Page 8 of 18 FirstFirst 123456789101112131415161718 LastLast
Results 351 to 400 of 896
  1. #351
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling





    Water cyclic heating between ~63-68'C.

    Observe the temperature drift even at TXV outlet stage.

    The white signal is TXV inlet temp - note that the trend of TXV inlet & outlet are NOT the same over time. The TXV outlet temp & evap outlet temp follow similar trends - although offset in temp.
    Last edited by desA; 16-08-2009 at 07:33 AM.


    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  2. #352
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    The TXV outlet temp & evap outlet temp follow similar trends - although offset in temp.
    Not too surprising since they are both subject to TXV modulation.

    I take it the bottleneck in the graph is the off cycle?

    If you could identify all of the lines, we may be able to spot other significant trends.

  3. #353
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by Gary View Post
    Not too surprising since they are both subject to TXV modulation.
    True. The need for an alternative over-arching control system - Tcomp,disc to evap air feed, is becoming very clear.

    I take it the bottleneck in the graph is the off cycle?
    To be honest, I'm currently more worried about the Te,sat drift upwards to 19'C, during the operational phase. In my view, the inward 'energy pump' via the evap, in excess of what the condenser can/should deliver (from a thermodynamic balance perspective), causes the cycle to lift, since the heat enters faster than it can be extracted.

    The heat-pump cycle seems to be inherently unstable - distinctly different to an aircon system which is inherently stable, if managed correctly. We can talk more about this at a later stage. The evap control provides the necessary decelerator effect.

    If you could identify all of the lines, we may be able to spot other significant trends.
    Give me a few hours - just returned back home from abroad.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  4. #354
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling



    Hopefully a little clearer picture.

    #Number key:


    Colour key (ignore numeric values, for now, as they are at a specific time instant):
    Last edited by desA; 17-08-2009 at 05:35 AM.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  5. #355
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Surprisingly, the inlet air temp (orange line) seems to have little effect on the other temps.
    Last edited by Gary; 17-08-2009 at 06:39 AM.

  6. #356
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    The inlet air line is rather interesting - it must be said:

    1. It is a bare thermocouple placed slightly upstream of the evap inlet filter - this explains the 'sensor chatter';
    2. The hot water vessel, for his particular test (not the lab machine), is an open vessel - located in the test room. The upward drift during the major heating portion of the run, can be explained by hot water steam-off.

    Please observe the correlation between the following signals:
    #30 - air inlet temp
    #27 - out exp
    #28 - outlet evap
    #29 - suction to comp

    #27/#28/#29 track the air inlet temp, with moderation, but, the curve shape is visible - rise (with slight delay), peak, roll-off. The TXV seems to be doing pretty well, but, it simply cannot track closely, at evap fixed air speed.

    The drifting air temp has to affect the Te,sat & associated evap temps. This can also be shown from an evap heat-transfer balance.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  7. #357
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    I've just performed a very crude experiment on the lab machine.

    It is conclusive the Te,sat rises in response to evap load push & consequent system imbalance.

    I was able to hold the Te,sat value at desired value, throughout the heating cycle, by varying evap fan speed. This is trick stuff...

    The question just has to be asked:
    Does anyone know of heat-pump designs where the evap duty is managed over the range of the heating cycle?
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  8. #358
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    I've just performed a very crude experiment on the lab machine.

    It is conclusive the Te,sat rises in response to evap load push & consequent system imbalance.

    I was able to hold the Te,sat value at desired value, throughout the heating cycle, by varying evap fan speed. This is trick stuff...
    It should be fairly simple to make this automatic.

    Install a temp control on the discharge line. Wire the dimmer in parallel with the temp control contacts.

    When the discharge temp reaches setpoint, its contacts open and the dimmer takes over.

  9. #359
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    ^ Can I perhaps ask you to set up a rough sketch of this logic? (pencil sketch, scanned up to tinypic.com, would be incredibly helpful).

    I'll work on setting that up in the next few days. This is beginning to get very interesting.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  10. #360
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    ^ Can I perhaps ask you to set up a rough sketch of this logic? (pencil sketch, scanned up to tinypic.com, would be incredibly helpful).

