EP3350519A1

EP3350519A1 - An airconditioner

Info

Publication number: EP3350519A1
Application number: EP16763000.3A
Authority: EP
Inventors: Israel MARTINEZ GALVAN
Original assignee: Electrolux Appliances AB
Current assignee: Electrolux Appliances AB
Priority date: 2015-09-18
Filing date: 2016-09-02
Publication date: 2018-07-25
Also published as: US20190041069A1; KR20180055833A; WO2017045934A1; CN108369015A

Abstract

An air-conditioner is provided. The air-conditioner comprising a compressor (301), and a condenser (302). The air conditioner has a desuperheater (303) provided in a flow path from the compressor to the condenser.

Description

An air-conditioner

TECHNICAL FIELD

The present disclosure relates to an air-conditioner. In particular the present disclosure relates to a portable air-conditioner.

BACKGROUND

Air conditioning (AC) is a collective expression for conditioning air into a desired state. It could be heating the air during cold periods, cooling the air during warmer periods or for cleaning the air if it contains unwanted particles. However, the expression air conditioning is most often used when emphasizing cooling. As a product, air conditioners can look and be used in various ways, but they all share the same basic technology.

Existing portable air-conditioners are often found to be large, hard to handle, noisy and inefficient. Furthermore, the connected exhaust air outlet that removes the heat from the room is often complicated and inefficient in its design. A known portable air-conditioner is for example described in the United States patent No. 2,234,753.

The design of portable AC systems differs from other Air Conditioners because all the components of the system are mounted inside of a packed unit which has to work inside of the conditioned space, releasing the residual energy (generated in the normal cooling process) through an air exhaust system which is usually connected to the outside.

In portable AC units there are two general procedures to cool down an air source condenser: single duct and dual duct methods. In the first one (single duct), the system takes air from its surroundings (conditioned space), forcing it to pass through the condenser surface and eventually removing the residual energy from it. Then, the hot air is expelled outdoors by using a single duct system. In this method, the intake air temperature has the indoor temperature conditions, which makes the energy exchange process more beneficial from standpoint of the refrigerant cycle.

In the dual duct method, the system uses an air intake duct to inject "hot" air from outdoor to cool down the condenser. Eventually the air coming from condenser at a relatively high temperature is released outdoors again by a secondary exhaust duct. In this method the air intake temperature is at the outdoor temperature conditions. This method can provide a quicker cooling effect for the user, since the system is not using the indoor air as a coolant media for condenser, but requiring in turn a larger size/volume of components to compensate the higher inlet outdoor temperatures.

Both methods, single and dual duct, have different limitations in terms of: air flow rates, size of the heat exchangers and also dimensions of the air piping system.

Those particularities requires that the portable AC systems make use of particular size of condensers, limiting the maximum air flow rate used by the system, since the air intake and air exhaust systems have to be as much compact as possible.

Air flow rates in portable AC systems are also limited by the noise levels, since larger air flow rates flowing through small diameter hoses lead to higher pressure drops and higher noise levels. In that sense, the single duct systems have a clear advantage over the dual duct systems, because the temperature difference between the intake air and the condensing temperature of the cycle is larger, requiring lower air flow rates to perform the heat rejection process. So, for portable AC systems, the condenser is one of the most critical components to design, since it has to exchange higher heat loads with a very limited air flow rate. Therefore, that particularity affects in a significant way the whole design of the condenser and the whole system performance.

One way to improve the condenser capacity in portable AC systems is by the use of the condensed water coming from the evaporator, at a relatively low temperature, in order to remove part of the heat load of the condenser. Some portable AC designs are provided with a drainage system that uses the water coming from evaporator which is dripped over the condenser, allowing a decrease of the surface temperature and subsequently getting lower condensing pressures in the cycle.

In addition to the dripping method, some other systems include the use of a wheel that splashes the excess of non-evaporated water from the bottom of condenser over its surface. This mechanism allows the elimination of part of the excess of water through the air stream that crosses the condenser.

