In-ceiling liquid desiccant air conditioning system

An air-conditioning system includes a plurality of liquid desiccant in-ceiling units, each installed in a building for treating air in a space in the building. Dedicated outside air systems (DOAS) for providing a stream of treated outside air to the building are also disclosed.

BACKGROUND

The present application relates generally to the use of liquid desiccant membrane modules to dehumidify and cool an air stream entering a space. More specifically, the application relates to the use of micro-porous membranes to separate the liquid desiccant from the air stream wherein the fluid streams (air, heat transfer fluids, and liquid desiccants) are made to flow turbulently so that high heat and moisture transfer rates between the fluids can occur. The application further relates to the application of such membrane modules to locally dehumidify spaces in buildings with the support of external cooling and heating sources by placing the membrane modules in or near suspended ceilings.

Liquid desiccants have been used in parallel to conventional vapor compression HVAC equipment to help reduce humidity in spaces, particularly in spaces that either require large amounts of outdoor air or that have large humidity loads inside the building space itself. Humid climates, such as for example Miami, Fla. require a large amount of energy to properly treat (dehumidify and cool) the fresh air that is required for a space's occupant comfort. Conventional vapor compression systems have only a limited ability to dehumidify and tend to overcool the air, oftentimes requiring energy intensive reheat systems, which significantly increases the overall energy costs because reheat adds an additional heat-load to the cooling coil or reduces the net-cooling provided to the space. Liquid desiccant systems have been used for many years and are generally quite efficient at removing moisture from the air stream. However, liquid desiccant systems generally use concentrated salt solutions such as solutions of LiCl, LiBr or CaCl2 and water. Such brines are strongly corrosive, even in small quantities, so numerous attempts have been made over the years to prevent desiccant carry-over to the air stream that is to be treated. One approach—generally categorized as closed desiccant systems—is commonly used in equipment dubbed absorption chillers, places the brine in a vacuum vessel which then contains the desiccant. Since the air is not directly exposed to the desiccant, such systems do not have any risk of carry-over of desiccant particles to the supply air stream. Absorption chillers however tend to be expensive both in terms of first cost and maintenance costs. Open desiccant systems allow a direct contact between the air stream and the desiccant, generally by flowing the desiccant over a packed bed similar to those used in cooling towers. Such packed bed systems suffer from other disadvantages besides still having a carry-over risk: the high resistance of the packed bed to the air stream results in larger fan power and pressure drops across the packed bed, thus requiring more energy. Furthermore, the dehumidification process is adiabatic, since the heat of condensation that is released during the absorption of water vapor into the desiccant has no place to go. As a result both the desiccant and the air stream are heated by the release of the heat of condensation. This results in a warm, dry air stream where a cool dry air stream was desired, necessitating the need for a post-dehumidification cooling coil. Warmer desiccant is also exponentially less effective at absorbing water vapor, which forces the system to supply much larger quantities of desiccant to the packed bed which in turn requires larger desiccant pump power, since the desiccant is doing double duty as a desiccant as well as a heat transfer fluid. The larger desiccant flooding rate also results in an increased risk of desiccant carryover. Generally air flow rates in open desiccant systems need to be kept well below the turbulent region (at Reynolds numbers of less than ˜2,400) to prevent carry-over of desiccant to the air stream.

Modern multi-story buildings typically separate the outside air supply that is required for occupant comfort as well as air quality concerns from the sensible cooling or heating that is also required to keep the space at a required temperature. Oftentimes in such buildings the outside air is provided by a duct system in a suspended ceiling to each and every space from a central outside air handling unit. The outside air handling unit dehumidifies and cools the air, typically to a temperature slightly below room neutral temperatures (65-70F) and a relative humidity level of about 50% and delivers the treated outside air to each space. In addition, in each space one or more fan-coil units (often called Variable Air Volume units) are installed that remove some air from the space, lead it through a water cooled or heated coils and bring it back into the space.

Between the outside air handling unit and the fan-coil units, the space conditions can usually be maintained at proper levels. However, it is well possible that in certain conditions, for example if outside air humidity is high, or if a significant amount of humidity is created within the space or if windows are opened allowing for excess air to enter the space, the humidity in the space raises to the point where the fan-coil in the suspended ceiling starts to condense water on the cold surfaces of the coil, leading to potential water damage and mold growth. Generally condensation in a ceiling mounted fan-coil is undesirable for that reason.

There thus remains a need for a system that provides a cost efficient, manufacturable and thermally efficient method to capture moisture from an air stream in a ceiling location, while simultaneously cooling such an air stream and while also eliminating the risk of condensation of such an air stream on cold surfaces. Furthermore such a system needs to be compatible with existing building infrastructure and physical sizes need to be comparable to existing fan-coil units.

