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Old 01-30-18, 02:34 PM   #5
ThMihov
Lurking Renovator
 
Join Date: Jan 2018
Location: Sofia
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Now the test results,from the first run.
I forgot to mention,that i have mounted a flow sensor after the indoor unit.It's like this one in the attachments.It's big,but it was about another project,so i have connected it with reducing bushes.I have tried to calibrate it,because it's default constant of 4.5 was not correct for my setup (maybe because of the reducers,maybe because of the working pressure-who knows?...),but i still get an error of about 200g.Way after that i took a look at it's specifications (shame on me) that says it's minimum flow is 10L/min or 600l/h which i can't achieve with that pump and such a narrow tubes of the indoor unit.After some calculations i have made after the test i roughly figured out the real flow and next time i will reclibrate it to get a real flow rate,and than to be able to make calculations automatically in software.
By the way-for the tests I'm using Arduino (although I'm not a fan of it),because it has million of libraries for it and is ideal for quick test,without writing much code.Usually I'm writing my own code in C and just using the board,because it's ready made and chinese clones on e-bay are at ridiculous
price,and are working fine
Back to the tests.At the time of the run,outside temp was between 1-2C at about 85% humidity.Water pressure in the system was 2bar (any recommendations about the working pressure by the way?),water temp 12C.Hooked up my refrigerant gauges and i started the machine.Since initially all the parts of the system needs to be heated (the tank,the plumbings,and etc.),I waited the water to heat up to 32C,for that time they should be heated up already,and started to measure the time needed to heat the water in the tank with 4C to 36C,and logging current consumption at that time.That was done with turned off indoor unit fan.The time was 6minutes and 32 seconds,and the average current consumption was 5.7A.
If we assume (ignoring the temperature difference) that specific heat capacity of water is 4.178kJ/K.kg,1 liter ow water is 1kg,and the total mass of heated water is 60kg,so total energy transferred to the water is
Q=cp*m*dT=4.178*60*4=1000kJ or in kW=1000/380sec =2.63kW
Since the average current consumption at that time was 5.7A this gives a power consumption of P=230*5.7=1300W or 1.3kW
So the COP must be 2.36/1.3=2
As i said earlier I'm not an HVAC guy,and i cant judge if that it normal or not,but according to my intuition it's not good,because according to the AC's manual it's COP at 7C outside temp is 3.6.If we assume that it's a cheap model and the real COP is lower than the stated above,say 3,that is still about 30% reduction for just a 5-6C reduction in the outside temperature,which i think is not normal.
Few words about the pressures-since there is only one service valve available,only one pressure can be measured at a time-either discharge in heating mode,or suction in cooling mode.
So the highest discharge pressure i got was about 35bar or about 55C temperature of condensation.When i turn the AC into defrost mode,the suction pressure is very low-about 5-6bar or -10C,although the suction coil is now the one that is into the tank,and the surrounding temp is greater than 35C....Since the defrost takes about 2 minutes,if i wait some time after that,the suction pressure will rise,but still both pressures are low,especially the suction.I think the AC is little undercharged,and after adding few grams of refrigerant,everything will be ok
As i said defrost-it needs defrost once an hour.For that time all surface of the outdoor unit is covered with frost.The time taken to melt everything was 2 minutes,which i think is OK
The last thing i'll mention in this post,because it became too long(again) is the heat output of the indoor unit.As i said earlier,since i don't believe on the flowmeter's readings,i decided to do the same test as earlier-as the water became 36C,i stopped the AC and turned on the indoor unit's fan and waited to see how long it takes to cool the water with 3C.The resulting time was 9min and 30sec or 570sec,so the output is Q=4.178*60*3=752kJ or 752/570=1.3kW-honestly,i was expecting a bigger number...anyway.
Initially my calibration procedure showed a flow rate of 140L/h,but that's way the power would be 0.7kW,but the real output is 1.3kW,so the real flowrate is ~260L/h.I'll use it to check if the flow rate has dropped by some reason-clog,or something else.
To double check the ouput i measured the difference beteween the input and return air temp from the indoor unit.The input was 14C and the output was 25C.According to the sticker on the unit,the flowrate of air at maximum fan speed is 420m3/h.Again simplifying that 1m3 of air is 1kg,than Q=1*420*11=4620kJ or divided by 3600 (1 hour) Q=1.28kW-very close to the first value,so it makes sense
I'll continue in the next post.
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