Air handling system

Abstract

An air treatment system is disclosed, the air treatment system comprising a dehumidification unit (10), an indirect evaporative cooling unit (100) and a steam compression unit (200), the dehumidification unit comprising a liquid desiccant system, the liquid desiccant system comprising a liquid desiccant for dehumidifying process air; the indirect evaporative cooling unit is used to cool the process air from the dehumidification unit and cool the liquid desiccant; the steam compression unit comprises a compressor (201), a condenser (202) and an evaporator (206) for further cooling the process air from the indirect evaporative cooling unit. The preferred desiccant is potassium formate.

Description

[0001] The invention relates to an air treatment system.

[0002] Air conditioning and space cooling are vital in hot and humid climates. However, air conditioning consumes a large amount of electricity and thus contributes to the production of greenhouse gases. Desiccant cooling is an attractive energy-saving alternative to conventional air conditioning to produce the cooling effect, but has not yet been widely adopted on a commercial scale.

[0003] In a liquid desiccant refrigeration system, the liquid desiccant circulates between a dehumidifier and a regenerator. Process air passes through the concentrated and cooled liquid desiccant in the dehumidifier, for example in a countercurrent manner, so as to transfer moisture and heat from the air to the liquid desiccant. The diluted liquid desiccant is then passed to the regenerator, where it is heated and a scavenger air stream is used to absorb moisture from the diluted liquid desiccant to regenerate the concentrated liquid desiccant. The concentrated liquid desiccant can then be reused in the dehumidifier.

[0004] However, there are many challenges in developing large-scale liquid desiccant refrigeration systems.

[0005] Therefore, the most commonly used liquid desiccants are solutions of lithium chloride, calcium chloride, and lithium bromide (LiCl, CaCl2, and LiBr, respectively), which are typically regenerated using an external source such as waste heat or solar heat at temperatures of about 80° C. Such high temperatures pose a challenge to the widespread use of this technology.

[0006] Furthermore, due to the toxicity of desiccants, they are not suitable for use in process air, especially at high velocities (e.g., above 10,000 cfm (16990 m 3 / hr)) is a health concern, especially when droplets of desiccant drift in the air into cooled enclosures or when the liquid desiccant comes into contact with personnel performing system maintenance.

[0007] Increases in liquid desiccant temperature above 30°C reduce the effectiveness of moisture capture in the process air due to increases in the partial pressure of the liquid desiccant. This in turn may require the provision of a continuous cooling source to control the temperature increase, particularly when the process air treated by the desiccant enters the system at temperatures above 30°C (as encountered in hot climates).

[0008] The economic feasibility of using typical inorganic liquid desiccants imposes constraints on the widespread use of dehumidification systems in typical heating, ventilation and air conditioning (HVAC) units. For example, LiCl can cost $1300 / 100 L. A more affordable desiccant is needed.

[0009] Environmental challenges arise from the use of liquid desiccant solutions including LiCl, CaCl2, and LiBr, which can cause significant damage to air conditioning systems due to their corrosive properties.

[0010] Solar-driven dehumidification systems offer the opportunity to continuously regenerate a dilute desiccant solution. However, solar radiation may be intermittently available, which may pose a practical limitation to adoption by the HVAC industry.

[0011] Regeneration of liquid desiccant using waste heat requires the availability of a permeable external supply source. This can limit the use of such systems to locations where a suitable waste heat source is available, making the concept less attractive and practical.

[0012] Another problem is crystallization of liquid desiccants. Crystallization can occur in liquid desiccant solutions stored at high concentrations as the temperature decreases, creating stress on the circulation pump. Aqueous salt desiccants may require continuous stirring to prevent crystallization, which in turn increases the energy consumption of the unit.

[0013] The present invention seeks to provide an air handling system which is an improvement over prior art systems. "Process air" is used herein to refer to the air being treated. The benefits of the invention discussed herein are most evident for process air of high humidity and temperature.

[0014] Therefore, according to a first aspect of the present invention, there is provided an air handling system comprising: a dehumidification unit comprising a liquid desiccant system comprising a liquid desiccant for dehumidifying process air; an indirect evaporative cooling unit for cooling the process air from the dehumidification unit and for cooling the liquid desiccant; and a steam compression unit comprising a compressor, a condenser and an evaporator for further cooling the process air from the indirect evaporative cooling unit.

