Air source heat pump issue! Need help.

[Ricardo Pimenta]

This is a mini split condenser heat pump converted from Air to Air to Air to water, that I have connected to a titanium heat exchanger from a swimming pool heat pump!

The mini split unit have 4 way valve and uses capillary metering device for heating and cooling the refrigerant is r410, this was installed with the purpose of cool water from a tank in the summer and heat it in winter maintaining a stable temperature of 24 in winter and 25 in summer.

After the installation during the summer running in cooling mode everything seems to the working fine, but now that it is switching to heat mode I have noted an excessive high discharge temperature! To the amount of water the tank have it takes a proximally 35 to 40 minutes to increase 1ºC and during the work time to increase this degree in the water temperature the discharge temperature will increase slowly until reaches 80ºC! In one of the first tests I made I leave it working until reaches the 50 minutes mark and achieved 90ºC in the discharge temperature measured at the services valves!

The condensing temperature it is stable at 35ºC during all the work time!

Can any one give me some tips? I am a little bit lost here.


Thank you

[monkey spanners]

A high suction superheat will lead to a high discharge superheat which is what you apear to have, i don't know what a normal mini split discharge temp would be as i've never had the need to measure it.

Reasons for a high suction superheat could be that the system is undercharged or that the cooling load is too high (or systems something you've made out of bits....) Many systems will cycle the condenser fan motor in heating to limit the discharge temperature getting too high, don't know how much of the original control system is still functional on your system.

Pressure and temperature measurements (refrigerant, air on air off, water in water out etc) would give the smarter members of the forum an idea of whats going on and what changes may need making or what faults correcting.

Jon

[Ricardo Pimenta]

Dear monkey spanners,

Thank you very much for your help!

Like you ask I will leave here some additional values that may help others to help me.

Those ware taken after 15 minutes of work

Outdoor air temperature: 10/9 ºC

Air ir: 10/9 ºC
Air out: 7 ºC

Water in: 24
Water out: 25

Refrigerant pipe temperatures taken near the services valves:

Discharge (Gas): 69 ºC

Return: (Liquid): 25 ºC


If anymore is needed, please ask that I will get it!

Thank you

[AlexG]

Ricardo, what is condensing pressure? For cooling mode and for heating mode system needs different amount of *****. Maybe now in heating mode your system is overcharged. Check subcooling.
Good luck and happy new year.

[desA]

My suggestion is for the OP to spend some time simulating his system in Coolpack. This will provide the design targets for condenser & evaporator - against compressor selection - to achieve the required/desired system balance. Run cap tube design estimates against this balance scenario.

Then go & estimate the heat-transfer from the evap & condensers you have installed. Check your cap tube against what is required for system balance.

Change what needs changing. Be aware that evap performance can be modified by fan speed/air flow, cond performance by fan speed (or water pump flow).

Once that is in place, select an appropriate mass charge & check evap superheat, condenser approach temps, to balance system.

[nike123]

Those ware taken after 15 minutes of work

Outdoor air temperature: 10/9 ºC

Air ir: 10/9 ºC
Air out: 7 ºC

Water in: 24
Water out: 25

Refrigerant pipe temperatures taken near the services valves:

Discharge (Gas): 69 ºC

Return: (Liquid): 25 ºC


If anymore is needed, please ask that I will get it!

Thank you

I don't see high discharge temperatures here.
What was evaporation pressure?
In this stage of project you should have connection port at suction and discharge pipe before 4Way valve to measure pressures.

Measure full set of data and post here.

• 
  Here is a list ofthe temps/pressures needed to troubleshoot a system:
  
  Evap air/water in temp
  Evap air/water out temp
  Low side pressure or saturation temp
  Suction line temp at evap outlet
  Suction line temp at compressor inlet
  
  
  Cond air/water in temp
  Cond air/water out temp
  High side pressure or saturation temp
  Liquid line temp at receiver or condenser outlet
  Liquid line temp at TXV/capillary inlet
  
• The more information provided the more accurate the diagnosis.
  

[AlexG]

Ricardo, in additional to nike123 did u calculate your plate exchanger correct (like desA mentioned)? Dont forget to add compressor consumtion to cooling capacity to find condenser capacity.

