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  1. #251
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    Re: AWHP superheat & sub-cooling



    Quote Originally Posted by Gary View Post
    At best the question of liquid line insulation is a trade-off. On the one hand we are losing the liquid heat, but on the other hand we reduce flashing in the evap. Given these test results, I would have to say it is too close to call.
    I also thought so, to be honest.

    Now, if you were to build a new machine & had the choice of insulated, or uninsulated liquid line (no VIC in this one) - what option would you take?

    Also a factor in this particular machine is that the liquid line filter-drier itself was uninsulated, & exposed directly to the evap off air stream - although the rest of the line was insulated - albeit with a rather loose (oversize) Aeroflex insulation. I wondered about the bulk of liquid sitting in the drier, being cooled.

    I would expect no such ambiguity with the VIC. Not only will it bring the liquid temp down close to Te,sat maximizing the evap capacity, but it will also recover the heat from the liquid, transferring it to the suction. We win in both directions.

    I expect the VIC to make a major difference.
    I'd expect the same. It will also reduce the size of the evap required for future machines.
    Last edited by desA; 05-08-2009 at 04:22 PM.


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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    Now, if you were to build a new machine & had the choice of insulated, or uninsulated liquid line (no VIC in this one) - what option would you take?
    In that case, I would leave it uninsulated.

    With the addition of the VIC, I would insulate everything from the condenser outlet to the TXV inlet.
    Last edited by Gary; 05-08-2009 at 06:16 PM.

  3. #253
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    Re: AWHP superheat & sub-cooling

    I'm thinking the next test run should be with the condenser insulated to see how much difference this makes.

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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    As I understand - from the compressor manufacturer's tech sheets - the right line of the compressor envelope may be crossed if compressor shell cooling is implemented.

    Quote Originally Posted by desA View Post

    It makes no sense at all to place the compressor in an insulated compartment heated by the condenser.

    This could have been avoided in this design by simply removing the partition section behind the compressor and placing that partition between the condenser and compressor. The compressor would then be in the evaporator compartment... and the condenser would be isolated and insulated.

    A simple fix for a big improvement.
    Last edited by Gary; 05-08-2009 at 11:59 PM.

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    Re: AWHP superheat & sub-cooling



    http://tinypic.com/r/33p3hj5/3

    Summary comments across runs #3,4,5:

    1. Runs 4/5 (32.9'C/31.5'C) are at slightly higher Ta,in than run #3 (30.7'C).

    2. Runs 4 to 5 :
    2.1 Compressor superheat decreases;
    2.2 Tc,exit increases => SC reduces;
    2.3 Compressor power reduces => COP increases.

    3. Run 4:
    3.1 Power anomaly due to V*I trading.
    3.2 Causes compressor base temp to increase to 63.2'C.

    In summary, removing the insulation from the liquid line is helpful (see points 2.1/2.2/2.3)
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    Re: AWHP superheat & sub-cooling

    Gary
    Originally Posted by desA
    Now, if you were to build a new machine & had the choice of insulated, or uninsulated liquid line (no VIC in this one) - what option would you take?
    In that case, I would leave it uninsulated.

    With the addition of the VIC, I would insulate everything from the condenser outlet to the TXV inlet.
    Agreed. This makes sense.
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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by Gary View Post
    It makes no sense at all to place the compressor in an insulated compartment heated by the condenser.

    This could have been avoided in this design by simply removing the partition section behind the compressor and placing that partition between the condenser and compressor. The compressor would then be in the evaporator compartment... and the condenser would be isolated and insulated.

    A simple fix for a big improvement.
    Absolutely agree.

    Quote Originally Posted by Gary View Post
    I'm thinking the next test run should be with the condenser insulated to see how much difference this makes.
    As a quick fix, I'll insulate the condenser portion from the compressor with some insulation I have to hand & run a test.

