DIY Geothermal Heat Pump. Season 3. Ep3. Heat pump design and assembly. Pt1.

G’day fellas! In this episode you’ll see how heat pumps work, we’ll look at most basic, simplified heat pump design to understand core principles of it’s operation.

We’ll also talk about why I’m using EEV instead of TXV, my slightly more complex version of heating machine with regenerative heat exchanger, where are the optimal places to install various sensors to control system operation.

Stay safe and enjoy the video!

Read the Transcript

• Greetings!
• Recently I saw how the old Moskvich is designed.
• Compared to modern cars, there is nothing under the hood at all.
• Only the poor lonely motor.
• And the wheel drive is immediately visible.
• Simple distributor and nothing more.
• And when you open the hood of a modern car, there are so many various parts that the head starts to spin, and immediately fear appears in your eyes 😨.
• The same applies to cooling/heating machines.
• In the basic configuration, the cooling machine is a very simple thing.
• I will now draw the minimal scheme that is required to create a cooling machine.
• Well, or a heating machine.
• They’re reversible.
• It gives heat on one side and cold on the other.
• Here is the minimum set of parts required.
• This is a heat exchanger called an “evaporator”.
• This is a heat exchanger called a “condenser”.
• This is a compressor.
• This is a throttle.
• And the most important component - freon.
• Freons can be different.
• Usually, people use the freon that is best suitable in their current situation.
• I will use 410th gas.
• Because it suits my situation.
• On the other hand, it is quite a good gas.
• The 410th gas gives the highest power density per volume.
• The same compressor, evaporator-condenser.
• This difference is not very big, but it’s there.
• Let’s look at how a heat pump works on this simplest scheme.
• What happens in this case.
• The evaporator is filled with freon.
• It removes heat from the geothermal loop or from the air circuit.
• And it boils during this process.
• The gas is pumped out by the compressor.
• Low pressure is generated here.
• Therefore, the gas is boiling.
• You can see how the gas boils in one of my previous videos about the thermal siphon.
• The gas is compressed by the compressor, the gas pressure increases.
• And already at a higher temperature, it begins to condense in another plate heat exchanger.
• Which is called a “condenser”.
• Condensing - condenser.
• The evaporator must be almost fully filled with freon.
• Well, it is clear that it cannot be filled 100%.
• It’s difficult for me to say the exact filing percentage, but I think that it is somewhere around 70 - 80 percent.
• The more the evaporator is filled, the higher the effective heat exchange area.
• It is clear that here, where the gas is located, the heat intake is very small.
• Therefore, only the part that is filled with freon works.
• And a slightly different process is observed in the condenser.
• It should not be filled with liquid freon.
• Condensation occurs on the walls of the heat exchanger.
• This condensate flows down, and, in theory, there should be a minimum of liquid freon in the condenser.
• After that, this liquid freon approaches the throttle, where throttling takes place through a thin hole.
• The throttle can be made in the form of a capillary tube.
• Here, the tubes are quite thick everywhere, but there is a very thin tube of a certain section.
• The cross-section of this tube is calculated.
• There are tables for calculating this tube for the required freon flow.
• Knowing how much liquid freon must pass through this throttle, we can calculate the thermal power of the * machine.
• Throttle tubes are very often used.
• Especially in those devices where you need to do everything very cheaply.
• For example, in refrigerators.
• In refrigerators, nothing is used other than this throttling tube.
• It is usually wound in a spiral shape.
• But often it is not very economical to use the throttle tube because in this case, the machine does not work in the most optimal mode.
• Therefore, either a TXV (thermostatic expansion valve) or an EEV (electronic expansion valve) is installed.
• I installed the EEV right away because, firstly, the EEV became relatively cheap, available for use,
• and since I use a control board that can work with the EEV, the use of the TXV becomes meaningless.
• I still have a board that controls it, it knows how to work with electronic expansion valves.
• And the difference in price now between the EEV and the TXV is close to 0.
• Therefore, I see no reason to use the TXV if you have a control board.
• If there is no control board and you want to create an analog machine, not a digital one, then you need to use a TXV with all that it implies.
• Figure out how to configure it …
• I will not return to this question anymore.
• I put TXV on my very first experimental machine.
• It is not clear how it works.
• With EEV you can clearly see how it works, how open it is, you can see how the regulation takes place, then with the TXV it’s not clear whether it works or not.
• This is the simplest machine.
• In my case, the heating/cooling machine will be a little more complicated.
• I want to throw a regenerative heat exchanger into the mix.
• If we look at this whole scheme, then after the condenser the liquid phase will come out of here with a temperature close to the temperature of the heating circuit.
• If, for example, it will be + 30 ℃ here, then here it will also be +30 ℃.
• Warm liquid freon reaches the throttle and throttles.
• At the same time, since boiling occurs, even after the throttle it immediately boils,
• here the boiling point will be close to the temperature of the geothermal loop.
• Heat is supplied, for example, with a temperature of + 2 ℃ and, accordingly, here +2 ℃.
• Consider the ideal case to simplify matters.
• It turns out that the difference of +30 ℃ and + 2 ℃ seems to be lost.
