Air conditioning assembly

Abstract

A heat exchanger unit for an air conditioning system comprising first and second end plates 250 connected to first and second heat exchangers 200a, 200b. Each heat exchanger comprises a first header 2

Description

Field of the Invention. The present invention relates generally to air conditioning assembly, in particular a fan conditioning assembly. Background There are various types of air conditioning units on the market, from small portable units up to central all-air conditioning systems that distribute air through ducts that are installed throughout a building. Fan coil unit installations are one of the most popular types of central air conditioning systems, with the majority of these installations using ceiling void mounted units. Alternatively cased or recessed units may be provided. The unit is often hidden above ceiling tiles and room air is sucked through open return air grilles in a false ceiling and then returned to the room via ducting, plenums and grilles. A. fan coil assembly typically comprises a unit having heating and cooling coils (heat exchanger), a condensate tray collector, a circulating fan and filter. The fan continuously recirculates air from the surrounding space / ceiling void through the coils. Ventilation is provided by a separate central air handling unit or by drawing it through an outside wall by the unit itself. This type of air conditioning system allows for high cooling capacity, relatively low capital equipment cost and allows for individual control of temperature within particular areas or zones. Fan coil unit installations may have water-side or air -side fan units. A. water-side fan coil unit controls the heating and cooling output by adjusting the water flow7 rate of hot or cold water passing through the heat exchanger. In contrast, an air-side fan coil unit controls the heating and cooling output by adjusting the flow rate of air passing through the heating or cooling heat exchanger. Conventionally the cooling water is generated by means of a separate chiller unit using a refrigeration process to cool water to a temperature lower than the internal ambient temperature target. Hot water is also generated, either by a boiler, heat pump of heat recovery process. Both of these services are connected to each fancoil unit within a building and the flow of either hot or cold water is controlled by valves fitted to each fancoil. However, while satisfactory for purpose, a requirement for carbon neutrality means that it is desirable to provide improvements in energy efficiency for these types of air conditioning units. The largest energy requirement is that required to cool the water within the chiller. Higher energy efficiencies can be achieved by supplying the cold water at a higher temperature. The heating water may be obtained at a lower energy cost if heat pumps or heat recovery systems are used but these require water to be supplied at lower temperatures, closer to room temperature. Furthermore, when the temperature difference between the cooling or heating medium and the air temperature is smaller, lower heat transfer values are achieved. The current way to overcome this is to provide a larger heat exchanger but there are often limitations on space and cost. It is an object of the present invention to provide an air conditioning assembly that overcomes, or at least alleviates, the abovementioned problems. Summary of the Invention. According to a first aspect of the present invention there is provided a heat exchanger unit for an air conditioning system, the unit comprising: a first end plate and a second end plate; a first heat exchanger comprising a first header, a second header and multiple microchannels extending between and in fluid communication with the first and second header, at least one fin being provided between adjacent microchannels, the heat exchanger being connectable to a first fluid transfer medium source; and a second heat exchanger comprising a first header, a second header and multiple microchannels in fluid communication with the first and second header, at least one fin being provided between adjacent microchannels, the heat exchanger being connectable to a second fluid transfer medium source; wherein said first and second heat exchanger are of different sizes and each exchanger is connected to the first and the second end plate. In the context of this disclosure, the term “microchannel” also includes “minichannels” and relates to a channel having a hydraulic diameter of less than 15mm, preferably less than 10 mm, more preferably being l-10mm. Preferably, the larger heat exchanger is connectable to a cooling medium source and the smaller heat exchanger is connectable to a heating medium source. More preferably, the width and height of each heat exchanger is substantially the same to enable easy connection to the same end plates and to provide a front