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Title:
SMART COOLING SYSTEM
Document Type and Number:
WIPO Patent Application WO/2017/162996
Kind Code:
A1
Abstract:
A cooling system for a building (3). A desiccant regenerating section (2) is used to regenerate diluted desiccant liquid into concentrated desiccant liquid using a solar or waste heat source (30), and a desiccant cooling section (1) is used to cool air and comprises a first mass-heat exchanger (11) and a second mass-heat exchanger (12). The first mass-heat exchanger (11) comprises a scavenging air pathway for evaporatively cooling a scavenging or return air stream which is then used to cool the concentrated desiccant liquid, and a process air pathway for dehumidifying a first incoming air stream (20) using the cooled concentrated desiccant liquid. The second mass-heat exchanger (12) comprises a first air pathway for evaporatively cooling the first incoming air stream using water, and an outlet for outputting the cooled air stream (16) to the building (3).

Inventors:
ELSARRAG ESAM (QA)
AL-HORR YOUSEF (QA)
Application Number:
PCT/GB2016/051874
Publication Date:
September 28, 2017
Filing Date:
June 23, 2016
Export Citation:
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Assignee:
GULF ORGANISATION FOR RES AND DEV (QA)
ELSARRAG ESAM (QA)
AL-HORR YOUSEF (QA)
International Classes:
F24F3/16
Domestic Patent References:
WO2009094032A12009-07-30
WO2002066901A12002-08-29
Foreign References:
US20150047382A12015-02-19
US20140245769A12014-09-04
US20140150481A12014-06-05
US20150233588A12015-08-20
US6134903A2000-10-24
Attorney, Agent or Firm:
GAUNT, Thomas et al. (GB)
Download PDF:
Claims:
CLAIMS

1. A cooling system for cooling air for a building, comprising :

a desiccant regenerating section for regenerating diluted desiccant liquid into concentrated desiccant liquid using a solar or waste heat source; and

a desiccant cooling section comprising a first mass- heat exchanger and a second mass-heat exchanger, wherein:

the first mass-heat exchanger comprises:

a scavenging air pathway for evaporatively cooling a scavenging or return air stream using water, the cooled scavenging or return air stream being used to cool the concentrated desiccant liquid, and

a process air pathway for dehumidifying a first incoming air stream using the cooled concentrated desiccant liquid; and the second mass-heat exchanger comprises:

a first air pathway for receiving the dehumidified first incoming air stream and evaporatively cooling the first incoming air stream using water; and

an outlet for outputting a cooled air stream for cooling the building.

2. A cooling system according to claim 1, wherein the first incoming air stream travelling through the first air pathway of the second mass-heat exchanger is directly evaporatively cooled to produce the cooled air stream.

3. A cooling system according to claim 1 or 2, wherein the second mass-heat exchanger further comprises a second air pathway for receiving a second incoming air stream.

4. A cooling system according to any preceding claim, wherein the evaporatively cooled first incoming air stream cools the second incoming air stream in the second mass-heat exchanger. 5. A cooling system according to any preceding claim, wherein the second air pathway is configured to dehumidify the second incoming air stream using the cooled concentrated desiccant liquid to produce a second cooled air stream. 6. A cooling system according to any preceding claim, wherein the desiccant cooling section further comprises a fan arrangement for generating airflow for forming the air streams . 7. A cooling system according to claim 6, wherein the fan arrangement comprises a first fan for generating the first incoming air stream.

8. A cooling system according to claim 6 or 7, wherein the fan arrangement comprises a second fan for generating the scavenging air stream.

9. A cooling system according to any one of claims 6 to 8, wherein the fan arrangement comprises a third fan for generating the second incoming air stream.

10. A cooling system according to any preceding claim, wherein the desiccant regenerating section comprises:

a solar or waste heat heating circuit; and

an evaporator for dehydrating the diluted desiccant liquid into concentrated desiccant liquid using heat from the solar or waste heat heating circuit.

11. A cooling system according to claim 10, wherein the solar or waste heat heating circuit comprises a heating surface for heating a drying air stream, and the evaporator dehydrates the diluted desiccant liquid using the heated drying air stream.

5 12. A cooling system according to claim 11, wherein the desiccant regenerating section comprises a mass-heat exchanger having a first heating pathway and a second heating pathway, wherein the heated drying air stream is directed through both the first heating pathway and a second heating 10 pathway,

wherein the diluted desiccant liquid is exposed to air in the first heating pathway for dehydrating it.