[0015] Thus, the system of the first aspect of the invention may be considered a hybrid system in which the three units, namely the dehumidification unit, the indirect evaporative cooling unit and the vapor compression unit are operated in large-scale, commercial capacities (e.g., 20,000 m 3 / hr or more) for energy efficiency and 100% fresh air handling. The system can be used to cool indoor or outdoor spaces independently in hot and humid climates. The system can be fully automated to manage the operating modes of different units based on outside weather conditions and air supply demand.

[0016] Thus, the air handling system of the first aspect of the present invention comprises a dehumidification unit including a liquid desiccant system.

[0017] The liquid desiccant system comprises a liquid desiccant for absorbing moisture from the process air and preferably comprises a dehumidifier including a drier within which the process air contacts the desiccant. The liquid desiccant system preferably comprises one or more heat exchangers for controlling the temperature of the desiccant.

[0018] Liquid desiccant properties such as electrical conductivity, dynamic viscosity, specific heat capacity and density, as well as operating parameters such as boiling point rise, regeneration temperature and energy storage density determine its potential for use as a liquid desiccant. Among these properties, surface vapor pressure is one of the most important parameters affecting heat and mass transfer in a dehumidifier. In addition, liquid desiccant should preferably be odorless, non-toxic, non-flammable and inexpensive.

[0019] The preferred desiccant for use in liquid desiccant systems is potassium formate (HCOOK). HCOOK is less corrosive and less expensive than conventional aqueous desiccant salts, and has a low crystallization temperature. HCOOK can effectively dehumidify air with high moisture content. The preferred temperature for solution regeneration of weak HCOOK can be as low as 45°C.

[0020] HCOOK aqueous solutions have low toxicity and viscosity and are neither corrosive nor volatile. In addition, at high solution concentrations, HCOOK can outperform conventional liquid desiccants by promoting a high vapor pressure reduction while maintaining a crystallization temperature of less than 0°C.

[0021] Using HCOOK as a liquid desiccant can result in a reduction in the atmospheric humidity ratio of more than 6 g / kg, which results in a reduction in latent heat and a reduction in the relative humidity of the process air. This in turn has the potential to reduce energy usage by 20% to 30%.

[0022] The preferred liquid desiccant for use in the liquid desiccant system thus comprises, consists essentially of, or consists of an aqueous solution containing HCOOK. Preferably, the only desiccant used in the liquid desiccant is HCOOK.

[0023] The liquid desiccant system preferably includes a dehumidifier, which preferably includes a dryer, in which the process air contacts the liquid desiccant. In the dryer, the process air passes through the liquid desiccant, for example in a crossflow, to transfer moisture and heat from the process air to the liquid desiccant. The dryer is preferably equipped with a controller to control the liquid desiccant flow rate and distribution to ensure optimal absorption efficiency of moisture and heat by controlling the liquid to process air ratio.

[0024] The dryer preferably includes an eliminator to help prevent liquid desiccant from being carried over into the process air. The eliminator can be configured, for example, by its geometry, thickness, layering, spacing, and / or materials used, to prevent liquid desiccant from being carried over into the process air at temperatures greater than 10,000 cfm (approximately 17,000 m 3 The eliminator thus preferably helps to eliminate health problems associated with liquid desiccant carryover, with a minimum pressure drop of less than 3%.

[0025] The dehumidifier is preferably further equipped with a collection tank for collecting the liquid desiccant solution from the desiccant, a pump for pumping the liquid desiccant to and from the collection tank, and a spray system for spraying the liquid desiccant into the process air.

[0026] In the air handling system of the first aspect of the present invention, the liquid desiccant is cooled by an indirect evaporative cooling unit. In this regard, the liquid desiccant system preferably includes one or more heat exchangers for controlling the temperature of the liquid desiccant. One or more heat exchangers preferably include a liquid-liquid sensible heat exchanger, and more preferably include a series of liquid-liquid sensible heat exchangers. In order to improve the heat transfer efficiency, one or more heat exchangers can be plate countercurrent heat exchangers. One or more heat exchangers preferably use cold water to reduce the temperature of the liquid desiccant. In a preferred embodiment, the liquid desiccant system includes a series of liquid-liquid sensible plate heat exchangers, through which the liquid desiccant is pumped from the collection tank and pumped to the collection tank. In a preferred embodiment, water from the indirect evaporative cooling unit is used in one or more heat exchangers to cool the temperature of the liquid desiccant. Therefore, in a particularly preferred embodiment, the liquid desiccant system includes a series of liquid-liquid sensible plate heat exchangers in a closed loop, which are in fluid communication with the indirect evaporative cooling unit, and the water from the indirect evaporative cooling unit is used to cool the liquid desiccant.

