Install a heat pump for home heating. How to choose the right heat pump? Heat pump transformation ratio Ktr

This autumn, there is an aggravation in the network about heat pumps and their use for heating country houses and dachas. In a country house that I built with my own hands, such a heat pump has been installed since 2013. This is a semi-industrial air conditioner that can effectively work for heating at outdoor temperatures down to -25 degrees Celsius. It is the main and only heating device in a one-story country house with a total area of ​​72 square meters.

2. Briefly recall the background. Four years ago, a plot of 6 acres was bought in a garden partnership, on which, with my own hands, without involving hired labor, I built a modern energy-efficient Vacation home. The purpose of the house is the second apartment, located in nature. Year-round, but not permanent operation. Required maximum autonomy in conjunction with simple engineering. In the area where the SNT is located, there is no main gas and you should not count on it. There remains imported solid or liquid fuel, but all these systems require complex infrastructure, the cost of construction and maintenance of which is comparable to direct heating with electricity. Thus, the choice was already partly predetermined - electric heating. But here arises a second, no less important point: limitation of electrical capacities in the garden partnership, as well as rather high tariffs for electricity (at that time - not a "rural" tariff). In fact, 5 kW of electric power has been allocated to the site. The only way out in this situation is to use a heat pump, which will save on heating by about 2.5-3 times, compared with the direct conversion of electrical energy into heat.

So let's move on to heat pumps. They differ in where they take heat from and where they give it away. An important point known from the laws of thermodynamics (Grade 8 high school) - a heat pump does not produce heat, it transfers it. That is why its COP (energy conversion factor) is always greater than 1 (that is, the heat pump always gives off more heat than it consumes from the network).

The classification of heat pumps is as follows: "water - water", "water - air", "air - air", "air - water". Under the "water" indicated in the formula on the left is meant the removal of heat from the liquid circulating coolant passing through pipes located in the ground or a reservoir. The efficiency of such systems is practically independent of the season and ambient temperature, but they require expensive and labor-intensive earthworks, as well as the availability of sufficient free space for laying a soil heat exchanger (on which, subsequently, it will be bad to grow anything in the summer, due to freezing of the soil). The "water" indicated in the formula on the right refers to the heating circuit located inside the building. It can be either a system of radiators or liquid underfloor heating. Such a system will also require complex engineering work inside the building, but it also has its advantages - with the help of such heat pump you can also get hot water in the house.

But the category of air-to-air heat pumps looks the most interesting. In fact, these are the most common air conditioners. While working for heating, they take heat from the outdoor air and transfer it to the air heat exchanger located inside the house. Despite some drawbacks (serial models cannot operate at ambient temperatures below -30 degrees Celsius), they have a huge advantage: such a heat pump is very easy to install and its cost is comparable to conventional electric heating using convectors or an electric boiler.

3. Based on these considerations, Mitsubishi Heavy duct semi-industrial air conditioner, model FDUM71VNX, was chosen. As of autumn 2013, a set consisting of two blocks (external and internal) cost 120 thousand rubles.

4. The outdoor unit is installed on the facade on the north side of the house, where there is the least wind (this is important).

5. The indoor unit is installed in the hall under the ceiling, from which, with the help of flexible soundproof air ducts, hot air is supplied to all living spaces inside the house.

6. Because the air supply is located under the ceiling (it is absolutely impossible to organize the supply of hot air near the floor in a stone house), it is obvious that you need to take the air on the floor. To do this, with the help of a special box, the air intake was lowered to the floor in the corridor (in all interior doors, overflow grilles were also installed in the lower part). Operating mode - 900 cubic meters of air per hour, due to constant and stable circulation, there is absolutely no difference in air temperature between the floor and ceiling in any part of the house. To be precise, the difference is 1 degree Celsius, which is even less than when using wall-mounted convectors under windows (with them, the temperature difference between floor and ceiling can reach 5 degrees).

7. Besides that indoor unit the air conditioner, due to its powerful impeller, is able to drive large volumes of air around the house in recirculation mode, we should not forget that people need fresh air in the house. Therefore, the heating system also acts as a ventilation system. Through a separate air duct from the street, fresh air is supplied to the house, which, if necessary, is heated (during the cold season) using automation and a channel heating element.

8. Distribution of hot air is carried out through these grilles located in the living rooms. It is also worth paying attention to the fact that there is not a single incandescent lamp in the house and only LEDs are used (remember this point, this is important).

9. Waste "dirty" air is removed from the house through the hood in the bathroom and in the kitchen. Hot water is prepared in a conventional storage water heater. In general, this is a fairly large expense item, because. well water very cold (from +4 to +10 degrees Celsius depending on the time of year) and one might reasonably notice that solar collectors can be used to heat water. Yes, you can, but the cost of investing in infrastructure is such that for this money you can heat water directly with electricity for 10 years.

10. And this is "TsUP". Air source heat pump master and main controller. It has various timers and simple automation, but we use only two modes: ventilation (during the warm season) and heating (during the cold season). The built house turned out to be so energy efficient that the air conditioner in it was never used for its intended purpose - to cool the house in the heat. LED lighting played a big role in this (heat transfer from which tends to zero) and very high-quality insulation (it's no joke, after arranging the lawn on the roof, we even had to use a heat pump this summer to heat the house - on days when the average daily temperature dropped below + 17 degrees Celsius). The temperature in the house is maintained year-round at least +16 degrees Celsius, regardless of the presence of people in it (when there are people in the house, the temperature is set to +22 degrees Celsius) and never turns off forced ventilation(because lazy).

11. The meter for technical electricity metering was installed in the fall of 2013. That is exactly 3 years ago. It is easy to calculate that the average annual consumption of electrical energy is 7000 kWh (in fact, this figure is slightly lower now, because in the first year the consumption was high due to the use of dehumidifiers during finishing work).

12. In the factory configuration, the air conditioner is capable of heating at an ambient temperature of at least -20 degrees Celsius. To work at lower temperatures, refinement is required (in fact, it is relevant when operating even at a temperature of -10, if the humidity is high outside) - installing a heating cable in a drainage pan. This is necessary so that after the defrosting cycle of the outdoor unit, the liquid water has time to leave the drain pan. If she does not have time to do this, then ice will freeze in the pan, which will subsequently squeeze out the frame with the fan, which will probably lead to the breaking of the blades on it (you can see photos of the broken blades on the Internet, I almost encountered this myself because . did not put down the heating cable immediately).

13. As I mentioned above, LED lighting is used everywhere in the house. This is important when it comes to air conditioning a room. Let's take a standard room in which there are 2 lamps, 4 lamps in each. If these are 50 watt incandescent lamps, then in total they consume 400 watts, while LED bulbs will consume less than 40 watts. And all energy, as we know from the physics course, eventually turns into heat anyway. That is, incandescent lighting is such a good medium-power heater.

14. Now let's talk about how a heat pump works. All it does is transfer heat energy from one place to another. This is how refrigerators work. They transfer heat from refrigerator compartment into the room.

There is such a good riddle: How will the temperature in the room change if you leave the refrigerator plugged into the outlet with the door open? The correct answer is that the temperature in the room will rise. For a simple understanding, this can be explained as follows: the room is a closed circuit, electricity flows into it through the wires. As we know, energy eventually turns into heat. That is why the temperature in the room will rise, because electricity enters the closed circuit from the outside and remains in it.

A bit of theory. Heat is a form of energy that is transferred between two systems due to temperature differences. In this case, thermal energy is transferred from a place with a high temperature to a place with a lower temperature. This is a natural process. Heat transfer can be carried out by conduction, thermal radiation or by convection.

