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Re: AWHP superheat & sub-cooling
I'm going to throw a spanner in the works here. :eek:
I've been 'reverse-simulating' from the measured power input, less the fan = compressor input power, to compute the system operating point.
This technique shows up some very interesting details, for this particular heat-pump:
1. The operating m'g [g/s] (refrigerant mass flow) always drags the theoretical maximum TXV orifice capability, by a long margin & seems to stay reasonably constant in the range Tc,sat=50'C to 65'C.
2. The theoretical maximum output of this unit is around 6.67 kW at the 'sweet spot' of orifice & compressor curves.
2A. This sweet spot is the same as my tank heat-up measurements.
3. My theoretical calculations for the coil used in this heat-pump, predict a maximum Qc of ~ 7kW (best-case scenario).
Tentative diagnostic:
1. Condenser coil is undersize;
2. This causes the TXV to throttle-back to a low m'g;
3. System bottleneck is currently the condenser;
4. Evap merely follows in what the condenser can manage.
Now, if there is agreement with this, here's what I propose to do - unless we have more business to do on this particular configuration:
a. Swap in a new larger tube condenser. I have a new 3-coil unit on hand (Qc ~ 10.51 kW);
b. Re-balance system & move forwards.
This will take some time, as I will be out of office most of next week. I expect to be able to push the unit up a few notches with such a modification.
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Re: AWHP superheat & sub-cooling
Concept - alternative for CPR
A thought, as an alternative to a CPR, in a budget heat-pump system. Could a suitably-sized (over-sized) service valve be used?
Lock the valve in a setting which reduces Te,sat until equals 15'C (pressure 0.387 MPa(g)), during set-up, or on-site installation. Servicing by trained, qualified personnel only.
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
desA
I'm going to throw a spanner in the works here. :eek:
I've been 'reverse-simulating' from the measured power input, less the fan = compressor input power, to compute the system operating point.
This technique shows up some very interesting details, for this particular heat-pump:
1. The operating m'g [g/s] (refrigerant mass flow) always drags the theoretical maximum TXV orifice capability, by a long margin & seems to stay reasonably constant in the range Tc,sat=50'C to 65'C.
2. The theoretical maximum output of this unit is around 6.67 kW at the 'sweet spot' of orifice & compressor curves.
2A. This sweet spot is the same as my tank heat-up measurements.
3. My theoretical calculations for the coil used in this heat-pump, predict a maximum Qc of ~ 7kW (best-case scenario).
Tentative diagnostic:
1. Condenser coil is undersize;
2. This causes the TXV to throttle-back to a low m'g;
3. System bottleneck is currently the condenser;
4. Evap merely follows in what the condenser can manage.
Now, if there is agreement with this, here's what I propose to do - unless we have more business to do on this particular configuration:
a. Swap in a new larger tube condenser. I have a new 3-coil unit on hand (Qc ~ 10.51 kW);
b. Re-balance system & move forwards.
This will take some time, as I will be out of office most of next week. I expect to be able to push the unit up a few notches with such a modification.
The compressor is rated at 7kW at Te,sat=15C and Tc,sat=40C.
The chart for run #7 doesn't show Tc,sat=40C, but it appears that if it did the Te,sat would have been at least 15C.
So... there doesn't appear to be a bottleneck.
However... with the larger condenser we could drop the cond approach down closer to 5K for improved performance.
In any case, a larger condenser won't hurt.
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
desA
Concept - alternative for CPR
A thought, as an alternative to a CPR, in a budget heat-pump system. Could a suitably-sized (over-sized) service valve be used?
Lock the valve in a setting which reduces Te,sat until equals 15'C (pressure 0.387 MPa(g)), during set-up, or on-site installation. Servicing by trained, qualified personnel only.
The lower cost alternative to the CPR is the MOP. Although the MOP raises superheat, the fan speed control will compensate for this and bring the superheat back down.
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
Gary
The compressor is rated at 7kW at Te,sat=15C and Tc,sat=40C.
The chart for run #7 doesn't show Tc,sat=40C, but it appears that if it did the Te,sat would have been at least 15C.
So... there doesn't appear to be a bottleneck.
However... with the larger condenser we could drop the cond approach down closer to 5K.