[0027] The liquid desiccant system preferably includes a regenerator for concentrating a liquid desiccant that has been diluted by absorbing moisture from the process air. Within the regenerator, a relatively hot, diluted liquid desiccant solution is exposed to a purge air flow, such as directed by an axial fan having an air flow proportional to the regenerated desiccant, and moisture is transferred from the diluted liquid desiccant solution to the purge air due to the difference in vapor pressure. The regenerator can regenerate a liquid desiccant, such as a solution containing HCOOK, at a rate greater than 25 g / s. The liquid desiccant system is preferably configured and controlled so that the liquid desiccant is passed from the dehumidifier to the regenerator when the concentration of the liquid desiccant drops below a predetermined threshold. For example, the threshold concentration may be below 60%.

[0028] The regenerator preferably includes a heat exchanger for raising the temperature of the liquid desiccant, and the regenerator may preferably also include an axial fan to guide the purge air. The regenerator may also preferably further include a liquid injection system for injecting the heated diluted liquid desiccant into the purge air flow, and a pump for pumping the liquid desiccant to the vicinity of the regenerator. In order to improve the heat transfer efficiency, the heat exchanger may be a liquid-liquid sensible plate heat exchanger. The heat exchanger can increase the temperature of the liquid desiccant in the regenerator to above 45°C. In a preferred embodiment, the heat exchanger uses the internal waste heat from the compressor of the vapor compression unit, which has the additional advantage of reducing the temperature of the compressor and thus improving its operating efficiency. In these embodiments, a liquid (e.g., water) can transport waste heat from the compressor to the heat exchanger to be independent of the closed-loop circulation of the refrigerant used in the vapor compression unit to avoid any cross-contamination between units.

[0029] The regenerator preferably includes an eliminator to reduce liquid desiccant losses within the purge air stream during the regeneration process. The eliminator may preferably include a cellulose pad having a preferred geometry, thickness, and spacing.

[0030] The preferred dehumidification process within the dehumidification unit of the system of the first aspect of the invention can therefore be summarized as follows. Liquid desiccant having a relatively high concentration and low temperature stored in a dehumidifier collection tank enters the dryer. In the dryer, the liquid desiccant contacts the process air, whereby heat and moisture are transferred from the process air to the liquid desiccant through the liquid desiccant having a lower vapor pressure than the process air being dehumidified, thereby drying the process air and increasing the temperature of the liquid desiccant and reducing the concentration of the liquid desiccant. The liquid desiccant then leaves the dryer and passes through one or more heat exchangers to reduce its temperature and therefore vapor pressure, for increasing the effectiveness of absorbing moisture from the process air, and then re-enters the collection tank, from which the desiccant is circulated through the spray system into the dryer using a pump at a controlled liquid flow rate. When the liquid desiccant becomes sufficiently dilute, for example when the concentration drops below a threshold level (e.g., 60%), the liquid desiccant is passed to a regenerator. Here, the diluted liquid desiccant is heated, preferably by passing it through a heat exchanger, thereby increasing its vapor pressure. The sweep air is then passed through a heated, diluted liquid desiccant to remove moisture (the vapor pressure of the liquid desiccant is higher than that of the sweep air) and thereby concentrate the liquid desiccant. The concentrated liquid desiccant is then passed back to the collection tank. The process of dehumidification and regeneration then continues.

[0031] The air handling system of the first aspect of the present invention further comprises an indirect evaporative cooling unit for cooling the air from the dehumidification unit and for cooling the liquid desiccant.

[0032] Evaporative cooling is the process of cooling air by the evaporation of water. Therefore, water absorbs a large amount of heat to evaporate (i.e., it has a high enthalpy of evaporation), and evaporative cooling involves the phase change of water from liquid to gas using the heat energy in the air. Indirect evaporative cooling is the process of cooling process air by heat exchange with a humidified sweep air stream without any direct mixing of the process air stream and the sweep air stream. This helps prevent, for example, moisture and contaminants from being transferred between the process air stream and the sweep air stream.