BRIEF SUMMARY

Provided herein are methods and systems used for the efficient dehumidification of an air stream using a liquid desiccant. In accordance with one or more embodiments, the liquid desiccant flows down the face of a thin support plate as a falling film and the liquid desiccant is covered by a membrane, while an air stream is blown over the membrane. In some embodiments, a heat transfer fluid is directed to the side of the support plate opposite the liquid desiccant. In some embodiments, the heat transfer fluid is cooled so that the support plate is cooled which in turn cools the liquid desiccant on the opposite side of the support plate. In some embodiments, the cool heat transfer fluid is provided by a central chilled water facility. In some embodiments, the thus cooled liquid desiccant cools the air stream. In some embodiments, the liquid desiccant is a halide salt solution. In some embodiments, the liquid desiccant is Lithium Chloride and water. In some embodiments, the liquid desiccant is Calcium Chloride and water. In some embodiments, the liquid desiccant is a mixture of Lithium Chloride, Calcium Chloride and water. In some embodiments, the membrane is a micro-porous polymer membrane. In some embodiments, the heat transfer fluid is heated so that the support plate is heated which in turn heats the liquid desiccant. In some embodiments, the thus heated liquid desiccant heats the air stream. In some embodiments, the hot heat transfer fluid is provided by a central hot water facility such as a boiler or combined heat and power facility. In some embodiments, the liquid desiccant concentration is controlled to be constant. In some embodiments, the concentration is held at a level so that the air stream over the membrane exchanges water vapor with the liquid desiccant in such a way that the air stream has a constant relative humidity. In some embodiments, the liquid desiccant is concentrated so that the air stream is dehumidified. In some embodiments, the liquid desiccant is diluted so that the air stream is humidified. In some embodiments, the membrane, liquid desiccant plate assembly is placed at a ceiling height location. In some embodiments, the ceiling height location is a suspended ceiling. In some embodiments, an air stream is removed from below the ceiling height location, directed over the membrane/liquid desiccant plate assembly where the air stream is heated or cooled as the case may be and is humidified or dehumidified as the case may be and directed back to the space below the ceiling height location.

In accordance with one or more embodiments, the liquid desiccant is circulated by a liquid desiccant pumping loop. In some embodiments, the liquid desiccant is collected near the bottom of the support plate into a collection tank. In some embodiments, the liquid desiccant in the collection tank is refreshed by a liquid desiccant distribution system. In some embodiments, the heat transfer fluid is thermally coupled through a heat exchanger to a main building heat transfer fluid system. In some embodiments, the heat transfer fluid system is a chilled water loop system. In some embodiments, the heat transfer fluid system is a hot water loop system or a steam loop system.

In accordance with one or more embodiments, the ceiling height mounted liquid desiccant membrane plate assembly receives concentrated or diluted liquid desiccant from a central regeneration facility. In some embodiments, the regeneration facility is a central facility serving multiple ceiling height mounted liquid desiccant membrane plate assemblies. In some embodiments, the central regeneration facility also serves a liquid desiccant Dedicated Outside Air System (DOAS). In some embodiments, the DOAS provides outside air to the various spaces in a building. In some embodiments, the DOAS is a conventional DOAS not utilizing liquid desiccants.

In accordance with one or more embodiments, a liquid desiccant DOAS provides a stream of treated outside air to a duct distribution system in a building. In some embodiments, the liquid desiccant DOAS comprises several sets of liquid desiccant membrane plate assemblies with heat transfer fluids for removing or adding heat to the liquid desiccants. In some embodiments, a first set of liquid desiccant membrane plates receives a stream of outside air. In some embodiments, the first set of liquid desiccant membrane plates also receives a cold heat transfer fluid. In some embodiments, the air stream leaving the first set of liquid desiccant membrane plates is directed to a second set of liquid desiccant membrane plates, which also receives a cold heat transfer fluid. In some embodiments, the second set of plates receives a concentrated liquid desiccant. In some embodiments, the concentrated liquid desiccant is provided by a central liquid desiccant regeneration facility. In some embodiments, the air treated by the second set of liquid desiccant membrane plates is directed towards a building and distributed to various spaces therein. In some embodiments, an amount of air is removed from said spaces and returned back to the liquid desiccant DOAS. In some embodiments, the return air is directed to a third set of liquid desiccant membrane plates. In some embodiments, the third set of liquid desiccant membrane plates receives a hot heat transfer fluid. In some embodiments, the hot heat transfer fluid is provided by a central hot water facility. In some embodiments, the central hot water facility is a boiler room, or a central heat and power facility. In some embodiments, the first set of liquid desiccant membrane plates receives a liquid desiccant from the third set of liquid desiccant membrane plates through a heat exchanger. In some embodiments, the liquid desiccant is circulated by a liquid desiccant pumping system, and utilizes one or more liquid desiccant collection tanks.