    I have to travel for a few days from Saturday, for around 10 days & will modify the metallic partition on the test machine, to split the compressor into the evap section, on my return.
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    Re: AWHP superheat & sub-cooling

    Refrigerant mass charge determination

    Now that we've reached a reasonable operating mass charge for the heat-pump, by bleeding off the excess charge, (the original charge had been based on the start-up mass requirement, not hot requirement) - how do we determine the correct charge for future machines, or re-fills?

    Do we:
    1. Charge at hot condition mass, then add in incremental charge (bleeding off air entrapment in lines), until system at desired operating conditions,
    or,
    2. Charge at start-up condition, then slowly bleed off refrigerant until system at desired operating conditions.

    With option (1) we know the final mass added to the system.
    With option (2), how will we determine the mass added to the system?
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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    Refrigerant mass charge determination

    Now that we've reached a reasonable operating mass charge for the heat-pump, by bleeding off the excess charge, (the original charge had been based on the start-up mass requirement, not hot requirement) - how do we determine the correct charge for future machines, or re-fills?

    Do we:
    1. Charge at hot condition mass, then add in incremental charge (bleeding off air entrapment in lines), until system at desired operating conditions,
    or,
    2. Charge at start-up condition, then slowly bleed off refrigerant until system at desired operating conditions.

    With option (1) we know the final mass added to the system.
    With option (2), how will we determine the mass added to the system?
    A minimum charge is that which fully feeds the evaporator. We have seen no rise in superheat at all so we are definitely above the minimum charge.

    The maximum charge is that which backs liquid up into the condenser.

    At this point we are riding the upper limits on the charge and if anything we could remove a little refrigerant.

    Under cold conditions (cold water and cold air) I would not be concerned if the SC drops so long as the SH does not rise substantially.
    Last edited by Gary; 06-08-2009 at 05:13 AM.

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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by Gary View Post
    A minimum charge is that which fully feeds the evaporator. We have seen no rise in superheat at all so we are definitely above the minimum charge.
    True. Ok.

    The maximum charge is that which backs liquid up into the condenser.
    We have been slowly moving from over-charge to the maximum charge point. Ok.

    At this point we are riding the upper limits on the charge and if anything we could remove a little refrigerant.
    Makes good sense.

    Under cold conditions (cold water and cold air) I would not be concerned if the SC drops so long as the SH does not rise substantially.
    Ok, got that. I would expect to see an SC drop-off under cold conditions, based on the previous unit performance.
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    Re: AWHP superheat & sub-cooling

    Hmmm... you mentioned the liquid line filter/drier. If you mount this vertically with the outlet at the bottom, this puts the liquid at the outlet, which could make a big difference if the charge becomes critical. In effect the filter/drier becomes a small receiver if there is vapor present (low SC).
    Last edited by Gary; 06-08-2009 at 05:48 AM.

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    Re: AWHP superheat & sub-cooling

    I assume we are still talking about a system without the VIC.

    The VIC is going to give this system massive subcooling at the TXV inlet. The charge would have to be extremely low to have any effect at all on the evaporator SH, making the charge very non-critical.

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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by Gary View Post
    Hmmm... you mentioned the liquid line filter/drier. If you mount this vertically with the outlet at the bottom, this puts the liquid at the outlet, which could make a big difference if the charge becomes critical. In effect the filter/drier becomes a small receiver if there is vapor present (low SC).
    Can you talk me through this a little further?

    The current test-machine has the filter-drier mounted almost horizontally.

    The current FD is an Alco EK 16 4S - with expected internal refrigerant holding at around 70'C, of 228.88g. This is a lot of refrigerant. I do trust my conversion from their Imperial fluid-based figure is correct.
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    Re: AWHP superheat & sub-cooling

    The TXV will fully feed the coil so long as there is solid liquid at its inlet.

    When the SC drops there is a liquid/vapor mixture moving through the line. As this mixture enters the drier it will separate with the liquid dropping to the bottom.

