Results 1 to 12 of 12
  1. #1
    Join Date
    Sep 2006
    Location
    Ohio
    Posts
    470

    Refrigerated Air Dryer

    I need some help with a custom built refrigerated air dryer I'm working on. This thing is just over a year old, has two ckts with R-134a and is 100% redundant, only one ckt is needed for the load. Each ckt has a Copeland 6 cylinder compressor with two unloaders, remote air cooled condenser with two fans, liquid receiver, suction accumulator, oil separator, TXV and two Hot Gas By-pass valves. One HGB injects into the suction line just before the accumulator and the other HGB injects between the TXV and the evap. With the HGB's off and the compressor fully loaded, I had 0* to 1* superheat at the compressor, 3* subcooling and the sight glass was flashing. The glycol/water temp would drop to 30* and the suction would drop to 10 psi. I started adjusting the Emerson txv and ended up making 23 turns to get the SH up to 15* at the outlet of the evap. and yes, the bulb is attached to the suction line. I added 6 lbs of 134a, that was all I had at the time. The SC went up to 4* and I had mostly clear glass. The water temp drops from 56* to 35* in less than 10 min. with the comp fully loaded, so I would shut it down until the water warmed up. The unloaders are controlled by a digital temperature controller and was set to unload 2 cylinders at 35* and 2 more at 33* and the freeze stat which is another temp controller was set at 25*, this cycles the compressor off and on. A factory tech set-up the unit and had been back several times because the compressors were either in a block of ice or the suction line at the compressors would be too hot to keep your hand on. I talked to the manufacturer and they said to keep the HGB valve closed that injects into the accumulator, adjust the other one to open at 28 psi, adjust the unloaders for 46* and 45* with a 5* diff. and set the condenser fan cycling controls for fan-1 at 175 psi cut-in, 125 psi cut-out. Fan-2 at 200 psi cut-in, 175 psi cut-out. I feel that the fan cycling pressures would be too high. With the unloaders set as stated, the suction still drops to 13 psi. I then set the HGB to start opening at 28 psi and it sounds like it is fully open at 25 psi. I still have to go back and add refrigerant to this ckt and replace the compressor on ckt #1, it is shorted to ground. I think it got too hot from both HGB's being open and the unloaders set too low. I feel that the evaporator barrel is too big, not enough water flow through it which makes the suction drop.

    What should I have on the following:
    1) What glycol/water temp should I have
    2) What temp should I set the unloaders for
    3) What should the freeze stat be set for.(this cycles the comp off & on)
    4) What should I set the fan cyc controls cut-in and cut-out at, (two fans)
    5) What air temp drop should I have (compressed air)
    6) For some reason do dryers have low Subcooling.

  2. #2
    Join Date
    Mar 2008
    Location
    North Queensland, Australia
    Posts
    1,051
    right hands, I'm a bit confused here. I thought you were talking about a compressed air drier. Meant to get the moisture out of the compressed air so it doesn't damage compressed air tools or for spray painting. Then I read glycol??
    The air driers I work on run the compressed air over the evaps in a sealed chamber. The coils are set up to stay above 0C (32F) so they won't ice up. The moisture collects in the bottom of the evap chamber till the blow down timer opens the blow down solenoid and dumps the water to a drain.
    If we're talking about the same thing, it sounds to me like your system is freezing up internally. That'd explain the lack of super heat.
    I'd want the suction pressure to be set up at or about 30PSI minimum.
    That is, of course, if we're talking about the same thing.
    Mistakes are a part of being human. Appreciate your mistakes for what they are: precious life lessons that can only be learned the hard way. Unless it's a fatal mistake, which, at least, others can learn from. Al Franken, "Oh, the Things I Know", 2002

  3. #3
    Join Date
    Sep 2006
    Location
    Ohio
    Posts
    470
    [QUOTE=Slatts;1918368]right hands, I'm a bit confused here. I thought you were talking about a compressed air drier. Meant to get the moisture out of the compressed air so it doesn't damage compressed air tools or for spray painting. Then I read glycol??

    Slatts,
    I am talking about a refrigerated air dryer. It's more or less a chiller. The glycol/water mixture is pumped through the evaporator and goes through several plate and frame heat exchangers. The compressed air goes through the other side of the plate snd frame heat exchangers where it is cooled and the moisture removed. The condensate is then removed with auto blow down valves.
    I'd like to keep the suction at or above 28 psi but in order to do so, the hot gas by-pass valves are open alot.

