ABSORPTION VACUUM DEHUMIDIFICATION SYSTEM AND METHOD USING THE SAME

Abstract

An absorption vacuum dehumidification system includes a vacuum section, an absorber, a desorber, a photovoltaic energy supply, a heat exchanger, a condenser, and a desiccant solution. The vacuum section has a feed side and a permeate side and comprising a hydrophilic membrane that separates the feed side than the permeate side. The absorber is connected to the permeate side of the vacuum section. The desorber is connected to the absorber to form a desiccant solution cycle path between the absorber and the desorber. The photovoltaic energy supply configured to power a heat source that provides hot liquid into the desorber. The heat exchanger is connected to the desiccant solution cycle path. The condenser is connected to the desorber. The desiccant solution flows along the desiccant solution cycle path.

Description

TECHNICAL FIELD

The present invention relates to an absorption vacuum dehumidification system, and more particularly, to an absorption vacuum dehumidification system that integrates an absorption refrigeration cycle into the system and a method using the same.

BACKGROUND

As the major electricity consumers in buildings, the energy performance of air-conditioning systems is always one of the main areas of research. In particular, the precise indoor temperature and humidity control is not an easy task, especially in tropical/sub-tropical regions. The situation is getting even more challenging in view of the threat from COVID-19 which necessitates the use of more fresh air for indoor ventilation.

The need for fresh air supply inevitably leads to a rise in energy demand and thus carbon emissions for ventilation, especially in tropical and sub-tropical regions. For regions with heavy moisture, an effective dehumidification mechanism is one of the needed solutions for maintaining air quality. The common use of cooling and reheating coils to achieve independent temperature and humidity may not be effective under a high latent load ratio. The employment of dedicated dehumidification systems in parallel with conventional air-conditioning equipment can be a better choice.

In particular, the shift to a heat-driven approach in which solar energy or waste heat from a trigeneration system is utilized as the driving power, can further escalate the sustainability of the dehumidification system in terms of reduction in carbon emissions.

Currently, the most common dehumidification systems employ solid or liquid desiccant dehumidification cycles. Both are thermally-driven which can use solar or waste heat, resulting in substantial reduction in electricity demand and hence carbon emissions. However, solid desiccant dehumidification systems are usually bulkier and may not be suitable in a densely-populated city.

Liquid desiccant dehumidifiers comparatively require less space. Nevertheless, one concern of using liquid desiccant dehumidifiers is the carryover of liquid desiccant to the air stream. As liquid desiccant is usually corrosive, this can lead to serious problems. Studies have been made to solve problem. FIG. 1 shows a mechanism of membrane dehumidification system using liquid desiccant according to a prior art. One consideration is to separate the liquid desiccant 10 and 12 and air stream 14 and 16 by a selective (such as hydrophilic) membrane 18. Water vapor 20 is then transferred from the moist air to the liquid desiccant through the membrane 18.

Zhai et al. [1] reviewed the techniques of applying membrane for dehumidification or cooling using liquid desiccant. The membrane may be fabricated in a tubular form with the liquid desiccant running inside the tube while the air passes through the outside of the tube [2-7]. It may also be flat sheets sandwiched between the liquid desiccant stream and the air stream [8-11]. In all cases, the liquid desiccant is in direct contact with the membrane. Hence, the requirement for the membrane material becomes more stringent due to the corrosive property of the liquid desiccant. Moreover, the dehumidification process is exothermic as phase change occurs when the moisture is transferred from the air side to the liquid desiccant side. This is not desirable as the air will be heated up unless the liquid desiccant is pre-cooled or inter-cooling is provided.

