Air to Water Heat Pump from the Air Conditioner. Defrosting with the Compressor Heat.

Brief Summary

Defrosting the evaporator with the heat of the compressor has certain disadvantages. If the temperature outside is quite low (-2°C …- 3°C), and even a slight wind is blowing, then it may turn out that you won’t be able to thaw the evaporator at all.

This is due to the low defrosting power (about 3 kW), which is clearly not enough in such weather conditions. Moreover, prolonged defrosting reduces the efficient operation of the heat pump.

The variant of defrosting the evaporator by turning the heat pump into reverse is more acceptable because about 10 kW is immediately supplied to it, which significantly speeds up the defrosting process. The evaporator will be thawed and dried in just a couple of minutes.

An air to water heat pump for house heating works optimally and efficiently when there is no need for defrosting, when the outside temperature is +2, +3, + 5°С.

At temperatures below 0°C, it will still be more efficient to use a geothermal heat pump.

Read the Transcript

• Merry Christmas and Happy New Year folks!
• Today we’ll structure our video in this way:
• First, I’ll show you how the defrosting system works on my air heat pump,
• and then, in the second part, I’ll show the defrosting process,
• and during this process,
• in real-time I’ll talk about the results that we’ve got.
• Alright, let’s get to it! enjoy!
• So, this is how the defrosting system works.
• A compressor outlet.
• It has a branch tube,
• 6 mm.
• Here it goes.
• Right into the pipe which is located after the ECV.
• In this way, we bypass the condenser.
• Together with ECV and the rest of the stuff.
• Our goal: when the system is frozen, detect this fact
• and turn on the electromagnetic valve.
• Or rather, first completely close the ECV, and then turn on the electromagnetic valve.
• You can hear how evaporator fans turned off.
• The compressor continues to run.
• After the fans turn off, it takes about 10 seconds. and the shunt valve is turned on.
• The so-called defrost valve.
• Now a certain amount of liquid freon has accumulated in the condenser.
• It is not present in the defrosting system.
• On the right side (area behind the compressor),
• the diagram doesn’t show a bypass circuit with a valve.
• A certain amount of liquid freon accumulated in the condenser and it remains there.
• The rest of the freon is circulating along this small circuit.
• The compressor heats it up to 63°C.
• And then, until it reaches the evaporator inlet, it is about 22°C and at the outlet of the evaporator, -6°C.
• This temperature is slowly increasing.
• You can also notice that the evaporator plates gradually become dark, i.e. defrosting is in progress.
• Of course, the tubes that are closer to the inlet to the evaporator are thawed first.
• And then those that are closer to the outlet of the evaporator will thaw.
• The disadvantage of defrosting with heat from the compressor is that the defrost power is rather small.
• Now, it’s 3.2 kW.
• And if suddenly, for some reason, the heat removal from the evaporator increases, for example, a strong wind blows.
• It may turn out that at temperatures of -2°C …- 3°C it is no longer possible to defrost the evaporator.
• Because the wind will virtually blow out all these 3 kW.
• And the outdoor unit will never thaw.
• This is a disadvantage of this method.
• If we’re defrosting by turning the heat pump in reverse,
• then, if we take my heat pump, not 3.5 kW or 3 kW will be supplied to the evaporator, but all 12 kW, or even more.
• Or even 20 kW, given that the heat carrier in the house will be around 30°C, the COP will go through the roof.
• It may even come up to 10.
• And, of course, the defrost process itself will be quite fast in this case.
• If in my case it takes about 10-20 minutes, depending on the conditions.
• Then, by reversing, it’s probably about 2 minutes.
• Most likely, defrosting there may take a minute, but still, then it will be necessary to blowdown and dry the evaporator.
• And the water should still have time to drain.
• A minute may not be enough.
• Hard to say. In order to answer this question, I’ll need to observe the system more.
• But based on the experience of other people with whom I spoke,
• they at least claim that you can thaw out in a minute.
• I hardly believe that, but in 2 - 3 minutes, it is quite possible.
• You see, the power consumption of the compressor drops.
• It’s difficult to say why.
• Maybe because less gaseous freon remains in the system, more and more freon accumulates in the condenser.
• Because it’s 76°C at the compressor outlet.
• In any case, part of the freon condenses in the condenser.
• It doesn’t turn off completely.
• And some part of it goes into the system through the defrosting valve.
• You see, at the evaporator inlet, it is already 42°C.
• At the outlet, it’s about 0°C.
• Defrosting will go on up to + 5°C at the outlet of the evaporator.
• 5°С is the experimental temperature, which showed that this method already starts to work.
• When you try to heat it up to + 10°C, the defrosting cycle is greatly lengthened. The evaporator is already dry, but we haven’t yet reached + 10°С. And if the wind also rises, then it can go up to + 10°С for another hour.
• And you probably won’t even reach these + 10°C, because there is a tendency of decreasing consumption by the compressor.
• I observed the figure around 2.1 kW.
• And what is 2 kW when the outside temperature is, for example, -4°C, with a slight wind?
• It’s almost nothing at all.
• It will never heat up to + 10°C.
• This is perhaps the main drawback of this method.
• Plus, this long defrosting reduces the heat pump’s efficient running time.
