Thermal pumps: instruction on application

Part I. What swings the thermal pump?

Thermal pumps: instruction on application

This term even more often can be heard today, when speech about heating of the individual house comes. However not all house owners understand that represents the thermal pump as it works and why so is called. And the main thing, is how applicable this decision in practice and whether it is favorable from the point of view of economy of a private household. However, about it a bit later, and at first we will deal with the device and a principle of its action.

When we speak about habitual heating or heating devices, usually we mean the certain source of heat which has been heated up to rather high temperature. It can be identified to the touch as "hot" or "warm" rather surrounding space of a room and the subjects located in it. From a school course of physics we remember that more warm bodies give heat to less warm, in it the essence of the second beginning of thermodynamics (simply, certainly) consists. Thus transfer is warm, for example, from heated up to +70°C a radiator to air of the room having temperature +18-20°C or about those, is carried out by itself. But the radiator needs to be heated up previously, and for this purpose in heating system hot water moves. It, in turn, heats up in a boiler room or at station where burn fuel. Fuel, transfer it is warm on distance — all this costs money therefore we pay every month for heating.

Nevertheless, round us is almost inexhaustible (or as them usually call, renewed) sources of absolutely free heat. After all any body having temperature above absolute zero (-273°C), possesses thermal energy which it can give. Most available of such sources — the soil, natural reservoirs, atmospheric air, etc. The problem that by itself energy is transferred only from warmer to colder body, and for an effective heat transfer a difference of temperatures should be considerable. Therefore to take away heat from the so-called low-potential sources which temperature is lower than temperature of heated rooms (for example, for Danfoss equipment it can fluctuate in limits from +15°C to – 10°C, that is to be negative), it is necessary to make some work. It is conditionally possible to tell that heat from low-potential sources "extort", therefore also the device by means of which it do, call the thermal pump.

There can be an impression that the thermal pump allows to bypass the second law of thermodynamics, however it, certainly, not so, differently the perpetual motion machine for a long time would be constructed. Everything occurs strictly within classical physics: laws of the nature cannot be overcome, but they can be used.

For example, to take away heat at the soil having temperature no more +10°C or less (including below 0°C), is necessary not water, and the certain other heat-carrier freezing at temperatures below – 20°C — the concentrated salt solution, solution пропиленгликоля and so forth. Cold or even the chilled earth quite willingly will warmly give to colder liquid. All system is arranged in such a manner that can select heat even at frozen soil with temperature approximately to – 8°C. In principle, everything honor as well as in traditional system of heating, only a temperature range another.

So, we found out how to select heat at cold soil, however the question remains open, after all the temperature of our heat-carrier is all the same lower, than temperature of rooms which need to be heated. And here various technical "cunnings" begin.

In traditional system of heating one thermal contour works conditionally: in it water circulates, in one place it heat up, in other — it gives received heat to our dwelling. That is heat transfer from an initial source (a copper or a heater) to a place of consumption is carried out in 2 stages.

In the thermal pump 3 contours, and transfer of heat occur in 4 stages. On the first we took away heat from soil. On the second — there is its transfer from the first (external) contour in the second — a so-called refrigerating contour. It works by the same principle, as a cooling contour in the household refrigerator or the conditioner. The coolant circulating in it (usually it is freon) has temperature of boiling and evaporation is much lower 0°C. The refrigerating contour is arranged in such a manner that in the evaporator (it is the heat exchanger where low-potential heat is transferred from a brine to a coolant), freon arrives in a liquid state. Thus its temperature is even lower, than at a brine. That is he is ready to select at it heat — those some degrees which the cold brine took away from slightly less cold soil.

Before getting to the evaporator, freon passes through the special drosseliruyushchy valve where its pressure sharply goes down, as we know, the less pressure, the temperature of boiling of substance is lower. Parameters of system are picked up in such a manner that as a result of pressure drop and cooling from contact to a brine (through a heat exchanger wall), freon begins to boil and passes from a liquid phase to the gaseous.

As we remember from a school course of physics, in the course of phase transition the evaporating substance absorbs thermal energy. So, at the second stage freon selects heat at a brine which comes back to the first contour cooled and ready to receiving a new portion of low-potential heat of the earth. The demanded task is executed: we "extorted" heat from soil.

Further business is entered by the electric compressor which compresses boiling gaseous freon, forcing it under big pressure in the following heat exchanger — the condenser. As a result of compression our cold gas is warmed up to high temperature. Through a condenser wall hot freon contacts to water or other heat-carrier from a heating contour. This heat-carrier is a little colder some the compressed freon as it already gave warmly to rooms while flew via heating devices. The compressed freon is condensed, passing to a liquid phase and in the course of transition giving warmly to the heat-carrier of a heating contour, that is heating up it. It is the third stage of transfer of heat. The hot heat-carrier arrives in heating system where the fourth stage — actually heating of rooms proceeds. The freon which has lost heat arrives in that drosseliruyushchy valve which dumps its pressure in front of the evaporator. At this stage pressure of a coolant falls, therefore it becomes again cold.

So, the circle became isolated. We learned, of what the component consists the thermal pump as they work and as it is possible to select heat at soil cold, apparently, and to use it for heating of rooms. But whether this heat for heating of all house will suffice, how many the electric power is required for operation of the thermal pump and how to establish it in the cottage? About it we will talk in the following part.

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