To relieve such problem, vacuum dehumidification (VD) is regarded as a potential alternative. In vacuum dehumidification, water vapor from a moist air stream is directly extracted away through a selective membrane to a low-pressure or vacuum section. The water vapor does not undergo a phase change and the process can be considered to be isothermal. FIG. 2 shows a schematic diagram of a conventional vacuum dehumidification system driven by an electrical vacuum pump according to a prior art. With moist air 30 fed into a “feed side 32” adjacent to a hydrophilic membrane 34, water vapor or permeate 36 is transferred to the “permeate side 38” through the membrane 34 under a water vapor pressure difference on both sides of the membrane 34. The permeate 36 is then extracted by the vacuum pump 40 driven by the electricity supply 42 to the ambient 44, and the dehumidified air 32 leaves as a retentate. As this dehumidification process is isothermal, the energy performance of the VD system is better.

The concept of vacuum dehumidification by using electrical vacuum pump is not new with a few patents which can be dated back to 1988 [12-19]. Qu et al. [20] thoroughly reviewed the research works of membrane dehumidification including vacuum dehumidification. Other studies on vacuum dehumidification [21-30] also only considered the use of electrical vacuum pump to develop the vacuum condition. In this regard, the energy efficiency of the vacuum pump is critical to the overall energy performance of the VD systems as remarked by Bui et al. [28]. This could be challenging for a small-capacity system which led the resulting system coefficient of performance (COP) not better than that of an absorption chiller. In other words, the primary energy consumption and consequently the carbon emissions could be even higher than those of an absorption chiller which is not favorable.

Besides the use of electrical vacuum pumps, there can be other ways to generate the vacuum condition, such as a thermally-driven mechanism. In this situation, solar or waste heat can be utilized which enhances the sustainability of the dehumidification systems. Recently, Fong and Lee [31] proposed a heat-driven vacuum dehumidification system which integrated the VD into the evaporator of an adsorption refrigeration cycle. As remarked by Fong et al. [32], an absorption chiller (AbC) is more energy efficient than an adsorption chiller if the temperature of the heat source is sufficiently high.

As outlined above, the current state of the art in dehumidification is characterized by a number of significant obstacles. To overcome these challenges, there is a critical need for innovative approaches that can create a more practical and energy-efficient system.

SUMMARY OF INVENTION

To address the problem as above, a novel heat-driven absorption vacuum dehumidifier (AbVD) is proposed, which integrates a vacuum dehumidifier into an absorption refrigeration cycle. This system achieves dehumidification of a moist air stream solely through a hydrophilic membrane inside a vacuum section, while maintaining the temperature of the air stream.

In accordance with a first aspect of the present invention, an absorption vacuum dehumidification system is provided, including a vacuum section, an absorber, a heat exchanger, a desorber, and condenser. The absorber is connected to a permeate side of the vacuum section, in which cooling water is input in and output from the absorber. Hot water is input to and output from the desorber. The heat exchanger is connected between the absorber and the desorber. Cooling water is input in and output from the condenser. A weak desiccant solution is pumped to the desorber and is heated up at the desorber. First water vapor is desorbed from the weak desiccant solution and is transferred to the condenser. The transferred first water vapor is cooled to become liquid water at the condenser. A strong desiccant solution leaving the desorber is pre-cooled at the heat exchanger before entering the absorber. The strong desiccant solution is diluted by absorbing second water vapor which is extracted from a moist air stream entering a feed side of the vacuum section through the hydrophilic membrane, and a dehumidified air stream is outputted from the vacuum section.

In accordance with a second aspect of the present invention, a method for an absorption vacuum dehumidification system is provided, including steps as follows: pumping a weak desiccant solution to a desorber, wherein the weak desiccant solution is heated up at the desorber by hot water inputted into the desorber such that first water vapor is desorbed from the weak desiccant solution and is then transferred to a condenser; inputting cooling water to the condenser, such that the transferred first water vapor is cooled down to become liquid water at the condenser; transferring a strong desiccant solution from the desorber to an absorber, wherein a heat exchanger is instructed to pre-cool the strong desiccant solution before the strong desiccant solution enters the absorber; and extracting second water vapor from a moist air stream which enters a feed side of a vacuum section through a hydrophilic membrane, so as to output a dehumidified air stream from the vacuum section, wherein the strong desiccant solution is diluted by absorbing the second water vapor inside the absorber.