    If the drier is horizontal, when the liquid level is below the halfway point, vapor will be fed to the TXV inlet and the SH will rise dramatically.

    If the drier is vertical with the outlet at the bottom then all available liquid will be sent to the TXV inlet.

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    Re: AWHP superheat & sub-cooling

    This is very useful information - very.

    What happens if the TXV inlet is mounted above the liquid discharge point from the filter-drier? Would a vertical orientation still be effective in this case?
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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    This is very useful information - very.

    What happens if the TXV inlet is mounted above the liquid discharge point from the filter-drier? Would a vertical orientation still be effective in this case?
    The relative location of the TXV doesn't matter.

    Small details can make a big difference.
    Last edited by Gary; 06-08-2009 at 07:23 AM.

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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by Gary View Post
    The relative location of the TXV doesn't matter.

    Small details can make a big difference.
    Very interesting. So the dynamics of how the liquid gets out of the filter-drier, with liquid flood at the bottom - vapour to the top & self-bleeding back to the condenser, are very important.

    A very useful point, indeed. Thanks so much for that.
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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by Gary View Post
    I assume we are still talking about a system without the VIC.
    I'd like to try & tune the current lab machine to its limit, without having to pull it apart. We can then extract all useful information, before installing the VIC.

    The VIC is going to give this system massive subcooling at the TXV inlet. The charge would have to be extremely low to have any effect at all on the evaporator SH, making the charge very non-critical.
    This is an extremely useful feature, especially with the pressure on to minimise refrigerant charge mass as far as possible.

    I plan to size the VIC & have a unit brought up, for installation into the lab machine. We can then fine-tune the concept further.
    Last edited by desA; 06-08-2009 at 09:13 AM.
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    Re: AWHP superheat & sub-cooling

    Condenser coil insulation update (details to follow):

    I wrapped some of the box insulation around the condenser coil & basically built a simple box around it. It stopped heat moving to the aluminium inner separation wall. An inner layer was also used inside the coil. Bare in mind that this stuff could hardly be described as effective insulation, by any stretch of the imagination.

    Well, well, well...

    At Tc,sat=75'C, SC reduces from 8.5K to 5.8K, approach reduces from 8.1K to 7.75K, Tw,out increases from 66.90'C to 67.25'C.

    Lol... Test details to follow later tonight.
    Last edited by desA; 06-08-2009 at 12:21 PM.
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    Re: AWHP superheat & sub-cooling



    http://tinypic.com/r/96dkav/3

    The experimental results for the condenser coil with a simple, rough insulation box around it.
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    Re: AWHP superheat & sub-cooling

    Comments - partially-insulated condenser:

    1. Tc,exit temperature rises => SC reduces from 8.5K to 5.8K !!!

    2. Tw,out temp rises slightly from 66.9'C to 67.25'C.

    3. Approach drops from 8.10K to 7.75K !!!

    4. I would not read too much into the current-voltage values as we had a fair 'V*I' challenge today, with supply voltage dropping as low as 185V around midday. The first data point was taken before the challenge & the test stopped. Resumed later in the day, for the latter tow data points. There seems to be power waves in the region & the effect can be heard in fans slowing down, lights dipping etc. This comes and goes & does not seem to be consistent - we're in a bad patch at the moment, it seems. (At the same time, I'm convinced that as the amperage rises to compensate that the local authorities collect on higher electrical toll fees.)
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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    Condenser coil insulation update (details to follow):

    I wrapped some of the box insulation around the condenser coil & basically built a simple box around it. It stopped heat moving to the aluminium inner separation wall. An inner layer was also used inside the coil. Bare in mind that this stuff could hardly be described as effective insulation, by any stretch of the imagination.

    Well, well, well...

    At Tc,sat=75'C, SC reduces from 8.5K to 5.8K, approach reduces from 8.1K to 7.75K, Tw,out increases from 66.90'C to 67.25'C.