Such methods help to decrease the condensing temperatures in the cooling cycle and also to remove part of the undesired condensed water generated in the normal operation process of the system.

There is a constant desire to improve the operation of air-conditioners. Hence, there is a need for an improved air-conditioner. SUMMARY

It is an object of the present invention to provide an improved air-conditioner that at least partly solves problems with existing air-conditioners. In accordance with one aspect problems related to the technology of the vapor compression cycles for air conditioners are targeted, in particular those related with portable AC units working with air source heat exchangers.

This object and others are obtained by the portable air conditioner as set out in the appended claims. Also disclosed are devices that can be used together with portable air-conditioners.

By the use of an external desuperheater which has the function to start the condensation of refrigerant before it enters into the condenser, normally an air cooled heat exchanger, it is possible to take advantage of a larger temperature difference between the hot gas delivered by the compressor and the cold water dripped from the evaporator surface.

In accordance with one embodiment an air-conditioner is provided. The air-conditioner has a compressor and a condenser. The air conditioner further has a desuperheater provided in a flow path from the compressor to the condenser.

In accordance with some embodiments the air-conditioner is a portable air-conditioner.

In accordance with some embodiments the desuperheater is located in an open cavity.

In accordance with some embodiments the air-conditioner is adapted to feed condensation water to the open cavity.

In accordance with some embodiments a pipe is provided and adapted to lead condensed water that drops from the evaporator to the open cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail by way of non-limiting examples and with reference to the accompanying drawings, in which: - Fig. 1 illustrates a T-S diagram for a standard refrigeration cycle which uses an air source heat exchanger as condenser,

- Fig. 2 illustrates a T-S diagram for a refrigeration cycle, which uses an external

desuperheater,

- Fig. 3 depicts an air-conditioner with an external desuperheater,

- Figs. 4 and 5 depicts different shapes of a portable air-conditioner in a side sectional view and a top sectional view respectively,

- Fig. 6 shows a possible configuration of an embodiment with a coating material over connection pipes .

- Fig. 7 show possible embodiments of coating elements over the connection pipes.

- Fig. 8 shows an embodiment including an auxiliary water pumping system to remove non- condensed water,

- Fig. 9 shows an embodiment with non-evaporated water collected in a water tank, and - Fig. 10 illustrates the general principles of an air conditioner system.

DETAILED DESCRIPTION

In standard portable ACs, working with air source heat exchangers, the heat rejection process starts when the hot gas delivered by the compressor enters into the condenser. Inside of condenser, the refrigerant at high pressure and temperature starts its cooling down process releasing its heat load through the air stream that crosses the heat exchanger surface.

At those conditions, a significant percentage of the total area of the condenser is intended first to decrease the bulk temperature of the gas until it reaches the saturation temperature in an internal de-superheating process. As the density of the superheated vapour flow is relatively low, the volume occupied by the refrigerant is relatively large, especially before to start the phase-change process of condensation. This fact makes that the size of the heat exchanger, especially the area and internal volume intended to de-superheating the refrigerant, tend to be larger to contain the hot gas in order to decrease its bulk temperature until it reaches the saturation conditions. Then, once the thermodynamic vapour quality of the refrigerant is equal to 1, the condensation and the subsequent subcooling processes will take place in the remainder heat exchanger internal volume.

Fig. 10 illustrates the general principles of an air conditioner system. The main parts of the system are the compressor 101, evaporator 103, condenser 105, and expansion device 107 such as a capillary tube. Also a condenser fan 109 and an evaporator fan 111 can be provided. The compressor is connected in a circuit with the condenser, the evaporator, and the expansion device. The refrigerant has the ability to turn from liquid into vapor, and by that change in temperature. The tempered refrigerant and the indoor air work in symbiosis to exchange heat to each other.

