GB2087530A

GB2087530A - Defrosting evaporators and drain troughs of heat pumps

Info

Publication number: GB2087530A
Application number: GB8133617A
Authority: GB
Original assignee: Svenska Flaktfabriken AB
Current assignee: Svenska Flaktfabriken AB
Priority date: 1980-11-12
Filing date: 1981-11-06
Publication date: 1982-05-26
Also published as: SE8007957L; FR2493972B1; FR2493972A1; GB2087530B; DE3142621A1

Abstract

The evaporators 4 and associated drain troughs 12 of an air treatment unit utilizing two heat pumps are defrosted by warm exhaust air conveyed along the underside of each drain trough 12 via a single damper 13 to one or both of the evaporators 4, the evaporators 4 being substantially horizontally situated over the drain troughs 12 at a distance therefrom. <IMAGE>

Description

SPECIFICATION A method of and apparatus for defrosting evaporators and drain troughs of air treatment aggregates or units having heat pumps This invention concerns a method of and apparatus for defrosting evaporators and drain troughs of air treatment aggregates or units having heat pumps.

Thermal energy is available even in very cold atmospheric air. With a heat pump this heat is taken advantage of and utilized, among other things, for the heating of supply air entering buildings. In this way heat pumps can even be utilized in a unit for the recovery of heat from air exhausted from buildings. Such a unit can consist of two separate circuits, of which the one circuit collects its heat from the exhaust air while the other circuit collects its heat from atmospheric air.

The heat pumps of such units can manage e.g. the heating of buildings, even with an atmospheric temperature of-50C, before additional heat is required.

The advantage of heat pumps is, as generally known, that more heat than that which corresponds to supplied power is obtained, i.e. the heat factor is greater than 1. Moreover invested capital is better utilized, especially in the case where the unit can be reconnected and used for cooling in the summertime.

With known heat recovery units which include heat pumps, such as refrigeration heat pumps, which are in operation during low atmospheric temperatures, there is the problem of keeping evaporators and drain troughs free from deposits of ice during the winter to the degree that an optimal operational reliability and efficiency is obtained.

During defrosting, water from melted ice is formed which is why the evaporators are located in drain troughs. During repeated defrostings of the evaporator during long periods of low atmospheric temperatures, lower sections of the evaporator and the drain trough do not have time to become completely defrosted and/or completely emptied of water from melted ice before the defrosting period has ended. During repeated defrostings a layer of ice is formed after each defrosting period, as a result of which a compact block of ice is gradually formed in the drain trough and on the lower section of the evaporator.

This block of ice affects the efficiency of the evaporator in a negative extent and with that the entire unit. The piping system of the evaporator is most often divided into several separate pipe circuits, which each are fed with a coolant medium from a distributor, which provides each circuit with an equal quantity of the coolant medium. During the formation of ice, the heat transfer capacity on the atmospheric side in the ice-coated section of the evaporator is greatly reduced which negatively affects the evaporation of the coolant medium in the pipe circuit which is located in this section of the evaporator.An expansion valve which is connected to the evaporator will under these conditions be controlled by the decreased evaporation of the coolant medium in this ice-affected circuit, whereby the supply of coolant medium to the entire evaporator is reduced, which naturally greatly decreases the ability of the evaporator to absorb heat and in this way its total efficiency as well as the above stated heat transfer capacity.

An object of the present invention is to eliminate the above stated disadvantages and to achieve a simple and reliable method, together with apparatus for carrying out the method, which gives a high average annual heat factor.

This object is achieved in accordance with the present invention in that there is provided a method of defrosting evaporators and drain troughs of air treatment aggregates or units having heat pumps, said units comprising compressors, a condensor, an expansion valve, evaporators and drain troughs characterised in that at least two heat pump aggregates are used, that exhaust air from a unit which is heated up by the air treatment aggregate is conveyed along the underside of the drain troughs, that a damper is arranged between the drain troughs, that by means of the setting of this damper the exhaust air is led through either the one or the other or both evaporators, and that the evaporators are horizontally arranged or with slight inclination over the drain trough at such a height that they do not come into direct contact with the drain troughs.