In accordance with a third aspect of the present invention, an absorption vacuum dehumidification system is provided, including a vacuum section, an absorber, a desorber, a photovoltaic energy supply, a heat exchanger, a condenser, and a desiccant solution. The vacuum section has a feed side and a permeate side and comprising a hydrophilic membrane that separates the feed side than the permeate side. The absorber is connected to the permeate side of the vacuum section. The desorber is connected to the absorber to form a desiccant solution cycle path between the absorber and the desorber. The photovoltaic energy supply configured to power a heat source that provides hot liquid into the desorber. The heat exchanger is connected to the desiccant solution cycle path. The condenser is connected to the desorber. The desiccant solution flows along the desiccant solution cycle path.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention are described in more details hereinafter with reference to the drawings, in which:

FIG. 1 shows a mechanism of membrane dehumidification system using liquid desiccant according to a prior art;

FIG. 2 shows a schematic diagram of a conventional vacuum dehumidification system driven by an electrical vacuum pump according to a prior art;

FIG. 3 shows a schematic diagram of an absorption vacuum dehumidification system according to some embodiments of the present invention;

FIG. 4 shows variation of cooling capacities of an absorption vacuum dehumidifier with cooling water supply temperature under different hot water supply temperatures;

FIG. 5 shows variation of coefficient of performance of an absorption vacuum dehumidifier with cooling water supply temperature under different hot water supply temperatures;

FIG. 6 shows variation of thermal power inputs of an absorption vacuum dehumidifier with cooling water supply temperature under different hot water supply temperatures;

FIG. 7 shows variation of a performance improvement index of coefficient of performance with cooling water supply temperature under different hot water supply temperatures;

FIG. 8 shows variation of a performance improvement index of coefficient of performance with cooling water supply temperature under different hot water supply temperatures; and

FIG. 9 shows variation of cooling capacities and coefficient of performance of an absorption vacuum dehumidifier with feed air supply temperatures.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, an absorption vacuum dehumidification system and a method using the same and the likes are set forth as preferred examples. It will be apparent to those skilled in the art that modifications, including additions and/or substitutions may be made without departing from the scope and spirit of the invention. Specific details may be omitted so as not to obscure the invention; however, the disclosure is written to enable one skilled in the art to practice the teachings herein without undue experimentation.

FIG. 3 shows a schematic diagram of an absorption vacuum dehumidification system 100 according to some embodiments of the present invention. The absorption vacuum dehumidification system 100 of the present invention can be referred to as an absorption vacuum dehumidifier as well. The absorption vacuum dehumidification system 100 includes a vacuum section 102, an absorber 110, a desorber 112, a heat exchanger 114, a condenser 116, a desiccant pump 118, and an expansion valve 120.

The vacuum section 102 includes a chamber in accordance with some embodiments. The vacuum section 102 can be referred to as a vacuum chamber, dehumidification chamber, or membrane dehumidification chamber. The vacuum section 102 has a feed side 104 and a permeate side 106 and includes a hydrophilic membrane 108 that separates the feed side 104 than the permeate side 106.

The absorber 110 is connected to the permeate side 106 of the vacuum section 102. In some embodiments, the absorption vacuum dehumidification system 100 further includes a vapor tube 122 connecting the vacuum section 102 to the absorber 110. In some embodiments, the vapor tube 122 is configured to deliver water vapor from vacuum section 102 to the absorber 110. During a dehumidification operation, the absorber 110 serves as a part of a desiccant solution cycle path, as the hydrophilic membrane 108 can be physically separated from a desiccant solution of the desiccant solution cycle path, such the configuration excludes the direct contact of the hydrophilic membrane with the corrosive desiccant solution, which can relieve the anti-corrosive requirement of the hydrophilic membrane and broaden the choice of the hydrophilic membrane materials for performance advancement. The absorber 110 can be connected to an external cooling water supply, so cooling water is input to and output from the absorber (i.e., cooling water in/out).