and rear surface area that is identical but the depth / breadth of the larger heat exchanger is greater than that of the smaller heat exchanger. Each heat exchanger may be tilted with respect to each end plate, i.e. the heat exchangers extend between the end plates at an angle in-between the vertical and horizonal planes of the end plates. Preferably, the angle of tilt of both heat exchangers is the substantially the same, i.e. the heat exchangers lie parallel to each other between the end plates. The angle may be any angle between the horizontal and vertical planes. More preferably, the angle of tilt is equal to or more than 28 degrees from the vertical plane. The heat exchangers may be arranged horizontally. The first and second headers of each heat exchanger are preferably respectively connected by any suitable means to the first and second end plates. Preferably, the first header of each heat exchanger is provided with appropriate pipework and control valves for connection to the first and second fluid transfer medium source. Additionally, the fins of each heat exchanger are preferably provided at a pitch of 6-7 fins per cm (around 17 fins per inch). The tubes of the microchannels are preferably spaced apart by a gap of 8-12mm, preferably around 10mm, with the fins filling this gap. Preferably, the fins are provided with a hydrophilic coating. Such hydrophilic topcoats lower surface friction, which allows condensation or environmental water to slide off the surface of the fin. Any suitable hydrophilic coating known in the art may be applied to the fins. It is also preferable to provide fins that are louvered to increase surface capacity. A second aspect of the present invention provides an air conditioning assembly comprising a casing with a front and a rear opening, a filter over the rear opening, at least one fan and a heat exchanger unit according to the first aspect of the invention, the at least one fan and heat exchanger being provided between the front and rear openings. The end plates of the heat exchanger according to the first aspect of the present invention are preferably installed within and / or attached to the casing. Any suitable casing may be used but preferably the casing is a rectangular box casing connectable to, or provided with, a discharge plenum. Preferably, the casing is made of aluminium. The heat exchanger unit may be provided upstream or downstream of the at least one fan. It is to be appreciated that the air conditioning assembly may be provided with one or more components of a conventional air conditioning assembly, such as being connectable to ductwork for the delivery and return of air to the casing and / or connectable to an air handling unit. The assembly should also be connectable to an appropriate pipework for delivery of the first and second fluid transfer mediums to and from the heat exchanger unit. Brief Description of the Drawings For a better understanding of the present invention and to show more clearly how7 it may be carried into effect, reference will now be made by way of example only to the accompanying drawings in which: Figure 1A is a perspective view7 of a typical prior art fan coil assembly ; Figure IB is a schematic cross-sectional view7 of a conventional fan coil assembly; Figure 1C is a perspective view of a heat exchanger for a conventional fan coil assembly; Figure 2 is a schematic diagram of a fan coil air conditioning system of the prior art installed within a room; Figure 3 is a perspective top view7 of a single microchannel heat exchanger for a fan conditioning assembly according to an embodiment of the present invention; Figure 4 is an exploded view7 of a pair of microchannel heat exchangers for a fan conditioning assembly according to an embodiment of the present invention; Figure 5 illustrates the pair of microchannel heat exchangers shown in Figure 4 assembled into heat exchanger unit; Figure 6 is an exploded view of the components of a fan conditioning assembly according to an embodiment of the present invention that includes the heat exchanger unit of Figure 5; Figure 7 is a schematic side perspective view of a fan conditioning assembly fitted with a microchannel heat exchanger unit according to an embodiment of the present invention, and Figure 8 is a rear view of a fan conditioning assembly fitted with a microchannel heat exchanger according to the invention. Detailed Description The present invention provides a modified fan air conditioning assembly that has improved energy efficiency compared with conventional systems. Figures 1A and 1B of the accompanying drawings illustrate a traditional fan coil unit 1 with a finned tube heat exchanger design. Figure 2 illustrates the installation of this type of unit within a room 50, such as an office. The fan coil unit has a casing 5 with a rear opening through which air can enter the unit. The unit is installed in a plenum 52 