  4. #4
    Join Date
    Mar 2008
    Location
    North Queensland, Australia
    Posts
    1,051
    [quote=hands;1918736]
    Quote Originally Posted by Slatts View Post
    right hands, I'm a bit confused here. I thought you were talking about a compressed air drier. Meant to get the moisture out of the compressed air so it doesn't damage compressed air tools or for spray painting. Then I read glycol??

    Slatts,
    I am talking about a refrigerated air dryer. It's more or less a chiller. The glycol/water mixture is pumped through the evaporator and goes through several plate and frame heat exchangers. The compressed air goes through the other side of the plates and frame heat exchangers where it is cooled and the moisture removed. The condensate is then removed with auto blow down valves.
    I'd like to keep the suction at or above 28 psi but in order to do so, the hot gas by-pass valves are open alot.
    No worries, 1 more circuit in the system.
    Does the system fully unload before the bypass valves open?
    Is the glycol mix correct? as in, it's not freezing in the chiller because it's been diluted is it?
    What's the glycol leaving and return temp? A low TD would indicate a frozen or fouled chiller.
    A low glycol TD across the compressed air heat exchanger when the compressed air is being used would make me suspect a frozen or fouled heat exchanger.
    Is there a filter or strainer in the blow down line before the blow down valve? I've had these block up on multi evap systems and allow the chamber to fill with water, causing the load to drop right off. Sounds a bit like your symptoms. Is the customer complaining about water in his compressed air?
    The idea of the HGBP valves is to keep the compressor running in low load conditions and maintain a minimum pressure / evap temp. I'd think the one that feeds before the evap should open first so it wouldn't be dumping hot gas in the inlet of the compressor.
    If the manufacturer said to set it at 28 PSI, that's 32F. Seems to me the anti freeze T'stat shouldn't be set any lower than about 28F. Maybe even 30F. I'd want to see the compressor fully unloaded by 30 PSI. I'd have it shut down on LP by about 25 PSI.
    The systems I work on have cool to cold air leaving the drier even on high load.
    With the HGB's off and the compressor fully loaded, I had 0* to 1* superheat at the compressor, 3* subcooling and the sight glass was flashing. The glycol/water temp would drop to 30* and the suction would drop to 10 psi. I started adjusting the Emerson txv and ended up making 23 turns to get the SH up to 15* at the outlet of the evap.
    Just to be sure, we're talking about super heat here, not just pipe temperature?
    OH yeh, sorry about the poor pun at the start of my last post. Couldn't help myself
    Last edited by Slatts; 07-08-2008 at 08:44 PM. Reason: add more info spelling
    Mistakes are a part of being human. Appreciate your mistakes for what they are: precious life lessons that can only be learned the hard way. Unless it's a fatal mistake, which, at least, others can learn from. Al Franken, "Oh, the Things I Know", 2002

  5. #5
    Join Date
    Sep 2006
    Location
    Ohio
    Posts
    470
    Slatts,
    I checked the dryer again and had a 6* TD across the compressed air piping, 11* TD across the evaporator barrel and 3* rise across the common headers of the five heat exchangers. The blow down valves are removing condensate from the heat exchangers.
    The compressor starts fully loaded and unloads as the water mix drops, I had them set to unload 2 cylinders at 46* and the other 2 at 45*. I found that it would unloaded for long periods of time and would wash the oil out of the compressor, so I set it up to run fully loaded and have the freeze stat cycle the compressor off at 35* & back on at 50*.
    Yesterday I went back to find the compressor going off on low pressure. The TXV wasn't opening at all. I purchased a new Power Assembly and installed it. I also found some debris under the cage assembly and the equalizing line was stopped up with thread sealant. I don't know why they used sealant on a flare connection. I started the system back up, the pressures are better, put I had 4* SH, 0* SC and the glass was flashing real bad. I adjusted the new Power Assembly 38 turns clockwise to increase the SH, but it only went up to 5*. I think the cage also needs replaced. I would of got one but I didn't have the part number. I added another 10 lbs of 134a and no difference. Now when you open the HGB valves, the by-pass lines get cold, but the inlet to the HGB is hot. It looks like liquid is in the discharge line if that is possible. I'm about ready to pull my hair out over this one.