13. A cooling system according to any one of claims 10 to 15 12, wherein the solar or waste heat heating circuit comprises a solar pond.

14. A cooling system according to claim 10, wherein the solar or waste heat heating circuit comprises a solar heater for

20 heating the diluted desiccant liquid, and the evaporator comprises a packed tower, a spray tower, or a falling film tower for dehydrating the heated desiccant liquid.

15. A cooling system according to any preceding claim, 25 wherein the desiccant liquid is seawater bittern.

16. A cooling system according to any preceding claim, comprising hybrid heat-mass exchanger for dehumidifying incoming air using the desiccant liquid through a membrane.

30

17. A cooling system substantially as hereinbefore described with reference to the accompanying drawings.

Description:
SMART COOLING SYSTEM

[001] The present invention concerns a cooling system for a building and, in particular, a desiccant air-conditioning system.

[002] Conventional air-conditioning systems for buildings that use refrigerants consume a lot of electricity. As such, there is considerable interest in improving the efficiency of air-conditioning systems in order to meet sustainability targets .

[003] One area of interest involves the use of desiccant cooling and dehumidification . Desiccant units do not require ozone-depleting refrigerants, and may make use of solar thermal energy, or waste heat, thus lowering peak electric demand .

[004] Typically a desiccant cooling system comprises a packed tower for dehumidification using a desiccant, an evaporative cooling heat exchanger, a solar regenerator and a thermal store. The principle of liquid desiccant cooling is that a hygroscopic liquid is brought into contact with air in a dehumidifier device. The air becomes drier, which increases its comfort level in humid climates. The dry air can also be subsequently cooled by evaporating water into it. To maintain the desiccant capacity of the desiccant liquid, it has to be regenerated, and this can be done using solar energy to drive off moisture.

[005] Unfortunately, the scale of implementation of current desiccant systems is very modest. One issue is that there are safety and environmental compatibility issues with conventional desiccant compounds. For example, typically lithium salts are used as desiccant compounds which have to be prevented from coming into contact with human occupants or crops. A further issue is that a large area of solar collection would be needed for regeneration of the desiccant. [006] The present invention therefore seeks to provide a more energy efficient cooling system for buildings, such as a multi-functional cooling system including a plurality of heat and mass exchangers (HMX) that can tackle the ambient conditions, be automatically switched, and can operate efficiently in all climate conditions. Embodiments of the invention may include a series of HMX fabricated from different materials and managed by smart control system.

[007] According to a first aspect of the present invention there is provided a cooling system for cooling air for a building, comprising: a desiccant regenerating section for regenerating diluted desiccant liquid into concentrated desiccant liquid using a solar or waste heat source; and a desiccant cooling section comprising a first mass-heat exchanger and a second mass-heat exchanger, wherein: the first mass-heat exchanger comprises: a scavenging air pathway for evaporatively cooling a scavenged or return air stream using water, the cooled scavenging or return air stream being used to cool the concentrated desiccant liquid, and a process air pathway for dehumidifying a first incoming air stream using the cooled concentrated desiccant liquid; and the second mass-heat exchanger comprises: a first air pathway for receiving the dehumidified first incoming air stream and evaporatively cooling the first incoming air stream using water; and an outlet for outputting a cooled air stream for cooling the building.

[008] In this way, the present invention provides an innovative approach to cooling buildings in hot climates that is suitable for all weather conditions, hence reducing energy consumption and costs. Importantly, the present invention allows for the use of seawater liquid desiccants, with the principal advantage of these compounds being that they are environmental compatible, thereby enabling regeneration and storage systems to be integrated in coastal areas, as is already done with normal solar salt works. Consequently they will allow much larger solar-powered cooling systems than previously achieved, enabling the exploitation of large coastal areas on 'city scale' without undue environmental impacts. Another important advantage achievable with embodiments of the invention is that they may contain a series of anti-corrosive heat and mass exchangers that provide multi-stage cooling based on the set and ambient conditions. Furthermore, all scavenging air used through the HMXs may be captured in one plenum and utilised to cool the hot desiccant and/or a DX condenser coil. Moreover, the water used for evaporative cooling may be, for example, sea water, ground water, or pure water. [009] Furthermore, as a result of the high efficiency achieved in embodiments of the present invention, the cooling system may be applied to a variety of applications, including large venues such as football stadiums and other semi-outdoor spaces, as well as cooling of greenhouses for crop production.

