GB2077407A

GB2077407A - Heat pump

Info

Publication number: GB2077407A
Application number: GB8114872A
Authority: GB
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 1980-05-16
Filing date: 1981-05-15
Publication date: 1981-12-16
Also published as: DE3018706A1; FR2482711A1

Abstract

The heat pump provides a connection (11) for ducting hot refrigerant gas from an expeller (1) directly to an evaporator (4) of the pump under the control of a solenoid valve (12) and a throttle (13). The evaporator is equipped with an icing sensor (16) which on sensing a, predetermined degree of icing of the evaporator opens the solenoid valve to permit gas to enter the evaporator through the throttle to effect de-icing. The consequent rise in pressure in the evaporator shuts off an expansion valve (5) through which condensate from a condenser (2) of the pump is normally fed to the evaporator. <IMAGE>

Description

SPECIFICATION Heat pump The invention relates to a heat pump.

A heat pump is known comprising a device for producing a hot refrigerant vapour, a condenser connected downstream of the device, and an evaporator for the refrigerant which is provided with an air inlet conduit and an air exhaust conduit and an expansion valve.

At inlet air temperatures below approximately 80C and at a high relative air humidity, icing of the evaporator can occur which at least considerably impairs the mode of operation of the heat pump.

Consequently, the object of the invention is to construct such a heat pump in which the evaporator can be defrosted in a short time at only a low additional expense.

There is provided by the present invention a heat pump having a device for producing a hot refrigerant vapour, a condenser connected downstream of the device, and an evaporator for the refrigerant which is provided with an air inlet conduit and an air exhaust conduit and an expansion valve, wherein a conduit for hot refrigerant vapour leads from the device directly to the inlet of the evaporator and incorporates a throttle for reducing the pressure in the conduit in operation to a value, in excess of the evaporator pressure, leading to condensation, and a solenoid valve which is arranged to be operated by an icing sensor, to open the conduit only when a predetermined degree of icing of the evaporator occurs.

An advantage of the present invention resides in the low energy expenditure for de-icing which essentially involves only a direct connection conduit between the expeller or the compressor on the one hand and the evaporator on the other hand, together with two valves which, if required, can also be combined.

At this juncture, it may be mentioned that a return conduit leading from the output of a compressor and by-passing the condensor, is known from German Offenlegungsshrift 25 19 409, F24J 3/00. However, in the latter instance, this conduit serves to supply superheated steam to the evaporator downstream of the heat exchanger, and to the compressor upstream of the heat exhanger, the steam being condensed at this location and then being fed to a flow medium reservoir, connected upstream of the evaporator, for the refrigerant. Thus, this known heat pump neither seeks to solve the problem on which the invention is based, nor is this problem automatically solved.

Also, German Offenlegungsschrift 27 36 434, F24J, 3/04 may be mentioned which describes an arrangement in which, in contrast to the present invention, the hot gas is carried in processing conduits and in a by-pass around a throttle.

Defrosting is effected by cooling the hot gas, and not by condensation, the defrosting performance being low with the acceptance of losses in the cold exchanger.

An embodiment of the invention will be further described hereinafter with reference to the accompanying drawing, in which the sole Figure is a schematic diagram of an embodiment of the invention.

Referring to the Figure, the conduits for gaseous or vaporized refrigerant, NH3 in the present instance, are indicated by two parallel solid lines, the conduits for liquid refrigerant are indicated by one solid line. Conduits for weak solution are shown by a solid line having dots, and conduits for rich solution are shown by dash-dot lines. Heating water conduits are indicated by lines which are broken at large distances apart, and air conduits are indicated by lines which are broken at short distances apart.

The absorption heat pump illustrated in the Figure is constructed in accordance with known principles. The not NH3 gas obtained by heat input in the expeller 1 first flows into the condenser 2 in which heat is transferred to the heating water.