Figure 1 shows a T-S diagram for a standard refrigeration cycle which uses an air source heat exchanger as condenser, which works under typical temperature conditions for a portable AC application. Figure 1 includes a line that represents the inlet and outlet temperatures of the air flow rate that crosses the condenser (blue line), and the standard approaches for the heat rejection sub-processes that take place inside of condenser: DSH, Phase-Change, Subcooling.

In the heat rejection process shown in fig 1, the superheated vapour rejects first sensible heat along the single-phase desuperheatmg zone (DSH). Then, condensation starts from the equilibrium vapour quality 1, where saturated refrigerant rejects latent heat during its condensation (2 -phase process). Finally, in the last part of the condenser, the subcooled liquid rejects sensible heat through the single-phase subcooling zone (SC). Desuperheatmg can be described as the process by which a superheated steam is restored to its saturated state, or the superheat temperature is reduced. This process can be performed by a desuperheater.

In air cooled condensers, the temperature of the air stream around the desuperheating section affects strongly the gas desuperheating process. Air surrounding temperature is usually affected by the circuiting design and other geometrical parameters like the relative location of the refrigerant inlet ports, the number of passes, the number of rows, air flow rates, etc. However, in the particular case of portable AC systems, the geometrical limitations in the dimensions of the air exhaust ducts restrict the air flow across the condenser, leading to achieve larger temperature gradients through the air path that crosses the condenser from inlet to outlet, therefore the air temperature around the desuperheating section tend to be much higher.

On the other hand, as the fluids flow arrangement is generally fixed in a counter-current flow type configuration, in most of the cases the desuperheating section of condenser rejects energy against an air flow that has previously exchanged energy with the first rows of condenser. This fact affects also to the increase of the air stream temperature that surrounds the back rows of condenser, where usually are located the desuperheater inlet ports.

Both effects, the higher temperature gradients of the air surrounding the desuperheating zone of condenser and the relative position of the inlet gas ports make that the wall temperatures of the pipes in the desuperheater area are normally higher than the saturation temperature of the refrigerant, leading a long an inefficient desuperheating process inside of condenser and subsequently requiring larger heat transfer areas to complete the

condensation process. In order to improve the heat transfer processes in air source condensers, in particular air cooled condensers used in portable air conditioners an external desuperheater can be provided. The desuperheater enables the heat transfer between the discharge gas delivered by the compressor, at high pressure and temperature, and the condensed water generated on the evaporator surface at a relatively low temperature.

In a standard condensation process, without the use of an external desuperheater, part of the energy exchange area is intended to decrease the temperature of the superheated gas until it reaches the saturation conditions. The area used to perform this process can be between 10 to 20% of the total heat transfer area of condenser. The heat load removed at those conditions is usually relatively small because of the low heat transfer coefficients achieved in the single phase exchange process, especially using air as secondary coolant media.

The use of an external desuperheater described herein takes advantage of the higher heat transfer coefficients achieved by a faster condensation of the refrigerant, because of the large temperature difference between fluids, but also because of the improvement in the heat transfer coefficients of the secondary coolant media (water), due to its partial evaporation (2 -phase process).

Figure 2 represents the T-S diagram for an improved cycle compared to Figure 1, which uses an external desuperheater. The external desuperheater can be installed just before the air cooled condenser.

Figure 2 represents the three different heat rejection sub-processes: desuperheating of vapour using condensed water, saturated condensation and subcooling, by the standard heat rejection against an air stream. In figure 2 are also represented the temperature profiles of secondary coolant media: condensed water in the case of desuperheatmg and air in the case of condensation and subcooling.