    I'll work on setting that up in the next few days. This is beginning to get very interesting.


    In effect, this gives you a two speed fan, with the second speed being adjustable.

    In addition, the fan starts through the temp control contacts, so the dimmer is not subjected to the heavier starting current of the fan motor. This is better for both the dimmer and the motor.

    The setpoint and differential on the temp control should be adjusted such that the contacts open at maximum allowable load and close at minimum allowable load.

    The dimmer should be adjusted such that the load is maintained just under the maximum allowable load on the hottest day (35C air in).

    We could improve upon this with a two stage temp control. With a two stage temp control the second set of contacts could shut off the fan if for any reason the discharge temp continues to rise above maximum.
    Last edited by Gary; 17-08-2009 at 08:05 PM.

  11. #361
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    Thanks very much - now clear.

    We could improve upon this with a two stage temp control. With a two stage temp control the second set of contacts could shut off the fan if for any reason the discharge temp continues to rise above maximum.
    I'd like to explore this option a little further, if possible.

    A further alternative to consider - a simple 2-step:
    What if a condenser fan speed controller is used - with a HP take-off, instead of temp at compressor discharge? The control signal would have to be modified to give reducing fan speeds with rising HP (the condenser control signal speeds up the fan with increasing HP).

    This modified signal can then be used to adjust fan speed.

    A variation on this is to have 2 fans, then stop one when the HP reaches a pre-determined value.

    Under these options, a correlation between the thermodynamic Q'e (evap load) & the Tc,sat (or HP value) can easily be developed. This then allows the HP circuit to be used to control the LP circuit temp.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  12. #362
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Have you tested the iced drier yet?

  13. #363
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by Gary View Post
    Have you tested the iced drier yet?
    Was trying to figure out a way to set up a holding tub around the drier, so that the ice stays in place. I'll play around a little later today...

    I had a further idea - to use evaporative cooling effect by wrapping the drier in a rag & then soaking it in water. The evap airstream should evaporate the water & drop the local temp around the drier.

    I'll get onto that...
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  14. #364
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    Revised plan of action:
    1. Modify partition separating condenser from compressor.
    2. Properly insulate condenser & partition walls.
    3. Test system response to these changes.
    4. Re-position filter drier to vertical orientation.
    5. Test system response to this change.
    6. Install water regulating valve.
    7. Test system response to this change.
    8. Adjust WRV & iterate adjustment/testing.
    How is the plan going?

  15. #365
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    ^ I only arrived back yesterday... 10h overnight bus trips in Asia are a killer... Add to that a border crossing.

    I'm off to sort out a few bits for the system, today. I have the tools to modify the panel, but still need some decent insulation - it was too heavy to lug up from BKK.

    Last edited by desA; 18-08-2009 at 04:04 AM.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  16. #366
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    ^ I only arrived back yesterday... 10h overnight bus trips in Asia are a killer... Add to that a border crossing.

    I'm off to sort out a few bits for the system, today. I have the tools to modify the panel, but still need some decent insulation - it was too heavy to lug up from BKK.

    I suppose next you'll be claiming that you require sleep... lol

  17. #367
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    A further alternative to consider - a simple 2-step:
    What if a condenser fan speed controller is used - with a HP take-off, instead of temp at compressor discharge? The control signal would have to be modified to give reducing fan speeds with rising HP (the condenser control signal speeds up the fan with increasing HP).

    This modified signal can then be used to adjust fan speed.

    A variation on this is to have 2 fans, then stop one when the HP reaches a pre-determined value.

    Under these options, a correlation between the thermodynamic Q'e (evap load) & the Tc,sat (or HP value) can easily be developed. This then allows the HP circuit to be used to control the LP circuit temp.
    There are a great many control strategies which can be made to work. To my mind, the key temperature is the discharge temperature.

  18. #368
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    To be honest, I'm currently more worried about the Te,sat drift upwards to 19'C, during the operational phase. In my view, the inward 'energy pump' via the evap, in excess of what the condenser can/should deliver (from a thermodynamic balance perspective), causes the cycle to lift, since the heat enters faster than it can be extracted.