In any case, a larger condenser won't hurt.
Just checking on the compressor rating again at Te,sat15'C, Tc,sat=40'C - using suppler software:
Sub-cooling SC=3K:
Q'e = 7.0 kW
W'in = 1.1 kW
Q'c = 8.1 kW
Sub-cooling SC=7K:
Q'e = 7.3 kW
W'in = 1.1 kW
Q'c = 8.4 kW
The reason for the showing the sub-cooling option is that the tube-in-tube coils seem quite happy to operate with a sub-cooling of 7-8.5K, whereas the best that a plate will give is around 0.5-4K (3K typical).
In this way, I must say, the tube-coil condensers seem to have their place as a combination condenser/sub-cooler. They are incredibly bulky, however.
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
Gary
The lower cost alternative to the CPR is the MOP. Although the MOP raises superheat, the fan speed control will compensate for this and bring the superheat back down.
Just some brief feedback on a CPR trial on another machine, is that these work incredibly well. I am most impressed indeed.
The 'boys' got onto the spanners & were trying to get the suction gas temp down to 15'C, instead of Te,sat=15'C. Frantic e-mail shows that Te,sat=-0.5'C was reached & the only reason for stoppage was that the Tcomp,disc rose to around 105'C.
Lol... :D
Training time tomorrow morning... :)
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Re: AWHP superheat & sub-cooling
I'm hoping to have a better idea of just how well these CPR's operate tomorrow. I have a sneaky feeling that this may be a super solution.
The trick then is surely to push the evap a little harder & push up the Te,sat to 15'C & hold it there. Perhaps this could assist in early startup performance?
So, basically - push the evap a little harder at startup, then back off as load climbs.
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
Gary
However... with the larger condenser we could drop the cond approach down closer to 5K for improved performance.
To expand on this:
If our approach is 10K, then we need Tc,sat=75C to get 65C leaving water.
If our approach is 5K, then we need Tc,sat=70C to get 65C leaving water.
So... reducing the approach will raise the COP.
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Re: AWHP superheat & sub-cooling
Fan-speed control system - re-visited
So far:
1. Input signal from compressor discharge temp;
2. Fan speed curve set to lower fan speed as heating cycle climbs;
3. Curve for (2) still to be determined;
4. Fan speed modulation mechanism to be discussed.
To address:
a. What should fan do when max Tcomp,d reached? Should it drop to say 50% to limit heat-generation?
b. Can a second input signal be used to trim the fan profile;
b.1 Target Tevap,exit; or
b.2 Pressure P,evap;
c. Could a simple 2-speed motor be used, with pressure switches controlling the speeds? (Much like the option used to stop 1-fan for a 2-fan system)
I think that a few other options have been discussed along the way, & can be added (slip my mind at the moment).
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
Gary
To expand on this:
If our approach is 10K, then we need Tc,sat=75C to get 65C leaving water.
If our approach is 5K, then we need Tc,sat=70C to get 65C leaving water.
So... reducing the approach will raise the COP.
Yes, very much so.
The larger coil I have will just need to be checked for optimum water flow circuiting as I seem to remember that all passes are in parallel. I'll check the 3x parallel refrigerant, 3x series water side as an option to 3x parallel refrigerant, 3x parallel water side.
One concern with the series water arrangement may be a slight condensing imbalance between the 3x parallel refrigerant coils... not overly sure about the inter-coil dynamics, for the moment.
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
desA
I'm hoping to have a better idea of just how well these CPR's operate tomorrow. I have a sneaky feeling that this may be a super solution.
The trick then is surely to push the evap a little harder & push up the Te,sat to 15'C & hold it there. Perhaps this could assist in early startup performance?
So, basically - push the evap a little harder at startup, then back off as load climbs.
Anything we do to improve the evap performance will have little effect at higher Ta,in temps as we are limiting the load with our CPR and/or fan speed control.
Where these improvements to evap performance will make a huge difference is at lower Ta,in temps, allowing us to design for lower ambients OR to downsize the evap.
