CH660776A5 - METHOD AND DEVICE FOR INCREASING THE TOTAL EFFICIENCY OF A HEAT PUMP SYSTEM. - Google Patents

Description

The invention relates to a method and a device for increasing the overall efficiency of a heat pump system, which consists of at least one compressor, at least one evaporator, a superheater, a three-way valve, a latent storage device and a refrigerant.

From DE-PS 955 718 a method for operating a heat pump is known, the relaxation taking place simultaneously at different pressure levels. In this way, compression is carried out in several stages at the various pressure levels. In this known method, the largest possible amount of heat is taken from a given amount of water in order to raise it to a higher temperature level.

All known heat pumps extract the heat contained in a heat source, such as river water, groundwater, earth, air or a latent ice storage, using the heat contained therein.

In places where water is not available as a heat source, pipes have already been laid directly into the earth, inside which a mixture of glycol and water circulates as a heat carrier. Latent ice storage systems, in which the entire water content is iced up and which take the energy required for evaporator operation from the adjacent soil, are also operated in this way.

If total icing of the contents of a latent ice store is not desired, the storage temperature during the icing phase is zero degrees C. However, the usable temperature level is lower, depending on the thickness of the ice jacket that has formed around the evaporator tubes . In order to guarantee heat exchange, large pipe lengths are required.

Such a process has several disadvantages. Glycol has very poor thermal properties. At low temperatures, the viscosity of the glycol-water mixture increases so much that even at temperatures of minus 10 ° C the compressor is overloaded by very low suction gas temperatures. The glycol mixture also has such a poor Reynold number that the energy required for pumping makes the entire system uneconomical. Therefore, the proportion of glycol in the glycol-water mixture must not be significantly above 30% by weight. Even at temperatures from 0 to minus 4 ° C, the heat transfer from ice via pipe to glycol becomes very poor. In addition, when using glycol in an intermediate circuit in the evaporator, a temperature difference, between the evaporating temperature of the refrigerant and the average temperature of the glycol-water mixture in the evaporator, of a delta T between 6 and 14 ° K is required. Another disadvantage is the fact that in the case of flat-laid earth collectors, relatively large land reserves are required in order to extract enough heat from the earth.

The object of the invention is to provide a method which brings about an increase in the overall efficiency of a heat pump system by avoiding extremely low evaporation temperatures. Extremely low temperatures mean evaporation temperatures below minus 10 to minus 12 ° C.

Another object is to provide an apparatus for performing the method that is simple and economical to manufacture.

The object is achieved according to claim 1 and is characterized in that the refrigerant evaporates directly by means of an evaporator in the latent storage and the saturated steam of the refrigerant is overheated in the superheater.

Due to the direct evaporation of the refrigerant, preferably from the group of halogenated hydrocarbons, in the tubes of an evaporator that is installed in a latent storage system operated with ice / water, significantly higher evaporation temperatures are possible than in systems that heat the heat using a heat transfer fluid , like glycol, from the latent storage. The higher evaporation temperatures result in a significantly higher performance figure than known systems. Metal pipes, in particular made of copper or its alloys, which are resistant to corrosion in cold water and have a high thermal conductivity, have proven to be particularly advantageous for the process. However, other metals, such as aluminum, as well as steel and alloys, which are provided with a protective coating against corrosion if necessary, can be used. By optimizing the pipe cross-sections and pipe spacing, the greatest possible utilization of the storage volume for the removal of latent heat can be achieved.

It has proven particularly advantageous to use the Verei5

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to limit the solution in the latent storage by supplying heat. If the latent storage is heavily iced, which could result in the evaporation temperatures falling below minus 10 ° C., an additional pump can be used as an auxiliary unit for regenerating the latent storage, but this is not essential for the method according to the invention. This pump can be operated with any kind of waste heat and can melt part of the ice in the latent storage again. Waste heat can be, for example, building exhaust air or industrial waste heat at a low temperature.

The pipe surface temperature in the latent storage is expediently limited to minus 8 to minus 10 ° C. In a particularly advantageous manner, as much water as possible from 0 ° C. should be converted into ice, since the transition from water to ice releases heat of fusion in the size of 93 watt-hours per kg of water. It is therefore desirable that the copper tubes with an outer tube diameter of 10 to 15 mm have an ice jacket up to a maximum of 200 mm. As the ice grows on the surface of the pipes, the surface for the water / ice heat exchange increases at the same time. It should be noted that when plates are used for the heat exchange of the evaporator, only one-dimensional growth of the ice layer takes place, while for tubes the growth takes place in two dimensions.