    Lol... Test details to follow later tonight.
    T,comp,b has dropped as well... seems our compressor likes the change, too.

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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by Gary View Post
    T,comp,b has dropped as well... seems our compressor likes the change, too.
    It certainly does. Makes sense in the end. Does no good to have an uninsulated condenser heating the compressor shell...

    I'll have to hold on further tests, as I'll be away for around 7-10 days, from Saturday. I'll get hold of some decent insulation for the condenser & wrap it better. In this way, we can stabilise that end, before moving forwards.
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    Re: AWHP superheat & sub-cooling

    If I could re-visit the refrigerant charging procedure for a minute.

    Is it better to slightly overcharge, then cut back until operating sweet point is found, or
    slightly underfill, then progressively add refrigerant until the sweet point is found?
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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    I'd like to try & tune the current lab machine to its limit, without having to pull it apart. We can then extract all useful information, before installing the VIC.
    I agree. We should fine tune everything else first.

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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    If I could re-visit the refrigerant charging procedure for a minute.

    Is it better to slightly overcharge, then cut back until operating sweet point is found, or
    slightly underfill, then progressively add refrigerant until the sweet point is found?
    I'm thinking we have already chosen the former path. Whatever gets us to the sweet point is a good procedure... and I'm hoping for a sweet range instead of a sweet point.

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    Re: AWHP superheat & sub-cooling

    Have you located a water regulating valve?

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    Re: AWHP superheat & sub-cooling

    Originally Posted by desA
    I'd like to try & tune the current lab machine to its limit, without having to pull it apart. We can then extract all useful information, before installing the VIC.
    Gary
    I agree. We should fine tune everything else first.
    At this stage, we could look at the design requirements for the VIC, though.

    Fluid 1 : Refrigerant - R-134A - liquid
    Entry condition : Liquid sub-cooled xx.xx'C off Tc,sat=75'C condition
    Exit condition : T,exit = T,inlet - y.y'C
    Allowable pressure drop = ?
    @ mass flowrate of refrigerant.

    Fluid 2 : Refrigerant - R-134A - vapour
    Entry condition : ?
    Exit condition : SH = 7K
    Allowable pressure drop = ?
    @ mass flowrate of refrigerant.

    Minimum/maximum nozzle velocities for oil transport.
    Minimum vertical height between nozzle centres.

    What else?
    Last edited by desA; 06-08-2009 at 03:59 PM.
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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by Gary View Post
    Have you located a water regulating valve?
    I'll be in BKK next week & will source one while I'm there.
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    Re: AWHP superheat & sub-cooling

    Originally Posted by desA
    If I could re-visit the refrigerant charging procedure for a minute.

    Is it better to slightly overcharge, then cut back until operating sweet point is found, or
    slightly underfill, then progressively add refrigerant until the sweet point is found?
    Gary
    I'm thinking we have already chosen the former path. Whatever gets us to the sweet point is a good procedure... and I'm hoping for a sweet range instead of a sweet point.
    How will we know the mass charge in the system - in case of future servicing?
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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    At this stage, we could look at the design requirements for the VIC, though.

    Fluid 1 : Refrigerant - R-134A - liquid
    Entry condition : Liquid sub-cooled xx.xx'C off Tc,sat=75'C condition
    Exit condition : T,exit = T,inlet - y.y'C
    Allowable pressure drop = ?
    @ mass flowrate of refrigerant.

    Fluid 2 : Refrigerant - R-134A - vapour
    Entry condition : ?
    Exit condition : SH = 7K
    Allowable pressure drop = ?
    @ mass flowrate of refrigerant.

    Minimum/maximum nozzle velocities for oil transport.
    Minimum vertical height between nozzle centres.

    What else?
    This is the point where we have moved beyond my area of expertise. Left to my own devices I would be resorting to trial and error.

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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    How will we know the mass charge in the system - in case of future servicing?
    I would pump all of the refrigerant out and weigh it, then double check by weighing it all back in and seeing if the operating parameters are the same.