above a suspended ceiling 54 and air is able to enter the room 50 via grilles 56a and be recycled back into the plenum 52 through return grilles 56b. Air may enter the rear of the casing from the outside (not shown) or a central air handling unit 60 may deliver air to and from the room plenum 52 containing the fan coil unit via a series of pipework 58. The arrow's included in Figure 2 illustrate air flow throughout the room. In the illustrated example, a single fan coil unit is shown but multiple units would normally be provided. Furthermore, the air handling unit may be connected to other fan coil units provided in other parts of a building. The fan coil unit has a filter 8 over the rear opening, a heat exchanger 2, one or more fans 4 and a discharge plenum 6. In operation, air is drawn through the filter 8 and the heat exchanger 2 by a fan 4. The heat exchanger 2 comprises heating and cooling coils 2 which are provided across the casing and are connected to pipes 12, 14 for the supply of hot or cold water to the coils. The flow of either hot or cold water is controlled by control valves fitted to each pipe. The fan coil heat exchanger 2 is provided with four connection pipes and two separate path streams to facilitate both the water and cold-water supplies (see Figures IB and IC). The illustrated example shows a draw-through system wherein the fan is positioned upstream of the rear opening and heat exchanger to draw7 air through the system. However, the fan may be placed downstream and blow7 the air through the unit. The filter 8 removes dust particles to both clean the air and protect the coil from blockage. The air temperature increases or decreases as it passes through the heat exchanger 2 based on the demands of the system controls and is then discharged via the discharge plenum 6 through the front of the unit and to the surrounding room 50. Heat exchangers for current ducted fan coils are manufactured from seamless copper tube mechanically expanded into aluminium fins, as illustrated in Figure IC. The fins are vertical and enable condensation formed during cooling of the air to fall to the base of the unit and be collected in a drip tray, often connected to an overflow pipe Cooling water for air conditioning is generated by means of a separate chiller unit using the refrigeration process to cool water to a temperature lower than the internal ambient temperature target. Hot water for heating is also generated, either by a boiler, heat pump or heat recovery process. Both these services are connected to each fan coil unit 1 within a building via pipework 12, 14. These types of fan coil unit air conditioning assemblies are extremely popular but environmental pressures mean that it is desirable to further improve the energy efficiency of heating, ventilating and air conditioning systems (“HVAC”) provided to a room. The modified fan air conditioning assembly according to the present invention incorporates a microchannel or minochannel heat exchanger 200 to improve energy efficiency of the device. Microchannel heat exchangers are known and have previously been used for refrigeration purposes. The microchannels have a hydraulic diameter of less than 15mm, preferably less than 10 mm, more preferably being 1- 1 Omm, for transport of the heat transfer medium (refrigerant) and are provided with fins between the channels. Each exchanger consists of a manifold with a header at each end. Pipework delivers refrigerant to one of the headers and this then flows through the channels, back down the opposing header and back through the microchannels. These microchannel heat exchangers are more efficient relative to their size when compared to the finned tube coils illustrated in Figures 1A to IC. This type of heat exchanger is also more compact, lighter in weight and easier to repair and clean. However, it is a challenge to use this technology within fan coil assemblies in order to take advantage of this extra efficiency whilst maintaining the footprint of the traditional four pipe finned tube heat exchanger. Microchannel heat exchangers hold condensation within the fins of the coil which reduces the efficiency of the heat exchanger as the condensate then blocks the flow of air across a large section of the heat exchanger. In this respect, the fins are tightly packed and the shape of the channels causes water to be retained. Condensate water can bridge between the fins of the microchannel heat exchanger and not drain away. This reduces the efficiency of the microchannel when used for cooling and increases the air side pressure drop. In contrast, conventional finned coil heat exchangers have vertical fins which allow gravity to remove any condensate formed by it falling under gravity into a condensate tray. Increasing the fin pitch of the microchannel heat exchanger is possible but is limited by the fact that it reduces the efficiency of the heat exchanger and