WO2012141979A1 - Compression-ratio dehumidifier - Google Patents

Abstract

Described is an improved dehumidifier for a more energy efficient approach to dehumidifying buildings, relying upon the psychrometric properties of compressed air. Employing a compressor and expander deployed on a common shaft, a motor attached to the shaft is used to drive the compressor. Moisture is removed from adiabatically compressed air at or near its saturation point, the dried air returned to the expander, where the energy of the compressed air stream is used to help drive the compressor, thus reducing the energy load on the motor.

Description

COMPRESSION-RATIO DEHUMIDIFIER

CROSS REFERENCE TO RELATED CASE

[0001] This PCT Application claims priority to US Provisional Patent Application 61/475,166, filed April 13, 2011, which application is incorporated herein by reference as if fully sent forth in its entirety.

STATEMENT OF GOVERNMENT SUPPORT

[0002] This invention was made with government support under Contract No, DE- AC02-05CH11231 awarded by the U.S. Department of Energy to the Regents of the U niversity of Cal ifornia for the operation and management of the Lawrence Berkeley National Laboratory, The government has certain rights in this invention.

FIELD OF INVENTION

[0003] This invention relates to a method and apparatus for dehumidification, and more particularly to an improved dehumidifler tha relies upon the psychrometric properties of compressed air to dehumidify indoor air to comfortable levels.

BACKGROUND OF THE INVENTION

[0004] Buildings are getting more efficient which means more dehumidification is needed relative to cooling. Previously, leaky and/or inefficient buildings did not require independent dehumidification because the large cooling systems used provided sufficient dehumidification. In fact, even in most residential buildings humidity is removed as an incidental consequence of operating cooing systems. However, as building envelopes in general have improved and in particular as we move toward zero energy homes, though cooling loads will be reduced, latent loads will not be reduced as much due to the continued need for ventilation due to the normal internal generation of moisture from building occupants and their activities. Thus, the incidental dehumidificatioii effect of cooling systems will become less and less sufficient for controlling humidity. In fact, in energy efficient buildings in hot, humid climates, problems are already starting to appear and conventional dehumidifiers are now being used, though costly and inefficient.

[0005] Humidity in buildings in general and residential buildings in particular needs to be controlled below certain levels (typically <60% relative humidity is desirable) for several reasons. First, surface condensation can lead to stmctural degradation such as rotting wood and peeling paint. The effect of this degradation can be both stmctural and aesthetic. Second, surface condensation and high humidity (>90% relative humidity) can lead to mold growth on surfaces which presents negative health and durability consequences. Third, indoor humidity contributes to mold and mite growth in general posing significant health risks, particularly with sensitive populations, such as the asthmatic. In addition, high indoor humidity is uncomfortable for occupants, often leading them to reduce thermostat setpoints to induce additional dehumidification from the cooling system,

[0006] Typical air conditioner systems use a refrigerant in a closed cycle. The refrigerant gets cold and that cold is used to cool down the air via a heat exchanger.

When the air gets cold enough water condenses on the heat exchanger and the air is dehumidified. Thus, with such systems, the only way to get dehumidificatioii is to cool the air. To get pure dehumidification, one has to reheat the air. That is, one first has to cool down the air to effect condensation; then heat it back up to the desired temperature. There are various ways to make this more efficient. None the less, the process is relatively energy intensive, and dehumidification without air cooling is not possible without reheating,

SUMMARY OF THE INVENTION [0007] Herein, a new Compression-ratio Dehumidifier (CRD) device is described for providing dehumidifieation, using the well-known psychrometric property of air, i.e., that it can hold more water vapor at lower pressures than it can at higher pressures.

Therefore, compressing moist air can cause condensation of liquid water. The liquid water can be removed and then the air re-expanded to provide dry, but not cooled, air.

[0008] This air cycle has been used in air conditioning systems by cooling the hot compressed air and then re-expanding it adiabatically. While this cycle works, it is far less energy efficient than conventional, refrigerant systems.

[0009] CRD, on the other hand, is optimized for dehumidifieation and recovers the energy in the compressed air and thus has the potential to be a more energy efficient dehumidifieation system. It is an open cycle (i.e. there is no "working fluid" other than the air itself). Instead, a change in pressure (rather than temperature) is used to get the water out of the air. So the physical principles and the limitations are completely different from the standard approach.