Refrigerant now in a liquid form flows from the condenser 2 by way of the cold exchanger 3 to the evaporator 4 whose chief components are the expansion valve 5 and the refrigerant/intake air heat exchanger 6. Thus, after it has expanded, the refrigerant absorbs its energy from the ambient air and consequently leaves the evaporator in the form of gas which passes through the cold exchanger 3 and flows to the absorber 7 in which the spiral 8, having the heating water flowing therethrough, effects the heat exchange with the heating water which is then fed to loads. Weak solution is also fed to the absorber 7 in addition to the gaseous refrigerant, and rich solution flows back into the expeller 1 from the absorber by way of the heat exhanger 9.

The direct conduit 11 leads to the inlet of the evaporator heat exchanger 6 from the connection conduit 10 between the expeller 1 and the condenser 2. The conduit 11, which consequently by-passes the condenser 2, incorporates two valves, that is to say, the solenoid valve 12 and the throttle 1 3. The differential pressure gauge 1 6 connected between the inlet air line 14 and the exhaust air line 1 5 opens the solenoid valve 12 only when a specific limiting value of the differential pressure between the conduits 1 4 and 1 5 signals the existence of troublesome icing in the evaporator 4.

The throttle 1 3 ensures that, when the solenoid valve 2 is open, the hot refrigerant vapour or gas then carried in the conduit 11 is only expanded up to a pressure value which lies above the previous evaporator pressure and which enables condensation above the icing temperature.

The thermal expansion valve 5 closes upon a pressure rise by the hot refrigerant gas which has flowed into the evaporator, so that the injection of condensate is stopped. When using diaphragm throttling instead of the injection valve 5, the conduit 11 has to be ciosed by, for example an additional solenoid valve.

The inlet air conduit 14 incorporates the blower 1 7 which is directly or indirectly triggered by the differential pressure gauge 1 6 and which is designed such that it assists the defrosting operation only at inlet air temperatures in excess of OOC.

A high defrosting performance and short defrosting times result from the condensation of the hot refrigerant vapour, fed through the conduit 11, in the evaporator 4. The defrosting cycle is terminated by closing of the solenoid valve 12 by, for example, a time delay. When the evaporator pressure then drops, the condensate produced in the evaporator is then completely evaporated again. The expansion valve 5 opens automatically towards the end of this evaporation process, and the heat pumping process is resumed.

Condensate produced during defrosting can thus remain in the evaporator, since it evaporates again later when the heat pumping operation is resumed. However, it is also possible to feed condensate directly to the absorber by a separate conduit, particularly when large quantities of condensate are produced.

Instead of the differential pressure at the evaporator, a different quantity, such as the difference between the intake air temperature and the vaporization temperature or the vaporization pressure can be detected as the characteristic quantity of the degree of icing.

Claims

1. A heat pump having a device for producing a hot refrigerant vapour, a condenser connected downstream of the device, and an evaporated for the refrigerant which is provided with an air inlet conduit and an air exhaust conduit and an expansion valve, wherein a conduit for hot refrigerant vapour leads from the device directly to the inlet of the evaporator and incorporates a throttle for reducing the pressure in the conduit in operation to a value, in excess of the evaporator pressure, leading to condensation, and a solenoid valve which is arranged to be operated by an icing sensor, to open the conduit only when a predetermined degree of icing of the evaporator occurs.

2. A heat pump as claimed in claim 1, wherein the expansion valve of the evaporator shuts off when a predetermined pressure rise occurs in the evaporator as a result of the refrigerant vapour which has flowed in.

3. A heat pump as claimed in claim 1 or 2, wherein a blower is located in the inlet air conduit or exhaust air conduit and is switched off when the conduit is open and at inlet air temperatures below OOC.

4. A heat pump as claimed in any of claims 1 to 3, wherein the icing sensor is a differential pressure gauge connected between the inlet air conduit and the exhaust air conduit of the evaporator, and the solenoid valve opens the conduit only when a predetermined differential pressure occurs.

5. A heat pump substantially as hereinbefore described with reference to the accompanying drawing.