  6. #6
    Join Date
    Mar 2008
    Location
    North Queensland, Australia
    Posts
    1,051
    Did you folow and read the link in the last post I sent?
    3* across the heat exchangers seems very low. Can you split and clean the Heat exchangers?
    Don't know if there's much more I can do for you from here.
    How about some temperatures and pressures instead of just Delta Ts
    What's the discharge line temperature where it leaves the compressor?
    HP
    LP
    suction line temp at the compressor and leaving the chiller.
    Liquid line temp just before the txv.
    all the temps you used to generate your figures.
    Mistakes are a part of being human. Appreciate your mistakes for what they are: precious life lessons that can only be learned the hard way. Unless it's a fatal mistake, which, at least, others can learn from. Al Franken, "Oh, the Things I Know", 2002

  7. #7
    Join Date
    Sep 2006
    Location
    Ohio
    Posts
    470
    Slatts,
    Here are some of the readings I had.
    Compressed air in=81*, out=76* = 5*
    Evap water in=47*, out=36* = 11*
    Heat exchangers water in=36*, out=39* = 3*
    Liquid line pressure after the receiver=130 psi, L.L. temp=100* = 3* SC
    Suction pressure at compressor= 15 psi, line temp at TXV bulb=30*=15 SH
    The pressures and tempreatures would change, but the SH and SC stayed about the same.
    After changing the Power Assembly, adjusting it 38 turns and adding R-134a.
    Liquid line pressure=140 psi, L.L. temp=107* = 0* SC
    Suction Pressure at comp.=35 psi, line temp at bulb =45*= 5* SH and line temp at the compressor was 46*= 6* comp SH.
    I didn't check the discharge line temperature at the compressor, I guess you want to know what the Discharge Super Heat is. I'm not sure what it should be for R-134a, that's why I didn't check it.
    The comp. amps were at 33 and the rated amp draw is 52. I was told by the factory that the rated amps is for R-22 and it would be lower for R-134a. It still looks like the system is low on refrigerant going by sub cooling.

  8. #8
    Join Date
    Mar 2008
    Location
    North Queensland, Australia
    Posts
    1,051
    Quote Originally Posted by hands View Post
    Slatts,
    Here are some of the readings I had.
    Compressed air in=81*, out=76* = 5*
    Evap water in=47*, out=36* = 11*
    Heat exchangers water in=36*, out=39* = 3*
    Are these the original readings, or after you changed the valve?
    was the compressor running unloaded at the time?
    It doesn't look to bad to me.

    Quote Originally Posted by hands View Post
    Liquid line pressure after the receiver=130 psi, L.L. temp=100* = 3* SC
    Suction pressure at compressor= 15 psi, line temp at TXV bulb=30*=15 SH
    The pressures and tempreatures would change, but the SH and SC stayed about the same.
    I'm assuming that, if you set up the condenser fans as per your 1st post, only 1 condenser fan was running?

    Quote Originally Posted by hands View Post
    After changing the Power Assembly, adjusting it 38 turns
    Full 360 degree turns?

    Quote Originally Posted by hands View Post
    and adding R-134a.
    Liquid line pressure=140 psi, L.L. temp=107* = 0* SC
    Each ckt has a Copeland 6 cylinder compressor with two unloaders, remote air cooled condenser with two fans, liquid receiver,
    With a liquid receiver in the system you must charge to a clear sight glass. You can then add some for the pot without affecting the superheat. You can't set the superheat while the system is short of gas. Let's clear the glass.

    Quote Originally Posted by hands View Post
    Suction Pressure at comp.=35 psi, line temp at bulb =45*= 5* SH and line temp at the compressor was 46*= 6* comp SH.
    Once again, you'll want to clear the glass, then set up the valve. with the suction at 35, is the HGB valve opening? It shouldn't be.
    That HGBV, is it a solenoid valve or a modulating valve? I'm assuming the latter.
    Are the unloaders still unloading at 45 and 46 as per the suppliers instructions? In which case the compressor was running full unloaded?

    Quote Originally Posted by hands View Post
    I didn't check the discharge line temperature at the compressor, I guess you want to know what the Discharge Super Heat is. I'm not sure what it should be for R-134a, that's why I didn't check it.
    Actually the comment about the hot suction line worried me. If your discharge line at the DSV gets to over 120C you're going to carbonise the oil. If your suction was that hot, your discharge temp must have been through the roof.

    Quote Originally Posted by hands View Post
    The comp. amps were at 33 and the rated amp draw is 52. I was told by the factory that the rated amps is for R-22 and it would be lower for R-134a. It still looks like the system is low on refrigerant going by sub cooling.
    At 35 psi the compressor should be running fully unloaded, in which case the Amps will reflect it.
    It's still short. It's not a critical charge system if it has a receiver. Just charge it to a clear sight glass. if it floods back (0 F SH) close the valve down as you go. once you have a clear sight glass, the SH will stabilise. More gas in the system won't affect it.