[ 0010] in one embodiment of the invention a compressor and an expander are provided, disposed on a common shaft, which shaft is driver by a common motor. In an exemplary embodiment hot, high pressure air from the compressor is directed to a heat exchanger where it undergoes cooling. This lower temperature, high pressure air steam is then directed to the expander where the energy of expansion is captured (in one embodiment by driving the turning of the blades of a turbine type expander), and returned to the system, contributing to the energy available for driving the common shaft, which in turn serves to reduce the power requirements placed on the common motor.

[ 0011] In one embodiment the cooling fluid of the heat exchanger can be pro vided by the exhaust from the expander. In another embodiment, the cooling fluid of the heat exchanger can be provided by a cooling tower, or depending upon its temperature, outdoor air. In a still further embodiment, the cooling fluid of the heat exchanger can be provided by cooled air from an associated air conditioning system.

BRIEF DESCRIPTION OF THE DRAWINGS [0012] The present invention is described with respect to particular exemplar}' embodiments thereof and reference is accordingly made to the drawings in which:

[0013] Fig. I is a schematic of a CRD system according to one aspect of the invention. In this embodiment, the CRD unit is a stand-alone unit that takes in humid ambient air and produces warmed but dried air. This air can be used directly, for example, as a Direct Outdoor Air System.

[0014] Fig. 2 is a schematic of an alternative embodiment of the invention in which an external source of cool or ambient air can be used to change the thermal properties of the outgoing air. This embodiment may be useful to eliminate the need for other air conditioning for example when the space requires a small amount of cooling.

[0015] Fig. 3 is a schematic of yet another embodiment of the invention in which the CRD is fully integrated into a conventional HVAC system and thus allows maximum and independent control of both temperature and humidity.

DETAILED DESCRIPTION OF THE INVENTION

[0016] The invention consists of a compression section (e.g. a compressor), an expansion section (e.g. an expander) and optional heat exchangers. In one embodiment, ambient air directed to the compression section is compressed to or past the point where moisture condenses. The condensed water is then drained away, and hot, dry high pressure air from the compressor section is directed to the expansion section.

[0017] In another embodiment, optionally employing a heat exchanger, the air need not be compressed all the way but close to the point of condensation, the heat exchanger cooling the compressed air stream to below its dew point such that moisture in the air condenses, the condensed water removed at the exchanger. Thereafter, in the expander the energy of compression is recovered. Optionally, the air can be passed through a final heat exchanger before it is delivered to an occupied space or to a standard HVAC system. The compression section and expansion sections may be integrated or separate. They are shown as separate but linked in Fig. 1, but this is not intended to be restrictive. Both the compressor and expander shown in the figure are depicted as being single-stage, but they could also be multistage. [0018] As shown in Fig, 1, the CRD system can comprise in its major components a motor 102, a compressor 104, and an expander 106, all three components on a common shaft 108, such that the energy recovered in the expander helps drive the compressor, thus reducing the energy required to run motor 104, In the illustra ted embodiment of the figure, optional heat exchanger 1 10 is used as an external moisture separator.

[0019] The motor can be electric, a compressed air turbine or power take off from an internal combustion engine or turbine, and is used to drive compressor 104 via shaft 108. The compressor and expander in addition to being turbines can comprise rotary epitrochoids or reciprocating devices. In the embodiment employing a rotary

epitrochoid, the compressor and expander are combined in a single device, in one housing (thereby making the CRD smaller), and includes a central eccentric rotor to pump air. Air enters the compression chamber, is compressed and then exits the chamber to the external moisture separator. It is then returned via an inlet of the expansion chamber where it expands before leaving the epitrochoid device.