[Ricardo Pimenta]

Many systems will cycle the condenser fan motor in heating to limit the discharge temperature getting too high, don't know how much of the original control system is still functional on your system.

In my last reply I forgot to mention that to build this system I bought a typical mini split unit of 9000btu's, that from factory it is controlled by the PCB under the indoor evaporator, but I only used the outdoor unit!

This way I do not have any fan cycle controller!

The defrost it is controlled by the thermostat that I am using now to control the unit.

Thanks

[Ricardo Pimenta]

Ricardo, what is condensing pressure? For cooling mode and for heating mode system needs different amount of *****. Maybe now in heating mode your system is overcharged. Check subcooling.
Good luck and happy new year.

Dear Alexg,

What I meant with "condensing pressure" is condensing temperature (300psi more or less 35ºc I think) under the water cooled condenser installed indoor.


Thank you

[Ricardo Pimenta]

My suggestion is for the OP to spend some time simulating his system in Coolpack. This will provide the design targets for condenser & evaporator - against compressor selection - to achieve the required/desired system balance. Run cap tube design estimates against this balance scenario.

Then go & estimate the heat-transfer from the evap & condensers you have installed. Check your cap tube against what is required for system balance.

Change what needs changing. Be aware that evap performance can be modified by fan speed/air flow, cond performance by fan speed (or water pump flow).

Once that is in place, select an appropriate mass charge & check evap superheat, condenser approach temps, to balance system.

Dear desA,

Thank you very much for trying to help,

I am not familiar with coolpack, that is a little bit out of my league,

I decided to assembly this unit based on a minisplit outdoor condenser, because this is unit already balanced to maintain the temperature I need 24ºC, typical used under air conditioner! And also it is already prepared for cooling and heating with the same amount of refrigerant I think!

To do this I got a factory made evaporador/condenser coil (Used in reversible heat pumps) with the same power of this unit (2,5KW +-) and only have increased refrigerant because the condenser/evaporator it is positioned at 10 meters distance from the outdoor unit and this from factory only bring refrigerant to 3 meters distance.

The unit was initially installed in the beginning of the last summer and besides of loosing some cooling power that I associate to the excessive distance between the units, everything seems to be working well.

I have initially noted a very high superheat, but after increase the refrigerant and regulate the flow to the recommend by the manufacturer and everything start to work well.

Because of this significant loss of cooling power in fact I have got a lower water flow than the one recommended by the manufacturer, only this way I have got the superheating at 8ºC to 10ºC depending of the outdoor temperature!

The problem is that after change the unit to heating mode it starts to over heat I think, because if I leave it working for 50 minutes for example, the unit will reach a discharge temperature of 90ºC working with r410 I think that this is to mutch?

The outdoor unit it is very clean, the indoor water cooled condenser it is a coil condenser and not a plate condenser it is working is counter flow has it should and it is also clean because we use a filter before it…

If there is anything else that I can provide please tell me and I will try to get it!

Thank you

Best Regards

[baycuclaudyu]

Hi Ricardo,
Can you send us some pictures of indoor heating water?
Maybe some schematics.
If the flow water did't wash entire heating evaporator, it is possible to increase the temperature inside the evaporator.

[Ricardo Pimenta]

Dear nike123,

Sorry for only reply now, but I have some additional work and have to get out of the office.

I don't see high discharge temperatures here.
What was evaporation pressure?
In this stage of project you should have connection port at suction and discharge pipe before 4Way valve to measure pressures.

Don't you think that a discharge of 69ºC is already a very high discharge temperature/pressure?
My table only have values until 65ºC that gives me 601PSI!

The problem is the compressor have that discharge temperature only after a few minutes of work, if I leave it working for 50 minutes the discharge will slowly go up until 85ºC to 90ºC...

About evaporation pressure has you should know those 9000btu’s air con outdoor condensers found in our market today, only came from factory with only one service port, low side in cooling and high side in heating, this way I really do not know what is the evaporating temperature working in heating mode!

Measure full set of data and post here.