    Have you double checked that the correct size TX valve is fitted?

    How's the compressed air? Is it dry?
    Mistakes are a part of being human. Appreciate your mistakes for what they are: precious life lessons that can only be learned the hard way. Unless it's a fatal mistake, which, at least, others can learn from. Al Franken, "Oh, the Things I Know", 2002

  9. #9
    Join Date
    Sep 2006
    Location
    Ohio
    Posts
    470
    Quote Originally Posted by Slatts
    Are these the original readings, or after you changed the valve?
    was the compressor running unloaded at the time?
    It doesn't look to bad to me.

    (Hands) It was before I changed the valve. I had shut the dryer off until the water temp reached 65*F, then started it and it was running loaded and HGB was off. After it runs for about 10 to 15 min., The suction would drop to 10 to 8 psi.



    (Slatts) I'm assuming that, if you set up the condenser fans as per your 1st post, only 1 condenser fan was running?

    (Hands) yes

    (Slatts) Full 360 degree turns?

    (Hands) Yes, full turns



    (Slatts) With a liquid receiver in the system you must charge to a clear sight glass. You can then add some for the pot without affecting the superheat. You can't set the superheat while the system is short of gas. Let's clear the glass.

    (Hands) I was adjusting the TXV to keep liquid out of the compressor while charging it. I could only get about 1 or 2 lps of refrigerant in before I had to shut it off due to low pressure and water. I have added 66 lbs. to the ckt, not sure how much it holds.The glass is flashing like crazy and I have found no major leaks unless the evap has one. I have never heard not to use subcooling to check charge if the system has a receiver. I have heard not to go by the sight glass alone.

    (Slatts) Once again, you'll want to clear the glass, then set up the valve. with the suction at 35, is the HGB valve opening? It shouldn't be.
    That HGBV, is it a solenoid valve or a modulating valve? I'm assuming the latter.
    Are the unloaders still unloading at 45 and 46 as per the suppliers instructions? In which case the compressor was running full unloaded?

    (Hands) The HGB valves were closed and I lowered the setpoint for the unloaders to keep the compressor loaded while trying the get the ckt charged. The HGB are capacity regulator type, I guess you would say they are modulating. I am keeping the compressor loaded all the time now and cycling it off and on with the freeze controller. When the compressor runs unloaded for a long time, the oil is getting washed out of the compressor and it starts sounding bad.


    (Slatts) Actually the comment about the hot suction line worried me. If your discharge line at the DSV gets to over 120C you're going to carbonise the oil. If your suction was that hot, your discharge temp must have been through the roof.

    (Hands) The factory guy had set up the HGB that injects into the suction line at the accumulator, to open first. So it would be open all the way at times which heated the compressor. I think thats what killed ckt -1 compressor.

    (Slatts) At 35 psi the compressor should be running fully unloaded, in which case the Amps will reflect it.
    It's still short. It's not a critical charge system if it has a receiver. Just charge it to a clear sight glass. if it floods back (0 F SH) close the valve down as you go. once you have a clear sight glass, the SH will stabilise. More gas in the system won't affect it.

    (Hands) By most indications, it still looks like it's short on gas, but now when the HGB valve opens, the line gets very cold from the HGB to the evap. It looks like liquid is flowing through it. Have you ever seen that before?

    (Slatts) Have you double checked that the correct size TX valve is fitted?

    (Hands) The TXV doesn't have any numbers on it, I don't know if it is correct or not. The only numbers were on the Power Assembly.

    (Slatts) How's the compressed air? Is it dry?

    There is quite a bit of water in the air lines. But Friday the dryer was off about all day due to the bad power assembly.

    I think the TXV cage assembly needs to be replaced too. The factory guys are going to replace the bad compressor for ckt 1 this week and they are going to bring a new cage. I just dont have faith in the guy that is coming out. When he did the start-up of this and another dryer, he didn't check the SH, SC or amp draws. He even started turning the TXV to keep the suction pressure up, but still didn't check SH. I feel that the evap is too big of this dryer. It has a 1 1/4" water line going in and out of the evaporator which has 6" flanges. I had asked the factory to check it, but they didn't want to even go there.

  10. #10
    Join Date
    Mar 2008
    Location
    North Queensland, Australia
    Posts
    1,051
    Quote Originally Posted by hands View Post
    There is quite a bit of water in the air lines. But Friday the dryer was off about all day due to the bad power assembly.