[ 0020] In the embodiment of Fig. 1 , humid air enters the CRD at inlet 112 to compressor 104. The humid air is adiabatically compressed at compressor 104, and leaves the compressor at a higher temperature and pressure via conduit 114, the compressed air close to or at saturation (i.e., the air is close to or at 100% relative humidity). The hot, high pressure air is carried by conduit 1 14 to heat exchanger 110 which cools the air below its dew point, and the moisture extracted from heat exchanger 110 removed via drain 116. Warm high pressure air leaving heat exchanger 1 10 via conduit 118 is transported to expander 106 where it is adiabatically expanded. The energy of compression recovered during expansion is returned to drive shaft 108, thus reducing the load on motor 102. Meanwhile, cool dry air exiting expander 106 is directed via conduit 120 to heat exchanger 1 10 where it is used to cool the incoming hot, high pressure entering via conduit 1 14. Lastly, warm dry air leaves heat exchanger 1 10 via conduit 122, where it can be discharged into an environment,

[0021] The arrangement shown in Fig. 2 illustrates a similar but alternative embodiment, Here, the CRD system 200 comprises in its major components a motor 202, a compressor 204, and an expander 206, all three components on a common shaft 208, such that the energy recovered in the expander helps drive the compressor, thus reducing the energy required from the motor to drive compressor 204. As with the system illustrated in Fig, 1, the motor 202 driving common shaft 208 can he electric, a compressed air turbine or a power take off from an internal combustion engine or turbine, rotary epitrochoid, and the like. Heat exchanger 210 is used to aid in moisture removal.

[0022] In this embodiment, humid air to be dried enters system 200 at compressor 204 via inlet 212. Here, as with the embodiment of Fig. 1, the air is adiabaticaily compressed and leaves compressor 204 at higher temperature and pressure via conduit 214 at or close to saturation. The hot high pressure air enters heat exchanger 210 where it is cooled to below its dewpoint and the moisture extracted from the heat exchanger via drain 216. Heat exchanger 210 is cooled by a working fluid (commonly air from outside the system or a cooling fluid such as water from a cooling tower) directed to heat exchanger 210 via conduit 224, the working fluid entering at a lo temperature and leaving at a high temperature via conduit 222. The warm high pressure air leaving heat heat exchanger 210 is directed to expander 206 via conduit 218. In expander 206 the warm high pressure air undergoes adiabatic expansion, the energy recovered from expansion used to drive shaft 208, thus reducing the load on motor 202. Finally, cool dry air leaves expander 206 via conduit 220 where it can be directed to condition an enclosed space,

[0023] in this illustrated embodiment, with outside air being used as the working fluid for cooling the adiabatically-heated air, treated air can be delivered cooler than in the embodiment of Fig. 1. Notably, different applications may desire different air delivery temperatures, which differences can be addressed by variations in CRD system set up such as illustrated in Fig. 2, this variation being just one of several alternati ve embodiments.

[0024] In still another embodiment illustrated in Fig, 3, CRD system 300 is integrated with an existing or to be installed air conditioning system to dehumidifv outdoor supply air. As with the embodiments of Fig. 1 and Fig, 2, the system includes a motor 302, a compressor 304, and an expander 306, all on a common shaft 308, such that the energy recovered in the expander serves to help drive the compressor, thus reducing the energy required for common motor 304. This system in turn is connected to the components of an air conditioning (AC) system, as further described below, The motor 304 driving common shaft 308 can be electric, a compressed air turbine or a power take off from an internal combustion engine or turbine,

[0025] Humid outdoor supply air enters the system through intake 332. Valve 334 is used to adjust the fraction of outdoor air tha t is fed to the dehumidification system via inlet 312, or directly into the return air stream 346 of the AC system. Air to be dehumidified enters the CRD system at inlet 312 leading to compressor 304. There, humid air is adiabatically compressed and leaves the compressor at a high temperature and pressure via conduit 314 at or close to saturation. This hot, high pressure air is fed into a heat exchanger 310 where it is cooled below its dewpoint and the moisture taken off from the heat exchanger at drain 316. In this embodiment, air from the air conditioning system is used as the cooling medium.

[0026] Warm high pressure air leaves heat exchanger 310 via conduit 318 and enters the expander 306. Here the warm high pressure air is adiabatically expanded in expander 306, energy recovered in the expansion process helping to drive common shaft 308. Concurrently cold, dry air leaving expander 306 via outlet 320 is delivered to the air conditioning system at a preselected point along transport conduit 350.