There are three classical aggregate states of matter, the transformation between which is carried out as a result of a change in temperature or pressure: solid, liquid, gaseous.

For change state of aggregation the body must either receive or give off thermal energy.

During melting (transition from a solid to a liquid state), thermal energy is absorbed.
During evaporation (transition from a liquid to a gaseous state), thermal energy is absorbed.
During condensation (transition from a gaseous state to a liquid state), thermal energy is released.
During crystallization (transition from a liquid to a solid state), thermal energy is released.

The heat pump uses two transient modes in its operation: evaporation and condensation, that is, it operates with a substance that is either in a liquid or in a gaseous state.

15. The refrigerant R410a is used as the working fluid in the heat pump circuit. It is a fluorocarbon that boils (changes from liquid to gas) at very low temperatures. Namely, at a temperature of - 48.5 degrees Celsius. That is, if ordinary water at normal atmospheric pressure boils at a temperature of +100 degrees Celsius, R410a freon boils at a temperature almost 150 degrees lower. Moreover, at a very negative temperature.

It is this property of the refrigerant that is used in the heat pump. By targeted measurement of pressure and temperature, it can be given the desired properties. Either it will be evaporation at ambient temperature with the absorption of heat, or condensation at ambient temperature with the release of heat.

16. This is what the heat pump circuit looks like. Its main components are compressor, evaporator, expansion valve and condenser. The refrigerant circulates in a closed circuit of the heat pump and alternately changes its state of aggregation from liquid to gaseous and vice versa. It is the refrigerant that transfers and transfers heat. The pressure in the circuit is always excessive compared to atmospheric pressure.

How it works?
Compressor draws in cold gaseous refrigerant low pressure coming from the evaporator. The compressor compresses it under high pressure. The temperature rises (the heat from the compressor is also added to the refrigerant). At this stage, we obtain a gaseous refrigerant of high pressure and high temperature.
In this form, it enters the condenser, blown with colder air. The superheated refrigerant gives up its heat to the air and condenses. At this stage, the refrigerant is in a liquid state, under high pressure and at an average temperature.
The refrigerant then enters the expansion valve. There is a sharp decrease in pressure in it, due to the expansion of the volume that the refrigerant occupies. The decrease in pressure leads to partial evaporation of the refrigerant, which in turn reduces the temperature of the refrigerant below ambient temperature.
In the evaporator, the pressure of the refrigerant continues to decrease, it evaporates even more, and the heat necessary for this process is taken from the warmer outside air, which is then cooled.
The fully gaseous refrigerant enters the compressor again and the cycle is completed.

17. I'll try to explain again in a simpler way. The refrigerant boils already at a temperature of -48.5 degrees Celsius. That is, relatively speaking, at any higher ambient temperature, it will have excess pressure and, in the process of evaporation, will take heat from the environment (that is, street air). There are refrigerants used in low-temperature refrigerators, their boiling point is even lower, down to -100 degrees Celsius, but it cannot be used to operate a heat pump to cool a room in the heat due to the very high pressure at high temperatures environment. R410a refrigerant is a kind of balance between the ability of the air conditioner to work both for heating and cooling.

Here, by the way, is a good documentary film shot in the USSR and telling about how a heat pump works. I recommend.

18. Can any air conditioner be used for heating? No, not any. Although almost all modern air conditioners work on R410a freon, other characteristics are no less important. Firstly, the air conditioner must have a four-way valve that allows you to switch to “reverse”, so to speak, namely, to swap the condenser and evaporator. Secondly, please note that the compressor (it is located on the lower right) is located in a thermally insulated casing and has an electric crankcase heater. This is necessary in order to always maintain a positive oil temperature in the compressor. In fact, at an ambient temperature below +5 degrees Celsius, even in the off state, the air conditioner consumes 70 watts of electrical energy. The second, most important point - the air conditioner must be inverter. That is, both the compressor and the impeller electric motor must be able to change performance during operation. This is what allows the heat pump to work efficiently for heating at outdoor temperatures below -5 degrees Celsius.

19. As we know, on the heat exchanger of the outdoor unit, which is the evaporator during heating operation, intensive evaporation of the refrigerant occurs with the absorption of heat from the environment. But in the outdoor air there are water vapor in a gaseous state, which condense, or even crystallize on the evaporator due to sharp decline temperature (outdoor air gives off its heat to the refrigerant). And intensive freezing of the heat exchanger will lead to a decrease in the efficiency of heat removal. That is, as the ambient temperature decreases, it is necessary to “slow down” both the compressor and the impeller in order to ensure the most efficient heat removal on the evaporator surface.

An ideal heat pump for heating only should have a surface area of ​​the external heat exchanger (evaporator) several times the surface area of ​​the internal heat exchanger (condenser). In practice, we return to the very balance that the heat pump must be able to work both for heating and cooling.

20. On the left, you can see the external heat exchanger almost completely covered with frost, except for two sections. In the upper, not frozen, section, freon still has a sufficiently high pressure, which does not allow it to effectively evaporate with the absorption of heat from the environment, while in the lower section it is already overheated and can no longer take heat from the outside. And the photo on the right gives an answer to the question why the external unit of the air conditioner was installed on the facade, and not hidden from view on flat roof. It is because of the water that needs to be diverted from the drainage pan in the cold season. It would be much more difficult to drain this water from the roof than from the blind area.

As I already wrote, during heating operation at a negative temperature outside, the evaporator on the outdoor unit freezes over, water from the outdoor air crystallizes on it. The efficiency of a frozen evaporator is noticeably reduced, but the air conditioner electronics automatically controls the heat removal efficiency and periodically switches the heat pump to the defrost mode. In fact, the defrost mode is a direct conditioning mode. That is, heat is taken from the room and transferred to an external, frozen heat exchanger in order to melt the ice on it. At this time, the fan of the indoor unit runs at minimum speed, and cool air comes out of the air ducts inside the house. The defrost cycle usually lasts 5 minutes and occurs every 45-50 minutes. Due to the high thermal inertia of the house, no discomfort is felt during defrosting.

21. Here is a table of heat output for this heat pump model. Let me remind you that the nominal energy consumption is just over 2 kW (current 10A), and the heat transfer ranges from 4 kW at -20 degrees outside, up to 8 kW at a street temperature of +7 degrees. That is, the conversion factor is from 2 to 4. It is how many times the heat pump saves energy compared to the direct conversion of electrical energy into heat.

By the way, there is another interesting point. The resource of the air conditioner when working for heating is several times higher than when working for cooling.

22. Last fall, I installed the Smappee electric energy meter, which allows you to keep statistics on energy consumption on a monthly basis and provides a more or less convenient visualization of the measurements taken.

23. Smappee was installed exactly one year ago, in the last days of September 2015. It also attempts to show the cost of electricity, but does so based on manually set rates. And there is an important point with them - as you know, we raise electricity prices 2 times a year. That is, for the presented measurement period, tariffs changed 3 times. Therefore, we will not pay attention to the cost, but calculate the amount of energy consumed.

In fact, Smappee has problems with the visualization of consumption graphs. For example, the shortest column on the left is the consumption for September 2015 (117 kWh). something went wrong with the developers and for some reason there are 11, not 12 columns on the screen for a year. But the total consumption figures are calculated accurately.

Namely, 1957 kWh for 4 months (including September) at the end of 2015 and 4623 kWh for the whole of 2016 from January to September inclusive. That is, a total of 6580 kWh was spent on ALL the life support of a country house, which was heated all year round, regardless of the presence of people in it. Let me remind you that in the summer of this year for the first time I had to use a heat pump for heating, and for cooling in the summer it did not work even once in all 3 years of operation (except for automatic defrost cycles, of course). In rubles, at current tariffs in the Moscow region, this is less than 20 thousand rubles a year, or about 1,700 rubles a month. Let me remind you that this amount includes: heating, ventilation, water heating, stove, refrigerator, lighting, electronics and appliances. That is, it is actually 2 times cheaper than the monthly payment for an apartment in Moscow of the same area (of course, excluding maintenance fees, as well as fees for major repairs).