    The heat-pump cycle seems to be inherently unstable - distinctly different to an aircon system which is inherently stable, if managed correctly. We can talk more about this at a later stage. The evap control provides the necessary decelerator effect.
    To my mind, Te,sat is not a concern so long as the compressor is kept cool. In fact, higher Te,sat reduces the compression ratio.

    Reducing the airflow reduces the efficiency of the system, and is thus counter-productive. As I see it, the discharge temp/fan control strategy is purely for limiting the compressor heat while we find more ways to load the evaporator right up to the max.
    Last edited by Gary; 18-08-2009 at 03:01 PM.

  19. #369
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    Originally Posted by desA
    To be honest, I'm currently more worried about the Te,sat drift upwards to 19'C, during the operational phase. In my view, the inward 'energy pump' via the evap, in excess of what the condenser can/should deliver (from a thermodynamic balance perspective), causes the cycle to lift, since the heat enters faster than it can be extracted.

    The heat-pump cycle seems to be inherently unstable - distinctly different to an aircon system which is inherently stable, if managed correctly. We can talk more about this at a later stage. The evap control provides the necessary decelerator effect.
    Gary:
    To my mind, Te,sat is not a concern so long as the compressor is kept cool. In fact, the higher Te,sat reduces the compression ratio.

    If the condenser can't handle the output of the evaporator, then a bigger water pump is needed... or perhaps a bigger condenser.

    Reducing the airflow reduces the efficiency of the system, and is thus counter-productive. As I see it, the discharge temp/fan control strategy is purely for limiting the compressor heat.
    Heat-pump philosophy
    The compressor is the heart of the system. To obtain a high COP, the evap & condenser must move in synchronous with the compressor, since we have an interacting system.

    As I see it, pushing in excess heat through the evaporator, must be extracted by the condenser, without forcing up the compressor motor power. The system starts at maximum COP & gradually slides down, as the system moves towards the hot condition.

    The evap fan is the input throttle, the condenser water flow is the condenser accelerator. Managing these two ends carefully, will keep the system on the correct thermodynamic balance & optimum COP curve. Increasing the condenser water flow will lower Tc,sat slightly, also increasing COP slightly. So, essentially, anything that forces a system imbalance may end up pulling the system away from the optimum thermodynamics.
    Last edited by desA; 18-08-2009 at 02:51 PM.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  20. #370
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    Fan speed regulation via dimmer switch

    How far can the motor speed safely be reduced?
    The dimmer switch introduces a slight motor hum.

    I've read about this hum & the reasons for it. Some folks suggest to rather use a fan speed controller - as per ceiling fan adjustment. Well, I did try that option today, without much success - the arcing between switch settings concerned me - as did the rapid fall-off in speed from 100% to supposed 80% position (turns out was more like 20%). Went back to the dimmer switch - hum & all - in combination with my sliding panel tricks.
    Last edited by desA; 18-08-2009 at 02:58 PM.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  21. #371
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    Lab machine retrofit

    I'll get onto the lab machine modifications tomorrow. The first work will be to open up the barrier around the compressor & to insulate the condenser with decent insulation (have three rolls on hand, plus some other materials). Didn't want to spend too much on this machine, as it is only for testing & evaluation purposes.

    The water regulating valve has still eluded me, but, for now, I propose to manually set the flow via an inline gate valve - until a suitable valve can be sourced. May have to drive a valve through an actuator & controller, if pressure/flow valve cannot be sourced. Any ideas on this?

    My HVAC supplier has my filter-drier on order, & so I'm loathe to cut into the refrigeration line until all parts are in-house. I can find alternative filter-driers, but did not want to change too many things at once - firm base to firm base.

    (Sidebar: This filter-drier oder thing is a direct consequence of the world economic slowdown. I'm talking about one of Thailand's main parts suppliers here, not some fly-by-night. The stock imports are slowing down - it's clear).
    Last edited by desA; 18-08-2009 at 03:08 PM.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  22. #372
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    If you can simply tilt the drier downward in the direction of flow, it will help.