[0010] In embodiments, the first incoming air stream travelling through the first air pathway of the second mass- heat exchanger is directly evaporatively cooled to produce the cooled air stream. This may both cool and re-humidify the dry process air, which may be preferable, particularly in dry, arid climates. The humidified air could then be used to cool a desiccant coil or DX coil, or to provide outdoor cooling or to cool a green house. [0011] In embodiments, the second mass-heat exchanger further comprises a second air pathway for receiving a second incoming air stream. [0012] In embodiments, the evaporatively cooled first incoming air stream cools the second incoming air stream in the second mass-heat exchanger. This may provide the cooled air stream through indirect evaporative cooling or produce a second cooled air stream.

[0013] In embodiments, the second air pathway is configured to dehumidify the second incoming air stream using the cooled concentrated desiccant liquid to produce a second cooled air stream.

[0014] In embodiments, the desiccant cooling section further comprises a fan arrangement for generating airflow for forming the air streams. [0015] In embodiments, the fan arrangement comprises a first fan for generating the first incoming air stream.

[0016] In embodiments, the fan arrangement comprises a second fan for generating the scavenging air stream.

[0017] In embodiments, the fan arrangement comprises a plenum that collects the scavenging air stream.

[0018] In embodiments, the system comprises a conventional DX or chilled water system electrical or solar driven systems .

[0019] In embodiments, the first heat and mass exchanger may comprise a membrane to enhance the transfer of moisture between the humid air and dry air streams. [0020] In embodiments, the air moves in plenums to reduce the pressure drop. [0021] In embodiments, all air entries and exits and fan speeds are automatically controlled via motorised dampers and variable speed drives. The system allows for higher air flow rates than normal to provide sufficient, efficient and effective cooling using low energy. In other words, the system is adapting water flow rates and air flow rates to meet the set requirements based on the ambient conditions.

[0022] In embodiments, the fan arrangement comprises a third fan for generating the second incoming air stream.

[0023] In embodiments, the desiccant regenerating section comprises: a solar or waste heat heating circuit; and an evaporator for dehydrating the diluted desiccant liquid into concentrated desiccant liquid using heat from the solar or waste heat heating circuit. In this way, solar thermal energy may be used for regeneration which thereby lowers electric demand .

[0024] In embodiments, the solar or waste heat heating circuit comprises a heating surface for heating a drying air stream, and the evaporator dehydrates the diluted desiccant liquid using the heated drying air stream.

[0025] In embodiments, the desiccant regenerating section comprises a mass-heat exchanger having a first heating pathway and a second heating pathway, wherein the heated drying air stream is directed through both the first heating pathway and a second heating pathway, wherein the diluted desiccant liquid is exposed to air in a counter manner in the first heating pathway for dehydrating it. The second heating pathway which is not exposed to the desiccant liquid thereby maintains the temperature of the heat exchanger.

[0026] In embodiments, the solar or waste heat heating circuit comprises a solar pond.

[0027] In embodiments, the solar or waste heat heating circuit comprises a solar heater for heating the diluted desiccant liquid, and the evaporator comprises a packed tower, a spray tower, or a falling film tower for dehydrating the heated desiccant liquid.

[0028] In embodiments, the desiccant liquid is seawater bittern .

[0029] In embodiments, the desiccant liquid is a mixture of sea water bittern and concentrated hygroscopic salts.

[0030] In embodiments, the system further comprises a hybrid heat-mass exchanger for dehumidifying incoming air using the desiccant liquid through a membrane.

[0031] Illustrative embodiments of the present invention will now be described with reference to the accompanying drawings in which:

Figure 1 shows a cooling system according to a first illustrative embodiment of the present invention;

Figure 2 shows an alternative regeneration section according to a second embodiment of the invention; and

Figure 3 shows a schematic diagram of an example arrangement for generating desiccant for use in the cooling system described in relation to Figures 1 and 2.