The desuperheatmg is carried out by the external desuperheater, where the film

condensation of the vapour appears almost instantaneously over the internal surface of the heat exchanger because under those conditions, the wall temperature of the desuperheater is far below of the saturation temperature of the refrigerant, since the heat exchanger is surrounded by the condensed water at relatively low temperature conditions. As the temperature of the water coming from evaporator is generally the dew point temperature of the air that leaves the evaporator, the heat rejection process inside of the desuperheater is then driven by: the sensible heat rejection due the vapour desuperheatmg, and the latent heat rejection to generate condensate refrigerant. Additionally, an additional sensible heat rejection, due the subcooling of condensate, can also have an important contribution in the total heat rejection process inside of

desuperheatmg if the wall temperature of the pipe is below of the saturation temperature of refrigerant. Inside of the external desuperheater, the temperature difference between the secondary coolant media (condensed water coming from evaporator), and the bulk temperature of the refrigerant can be several tens of degrees. This temperature difference is much higher than the one observed in the typical desuperheatmg process inside of standard air source condensers (air-to-refrigerant bulk temp), which in turn can be just some few degrees.

The fact that the condensation process can start before the refrigerant enters to the condenser is of importance for the efficiency increase of air source condensers, since more area of the condenser will be subsequently intended to continue the saturated condensation process, which has higher heat transfer coefficients than the single-phase desuperheating process between the hot gas and air.

To allow the heat transfer process, a desuperheater is located in an open cavity condensation water pool where the cold water from the evaporator can drop and be in contact with the surface of the desuperheater, allowing the condensation of the gas, and the evaporation of part of the water.

An exemplary embodiment of an air-conditioner, in particular a portable air-conditioner with such an external desuperheater is shown in Figure 3. In Fig. 3, 301 is a compressor,

302 is an air source condenser, 303 is an external desuperheater, 304 is a condensation water pool where the desuperheater is located and where the heat transfer process takes place, 305 is a condensed water pipe from evaporator at low temperature, 306 is a condenser fan. The desuperheater heat exchanger 303 can in one embodiment be placed in an open pool 304, where the condensed water that drops from the evaporator is released by a pipe 305. In the pool, the heat exchange process takes place due to the large temperature difference between both fluids. Eventually, part of the condensed water is evaporated while the hot gas starts to condensate.

The desuperheater section is located in the bottom side after the condenser 302, which allows the proper dragging of the evaporated moisture by the air stream coming from condenser. At these conditions, the air stream flowing through the condenser has higher temperature and lower relative humidity, therefore its capacity to retain the evaporated water that is generated in the desuperheater is also higher.

The design of the desuperheater comprises a pipe heat exchanger with one or more passes, mounted inside of an open water pool. Further it is possible to adjust the shape of the desuperheater heat exchanger 303 can differ according the geometry and space of the air condition unit in which the desuperheater 303 is located.

Other possible variants can include different geometries of the desuperheater 303, like the use of different types of fins or internal geometries inside of pipes (micro finned internal surfaces), in order to increase the heat transfer area of the desuperheater 303.

Additionally, the water pool can also adopt different configurations, depending of the particular geometry of the unit and the relative position of other components into the system. In that sense, the desuperheater can have rectangular, cylindrical of any other design. Two possible options are presented in the figures 4 and 5.

Under certain humidity conditions, the desuperheater may not be able to remove all the condensate generated by the evaporator. In order to prevent a limited performance of the moisture evaporative system at high humidity conditions, the system can be modified to include a water tank in the bottom of the condenser.

In figure 4, 401 represents a compressor, 402 is an air source condenser, 403 is a desuperheater, 404 is a condensation water pool, 405 is a condensed water pipe from evaporator, 406 is the discharge line from compressor, 407 is the noise insulation coat that wraps the compressor.

Figure 5 shows also a possible variation in which can be included the possibility of using an auxiliary water tank which can store the non-evaporated water in case of extreme humidity conditions.

In figure 5, 501 is the compressor, 502 is a cylindrical type condenser, 503 is the desuperheater, 504 is the condensation water pool, 505 is the condensed water pipe from evaporator, 506 is the discharge line from compressor, 507 is the noise insulation coat that wraps the compressor, 508 is a noise insulation material around the compressor, 509 is an auxiliary water tank to recover the non-evaporated water, 510 is the base for the condenser fan, 511 is part of the structure that holds all components of the system. In accordance with some embodiments a coating element can be wrapped around the pipes that connect the desuperheater to the compressor and the desuperheater to the condenser.