  23. #373
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    Heat-pump philosophy
    The compressor is the heart of the system. To obtain a high COP, the evap & condenser must move in synchronous with the compressor, since we have an interacting system.
    I agree.

    Quote Originally Posted by desA View Post
    As I see it, pushing in excess heat through the evaporator, must be extracted by the condenser, without forcing up the compressor motor power. The system starts at maximum COP & gradually slides down, as the system moves towards the hot condition.
    The excess heat is being returned to the evaporator in the form of hot liquid entering the TXV. That's what the iced drier test is going to demonstrate.

    Quote Originally Posted by desA View Post
    The evap fan is the input throttle, the condenser water flow is the condenser accelerator. Managing these two ends carefully, will keep the system on the correct thermodynamic balance & optimum COP curve. Increasing the condenser water flow will lower Tc,sat slightly, also increasing COP slightly. So, essentially, anything that forces a system imbalance may end up pulling the system away from the optimum thermodynamics.
    If the condenser is the weak link, and I'm not certain that it is, then why decelerate the rest of the system to match the weak link? Let's find ways to strengthen that link.
    Last edited by Gary; 18-08-2009 at 04:04 PM.

  24. #374
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by Gary View Post
    If you can simply tilt the drier downward in the direction of flow, it will help.
    Ok, great. That can certainly be done. I've got a decent pipe-bender here. I'll work on getting that set tomorrow.

    Thanks for that advice.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  25. #375
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    Originally Posted by desA
    As I see it, pushing in excess heat through the evaporator, must be extracted by the condenser, without forcing up the compressor motor power. The system starts at maximum COP & gradually slides down, as the system moves towards the hot condition.
    Gary:
    The excess heat is being returned to the evaporator in the form of hot liquid entering the TXV. That's what the iced drier test is going to demonstrate.
    This makes absolute sense, in that the evap/condenser imbalance will force heat-recirculation within the refrigerant loop itself. This is obviously something we really don't need.

    I'll get that test done early tomorrow, before modifying the machine. Then at least we only have one change at a time.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  26. #376
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    Originally Posted by desA
    The evap fan is the input throttle, the condenser water flow is the condenser accelerator. Managing these two ends carefully, will keep the system on the correct thermodynamic balance & optimum COP curve. Increasing the condenser water flow will lower Tc,sat slightly, also increasing COP slightly. So, essentially, anything that forces a system imbalance may end up pulling the system away from the optimum thermodynamics.
    Gary:
    The condenser is the weak link. Why decelerate the rest of the system to match the weak link? Let's find ways to strengthen that link.
    The condenser will always be the bottle-neck, if the system is sized on what appears to be an air-conditioning philosophy. "Design evap oversize, blast-cool condenser if P,hi goes up too far".

    For the heat-pump, it seems that the condenser must be sized properly to pull out the heat correctly. The evap throttle is there to lag the condenser pull, as I see it.

    Now, how to push the condenser further?
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  27. #377
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    I'm not certain that the condenser is indeed the weak link. Is the condenser unable to handle that heat?... or is that heat being stolen away from the condenser?
    Last edited by Gary; 18-08-2009 at 04:18 PM.

  28. #378
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    Originally Posted by Gary
    If you can simply tilt the drier downward in the direction of flow, it will help.
    desA:
    Ok, great. That can certainly be done. I've got a decent pipe-bender here. I'll work on getting that set tomorrow.

    Thanks for that advice.
    All done. The downward slope is now around 30' off the horizontal, facing downwards in direction of flow.

    What reaction are we expecting to see from the system?
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  29. #379
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    All done. The downward slope is now around 30' off the horizontal, facing downwards in direction of flow.

    What reaction are we expecting to see from the system?
    If the system is sufficiently charged, then it probably won't make any difference. If the system were a little undercharged, then it would make a BIG difference. Liquid at the TXV inlet as opposed to vapor at the TXV inlet.
    Last edited by Gary; 18-08-2009 at 04:47 PM.