reduces the space saving benefit provided by the use of such a device. Current copper tube aluminium finned heat exchangers can easily have their heating and cooling circuits combined into the same heat exchanger. This cannot be achieved with microchannels. Furthermore, the airside pressure drop on microchannel heat exchangers can be higher than finned coil heat exchangers, requiring higher fan power inputs to overcome the increase in air side pressure. The inventors have arrived at a modified heat exchanger for installation within an air conditioning unit that addresses these problems. The solution to maximi sing efficiency relative to space is a use one or more of a combination of solutions within the air conditioning assembly. This is illustrated in Figures 3 to 8 of the accompanying drawings. Identical features to those already discussed in relation to Figures I to 2 are given the same reference numerals for the sake of simplicity. Each fan air conditioning assembly is provided with two differently sized microchannel heat exchangers 200a, 200b to one pair of endplates 250 which are then incorporated into a casing 5 (see Figures 6 to 8). A larger heat exchanger 200b is provided for the cooling medium and a smaller heat exchanger 200a is provided for the heating medium. This gives maximum utilisation of space and allows the fixing of water valves to the exterior of the unit in the traditional way. In a preferred embodiment and as shown in Figures 4 and 5, the width and height of each heat exchanger is substantially the same to enable easy connection to the same end plates 250 and to provide a front and rear surface area that is identical but the depth / breadth of the larger heat exchanger is greater than that of the smaller heat exchanger. Example microchannels for incorporating into heat exchangers of the present invention are microchannels with a diameter of 1.7mm x 5mm and 2mm x 10mm, but are not limited thereto. Each heat exchanger 200a, 200b is tilted with respect to each end plate 250, i.e., the heat exchangers extend between the end plates at an angle in-between the vertical and horizonal planes of the end plates. The angle of tilt of both heat exchangers is the substantially the same, i.e., the heat exchangers lie parallel to each other between the end plates. More preferably, the angle of tilt is equal to or more than 28 degrees from the vertical plane, through to the horizontal. However, any angle between vertical and horizontal may be used. This angle of tilt allows the condensate to drain away with the assistance of gravity. It also maximises the microchannel face surface air, minimising air side pressure drop across it. Additionally, the tilt at the top is provided in the direction of airflow, giving further assistance to the condensate drainage. An angle of 28 degrees or more is best for drainage but there are also advantages to providing horizontal heat exchangers, such as enabling the use of ambidextrous coils (the same coil can be used for left and right handed units). The first and second headers 202, 204 of each heat exchanger 200a, 200b are connected by any suitable fixing means to the first and second end plates 250. For example, in the illustrated embodiment, mounting clips 242 connect the headers to the end plates by rivets 244. The first header 202 of each heat exchanger 200a, 200b is provided with appropriate pipework 120, 140 and control valves for connection to the first and second fluid transfer medium source. A pipe support plate 248 and air gap sealing plate 246 are also provided to provide satisfactory connection of the pipes to the end plates. Additionally, the tubes of each the heat exchanger have fins 206 (see Figure 3) which are preferably provided at a pitch of 6-7 fins per cm (around 17 fins per inch). The tubes of the microchannels are preferably spaced apart, by a gap of 8-12mm, preferably around 10mm, with the fins filling this gap. A minimum reduction in fin pitch is made to ensure condensate drains away from the microchannel heat exchanger. The reduction in fin pitch of the microchannel improves both the water retention issue and the air side pressure drop issue. The fins may be provided with a hydrophilic coating to lower surface friction, which allows condensation or environmental water to slide off the surface of the fin and may also be louvered to increased surface capacity. Tests carried out on various sizes of air conditioning units having the dual microchannel heat exchangers according to the invention have provided at least a 30% increase in performance for a microchannel heat exchanger relative to an equivalently sized finned tubed heat exchanger, with lower water side pressure drops and equivalent air side pressure drops. Further modifications to the fan air conditioning assembly may be made without departing from the principles embodied in the examples described and illustrated herein.