• 
  Here is a list ofthe temps/pressures needed to troubleshoot a system:
  
  Evap air/water in temp
  Evap air/water out temp
  Low side pressure or saturation temp
  Suction line temp at evap outlet
  Suction line temp at compressor inlet
  
  
  Cond air/water in temp
  Cond air/water out temp
  High side pressure or saturation temp
  Liquid line temp at receiver or condenser outlet
  Liquid line temp at TXV/capillary inlet
• The more information provided the more accurate the diagnosis.

About those values I have tried to give some of them in my previous answers:


Evap air in temp = 10/9 ºC
Evap air out temp = 7ºC
Low side pressure or saturation temp (I do not have a service port to get that value)
Suction line temp at evap outlet = starts in 45 ºC more or less and it goes up until 90ºC after 50 minutes for work
Suction line temp at compressor inlet = 25 ºC (Measured at the return line near the service valves) I think that here you want the temperature of the input of the compressor after the capillary and evaporator correct? I can uncover the compressor and check that in the next few days?


Cond water in temp = 24 ºC
Cond water out temp = 25 ºC
High side pressure or saturation temp = 35 ºC (Stable)
Liquid line temp at receiver or condenser outlet = 25 ºC (Near service valves)
Liquid line temp at TXV/capillary inlet (Those mini split unit have the capillary in the outdoor machine in this case the evaporator)


Thank you once more to all
Best Regars

[Ricardo Pimenta]

Hi Ricardo,
Can you send us some pictures of indoor heating water?
Maybe some schematics.
If the flow water did't wash entire heating evaporator, it is possible to increase the temperature inside the evaporator.

Dear baycuclaudyu,

Thank you for your help,

It certainly could be something like this, but in my case I think that it should not be because this is a coil in shell condenser where the water enters in the bottom and get out in the top this way the coil do not stay out of water inside of the shell I also have a water flow valve that it stops the compressor in the case of water pump malfunction...

But I will provide a photograph and maybe a technical drawing of the heat heat exchanger.


best regards

[nike123]

Don't you think that a discharge of 69ºC is already a very high discharge temperature/pressure?
My table only have values until 65ºC that gives me 601PSI!

Problem is here that you think that discharge temperature is actually condensation saturation temperature and therefore you think is high.
Discharge temperature is condensation saturation temperature plus discharge superheat.
That superheat could be as high as 30-50K which depend on suction superheat.

You already gave us condensation saturation temperature of 35°C and that is 20,3 bar (294,5 PSI) condensation pressure if refrigerant is R410A. Did you actualy measured pressurre at service port here and than gave us coresponding saturation temperature? If yes, that gives us discharge superheat of 30K at begining of operation and 55K at end of operation.
That part at the end of operation could be slightly high and it should be addressed if at the end of operation CST (condensation saturation temperature) is still 35°C. It could indicate mild undercharge but we need superheat to conclude that.

The problem is the compressor have that discharge temperature only after a few minutes of work, if I leave it working for 50 minutes the discharge will slowly go up until 85ºC to 90ºC...

Which is normal temperature for AC discharge. You should be concerned if it is high as 110°C or more.

About evaporation pressure has you should know those 9000btu’s air con outdoor condensers found in our market today, only came from factory with only one service port, low side in cooling and high side in heating, this way I really do not know what is the evaporating temperature working in heating mode!

That is why I said that, in this phase of project, you should have service ports on suction and discharge line near compressor and before 4-way valve. Later, when you make all adjustments and finish your project that ports could be welded.

Evap air in temp = 10/9 ºC
Evap air out temp = 7ºC

If you give us dry bulb and wet bulb temperatures entering and exiting and outdoor unit model# than we could find airflow of outdoor unit and calculate what is evaporator doing.

ow side pressure or saturation temp (I do not have a service port to get that value)

Than make it!

Suction line temp at evap outlet = starts in 45 ºC more or less and it goes up until 90ºC after 50 minutes for work

These are not suction line temperatures. These are discharge line temperatures and they are fine. These two lines are part of condenser in heating mode.
One is discharge line from compresor thru 4-way valve to condenser and another is liquid line from condenser to the capillary in outdoor unit.

Suction line temp at compressor inlet = 25 ºC

Again that is not suction line. That is liquid line after condenser. temperature of that line is useful to calculate condenser subcooling.