The desorber 112 is connected to the absorber 110 to form a desiccant solution cycle path between the absorber 110 and the desorber 112. Herein, the desiccant solution cycle path means a desiccant solution can flow from the absorber 110 to the desorber 112 and then flow back from the desorber 112 to the absorber 110. The desorber 112 can be connected to a heat source 130, so hot water is input to and output from the desorber 112 (i.e., hot water in/out). For example, the absorption vacuum dehumidification system 100 further includes an energy supply configured to power the heat source 130 that is connected to the desorber 112 and provides hot liquid into the desorber 112.

The heat exchanger 114 is connected between the absorber 110 and the desorber 112 and thus is connected to the desiccant solution cycle path. The desiccant pump 118 is disposed between the absorber 110 and the heat exchanger 114 so thus is in communication with the desiccant solution cycle path. The expansion valve 120 is disposed between the absorber 110 and the heat exchanger 114 so thus is in communication with the desiccant solution cycle path. As such, the desiccant solution cycle path includes a first desiccant solution path P1 and a second desiccant solution P2. The first desiccant solution path P1 is from the absorber 110 to the desorber 112 at least through the desiccant pump 118 and the heat exchanger 114. The second desiccant solution path P2 is from the desorber 112 to the absorber 110 at least through the heat exchanger 114 and the expansion valve 120.

The condenser 116 is connected to the desorber 112 and is configured to receive water vapor form the desorber 112. The absorber 110 can be connected to an external cooling water supply, so cooling water is input in and output from the condenser 116 (i.e., cooling water in/out). The condenser 116 may further include an outlet configured to flow liquid water out from the condenser 116.

In the following, the absorption vacuum dehumidification operation is described as starting from the absorber 110, which is shown for explanation purposes only but the invention is not so limited as other configurations may also be used.

A desiccant solution can flow within the desiccant solution cycle path. In some embodiments, the desiccant solution includes lithium bromide. For example, a weak desiccant solution inside the absorber 110 is pumped to the desorber 112 along the first desiccant solution path P1 by the desiccant pump 118. At the desorber 112, the weak desiccant solution is heated by hot water input to the desorber 112 such that water vapor is desorbed from the weak desiccant solution and is then transferred to the condenser 116. At the condenser 116, cooling water is input to the condenser 116, so the transferred water vapor is cooled down to become liquid water which can be collected for other purpose. In some embodiments, the air pressure inside the condenser 116 is equal to the air pressure inside the desorber 112.

After desorbing the water vapor from the weak desiccant solution, it is transformed into a strong desiccant solution which is then transferred from the desorber 112 to the absorber 110 along the second desiccant solution path P2. Herein, the terms “weak desiccant solution” and “strong desiccant solution” are relative to each other with respect to concentration thereof; for example, the weak desiccant solution has a concentration of 0.06 weaker than that of the strong desiccant solution. In some embodiments, the concentration includes a concentration of lithium bromide. In some embodiments, the weak desiccant solution may have a concentration of 0.56, and the strong desiccant solution may have a concentration of 0.62. During the transfer of the strong desiccant solution, the heat exchanger 114 (such as a desiccant-to-desiccant heat exchanger) is instructed to pre-cool the strong desiccant solution leaving the desorber 112 before the strong desiccant solution enters the absorber 110. Once pre-cooled, the strong desiccant solution flowing from the heat exchanger 114 is throttled by the expansion valve 120 and then fed into the absorber 110.

At the absorber 110, the strong desiccant solution is diluted by absorbing water vapor. This process is facilitated by supplying cooling water to the absorber 110 to lower the temperature and maintain a low pressure condition inside the absorber 110. As the cooling water enters and exits the absorber 110, it cools down the strong desiccant solution inside the absorber 110, allowing water vapor to be absorbed by the cooled strong desiccant solution. This results in a lower concentration of the desiccant solution, which can be referred to as a weak desiccant solution and then be recycled back to the desorber 112 to complete the cycle. The low pressure maintained in the absorber 110 also results from the absorption of the water vapor into the strong desiccant solution.