[0027] The return air from the air conditioning system, transported via conduit 346, is passed through cold coil 348 to produce cooler air, which cooler air exits via transport conduit 350. Moisture at cold coil 348 may be removed via drain line 352. In line 350 cooler air can be mixed with cold dry air from the CRD system (introduced via transport line 320) to produce cool air at a controlled humidity. In this embodiment, the CRD reduces the need for cold coil 348 to be so cold as to be able to remove humidity itself. This reduces the cooling energy requirements of coil working fluid 352. The combined cool dryer air and cool controlled humidity air pass through blower 354 and then on to heat exchanger 310 via transport conduit 356.

[0028] Warmer, controlled humidity air leaves heat exchanger 310 via conduit 358, where it can then be introduced into heat exchanger 360. The delivered temperature of the supply air in conduit 362 is controlled by hot heat exchanger 360, heated by a working fluid 364, such as water or phase change refrigerant, to achieve the desired delivered air conditions. The energy used to reheat the air in the heat exchanger 360 is reduced compared to a non CRD system because the entering air is at a higher temperature than if cold heat exchanger 348 had been used to cool the air to the temperature required for the desired humidity level. As illustrated, at the end of the process supply air leaves the system via transport conduit 362 at the desired controlled humidity and temperature.

[0029] If heat is added or subtracted at the high-pressure stage, the temperature/ humidity of the exiting air can be modified (e.g., cooling the compressed air with outdoor air means that the re-expanded air will be colder and dryer, leading to low sensible heat ratio (SHR) cooling— albeit at an efficiency cost). For a climate that needs very little sensible cooling but a lot of dehumidification, the efficiency loss is made up for by eliminating the conventional air conditioner completely. If heat is added from a solar thermal device, it could be possible to make the CRD operate and mn like a sterling engine as a Zero Energy Dehumidifier (ZED).

EXAMPLES

[0030] The below tables present exemplar values illustrating the pressures, temperatures, relative humidity and humidity ratios of treated humid air streams at various stages of the process. In particular, these exemplar}' values are presented for a system such as illustrated in Fig. 1. It is to be appreciated that exact values in the field may vary depending upon system set up, such as have been illustrated in Figs. 2 and 3.

EXAMPLE 1 (Dehumidifying Outdoor Air)

EXAMPLE 2 (Dehumidifying Inside Air)

[0033] The CRD system of this invention can easily be integrated with home ventilation systems. It can dehumidify outside air before it is supplied to the home (requiring less energy to dehumidify high humidity air in hot humid climates) or connected to a heat recovery ventilator such that air leaving a home can be used to cool the hot compressed air of the CRD.

[0034] Reco vering the heat of compression and then doing an adiabatic expansion makes it possible to recover part of the latent heat as mechanical energy with a well- designed compressor-expander combination. In addition, using air as its working fluid, the system does not have the environmental hazards associated with refrigerants or desiccants. With standard compressed air systems water removal is considered a technical problem to be overcome. However, with the CRD systems of this invention water removal is an integral feature.

[0035] Compression Ratio dehumidification technology addresses a growing concern as energy efficiency standards became broadly adopted nationwide. These standards reduce the allowable amounts of energy which may be used to control indoor temperatures. While this approach reduces energy use by lowering an HVAC unit's heating or cooling load, it removes a natural source of dehumidification. As a result, buildings have seen a rise in moisture, which leads to mold growth, water damage, personal discomfort and/or health problems. Building occupants and owners will want to address moisture issues with an energy efficient technology such as CRD,

[0036] The compression ratio dehumidifier takes a completely different approach to removing moisture from air. The key to its potential for high performance is the recovery of the pressure used to force the moisture out of the air. If this can be reco vered with any reasonable efficiency, then the only power requirements are those to move the air. Thus there are substantial potential savings in operating costs,

[0037] The CRD system of this invention does not require market restructuring. It can be designed to function the same way as existing dehumidifiers in that it can be designed to run on standard 120 V household power, can be of similar dimensions and weight to existing systems, and can be distributed and sold through existing channels. It can also be rated using the same metrics and test methods as existing dehumidifiers; important because the same rating methods that currently exist, such as ENERGY STAR labels can be applied. Further, there are no regulator}_' barriers to the introduction of this technology, though regulations requiring better performance from dehumidifiers may accelerate market acceptability and desirability. The environmental issues are substantially less than the current state-of-the-art refrigerant-and desiccant-based systems because no chemicals are required for operation, In addition, production should be straightforward because the technology uses existing manufacturing processes.

