The present invention is related to the field of environmental control systems and more particularly, to the field of systems which combine dehumidification and air conditioning.
In general, air conditioning systems not only reduce the temperature of the ambient air, but also remove substantial amounts of water from it. This is especially true when the air conditioner is treating xe2x80x9cfreshxe2x80x9d air inputted from outside the controlled environment. However, such combined air conditioning/dehumidification is generally inefficient. Furthermore, since some of the potential cooling power of the air-conditioner is used for dehumidification, the effective cooling capacity of the air conditioner is significantly reduced.
It is known in the art to provide dehumidification of air prior to its being cooled. In some cases, the mechanisms of the dehumidifier and the air conditioner are not integrated. In such cases, while there is an increase in the cooling capacity of the air conditioner, the overall efficiency of the system is relatively poor.
U.S. Pat. No. 4,984,434 describes an integrated system in which air to be cooled is first dehumidified by passing it through a desiccant type dehumidifier before being cooled by contact with an evaporator of an air conditioner. Regeneration of the desiccant is performed by passing the water containing desiccant over the condenser of the air conditioning system.
This system suffers from a number of limitations. Firstly, it dehumidifies all of the air being cooled. Since most of the air inputted to the dehumidifier is from the controlled space (and thus fairly dry already) the dehumidifier does not remove much water from the air and thus does not provide much cooling for the condenser. This would cause an overall increase in the temperature of the desiccant and a reduction in the efficiency of both the dehumidifier and the air-conditioner. A second problem is that such a system is not modular, namely, the dehumidifier must be supplied as part of the system. Furthermore, adding a dehumidifier to an existing air conditioning system and integrating the dehumidifier and air conditioner to form the system of this patent appears to be impossible.
Another type of dehumidifying/air conditioning system is also known. In this type of system, as described, for example in U.S. Pat. Nos. 5,826,641, 4,180,985 and 5,791,153, a dry desiccant is placed in the air input of the air-conditioner to dry the input air before it is cooled. Waste heat (in the form of the exhaust air from the condenser) from the air conditioner is then brought into contact with the desiccant that has absorbed moisture from the input air in order to dry the desiccant. However, due to the relatively low temperature of the air exiting the air conditioner, the amount of drying available from the desiccant is relatively low.
The above referenced U.S. Pat. No. 4,180,985 also describes a system using liquid desiccant as the drying medium for the dehumidifying system. Here again, the low temperature of the exhaust as from the air conditioner reduces substantially the efficiency of the system.
Prior art desiccant based dehumidifiers generally require the movement of the desiccant from a first region in which it absorbs moisture to a second regeneration region. In the case of solid desiccants, this transfer is achieved by physically moving the desiccant from a dehumidifying station to a regeneration station, for example by mounting the desiccant on a rotating wheel, a belt or the like. In liquid desiccant systems two pumps are generally provided, one for pumping the liquid to the regeneration station and the other for pumping the liquid from the regeneration station to the dehumidifying station. In some embodiments, a single pump is used to pump from one station to the other, with the return flow being gravity fed.
The operation of standard air conditioning systems and the desiccant systems described above is illustrated with the aid of FIG. 1. FIG. 1 shows a chart of temperature vs. absolute humidity in which iso-enthalpy and iso-relative humidity curves are superimposed. Normal air conditioners operate on the principle of cooling the input air by passing it over cooling coils. Assuming that the starting air conditions are at the spot marked with an X, the air is first cooled (curve 1) until its relative humidity is 100% at which point further cooling is associated with condensation of moisture in the air. In order for there to be removal of liquid from the air, it must be cooled to a temperature that is well below a comfort zone 4. The air is heated to bring it to the comfort zone, generally by mixing it with warmer air already in the space being cooled. This excess cooling in order to achieve dehumidification is a major cause of low efficiency in such systems, under certain conditions.
Normal dehumidifier systems actually heat the air while they remove air from it. During dehumidification (curve 2) the enthalpy hardly changes, since there is no removal of heat from the system of air/desiccant. This results in an increase in temperature of both the desiccant and the air being dried. This extra heat must then be removed by the air conditioning system, lowering its efficiency.
In all dehumidifier systems mechanical power must be exerted to transfer the desiccant in at least one direction between a regenerating section and a dehumidifying section thereof. For liquid systems, pumps are provided to pump liquid in both directions between the two sections or between reservoirs in the two sections. While such pumping appears to be necessary in order to transfer moisture and/or desiccant ions between the two sections, the transfer is accompanied by undesirable heat transfer as well.
An aspect of some preferred embodiments of the invention is concerned with a combined dehumidifier/air conditioner is which a relatively low level of integration is provided. In preferred embodiments of the invention, heat generated by the condenser is used to remove liquid from the desiccant. However, unlike the above referenced prior art, the air conditioner condenser continues to be cooled by outside air. The heated air which exits the air-conditioner, containing waste heat, is used to remove moisture from the desiccant.