In accordance with one or more embodiments, a liquid desiccant DOAS provides a stream of treated outside air to a duct distribution system in a building. In some embodiments, the liquid desiccant DOAS comprises several sets of liquid desiccant membrane plate assemblies with heat transfer fluids for removing or adding heat to the liquid desiccants. In some embodiments, a first set of liquid desiccant membrane plates receives a stream of outside air. In some embodiments, the air stream leaving the first set of liquid desiccant membrane plates is directed to a second set of liquid desiccant membrane plates, which receive a cold heat transfer fluid. In some embodiments, the second set of plates receives a concentrated liquid desiccant. In some embodiments, the concentrated liquid desiccant is provided by a central liquid desiccant regeneration facility. In some embodiments, the air treated by the second set of liquid desiccant membrane plates is directed towards a building and distributed to various spaces therein. In some embodiments, an amount of air is removed from said spaces and returned back to the liquid desiccant DOAS. In some embodiments, the return air is directed to a third set of liquid desiccant membrane plates. In some embodiments, the first set of liquid desiccant membrane plates receives a liquid desiccant from the third set of liquid desiccant membrane plates. In some embodiments, the first set of liquid desiccant membrane plates also receives a heat transfer fluid from the third set of plates. In some embodiments, the system recovers both sensible and latent energy from the return air stream entering the third set of liquid desiccant membrane plates. In some embodiments, the liquid desiccant is circulated by a liquid desiccant pumping system, and utilizes one or more liquid desiccant collection tanks. In some embodiments, the heat transfer fluid is circulated between the first set of liquid desiccant membrane plates and the third set of liquid desiccant membrane plates.

In accordance with one or more embodiments, a liquid desiccant DOAS provides a stream of treated outside air to a duct distribution system in a building. In some embodiments, the liquid desiccant DOAS comprises several sets of liquid desiccant membrane plate assemblies with heat transfer fluids for removing or adding heat to the liquid desiccants. In some embodiments, a first set of liquid desiccant membrane plates receives a stream of outside air. In some embodiments, the air stream leaving the first set of liquid desiccant membrane plates is directed to a second set of liquid desiccant membrane plates, which receive a cold heat transfer fluid. In some embodiments, the second set of plates receives a concentrated liquid desiccant. In some embodiments, the concentrated liquid desiccant is provided by a central liquid desiccant regeneration facility. In some embodiments, the air treated by the second set of liquid desiccant membrane plates is directed towards a building and distributed to various spaces therein. In some embodiments, an amount of air is removed from said spaces and returned back to the liquid desiccant DOAS. In some embodiments, this return air is directed to a third set of liquid desiccant membrane plates. In some embodiments, the first set of liquid desiccant membrane plates receives a liquid desiccant from the third set of liquid desiccant membrane. In some embodiments, the first set of liquid desiccant membrane plates also receives a heat transfer fluid from the third set of plates. In some embodiments, the system recovers both sensible and latent energy from the return air stream entering the third set of liquid desiccant membrane plates. In some embodiments, the air leaving the third set of liquid desiccant membrane plates is directed to a fourth set of liquid desiccant membrane plates. In some embodiments, the fourth set of liquid desiccant membrane plates receives a hot heat transfer fluid from a central hot water facility. In some embodiments, the hot heat transfer fluid received by the fourth set of liquid desiccant membrane plates is used to regenerate the liquid desiccant present in the fourth set of liquid desiccant membrane plates. In some embodiments, the concentrated liquid desiccant from the fourth set of liquid desiccant membrane plates is directed to the second set of liquid desiccant membrane plates by a liquid desiccant pumping system through a heat exchanger. In some embodiments, the liquid desiccant between the first and third set of liquid desiccant membrane plates is circulated by a liquid desiccant pumping system, and utilizes one or more liquid desiccant collection tanks. In some embodiments, a heat transfer fluid is circulated between the first and third set of liquid desiccant membrane plates so as to transfer sensible energy between the first and third set of liquid desiccant membrane plates.

