CZ306309B6 - Method of increasing performance factor and output of heat pumps - Google Patents

Abstract

A coolant (1) aerosol, supercooled to the level lower than that of the coolant evaporating temperature in front of the evaporator (2) is sucked in a compressor (3) housing (3.1). The coolant (1) supercooling and generation of aerosol is solved by the bypass (6) of the evaporator (2), which provides injection of a needful amount of the liquid coolant into gas after the evaporator. In the compressor (3) housing (3.1), the liquid coolant (1) evaporates; gas is preheated, sucked in by the compressor, pressed and heated. At the same time, the coolant (1) evaporating temperature in front of the evaporator (2) increases. This makes possible suction of a grater weight amount of the coolant (1) by the compressor (3) and by a slight increase of the compressor electric power demand a substantial increase of a performance factor and output of a heat pump. The invented method can be used for all designs of the heat pumps using a hermetically closed compressor with electric motor.

Description

Method of increasing the heating factor and output of heat pumps

Field of technology

The invention relates to a method of increasing the heating factor and output, in particular to obtain usable thermal energy - heat of up to 50 ° C and more, for heating and hot water from low-potential heat sources of up to -20 ° C and less by means of heat pumps.

Prior art

The basic elements of a heat pump are: refrigerant circuit, to which it is connected: exhaust, compressor, condenser, expansion device.

The heat pump must or may be equipped with other components that make it possible to improve the operation of the heat pump, and the use of which makes various modifications.

The basic function of the heat pump is that liquid refrigerant is injected into the heat pump evaporator under high pressure by an expansion device, which sharply reduces its temperature and pressure. Here, heat is absorbed from the surroundings (from the ground, air, water) as a result of the difference between the evaporating temperature of the refrigerant, eg -10 ° C, and the surrounding heat source, eg -2 ° C. The injected liquid refrigerant is converted to gas in the evaporator and, compared to the evaporating temperature at the beginning of the evaporator, it is superheated by 3 to 5 ° C and more at the end of the evaporator. This means that the superheated refrigerant gas has a temperature of -7 to -5 ° C at the end of the evaporator, at the temperatures given as an example. The refrigerant gas is compressed in the compressor. An increase in pressure results in an increase in temperature. The heat generated by the friction of the moving parts of the compressor also contributes to the increase in the temperature of the refrigerant gas, in the case of a hermetically sealed compressor also the heat generated by the washing of the electric motor.

In the condenser, the thermal energy thus obtained is transferred to the heating medium (water, air). The gaseous refrigerant liquefies during this process and is thus ready to be injected into the evaporator. The cycle is thus closed and runs continuously.

To operate, a heat pump needs a certain amount of energy, usually electric. There are other compressor drives, for example an internal combustion engine or there is a gas-driven absorption heat pump. These heat pumps are not the subject of the invention.

The energy taken from nature is usually 1.5 to 4 times higher than the energy consumption to drive the heat pump compressor. The measure of the energy performance of a heat pump is therefore the ratio of output energy and energy for the drive. The ratio is called the heating factor (COP). It is a dimensionless number and its size varies according to the conditions usually in the range of 2.5 or less, but always more than 1 to 5 and more.

The principle of the heat pump has been known for more than 150 years (Kelvin 1852), with the first heat pump being built in 1932. A description and function are given in every literature dealing with heat pumps.

To understand the technical solution, I present the following known findings that were used for the technical solution.

When using an non-flooded or dry evaporator (used for a heat pump), into which the inflow of liquid refrigerant is controlled by a thermostatic expansion valve (TEV), superheated refrigerant vapor flows into the compressor suction line, which overheats increases in case of using an additional evaporator with internal heat exchange. Due to the overheating of the refrigerant steam, the compressor sucks in a smaller amount of refrigerant by weight,

- 1.

thereby reducing its performance and significantly increasing the gas temperature after compression. These side effects must be kept within the required limits by regulatory interventions. The intake vapors can be cooled by direct injection of an appropriate amount of liquid refrigerant into the compressor suction line. A thermostatic expansion valve is used, which in accordance with the temperature of the superheated suction vapors injects liquid refrigerant from the liquid coolant collector. Pour. (1)

Copeland uses in its ZF series scroll compressors the injection of liquid refrigerant into the space between the compressor rotors. A capillary or special injection valve DTC is used as the injection element, which is controlled by the temperature of the refrigerant vapor in the discharge behind the compressor. Liquid refrigerant is injected from the coolant collector. Pour. (4)

The gaseous refrigerant can be superheated before entering the compressor only in the compressor space of the hermetically sealed compressor. Pour. (2)

It is necessary for the compressor to suck only gas without refrigerant drops. Otherwise, the compressor may be destroyed by a liquid shock.