  30. #380
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by Gary View Post
    I'm not certain that the condenser is indeed the weak link. Is the condenser unable to handle that heat?... or is that heat being stolen away from the condenser?
    Condenser review
    1. Tube-in-tube coil;
    2. Estimated heat-transfer = 7kW (heat-transfer simulation - internal procedure)
    3. Compressor calculations - Te,sat=12.5'C:
    3.1 At Tc,sat=40'C : Qc=7.8kW;
    3.1 At Tc,sat=50'C : Qc=7.5kW;
    3.3 At Tc,sat=70'C : Qc=6.8kW;
    4. Condenser originally un-insulated (lab m/c), located inside condenser/compressor compartment.
    5. Condenser response to rough insulation fit-up was increase of around 10% on overall heat duty.

    So, I'd say that the condenser is marginally sized - with no over-surface margin to play with. The lack of insulation is daft.

    I'll have the insulation looking pretty good tomorrow - we can then see what it's effect is - before I remove the partition.

    When running this system, it always feels like the condenser is under-performing.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  31. #381
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    Originally Posted by desA
    All done. The downward slope is now around 30' off the horizontal, facing downwards in direction of flow.

    What reaction are we expecting to see from the system?
    Gary:
    If the system is sufficiently charged, then it probably won't make any difference. If the system were a little undercharged, then it would make a BIG difference.
    For this condenser, when we insulated it - the approach temps reduced from 8.1K to 7.75K (at Tc,sat=75'C), & SC reduced dramatically from 8.5K to 5.8K.

    Before that point, the data seemed to point to a slightly overcharged system. After the insulation addition, it may in fact be close to correct charge, or marginally under-charged.

    What big changes could be expected for an under-charged system?
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  32. #382
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    Condenser review
    1. Tube-in-tube coil;
    2. Estimated heat-transfer = 7kW (heat-transfer simulation - internal procedure)
    3. Compressor calculations - Te,sat=12.5'C:
    3.1 At Tc,sat=40'C : Qc=7.8kW;
    3.1 At Tc,sat=50'C : Qc=7.5kW;
    3.3 At Tc,sat=70'C : Qc=6.8kW;
    4. Condenser originally un-insulated (lab m/c), located inside condenser/compressor compartment.
    5. Condenser response to rough insulation fit-up was increase of around 10% on overall heat duty.

    So, I'd say that the condenser is marginally sized - with no over-surface margin to play with. The lack of insulation is daft.

    I'll have the insulation looking pretty good tomorrow - we can then see what it's effect is - before I remove the partition.

    When running this system, it always feels like the condenser is under-performing.
    And yet the approach keeps improving.

  33. #383
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    ^ Very true.

    I'll get the insulation as tight as possible & probably close in the modified compartment to seal the coil end from the compressor. With all the piping in the way, this divide will probably be some sheet insulation, sealed along the edges with insulation.

    What would you expect the temperature of the outside surface of a well insulated condenser to be?
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  34. #384
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    For this condenser, when we insulated it - the approach temps reduced from 8.1K to 7.75K (at Tc,sat=75'C), & SC reduced dramatically from 8.5K to 5.8K.

    Before that point, the data seemed to point to a slightly overcharged system. After the insulation addition, it may in fact be close to correct charge, or marginally under-charged.

    What big changes could be expected for an under-charged system?
    If the system were undercharged we would have seen high superheat. I would not expect any changes from tilting the drier on this system.

    However... tilting the drier gives you a lot more wiggle room on the charge, which can make a big difference when these systems are serviced in the field.
    Last edited by Gary; 18-08-2009 at 05:16 PM.

  35. #385
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    ^ Agreed. Angling the filter-drier with the exit towards the bottom makes for sound engineering.

    I think that many of us never really thought about it as if it were a funnel system - managing full liquid to the TXV.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  36. #386
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    ^ Agreed. Angling the filter-drier with the exit towards the bottom makes for sound engineering.

    I think that many of us never really thought about it as if it were a funnel system - managing full liquid to the TXV.
    This is extremely important on cap tube systems as the charge is critical.

    It is less important on TXV systems because they either have a receiver for extra refrigerant or they back extra refrigerant up into the condenser, thus assuring a full flow of solid liquid through the drier.

    Having neither of these options, the charge becomes critical on this system and the drier, such as it is, is the closest thing we have to a receiver... if it is tilted downwards.
    Last edited by Gary; 18-08-2009 at 05:40 PM.