In accordance with one or more embodiments, a liquid desiccant DOAS provides a stream of treated outside air to a duct distribution system in a building. In some embodiments, the liquid desiccant DOAS comprises several sets of liquid desiccant membrane plate assemblies and conventional cooling or heating coils with heat transfer fluids for removing or adding heat to the liquid desiccants and heating and cooling coils. In some embodiments, a first cooling coil receives a stream of outside air. In some embodiments, the first cooling coil also receives a cold heat transfer fluid in such a way as to condense moisture out of the outside air stream. In some embodiments, the air stream leaving the first set cooling coil is directed to a first set of liquid desiccant membrane plates, which also receive a cold heat transfer fluid. In some embodiments, the first set of liquid desiccant membrane plates receives a concentrated liquid desiccant. In some embodiments, the air treated by the first set of liquid desiccant membrane plates is directed towards a building and distributed to various spaces therein. In some embodiments, an amount of air is removed from said spaces and returned back to the liquid desiccant DOAS. In some embodiments, this return air is directed to a first hot water coil. In some embodiments, the first hot water coils receives hot water from a central hot water facility. In some embodiments, the hot water facility is a central boiler system. In some embodiments, the central hot water system is a combined heat and power facility. In some embodiments, the air leaving the first hot water coil is directed to a second set of liquid desiccant membrane plates. In some embodiments, the second set of liquid desiccant membrane plates also receives a hot heat transfer fluid from a central hot water facility. In some embodiments, the hot heat transfer fluid received by the second set of liquid desiccant membrane plates is used to regenerate the liquid desiccant present in the second set of liquid desiccant membrane plates. In some embodiments, the concentrated liquid desiccant from the second set of liquid desiccant membrane plates is directed to the first set of liquid desiccant membrane plates by a liquid desiccant pumping system through a heat exchanger. In some embodiments, the liquid desiccant between the first and second set of liquid desiccant membrane plate is circulated by a liquid desiccant pumping system, and utilizes one or more liquid desiccant collection tanks.

In accordance with one or more embodiments, a liquid desiccant DOAS is providing a stream of treated outside air to a duct distribution system in a building. In some embodiments, the liquid desiccant DOAS comprises a first and a second set of liquid desiccant membrane module assemblies and a conventional water-to-water heat pump system. In some embodiments, the water-to-water heat pump system is thermally coupled to a building's chilled water loops. In some embodiments, one of a first set of membrane modules is exposed to the outside air is also thermally coupled to the buildings chilled water loop. In some embodiments, the water-to-water heat pump is coupled so that it cools the building cooling water before it reaches the first set of membrane modules resulting in a lower supply air temperature from the membrane modules. In some embodiments, the water-to-water heap pump is coupled so that it cools the building cooling water after is has interacted with the first set of membrane modules resulting in a higher supply air temperature to the building. In some embodiments, the system is set up to control the temperature of the supply air to the building by controlling how the water from the building flows to the water-to-water heat pump and the first set of membrane modules. In accordance with one or more embodiments, the water-to-water heat pump provides hot water or hot heat transfer fluid to a second set of membrane modules. In some embodiments, the heat form the hot heat transfer fluid is used to regenerate a liquid desiccant in the membrane modules. In some embodiments, the second set of membrane modules receives return air from the building. In some embodiments, the second set of membrane modules receives outside air from the building. In some embodiments, the second set of membrane modules receives a mixture of return air and outside air. In some embodiments, the outside air directed to the first set of membrane modules is pre-treated by a first section of an energy recovery system and air directed to the second set of membrane modules is pre-treated by a second section of an energy recovery system. In some embodiments, the energy recovery system is a desiccant wheel, an enthalpy wheel, a heat wheel or the like. In some embodiments, the energy recovery system comprises a set of heat pipes or an air to air heat exchanger or any convenient energy recovery device. In some embodiments, the energy recovery is accomplished with a third and a fourth set of membrane modules wherein the sensible and/or the latent energy is recovered and passed between the third and fourth set of membrane modules.

In no way is the description of the applications intended to limit the disclosure to these applications. Many construction variations can be envisioned to combine the various elements mentioned above each with its own advantages and disadvantages. The present disclosure in no way is limited to a particular set or combination of such elements.

DETAILED DESCRIPTION

FIG. 1depicts a typical implementation of an air conditioning system for a modern building wherein the outside air and the space cooling and heating are provided by separate systems. Such implementations are known in the industry as Dedicated Outside Air Systems or DOAS. The example building has two stories with a central air handling unit100on the roof105of the building. The central air handling unit100provides a treated fresh air stream101to the building that has a temperature that is usually slightly below room neutral conditions (65-70F) and has a relative humidity of 50% or so. A ducting system103provides air to the various spaces and can be ducted to the spaces directly or into a fan-coil unit107mounted in a suspended ceiling cavity106. The fan-coil unit107draws air109from the space110and pushes it through a cooling or heating coil115mounted inside the fan-coil unit107. The cooled or heated air108is then directed back into the space where it provides a comfortable environment for occupants. To maintain air quality some of the air109that is removed from the space and is exhausted through ducts104and directed back to the central air handling unit100. Since the return air102to the air handling unit100is still relatively cool and dry (in summer or warm and moist in winter as the case may be), the central air handling unit100can be constructed so as to recover or use some of the energy present in the return air stream. This is oftentimes accomplished with total energy wheels, enthalpy wheels, desiccant wheels, air to air energy recovery units, heat pipes, heat exchangers and the like.