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
desA
Fan-speed control system - re-visited
So far:
1. Input signal from compressor discharge temp;
2. Fan speed curve set to lower fan speed as heating cycle climbs;
3. Curve for (2) still to be determined;
4. Fan speed modulation mechanism to be discussed.
To address:
a. What should fan do when max Tcomp,d reached? Should it drop to say 50% to limit heat-generation?
b. Can a second input signal be used to trim the fan profile;
b.1 Target Tevap,exit; or
b.2 Pressure P,evap;
c. Could a simple 2-speed motor be used, with pressure switches controlling the speeds? (Much like the option used to stop 1-fan for a 2-fan system)
I think that a few other options have been discussed along the way, & can be added (slip my mind at the moment).
The fan could have simple on/off control and would work reasonably well, but the short cycling may ultimately shorten the life of the fan motor.
Cycling between two speeds would be easier on the motor, but the lower speed must be sufficient to bring down the discharge temp within a reasonable time period.
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Re: AWHP superheat & sub-cooling
You mentioned earlier that the fan is small relative to the evap. This being the case, we could get a lot more performance out of the evap at lower ambients by increasing the airflow.
The fan and the evap should be matched to each other. If anything we might want to oversize the fan a little relative to the evap.
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
desA
The 'boys' got onto the spanners & were trying to get the suction gas temp down to 15'C, instead of Te,sat=15'C. Frantic e-mail shows that Te,sat=-0.5'C was reached & the only reason for stoppage was that the Tcomp,disc rose to around 105'C.
Did the boys notice if the evap superheat went up or down as they closed off the CPR to Te,sat=15C?
Their inability to get the suction line temp down to 15C would seem to indicate that the coil was not flooded.
Also notable is that the Tcomp,disc rose to 105C. The fan control would have brought this down. Yet another confirmation of the advantages of 'belt and braces' controls. :)
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
desA
The 'boys' got onto the spanners & were trying to get the suction gas temp down to 15'C, instead of Te,sat=15'C. Frantic e-mail shows that Te,sat=-0.5'C was reached & the only reason for stoppage was that the Tcomp,disc rose to around 105'C.
For clarity, it should be noted that they are not adjusting the Te,sat to 15C, but rather they are adjusting the CPR to allow no more than 57psi at the compressor inlet.
In order to make this adjustment, the pressure in the evap must be more than 57psi at the time of adjustment.
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
Gary
Anything we do to improve the evap performance will have little effect at higher Ta,in temps as we are limiting the load with our CPR and/or fan speed control.
Yes - very true.
Quote:
Where these improvements to evap performance will make a huge difference is at lower Ta,in temps, allowing us to design for lower ambients OR to downsize the evap.
I would most definitely like to explore both options:
1. Designing for lower ambients (where required);
2. Downsizing the evap.
Option (1) would be useful for machines going to colder climates - I need to get a good handle on this aspect.
Option (2) would be useful under local conditions, for ultra-compact machines. The single-most determining factor in AWHP space package is the evaporator !!!size!!!. Face area is a major issue, as coil efficiency gains drop off with increasing core depth/thickness/rows.
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
Gary
The fan could have simple on/off control and would work reasonably well, but the short cycling may ultimately shorten the life of the fan motor.
I agree. There will be a certain recovery time for the fan motor, I'd imagine - to prevent gradual heat build-up at each re-start. I'd have to look into the minimum recovery time on this. Very interesting point.
Quote:
Cycling between two speeds would be easier on the motor, but the lower speed must be sufficient to bring down the discharge temp within a reasonable time period.
Now this is definitely something I can test on the current rig.
A proposal:
1. Run the system up to Te,sat=70-75'C, on full fan speed;
2. Cut fan speed to proposed 'hot run' condition via dimmer switch;
3. Observe & time Tcomp,d response.
4. Return fan to 100% condition - let system stabilise;
5. Cut fan speed more aggressively;
6. Observe & time Tcomp,d response.
This will give us some very useful information.
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
Gary
You mentioned earlier that the fan is small relative to the evap. This being the case, we could get a lot more performance out of the evap at lower ambients by increasing the airflow.
On the test rig, the fan is overly-large for the evap design.
The design velocity is 2.03 m/S, whereas the current fan causes a face entry velocity in the region of 3.3-3.6 m/s - i.e. is over-sized - fixed speed fan, with dimmer now attached.