When using finned tubes, the surface area can be increased, but the cost of the tubes increases disproportionately.

The process is operated without additional pumps. The compressor alone serves as the driving force for circulating the refrigerant. On the suction side of the compressor, for example, work is carried out at a pressure of 2 bar and on the pressure side at 12 bar. It has proven to be advantageous to maintain a pressure difference of 5 to 20 bar, preferably 10 bar.

The refrigerant, in the form of a halogenated hydrocarbon, is advantageously pumped through the latent storage device by the compressor.

A second evaporator can be fed with outside air as a heat source with less heat requirement and relatively high outside temperatures.

To further increase the efficiency and thus the performance figure, an overheater is provided before entering the compressor, so that the saturated steam coming from one of the evaporators is overheated to a higher temperature level with a second heat source. The condensate of the refrigerant after the compressor, which e.g. with a temperature of approx. 40 ° C is available. To protect the compressor against erosion from residual drops, a small heat exchanger is occasionally connected upstream in a known manner, which is intended to evaporate such drops.

An embodiment of the invention will be explained with reference to drawings. Show it:

1 is a diagram of an embodiment of the heat pump system according to the invention,

2 shows a latent storage in longitudinal section, FIG. 3 pipe inserts into the latent storage according to FIG. 2, FIG. 3a pipe arrangement of FIG. 3,

4 variation of the tube inserts and FIG. 4a tube arrangement from FIG. 4.

Figure 1 shows the principle diagram of a heat pump system. At outside air temperatures above about 2 ° C, the heat pump initially runs with outside air as a heat source. A compressed refrigerant passes from a compressor 1 to the condenser 2, where it is liquefied at, for example, 50.degree. It passes through a superheater 3, where the refrigerant is cooled, for example, from 50 to 10 ° C. A three-way valve 4 is set so that it leads to an expansion valve 5. The cooled refrigerant flows through a distributor head 6 into the evaporator 7, which extracts heat from the outside air. The saturated refrigerant steam is overheated in the superheater 3 by cooling about 40 degree refrigerant condensate, so that it can enter the compressor at about + 5 ° C. This first heat source can be used up to a certain switching point.

Below this predetermined switchover point, a second heat source, the Eis 7Wasser latent storage, is used.

By switching the three-way valve, the refrigerant coming from the superheater 3 is passed in a first analog manner via an expansion valve 5 'and a distributor head 6' directly through the evaporator 9, which is located within the latent storage 8. The refrigerant is therefore evaporated in the tubes of the evaporator 9, which are in direct contact with the water and / or the ice of the latent storage 8. The evaporated refrigerant is overheated in the same way as in the circuit with outside air in the superheater 3. A pump 10 is intended for regeneration from the latent storage 8.

The latent storage 8 advantageously consists of a concrete container, but can also be made of a plastic container or a metal container. 2, 11 coils 12 are attached to the inside of vertical supports, which form the evaporator 9. These tubes are provided with an inlet 13 and an outlet 14 for the refrigerant.

After arranging the tubes 12 according to FIGS. 3 and 3a, 78.5% of the latent storage content 8 can be iced over before the individual ice jackets 15 grow together. The distance from the center to the center of the pipes is, for example, 200 mm in a storage volume of, for example, 10 m3.

In an arrangement according to FIGS. 4 and 4a, a utilization of the memory content of theoretically 90.5% can be achieved.

The storage size can be determined based on the meteorological data of the place of use. An evaporator is provided within the container provided as a latent storage device, which in its simplest form consists of copper tubes which are arranged in any arrangement at intervals of (200 mm). A smooth surface is preferred, which favors a uniform coating of ice. The surface can also carry smooth profiles. An outer pipe diameter of 10 to 15 mm has proven to be suitable to ensure the desired evaporation of the refrigerant in the pipes.

The invention will be described in more detail with reference to comparative examples. The following abbreviations are used in the table below.

Te = earth temperature

TVe = glycol inlet temperature in the evaporator

Ty A = glycol outlet temperature from the evaporator

Tm = average glycol temperature in the evaporator

T0 - evaporating temperature

Tr = pipe surface temperature tm = mean temperature difference between

Evaporation temperature T0 and glycol temperature

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At

Te

TVE

Tva

TM

Atm

To

State of the game.

Heat source

I.