In contrast to the prior art, in which the heated air is the sole source of energy for the regeneration of the desiccant, in preferred embodiments of the invention, a heat pump is utilized to transfer energy from relatively cool desiccant to heat the desiccant during regeneration, in addition to the heat supplied from the exhaust of the air conditioning portion of the system. This results in a system in which the air conditioner does not have to overcool the air to remove moisture and the dehumidifier does not heat the air in order to remove moisture. This is in contrast with the prior art systems in which one or the other of these inefficient steps must be performed.
In some preferred embodiments of the invention combined dehumidifier/air-conditioner in which only xe2x80x9cfreshxe2x80x9d, untreated air is subject to dehumidification prior to cooling by the air conditioner. This allows for both the dehumidifier and the air-conditioner to operate at high efficiency, since the dehumidifier will be operating on only wet xe2x80x9cfreshxe2x80x9d air and the air conditioner will be cooling only relatively dry air.
Thus, in preferred embodiments of the invention, the amount of waste heat generated by the air-conditioner is relatively high and the heat requirements of the dehumidifier are relatively low, since a major portion of the heat for regeneration is supplied by the heat pump.
According to an aspect of the invention a simple method of integration of an air conditioner and dehumidifier is provided. In accordance with a preferred embodiment of the invention, the air conditioner and dehumidifier are separate units without conduits for air connecting the units. However, unlike prior art unintegrated units, the present invention provides advantages of utilizing waste heat from the air conditioner to provide regeneration energy for the dehumidifier.
According to an aspect of some preferred embodiments of the invention, in the steady state, moisture is transferred from the dehumidifier portion of a system to the regenerator without the necessity of transferring liquid from the regenerator back to the dehumidifier.
In general, in liquid dehumidifier systems, moisture must be transferred from the dehumidifier section to the regenerator section. Since the moisture is in the form of a moisture rich (low concentration) desiccant, this is performed by pumping or otherwise transferring the desiccant. Since the desiccant also contains desiccant ions, these must be returned to the dehumidifier to maintain the desiccant ion level required for dehumidification. This is generally achieved by pumping high concentration desiccant from the regenerator to the dehumidifier section. However, in addition to pumping ions, moisture is also transferred. While the extra energy utilized for pumping may or may not be significant, the inadvertent heat transfer implicit in pumping of the moisture back to the dehumidifier is significant in reducing the efficiency of the system.
In a preferred embodiment of the invention, reservoirs in the dehumidifier and regenerator sections are connected with a passageway that allows only limited flow. Preferably, the passageway takes the form of an aperture in a wall common to the two reservoirs.
During operation, the absorption of moisture in the dehumidifying section increases the volume in the dehumidifier reservoir, resulting in the flow, by gravity, of moisture rich (low concentration) desiccant from the dehumidifier reservoir to the regenerator reservoir. This flow also carries with it a flow of desiccant ions, which must be returned to the dehumidifier section. As indicated above, in the prior art, this is achieved by pumping ion rich desiccant solution from the regenerator to the dehumidifier section. In a preferred embodiment of the invention, the return flow of ions is achieved, by diffusion of ions, via the aperture, from the high concentration regenerator reservoir to the low concentration reservoir. The inventors have found that, surprisingly, diffusion is sufficient to maintain a required concentration of ions in the dehumidifier section and that the return flow is not associated with an undesirable heat transfer associated with the transfer of (hot) moisture together with the ions, as in the prior art.
In especially preferred embodiments of the invention, no pumps are used to transfer desiccant between the reservoirs or between the dehumidifier section and the regenerator, in either direction.
There is thus provided, in accordance with a preferred embodiment of the invention, an air conditioning and dehumidifier system for controlling the environment of a controlled area, comprising:
an air conditioner comprising:
a cooling unit in which air is cooled;
a first inlet to the cooling unit drawing air from the area;
a second inlet to the cooling unit drawing fresh air from outside the area;
an outlet to the area via which cooled air is transferred to the area;
a heat exchanger at which heat removed from air by the cooling unit is removed from the air conditioner;
an air inlet to the heat exchanger into which relatively cool outside air is drawn, heat being transferred to said air from said heat exchanger; and
a heated air outlet from the heat exchanger from which the heated air exits;
a dehumidifying unit utilizing liquid desiccant, comprising:
a drying unit having a wet air inlet and a dry air outlet from which air dried by the drying unit exits and in which liquid desiccant dries the air and removes heat from it;
a regenerator unit in which moisture removed from air by the drying unit is removed from the liquid desiccant;
a hot air inlet to the regenerator unit;
a wet air outlet from the regenerator unit via which air entering the hot air inlet exits after moisture is transferred to it; and
a heat pump that transfers heat from relatively cooler liquid desiccant in the dehumidifying unit to relatively warmer liquid desiccant;
a conduit connecting the heated air outlet of the air conditioner to the hot air inlet of the dehumidifying; and
a conduit connecting the dry air outlet of the dehumidifying unit to the second inlet of the air conditioner.