• Let’s imagine that the humidity is high, almost 100%.
• There is no fog yet, but the humidity is off the scale.
• Defrosting occurs sometimes even in 25 minutes.
• That is, 25 minutes of operation, and the heat pump goes into the defrosting mode.
• Defrosting lasts an average of 20 minutes.
• So, for about 10 minutes the heating process itself takes place,
• then blowdown, then another 7 minutes for the compressor idle time to equalize the pressure.
• In a result, the heat pump is running 50% of the time.
• 50% of the time it is idle, doing nothing.
• Defrosting.
• And our useful power is reduced by 2 times.
• With reverse defrosting it is not so critical.
• This effect is reduced, but it is still present.
• And this heat that you blew into the house, and then use for defrosting, it also needs to be accumulated.
• And this takes time.
• Let’s say you have a heat pump running in reverse for 2 minutes.
• In order to accumulate this heat, you need to spend 4 minutes.
• In any case, the defrosting time will not be 2 minutes, but 6 minutes (2 + 4).
• That’s why the air heat pump is not so good.
• A geothermal heat pump is probably better.
• The air heat pump works great when no defrosting is needed.
• When it’s +2, +3, + 5°С outside.
• Then the COP will be 3 - 3.5, maybe even 5.
• Now, in this mode, when it’s about 0°C outside, the average COP is around 2.
• 2.2, 2.5 - when it is already + 2°C.
• And when it’s + 5°C, the COP is immediately higher than 3.
• So, see for yourself.
• Probably, the efficiency of the heat pump can be improved.
• Due to the fact that a warm floor will be used and you will not heat the water to 47°C like me.
• Now you can see that the defrosting process will end soon.
• I deliberately moved aside so that you could see the fans turn on.
• It’ll shut down right now.
• It’s turned off and fans turned on.
• [annoying telephone ringtone]
• The evaporator is drying out of moisture residues.
• The fans have turned off.
• The defrost process has ended.
• Switched to heating mode.
• It will turn on, in this case, after 7 minutes.
• This is my timeout.
• So, this is how it looks.
• I won’t do anything else to this unit.
• I will move towards the geothermal heat pump.
• Wish you all the best.
• Hope you’ll use my experience.
• And won’t repeat my mistakes.
• Bye, everyone!
• See you, fellas.
• On the vast outskirts of the internet.
• Bye Byeee!
• Taking this opportunity with the help of the site of the people’s heat pump (the link will be in the description).
• I would like to show you something.
• Here’s what happened just today.
• In the evening it was still about 0°С.
• At night, the temperature dropped to -12°C.
• And around 12 o’clock.
• We got this output:
• Almost 19 kWh consumed.
• Generated - 28 kWh.
• The total COP is less than 2.
• Of course, this also includes the energy that was used for defrosting.
• But it’s very, very sad.
• Now, as for how it all works.
• There is a “Detailed Statistics” here.
• So that you understand what defrosting looks like.
• This parameter drops to 0, it’s the level of the ECV opening.
• By this, you can clearly say that there was defrosting happening.
• Here the ECV closed, defrosting was in progress, the freon temperature at the compressor outlet was rising.
• Then the defrosting was over and it stopped.
• I mean, the defrosting continued.
• If it started at 5:16, it ended at 5:33.
• It seems not too long.
• But this is the almost ideal case because there was no wind at all.
• At all!
• If there was a wind, this process could take much longer.
• And now, if we look at the COP when everything is more or less settled down.
• We have COP around 2.37.
• With the outside temperature of -10°C.
• And when the water temperature rises in the heating system, then COP is 2.0.
• Well, minus the defrosting.
• Even if you’ll have almost no defrosting happening or an almost perfect compressor.
• The water will need to be heated not to 50°C, but only to 32°C.
• Here, you see, the temperature at the condenser outlet is 32.7°C.
• The warm floor will still not work if the temperature is less than 30°C.
• This is how warm floors will work.
• So, in fact, you’ll get this COP:
• 2.0
• And if there is still a defrosting happening, everything will be sad.
• Now I’ll show you how it works when the temperature is higher.
• Now let’s move somewhere.
• For example, let’s see what happened on December 27.
• There was a very high humidity here, so work and defrosting was constantly going on.
• If you want, you can pause the video and look at the numbers.
• The total COP there was 2, maybe a little more.
• It’s difficult to show here, if only you could select a range and see what the overall COP is.
• But this cannot be done here in this software.
• What else do we have here…
• Here, you can see, the air was quite dry, so it did not always enter the defrosting mode.
• And here, for example, the humidity was very high.
• Then, apparently, the humidity decreased.
• In general, everything that we see on industrial air-to-water or air-to-air heat pumps is hidden from the user.
• And all these nuances are not visible.
• How hard it works you will understand only when it dies,
• or something happens to it and the specialists will come and say: “Something went wrong here”.
• I don’t think that an industrial air heat pump is fundamentally different from what I have.
• Granted, there may be some differences.
• Yes, the overall picture might be slightly better there.
• But it will not be fundamentally different.
• The same processes that I observe will be observed in industrial heat pumps.
• So, it’s for you to decide.
• What is good, what is bad and which way to choose.
• See you in the next video! Don’t forget to smack that subscribe button!