GB2062829A

GB2062829A - Heat pump or refrigeration circuits

Info

Publication number: GB2062829A
Application number: GB8020903A
Authority: GB
Original assignee: Teknoterm Systems AB
Current assignee: Teknoterm Systems AB
Priority date: 1979-06-28
Filing date: 1980-06-26
Publication date: 1981-05-28
Also published as: FR2460458A1; DE3023459A1; DK277480A; SE7905682L; NO801865L; JPS5634068A

Abstract

The evaporator (6) of a heat pump or refrigeration circuit is defrosted by use of a switching device 7. The refrigerant by-passes the condenser (4) and the choke valve (5) so that the refrigerant from the compressor (1) flows directly to the evaporator (6) and heats and defrosts the evaporator. Prior to this the refrigerant gas is preferably heat- exchanged with water of e.g. a water heater (3), which water suitably has been heated by the heat pump compressor (1) during its normal duty between defrostings. A small amount (9) of heat exchanged refrigerant gas preferably flows during the defrosting operation to the inlet of the compressor (1) in order to gasify in that inlet liquefied refrigerant, which may be present in the cooled refrigerant gas flowing from the evaporator (6). <IMAGE>

Description

SPECIFICATION Heat pump or refrigeration circuits The present invention relates to heat pump or refrigeration circuits. A heat pump may be used as the main component of a heating system in a house or the like. As is known, it is necessary periodically to defrost the evaporator of such a system.

When the ice layer on a heat pump evaporator grows thick, the efficiency of the heat pump decreases. Thus, it is desirable to have the evaporator defrosted at least once every 24 hours.

It is known in the art to heat an evaporator of a heat pump by a metal bar, which is heated by electrical means and pushed into a hole in the evaporator, the evaporator as a whole being a metal sheet box. However, an evaporator provided with such a hole and such a bar is quite expensive to produce, particularly where the evaporator has a large surface, and furthermore, the heat generated in the bar is transmitted only slowly out into the extended sheet portions of the evaporator and the flanges of these portions, unless uneconomical amounts of electrical heat are used.

It is also known in the art to let the hot refrigerant gas coming from the heat pump compressor flow, by means of a reversing valve, e.g. one including a magnet, to the evaporator in order to melt the ice on the evaporator and use the condenser or the condenser group of the heat pump system as an evaporator and thus let cold refrigerant gas coming from the choke valve of the heat pump flow through the condenser. Such a defrosting of the evaporator has several advantages. It is possible to carry it through quickly, because the heat of the hot refrigerant gas is transmitted efficiently into the sheets and flanges of the evaporator, and it is economical.

However, the condenser or the condenser group turns cold in the process, moisture is condensed on it and water starts trickling from it and this is a clear drawback, at least as far as certain forms of heat pump devices designed for house heating are concerned.

It has now been discovered, quite surprisingly, that it is not necessary to reverse roles of the evaporator and the condenser of the heat pump to achieve a quick, efficient and economical defrosting of the evaporator.

According to one aspect of the invention, there is provided a heat pump or refrigeration circuit comprising: an evaporator; a compressor; a condenser; and expander; and a switching means which in a first condition is arranged to allow refrigerant to flow from the compressor to the evaporator via the condenser and the expander and which in a second condition is arranged to allow refrigerant to flow from the compressor to the input of the evaporator whilst by-passing the condenser and expander.

Preferably, in said second condition an amount of refrigerant is arranged to pass from said compressor to the input of the compressor which amount of refrigerant is smaller than the amount flowing to the input of the evaporator.

Preferably, at the output of the compressor is provided in the refrigerant flow path cooling means for cooling at least some of the refrigerant to its condensation temperature.

Preferably, said cooling means comprises a coil within a water reservoir.

According to a further aspect of the invention, there is provided a method of operating a heat pump or refrigeration circuit in which method in a first condition for normal operation refrigerant flows from a compressor via a switching means, a condenser, an expander and an evaporator before returning to the compressor and in which in a second condition for defrosting the evaporator the switching means is operated to cause refrigerant to flow from the compressor to the evaporator whilst bypassing the condenser and expander before returning to the compressor.

For a better understanding on the invention, and to show how the same may be carried into effect, reference will now be made, by way of example to the accompanying drawings in which Figure 1 illustrates a heat pump circuit in a first condition; and Figure 2 illustrates the heat pump circuit in a second condition.

Figure 1 shows the flow path of refrigerant gas in a heat pump (see international patent application No. PCT/SE 79100078), which operates partially in a conventional manner to heat water in a water heater 3 by means of a coil of piping 2 as well as the rooms (not shown) of a house by means of a condenser group 4. A compressor 1 pumps superheated refrigerant gas through the coil 2, positioned in the water heater 3. As a result, the water content of heater 3 is heated, and the temperature of the refrigerant gas is lowered. From heater 3, the refrigerant gas flows via a flow switch 7 into the condenser group 4 where it condenses to liquefied refrigerant and yields its latent heat of vaporisation, which is utilised directly to heat the rooms.By means of a choke valve 5, the pressure of the refrigerant liquid is reduced and in an evaporator 6 the refrigerant liquid is gasified to refrigerant gas by means of heat from the air which passes by the evaporator.

The refrigerant gas is then repressurised by the compressor 1. When flow switch 7 is operated to switch the flow direction, the condition illustrated in Figure 2 obtains.