Preferably, moisture removal from the desiccant is aided by providing heat to the regenerator.
In a preferred embodiment of the invention, the system includes at least one pump to pump desiccant between the driving unit and the regenerator.
Preferably, the relatively cooler liquid desiccant is in a dehumidifier sump that receives desiccant after it has absorbed moisture from the outside air.
Preferably, the drying unit comprises a chamber in which said moisture is removed from the outside air and wherein the heat is removed by the heat pump from liquid desiccant being transported to the chamber. Preferably, the drying unit comprises a dehumidifier sump that receives desiccant after it has absorbed moisture from the outside air and wherein the heat is removed by the heat pump from liquid desiccant being transported to the chamber from the sump.
In a preferred embodiment of the invention, the regenerator unit comprises a compartment that contains liquid desiccant being regenerated and wherein the heat is transferred directly by the heat pump to said desiccant in said compartment.
Preferably, the regenerator unit comprises a compartment that contains liquid desiccant being regenerated and wherein the heat is transferred by the at least one heat pump to liquid desiccant being transported to the compartment. Preferably, the regenerator unit comprises a regenerator sump that receives desiccant after moisture has been removed from it and wherein the heat is transferred to desiccant being transported to the chamber from the regenerator sump.
In a preferred embodiment of the invention, the air conditioner includes a fan to draw air into the cooling unit and wherein the fan is also operative to draw air into the wet air inlet of the drying unit.
In a preferred embodiment of the invention, the air conditioner includes a fan to draw air into the heat exchanger and wherein the fan is also operative to force air exiting the heat exchanger into the hot air inlet of the regenerator.
In a preferred embodiment of the invention, the air conditioner utilizes a refrigerant to which heat is transferred in a condenser in said cooling unit and from which refrigerant heat is transferred in an evaporator in said heat exchanger.
In a preferred embodiment of the invention, the air conditioner cools an interior space and wherein the heat exchanger is outside the space.
Preferably, the wet air inlet communicates to an area outside the controlled area.
In a preferred embodiment of the invention, the controlled area is at least a portion of a building.
In a preferred embodiment of the invention, the proportion of air drawn into the cooling unit via the first and second inlets thereto is at least partially controllable.
There is further provided, in accordance with a preferred embodiment of the invention, a dehumidifier system comprising:
a liquid desiccant in two reservoirs, one of which contains a higher desiccant concentration than the other;
a dehumidifier unit into which moist air is introduced and from which less moist air is removed after dehumidification by liquid desiccant transferred thereto;
a regenerator unit which receives desiccant solution that has absorbed from the moist air and removes moisture from it; and
a passageway connecting the reservoirs, via which passageway, during steady state operation of the dehumidifier, there is a net flow of moisture from the reservoir having the lower desiccant concentration to the other reservoir without there being a net flow of desiccant ions through the passageway.
Preferably, the passageway is an aperture such that the level of liquid desiccant in the two reservoirs is the same.
In a preferred embodiment of the invention, there is no pumping of liquid desiccant from one reservoir to the other. Preferably, the transfer of moisture is by gravity.
In a preferred embodiment of the invention, there is no transfer of liquid desiccant between the reservoirs except via apertures connecting the reservoirs.
In a preferred embodiment of the invention, the two reservoirs include a first reservoir which receives said liquid desiccant from said dehumidifying chamber after said desiccant absorbs moisture thereat. Preferably, liquid desiccant is transferred to the dehumidifying chamber from the first reservoir.
In a preferred embodiment of the invention, the two reservoirs include a second reservoir which receives said liquid desiccant from said regenerator after removal of moisture therefrom. Preferably, liquid desiccant is transferred to the regenerating chamber from said second reservoir.
In a preferred embodiment of the invention, the dehumidifier includes a heat pump that transfers heat from relatively cooler liquid desiccant to relatively warmer liquid desiccant. Preferably, the heat pump pumps heat from the reservoir having the lower concentration of desiccant to that having the higher concentration of desiccant. In a preferred embodiment of the invention, the heat pump transfers heat from desiccant in a conduit carrying desiccant to the dehumidifier unit.
In a preferred embodiment of the invention, a substantial temperature differential is maintained between the first and second reservoirs. Preferably, the temperature differential is at least 5xc2x0 C. In some preferred embodiments of the invention, the temperature differential is at least 10xc2x0 C. or at least 15xc2x0 C.
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