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    Re: AWHP superheat & sub-cooling

    Originally Posted by desA
    At this stage, we could look at the design requirements for the VIC, though.

    Fluid 1 : Refrigerant - R-134A - liquid
    Entry condition : Liquid sub-cooled xx.xx'C off Tc,sat=75'C condition
    Exit condition : T,exit = T,inlet - y.y'C
    Allowable pressure drop = ?
    @ mass flowrate of refrigerant.

    Fluid 2 : Refrigerant - R-134A - vapour
    Entry condition : ?
    Exit condition : SH = 7K
    Allowable pressure drop = ?
    @ mass flowrate of refrigerant.

    Minimum/maximum nozzle velocities for oil transport.
    Minimum vertical height between nozzle centres.

    What else?
    Gary
    This is the point where we have moved beyond my area of expertise. Left to my own devices I would be resorting to trial and error.
    No problem. I'll work on a tentative specification next week, on my travels & post it up for comment.

    My initial thoughts are to design the VIC to the work case scenario & then rate its performance at start-up & mid-range. Would you think the worst case scenario would be at start-up, or hot-condition?
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    Re: AWHP superheat & sub-cooling

    Originally Posted by desA
    How will we know the mass charge in the system - in case of future servicing?
    Gary
    I would pump all of the refrigerant out and weigh it, then double check by weighing it all back in and seeing if the operating parameters are the same.
    How would you know that you'd got every last gram of refrigerant out of the machine? What about the oil charge?
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    Re: AWHP superheat & sub-cooling

    A further technical question.

    Would you ever consider using a low back-pressure check-valve in the discharge line?
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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    How would you know that you'd got every last gram of refrigerant out of the machine? What about the oil charge?
    I would pull down to a deep vacuum. That's the best you can do... and its what a service tech should do before refilling.

    The oil charge comes with the compressor. It is not normally something we need to worry about.
    Last edited by Gary; 06-08-2009 at 05:42 PM.

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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    A further technical question.

    Would you ever consider using a low back-pressure check-valve in the discharge line?
    This is something you should discuss with the compressor manufacturer and follow their recommendation.

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    Re: AWHP superheat & sub-cooling

    ^ What feedback is there, in the field, regarding scroll-type compressors with low mass, disc-type check valves installed in the compressor discharge tube?

    Are these discs always reliable - especially at continual high operating temperatures?

    I have heard of failures in this aspect, regarding disc damage, & failing to seal off the compressor against reverse expansion. This has always been a particular concern.

    Would addition of such a check valve fall into the compressor manufacturer's responsibility, or the refrigerant loop designer?
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    Re: AWHP superheat & sub-cooling

    What performance degradation, if any, could be expected from the installation of a properly-sized, check-valve in the discharge line?

    Why I ask, is that the lab test machine has a 1/2" check valve installed. This can be seen in the condenser/compressor gallery picture from yesterday.
    Last edited by desA; 06-08-2009 at 06:08 PM.
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    Re: AWHP superheat & sub-cooling

    In general any restriction in the discharge line puts stress on the compressor. I would not do it unless the compressor manufacturer requires it... and then I would want a rock solid reason for it. It's a pretty safe bet that if they require it, they have a rock solid reason.

    I'm guessing it has something to do with pushing the scroll in reverse.
    Last edited by Gary; 07-08-2009 at 02:05 AM.

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    Re: AWHP superheat & sub-cooling

    Gary:
    For our purposes:

    It can be assumed that the liquid will gain considerable subcooling between the condenser outlet and the TXV inlet. Thus far, our ideal SC seems to be 7K at the condenser outlet at 75C Tc,sat. I assume that this will rise well above the 8.5K minimum long before it reaches the TXV inlet.
    Now that we have managed to obtain, after partially insulating the condenser, at Tc,sat=75'C, a SC = 5.8K and approach = 7.75K, where do we go from here?