However, following the information provided by the compressor manufacturer, there is no need to worry about gas droplets being sucked into the compressor if a hermetically sealed compressor is used, because the interior of the compressor package has a large internal volume to protect the compressor from liquid shock.

Another used finding is that the scroll compressor is resistant to the suction of a small amount of droplets in the gas.

Influences on the intensity of heat transfer include the alternating electric electric field as well as vibrations.

The force field increases the heat transfer with undevolved boiling of the chiadiva 2.3 times and with unfolding bubble boiling 20 times. Pour. (3)

List of used literature:

1. Cooling technology, Doc. Ing. Vaclav Hoch 1991

2. Heat pumps, Prof. Ing. Zdenek Dvorak 1987

3. Cooling technology II. (exchangers), Prof. Ing. Zdeněk Dvořák 1986

4. Rotary hermetic scroll compressors ZS - ZF by Copeland technical data, ALFACO Choceň s.r.o. 2003

The essence of the invention

The heat pump in the modification according to the invention is based on the prior art, in which a blaster, a compressor in a hermetically sealed package, a condenser, an expansion device and the following modifications and changes forming the invention are connected to the refrigerant circuit.

The invention is characterized in that the sucked-in refrigerant in the aerosol state is subcooled by 1 to 3 ° C below the evaporating temperature of the refrigerant before the evaporator before entering the hermetic compressor package.

The cooling of the gas and the formation of an aerosol occur due to the change of the liquid part of the refrigerant injected into the superheated gas behind the evaporator into a gas, when it needs heat to evaporate, which it takes away from the gas.

The gaseous refrigerant thus becomes an aerosol, i.e. a gas with a certain proportion of small drops, before being sucked into the compressor package. Due to the force of the electric electric field and vibrations in the space of the compressor housing, the heat located there is intensively transferred to the refrigerant. Tiny drops

- Ί GB 306309 B6 gasify and the gas is superheated to the required temperature before entering the compressor so that it is free of refrigerant droplets.

The compressor housing thus not only performs the function of a superheater, but also becomes a heat exchanger with direct heat exchange, without dividing walls, where the refrigerant droplets evaporate and subsequently slightly overheat before being sucked into the compressor. Cooling of the refrigerant gas also reduces its volume and, as an accompanying phenomenon, increases the evaporating temperature of the refrigerant before the exhaust. This allows an increased supply of refrigerant to the suction tract of the heat pump and the suction of a larger amount of refrigerant by weight through the compressor.

These phenomena result in a slight increase in the electric current input of the compressor, but with a significant increase in the heating factor and the output of the heat pump.

Achieving this goal is solved by using the bypass of the outlet, which is formed by the refrigerant flow distributor behind the expansion device I, the expansion device II, which is connected in series with the expansion device I, the refrigerant flow mixer behind the outlet and the connecting pipe.

Relation of the invention to the prior art.

The principle of reducing the temperature of the intake gaseous refrigerant before entering the compressor housing is the same in both the known technique and the invention. The method of execution is different.

The prior art uses a parallel (connected) expansion device.

Also, reducing the refrigerant temperature in the compressor uses an expansion device arranged in parallel (next to each other).

The arrangement according to the invention uses the connection of expansion devices in series (in series), where the expansion device II is part of the exhaust bypass.

Technical conditions for using the invention

Compressor

Compressors of various designs and constructions can be used for conventional heat pumps. Depending on the method of vapor compression, there are at least 9 types of compressors, which can be open (seal), semi-hermetic and hermetic.

For the heat pumps according to the invention, it is possible to use any refrigeration compressor with an electric drive in a hermetically sealed package, as well as in a semi-hermetic-divided package.

For a heat pump treated according to the invention, the same powerful compressor is used as for a heat pump without treatment. Depending on the design of the heat pump, the heat pump according to the invention must be equipped with the same start-up device and the refrigerant suction device from the suction line before shutting down the compressor as well as a heat pump without modification according to the invention.

Accessories can also be used as with conventional heat pumps, such as a heating cable to preheat the oil before starting, to prevent the oil from foaming. If a heating cable is used, its temperature sensor must be located at the bottom of the compressor housing and on the opposite side of the inlet suction pipe into the housing. Alternatively, it is possible to use thermal insulation of the compressor housing. However, this is not suitable if the compressor will operate in a warmer environment than its operating surface temperature.

The invention is also applicable to a heat pump equipped with a scroll compressor EVI, which uses residual (specific) heat in the liquid refrigerant. In this case, the bypass must be used for the main outlet, not for the additional heat exchanger with internal heat exchange.