Claims

1. A heat exchanger unit for an air conditioning system, the unit comprising:a first end plate and a second end plate;a first heat exchanger comprising a first header, a second header and multiple microchannels extending between and in fluid communication with the first, and second header, at least one fin being provided between adjacent microchannels, the heat exchanger being connectable to a first fluid transfer medium source; anda second heat exchanger comprising a first header, a second header and multiple microchannels in fluid communication with the first and second header, at least one fin being provided between adjacent microchannels, the heat exchanger being connectable to a second fluid transfer medium source;wherein said first and second heat exchanger are of different sizes and each exchanger is connected to the first and the second end plate.

2. The heat exchanger unit as claimed in claim 1, wherein the microchannels of the heat exchangers have a hydraulic diameter of less than 15mm, preferably less than 10 mm, more preferably being l-10mm.

3. The heat exchanger unit as claimed in claim 1 or claim 2, wherein the larger heat exchanger is connectable to a cooling medium source and the smaller heat exchanger is connectable to a heating medium source.

4. The heat exchanger unit as claimed in any one of claims 1 to 3, wherein the width and height of each heat exchanger is substantially the same to enable easy connection to the same end plates and to provide a front and rear surface area that is identical but the depth / breadth of the larger heat exchanger is greater than that, of the smaller heat exchanger.

5. The heat, exchanger unit as claimed in any one of the preceding claims, wherein the heat exchanger lies horizontal to the end plate.

6. The heat exchanger unit as claimed in any one of claims 1 to 4, wherein each heat exchanger is tilted with respect to each end plate, i.e. the heat exchangers extendbetween the end plates at an angle in-between the vertical and horizonal planes of the end plates.

7. The heat exchanger unit as claimed in claim 6, wherein the angle of tilt of both heat exchangers is the substantially the same, i.e. the heat exchangers lie parallel to each other between the end plates.

8. The heat exchanger unit as claimed in claim 6 or claim 7, wherein the angle of tilt is equal to or more than 20 degrees from the vertical plane, more preferably at least 28 degrees.

9. The heat exchanger unit as claimed in any one of the preceding claims wherein the first and second headers of each heat exchanger are respectively connected to the first and second end plates.

10. The heat exchanger unit as claimed in any one of the preceding claims, wherein the first header of each heat exchanger is provided with appropriate pipework and control valves for connection to the first and second fluid transfer medium source.

11. The heat exchanger unit as claimed in any one of the preceding claims, wherein each heat exchanger is provided with a plurality of fins, wherein the fins of each heat exchanger are provided at a pitch of 6-7 fins per cm (around 17 fins per inch ).

12. The heat exchanger unit as claimed in any one of the preceding claims wherein adjacent microchannels are spaced apart by a gap of 8-12mm, preferably around 10mm, with the at least one fin filling this gap.

13. The heat exchanger unit as claimed in any one of the preceding claims, wherein the at least one fin is provided with a hydrophilic coating.

14. The heat exchanger unit as claimed in any one of the preceding claims, wherein the at least one fin is louvered to increase surface capacity.

15. An air conditioning assembly comprising a casing with a front and a rear opening, a filter over the rear opening, at least one fan and at least one heat exchanger unit, the at least one heat exchanger unit being as claimed in any one of the preceding claims, the at least one fan and heat exchanger being provided between the front and rear openings.

16. The air conditioning assembly as claimed in claim 15, wherein the end plates of the heat exchanger are installed within and / or attached to the casing.

17. The air conditioning assembly as claimed in claim 15 or claim 16, wherein the casing is a rectangular box casing connectable to, or provided with, a discharge plenum.

18. The air conditioning assembly as claimed in claim 15, 16 or 17, wherein the heat exchanger unit is provided upstream or downstream of the at least one fan.

19. The air conditioning assembly as claimed in any one of the claims 15 to 18 further comprising ductwork connectable to the assembly for the delivery and return of air to the casing and / or connectable to an air handling unit.

20. The air conditioning assembly as claimed in any one of claims 15 to 19 further comprising pipework for delivery of the first and second fluid transfer mediums to and from the heat exchanger unit.

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