  37. #387
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by Gary View Post
    It is less important on TXV systems because they either have a receiver for extra refrigerant or they back extra refrigerant up into the condenser, thus assuring a full flow of solid liquid through the drier.

    Having neither of these options, the charge becomes critical on this system and the drier, such as it is, is the closest thing we have to a receiver... if it is tilted downwards.
    That is pretty cunning, I must say...

    Now, that said, would it then be a useful design strategy to perhaps use large-size (larger than for reasonable water extraction) filter-driers for these systems?
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  38. #388
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    That is pretty cunning, I must say...

    Now, that said, would it then be a useful design strategy to perhaps use large-size (larger than for reasonable water extraction) filter-driers for these systems?
    Throughout our tests the superheat has remained impressively stable, even with the drier horizontal. I see no particular need for more surplus refrigerant, so no need for a larger drier.

  39. #389
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    When running this system, it always feels like the condenser is under-performing.
    No matter how well the condenser performs, the leaving refrigerant temp can be no lower than the incoming water temp. As the incoming water temp rises, the leaving refrigerant temp must rise and the temp at the TXV inlet must rise and the Te,sat must rise... unless the liquid line is cooled.

    VIC to the rescue.
    Last edited by Gary; 18-08-2009 at 10:16 PM.

  40. #390
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by Gary View Post
    Throughout our tests the superheat has remained impressively stable, even with the drier horizontal. I see no particular need for more surplus refrigerant, so no need for a larger drier.
    Thanks Gary.

    The driers typically used, contain around 207 to 257g of refrigerant. This is already around 20-25% of the total refrigerant circuit mass charge, so if mounted vertically, the filter-drier would provide an excellent storage & feed buffer for the HP circuit.

    I'd imagine that, for this kind of device, a taller-slimmer drier may feed better than a shorter-fatter option. A few things for me to think about down the track.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  41. #391
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    Initial feedback after today's system retrofit

    1. Create air opening in partition - to allow flow over the compressor;
    2. Insulate condenser coil thoroughly;
    3. Tilt filter-drier (last evening).

    Initial runs are showing SC ~ 1.6K... lol...

    I'll do a complete proving run tomorrow, then work out how much refrigerant to add back in...
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  42. #392
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    Initial feedback after today's system retrofit

    1. Create air opening in partition - to allow flow over the compressor;
    2. Insulate condenser coil thoroughly;
    3. Tilt filter-drier (last evening).

    Initial runs are showing SC ~ 1.6K... lol...

    I'll do a complete proving run tomorrow, then work out how much refrigerant to add back in...
    How is the superheat looking?

  43. #393
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by Gary View Post
    How is the superheat looking?
    I did look at that, but will do a full set of runs tomorrow. SH was around the 7-7.5K mark, much like in the past. That part seems to be behaving itself.

    What was interesting is that the SC at TXV inlet is around 7.5K (added this sensor today). This means that the bare liquid line, with filter-drier in the evap off stream, is cooling fairly well.

    I hope to have a full set of readings tomorrow. I'll do the run at 100% fan speed, so as not to distort the picture. We can then compare like-with-like.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  44. #394
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Have you added a Tw,in sensor? This is a crucial measurement that has been missing from past runs.

  45. #395
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    I did look at that, but will do a full set of runs tomorrow. SH was around the 7-7.5K mark, much like in the past. That part seems to be behaving itself.
    The refrigerant charge is sufficient to feed the coil, then.

    So the question at this point is, how much refrigerant charge works best for the condenser?

  46. #396
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    The water regulating valve has still eluded me, but, for now, I propose to manually set the flow via an inline gate valve - until a suitable valve can be sourced. May have to drive a valve through an actuator & controller, if pressure/flow valve cannot be sourced. Any ideas on this?
    Maybe this will help:

    http://www.grainger.com/Grainger/sta..._reseller.html

    http://www.grainger.com/Grainger/items/4LZ98

    http://www.grainger.com/Grainger/wwg...=27&submit.y=3

    Hmmmm... these seem to be limited to 260psi (Tc,sat = 65C), which may not be high enough for our purposes.