For carrying out the above mentioned method the present invention also provides apparatus for carrying out the method according to the preceding claims comprising compressors, a condensor, an expansion valve, evaporators and drain troughs, characterised by a supply duct for supplying exhaust air to the underside of the drain troughs, a damper between the troughs for reconnection of the exhaust air between the evaporators and evaporators which are horizontally or with slight inclination situated at a distance above the drain troughs.

The apparatus of the invention preferably has at least two evaporators, in a horizontal position, which do not have direct contact with the drain troughs. The drain troughs may be arranged in such a way that the exhaust air of the apparatus passes by the undersides of the troughs, which prevents undesired formation of ice in the troughs without the need for additional trough heating means, for example, electrical radiators. The exhaust air flows afterward between the drain troughs and over a damper, which controls the flow of exhaust air to one or several chosen evaporators. The flow of exhaust air can be utilized partly as one single heat source partly together mixed with mixed-up outside air. The exhaust air can, by means of this arrangement, even be utilized as a heat source for the defrosting of he ice coated evaporator above the drain trough.The compressors and other heat emitting components are advantageously located in the flow of exhaust air in front of the drain troughs and the evaporators.

During defrosting of an evaporator, the fan of the evaporator and the compressor are turned off, whereby the evaporator is emptied of its liquid coolant medium by means of so called pumpdown-stop of the compressor. The warm exhaust air then flows through the ice coated evaporator, wherein the ice melts and the resulting water drops downward into the drain trough, whose condensate discharge line is also situated in the warm flow of exhaust air and is connected to some frost-free outlet inside the building. This way of arranging the drainage of condensate of the drain trough eliminates the formation of ice plugs in the pipeline, which previously could cause on the one hand flooding on the other further formation of ice in the drain trough.

Defrosting with the use of exhaust air according to the invention implies that defrosting need not occur with warm gas from the compressor, which is why no reversing valve is needed which otherwise reconnects between evaporator and condensor. In this way an indoor battery does not consume any heat, which normally would need to be compensated for with extra eiectric heat or the like. Moreover no energy is conveyed to the compressor as long as it is turned off during the defrosting period.

This manner of utilizing the exhaust air renders a reliable method for defrosting and at the same time increases the efficiency and average annual heat factor.

The invention will now be described further, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a schematic representation of a heat pump unit of preferred apparatus of the invention; Fig. 2 is a sectional view through an air treatment unit according to the invention; and Fig. 3 is a vertical section through the air treatment unit of Fig. 2.

Referring firstly to Fig. 1 the heat pump comprises a compressor 1, in which a gaseous coolant medium is compressed, whereby its temperature rises. The medium is conveyed to a condensor 2 in a room or the like, which is to be heated. The air in the room is heated and the coolant medium is cooled in the condensor 2, after which the coolant medium is conveyed to an expansion valve 3. There the coolant medium pressure is decreased and its temperature falls, after which the coolant medium is conveyed to an evaporator 4. To this evaporator 4 is conveyed e.g.

atmospheric air or exhaust air from the room. The air heats up the cold coolant medium after which the coolant medium is fed back to the compressor 1 and the cycle is repeated. Since atmospheric air as well as exhaust air have a certain humidity, at lower air temperatures, the formation of frost in the evaporator 4, as discussed in the introduction, of this specification is very liable to occur.

The right hand side of figure 2 illustrates a known arrangement of two condensors 2 and a post heater 5. The heater can for example be an electric battery and give required additional heat if the condensor's heat should not be sufficient to heat the supply air to the temperature which has been set on a room transmitter or supply air transmitters (not illustrated). A filter 6 is fixed in front of one of the condensors 2, to filter the atmospheric air and the exhaust air. In front of the filter 6 is an air mixture adjusting damper 7.

