DE3029014A1 - Heat pump extracting heat from air or water - uses medium or other medium in liquid or vapour form to cool refrigerant - Google Patents

Abstract

The heat pump which circulates a refrigerating medium which vapourises at a constant lower temp. to extract heat from a second medium such air or an underground water source, compresses the first medium in one or more compressors to extract useful heat. This first medium is cooled down by the second medium by using an additional heat exchanger. The temp. difference between them is at least 30 deg.K. In another system a further medium is used for the cooling operation. In a further system, the second medium in its vapourised form is used for the cooling operation using an additional heat exchanger.

Description

302S0U 2

IMPROVEMENT OF THE CAPACITY OF HEAT PUMPS THANKS TO SUBCOOLING THE LIQUID REFRIGERANT WITHOUT SIMULTANEOUSLY OVERHEATING OF THE SUCTION GAS

TECHNICAL DESCRIPTION

1, HEAT PUMPS

From the German patent specification No. 6 75 840 are heat pumps already known by their nature.

The basic idea of obtaining heat at a low temperature in order to raise it to a higher temperature level and for Using heating or other purposes dates back to the 19th century. CARNOT had already developed the idea to create a circuit with a medium in such a way that heat is withdrawn at a low temperature, i.e. absorbed by the medium and is released again at a higher temperature (CARNOT heat pump theory).

Only later, towards the end of the 19th century, did this idea come about realized; At that time, LINDE built the first economically viable refrigeration system with the refrigerant NH3.

The development, which was characterized by the constantly growing use of primary energy, left the thought the use of heat from the refrigeration system process little space. Rather, refrigeration technology developed to keep food fresh and conservation as well as for other purposes with their unmistakable economic benefits.

Only the recent shortage of energy and the becoming conscious future developments in terms of availability of primary energy as well as environmental problems left the application the existing technologies from refrigeration technology for heat pump systems.

A variety of such heat pumps have been used in recent years built for heating and other purposes. The profitability of these systems is due to the increase in price of conventional energy sources are no longer questioned. However, there is still a significant one at present Divergence between what is theoretically possible and what is actually achieved performance figure. Put simply, the performance figure is the ratio between the benefit and the effort of a Cold or heat pump system (see DIN 8900).

The object of this invention is an effective measure for improving the coefficient of performance of heat pump systems.

The heat pump works according to the following principle:

- A liquid medium (refrigerant) evaporates at constant low temperature and thereby withdraws heat from another medium, e.g. groundwater, circulating air, etc.

- The now gaseous refrigerant is now compressed in one or more compressors in order to increase the pressure to prepare the liquefaction at high temperature for the use of the heat.

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- The compressed refrigerant is in the condenser, the

here acts as a heat source, the one absorbed in the evaporator Heat plus the heat equivalent of the compressor work to a heating medium.

- The now liquefied refrigerant, which of course still is approximately at the condensation temperature, the pressure is lowered in a throttle device (expansion valve) and fed back to the evaporator.

2. RIN UNDERCOOLING

The high temperature of the liquid in front of the expansion valve has a disadvantageous effect because it is disproportionate large losses occur when throttling in the expansion valve.

This disadvantage has often been countered in the past by the fact that the liquid in one by the cold suction gas the built-in heat exchanger was subcooled. However, this method has the considerable disadvantage that the spec. Volume of the suction gas increased not insignificantly and thus the amount of refrigerant drawn in by the compressor is reduced.

The "gain" on the liquid side is largely canceled out by the loss on the suction side, so that this measure is questionable in its effectiveness.

3rd INVENTION : Effective measure for fluid

uη cooling

T he task according to the invention consists in the under 2. mentioned disadvantages of liquid subcooling due to suction gas heating to avoid over the enlargement of the spec. Volume of the suction gas also has the following disadvantages to call:

-the heated suction gas leads to higher compression end temperatures, which can lead to damage and shortening the service life of the compressor,

-In hermetic compressors, the motor winding is often cooled by the cold suction gas (suction gas-cooled Compressors). If the suction gas is heated, this cooling is no longer guaranteed; the engine can fail.

All heat pumps are characterized by the fact that a relatively cold medium (water or air, etc.) has the necessary Heat is withdrawn.

The higher the temperature of this medium, the more economical the process runs, i.e. the cheaper the COP becomes.

In general, the higher the temperature at which the heat is extracted, the more favorable the coefficient of performance is, at the temperature Low at "which the heat is given off.

In summary, the following considerations led to the invention, the subject of this application is:

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a.) The refrigerant liquid leaves the condenser at approximately the condensation temperature. A hypothermia in the condenser - as is usual with refrigeration systems - it is not possible in the condenser, as the temperature of the heating medium is required for this usually not sufficient, i.e. too high.

b.) The liquid must be subcooled in order to improve the COP and function of the heat pump system.

- The absorbed heat of evaporation increases.

- The formation of vapor bubbles in the throttle body is severely restricted. This improves the heat transfer conditions in the evaporator.

- Formation of vapor bubbles in front of the throttle device is avoided and thus the effectiveness of the throttling device is ensured.

c.) - The subcooling of the liquid refrigerant must not done by the cold suction gas.

d.) A previous heating of the medium, from which the heat is to be withdrawn, has a favorable effect, as it does this the evaporation temperature of the refrigerant is increased.

The above points are taken into account in that

- an additional heat exchanger for subcooling the liquid is built in by the medium from which the heat is to be extracted

or , if this proves to be unfavorable or impracticable in terms of process and design in individual cases (e.g. air / water or air / air heat pumps),

- an additional heat exchanger for subcooling the liquid through which the evaporating cold refrigerant is installed.

With only minor differences, both measures lead to sustainable Improvement of the operation of heat pump systems.

The following improvements are achieved:

- Increase in the amount of heat absorbed in the evaporator per kg of refrigerant.

- Reduction of the throttle steam formation behind the expansion valve.

- Avoidance of vapor bubble formation in front of the "expansion valve and thus increasing the functional reliability of the heat pump.

- Increase in the evaporation temperature to improve the coefficient of performance.

- If necessary, preheating of the medium from which the heat is to be extracted.

-4-ORIGiNAL INSPECTED

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Practical tests have shown that the improvement in the coefficient of performance alone is 10 to 15% , depending on the temperature and pressure ranges with which the heat pump is operated.

In particular, however, the functional advantages should be emphasized.

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Claims (1)

3023014 SUBSCRIBED Claims e f 1 _β Subcooling of the liquid refrigerant to a temperature that is over -30 K lower than rs: due to the medium from which the energy is withdrawn (pass, other liquids, air) in an additional heat exchanger. Hypothermia as mentioned under 1, but by any other available cold medium " 3 © Subcooling of the liquid refrigerant by the evaporating refrigerant in an additional heat exchanger ,,