    On the other hand, modifying it may be as simple as adding a spacer under the spring.

    http://www.grainger.com/Grainger/rp_...&iw=713&ih=600

    And here a manufacturers tech bulletin:

    http://cgproducts.johnsoncontrols.co...PDF/125687.PDF

    High pressure valves:

    http://cgproducts.johnsoncontrols.co...DF/1900575.PDF

    http://cgproducts.johnsoncontrols.co...F/12011514.PDF
    Last edited by Gary; 19-08-2009 at 08:29 PM.

  47. #397
    Join Date
    Apr 2001
    Location
    New Port Richey, Florida - USA
    Age
    78
    Posts
    5,072
    Rep Power
    34

    Re: AWHP superheat & sub-cooling

    Here is another small detail that can make a big difference:

    When installing a device which uses a sensing bulb (TXV, temp control, etc.) the bulb should be mounted with the cap tube upwards.

    If the cap tube is on the bottom, when the bulb gets warm the liquid portion of the charge can be pushed through the cap tube to the power element. Then the power element temp is sensed instead of the bulb temp.

    It is also a good idea for the power element to be above the bulb with its cap tube on the bottom, so that any liquid can drain back to the sensing bulb.

    Like the fine print in a contract, the devil is in the details.
    Last edited by Gary; 19-08-2009 at 09:11 PM.

  48. #398
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    Filter-drier retention time
    Quote Originally Posted by desA View Post
    The driers typically used, contain around 207 to 257g of refrigerant. This is already around 20-25% of the total refrigerant circuit mass charge, so if mounted vertically, the filter-drier would provide an excellent storage & feed buffer for the HP circuit.
    Based on the compressor currently in the lab heat-pump:
    m'g = 38.4 g/s (refrigerant mass flow at nominal operating point)
    Retention time in F-D = 257/38.4 = 6.7 sec

    This provides a very handy accumulator, gas-liquid separator effect.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  49. #399
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by Gary View Post
    Have you added a Tw,in sensor? This is a crucial measurement that has been missing from past runs.
    I've been 'sensor challenged' up here & will have to get a few more thermocouples sent up. (Tried last trip to BKK, but they were incredibly slow in dealing )

    In the meantime, I can rig up a spare tank sensor, via a controller readout, onto the outside of the water inlet pipe. This may give a little thermal lag, but should be reasonable, if I lag it well-enough.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

  50. #400
    Join Date
    Mar 2009
    Location
    KZN, South Africa
    Age
    63
    Posts
    2,212
    Rep Power
    20

    Re: AWHP superheat & sub-cooling

    Originally Posted by desA
    I did look at that, but will do a full set of runs tomorrow. SH was around the 7-7.5K mark, much like in the past. That part seems to be behaving itself.
    Gary:
    The refrigerant charge is sufficient to feed the coil, then.

    So the question at this point is, how much refrigerant charge works best for the condenser?
    Agreed. It seems that the combination of unlagged liquid line & filter-drier tilting, have assisted the TXV in terms of feed temperature & liquid feed consistency. Excellent.

    After today's test runs, we'll have an idea of how much refrigerant charge to add in to satisfy the condenser sub-cooling.
    Engineering Specialist - Cuprobraze, Nocolok, CD Technology
    Rarefied Technologies ( SE Asia )

Similar Threads

  1. 9 superheat & subcooling scenarios
    By nike123 in forum Fundamentals
    Replies: 39
    Last Post: 19-07-2011, 03:16 AM
  2. Superheat and Subcooling
    By Chunk in forum Fundamentals
    Replies: 42
    Last Post: 15-01-2011, 02:24 AM
  3. Replies: 5
    Last Post: 14-09-2009, 07:33 AM
  4. Low superheat and sucooling
    By jayaeros in forum Trouble Shooting
    Replies: 23
    Last Post: 05-07-2009, 06:21 AM
  5. Compressor loading, cooling, and range of operation.
    By Air duster in forum Fundamentals
    Replies: 10
    Last Post: 02-04-2008, 08:39 AM

Posting Permissions

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