Regarding the water vapor inside the absorber 110, it flows from the vacuum section 102 via the vapor tube 122. As a moist air stream A1 enters the feed side 104 of the vacuum section 102, water vapor 109 can be extracted from there through the hydrophilic membrane 108 in which the extraction involves permeation. More specifically, driven by a water vapor pressure difference on both sides of the hydrophilic membrane 108, the water vapor 109 can be extracted directly from the moist air stream A1 to the permeate side 106 with lower pressure through the hydrophilic membrane 108. Therefore, the moist air stream A1 can become dehumidified and is to be output from the vacuum section 102, so what leaves the vacuum section 102 is a dehumidified air stream A2. The extracted water vapor 109 flows from the vacuum section to the absorber 110 and is to be absorbed by the strong desiccant solution. In some embodiments, the air pressure inside the absorber 110 is equal to the air pressure inside the permeate side 106 of the vacuum section 102.

By the above configuration, absorption vacuum dehumidification is completed with the desiccant solution cycle path. Since the feed side 104 of the vacuum section 102 is physically separated from the desiccant solution cycle path at least by the vapor tube 122 and the permeate side 106, the feed side 104 can provide a flowing path to allow the moist air stream A1 to flow through the feed side 104 without involving with the desiccant solution cycle path. As such, the dehumidification process to the air stream (i.e., the moist air stream A1 and the dehumidified air stream A2) is maintained isothermal and does not heat up the air stream, which can achieve higher cooling capacity accordingly.

the above mechanism or effect can be verified through the following content and diagrams. To investigate the performance of the absorption vacuum dehumidifier (AbVD), a mathematical model is derived for comparison with the conventional absorption chiller (AbC).

The formulations for the respective physical properties are based on those presented by Patek and Klomfar [33]. For the refrigerant (water), the corresponding state properties are evaluated according to the equations adopted by Florides et al. [34].

The heat input and cooling capacity of the AbVD could be calculated from:

Q _heat =M _hw c _p,w(T_hw,o−T_hw,i)  (1)

Q _vs =m _da(h_a,i−h_a,o)  (2)

For the absorption chiller (AbC), the respective cooling capacity was then:

Q _evap =M _ew C _p,w(T_ew,i−T_ew,o)  (3)

The COP of the AbC and AbVD was given by:

$\begin{array}{cc}{\mathrm{COP}}_{AbC}=\frac{Q_{evap}}{Q_{heat}}& \left(4\right)\end{array}$ $\begin{array}{cc}{\mathrm{COP}}_{AbVD}=\frac{Q_{\mathrm{vc}}}{Q_{heat}}& \left(5\right)\end{array}$

To compare the performance between the AbC and the AbVD, a performance improvement index (PII) in term of the cooling capacity (CAP) and COP was defined so that:

$\begin{array}{cc}{\mathrm{PII}}_{CAP}=\frac{Q_{\mathrm{vs}}}{Q_{evap}}-1& \left(6\right)\end{array}$ $\begin{array}{cc}{\mathrm{PII}}_{COP}=\frac{CO{P}_{\mathrm{AbVD}}}{CO{P}_{AbC}}-1& \left(7\right)\end{array}$

To compare the performance between the AbVD and the conventional AbC, the parameter values from Heroid et al. [35] is adopted for the AbC and similar components in the AbVD. Regarding the vacuum section of the AbVD, respective parameter values from Bukshaisha and Fronk [26] is selected for the membrane which corresponded to a water permeance of approximately 2.38×10⁻⁶ kmol/s m² kPa.