[0033] Thus, in the air handling system of the first aspect of the present invention, the dehumidified process air from the dehumidification unit enters the indirect evaporative cooling unit, in which the process air is cooled by heat exchange with the humidified sweep air flow. Sensible heat from the process air is absorbed by the water in the sweep air flow, thereby cooling the process air. This in turn can lead to energy savings (e.g., up to 30%) due to the reduction in the load on the evaporator coil of the vapor compression unit. The reduction in process air temperature can be up to 15°C, depending on the heat transfer efficiency between the two air flows. The indirect evaporative cooling unit preferably includes a cross-flow plate sensible heat exchanger for exchanging heat between the process air and the humidified sweep air flow, and may also preferably include a water sprinkler for humidifying the sweep air flow. The water sprinkler is preferably configured to be controllable by a controller to optimize the heat transfer efficiency of the air to the water.

[0034] In a preferred embodiment, the cooled sweep air exiting the indirect evaporative cooling unit passes through the condenser of the vapor compression unit to assist in the cooling of the refrigerant. This reduces the pressure of the refrigerant and in turn reduces the load on the compressor of the vapor compression unit and therefore reduces its power consumption. The indirect evaporative cooling unit preferably also includes an eliminator configured to help prevent water droplets from being retained in the sweep air and therefore being carried into the condenser coils in a preferred embodiment and also configured to maintain the water level in the indirect evaporative cooling unit.

[0035] The indirect evaporative cooling unit is also used to cool the liquid desiccant, and in this regard, water from the indirect cooling unit can be passed to the dehumidifier to cool the liquid desiccant after contact with the process air (e.g., in one or more heat exchangers). The indirect evaporative cooling unit preferably includes a water collection tank for containing and collecting water used in the water sprayer. This water can therefore be used to cool the liquid desiccant, as well as to cool the sweep air. The water collection tank of the indirect evaporative cooling unit can also be used to supply water to adiabatically cool the vapor compression unit condenser using a direct evaporative pad as described herein, and can also be used to store cold condensed water from the vapor compression unit evaporator coil.

[0036] The air handling system of the first aspect of the invention further comprises a vapour compression unit for cooling the process air from the indirect evaporative cooling unit.

[0037] Vapor compression cooling is a process in which a refrigerant is compressed in a compressor, cooled in a condenser, expanded (e.g., through an expansion valve or throttle valve), and evaporated. Thus, the refrigerant (usually a gas) is compressed in the compressor to increase its temperature and pressure. The compressed refrigerant then passes to the condenser, where heat is transferred from the refrigerant to the passing air, thereby reducing the temperature of the refrigerant while maintaining a substantially constant pressure. The cooled refrigerant is then expanded, e.g., through an expansion valve or throttle valve, which reduces the pressure and temperature of the refrigerant. The refrigerant then evaporates, absorbing heat from its surroundings and thereby cooling its surroundings.

[0038] The vapour compression unit used in the air handling system of the first aspect of the invention thus comprises a compressor, a condenser and an evaporator. As described above, in a preferred embodiment, the condenser is cooled by the cooled sweep air leaving the indirect evaporative cooling unit to assist in the cooling of the refrigerant. This in turn reduces the load on the compressor and reduces its power consumption.

[0039] The vapor compression unit may employ direct evaporative cooling to improve efficiency. Thus, the sweep air stream may be cooled by direct evaporative cooling and passed through a condenser to assist in cooling. The sweep air stream may be moistened by, for example, passing through a hygroscopic pad, which may be moistened with water, such as from one or more water sprayers. The pad may, for example, be a cellulose pad. In a preferred embodiment, the water is sourced from an indirect evaporative cooling unit, such as a water collection tank as described herein. Cooling the refrigerant reduces its pressure and therefore reduces the load on the compressor, aiding system performance and efficiency. For example, by using direct evaporative cooling in this manner, the power consumption of the compressor may be reduced by more than 5% and the coefficient of performance increased by more than 5%.

[0040] It should be noted that at high relative humidity (RH) (e.g. at 80% or above), the improvement in the efficiency of the steam compression unit by direct evaporative cooling may become negligible in terms of the performance of the condenser, and therefore the water supply may be controlled to be disconnected at higher RH (e.g. when RH>80%).