The exhaust air is blown into the air treatment aggregate with the aid of an exhaust air fan 8. The flow of exhaust air through the arrangement which is illustrated on the right hand side of Fig. 2 and which comprises the lower damper 7, the filter 6 the condensors 2 and the postheater 5 to a supply air fan 9 which blows out the treated air to the room is known.

The remaining portion of the exhaust air is conveyed through the arrangement shown on the left hand side of Fig. 2. In this arrangement exhaust air passes an exhaust air damper 10 and compressors 1, which are cooled, and eventually a liquid separator, which is schematically indicated at 11, after which the warm, and by means of the heat of the compressors 1, additionally heated up exhaust air is conveyed along the under side of two drain troughs 12. The drain troughs are heated whereby eventually previously formed ice is melted and the resulting water runs off via a pipe (not shown), which likewise is located in the warm flow of exhaust air, to a suitable outlet.

As indicated by arrows in Fig. 3 the exhaust air continues outward between the drain troughs 12 to a damper 13 and is led to the one or both of the evaporators 4. If the flow of exhaust air is great enough, according to that which is shown in Fig. 3, outside air is not utilized as a heat source for the right hand side evaporator 4 (as illustrated in Fig. 3) and the exhaust air damper 13 then is set in the position which is illustrated in Fig. 3. Heat pump fan 14 of the right hand side evaporator 4 does not in operate. The left hand evaporator 4 aquires its heat solely from atmospheric air, and its associated heat pump fan 14 does not operate.

The left hand evaporator 4 can consequently have a formation of ice, while at the right hand evaporator 4 - if it has beforehand been connected to cold atmospheric air -- defrosting can even occur with the illustrated setting of the system.

The unit which is illustrated in Fig. 2 can even be used as a cooling unit during the summertime.

By means of a four port valve the condensors are then reconnected in order to serve as evaporators while the evaporators are reconnected to serve as condensors. The condensor fans are in operation, controlled by the condensation temperature. The evaporators can cool a mixture of return air and outside air or only outside air to a temperature which is controlled by a room transmitter or a supply air temperature transmitter.

Claims

1. A method of defrosting evaporatos and drain troughs of air treatment aggregates or units having heat pumps, said units comprising compressors, a condensor, an expansion valve, evaporators and drain troughs, characterised in that at least two heat pump aggregates are used, that exhaust air from a unit which is heated up by the air treatment aggregate is conveyed along the underside of the drain troughs, that a damper is arranged between the drain troughs that by means of the setting of this damper the exhaust air is led through either the one or the other or both evaporators, and that the evaporators are horizontally arranged or with slight inclination over the drain troughs at such a height that they do not come into direct contact with the drain troughs.

2. A method as claimed in claim 1 characterised in that the compressor is turned off while the corresponding evaporator is defrosted with exhaust air.

3. A method as claimed in claim 1 or 2 characterised in that the compressors and/or liquid separator and/or condense melt-water recipients and pipes are also placed in the warm flow of exhaust air in front of the evaporators.

4. A method as claimed in claim 1, 2 or 3, characterised in that the drain troughs under the evaporator which is heated by exhaust air as well as the evaporator which is heated by atmospheric air, is swept by exhaust air along its under sides while the evaporators which are located above these, are defrosted intermittently when needed.

5. A method of defrosting evaporators and drain troughs of air treatment aggregates or units substantially as hereinbefore described with reference to the accompanying drawings.

6. Apparatus for carrying out the method according to the preceding claims comprising compressors, a condensor, an expansion valve, evaporators and drain troughs, characterised by a supply duct for supplying exhaust air to the underside of the drain troughs, a damper between the troughs for reconnection of the exhaust air between the evaporators and evaporators which are horizontally or with slight inclination situated at a distance above the drain troughs.

7. Apparatus as claimed in claim 6, characterised in that the compressors lie in front of the evaporators in the exhaust air.

8. Apparatus for defrosting evaporators and drain troughs of air treatment aggregates or units substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.