• If we supplied freon here with a temperature of + 2 ℃, then this delta for which freon needs to be heated, is lost.
• Therefore, if we break this chain here …
• Artists from the word “fart”😊.
• And break the chain …
• Right here.
• What will we get?
• We get that since here freon comes out at +2 ℃, it will heat up in this heat exchanger.
• Remember we’re considering an ideal case.
• And here it heats up to +30 ℃.
• Thus, we save the heat that would’ve been lost after throttling.
• And already here, the compressor gets not +2 ℃ as it was earlier, but + 30 ℃.
• In fact, the temperatures will be different, but we are talking about the ideal case.
• Thus, we keep this warmth.
• In relative terms, this will not be very much.
• We’ll be able to save 2 - 3% in this way.
• To understand the order of the numbers, you can take the heat capacity of the freon itself, take the heat of vaporization, and calculate the order of these numbers.
• Everyone decides for themselves whether to chase these numbers or not.
• By complicating the cooling machine itself.
• Next.
• In order for the electronics to regulate the degree of opening of the throttle, in my case the EEV, we need to put a sensor that will measure the pressure in the system.
• On the one hand, here, at this point, we have to measure temperature and pressure.
• To maintain optimal freon supercooling.
• This is where we install the pressure sensor.
• And here we install the temperature sensor.
• And we connect it to the control board.
• In addition, a temperature sensor is installed at the compressor outlet so that if overheating occurs, the electronics can go into emergency mode.
• In addition to the emergency temperature sensor, an alarm pressure switch is also installed.
• Why is it needed?
• If there is a problem in the line, the EEV is closed, something else is there, the EEV is broken, the compressor presses high pressure, the relay is activated and the whole thing is turned off.
• The emergency protection is triggered.
• In addition, we install liquid temperature sensors.
• On the heating circuit and on the geothermal loop.
• Temperature sensors are installed at the inlet and outlet on one and the other side.
• In addition, 2 flow sensors are installed.
• At this point and at this point.
• Knowing how much heat we took from the geothermal loop, how much we gave to the heating circuit, we know how much power the compressor consumes,
• we can calculate the heat balance of our machine.
• I would like to draw your attention to the direction of movement of liquids and gases in this system.
• Freon is moving in this direction.
• Accordingly, the liquid in the condenser must move in the opposite direction.
• Like this.
• This is the basic rule.
• The opposite direction of movement of liquids in heat exchangers.
• Here, accordingly, freon moves in this way.
• In the geothermal loop, the coolant must move towards.
• And when you assemble your heating machine, this must be clearly taken into account.
• Otherwise, you can lose a few degrees in the heat exchanger if the direction is wrong.
• Now you’ve seen how my heat pump works.
• You will now see how it looks in real life.
• Before the video of the heating machine operation, I will give brief explanations after I show how I soldered the heating machine itself.
• I soldered my heat pump with an oxygen-propane torch.
• Today it is possible to use, like me, an oxygen-propane burner, or now there is an affordable MAPP burner.
• You can google how to use it and what it is.
• Today it looks more interesting in comparison with propane-oxygen because it does not require an oxygen cylinder, a propane cylinder, a reducer, a burner …
• Everything looks a little simpler.
• I have not tried how it welds, better or worse,
• but for those who are just starting to do this, perhaps it will be better.
• It will be cheaper in terms of equipment.
• Although gas itself is expensive, it will be more interesting due to the fact that you do not need to buy a bunch of these heavy cylinders.
• Well, let’s go 🚂!
• So, what do we have here?
• Let’s start with the compressor.
• This is a high-pressure line. Injection.
• Schrader valve.
• High-pressure sensor.
• Rather, a high-pressure switch.
• This line enters the PHE (plate heat exchanger).
• After PHE, to the control peephole.
• And here you can see a recuperative heat exchanger.
• A thin tube is soldered to this thick tube that comes out of the evaporator.
• Soldered with copper solder along the entire length.
• This makes a loop.
• Here it went up …
• Soldered to a thick tube.
• To the loop all over its length.
• And now it comes out of the loop.
• Enters the filter-drier.
• Enters the EEV.
• From the EEV it goes to the PHE (plate heat exchanger), which is the evaporator.
• And from the evaporator, through the same recuperative heat exchanger, through this loop …
• I hope you can see it.
• It gets to the pressure sensor,
• and goes to the inlet of the compressor, the suction.
• This is how it looks.
• On plate heat exchangers, on the evaporator there is …
• The supply will be from the top.
• Out from the bottom.
• There is a pulse counter at the output. Flow sensor.
• The same is on the condenser.
• This is the supply.
• There is also a counter on it.
• And the way out.
• The coolant will go out into the heating system.
• There is a slight inaccuracy in that picture that you just saw.
• The pressure sensor should be closer to the PHE.
• Not closer to the compressor, but closer to the PHE.
• I have already rearranged it, but in the video, you see it closer to the compressor.
• There, on both sides, a Schroeder valve was installed, so it was not difficult to rearrange it.
• That’s a little gotcha for you to consider.
• You will see how I will run this heat pump in the next series.
• Because this already took 25 minutes, which is quite a lot for one part.
• Alright. See you in the next video. Bye!