[0041] The process air eventually passes through the evaporator for cooling to the required temperature. In the event that the process air is cooled below its dew point, the collected cold condensed water can be returned to the indirect evaporative cooling unit to reduce the temperature of the water used in the indirect evaporative cooling unit and thus help reduce the temperature of the liquid desiccant by heat exchange, as described above.

[0042] As described above, in a preferred embodiment, waste heat from the compressor of the vapor compression unit is used to heat the diluted liquid desiccant during the regeneration process by heat exchange. This improves the efficiency of the compressor during the regeneration process.

[0043] The process air leaving the vapor compression unit may then be blown into the space to be cooled, preferably via an electronically commutated (EC) fan for enhanced control and reduced energy consumption.

[0044] According to a second aspect of the present invention there is provided the use of a solution comprising potassium formate as a liquid desiccant in a system according to any preceding claim. Preferably HCOOK is the only desiccant present in the liquid desiccant.

[0045] Illustrative embodiments of the present invention will now be described in detail with reference to the accompanying drawings, in which:

[0046] Figure 1 is a schematic diagram of an embodiment of an air treatment system according to the first aspect of the present invention;

[0047] Figure 2 It shows Figure 1 A schematic diagram of a dehumidification unit of the embodiment shown in FIG.

[0048] Figure 3 It shows Figure 1 Schematic diagram of the indirect evaporative cooling unit and the vapor compression unit of the embodiment shown in FIG.

[0049] In the drawings, process air is represented by the arrow referenced "A" and is Figure 1 Enter the system on the right side and Figure 1 Exit the system on the left side.

[0050] therefore, Figure 1 An air handling system according to a first aspect of the invention is shown. The air handling system comprises a dehumidification unit for dehumidifying process air, an indirect evaporative cooling unit for cooling the process air from the dehumidification unit and for cooling a liquid desiccant, and a vapour compression unit for further cooling the process air from the indirect evaporative cooling unit, generally indicated by reference numerals 10, 100 and 200, respectively.

[0051] The dehumidification unit 10 includes a liquid desiccant system including a dehumidifier, generally indicated by the reference numeral 20, and a regenerator, generally indicated by the reference numeral 30. Figure 2 A dehumidification unit 10 is also illustrated in the figure.

[0052] The dehumidifier 20 used in the illustrated embodiment includes a desiccant (with a flow path in Figure 1 and Figure 2 ), a dryer 21 in which process air contacts a desiccant, a collection tank 24, and one or more heat exchangers 22 for controlling the temperature of the desiccant, as indicated.

[0053] The preferred desiccant for dehumidifiers is an aqueous solution containing potassium formate (HCOOK). HCOOK is less corrosive and cheaper than conventional aqueous desiccant salts and has a low crystallization temperature. HCOOK can effectively dehumidify air with a high moisture content. The preferred temperature for regeneration of a solution of weak HCOOK is above 45°C.

[0054] HCOOK aqueous solutions have low toxicity and viscosity and are neither corrosive nor volatile. In addition, at high solution concentrations, HCOOK can outperform conventional liquid desiccants by promoting a high vapor pressure reduction while maintaining a crystallization temperature of less than 0°C.

[0055] Using HCOOK as a desiccant in the dehumidifier 20 can result in a reduction in the atmospheric humidity ratio of more than 6 g / kg, which results in a reduction in latent heat and a reduction in the relative humidity of the process air A. This in turn has the potential to reduce energy usage by 20% to 30%.

[0056] The dehumidifier 20 includes a dryer 21 in which the process air A contacts a liquid desiccant. In the dryer 21, the process air A passes through the liquid desiccant in a cross flow so as to transfer moisture and heat from the process air A to the liquid desiccant. In the illustrated embodiment, the liquid desiccant is held in a collection tank 24, and the process air A passes through a liquid desiccant spray provided by a sprayer 23. The dryer 21 is equipped with a controller (not shown) to control the liquid desiccant flow rate and distribution, thereby ensuring optimal absorption efficiency of moisture and heat by controlling the liquid to process air A ratio.