[0038] The foregoing detailed description of the present invention is provided for purposes of illustration and is not intended to be exhausti ve or to limit the in vention to the embodiments disclosed.

Claims

We Claim:

1 . An apparatus for removing moisture from air comprising a compressor and an expander wherein:

a) in the compressor ambient air is compressed to or past the point moisture condenses out, and is removed; and,

b) the thus dried air is passed to an expander where the energy of compression is recovered.

2. The apparatus of claim 1 additionally including a heat exchanger disposed between the compressor and the expander,

3. A device from removing moisture from air including:

a) compressor means for adiabatically compressing air;

b) expander means for adiabatically expanding compressed air;

c) a shaft common to said compressor means and expander means; and d) drive means for rotating said common shaft.

4. The device of claim 3 further including a heat exchange means disposed between said compressor means and expander means for reducing the temperature of said compressed air.

5. The de vice of claim 3 wherein the compressor means comprises a turbine.

6. The device of claim 3 wherein the expander means comprises a turbine.

7. The device of claim 1 wherein the drive means is a motor.

8. The device of claim 3 wherein the heat exchange means is a heat exchanger.

9. The device of claim 8 where the heat exchanger includes a drain.

10. In a method from removing moisture from air, the steps of;

a) directing a stream of humid air to a compressor;

b) adiabatically compressing said steam of humid air to a high pressure, such that moisture condenses out,

c) directing the dry high pressure air stream to an expander where it adiabatically expands; and,

d) recovering the energy of expansion and directing said recovered energy to the compressor,

11. A method from removing moisture from air comprising the steps of;

a) directing a stream of humid air to a compressor;

b) adiabatically compressing said steam of humid air to a high pressure, wherein the temperature of the air is also raised;

c) directing said high pressure, raised temperature air stream to a heat exchanger wherein the high pressure air stream is cooled such that moisture condenses from said high pressure stream to dry said air stream;

d) directing the cooled, dry high pressure air stream to an expander where it adiabatically expands, thus further cooling the cooled, dry air stream; and, e) exhausting said cooled, dry air stream.

12. The method of claim 1 1 wherein the cooled, dry air stream is used as the cooling medium in said heat exchanger to lower the temperature of the incoming high pressure, raised temperature air stream.

13. The method of claim 1 1 wherein the adiabatically compressed air is compressed to the point of saturation or near saturation.

14. The method of claim 12 wherein the said cooled, dry air stream after it leaves the heat exchanger is exhausted into the occupant space of a building.

15. The method of claim 11 wherein a separate cooled air or outside air stream is used as the cooling medium in said heat exchanger,

16. The method of claim 15 wherein the cooled, dry air stream from the expander is exhausted into the occupant space of a building.

17. The method of claim 11 wherein the energy of expansion is used to drive the expander.

18. An energy efficient system for reducing the amount of energy needed to remove moisture from an incoming humid air stream comprising a compressor and an expander mounted to a common shaft, the shaft driven by a motor, an inlet to and an outlet from said compressor whereby said humid air stream can be introduced to said compressor and adiabatically compressed to saturation or near saturation, the outlet from said compressor connected to an inlet of a heat exchanger to provide a transport path for said compressed air stream from said compressor to said heat exchanger, cooling means in said heat exchanger provided to lower the temperature of said compressed air steam to below its saturation temperature, an outlet from said heat exchanger in communication with an inlet to said expander to provide a transport pathway for said high pressure air stream to said expander, and an outlet from said expander for exhausting said air stream, whereby the energy of expansion of the introduced air stream into the expander is captured to help drive the expander, and thus reduce the load on the motor required to drive the compressor,

19. The energy efficient system of claim 18 wherein both the compressor and expander comprise turbines.

20. The energy efficient system of claim 16 wherein the compressor and expander are rotary epitrochoids.

21. The energy efficient system of claim 16 wherein the compressor and expander are reciprocating pistons. 22, The energy efficient system of claim 16 wherein the compressor and expander are scroll-type pumps.