The fan coils115inFIG. 1also require cold water (for cooling operation) or warm water (for heating operation). Installing water lines in buildings is expensive and oftentimes only a single water loop is installed. This can cause problems in certain situations where some spaces may require cooling and other spaces may require heating. In buildings where a hot water- and a cold water loop are available at the same time, this problem can be solved by having some fan coil units115provide cooling where others are providing heating to the respective spaces. Spaces110can often be divided into zones by physical walls111or by physical separation of fan-coil units.

The fan coil units107thus utilize some form of hot and cold water supply system112as well as a return system113. A central boiler and/or chiller plant114is usually available to provide the required hot and/or cold water to the fan-coil units.

FIG. 2illustrates a more detailed view of a fan-coil unit107. The unit includes a fan201, which removes air109from the space below. The fan pushes air through the coil202which has a water supply line204, a water return line203. The heat in the air109is rejected to the cooling water204thereby producing colder air108and warmer water203. If the air109entering the coil is already relatively humid, it is possible for condensation to occur on the coil since the cooling water is typically provided at temperatures of 50F or below. A drain pan205is then required to be installed and condensed water is required to be drained so as to not create problems with standing water which can result in fungi, bacteria and other potentially disease causing agents such as legionnaires. Modern buildings are often much more air-tight than older buildings which can amplify the humidity control problem. Furthermore in modern buildings, internally generated heat is better retained resulting in a greater demand for cooling earlier in the season. The two effects combine to increase the humidity in the space and result in larger energy consumption than might have been expected.

FIG. 3shows a flexible, membrane protected, counter-flow 3-way heat and mass exchanger disclosed in U.S. Patent Application Publication No. 20140150662 meant for capturing water vapor from an air stream while simultaneously cooling or heating the air stream. For example, a high temperature, high humidity air stream401enters a series of membrane plates303that cool and dehumidify the air stream. The cool, dry, leaving air402is supplied to a space such as, e.g., a space in a building. A desiccant is supplied through supply ports304. Two ports304are provided on each side of the plate block structure300to ensure uniform desiccant distribution on the membrane plates303. The desiccant film falls through gravity and is collected at the bottom of the plates303and exits through the drain ports305. A cooling fluid (or heating fluid as the case may be) is supplied through ports405and306. The cooling fluid supply ports are spaced in such a way as to provide uniform cooling fluid flow inside the membrane plates303. The cooling fluid runs counter to the air stream direction401inside the membrane plates303and leaves the membrane plates303through ports307and404. Front/rear covers308and top/bottom covers403provide structural support and thermal insulation and ensure that air does not leave through the sides of the heat and mass exchanger.

FIG. 4shows a schematic detail of one of the plate structures ofFIG. 3. The air stream251flows counter to a cooling fluid stream254. Membranes252contain a liquid desiccant253that falls along the wall255that contains a heat transfer fluid254. Water vapor256entrained in the air stream is able to transition the membrane252and is absorbed into the liquid desiccant253. The heat of condensation of water258that is released during the absorption is conducted through the wall255into the heat transfer fluid254. Sensible heat257from the air stream is also conducted through the membrane252, liquid desiccant253and wall255into the heat transfer fluid254.

FIG. 5shows a new type of liquid desiccant system as shown in U.S. Patent Application Publication No. 20120125020. The conditioner451comprises a set of plate structures that are internally hollow. A cold heat transfer fluid is generated in cold source457and entered into the plates. Liquid desiccant solution at464is brought onto the outer surface of the plates and runs down the outer surface of each of the plates. In some embodiments -described further below- the liquid desiccant runs behind a thin membrane that is located between the air flow and the surface of the plates. Outside air453is now blown through the set of wavy plates. The liquid desiccant on the surface of the plates attracts the water vapor in the air flow and the cooling water inside the plates helps to inhibit the air temperature from rising. The plate structures are constructed in such a fashion as to collect the desiccant near the bottom of each plate. The treated air454is now put in the building directly without the need for any additional treatment.