    Would we be looking to increase SC slightly more, back to 7K, by adding refrigerant, or is 5.8K sufficient for now?

    What I'm seeing here is a trade-off for COP,hp between the additional heat-transfer to the water via sub-cooling, versus the lower compressor input power.

    From a heat-exchanger design perspective:
    Assuming an acceptable temperature-cross for the condenser of (-Tcross)=Tcond,exit - Twater,out = 0.9K, then for the last run, with Twater,out=67.25'C, the lowest acceptable outlet temp from the condenser should be:

    Tcond,exit = 67.25 + 0.9 = 68.15K

    Sub-cooling : SC = 75 - 68.15 = 6.85K

    So, I estimate that we should try to increase SC from 5.8K to 6.85K at some point.
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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    Now that we have managed to obtain, after partially insulating the condenser, at Tc,sat=75'C, a SC = 5.8K and approach = 7.75K, where do we go from here?

    Would we be looking to increase SC slightly more, back to 7K, by adding refrigerant, or is 5.8K sufficient for now?

    What I'm seeing here is a trade-off for COP,hp between the additional heat-transfer to the water via sub-cooling, versus the lower compressor input power.

    From a heat-exchanger design perspective:
    Assuming an acceptable temperature-cross for the condenser of (-Tcross)=Tcond,exit - Twater,out = 0.9K, then for the last run, with Twater,out=67.25'C, the lowest acceptable outlet temp from the condenser should be:

    Tcond,exit = 67.25 + 0.9 = 68.15K

    Sub-cooling : SC = 75 - 68.15 = 6.85K

    So, I estimate that we should try to increase SC from 5.8K to 6.85K at some point.
    Partially insulating the condenser gave us a drop in SC, so I assume that fully insulating it would also drop the SC.

    But at this point, since we don't have the proper insulation materials or the water regulating valve, and we are not ready to make the partition changes, nor remount the drier vertically... then what's left is to raise the SC to 6.85K or thereabouts and see what that does.
    Last edited by Gary; 07-08-2009 at 05:29 AM.

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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by Gary View Post
    Partially insulating the condenser gave us a drop in SC, so I assume that fully insulating it would also drop the SC.
    Agreed. We had a fairly large change in SC from 8.5K to 5.8K represents -31.8% change. That's significant.

    Additional insulation will further affect SC, to be sure.

    But at this point, since we don't have the proper insulation materials or the water regulating valve, and we are not ready to make the partition changes, nor remount the drier vertically... then what's left is to raise the SC to 6.85K or thereabouts and see what that does.
    Very fair comments. Leave this with me, I'll get all the materials to hand during my trip next week. I suggest the following 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 PRV & iterate adjustment/testing.
    Last edited by desA; 07-08-2009 at 05:37 AM.
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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    8. Adjust PRV & iterate adjustment/testing.
    PRV?

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    Re: AWHP superheat & sub-cooling

    ^

    The water flow regulating valve, using pressure as reference input. What acronym would that be?
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    Re: AWHP superheat & sub-cooling

    One of our initial assumptions was that we would not be able to exceed Te,sat=15C, but in fact we have gone considerably beyond this. I'm wondering if there is some max that we need to stop at. Possibly a max amperage?... or a max V*I? Any idea what point the internal overload trips at?
    Last edited by Gary; 07-08-2009 at 05:55 AM.

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    Re: AWHP superheat & sub-cooling

    Quote Originally Posted by desA View Post
    ^

    The water flow regulating valve, using pressure as reference input. What acronym would that be?
    As far as I know it would be WRV.

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    Re: AWHP superheat & sub-cooling

    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.
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    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.
    Sounds like a good plan.

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    Re: AWHP superheat & sub-cooling

    While I'm on the shopping trail, is there anything else I should get? Over here, due to distance from major metropolitan areas, I need to plan a little in advance in order to get parts & components.
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