24. And now let's calculate how much money the heat pump saved in my case. We will compare with electric heating, using the example of an electric boiler and radiators. I will count at pre-crisis prices, which were at the time of the installation of the heat pump in the fall of 2013. Now heat pumps have risen in price due to the collapse of the ruble, and the equipment is all imported (the leaders in the production of heat pumps are the Japanese).

Electric heating:
Electric boiler - 50 thousand rubles
Pipes, radiators, fittings, etc. - another 30 thousand rubles. Total materials for 80 thousand rubles.

Heat pump:
Channel air conditioner MHI FDUM71VNXVF (outdoor and indoor unit) - 120 thousand rubles.
Air ducts, adapters, thermal insulation, etc. - another 30 thousand rubles. Total materials for 150 thousand rubles.

Do-it-yourself installation, but in both cases it is about the same in time. Total "overpayment" for a heat pump compared to an electric boiler: 70 thousand rubles.

But that's not all. Air heating using a heat pump is at the same time air conditioning in the warm season (that is, air conditioning still needs to be installed, right? So we’ll add at least another 40 thousand rubles) and ventilation (mandatory in modern sealed houses, at least another 20 thousand rubles).

What do we have? "Overpayment" in the complex is only 10 thousand rubles. It is still at the stage of putting the heating system into operation.

And then the operation begins. As I wrote above, in the coldest winter months the conversion factor is 2.5, and in the off-season and summer it can be taken equal to 3.5-4. Let's take the average annual COP equal to 3. Let me remind you that 6,500 kWh of electrical energy is consumed in a house per year. This is the total consumption of all electrical appliances. Let's take for simplicity of calculations at a minimum that the heat pump consumes only half of this amount. That is 3000 kWh. At the same time, on average, for the year he gave 9000 kWh of thermal energy (6000 kWh "dragged" from the street).

Let's translate the transferred energy into rubles, assuming that 1 kWh of electrical energy costs 4.5 rubles (average day/night tariff in the Moscow region). We get 27,000 rubles of savings, compared with electric heating only for the first year of operation. Recall that the difference at the stage of putting the system into operation was only 10 thousand rubles. That is, already for the first year of operation, the heat pump SAVED me 17 thousand rubles. That is, it paid off in the first year of operation. Let me remind you that this is not permanent residence, at which the savings would be even greater!

But do not forget about the air conditioner, which specifically in my case was not required due to the fact that the house I built turned out to be over-insulated (although a single-layer aerated concrete wall is used without additional insulation) and it simply does not heat up in the summer in the sun. That is, we will throw off 40 thousand rubles from the estimate. What do we have? In this case, I began to SAVE on the heat pump not from the first year of operation, but from the second. It's not a big difference.

But if we take a water-to-water heat pump or even an air-to-water heat pump, then the figures in the estimate will be completely different. That is why an air-to-air heat pump offers the best price/performance ratio on the market.

25. And finally, a few words about electric heaters. I was tormented by questions about all sorts of infrared heaters and nano-technologies that do not burn oxygen. I will answer briefly and to the point. Any electric heater has an efficiency of 100%, that is, all electrical energy is converted into heat. In fact, this applies to any electrical appliances, even an electric light bulb gives off heat exactly in the amount in which it received it from the outlet. If we talk about infrared heaters, then their advantage lies in the fact that they heat objects, not air. Therefore, the most reasonable application for them is heating on open verandas in cafes and at bus stops. Where there is a need to transfer heat directly to objects / people, bypassing air heating. A similar story about the burning of oxygen. If somewhere in the brochure you see this phrase, you should know that the manufacturer is holding the buyer for a sucker. Combustion is an oxidation reaction, and oxygen is an oxidizing agent, that is, it cannot burn itself. That is, this is all the nonsense of amateurs who skipped physics lessons at school.

26. Another option for saving energy when electric heating(it does not matter, direct conversion or with the help of a heat pump) is the use of the heat capacity of the building envelope (or a special heat accumulator) to accumulate heat when using a cheap night electric tariff. That's what I'll be experimenting with this winter. According to my preliminary calculations (taking into account the fact that next month I will pay the village electricity tariff, because the building is already registered as a residential building), even despite the increase in electricity tariffs, next year I will pay for the maintenance of the house less than 20 thousand rubles (for all consumed electrical energy for heating, water heating, ventilation and equipment, taking into account the fact that the house is maintained at a temperature of about 18-20 degrees Celsius all year round, regardless of whether there are people in it).

What is the result? A heat pump in the form of a low-temperature air-to-air conditioner is the easiest and most affordable way to save on heating, which can be doubly important when there is a limit on electrical power. I am completely satisfied with the installed heating system and do not experience any discomfort from its operation. In the conditions of the Moscow region, the use of an air source heat pump fully justifies itself and allows you to recoup the investment no later than in 2-3 years.

By the way, do not forget that I also have Instagram, where I publish the progress of work almost in real time -

By the end of the 19th century, powerful refrigeration plants appeared that could pump at least twice as much heat as was spent on putting them into action. It was a shock, because formally it turned out that a thermal perpetual motion machine is possible! However, upon closer examination, it turned out that perpetual motion is still far away, and low-grade heat produced using a heat pump and high-grade heat obtained, for example, by burning fuel, are two big differences. True, the corresponding formulation of the second law was somewhat modified. So what exactly are heat pumps? In a nutshell, a heat pump is a modern and high-tech appliance for heating and air conditioning. Heat pump collects heat from the street or from the ground and sends it to the house.

How a heat pump works

How a heat pump works simple: due to mechanical work or other types of energy, it provides the concentration of heat, previously evenly distributed over a certain volume, in one part of this volume. In the other part, respectively, a deficit of heat is formed, that is, cold.

Historically, heat pumps were first widely used as refrigerators - in fact, any refrigerator is a heat pump that pumps heat from the refrigeration chamber to the outside (into the room or outside). There is still no alternative to these devices, and with all the variety of modern refrigeration technology, the basic principle remains the same: heat is pumped out of the refrigeration chamber due to additional external energy.

Naturally, almost immediately they noticed that the noticeable heating of the condenser heat exchanger (for a household refrigerator, it is usually made in the form of a black panel or a grill on the back wall of the cabinet) could also be used for heating. It was already the idea of ​​a heat pump based heater in its modern form- a refrigerator, on the contrary, when heat is pumped into a closed volume (room) from an unlimited external volume (from the street). However, in this area, the heat pump has a lot of competitors - starting with traditional wood stoves and fireplaces and ending with all kinds of modern heating systems. Therefore, for many years, while the fuel was relatively cheap, this idea was regarded as nothing more than a curiosity - in most cases it was absolutely unprofitable economically, and only very rarely was such use justified - usually for the utilization of heat pumped out by powerful refrigeration units in countries with not too cold climate. And only with the rapid rise in energy prices, the complication and rise in the cost of heating equipment and the relative cheapening against this background of the production of heat pumps, such an idea becomes economically viable in itself, because having paid once for a rather complex and expensive installation, then it will be possible to constantly save on reduced fuel consumption. Heat pumps are the basis of the growing ideas of cogeneration - the simultaneous production of heat and cold - and trigeneration - the production of heat, cold and electricity at once.