[0032] Figure 1 shows a cooling system according to a first illustrative embodiment of the present invention. The cooling system comprises a cooling section 1 and a desiccant regeneration section 2. The sections are in fluid communication with one another so that used weak desiccant fluid from the cooling section 1 can flow through pipe 21 back to the desiccant regeneration section 2 for regeneration. The regenerated concentrated desiccant is then provided from the desiccant regeneration section 2 back to the cooling section 1 through pipe 22. [0033] Cooling section 1 is connected to a building's interior or space 3 through conditioned air duct or unit outlet 4. Air from the interior of the building is also recycled through return air duct 5. The cooling and de- humidification process using cooling section 1 will now be described.

[0034] Return air from the interior space of the building or fresh air from outside the building is drawn by secondary fan 6 through scavenging air inlet 19 and then through a second pathway of secondary heat-mass exchanger 11 (HMX-2) . This forms a so-called scavenging air stream. Valves are provided in return air duct 5 to control the levels of return air and fresh air in the scavenging air stream. The scavenging air stream is evaporatively cooled via water sprayers 9. The cooled scavenging air is then directed over cooling coil 7 to cool the regenerated hot concentrated desiccant delivered through pipe 22 either directly or indirectly (waste energy recovery system) . Such a waste energy recovery system could also be enhanced by indirect or direct evaporative cooling. The scavenging air is then exhausted through secondary fan 6.

[0035] Relatively warm and humid fresh air to be processed (cooled) enters through process air inlet 20 and is drawn through a first pathway of heat-mass exchanger 11 by primary fan 15. The process air stream travels through the first pathway of heat-mass exchanger 11 where the cooled liguid desiccant is sprayed via sprayers 10 which is fed through desiccant pipes 8 from cooling coil 7. As a result, the process air is cooled and dehumidified due to the heat and mass transfer with the liquid desiccant. At the same time, the cooled scavenging air passing though the second pathway of the heat exchanger also assists the dehumidifying and cooling process of the process air as it absorbs heat generated by the absorption process. A further assistance to the dehumidification process may be achieved by the provision of membrane to the HMX-2 to assist the dehumidification process . [0036] The dehumidified and cooled process air is then delivered to another stage to further cool it down. Here, the process air passes to a first pathway of primary heat-mass exchanger 12 (HMX-1) where it is either indirectly or directly evaporatively cooled via water sprayers 9 as it passes through the first pathway of primary heat-mass exchanger 12. This utilises direct evaporative cooling which acts to lower the temperature and increases air humidity, which is advantageous in dry, arid climates, where it makes air in the building's interior more comfortable. In alternative embodiments, the dehumidified and cooled process air may also be further cooled down using a conventional vapour compression system or indirect evaporative cooling, or combinations of these and direct evaporative cooling. Indirect evaporative cooling would allow the dehumidified process air to be further cooled without elevating it's humidity .

[0037] The cooled process air is then directed to primary cooling coil 14 to further cool the air, after which the primary fan 15 pumps it through conditioned air duct 4 into the building's interior or exterior space 3.

[0038] At the same time as the above, relatively warm and humid fresh air from outside the building will be drawn through a second pathway of primary heat-mass exchanger 12 (HMX-1) from fresh air inlet 18 through to outlet 13, drawn by an extract fan provided in the outlet 13. Fan 6 and outlet 13 are combined in one exhaust plenum. In this secondary fresh air stream, water or sea water is sprayed via sprayers 10 with cooled concentrated liquid desiccant fed through desiccant pipes 8, acting to cool and dehumidify this air stream. This secondary fresh air stream is also sensibly cooled via heat exchange with the process air stream. The secondary fresh air stream is thereby cooled and may be used to cool different building space or may also be fed into the same building's interior 3.