Quote:
The fan and the evap should be matched to each other. If anything we might want to oversize the fan a little relative to the evap.
Already in place on the lab test machine. :)
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Re: AWHP superheat & sub-cooling
Quote:
Quote:
Originally Posted by desA
The 'boys' got onto the spanners & were trying to get the suction gas temp down to 15'C, instead of Te,sat=15'C. Frantic e-mail shows that Te,sat=-0.5'C was reached & the only reason for stoppage was that the Tcomp,disc rose to around 105'C.
Gary:
Did the boys notice if the evap superheat went up or down as they closed off the CPR to Te,sat=15C?
According to the info received:
Tevap, out : CPR open @ 22'C : CPR closed @ 22'C
Tbefore,CPR : CPR open @ 20'C : CPR closed @ 19'C
Tafter,CPR : CPR open @ 19.5'C : CPR closed @ 17.7'C
The difference between Tevap,out & Tbefore,CPR is attributed to heat losses from the suction line off evap exit. Insulation still to be wrapped after final proving runs.
The difference between Tbefore,CPR & Tafter,CPR is predicted to occur - the temperature should drop in the order of around 2-3K. This can be seen if a calculation is performed across an adiabatic throttle valve, where a pressure drop occurs. The gas will cool slightly, not heat up.
I wanted to wait until the tests had run before discussing the temp drop across the CPR - I'd simulated this once, & used hand-calcs to prove the same.
Quote:
Gary:
Their inability to get the suction line temp down to 15C would seem to indicate that the coil was not flooded.
Can you explain this a little more, please?
Quote:
Also notable is that the Tcomp,disc rose to 105C. The fan control would have brought this down. Yet another confirmation of the advantages of 'belt and braces' controls.
Agreed. 'Belt & braces', or 'grab & tickle'? :D
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Re: AWHP superheat & sub-cooling
Quote:
Quote:
Originally Posted by desA
The 'boys' got onto the spanners & were trying to get the suction gas temp down to 15'C, instead of Te,sat=15'C. Frantic e-mail shows that Te,sat=-0.5'C was reached & the only reason for stoppage was that the Tcomp,disc rose to around 105'C.
desA:
For clarity, it should be noted that they are not adjusting the Te,sat to 15C, but rather they are adjusting the CPR to allow no more than 57psi at the compressor inlet.
In order to make this adjustment, the pressure in the evap must be more than 57psi at the time of adjustment.
You are correct. It's an odd thing running a test by remote across cultural & language barriers - concepts get twisted in the translation. We could have settled this in 30 minutes tops, if I'd been on site during the test. Anyway, the boys can now learn something - it's good for the young engineers in that group -they're smart & have enquiring minds.
What actually happened is that with the CPR in its original factory setting, it was already affecting the evap Te,sat drift, in that it was settling at around 11.25'C & so actually needed to be backed off.
What had been communicated to me was a Te,sat=19'C & so I instructed to drop the CPR setpoint down to a lower value. Actually, the incorrect information had been provided, as Te,sat=11.25'C in the evap, with no upward drift.
So, the correct remedy, is to back it off slightly, wait for the Te,sat drift to set in & pull Te,sat above 15'C (look at LP pressure gauge). then gradually adjust setting in 1/4 turn intervals, 10 minute settling time, until Te,sat=15'C (0.387MPa(g)) is held.
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
Gary
For clarity, it should be noted that they are not adjusting the Te,sat to 15C, but rather they are adjusting the CPR to allow no more than 57psi at the compressor inlet.
In order to make this adjustment, the pressure in the evap must be more than 57psi at the time of adjustment.
We have a pressure service port between CPR & compressor suction. I've instructed to watch the LP gauge & set the CPR to begin constricting at Te,sat=15'C (0.387 MPag = 56.1 psig).
Had the boys on the phone this morning. A new paradigm of distance learning has dawned. :D
See me getting on a plane & flying down there to get this settled. Seems such a waste of money & time to do a 30 minute job... :(
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
desA
Now this is definitely something I can test on the current rig.