The liquid desiccant is collected at the bottom of the wavy plates at461and is transported through a heat exchanger463to the top of the regenerator to point465where the liquid desiccant is distributed across the plates of the regenerator. Return air or optionally outside air455is blown across the regenerator plates and water vapor is transported from the liquid desiccant into the leaving air stream456. An optional heat source458provides the driving force for the regeneration. The hot transfer fluid460from the heat source can be put inside the plates of the regenerator similar to the cold heat transfer fluid on the conditioner. Again, the liquid desiccant is collected at the bottom of the plates452without the need for either a collection pan or bath so that also on the regenerator the air can be vertical. An optional heat pump466can be used to provide cooling and heating of the liquid desiccant but can also be used to provide heat and cold as a replacement of cooler457and heater458.

FIG. 6illustrates an in-ceiling fan coil unit501in accordance with one or more embodiments that uses a3-way membrane liquid desiccant module502to dehumidify air in a space. Air109from the space is pushed by fan503through the 3-way membrane module502wherein the air is cooled and dehumidified. The dehumidified and cooled air108is then ducted to the space where it provides cooling and comfort. The heat that is released during the dehumidification and cooling in the membrane module502is rejected to a circulating water loop511, which circulates from the membrane module502to heat exchanger509and water pump510. The heat exchanger509receives cold water from building chilled water loop204, which ultimately rejects the heat of cooling and dehumidification. To achieve the dehumidification function, a desiccant506is provided to the membrane module502. The desiccant drains into a small storage tank508. Desiccant from the tank508is pumped up to the membrane module502by liquid desiccant pump507. Since ultimately the liquid desiccant gets further and further diluted by the dehumidification process, a concentrated desiccant is added by a liquid desiccant loop504. Dilute liquid desiccant is removed from the tank508and pumped through lines505to a central regeneration facility (not shown).

FIG. 7illustrates how the in-ceiling liquid desiccant membrane fan-coil unit ofFIG. 6can be deployed in the building ofFIG. 1where it replaces the conventional fan-coil units. As can be seen in the figure, fan-coil unit501containing the membrane module502is now replacing the conventional fan-coil units. Liquid desiccant distribution lines504and505a receiving liquid desiccant from a central regeneration system601. Central liquid desiccant supply lines602and603can be used to direct liquid desiccant to multiple floors as well as to a roof based liquid desiccant DOAS. The air handling unit604can be a conventional non-liquid desiccant DOAS as well.

FIG. 8illustrates an alternate embodiment of the DOAS604ofFIG. 7wherein the system uses liquid desiccant membrane plates similar to plates452shown inFIG. 6. The DOAS701ofFIG. 8takes outside706and directs it through a first set of liquid desiccant membrane plates703which are cooled internally by a chilled water loop704and dehumidified by a liquid desiccant in a loop717. The air then proceeds to a second set of liquid desiccant membrane plates702, which is also cooled internally by the chilled water loop704. The air stream706has thus been dehumidified and cooled twice and proceeds as supply air101to spaces in the building as was shown inFIG. 7. The heat released by the cooling and dehumidication processes is released to the chilled water704and the water return705to a central chiller plant is thus warmer than the incoming chilled water.

Return air102from the spaces in the building is directed over a third set of liquid desiccant membrane plates720. These plates are internally heated by hot water loop708. The heated air is directed to the outside where it exhausted as air stream707. The liquid desiccant running over the membrane plates720is collected in a small storage tank715, and is then pumped by pump716through loop717and liquid-to-liquid heat exchanger718to the first set of plates703. The hot water inside plate set720helps to concentrate the desiccant running over the surface of the plate set704. The concentrated desiccant can then be used to pre-dehumidify the air stream706on plate set703, essentially functioning as a latent energy recovery device. A second desiccant loop714is used to further dehumidify the air stream706on the second plate set702. The desiccant is collected in a second storage tank712, and is pumped by pump713through loop714to plates702. Diluted desiccant is removed through desiccant loop711and concentrated liquid desiccant is added to the tank712by supply line710.

FIG. 9illustrates another embodiment similar to the system ofFIG. 8wherein the hot water loop708-709has been omitted. Instead, a circulating water loop802provided by run-around pump801is used the transfer sensible heat from the incoming air stream. The system thus set up is able to remove moisture from the incoming air stream706in the membrane plate set703by the liquid desiccant loop717and add this moisture to the return air102in membrane plate set704. Simultaneously the heat of the incoming air706is moved by the run-around loop802and rejected to the return air stream102. In this manner the system is able to recover both sensible and latent heat from the return air stream102and use it to pre-cool and pre-dehumidify the incoming air stream706. Additional cooling is then provided by the membrane plate set702and fresh liquid desiccant is provided by supply line710as before.