[0057] The dryer 21 preferably includes an eliminator (not shown) to help prevent the liquid desiccant from being carried over into the process air. The eliminator can be configured, for example, by its geometry, thickness, spacing, layering, and / or materials used, to prevent the liquid desiccant from being carried over into the process air at temperatures greater than 10,000 cfm (approximately 17,000 m 3 The eliminator thus preferably helps to eliminate health problems associated with liquid desiccant carryover, with a minimum pressure drop of less than 3%.

[0058] The dehumidifier 20 includes a plurality of heat exchangers 22 for controlling the temperature of the liquid desiccant. In the illustrated embodiment, the heat exchangers 22 are plate-type countercurrent liquid-liquid sensible heat exchangers and use cold water from the indirect evaporative cooling unit 100 to cool the liquid desiccant.

[0059] The liquid desiccant system includes a regenerator 30 for concentrating a liquid desiccant that has been diluted by absorbing moisture from process air A in the dryer 21. Within the regenerator 30, the relatively hot, diluted liquid desiccant solution is exposed to a purge air flow (indicated by arrow "B") provided via an axial fan 36, and moisture is transferred from the diluted liquid desiccant solution to the purge air B due to the difference in vapor pressure. The regenerator 30 can regenerate the liquid desiccant at a rate greater than 25 g / s. The liquid desiccant system is configured and controlled so that the liquid desiccant is passed from the dehumidifier 21 to the regenerator 30 when the concentration of the liquid desiccant drops below a predetermined threshold. For example, the threshold concentration may be below 60%.

[0060] The regenerator 30 in the illustrated embodiment includes a liquid desiccant reservoir 33 for receiving diluted liquid desiccant from the dehumidifier 20. The regenerator 30 also includes a liquid-liquid sensible plate countercurrent heat exchanger 31 to increase the temperature of the liquid desiccant. The heat exchanger 31 can increase the temperature of the liquid desiccant in the regenerator 30 to, for example, above 45°C. In the illustrated embodiment, the heat exchanger 31 uses waste heat from the compressor 201 of the vapor compression unit 200, which has the added advantage of reducing the temperature of the compressor 201, thereby improving the operating efficiency of the compressor. In the illustrated embodiment, the waste heat from the compressor 201 is used to heat water via the heat exchanger 35, which in turn heats the liquid desiccant in the heat exchanger 31, as shown. Figure 1 and Figure 2 as shown in .

[0061] In the illustrated embodiment, the regenerator 30 includes a sprayer 34 for spraying hot liquid desiccant into the sweep air B and an eliminator 32 for reducing liquid desiccant losses within the sweep air flow B during the regeneration process. The eliminator 32 may include a cellulose pad.

[0062] like Figure 1 and Figure 2The dehumidification process within the dehumidification unit 10 of the illustrated system of the first aspect of the present invention can be described as follows. A liquid desiccant having a relatively high concentration ("strong") and low temperature enters the dryer 21 from the collection tank 24 via the sprayer 23. In the dryer 21, the liquid desiccant is sprayed into the process air A, whereby, since the liquid desiccant has a lower vapor pressure than the process air A being dehumidified, heat and moisture are transferred from the process air A to the liquid desiccant, thereby cooling and drying the process air A, and increasing the temperature and reducing the concentration of the liquid desiccant. The warm liquid desiccant passes out of the dryer 21 into the collection tank 24, and passes through the heat exchanger 22 to reduce its temperature (and therefore vapor pressure, for increasing the effectiveness of absorbing moisture from the process air), and then returns to the dryer 21. When the liquid desiccant becomes sufficiently dilute ("weak"), for example when the concentration drops below a threshold level (e.g., below 60%), the liquid desiccant passes to the regenerator reservoir 33. From here, the weak liquid desiccant passes through the heat exchanger 31, thereby increasing its vapor pressure. The heated, diluted liquid desiccant passes from heat exchanger 31 to sprayer 34 where it is sprayed into the sweep air B to remove moisture (the vapor pressure of the liquid desiccant is higher than that of the sweep air) and thereby concentrate the liquid desiccant. The concentrated ("strong") liquid desiccant is then passed back to collection tank 24. The liquid desiccant flow path is Figure 1 and Figure 2 Shown in.

[0063] The illustrated embodiment of the air handling system of the first aspect of the invention further comprises an indirect evaporative cooling unit 100 for cooling the air from the dehumidification unit 10 and for cooling the liquid desiccant, such as Figure 1 and Figure 3 As shown in the figure.