A proposal:
1. Run the system up to Te,sat=70-75'C, on full fan speed;
2. Cut fan speed to proposed 'hot run' condition via dimmer switch;
3. Observe & time Tcomp,d response.
4. Return fan to 100% condition - let system stabilise;
5. Cut fan speed more aggressively;
6. Observe & time Tcomp,d response.
This will give us some very useful information.
I would like to see a full set of measurements at each hot run condition.
You might base the hot run settings on progressively lower increments of face velocity.
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Re: AWHP superheat & sub-cooling
Have you informed you guys to set the CPR to the new port pressure (I thought most CPRs already have a port on the outlet) The pressure that is entering the compressor, They are not trying to control the pressure in the evap with valve? Could Te before the valve and Te after the valve be causing a misunderstanding
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
desA
The larger coil I have will just need to be checked for optimum water flow circuiting as I seem to remember that all passes are in parallel. I'll check the 3x parallel refrigerant, 3x series water side as an option to 3x parallel refrigerant, 3x parallel water side.
One concern with the series water arrangement may be a slight condensing imbalance between the 3x parallel refrigerant coils... not overly sure about the inter-coil dynamics, for the moment.
An advantaqe to parallel circuits is less pressure drop.
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Re: AWHP superheat & sub-cooling
^^No port on a CPR, but have a service port between CPR & compressor.
They have been instructed - simple version - to run up the unit, back off CPR until the desired pressure set point of 0.387 MPag has been achieved.
The thing with these tweeks is that the original setting of the CPR, as received, held the evap Te,sat lower than the set-point limit for the CPR. In other words, the CPR was already operating in its P-band range. The system was overly-conservative.
To allow the CPR to be set properly, the setting needs to be backed off, to allow the natural Te,sat drift upwards (the test bay is > 32'C). When the Te,sat hits 15'C (per LP service gauge), then !!!slowly!!! lower CPR set-point.
This thing is a beauty & only needs a tickle (feminine tendencies) to get to where we need to go.
My problem here is that I'm currently around 700km from my build site, with a language barrier in between, plus 'engineers' who are in name, but aren't really. :(
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Re: AWHP superheat & sub-cooling
That makes it a little more difficult!!!!!
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
Gary
An advantaqe to parallel circuits is less pressure drop.
Very true. Thanks for that.
The downside is that the water velocity per tube, will now be reduced due to the third // pass. I'll need to check flow Reynolds number & make sure it does not drop into the laminar, or transition range. This will place a lower operating band constraint on the pumping flow-rate. Not a train-smash, but does need to be checked.
No problem, that's on my checklist for the re-build project.
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
mad fridgie
That makes it a little more difficult!!!!!
Where's the hair-pulling emoticon...
:confused:
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Re: AWHP superheat & sub-cooling
Quote:
Quote:
Originally Posted by desA
Now this is definitely something I can test on the current rig.
A proposal:
1. Run the system up to Te,sat=70-75'C, on full fan speed;
2. Cut fan speed to proposed 'hot run' condition via dimmer switch;
3. Observe & time Tcomp,d response.
4. Return fan to 100% condition - let system stabilise;
5. Cut fan speed more aggressively;
6. Observe & time Tcomp,d response.
Gary:
This will give us some very useful information.
I would like to see a full set of measurements at each hot run condition.
You might base the hot run settings on progressively lower increments of face velocity.
It shall be done - excellent suggestion.
(Sidebar: I'll need to set up my video cam to record the frantic dances performed during such tests. I currently do everything manually, swapping instruments in & out. It would look hilarious on a video... :D )
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Re: AWHP superheat & sub-cooling
I'm trying to sort out the water flow through the condenser in this picture:
http://i29.tinypic.com/2604pee.jpg
In each coil, the water should flow into the bottom, spiral upwards, and then flow out the top. The entrance manifold should have the water entering the bottom and the exit manifold should have the water exiting the top.
Is it just me, or is this piping all wrong?
Does anyone else see a problem with this?
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Re: AWHP superheat & sub-cooling
I'll pull out my spare unit of that type, to get a better look at it.
The way I seem to remember it is configured with inlet & exit manifolds on both ends, but that the connections were placed on the top ends of the manifolds.
I'll go out to the lab & take some pics of the bare coil & an installed unit.