0 ° C

- 2nd

° C

6 ° C

- 4 ° C

11.5 ° K

-15.5 ° C

Icing begins in the ground

II

- 8 ° C TR

-10

° C

-14 ° C

-12 ° C

11.5 ° C

-23.5 ° C

maximum iced up

III

0 ° C

- 2nd

° c

- 6 ° C

- 4 ° C

11.5 ° C

-15.5 ° C

Icing begins in latent storage

IV

- 6 ° C

- 8th

° c

-12 ° C

-10 ° C

11.5 ° K

-21.5 ° C

maximum iced up

V

0 ° C

0.5 ° K

- 0.5 ° C

Icing begins in latent storage

VI

-10 ° C

0.5 ° K

-10.5 ° C

maximum iced up

15

Examples I to IV serve for comparison and are operated with glycol / water as the refrigerant.

Examples I and II show the operation of a flat ground collector with a glycol circuit. The operation of the plant becomes critical due to the glycol mixture, which may contain a maximum of 35% glycol and is therefore only freeze-proof down to minus 18 °.

Examples III and IV show the operation of an ice latent storage device with a glycol circuit, which is continuously regenerated by different waste heat. Maximum icing therefore rarely occurs and is limited to an ice jacket around the pipes of approximately 200 mm. In the case of ice latent stores, which have to derive their energy from the cooling of the surrounding earth, the corresponding temperatures are much lower.

Examples V and VI show the results according to the invention. It can be seen that despite the lower temperatures of the pipe surface, VI according to the invention, compared to Example IV, achieves an evaporation temperature which is 11 ° K higher.

The required heat output of a heat pump is reduced by around 35% when the evaporation temperature is increased from 10 ° to 12 ° K. It follows that a smaller heat pump can be used for a given heating output. Due to the higher evaporation temperature To, a 20 to 25% higher coefficient of performance is achieved than with known heat pumps that are operated with glycol as an intermediate circuit.

The advantages of the direct evaporation of refrigerant in the latent storage can be seen in the fact that much higher evaporation temperatures can be achieved. The higher evaporation temperatures result in performance figures that cannot be achieved with the known methods. Overheating the refrigerant in a second evaporator by subcooling the returning condensate brings a further improvement in the performance of the system.

The use of water in the latent storage instead of an intermediate heat transfer circuit, in addition to saving on the heat transfer medium and the required system parts and their installation, has the advantage that water can be frozen and thawed as often as required without changing its chemical and physical properties.

The system is significantly simplified by eliminating the glycol intermediate circuit. The design is therefore the most cost-effective solution to date. Both the static heat above the zero degree range and the latent heat from the change in the water / ice aggregate state are used.

The main areas of application are the environmentally friendly heating of buildings, apartments and single-family houses. The invention can also be used wherever heat is required for heating the room.

The subject of the invention is eminently suitable in connection with motor-operated total energy systems and for the use of periodically or continuously occurring waste heat at a low temperature level such as industrial waste heat or building exhaust air.

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1 sheet of drawings

Claims (15)

660 776 1. A method for increasing the overall efficiency of a heat pump system, which consists of at least one compressor, at least one evaporator, a superheater, a three-way valve, a latent storage device and a refrigerant, characterized in that the refrigerant is directly in the latent storage device (8) by means of an evaporator (9) ) evaporates and the saturated steam of the refrigerant is overheated in the superheater (3). 2. The method according to claim 1, characterized in that the icing in the latent storage (8) is limited by the supply of heat. 2nd PATENT CLAIMS 3. The method according to claim 2, characterized in that the latent storage (8) is regenerated with waste heat. 4. The method according to claim 3, characterized in that the building exhaust air is used as waste heat. 5. The method according to claim 2, characterized in that the icing limit is set to a resulting pipe surface temperature during operation from minus 8 ° to minus 12 ° C. 6. The method according to claim 1, characterized in that the pressure difference between the suction and pressure side of the compressor (1) is limited in a range from 5 to 20 bar. 7. The method according to claim 2, characterized in that the refrigerant is circulated by the compressor (1). 8. The method according to claim 1 or 2, characterized in that a refrigerant is pumped through the latent storage (8). 9. The method according to claim 1, characterized in that a second evaporator (7) is fed with outside air. 10. The method according to claim 1, characterized in that the refrigerant condensate from the condenser (2) is supercooled in the superheater (3). 11. The device for carrying out the method according to claim 1, characterized in that a container provided with water serves as a latent storage (8) (Fig. 1). 12. The apparatus according to claim 11, characterized in that an evaporator (9) is installed in the latent memory (8). (Fig. 2). 13. The apparatus according to claim 12, characterized in that the evaporator (9) consists of tubes (Fig. 2). 14. The apparatus according to claim 13, characterized in that the tubes of the evaporator (9) have a smooth surface. 15. The apparatus according to claim 13, characterized in that the tubes of the evaporator (9) are profiled.