonnage.

    TXV's will normally throttle to around 35% of their rated capacity before they start losing control and getting erratic, so you should be fine with 2 50's if you control the system in such a way that you can drop half the coil by using a solenoid valve. If your coil is not serpentine, or you do not have separate drain pans on top and bottom, you will need to operate the bottom half as the lead coil or you'll have carryover problems with condensate.

    This'll all be a lot easier if you have electric unloaders on the compressor.

  3. #3
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    whats up K?
    the compressor is a carrier 6l
    I think it is actually an 80 ton and unloads to 20 tons.
    so if each coil is 40 tons and i used two ove 40's
    each circuit woul unload to 10 tons
    the txv's ove 40 would only go down to about 15 tons?
    should i use two ove 30's?????????????????????????????????????????
    how much over the nominal tonnage will the txv go??


    thanks

    st65



    Quote Originally Posted by klove View Post
    You normally size TXV's based on 100 psi drop across the valve to get its rated tonnage. If you're on a dx coil with a distributor, you have to take into account the pressure drop thru the distributor, also. On the majority of dx chillers, all you have is a perforated distribution plate, so the pressure at the valve outlet (for all practical purposes) is your evap pressure. In the case of the latter, you can downsize rated tonnage and still get correct system capacity. On the former, you can jockey it around some, but generally need to stay close to the nominal system tonnage.

    TXV's will normally throttle to around 35% of their rated capacity before they start losing control and getting erratic, so you should be fine with 2 50's if you control the system in such a way that you can drop half the coil by using a solenoid valve. If your coil is not serpentine, or you do not have separate drain pans on top and bottom, you will need to operate the bottom half as the lead coil or you'll have carryover problems with condensate.

    This'll all be a lot easier if you have electric unloaders on the compressor.
    I WILL SELL WORK,GENERATE BUSINESS, GO GET NEW CUSTOMERS!
    YOU SHUT THE HELL UP AND QUIT RUNNING YOUR MOUTH!

  4. #4
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    If this is an air cooled condenser we can assume 300psi head at 100deg OAT.
    50lbs drop across the condenser. 60 lb evap press with some other distributer drop and such. That puts us at 200 lbs delta p. A 30 ton sporlan will do about 1.4 times nominal at 100 lbs delta p. So a OVE 30 will do around
    42 tons at 200 lbs delta p. (disclaimer: I am not looking at the Sporlan book but this is how I would make a valve selection). If its DX VAV I would pick the smallest valve that would do the max tonnage required at that delta P. This will insure the best light load superheat contol. Also, the evap coil arrangement and staging is critical.

    This whole thread feels like bait to me though!
    "Dying aint much, its living thats hard." (Josey Whales)

  5. #5
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    Hey ST,
    CaptJack gave some good words in his post on this subject. Not really knowing the specifics of how your system is set up, though, it's hard to get into real specifics about the sizing of the valves. His comment on the condensor pressure is what I was getting at when I said they're rated at 100 psid. Sizing the valve is totally dependent on the conditions you have, i.e.; air-cooled and water-cooled are two totally different animals unless you're running 125 degree water into this thing. Best advice I think can be given here is that Sporlan bulletins 10-9 and 10-10 give some great info on valve selection and sizing. One thought though - I would rather size to the small side (OVE 30 if it'll do 41 tons under your design conditions) than to the large side and have a valve that won't throttle down far enough when you completely unload.

  6. #6
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    thanks you guys.
    30 it is!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!1
    st65
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  7. #7
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    Super, you need to look at that 30 ton valve at 200 lbs and see what it will due for sure. I only guessed! We may need to talk about the evap more as well.

    Does it have innertwined coils?
    How many coils?
    Are they 2 stacked coils?
    Any hot gas bypass?
    how many Liq line solinoid valves?
    "Dying aint much, its living thats hard." (Josey Whales)

  8. #8
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    Quote Originally Posted by CaptJackSparrow View Post
    Super, you need to look at that 30 ton valve at 200 lbs and see what it will due for sure. I only guessed! We may need to talk about the evap more as well.

    Does it have innertwined coils?
    How many coils?
    Are they 2 stacked coils?
    Any hot gas bypass?
    how many Liq line solinoid valves?
    Unless you've looked at the selection data and sized these things for yourself based on this individual systems particulars and come up with the 30 as YOUR choice, I have to agree with the above statement 100%.

  9. #9
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    I agree with the above, undersizing is better than oversizing and the 06L will run almost forever at higher superheats, but have a shorter life at lower ones.

    Be sure to use high velocity risers on the suction for oil return at minimum capacity.

  10. #10
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    Quote Originally Posted by JRINJAX View Post
    I agree with the above, undersizing is better than oversizing and the 06L will run almost forever at higher superheats, but have a shorter life at lower ones.

    Be sure to use high velocity risers on the suction for oil return at minimum capacity.
    do you know from experience??????????????????????/
    I WILL SELL WORK,GENERATE BUSINESS, GO GET NEW CUSTOMERS!
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  11. #11
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    Thats why more info is needed!

    If I have a vav system I would size the valves small as possible. If constant volume maybe not. If I can split one coil out on two valves and get two small valves that are better matched I might do that. I would try my best to aget a valve that would do the max tonnage but given a choice of high superheat at the top or low superheat at the bottom I wolud pick high at the top!
    "Dying aint much, its living thats hard." (Josey Whales)

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