A modified reciprocating compressor for a system using residual heat in the liquid refrigerant can also be used instead of the scroll EVI scroll compressor. In this case, however, a perfect device must be used to separate the refrigerant droplets from the gas.

Evaporator: Commonly used for a heat pump, ie dry, gradually flooded.

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In general, the heat transfer area of the evaporator should be in the ratio power / area = 1 kW / 3600 cm ² . The modification for a heat pump modified according to the invention, which is expected to increase the output by about 50%, does not require an increase in the heat exchange area of the evaporator.

Condenser: The heat transfer surface must correspond to the increased output of the heat pump according to the invention.

Heat pump without treatment = 1 kW / 2400 cm ² .

The heat pump according to the invention, where an increase in output of about 50%, i.e. to 1.5 kW, is assumed, the condenser must also be increased by 50%, ie to 3600 cm ² .

The refrigerant circuit consists of a suction part (from the expansion device to the compressor) and a discharge part (from the compressor to the expansion device).

The refrigerant circuit is filled with refrigerant.

A refrigerant is a substance which, as a liquid, has a very low evaporating temperature (-10 to -50 ° C) and liquefies easily as a gas. Refrigerants are marked with the letter "R" to which a number or a letter is assigned, which expresses the chemical composition of the refrigerant.

The same refrigerant is used for the heat pump according to the invention as for the heat pump without applying the invention. The heat pump according to the invention requires a larger amount of refrigerant by about 25% compared to a conventional heat pump. Manifold on the evaporator bypass.

It is placed just behind the expansion device I, i.e. in front of the evaporator, or in front of the refrigerant distributor to the individual sections of the evaporator.

The evaporator bypass manifold must ensure that liquid refrigerant enters the expansion device II from the manifold. It is made according to the known principle of a droplet-gas separator, where the liquid is drained from the bottom, the aerosol with the predominance of drops is sucked into the evaporator from the top. The manifold can be in various designs. E.g. with rectilinear coolant flow, with rotating coolant flow, as a vortex tube (Ranque), etc.

In general, the refrigerant injected by the expansion device I entering the manifold must have a higher flow rate than it has in the suction line so that the liquid is not sufficient to change direction and settles in the line before the expansion device II.

It follows that in the case of a straight refrigerant manifold, the inlet pipe must have 50% less clearance than the suction line and terminated above the bottom of the manifold. The clearance of the manifold casing must be 2 to 3 times larger than the suction line has a casing length 3 times larger than its clearance.

The stated values have a relatively large tolerance.

The mixer is made of a small vessel, into which the suction pipe opens and opens at the top. The connecting tube from the expansion device 11 opens into the bottom. The mixer can also be made in another way, for example by a simple "T" piece of the same dimension as the suction line. If TEV I is used as expansion device I, the mixer must be located behind the outlet and temperature sensor (bulb) of expansion valve I.

The function of the connecting pipe from the expansion device II with the mixer is clear from the name.

Expansion equipment:

I. it can be a thermostatic expansion valve (TEV), an electronic expansion valve (EEV), an automatic expansion valve (AEV) or a capillary.

II. the bypass can be TEV, EEV, AEV, capillary, manually adjustable throttle valve or nozzle. TEV seems to be the most suitable, where TEV I is with either external or internal pressure equalization depending on the pressure losses of the evaporator. TEV II is used with internal pressure equalization. The TEV pump is located in front of the compressor.

When using EEV, up to 5% higher COP can be achieved, but the acquisition costs are several times higher than when using TEV.

Other expansion devices are cheaper, but have a limited range of both low potential source (NPZ) temperatures and condensing temperatures.

The dimensions of the pipes and other components of the heat pump, not yet mentioned, are identical for a heat pump not modified or modified according to the invention.

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The adjustment of the expansion device I, or its dimensions, is the same for both a heat pump modified according to the invention and an unmodified heat pump. It must ensure that the refrigerant overheats above the evaporating temperature of the refrigerant before discharge by 3 to 5 ° C at the end of discharge.

The nozzle sizes for TEV I and TEV II are the same. However, if a capillary is used instead of TEV I, it must be larger on the heat pump according to the invention than the capillary on the heat pump without modification according to the invention.

The adjustment of the expansion device II, or its dimensions, must ensure that the refrigerant is subcooled before entering the compressor package by 1 to 3 ° C compared to the evaporating temperature of the refrigerant at the beginning of the outlet.

The oil temperature in the compressor housing should not fall below +10 ° C after the compressor has started. A lower temperature indicates that too much liquid refrigerant fraction is sucked into the compressor package, which reduces the performance of the heat pump and COP.

It is necessary to have a water drainage device under the heat pump, for a heat pump of any design. During operation, it forms on the entire bypass of the effluent and further on the continuing pipeline to the icing compressor. This melts when the heat pump is switched off and the resulting water must be drained off.