The apparatus as described herein can be configured to allow condensed water dripping from the evaporator to be released over the pipes covered by the coating element allowing the increase of the heat transfer area of the desuperheater, and facilitating the evaporation and removal of the condensed water through the hot air steam that flows from condenser.

Figure 6 shows a possible configuration of such an embodiment with a coating material over connection pipes.

In figure 6, 601 represents the compressor, 602 represents the air source condenser, 603 represents the desuperheater, 604 represents the water pool, 605 represents the condensed water pipe from evaporator, 606 represents the condenser fan, 607 represents the coating material covering the discharge pipe and the connection between the desuperheater and condenser.

In figure 6, the air stream after condenser has at low relative humidity and high temperature which allows the proper dragging of the evaporated moisture by the air stream coming from condenser.

The material of the coating element can be any natural or synthetic fabric manufactured with a cylindrical shape or with a flat mesh wrapped around the pipes, allowing the temporary retention of the water around the pipes while the evaporation of the water takes place. Alternatively to the coating element, the pipes can be coiled by a helix shaped fin that can allow the dripping of the cold water from evaporator and its evaporation by the heat exchange with the hot surface of the finned tube.

Figure 7 shows a possible embodiment of the coating element over the connection pipes.

In accordance with another embodiment a water pump system can be added to spray the non-condensed water from the auxiliary tank to the top of the condenser, where the pumped water is allowed to drip over the condenser surface. In such an embodiment, the non- evaporated water can continue cooling down the temperature of the condenser surface, once the refrigerant is on saturated conditions, and simultaneously the system can pump water through the air stream that crosses the condenser. Figure 8 shows an embodiment including an auxiliary water pumping system to remove the non-condensed water.

The spray of the water has to be done preferable over the inner row of the condenser, to avoid that the water droplets that fill the gaps between fins can block the air path, creating additional pressure drops in the air stream, and decreasing the condenser air flow rate. In figure 8, 801 represents the compressor, 802 is the condenser, 803 is the desuperheater, 804 is the condensation water pool, 805 is the condensed water pipe from evaporator, 806 is the auxiliary water tank, 807 is the water pump, 808 is the water pipe from the tank to the spray system, 809 is the water spray element in condenser top, 810 is the water drainage system.

In accordance with other embodiments it is possible to take advantage of the low

temperature of the condensed water coming from evaporator to decrease the condensing pressure of the cycle in other ways. For example the effect can be achieved alternatively by the release first the condensed water over the condenser. Then, the remaining non- evaporated water can be collected in a water tank located for example at the bottom side after the condenser, and pumped over the desuperheater water pool. Figure 9 shows an exemplary design of such an embodiment. In figure 9, 901 is the compressor, 902 is the condenser, 903 is the desuperheater, 904 is the non-evaporated water pool, 905 is the condensed water pipe from evaporator, 906 is the auxiliary water tank, 907 is the water pump, 908 is a water pipe from the tank to the desuperheating water pool, 909 is a condenser water spray element placed in condenser top, 910 is the non-evaporated water drainage.

A difference between the embodiment from figure 8 and the one shown in figure 9 is the temperature difference between the heat sources and heat sinks of the different heat rejection sub processes. Constructively the version proposed in figure 9 can have some advantages; however from the energy efficiency standpoint the embodiment shown in figure 8 typically represents a more energy efficient solution.

One limitation in the embodiment shown in figure 9 is that the heat transfer area in de desuperheater typically has to be slightly larger than the one proposed in the solution of figure 8 in order to allow that the bulk temperature of the refrigerant be closer to the thermodynamic equilibrium before the refrigerant enters into the condenser, since the temperature difference between both fluids is smaller.

Using the air-conditioner as described herein provides a practical solution to minimize the size of air cooled condenses, commonly used in portable AC systems, but also for other systems working with Air as coolant media.