[0064] Thus, in the illustrated embodiment, dehumidified process air A from the dehumidification unit 10 is passed into the indirect evaporative cooling unit 100 where it is cooled by heat exchange with a humidified sweep air stream (indicated by arrow "C"). Sensible heat from the process air A is absorbed by the water in the sweep air stream C, thereby cooling the process air A. This in turn can result in energy savings (e.g., up to 30%) due to the reduction in load on the evaporator coils of the vapor compression unit. The reduction in process air temperature can be as much as 15°C, depending on the efficiency of the heat transfer between the two air streams. The illustrated indirect evaporative cooling unit 100 includes a cross-flow plate sensible heat exchanger 102 for exchanging heat between the process air A and the humidified sweep air stream C, and a water sprinkler 103 for humidifying the sweep air stream with water from a water collection tank 101. The water sprinklers 103 are preferably configured with appropriate nozzles evenly distributed to cover the sweep air flow C, and can be controlled by a controller (not shown) to optimize the heat transfer efficiency between air and water.

[0065] The cooled sweep air C leaving the indirect evaporative cooling unit 100 passes through the condenser 202 of the vapor compression unit 200 to assist in the cooling of the vapor compression unit refrigerant. This reduces the pressure of the refrigerant and, in turn, reduces the load on the compressor 201 of the vapor compression unit 200 and, therefore, reduces its power consumption. In the illustrated embodiment, the indirect evaporative cooling unit 100 also includes an eliminator 104 that is configured to help prevent water droplets from being retained by the sweep air and, therefore, entering the coils of the condenser 202, and also maintain the water level in the indirect evaporative cooling unit 100. After passing through the condenser 202, the sweep air C is exhausted by the fan 105.

[0066] Water from the indirect evaporative cooling unit 100 passes to the dehumidifier 20 , as indicated in the figure, to cool the liquid desiccant after contact with process air A in the heat exchanger 22 .

[0067] The illustrated embodiment of the air treatment system of the first aspect of the invention further comprises a steam compression unit 200 for cooling the process air A from the indirect evaporative cooling unit 100, such as Figure 1 and Figure 3 As shown in the figure.

[0068] The vapor compression unit 200 includes a compressor 201, a condenser 202, and an evaporator 206. As described above, in the illustrated embodiment, the condenser 202 is cooled by the cooled purge air C leaving the indirect evaporative cooling unit 100 to assist in the cooling of the refrigerant. This in turn reduces the load on the compressor 201 and reduces power consumption.

[0069] In the illustrated embodiment, the vapor compression unit 200 employs direct evaporative cooling to improve efficiency. Thus, a purge air stream (indicated by arrow "D") can be cooled by direct evaporative cooling and passed through a condenser 202 to assist in cooling. The purge air stream D can be moistened by, for example, passing through a hygroscopic pad 203, which is moistened with water from a water sprayer 204. The pad can be, for example, a cellulose pad. In the illustrated embodiment, the water comes from an indirect evaporative cooling unit water collection tank 101, as shown in the figure. Cooling the refrigerant reduces its pressure and thus reduces the load on the compressor 201, contributing to system performance and efficiency. For example, by using direct evaporative cooling in this manner, the power consumption of the compressor 201 can be reduced and the coefficient of performance increased by more than 5%. It should be noted that at high relative humidity (RH), such as 80% or above, the improvement in the efficiency of the vapor compression unit 200 by direct evaporative cooling can become negligible relative to the performance of the condenser, and the water supply can therefore be controlled to be cut off at higher RH (e.g., when RH>80%).

[0070] The process air A that passes through the coils of the evaporator 206 to reduce its temperature can be cooled below its dew point, and the water collected at this stage can be returned to the indirect evaporative cooling unit water collection tank 101 to reduce the temperature of the water used in the indirect evaporative cooling unit 100 and thereby help reduce the temperature of the liquid desiccant through heat exchange, as described above.

[0071] As described above and Figure 1 and Figure 2 As shown in FIG. 2 , in a preferred embodiment, waste heat from the compressor 201 of the vapor compression unit 200 is used to heat the diluted liquid desiccant during the regeneration process by heat exchange. This increases the efficiency of the compressor 201 .