(Measured at the return line near the service valves) I think that here you want the temperature of the input of the compressor after the capillary and evaporator correct?

Nope, I want temperature and pressure at suction line ( temperature at least 20 cm before compressor) but at portion between compressor and 4-way valve.

I can uncover the compressor and check that in the next few days?

Uncover, recuperate refrigerant, weld two ports on real suction and discharge. leak test, vacuum dry, charge recuperated amount and make measurements listed in my previous post.

[The Viking]

I have been following this thread with interest and managed to keep my fingers away from the keyboard

Ricardo,
The outdoor unit you utilised was one part of a system that been fully developed, thousands of R&D hours by experienced engineers had gone in to that system in order to ensure it's performance. It would have been hooked up to a computer recording temperatures and pressures all over the system, most likely the system had 10's of pressure ports and even more temperature sensors attached during this process.

By changing the indoor unit the way you done here, the R&D process has to be started from scratch. As been pointed out above, that might mean fitting additional ports and sensors.

Oh, BTW.
Discharge temperatures on heatpumps can go well above 90*C during normal working conditions, it only becomes critical at about 110*...

[Ricardo Pimenta]

Dear baycuclaudyu,

Like I told you before here it is a photograph from the heat exchanger I am using, those are factory made to be used in swimming pool heat pumps.

Dear baycuclaudyu,

Thank you for your help,

It certainly could be something like this, but in my case I think that it should not be because this is a coil in shell condenser where the water enters in the bottom and get out in the top this way the coil do not stay out of water inside of the shell I also have a water flow valve that it stops the compressor in the case of water pump malfunction...

But I will provide a photograph and maybe a technical drawing of the heat heat exchanger.


best regards

[Ricardo Pimenta]

Dear Viking,

I would like to tank you for your intervention,

By changing the indoor unit the way you done here, the R&D process has to be started from scratch. As been pointed out above, that might mean fitting additional ports and sensors.

I certainly agree with you, and I would be pleasant to have all the necessary equipment and knowledge to follow all those steps...

but has you should understand this is a single private project to my self and my only goal for now is to get the system working with the best performance possible.

Discharge temperatures on heatpumps can go well above 90*C during normal working conditions, it only becomes critical at about 110*...

About heat pumps unfortunately I do not have to much information about that kind of systems, but you do seem to know their parameters, do you know if those reversible systems that we usually see out there have some type of fan cycling control when working in heating mode?

Do you also know what should be their usual evaporator superheat when cooling and subcooling when heating?

Thank you once more

Best Regards

[AlexG]

Ricardo, suprheat on cooling and heating mode are usualy same (5...10K). Subcooling as well (3...8K). Your water exchanger looks nice but how did you select it? Did you use software from manufacturer?
And you said about 35C cond temperature. How did u check it? By pressure gauge?

on heatind mode fan on your air cooled evaporator must be always ON.

regards

[The Viking]

Ricardo,
You have successfully built an heat pump that delivers more energy than it consumes, be proud of yourself.
Yes it is likely that it is possible to tweak a bit more performance from it but to achieve that you will need an experienced engineer with the right tools actually being hands on with your unit in front of him/her.

Back when I just qualified as an engineer, after 5 years as an apprentice, I was given an old cold room system to utilise as a heat pump at home.
After I designed, modified and installed it I were well pleased with myself. It then delivered 1:2.5 (for every kW it consumed 2.5kW were produced), o boy were I proud.
My old mentor then came along and looked at it and after he tweaked it the COP shot up to over 1:3!!!
Remember, I had all the training / the right tools / all the equipment and his advice just on the other end of a phone line, the only difference were about 30 years worth of experience being hands on...

Now, your fan.
As your outdoor coil isn't a block of ice, the fan controls works as intended (Remember, the outdoor unit was always designed as a heat pump). If the fan were controlled for cooling mode, it would have stopped and the coil frozen.

And the discharge temp,
It is perfectly normal. Start to worry if it reaches 100*C.

Now,
Go have a beer and give yourself a pat on the back for a job well done.
If you are serious about getting the last bit of performance out of your system, then the best you can do would be to find an experienced engineer to come over and join you for that beer...

[AlexG]

Viking, brilliant!!!