The possibility of minimising the condenser size is achieved by providing a zoning of the different heat exchange sub-processes. Also desuperheating of the hot gas delivered by compressor is provided. By carrying out a desuperheating process outside of the condenser, the area and internal volume that typically are intended to this process can be re-assigned to complete the phase change process (condensation) and subcooling inside of the air cooled condensers.

As the 2phase change and subcooling processes have larger heat transfer coefficients, the total area required in the heat rejection process in the condenser will be smaller for a given capacity. In turn, for a given size of condenser, the desuperheater can favour a larger enthalpy difference in the cycle, providing higher cooling capacities in a standard system, without affecting significantly the power consumption of compressor, and therefore, increasing also the cycle efficiency of the refrigeration cycle. On the other hand, the design of the desuperheater allows the effective removal of the undesired condensed water generated in the cooling process; at the same time that the Air conditioner takes advantage of the higher heat transfers coefficients obtained by the evaporation of the water. An advantage of the technology described herein is that the heat rejection process in a portable AC unit can start before the refrigerant enters into the condenser, allowing either the minimization of a standard air cooled condenser size or the increase of cooling capacity for a given condenser size. Using the methods and devices as described herein makes it possible to take advantage of the larger temperature difference between both flows allowing a compact and efficient design of the desuperheater, which allows in turn a more effective condensing process. This effect is achieved by the increase of the heat transfer area destined to perform the 2-phase process of condensation, which provide better heat transfer coefficients and which is normally intended to the single-phase process of desuperheating in a conventional method.

The technology described herein can further improve the conventional method used to remove the undesired condensed water generated in the normal cooling process of an AC system, particularly in portable units.

In accordance with some embodiments a mechanism that splash condensed water between the condenser rows. Through this method, the non- evaporated water is pulverized in small droplets and atomised over the condenser surface, forcing its removal through the air flow stream that crosses the condenser, more than its evaporation.

A drawback of splashing the water could be that the water droplets that move into the air stream can eventually be agglomerated or condensate again over the air exhausts ducts, dripping inside of the ducting system and creating water leak problems for the user.

In addition, to the improvements on the thermodynamic cycle obtained by the use to the technology described herein, there is an additional benefit offered by the reduction of the pressure drop inside of the refrigerant circuits of the condenser, especially for those geometries with small hydraulic diameters like mini tubes or micro-channels. Lower pressure drops leads to lower power consumptions and more efficient systems.

Another advantage of the technology described herein is the possibility to increase the charge of refrigerant, without affecting the condensing pressure, to increase the refrigerant enthalpy difference in the condenser but also in the evaporator, which eventually will allow to increase the cooling capacity of the system. By starting the condensation process in an external desuperheater it is also possible to decrease the heat loses from compressor surface, increasing its reliability without affecting its mechanical performance. The designs proposed for the desuperheater have the additional advantage that

prevents/reduce the resonances introduced by the tangential vibrations due the varying torque produced by the compressor motor.

Hence, in accordance with the above an alternative to conventional methods that helps to decrease the condensing temperature of the cycle in a more efficient way is provided. This is achieved by an efficient zoning of the heat rejection processes using the condensed water that drips from the evaporator.

Hence a more efficient energy exchange process carried out by an external desuperheater installed between compressor and condenser. This method takes advantage of the larger temperature difference between the hot discharge gas delivered by the compressor, and the condensed chilly water dripping from the evaporator surface.

Claims

1. An air-conditioner comprising a compressor (301), and a condenser (302), the air conditioner being characterized by a desuperheater (303) provided in a flow path from the compressor to the condenser.

2. The air-conditioner according to claim 1, wherein the air-conditioner is a portable air- conditioner.

3. The air-conditioner according to claim 1 or 2, wherein the desuperheater is located in an open cavity (304).

4. The air-conditioner according to claim 3, wherein the air-conditioner is adapted to feed condensation water to the open cavity.

5. The air-conditioner according to claim 4, further comprising a pipe (305) adapted to lead condensed water that drops from the evaporator to the open cavity.