In the illustrated circuit, defrosting of the evaporator 6 of the circuit may be achieved if: 1) the condenser and the choke valve are disconnected from the heat pump circuit temporarily by flow switch 7 e.g. for half an hour every 24 hours, and 2)The heat pump compressor 1 is employed to circulate the refrigerant gas in a circuit comprising in the flow direction only the evaporator, the compressor and the heat exchange coil of piping of a water heater or the like. The water of the water heater has been heated to a temperature of e.g. 60-700C, preferably by the heat pump.

Thus, the new short circuit does not function as a heat pump during the defrosting operation. It transmits instead heat from the water reservoir 3 directly to the evaporator by means of the refrigerant gas, which will be pressurised to a high degree due to the fact that all the refrigerant of the circuit is gasified.

Thus, there is illustrated a method of defrosting a heat pump evaporator, to which heat pump a water heater or the like is connected. Such a device is described in international patent application No. PCT/SE 79100078. In this device the refriserant gas coming from the compressor is, during the normal operation of the heat pump, heat exchanged with the water in the water heater, when the refrigerant gas flows through a coil of piping placed in the water. The refrigerant gas temperature is lowered thereby, roughly to its condensation temperature, before its entry into the heat pump condenser or condenser group, which functions as a radiator. The advantages of such an arrangement are described in said PCTapplication.

Figure 2 shows how the evaporator 6 is defrosted. The hot refrigerant gas, when it has left the coil of piping 2 flows through switch 7 partly through a reiatively large diameter pipe 8 to the evaporator 6 and partly through a piece of relatively fine pipe 9 to the inlet of the compressor 1. Thus, a proportionately large amount of hot refrigerant gas flows through the evaporator 6, which is thereby defrosted, and a proportionately small amount of hot refrigerant gas flows into the inlet of the compressor 1 in order to gasify possible liquefied refrigerant in the gas flowing from evaporator 6 where it has been cooled due to the defrosting operation. The amount of hot refrigerant gas which is to flow through pipe 9, may be calculated at any moment in dependence upon the tendency to condensation of the refrigerant gas during the defrosting operation.It is desirable to let only sufficient hot refrigerant gas flow through pipe 9 to eliminate refrigerant condensate at the inlet of the compressor since then the work performed by the compressor will be as small as possible and the efficiency of the defrosting operation very good.

Thus, the essential feature of the illustrated circuit is that when the evaporator is to be defrosted the refrigerant gas after its passage through the compressor and the coil of piping in the water heater, in which it is heat exchanged with the hot water, by-passes the condensor or the condensor group as well as the choke valve and flows directly to the evaporator in order to melt the ice on the evaporator. Preferably a small portion of the amount of refrigerant gas, which has flowed through the coil in the water heater is brought back to the entry of the compressor in order to heat the refrigerant gas coming from the evaporator in order to gassify possible liquefied refrigerant there in and thereby prevent breakdown of the compressor due to hammering.

Claims

1. A heat pump or refrigeration circuit comprising: and evaporator; a compressor; a condensor; an expander; and a switching means which in a first condition is arranged to allow refrigerant to flow from the compressor to the evaporator via the condenser and the expander and which in a second condition is arranged to allow refrigerant to flow from the compressor to the input of the evaporator whilst by-passing the condenser and expander.

2. A circuit according to claim 1 wherein in said second condition an amount of refrigerant is arranged to pass from said compressor to the input of the compressor which amount of refrigerant is smaller than the amount flowing to the input of the evaporator.

3:A circuit according to claim 1 or 2 wherein at the output of the compressor is provided in the refrigerant flow path cooling means for cooling at least some of the refrigerant to its condensation temperature.

4. A circuit according to claim 3 wherein said cooling means comprises a coil within a water reservoir.

5. A circuit according to any one of claims 1 to 4 wherein said expander is a choke valve.

6. A heat pump or refrigeration circuit substantially as hereinbefore described with reference to the accompanying drawing.

7. A building containing the heat pump or refrigeration circuit of any one of the preceding claims.

8. A method of operating a heat pump or refrigeration circuit in which method in a first condition for normal operation refrigerant flows from a compressor via a switching means, a condenser, an expander and an evaporator before returning to the compressor and in which in a second condition for defrosting the evaporator the switching means is operated to cause refrigerant to flow from the compressor to the evaporator whilst by-passing the condenser and expander before returning to the compressor.

9. A method of operating a heat pump or refrigeration circuit substantially as hereinbefore described with reference to the accompanying drawing.

10. A method of defrosting the evaporator of a heat pump device in a house or the like (e.g.

according to PCT/SE 7910078), in which device hot refrigerant gas coming from a compressor is heat exchanged in a coil of piping with water of a water heater or the like and thereby is cooled mainly to its condensation temperature before its entry into a condenser group, functioning as radiators of the device,characterised in that the refrigerant gas, which is pushed through the coil of piping in the water heater or the lik.e by the compressor by passes the condenser group and the choke valve of the device and flows directly to the evaporator which is heated and freed from its ice, and besides, a small amount of the refrigerant gas, which has been pushed through the coil of piping in the water heater is led to the inlet of the compressor also by means of the compressor in order to heat said inlet refrigerant gas which is coming from the evaporator and has been cooled due to the defrosting operation, and to gasify liquefied refrigerant, if any, in the refrigerant coming from the evaporator.