[0039] Diluted (weak) desiccant liquid used in the cooling process is collected at outlets in the bottom of primary and secondary heat-mass exchanger 11 and 12, which feed into collection pipes 17. Collected diluted (weak) desiccant liquid is then fed to the regeneration section 2 through pipe 21. [0040] In this embodiment, the regeneration section 2 comprises a tertiary heat-mass exchanger 31 (HMX-3) . Warm ambient air enters through inlet 29 drawn by tertiary fan 28. The ambient air is directed to heating coil 26 where it is heated. The heating coil 26 is heated via a solar source 30, such as a solar pond, solar collector or thermal store, and heat is delivered via connection 27. After the air stream is heated, it is splits to two air streams that are directed through paths on different sides of the tertiary heat-mass exchanger 31. The percentage of hot air split for each side is done by control dampers. The diluted desiccant is sprayed on one side of the heat-mass exchanger 31 and the heated air stream removes moisture from the desiccant to concentrate it. The other air stream is used to maintain temperature. The air is then exhausted to the atmosphere with a relatively high humidity through outlet 23. The concentrated and heated desiccant is then collected through outlets in the bottom of tertiary heat-mass exchanger 31, from where it is fed back to the cooling section 1 through pipe 22. [0041] Figure 2 shows an alternative regeneration section according to a second embodiment of the invention. This alternative regeneration section may be similarly connected to the cooling section 1 of Figure 1 through pipes 22 and 21. In this embodiment, the diluted desiccant liquid is delivered through pipe 21 to solar heater/ thermal store 32. The heated dilute desiccant liquid is then fed from the solar heater 32 to a packed tower, spray tower or falling film tower 34, which evaporates off excess liquid to produce hot concentrated desiccant. The hot concentrated desiccant is then re-circulated back to the cooling section 1 through pipe 22.

[0042] Figure 3 shows a schematic diagram of an example arrangement for generating desiccant for use in the cooling system described above. As shown, embodiments of the present invention preferably use sea water bittern from a solar pond as the desiccant liquid source, although the desiccant source could be salt or organic. Desiccant from a solar pond could be directly transferred to a packer or sprayed to evaporate the moisture falling fill. Another option is to use the solar pond heat to a thermal store where it is, then used to regenerate the desiccant when required.

[0043] As will be appreciated from the above, embodiments of the present invention may therefore provide a cooling system for cooling air for a building, comprising: a desiccant regenerating section for regenerating diluted desiccant liquid into concentrated desiccant liquid using a solar or waste heat source; and a desiccant cooling section comprising a first mass-heat exchanger and a second mass-heat exchanger, wherein: the first mass-heat exchanger comprises: a scavenging air pathway for fresh or return air from the conditioned space to be evaporatively cooled using water, such as ground water or sea water. Within the first HMX a liquid desiccant is sprayed in a parallel or a counter manner to the process air. As a result the process air is cooled and dehumidified. Nevertheless, the wasted tempered scavenging air stream is not wasted as it is diverted to cool the concentrated hot desiccant that is produced from the regeneration process. The second mass-heat exchanger comprises: a first air pathway for receiving the dehumidified first incoming air stream from the first heat and mass exchanger. In this stage, the dehumidified process air will be indirectly cooled in the heat and mass exchanger via a scavenging or return air stream that is evaporatively cooled using water, such as sea water. The cooled air stream is either enhanced by evaporative cooling or by a chilled coil, or supplied directly to the building depending on its conditions .

[0044] It will be understood that the embodiment illustrated above shows applications of the invention only for the purposes of illustration. In practice the invention may be applied to many different configurations, the detailed embodiments being straightforward for those skilled in the art to implement.

[0045] In this respect, for example, although Figure 1 shows fans at either end of the cooling section for drawing air there through, other fan positions are possible. For example, a single fan could be provided between the primary and secondary heat-mass exchangers for sucking dehumidified air through the secondary heat-mass exchanger and pushing it through the primary heat-mass exchanger.

[0046] Furthermore in the above illustrative embodiment, the heat-mass exchangers are provided as plate heat exchangers, which have first and second pathways and can simultaneously handle two air streams and two liquid streams. However, alternative heat-mass exchangers are possible. For instance, the system may incorporate a hybrid heat-mass exchanger where fresh air is dehumidified via the liquid desiccant and a membrane. The moisture is transferred from the fresh air to dry air through a membrane. The liquid desiccant is sprayed the over the hybrid heat-mass exchanger, as a result the fresh air is cooled and dehumidified. Such a hybrid heat-mass exchanger could be used as the secondary heat mass exchanger 11 shown in Figure 1 or be provided as an additional a heat mass exchanger before the secondary heat mass exchanger 11.

[0047] Furthermore, at the primary heat exchanger 12 (HMX- 1), the dehumidiefied process air may be split into two streams, where air stream one travelling through the first pathway is evaporatively cooled and air stream two travelling through the second pathway sensibly cooled via heat exchange with air stream one. The two air streams can then be used to cool different or the same space.