[0072] The process air A leaving the vapour compression unit 200 is then blown by the EC fan 205 into the space to be cooled.

[0073] It should be understood that the above embodiments describe the present invention for illustrative purposes only. In fact, the present invention can be applied to many different configurations, and detailed embodiments are readily apparent to those skilled in the art.

Claims

1. An air handling system, the air handling system comprising a dehumidification unit, an indirect evaporative cooling unit and a vapor compression unit, the dehumidification unit comprising a liquid desiccant system, the liquid desiccant system comprising a liquid desiccant for dehumidifying process air; the indirect evaporative cooling unit for cooling the process air from the dehumidification unit and for cooling the liquid desiccant; the vapor compression unit comprising a compressor, a condenser and an evaporator for further cooling the process air from the indirect evaporative cooling unit; the liquid desiccant system comprising one or more heat exchangers for controlling the temperature of the liquid desiccant, the one or more heat exchangers being in fluid communication with the indirect evaporative cooling unit for cooling the liquid desiccant using water from the indirect evaporative cooling unit; wherein, The indirect evaporative cooling unit comprises a cross-flow plate heat exchanger for exchanging sensible heat between process air and a humidified sweep air stream C; the system is configured such that the cooled sweep air stream C leaving the indirect evaporative cooling unit passes through the condenser of the steam compression unit.

2. The system of claim 1, wherein the system is configured to 3 / hr and above capacity to handle fresh air.

3. The system according to claim 1 or 2, wherein: The liquid desiccant includes a solution containing potassium formate.

4. The system of claim 3, configured to reduce the atmospheric humidity ratio by more than 6 g / kg.

5. The system according to claim 1, wherein: The liquid desiccant system includes a series of liquid-liquid sensible plate counter-flow heat exchangers.

6. The system according to claim 1, wherein: The liquid desiccant system includes a dryer having an eliminator to reduce carryover of liquid desiccant into the process air.

7. The system according to claim 6, wherein: The eliminator is configured to operate at a height above 13592m 3 / hr rate with less than 3% minimum pressure drop to reduce liquid desiccant carryover.

8. The system according to claim 1, wherein: The liquid desiccant system includes a regenerator for concentrating a liquid desiccant that has been diluted by absorbing moisture from the process air.

9. The system according to claim 8, wherein: The regenerator is configured to regenerate the liquid desiccant at a rate greater than 25 g / s.

10. The system according to claim 8 or 9, wherein: The liquid desiccant system is configured to deliver liquid desiccant to the regenerator when a concentration of the liquid desiccant drops below a predetermined threshold.

11. The system according to claim 10, wherein: The threshold is less than 60%.

12. The system according to claim 8, wherein: The regenerator includes a heat exchanger for raising the temperature of the liquid desiccant.

13. The system according to claim 12, wherein: The heat exchanger is a liquid-liquid sensible heat exchanger.

14. The system according to claim 12 or 13, wherein: The heat exchanger uses internal waste heat from the compressor of the vapor compression unit to heat the liquid desiccant.

15. The system according to claim 8, wherein: The regenerator includes an eliminator for reducing liquid desiccant losses within the purge air stream B during the regeneration process, moisture being transferred from a dilute liquid desiccant solution to the purge air stream B.

16. The system of claim 15, wherein: The eliminator includes one or more cellulose pads.

17. The system of claim 1, wherein: The indirect evaporative cooling unit includes an eliminator configured to help prevent water droplets from being retained in the sweep air flow C.

18. The system of claim 1, wherein: The vapor compression unit is configured to employ direct evaporative cooling.

19. The system of claim 18, configured to pass a sweep air flow C through the condenser to aid cooling.

20. The system of claim 19, wherein: The sweep air stream C is humidified via a moisture absorbing pad to help adiabatically cool the condenser.

21. The system of claim 20, wherein: The pad comprises a cellulose pad.

22. A system according to claim 20 or 21, configured to obtain water from the indirect evaporative cooling unit for wetting the pad.

23. The system of claim 1, configured to return water captured from the coils of the evaporator of the vapor compression unit to the indirect evaporative cooling unit.

24. The system of claim 1 including an electronically commutated fan for blowing cooled and dehumidified process air into a desired space.

25. Use of a solution containing potassium formate as a liquid desiccant in a system according to any one of claims 1 to 24.

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