Advantageous effects of the invention in relation to the prior art.

Achieved values of increase in output and heating factor (COP) on experimental heat pumps according to the invention compared to untreated heat pumps were + 25 to 50% depending on the heat pump design and operating conditions, under extreme conditions the increase was more than double, ie + 100 and more% at minimal cost of treatment of heat pumps according to the invention.

Attempts have also been made to apply the invention to a heat pump of an EVI system using a modified reciprocating compressor in a split-semi-hermetic package, and the invention has also proved successful here.

Furthermore, comparative experiments were performed with a heat pump using 2 expansion devices arranged in parallel, i.e. a technique known, with a heat pump system according to the invention, and also in this comparison the heat pump according to the invention was better.

Explanation of drawings

Fig. 1 is a basic diagram of a heat pump.

Fig. 2 is a diagram of a heat pump with 2 expansion devices connected in series, including the bypass of the burner, which is the subject of the invention

Examples of embodiments of the invention

The heat pump according to FIG. 1 is formed by a refrigerant circuit 1, in which a outlet 2, a compressor 3, a condenser 4 and an expansion device 5 are connected. The cooled medium from which heat is removed is denoted as 7 and the heated medium is indicated as 8. pumps heats.

The embodiment according to the invention in FIG. 2 is a known embodiment according to FIG. 1 extended by a bypass 6 of the outlet 2 by connecting the suction line of the chiadiva circuit 1 before and after the outlet 2.

The bypass 6 is formed by a refrigerant flow divider 6.1 after the expansion device I 5.1, the expansion device II 62 by a refrigerant flow mixer 6.4 behind the outlet 2 and a connecting line 6.3, with the proviso that a compressor must be used in a hermetically sealed container.

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At the bypass 6 there is an expansion device II 6.2 ensuring the suction of such an amount of refrigerant that forms an aerosol and lowers the refrigerant temperature in the suction line of the refrigerant circuit 1 before entering the package 3.1 of the hermetically sealed compressor 3 to a level lower than the evaporating temperature of the refrigerant at the beginning of the outlet 2. the volume of the sucked-in coolant is reduced and at the same time the evaporating temperature of the coolant before the effluent 2 is increased.

This will allow a larger amount of refrigerant to be sucked in by the compressor 3 and, as a result, with a slight increase in the power input of the compressor 3, a significant increase in the heating factor and the output of the heat pump.

The invention is applicable to all embodiments of heat pumps using a compressor 3 with an electric motor enclosed in a hermetic or semi-hermetic split package 3.1. A number of experiments have been performed on experimental heat pumps of all embodiments and types using the invention. Based on their results, usability for industrially produced heat pumps can be assumed.

Claims (8)

PATENT CLAIMS A method of increasing the heating factor and output of heat pumps formed by a refrigerant circuit in which a refrigerant outlet is connected to remove heat from a gaseous or liquid refrigerant, a compressor in a hermetic package to compress and heat the refrigerant gas, a condenser to liquefy the refrigerant and transfer its heat to the heated refrigerant pressure and expansion device, characterized in that the compressor (3) in a hermetically sealed package (3.1) sucks into the compressor package (3.1) an aerosol of refrigerant (1), which is subcooled to the compressor package (3.1) before entering the compressor package (3.1). level lower than the evaporating temperature of the coolant (1) before the outlet (2), then the liquid fraction in the gaseous refrigerant (1) is evaporated due to heat, force electric field and vibrations caused by electric motor and compressor (3) and further the gaseous refrigerant ( 1) superheated and sucked into the compressor (3), where the subcooling of the coolant (1) and the formation of the aerosol of the coolant (1) ensures the bypass (6) of the effluent (2) formed by the distributor (6) .1) refrigerant flow (1) downstream of expansion device 1 (5.1), expansion device II (6.2) connected in series with expansion device I (5.1), connecting pipe (6.3) from expansion device II (6.2) to refrigerant flow mixer ( 6.4) behind the outlet (2), which in combination with the subcooling of the refrigerant (1) in front of the compressor casing (3.1) ensures an increase in the evaporating temperature of the refrigerant (1) in front of the outlet (2) and thus suction of more mass of refrigerant (1) . 1 drawing List of reference marks: 1 refrigerant circuit, refrigerant 2 springs 3 compressor 3.1 hermetic compressor housing 4 capacitor 5 expansion devices 5.1 expansion device 1 6 exhaust bypass 6.1 refrigerant flow distributor 6.2 Expansion devices II 6.3 connecting pipes bypasses 6.4 the flow mixer cools 7 cooled medium 8 heated medium