To be honest, I don't particularly like these condensers - too bulky, heavy, pretty inefficient, but, they are able to use a good level of condensate sub-cooling, leading to reasonable COP's.
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
desA
The way I seem to remember it is configured with inlet & exit manifolds on both ends, but that the connections were placed on the top ends of the manifolds.
Draw a simple ladder diagram, consisting of two parallel vertical lines with three horizontal lines between them. In other words, a ladder with three rungs.
Measure the distances from the top of one vertical line, through each of the horizontal lines, to the top of the other vertical line. The path through each horizontal will give you a different length, a different resistance, a different flow.
Now measure the distances from the bottom of one vertical to the top of the other vertical. No matter which path through the horizontals is taken, there is equal distance, equal resistance, equal flow.
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Re: AWHP superheat & sub-cooling
http://i25.tinypic.com/2eztsg2.jpg
There it is.
Can I ask you to explain your 'ladder concept' a little more? I actually have manufacturer's sketches for these, with dimensions - if these will help.
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Re: AWHP superheat & sub-cooling
looks right counter flow, also looks like a double barrier, (if so I would reley on trail and error, therory does not seem to work)
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
desA
http://i25.tinypic.com/2eztsg2.jpg
There it is.
Can I ask you to explain your 'ladder concept' a little more? I actually have manufacturer's sketches for these, with dimensions - if these will help.
The shortest distance between water in and water out would seem to be through the top coil. Seems like there would be far less water flow through the other two coils.
It looks wrong on the refrigerant side, too.
Maybe those sketches would help.
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
mad fridgie
looks right counter flow, also looks like a double barrier, (if so I would reley on trail and error, therory does not seem to work)
Theory always works... if you use the right theory, that is. :D
I had the turbulation part right - missed the air-gap effect due to the double wall. I'll add that in & re-check.
My estimate was ~ 7 kW max. Practically, the unit operated at 6.7kW... (Heat-exchanger design was a past life... :)
:o
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
Gary
The shortest distance between water in and water out would seem to be through the top coil. Seems like there would be far less water flow through the other two coils.
It looks wrong on the refrigerant side, too.
Maybe those sketches would help.
I'll sketch those out in the morning.
Manifolds are funny things - some combinations work better than others.
I feel that the refrigerant should be flowing downwards after exit, with the water flowing upwards.
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Re: AWHP superheat & sub-cooling
Had an interesting day, all told.
Made a minor modification (not fan) to the current test rig. The thing now runs as sweet as a whistle, making hot water at Tw,o=70.4'C.
Tsat,equivalant to compressor suction was contained at under 14'C, Tcomp,d was allowed to max out at 107'C, Tc,sat~74'C.
The evaporator Te,sat was ~ 17.5'C.
In my view, refrigerant circuits are inherently unstable beasts & really do need to be taken in hand for heat-pump duty. Today's exercise merely reinforced that.
I'll see if the mod still holds during the day tomorrow, where the temps are sure to be hotter.
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
desA
I'll sketch those out in the morning.
Manifolds are funny things - some combinations work better than others.
I feel that the refrigerant should be flowing downwards after exit, with the water flowing upwards.
It seems unlikely that a condenser manufacturer would make such a basic mistake in design. It is entirely possible that the water input/refrigerant output may be shifted within the header manifolds where we can't see it.
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Re: AWHP superheat & sub-cooling
Quote:
Originally Posted by
desA
Had an interesting day, all told.
Made a minor modification (not fan) to the current test rig. The thing now runs as sweet as a whistle, making hot water at Tw,o=70.4'C.
Tsat,equivalant to compressor suction was contained at under 14'C, Tcomp,d was allowed to max out at 107'C, Tc,sat~74'C.
The evaporator Te,sat was ~ 17.5'C.
In my view, refrigerant circuits are inherently unstable beasts & really do need to be taken in hand for heat-pump duty. Today's exercise merely reinforced that.
I'll see if the mod still holds during the day tomorrow, where the temps are sure to be hotter.
Hmmm... apparently you have restricted the suction line to simulate the CPR, but I wouldn't think that would account for the major difference in condenser approach.
I'll take a wild guess and say you reversed the water flow through the condenser?