Since the heat pump is the essence of any refrigeration unit, we can say that the concept of "refrigeration machine" is its pseudonym. True, it should be borne in mind that despite the universality of the principles of operation used, the designs of refrigeration machines are still focused specifically on the production of cold, and not heat - for example, the generated cold is concentrated in one place, and the resulting heat can be dissipated in several different parts of the installation , because in a conventional refrigerator the task is not to utilize this heat, but simply to get rid of it.

Heat pump classes

Currently, two classes of heat pumps are most widely used. One class can be attributed to thermoelectric Peltier, and to another - evaporative, which, in turn, are divided into mechanical compressor (piston or turbine) and absorption (diffusion). In addition, interest is gradually increasing in the use of vortex tubes as heat pumps, in which the Ranque effect operates.

Heat pumps based on the Peltier effect

Peltier element

The Peltier effect lies in the fact that when a small constant voltage is applied to the two sides of a specially prepared semiconductor wafer, one side of this wafer heats up and the other cools. Here, in general, the thermoelectric heat pump is ready!

The physical essence of the effect is as follows. The plate of the Peltier element (aka "thermoelectric element", eng. Thermoelectric Cooler, TEC), consists of two layers of a semiconductor with different levels of electron energy in the conduction band. When an electron passes under the action of an external voltage into a higher-energy conduction band of another semiconductor, it must acquire energy. When he receives this energy, the place of contact of the semiconductors is cooled (when the current flows in the opposite direction, the opposite effect occurs - the place of contact of the layers heats up in addition to the usual ohmic heating).

Advantages of Peltier elements

The advantage of Peltier elements is the maximum simplicity of their design (what could be simpler than a plate to which two wires are soldered?) And the complete absence of any moving parts, as well as internal flows of liquids or gases. The consequence of this is absolute noiselessness of operation, compactness, complete indifference to orientation in space (provided sufficient heat dissipation is ensured) and very high resistance to vibration and shock loads. And the operating voltage is only a few volts, so a few batteries or a car battery are quite enough to work.

Disadvantages of Peltier elements

The main disadvantage of thermoelectric elements is their relatively low efficiency - it can be tentatively considered that they will need twice as much external energy supplied per unit of pumped heat. That is, by supplying 1 J of electrical energy, we can remove only 0.5 J of heat from the cooled area. It is clear that all the total 1.5 J will be released on the "warm" side of the Peltier element and they will have to be taken to external environment. This is many times lower than the efficiency of compression evaporative heat pumps.

Against the background of such a low efficiency, other disadvantages are usually not so important, and this is a small specific productivity combined with a high specific cost.

Using Peltier elements

In accordance with their characteristics, the main field of application of Peltier elements is currently usually limited to cases where it is required not to cool something that is not too powerful, especially in conditions of strong shaking and vibrations and with severe restrictions on weight and dimensions, - for example, various components and parts of electronic equipment, primarily military, aviation and space. Perhaps, Peltier elements are most widely used in everyday life in low-power (5..30 W) portable automobile refrigerators.

Evaporative compression heat pumps

Working cycle diagram of an evaporative compression heat pump

The principle of operation of this class of heat pumps is as follows. The gaseous (in whole or in part) refrigerant is compressed by the compressor to a pressure at which it can turn into a liquid. Naturally, this heats up. The heated compressed refrigerant is fed into the condenser radiator, where it is cooled to the ambient temperature, giving it excess heat. This is the heating zone (back wall of the kitchen refrigerator). If at the inlet of the condenser a significant part of the compressed hot refrigerant still remained in the form of vapor, then when the temperature decreases during heat exchange, it also condenses and passes into a liquid state. The relatively cooled liquid refrigerant is fed into the expansion chamber, where, passing through a throttle or expander, it loses pressure, expands and evaporates, at least partially turning into a gaseous form, and, accordingly, cools down - significantly below the ambient temperature and even below the temperature in cooling zone of the heat pump. Passing through the channels of the evaporator panel, the cold mixture of liquid and vaporous coolant removes heat from the cooling zone. Due to this heat, the remaining liquid part of the refrigerant continues to evaporate, maintaining a stable low temperature of the evaporator and ensuring efficient heat removal. After that, the refrigerant in the form of vapor reaches the inlet of the compressor, which pumps it out and compresses it again. Then everything is repeated from the beginning.

Thus, in the “hot” section of the compressor-condenser-throttle, the refrigerant is under high pressure and predominantly in a liquid state, and in the “cold” section of the throttle-evaporator-compressor, the pressure is low, and the refrigerant is mainly in a vapor state. Both compression and rarefaction are created by the same compressor. On the opposite side of the tract from the compressor, the high and low pressure zones separate the throttle, which limits the flow of the refrigerant.

Powerful industrial refrigerators use poisonous but effective ammonia, efficient turbochargers and sometimes expanders as a refrigerant. In domestic refrigerators and air conditioners, the refrigerant is usually safer freons, and piston compressors and “capillary tubes” (throttles) are used instead of turbine units.

In the general case, a change in the state of aggregation of the refrigerant is not necessary - the principle will work for a constantly gaseous refrigerant - however, a large heat of change in the state of aggregation greatly increases the efficiency of the operating cycle. But if the refrigerant is in liquid form all the time, there will be no effect in principle - after all, the liquid is practically incompressible, and therefore neither increasing nor relieving pressure will change its temperature ..

Chokes and expanders

The terms "throttle" and "expander" used repeatedly on this page usually say little to people who are far from refrigeration technology. Therefore, a few words should be said about these devices and the main difference between them.

A choke in technology is a device designed to normalize the flow due to its forced restriction. In electrical engineering, this name has been assigned to coils designed to limit the rate of current rise and are usually used to protect electrical circuits from impulse noise. In hydraulics, throttles are usually called flow restrictors, which are specially designed channel constrictions with a precisely calculated (calibrated) clearance that provides the desired flow or the necessary flow resistance. A classic example of such chokes are jets, which were widely used in carburetor engines to ensure the calculated flow of gasoline during the preparation of the fuel mixture. The throttle valve in the same carburetors normalized the flow of air - the second necessary ingredient in this mixture.

In refrigeration, a throttle is used to restrict the flow of refrigerant into the expansion chamber and maintain the conditions there for efficient evaporation and adiabatic expansion. Too much flow can generally lead to filling the expansion chamber with refrigerant (the compressor simply does not have time to pump it out) or, at least, to the loss of the necessary vacuum there. But it is the evaporation of the liquid refrigerant and the adiabatic expansion of its vapor that ensures the drop in the temperature of the refrigerant below the ambient temperature necessary for the operation of the refrigerator.

Principles of operation of the throttle (left), piston expander (center) and turbo expander (left).

In the expander, the expansion chamber has been somewhat modernized. In it, the evaporating and expanding refrigerant additionally makes mechanical work, moving the piston located there or rotating the turbine. In this case, the restriction of the refrigerant flow can be carried out due to the resistance of the piston or turbine wheel, although in reality this usually requires a very careful selection and coordination of all system parameters. Therefore, when using expanders, the main flow regulation can be carried out by a throttle (calibrated narrowing of the liquid refrigerant supply channel).

The turbo-expander is effective only at high flows of the working fluid; at a low flow, its efficiency is close to conventional throttling. A piston expander can operate efficiently with a much lower consumption of the working fluid, but its design is an order of magnitude more complicated than a turbine: in addition to the piston itself with all the necessary guides, seals and a return system, inlet and outlet valves with appropriate control are required.