FIG. 10illustrates yet another embodiment similar to the systems ofFIG. 8andFIG. 9wherein energy is recovered as was shown inFIG. 9from the incoming air stream706and applied to the return air stream102. As shown inFIG. 8the remaining cooling and dehumidification is provided by membrane plate set702which is internally cooled by chilled water loop704. However in this embodiment a fourth set of membrane plates903is employed which receives hot water from hot water loop708. Liquid desiccant is provided by pump901and loop902and the concentrated liquid desiccant is returned to desiccant tank712. This arrangement eliminates the need for the external liquid desiccant supply and return lines (710and711inFIG. 8), since the membrane plates903function as an integrated regeneration system for the liquid desiccant.

FIG. 11illustrates another embodiment of the previously discussed systems. In the figure, a pre-cooling coil1002is connected by supply1001to the chilled water loop704. The incoming outside air706which is typically high in humidity will condense on coil1002and water will drain off the coil. The remaining cooling and dehumidification is then again performed by liquid desiccant membrane module702. The advantage of this arrangement is that the water condensed on the coil does not end up in the desiccant and thus does not need to be regenerated. Also shown in the figure is a preheating coil1003supplied by lines1004from a hot water loop708. The pre-heating coil1003increases the temperature of the return air stream102which enhances the efficiency of the regeneration membrane module903since the liquid desiccant902is not cooled as much by the air stream102as would otherwise be the case.

FIG. 12illustrates the psychrometric processes typically involved with the energy recovery methods shown in the previous figures. The horizontal axis shows the dry-bulb temperature (in degrees Celsius) and the vertical axis shows the humidity ratio (in g/kg). Outside Air1101(OA) at 35C and 18 g/kg enters the system as does return air1102(RA) from the space, which is typically at 26C, 11 g/kg. Latent energy recovery such as was shown inFIG. 8reduces the humidity of the outside air to a lower humidity (and a somewhat lower temperature) at1105(OA′). At the same time the return air absorbs the humidity (and some of the heat) at1104(RA′). A sensible energy recovery system would have resulted in points1107(OA′) and1108(RA″). Simultaneous latent and sensible recovery as was shown inFIGS. 9 and 10results in a transfer of both heat and moisture from the incoming air stream to the return air stream, points1106(OA″) and1103(RA″).

In many buildings only a central cold water system is available and there may not be a simple source of hot water available for regeneration of the liquid desiccant. This can be solved by using a system shown inFIG. 13similar to the central air handling systems ofFIG. 8-10, but wherein the primary set of membrane modules702is coupled to a building cold water loop as before, but the regeneration is provided by an internal compressor system that is just there to provide heat for liquid desiccant regeneration in membrane modules1215. It should be clear that likeFIG. 8-10, another set of membrane modules703and720could be provided to provide latent or sensible energy recovery or both, from the leaving air102of the building. This is not shown in the figure so as to not overly complicate the figure. It should also be clear that such energy recovery could be provided by other more conventional means such as a desiccant- (enthalpy-) or heat wheels or a heat pipe system or other conventional energy recovery methods such as run-around water loops and air to air heat exchangers. Generally one portion of such an energy recovery system would be implemented in the air stream102before it enters the membrane modules1215, and the other portion of the energy system would be implemented in the air stream706before it enters the membrane modules702. In buildings where little or no return air102is available, the air stream102can simply be outside air.