    I think the TXV cage assembly needs to be replaced too. The factory guys are going to replace the bad compressor for ckt 1 this week and they are going to bring a new cage. I just dont have faith in the guy that is coming out. When he did the start-up of this and another dryer, he didn't check the SH, SC or amp draws. He even started turning the TXV to keep the suction pressure up, but still didn't check SH. I feel that the evap is too big of this dryer. It has a 1 1/4" water line going in and out of the evaporator which has 6" flanges. I had asked the factory to check it, but they didn't want to even go there.
    I'm beginning to think that this machine is too big for the job.
    If the power element fails the valve will close. The machine should have pumped down and gone out on LP. Unless of course the HGBVs were holding the suction up.
    In order to lift the back pressure the commissioner should have adjusted the HGBVs not the TX.
    For critical charge systems, that's to say, systems without receivers, SC is more of an issue. just clear the SG.
    This one is now between you and the manufacturer.
    All my ideas are in the previous posts.
    We're going round in circles now. You need to either get the manufacturer to get more involved or get someone in who is good with chillers to look at it.

    Best of luck hands
    Mistakes are a part of being human. Appreciate your mistakes for what they are: precious life lessons that can only be learned the hard way. Unless it's a fatal mistake, which, at least, others can learn from. Al Franken, "Oh, the Things I Know", 2002

  11. #11
    Join Date
    Sep 2002
    Posts
    12,299

    Let's start over again - first things first

    First - stop adjusting the TXV's!

    Then make sure the glycol ratio is correct so that you cannot freeze the brine. But not more than that. Excess glycol is a bad thing.

    Then make sure your loop is full - no air, and that your pumps are amped up - check the pump curves and chiller barrel specs - to get the proper pressure drops across the chiller barrels to make sure you are moving the right amount of flow.

    Start up the compressor and set both HGBP valves to 35 lbs. or so. That will keep the unit running while you add refrigerant. Then charge to 10-12 degrees liquid subcooling.

    Since you have opened the TXV's so much - watch your suction superheat while you add refrigerant! It if drops below 10 degrees immediately stop charging and adjust the SSH back up to 20 degrees. Then resume charging to get the right subcooling.

    Until you have the subcooling right you cannot trust your TXV's. It you can't trust the TXV's - you are risking the valves and the rest of the compressor. That big Copey wants 18 degrees SSH at the suction valve. Make sure it gets it.

    When you get those stabilized close the accumulator HGBP and let the TXV end HGBP valve do the work. When the machine unloads you will want as much velocity through the chiller as possible - to keep the oil coming back to the compressor.

    Start there and let's see how it balances out.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  12. #12
    Join Date
    Sep 2006
    Location
    Ohio
    Posts
    470
    Quote Originally Posted by Poodle Head Mikey View Post
    First - stop adjusting the TXV's!

    Then make sure the glycol ratio is correct so that you cannot freeze the brine. But not more than that. Excess glycol is a bad thing.

    Then make sure your loop is full - no air, and that your pumps are amped up - check the pump curves and chiller barrel specs - to get the proper pressure drops across the chiller barrels to make sure you are moving the right amount of flow.

    Start up the compressor and set both HGBP valves to 35 lbs. or so. That will keep the unit running while you add refrigerant. Then charge to 10-12 degrees liquid subcooling.

    Since you have opened the TXV's so much - watch your suction superheat while you add refrigerant! It if drops below 10 degrees immediately stop charging and adjust the SSH back up to 20 degrees. Then resume charging to get the right subcooling.

    Until you have the subcooling right you cannot trust your TXV's. It you can't trust the TXV's - you are risking the valves and the rest of the compressor. That big Copey wants 18 degrees SSH at the suction valve. Make sure it gets it.

    When you get those stabilized close the accumulator HGBP and let the TXV end HGBP valve do the work. When the machine unloads you will want as much velocity through the chiller as possible - to keep the oil coming back to the compressor.

    Start there and let's see how it balances out.
    There is no air in the water loop and the pumps are just under rated amp draw. There are no specs on the evaporator barrel, but I will bring this up when the factory guys come in.
    I can't get the SSH more than 6*F. As far as setting the HGB valves at 35* while charging, you won't get a true SC reading if they are open, you should always check the charge with the compressor loaded and the HGB closed.

    As I stated before, when the HGB valves open, the outlet lines are getting very cold, like liquid might be passing through them. This didn't happen until I replaced the power assembly and added the last 10 lbs of refrigerant. Keep in mind that this point I had 0* SC. Any ideas what would cause this.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event