The advantage of an expander over a throttle is more efficient cooling due to the fact that part of the thermal energy of the refrigerant is converted into mechanical work and is removed from the thermal cycle in this form. Moreover, this work can then be used for the benefit of business, say, to drive pumps and compressors, as is done in the Zysin refrigerator. But a simple throttle has an absolutely primitive design and does not contain a single moving part, and therefore, in terms of reliability, durability, as well as simplicity and cost of manufacture, it leaves the expander far behind. It is these reasons that usually limit the scope of expanders to powerful cryogenic technology, while household refrigerators use less efficient, but practically eternal chokes, called “capillary tubes” there and representing a simple copper tube of a sufficiently long length with a small diameter gap (usually from 0.6 to 2 mm), which provides the necessary hydraulic resistance for the calculated refrigerant flow.

Advantages of compression heat pumps

The main advantage of this type of heat pumps is their high efficiency, the highest among modern heat pumps. The ratio of energy supplied from the outside and pumped over can reach 1:3 - that is, for each joule of energy supplied from the cooling zone, 3 J of heat will be pumped out - compare with 0.5 J for Pelte elements! In this case, the compressor can stand separately, and the heat generated by it (1 J) does not have to be removed to the external environment in the same place where 3 J of heat pumped out from the cooling zone are given off.

By the way, there is a different from the generally accepted, but very curious and convincing theory of thermodynamic phenomena. So, one of her conclusions is that the work of compressing a gas can, in principle, be only about 30% of its total energy. And this means that the ratio of supplied and transferred energy of 1:3 corresponds to the theoretical limit and cannot be improved in principle with thermodynamic methods of heat transfer. However, some manufacturers already claim to achieve a ratio of 1:5 and even 1:6, and this is true - after all, in real refrigeration cycles, not only the compression of the gaseous refrigerant is used, but also a change in its state of aggregation, and it is the latter process that is the main one.. .

Disadvantages of compression heat pumps

The disadvantages of these heat pumps include, firstly, the very presence of a compressor, which inevitably creates noise and is subject to wear, and secondly, the need to use a special refrigerant and maintain absolute tightness throughout its entire working path. However, household compression refrigerators that have been continuously operating for 20 years or more without any repair are not at all uncommon. Another feature is a rather high sensitivity to position in space. On the side or upside down, both the refrigerator and the air conditioner are unlikely to work. But this is due to the features of specific designs, and not to general principle work.

As a rule, compression heat pumps and refrigeration units are designed with the assumption that all the refrigerant is in the vapor state at the compressor inlet. Therefore, if a large amount of unevaporated liquid refrigerant enters the compressor inlet, it can cause water hammer in it and, as a result, serious damage to the unit. The reason for this situation can be both equipment wear and too low a condenser temperature - the refrigerant entering the evaporator is too cold and evaporates too sluggishly. For a conventional refrigerator, this situation may arise if you try to turn it on in a very cold room (for example, at a temperature of about 0 ° C and below) or if it has just been brought into a normal room from frost. For a compression heat pump working for heating, this can happen if you try to warm a frozen room with it, even though it is also cold outside. Not very complex technical solutions eliminate this danger, but they increase the cost of the design, and during normal operation, mass household appliances there is no need for them - such situations do not arise.

Use of compression heat pumps

Due to its high efficiency, it is this type of heat pump that has become almost ubiquitous, displacing all others into various exotic applications. And even the relative complexity of the design and its sensitivity to damage cannot limit their widespread use - almost every kitchen has a compression refrigerator or freezer, or even more than one!

Evaporative absorption (diffusion) heat pumps

Working cycle of evaporators absorption heat pumps very similar to the operating cycle of the evaporative compression units discussed just above. The main difference is that if in the previous case the vacuum required for the evaporation of the refrigerant is created during the mechanical suction of vapors by the compressor, then in absorption units the evaporated refrigerant enters the absorber unit from the evaporator, where it is absorbed (absorbed) by another substance - the absorbent. Thus, the vapor is removed from the volume of the evaporator and a vacuum is restored there, which ensures the evaporation of new portions of the refrigerant. Necessary condition is such an “affinity” of the refrigerant and the absorbent that the forces of their binding during absorption can create a significant vacuum in the volume of the evaporator. Historically, the first and still widely used pair of substances is ammonia NH3 (refrigerant) and water (absorbent). When absorbed, ammonia vapor dissolves in water, penetrating (diffusing) into its thickness. From this process came the alternative names for such heat pumps - diffusion or absorption-diffusion.
In order to separate the refrigerant (ammonia) and the absorbent (water) again, the spent and ammonia-rich water-ammonia mixture is heated in the desorber by an external source of thermal energy up to boiling, then cooled somewhat. Water condenses first, but at high temperatures immediately after condensation, it can hold very little ammonia, so most of the ammonia remains in the form of vapor. Here, the pressurized liquid fraction (water) and the gaseous fraction (ammonia) are separated and separately cooled to ambient temperature. The cooled water with a low ammonia content is sent to the absorber, and the ammonia, when cooled in the condenser, becomes liquid and enters the evaporator. There, the pressure drops and the ammonia evaporates, cooling the evaporator again and taking heat from outside. The ammonia vapor is then recombined with water, removing excess ammonia vapor from the evaporator and maintaining a low pressure there. The solution enriched with ammonia is again sent to the desorber for separation. In principle, it is not necessary to boil the solution to desorb ammonia; simply heat it close to the boiling point, and the “excess” ammonia will evaporate from the water. But boiling allows the separation to be carried out most quickly and efficiently. The quality of such separation is the main condition that determines the vacuum in the evaporator, and therefore the efficiency of the absorption unit, and many tricks in the design are aimed precisely at this. As a result, in terms of the organization and number of stages of the working cycle, absorption-diffusion heat pumps are perhaps the most complex of all common types of such equipment.

The "highlight" of the principle of operation is that for the generation of cold, the heating of the working fluid is used here (up to its boiling). At the same time, the type of heating source is unimportant - it can even be an open fire (burner flame), so the use of electricity is not necessary. To create the necessary pressure difference, which determines the movement of the working fluid, sometimes mechanical pumps can be used (usually in powerful installations with large volumes of the working fluid), and sometimes, in particular in household refrigerators, elements without moving parts (thermosyphons).

Absorption-diffusion refrigeration unit (ADCA) of the Morozko-ZM refrigerator. 1 - heat exchanger; 2 - solution collector; 3 - hydrogen accumulator; 4 - absorber; 5 - regenerative gas heat exchanger; 6 - dephlegmator ("dehydrator"); 7 - capacitor; 8 - evaporator; 9 - generator; 10 - thermosyphon; 11 - regenerator; 12 - tubes of weak solution; 13 - steam outlet pipe; 14 - electric heater; 15 - thermal insulation.

The first absorption refrigeration machines (ABHM) on an ammonia-water mixture appeared in the second half of the 19th century. In everyday life, due to the toxicity of ammonia, they were not widely used at that time, but they were very widely used in industry, providing cooling down to -45 ° C. In single-stage ABCM, theoretically, the maximum cooling capacity is equal to the amount of heat spent on heating (in reality, of course, it is noticeably less). It was this fact that reinforced the confidence of the defenders of the very formulation of the second law of thermodynamics, which was mentioned at the beginning of this page. However, absorption heat pumps have now overcome this limitation. In the 1950s, more efficient two-stage (two condensers or two absorbers) lithium bromide ABCMs appeared (refrigerant - water, absorbent - lithium bromide LiBr). Three-stage variants of ABHM were patented in 1985-1993. Their prototypes are 30–50% more effective than two-stage ones and approach mass models of compression plants.

Advantages of absorption heat pumps

The main advantage of absorption heat pumps is the ability to use not only expensive electricity for their work, but also any heat source of sufficient temperature and power - superheated or exhaust steam, the flame of gas, gasoline and any other burners - up to exhaust gases and free solar energy.