InFIG. 13the outside air stream706enters a set of3-way membrane plates or membrane modules702. The membrane modules702receive a heat transfer fluid1216that is provided by liquid pump1204through water-to-water heat exchanger1205. The heat exchanger1205is a convenient way to provide pressure isolation between the usually higher (60-90 psi) building water circuit704and the low pressure heat transfer fluid circuit1216/1217which is generally only 0.5-2 psi. The heat transfer fluid1216is cooled down by the building water704in the heat exchanger1205. The leaving building cooling water1206also is directed through a water-to-refrigerant heat exchanger1207which is coupled to a conventional water-to-water heat pump. The cold heat transfer fluid1216provides cooling to the membrane modules702which also receive a concentrated liquid desiccant714. The liquid desiccant714is pumped by pump713and absorbs water vapor from the air stream706and the air is simultaneously cooled and dehumidified as is discussed, e.g., in U.S. Patent Application Publication No. 2014-0150662, and is supplied to the building as supply air101. The diluted liquid desiccant1218that leaves the membrane modules702is collected in desiccant tank712and now needs to be regenerated. A conventional compressor system (known in the HVAC industry as a water-to-water heat pump) comprising of compressor1209, a liquid-to-refrigerant condenser heat exchanger1201, an expansion device1212and a liquid to refrigerant evaporator heat exchanger1207. Gaseous refrigerant1208leaves the evaporator1207and enters the compressor1209where the refrigerant is compressed, which releases heat. The hot, gaseous refrigerant1210enters the condenser heat exchanger1201where the heat is removed and transferred into heat transfer fluid1214and the refrigerant is condensed to a liquid. The liquid refrigerant1211then enters the expansion device1212where it rapidly cools. The cold liquid refrigerant1213then enters the evaporator heat exchanger1207where it picks up heat from the building water loop704, thereby reducing the temperature of the building water. The thus heated heat transfer fluid1214creates a hot liquid heat transfer fluid1202which is directed to the regenerator membrane modules1215which are similar in nature to conditioner membrane modules702but could be sized differently to account for differences in air streams and temperatures. The hot heat transfer fluid1202now causes the dilute liquid desiccant902to release its excess water in the membrane modules1215which is exhausted into the air stream102resulting in a hot, humid air stream707leaving said membrane modules1215. An economizer heat exchanger1219can be employed to reduce the heat load from the regenerator hot liquid desiccant1220to the cold liquid desiccant in the desiccant tank712.

The hot heat transfer fluid is pumped by pump1203to the regenerator membrane modules1215, and the cooler heat transfer fluid1214is directed back to the condenser heat exchanger1201where it again picks up heat. The advantage of the setup discussed above is clear: the local water-to-water heat pump is only used if liquid desiccant needs to be regenerated and thus can be used at times when electricity is inexpensive since concentrated liquid desiccant can be stored in tank712for use when needed. Furthermore, when the water-to-water heat pump is running, it actually cools the building water loop704down, thereby reducing the heat load on the central chilled water plant. Also when a building only has a cold water loop, which is commonly the case, there is no need to install a central hot water system. And lastly the regeneration system could be made to work even if no return air is available, and if there is return air, an energy wheel or conventional energy recovery system can be added, or a separate set of liquid desiccant energy recovery modules such as shown inFIGS. 8-10can be added.

FIG. 14illustrates the temperatures of the heat transfer fluid (often plain water) in the water lines of the system ofFIG. 13. The building water704enters at temperature Twater,ininto the evaporator heat exchanger1207. The heat transfer fluid is cooled by the refrigerant in the evaporator1207as discussed above resulting in the fluid leaving at temperature Twater,after evap.hx1206. The heat transfer fluid then enters the conditioner heat exchanger1205where it picks up heat from the conditioner fluid loop1216/1217. The run-around heat transfer loop1216/1217(indicated by temperature profile1301and1302in the heat exchanger1205) is usually implemented in a counter-flow orientation resulting in a slightly warmer water temperature Twater, in cond.hmxthat services the membrane modules702. The heat transfer fluid then leaves the system at705and is returned to the central chiller plant (not shown) where it is cooled down. It should be obvious that the heat exchangers1205and1207can also be reversed in order or operated in parallel. The order of the heat exchangers makes little difference in operating energy, but will affect the outlet temperature for the supply air701: generally the supply air701will be colder if the building water enters heat exchanger1207first (as shown). Warmer air is provided if the building water enters heat exchanger1205first (as would happen if the flow from704to705is reversed). This obviously also can be used to provide a temperature control mechanism for the supply air.

The regeneration heat transfer fluid loop is also illustrated inFIG. 14. The heat transfer fluid (often water) having temperature Twater, in1214entering the condenser heat exchanger1201is first heated by the refrigerant resulting in temperature Twater, after cond.hxin1202. The hot heat transfer fluid1202is then directed to the regenerator membrane module resulting in Twater, after regeneratorin1214. Since this is also a closed loop the water temperature is then the same as it was at the beginning of the graph as indicated by arrow1303. For simplicity small parasitic temperature increases such as those caused by pumps and small losses such as those caused by pipe losses have been omitted from the figure.

Having thus described several illustrative embodiments, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to form a part of this disclosure, and are intended to be within the spirit and scope of this disclosure. While some examples presented herein involve specific combinations of functions or structural elements, it should be understood that those functions and elements may be combined in other ways according to the present disclosure to accomplish the same or different objectives. In particular, acts, elements, and features discussed in connection with one embodiment are not intended to be excluded from similar or other roles in other embodiments. Additionally, elements and components described herein may be further divided into additional components or joined together to form fewer components for performing the same functions. Accordingly, the foregoing description and attached drawings are by way of example only, and are not intended to be limiting.