The second advantage of these units, which is especially valuable in domestic applications, is the ability to create structures that do not contain moving parts, and therefore are practically silent (in Soviet models of this type, one could sometimes hear a quiet gurgling or slight hiss, but, of course, this does not go anywhere). compared to the noise of a running compressor).

Finally, in household models the working fluid (usually a water-ammonia mixture with the addition of hydrogen or helium) in the volumes used there does not pose a great danger to others even in the event of an emergency depressurization of the working part (this is accompanied by a very unpleasant stench, so it is impossible not to notice a strong leak, and a room with the emergency unit will have to leave and ventilate “automatically”; ultra-low concentrations of ammonia are natural and absolutely harmless). In industrial installations, the volumes of ammonia are large and the concentration of ammonia in case of leaks can be fatal, but in any case, ammonia is considered environmentally friendly - it is believed that, unlike freons, it does not destroy the ozone layer and does not cause a greenhouse effect.

Disadvantages of absorption heat pumps

The main disadvantage of this type of heat pumps- lower efficiency compared to compression.

The second disadvantage is the complexity of the design of the unit itself and the rather high corrosion load from the working fluid, either requiring the use of expensive and difficult to process corrosion-resistant materials, or reducing the unit's service life to 5..7 years. As a result, the cost of "hardware" is noticeably higher than that of compression plants of the same capacity (first of all, this applies to powerful industrial units).

Thirdly, many designs are very critical to placement during installation - in particular, some models of household refrigerators required installation strictly horizontally, and even with a deviation of several degrees they refused to work. The use of forced movement of the working fluid with the help of pumps largely eliminates the severity of this problem, but lifting with a silent thermosyphon and draining by gravity requires very careful alignment of the unit.

Unlike compression machines, absorption machines are not so afraid of too low temperatures - their efficiency is simply reduced. But it was not without reason that I placed this paragraph in the disadvantages section, because this does not mean that they can work in severe cold - in the cold, an aqueous solution of ammonia will simply freeze, unlike freons used in compression machines, the freezing point of which is usually below -100 ° C. True, if the ice does not break anything, then after thawing the absorption unit will continue to work, even if it has not been disconnected from the network all this time, because there are no mechanical pumps and compressors in it, and the heating power in household models is small enough to boil in the area the heater has not become too intense. However, it all depends on the features of a particular design ...

Use of absorption heat pumps

Despite somewhat lower efficiency and relatively higher cost compared to compression plants, the use of absorption heat engines is absolutely justified where there is no electricity or where there are large volumes of waste heat (exhaust steam, hot exhaust or flue gases, etc. - up to pre-solar heating). In particular, special models of refrigerators are produced, powered by gas burners, designed for motorists and yachtsmen.

Currently in Europe gas boilers sometimes they are replaced by absorption heat pumps with heating from a gas burner or diesel fuel - they allow not only to utilize the heat of combustion of the fuel, but also to “pump up” additional heat from the street or from the depths of the earth!

As experience shows, in everyday life options with electric heating are also quite competitive, primarily in the low power range - somewhere from 20 to 100 watts. Smaller powers are the realm of thermoelectric elements, and at higher powers, the advantages of compression systems are still undeniable. In particular, among the Soviet and post-Soviet brands of refrigerators of this type, Morozko, Sever, Kristall, Kiev were popular with a typical volume of the refrigerator chamber from 30 to 140 liters, although there are also models of 260 liters (" Crystal-12"). By the way, when evaluating energy consumption, it is worth considering the fact that compression refrigerators almost always operate in a short-period mode, while absorption refrigerators usually turn on for a much longer period or even work continuously. Therefore, even if the rated power of the heater is much less than the power of the compressor, the ratio of the average daily energy consumption may be quite different.

Vortex heat pumps

Vortex heat pumps The Rank effect is used to separate warm and cold air. The essence of the effect is that the gas tangentially fed into the pipe at high speed is twisted and separated inside this pipe: cooled gas can be taken from the center of the pipe, and heated gas from the periphery. The same effect, although to a much lesser extent, also applies to liquids.

Advantages of vortex heat pumps

The main advantage of this type of heat pumps is the simplicity of design and high performance. The vortex tube contains no moving parts, and this provides it with high reliability and long service life. Vibration and position in space have practically no effect on its operation.

A powerful air flow well prevents freezing, and the efficiency of the vortex tubes is weakly dependent on the temperature of the inlet flow. The practical absence of fundamental temperature restrictions associated with hypothermia, overheating or freezing of the working fluid is also very important.

In some cases, the possibility of achieving a record high temperature separation in one stage plays a role: the literature gives figures for cooling by 200° and more. Usually one stage cools the air by 50..80°C.

Disadvantages of vortex heat pumps

Unfortunately, the efficiency of these devices is currently noticeably inferior to the efficiency of evaporative compression plants. In addition, for efficient operation, they require a high speed of supply of the working fluid. The maximum efficiency is noted at an input stream speed equal to 40..50% of the speed of sound - such a stream itself creates a lot of noise, and in addition, it requires a productive and powerful compressor- the device is also by no means quiet and rather capricious.

The absence of a generally accepted theory of this phenomenon, suitable for practical engineering use, makes the design of such units an empirical exercise in many respects, where the result is highly dependent on luck: “guessed it or not guessed it”. A more or less reliable result is obtained only by reproducing already created successful samples, and the results of attempts to significantly change certain parameters are not always predictable and sometimes look paradoxical.

Use of vortex heat pumps

However, the use of such devices is currently on the rise. They are justified primarily where there is already gas under pressure, as well as in various fire and explosion hazardous industries - after all, it is often much safer and cheaper to supply a flow of air under pressure to a hazardous area than to pull protected electrical wiring there and install electric motors in a special design .

Limits of efficiency of heat pumps

Why are heat pumps still not widely used for heating (perhaps the only relatively common class of such devices is inverter air conditioners)? There are several reasons for this, and in addition to the subjective ones associated with the lack of heating traditions using this technique, there are also objective ones, the main ones being frosting of the heat extractor and a relatively narrow temperature range for efficient operation.

In vortex (primarily gas) installations, there are usually no problems with hypothermia and freezing. They do not use a change in the state of aggregation of the working fluid, and a powerful air flow performs the functions of the "No Frost" system. However, their efficiency is much less than that of evaporative heat pumps.

hypothermia

In evaporative heat pumps, high efficiency is ensured by changing the state of aggregation of the working fluid - the transition from liquid to gas and vice versa. Accordingly, this process is possible in a relatively narrow temperature range. At too high temperatures, the working fluid will always remain gaseous, and at too low temperatures, it will evaporate with great difficulty or even freeze. As a result, when the temperature goes beyond the optimal range, the most energy-efficient phase transition becomes difficult or is completely excluded from the operating cycle, and the efficiency of the compression unit drops significantly, and if the refrigerant remains constantly liquid, then it will not work at all.

freezing

Extraction of heat from the air

Even if the temperatures of all the heat pump units remain within the required limits, during operation the heat extraction unit - the evaporator - is always covered with moisture droplets condensing from the surrounding air. But liquid water flows off it on its own, not particularly hindering heat transfer. When the temperature of the evaporator becomes too low, the condensate drops freeze, and the newly condensed moisture immediately turns into frost, which remains on the evaporator, gradually forming a thick snow coat - this is exactly what happens in the freezer of an ordinary refrigerator. As a result, the heat exchange efficiency is significantly reduced, and then it is necessary to stop the operation and thaw the evaporator. As a rule, in the evaporator of the refrigerator, the temperature drops by 25..50°C, and in air conditioners, due to their specifics, the temperature difference is smaller - 10..15°C. Knowing this, it becomes clear why most air conditioners cannot be adjusted to a temperature lower than +13..+17°С - this threshold is set by their designers to avoid icing of the evaporator, because the defrosting mode is usually not provided. This is also one of the reasons why almost all air conditioners with inverter mode do not work even at not very high negative temperatures - only recently models have begun to appear that are designed to work in frosts down to -25 ° C. In most cases, already at –5..–10°C, the energy costs for defrosting become comparable to the amount of heat pumped in from the street, and pumping heat from the street turns out to be inefficient, especially if the humidity of the outside air is close to 100% - then the external heat extractor is covered with ice especially fast.

Extraction of heat from soil and water

In this regard, as a non-freezing source of "cold heat" for heat pumps, heat from the depths of the earth has been increasingly considered recently. This does not mean the heated layers of the earth's crust, located at a depth of many kilometers, and not even geothermal water sources (although, if you are lucky and they are nearby, it would be foolish to neglect such a gift of fate). This refers to the "ordinary" heat of the soil layers located at a depth of 5 to 50 meters. As is known, in middle lane the soil at such depths has a temperature of the order of +5°C, which changes very little throughout the year. In more southern regions this temperature can reach +10°С and higher. Thus, the temperature difference between the comfortable +25°C and the ground around the heat extractor is very stable and does not exceed 20°C regardless of the frost outside the window (it should be noted that usually the temperature at the heat pump outlet is +50..+60°C, but and a temperature difference of 50 ° C is quite within the power of heat pumps, including modern household refrigerators, calmly providing in the freezer -18 ° C at a temperature in the room above + 30 ° C).

However, if you bury one compact but powerful heat exchanger, it is unlikely that the desired effect will be achieved. In fact, the heat extractor in this case acts as an evaporator of the freezer, and if there is no powerful heat inflow in the place where it is located (a geothermal source or an underground river), it will quickly freeze the surrounding soil, on which all heat pumping will end. The solution may be to extract heat not from one point, but evenly from a large underground volume, however, the cost of building a heat extractor covering thousands of cubic meters of soil at a considerable depth will most likely make this solution absolutely unprofitable economically. A less expensive option is to drill several wells with an interval of several meters from each other, as was done in an experimental "active house" near Moscow, but this is not cheap either - anyone who has made a well for water can independently estimate the costs of creating a geothermal fields of at least a dozen 30-meter wells. In addition, a constant heat extraction, although less strong than in the case of a compact heat exchanger, will still reduce the temperature of the ground around the heat extractors compared to the initial one. This will lead to a decrease in the efficiency of the heat pump during its long-term operation, and the period of temperature stabilization at a new level may take several years, during which the conditions for heat extraction will deteriorate. However, one can try to partially compensate for the winter heat loss by its enhanced injection to a depth in the summer heat. But even without taking into account the additional energy costs for this procedure, the benefits of it will not be too great - the heat capacity of the ground heat accumulator reasonable size is quite limited, and it is clearly not enough for the entire Russian winter, although such a supply of heat is still better than nothing. In addition, there are very great importance has a level, volume and speed of groundwater flow - abundantly moistened soil with a sufficiently high water flow rate will not allow to make “reserves for the winter” - flowing water will carry away the injected heat with it (even a meager movement of groundwater by 1 meter per day will carry away stored heat to the side by 7 meters, and it will be outside working area heat exchanger). True, the same groundwater flow will reduce the degree of cooling of the soil in winter - new portions of water will bring new heat, received by them away from the heat exchanger. Therefore, if there is a deep lake nearby, a large pond or a river that never freezes to the bottom, then it is better not to dig the soil, but to place a relatively compact heat exchanger in a reservoir - unlike stationary soil, even in a stagnant pond or lake, free water convection can provide much more efficient heat supply to the heat extractor from a significant volume of the reservoir. But here it is necessary to make sure that the heat exchanger will under no circumstances supercool to the freezing point of water and will not start to freeze ice, since the difference between convection heat transfer in water and the heat transfer of an ice coat is huge (at the same time, the thermal conductivity of frozen and unfrozen soil often differs not so much strongly, and an attempt to use the enormous heat of crystallization of water in the ground heat extraction under certain conditions can justify itself).

The principle of operation of a geothermal heat pump is based on the collection of heat from the soil or water, and transfer to the heating system of the building. To collect heat, the non-freezing liquid flows through a pipe located in the soil or reservoir near the building to the heat pump. A heat pump, like a refrigerator, cools the liquid (removes heat), while the liquid is cooled by approximately 5 °C. The liquid again flows through the pipe in the outer soil or water, regains its temperature, and again enters the heat pump. The heat extracted by the heat pump is transferred to the heating system and/or for heating hot water.

It is possible to extract heat from underground water - underground water with a temperature of about 10 ° C is supplied from the well to the heat pump, which cools the water to +1 ... + 2 ° C, and returns the water underground. Any object with a temperature above minus two hundred and seventy-three degrees Celsius has thermal energy - the so-called "absolute zero".

That is, a heat pump can take heat from any object - earth, water, ice, rocks, etc. If the building, for example, in summer, needs to be cooled (air-conditioned), then the reverse process occurs - heat is taken from the building and discharged into the ground (reservoir). The same heat pump can work in winter for heating, and in summer for cooling the building. Obviously, a heat pump can heat water for domestic hot water, air conditioning through fan coil units, heat a swimming pool, cool, for example, an ice rink, heat roofs and walkways from ice ...
One piece of equipment can perform all the functions of heating and cooling a building.

Many members of our portal have been using heat pumps for a long time and consider them in the best possible way heating. The heat pump is still an expensive device, and its payback period is long. But there are good experiences self-manufacturing heat pumps: this avoids some unrealistic costs.

• How a heat pump works
• How to make a heat pump with your own hands
• Is it profitable to make a heat pump

How a heat pump works

Explaining the principle of operation of a heat pump, people often recall a refrigerator, where the heat “taken off” from the products in the chamber is discharged into the radiator on the back wall.

Saga Member FORUMHOUSE

The principle of operation of a heat pump is like a refrigerator: the grate on its back heats up, the freezer cools. If we lengthen the tubes with freon and lower them into the bath, then the water in it will cool, and the refrigerator grill will heat up; the refrigerator will pump heat from the bath and heat the room.

Air conditioners and heat pumps operate on the same principle. The operation of the devices is based on the Carnot cycle.

The coolant moves along the ground or water, in the process "removing" heat and raising its temperature by several degrees. In the heat exchanger, the coolant gives off the accumulated heat to the refrigerant, which becomes steam, enters the compressor, where its temperature rises. In this form, it is supplied to the condenser, gives off heat to the OS coolant at home, and after cooling, turns into a liquid again and enters the evaporator, where it heats up from a new portion of the heated coolant. The cycle is repeated.

Although a heat pump will not work without electricity, it is a beneficial device, since it produces 3-7 times more heat than it consumes electricity.

We will analyze this with a specific example of our user who made a heat pump with his own hands.

Heat pumps work on the energy of natural sources of the body:

• soil;
• water;
• air.

There are two ways to collect heat from the ground (below the freezing depth, its temperature is always about +5 - +7 degrees):

• horizontal ground collector
• laid horizontally different ways pipes.

“Brine” flows through the pipes - FORUMHOUSE often uses propylene glycol, which takes the heat of the earth, transfers it to the refrigerant, and after cooling, it is again sent to the ground collector.

A heat pump is a device that can provide your home with heating in winter, cooling in summer and hot water production. all year round.

A heat pump uses energy from renewable sources - heated air, earth, rock or water - to produce heat energy. This transformation is carried out with the help of special substances -.

How a heat pump works

Structurally, any heat pump consists of two parts: the outer one, which "takes" the heat from renewable sources, and the inner one, which gives this heat to the heating or air conditioning system of your home. Modern heat pumps are characterized by high energy efficiency, which in practical terms means the following - the consumer, i.e. the owner of the house, using a heat pump, spends on heating or cooling his home, on average, only a quarter of the money that he would spend if there was no heat pump.

In other words, in a system with a heat pump, 75% of useful heat (or cold) is provided by free sources - heat from the earth, groundwater or heated indoors and used air thrown out into the street.

Consider how, perhaps, the most popular heat pump in everyday life, which operates due to the heat of the earth, works. The heat pump works in several cycles.

Cycle 1, evaporation

The outer part of the "earth" heat pump is a closed system of pipes buried in the ground to a certain depth, where the temperature is stable all year round and is 7-12°C. In order to "collect" enough energy from the earth, it is required that the total area occupied by the underground pipe system be 1.5-2 times the entire heated area of ​​​​the house. These pipes are filled with refrigerant that heats up to ground temperature.

The refrigerant has a very low boiling point, so it can go into a gaseous state even at ground temperature. Further, this gas enters.

Cycle 2, compression

It is this compressor that consumes all the energy necessary for the operation of the heat pump, but compared, for example, with heating from, these costs are noticeably lower. We will return to the comparison of costs later.

So, heated to a temperature of 7-12°C, the gaseous refrigerant from underground pipes in the compressor chamber is strongly compressed, which leads to its sharp heating. To understand this, just remember how a regular bicycle pump heats up when you inflate tires. The principle is the same.

Note to the owner

“The heat pump is modern heating. But the actual values ​​of the efficiency of heat pumps depend on temperature conditions, i.e. on cold days, their effectiveness drops. It is about 150% at -20°C, and about 300% at a source temperature of +7°C.”

Cycle 3, condensation

After the compression cycle, we have received hot steam under high pressure, which is already supplied to the internal, “home” part of the heat pump. Now this gas can be used for the system air heating or for heating water in the system of water heating and hot water supply. Also, this hot steam can be used with the "" system.

Giving heat to the heating system, the hot gas cools, condenses and turns into a liquid.

Cycle 4 expansion

This liquid enters the expansion valve, where its pressure is reduced. The low pressure liquid refrigerant is now sent back to the underground to be heated to ground temperature. And all cycles are repeated.

Efficiency of using heat pumps

For every 1 kW of electricity consumed by a heat pump to operate its compressor, on average, about 4 kW of useful heat energy is generated. This corresponds to 300% efficiency.

Comparison of heating with a heat pump with other methods.

Data provided by the European Heat Pump Association (EHPA)

Heating type	Energy efficiency, %

It should be understood that the performance of heat pumps differs, depending on the specific conditions in which your device operates. So, if you use an "earth" heat pump, and you have clay soil in your area, then the efficiency of the heat pump will be about twice as high as if the heat pump pipes were in sandy soil.

It should also be remembered that the laying of the underground part should be carried out below the freezing mark of the soil. Otherwise, the heat pump will not work at all.

The actual efficiency values ​​of heat pumps depend on temperature conditions, i.e. on cold days, their effectiveness drops. It is about 150% at -20 °C, and about 300% at a source temperature of +7 °C. But technology does not stand still - modern models are more energy efficient, and this trend continues.

Heat pumps for home cooling

By its principle of operation, a heat pump is similar to or. Therefore, in the summer, it can be used not for heating the house, but for cooling or air conditioning. Recall that, if we are talking about an "earth" heat pump, then the temperature of the soil is stable within 7-12 ° C all year round. And with the help of a heat pump, it can be transferred to the premises of the house.

The principle of operation of a cooling system using a heat pump is similar to a heating system, only radiators are used instead. With passive cooling, the coolant simply circulates between the fan coil units and the well, i.e. cold from the well directly enters the air conditioning system, but the compressor itself does not work. If passive cooling is not sufficient, the heat pump compressor is switched on, which additionally cools the heating medium.

Types of heat pumps

Household heat pumps are of 3 main types, differing in external heat source:

• "ground" or "ground-water", "ground-air";
• "water" or "water-water", "water-air";
• "air" or "air-to-water", "air-to-air".

"Ground" heat pumps

The most popular are heat pumps that use the heat of the earth. They have already been discussed above. These are the most effective, but also the most expensive of all types. Pipes going underground can be located vertically or horizontally. Depending on this, "ground" heat pumps are divided into vertical And horizontal.

Vertical heat pumps require immersion of pipes through which the refrigerant circulates to a considerable depth: 50-200 m. True, there is an alternative - to make not one such well, but several, but more “shallow”. The distance between such wells must be at least 10 m. To calculate the drilling depth, one can roughly estimate that a 10 kW heat pump will require wells (one or more) with a total depth of about 170 m. It should also be remembered that it is useless to drill very shallow - less 50 m - wells.

At horizontal laying expensive drilling to great depths is not required. The depth of laying pipelines with this method is about 1 m, depending on the installation region, this value can either decrease or increase. With this method, the refrigerant pipe is laid so that the distance between adjacent sections is at least one and a half meters, otherwise heat collection is not effective.

Note to the owner

“If you live in a temperate zone - for example, in the Northwest - then the most efficient option for you is a heat pump that uses the heat of the earth. Moreover, it is better to install vertical version heat pump - especially if your house is on rocks.

To install a heat pump with a capacity of 10 kW, a total buried pipe length of about 350-450 m is required. If you take into account the restrictions associated with the proximity of different sites to each other, then you will need a plot of land with dimensions of 20 by 20 meters. Whether there is such a free site available is a big question.

How to choose the right heat pump

If you live in a temperate zone - for example, in the Northwest - then the most efficient option for you is a heat pump that uses the heat of the earth. Moreover, it is better to install a vertical version of the heat pump - especially if your house is located on rocks, where it is problematic to find a free large plot of land. But this type of heat pump is the most expensive in terms of capital costs.

In a mild climate zone - for example, in Sochi - it is possible to install an air-to-water heat pump, which does not require excessive capital costs and is especially effective in areas where seasonal temperature fluctuations are relatively small.

Depending on the principle of operation, there are and. Electric models are more popular.

One more important note. A good idea is combined models of heat pumps, which combine the classic version of the heat pump with gas or electric heater. Such heaters can be used in adverse weather conditions when the efficiency of the heat pump is reduced. As already mentioned, a decrease in efficiency is especially characteristic of air-to-water and air-to-air heat pumps.

The combination of these two heat sources reduces the cost of capital expenditures and increases the payback period of the heat pump installation.

Advantages and disadvantages of heat pumps

The main advantage of heat pumps is their low operating costs. Those. the cost of heat or cooling produced to the end user is the lowest compared to other heating/cooling methods. In addition, the heat pump system is practically safe for the home. Consequently, the requirements for the ventilation systems of its premises are simplified and the level of fire safety. This also has a positive effect on the cost of installing these systems.

Heat pumps are easy to operate and very reliable, and yet - almost silent.

Another plus is that you can easily switch the heat pump from heating to cooling if necessary. You just need to have at home not only heating, but also fan coil units.

What is a heat pump for home ✮Large selection of heat pumps on the website portal

But they also have disadvantages, the main of which is the reverse side of the main plus - the capital costs for their installation are very significant. Until recently, another disadvantage of heat pumps was the relatively low coolant temperature - no more than 60 C. But recent developments have made it possible to eliminate this disadvantage. True, the price of such models is higher than the standard ones.