The feed air flow rate is taken as 0.62 m³/s at an entering condition of 33° C. db and 67% RH. The selected air flow rate and total membrane area are based on the criterion that the resulting desorber and absorber pressures of the AbVD will be similar to those of the AbC. Then, respective parametric studies are conducted to evaluate the performances of the AbVD under different operating conditions.

Performance of the AbVD at Default Conditions

TABLE 1
Summarized performances of the AbVD.
Parameter Value
Pdes      7.213
Pabs      0.666
Thw, o    96.53
Tabw, o   37.52
Tcw, o    34.50
Qheat     14.523
Qvc       11.658
COP       0.803
PIICAP    0.097
PIICOP    0.103

Table 1 summarizes the performances of the AbVD system under the default operating conditions. It could be found that the performances of the AbVD are better than those of the AbC in terms of both cooling capacity and COP with improvement measured around 10%. This is beneficial particularly when the primary energy consumption is considered. In fact, by comparing the AbVD with a conventional chilled water air-conditioning system, there is no need to have evaporator coil in the chiller and cooling coil in the air-handling equipment. Hence, a better energy performance will result.

Sensitivity Analysis of the AbVD Performances Under Different Operating Conditions

Referring to FIG. 4 and FIG. 5, the variation of the system cooling capacities and COP's of the AbVD with the cooling water supply temperature under different hot water supply temperatures are illustrated. The trends for the cooling capacities as indicated in FIG. 4 are close to those of a conventional absorption chiller in which the cooling capacity decreased with an increase in the cooling water supply temperature or decrease in hot water supply temperature.

However, the trends for the COP's shown in FIG. 5 appear to be different from those of an absorption chiller in which the COP should reach a maximum at some hot water supply temperatures as indicated in [35] although the fluctuation range is only mild based on the span of hot water supply temperatures investigated. Instead for the AbVD, the COP decreases monotonically with an increase in hot water supply temperatures over the range of cooling water supply temperatures considered.

To explain such a different observation, it should be reminded that unlike the AbC, the refrigerant side of the AbVD is basically an open circuit. The condenser pressure plays no role on the cooling capacity of the AbVD. It is only the evaporator pressure that could affect the cooling capacity. To further account for these results, FIG. 6 shows the variation of the thermal power input with the cooling water supply temperature at different hot water supply temperatures for the AbVD.

Referring to FIG. 6, the patterns look normal as compared to those of the AbC. However, it can be found that the rates of change of the thermal power input with the hot water supply temperature are higher than those of the cooling capacity. Consequently, the COP decreased with an increase in hot water supply temperature. From FIG. 5 and FIG. 6, a compromise should be made between the cooling capacity and COP when selecting the optimal hot water supply temperature.

FIGS. 7 and 8 show the corresponding variation of PII_COP and PII_CAP under different combinations of the hot and cooling water supply temperatures. Both PII's increased substantially with an increase in cooling water temperature and/or a decrease in hot water temperature. This is particularly attractive for a solar cooling system in which the system capacity and COP of the AbVD does not deteriorate so much as compared to that of AbC when the solar energy is not sufficient. Indeed, with a hot temperature of 70° C. and a cooling water temperature of above 25° C., the capacity and COP of the AbC already become zero. Meanwhile, the AbVD can still function under such circumstances which facilitated its operation in a solar cooling system.

FIG. 9 depicts the variation of the system performances of the AbVD with the feed air temperature. In this analysis, the same humidity ratio as that of the default air condition is employed. It can be found that the impact of the feed air temperature on the AbVD performance is limited. This is contrary to the case with the employment of the AbC plus a cooling coil as the cooling capacity would decrease with a reduction in the feed air temperature under such circumstance. Based on FIG. 9, it can be expected that PII_CAP should increase with a decrease in supply air temperature.

Based on above, it is found that the AbVD offered around 10% improvement in the system cooling capacity and COP respectively under the design conditions. The COP of the AbVD is even better than that based on the electrical vacuum dehumidifiers of similar cooling capacity which highlights the merit of the proposed AbVD over the electrical vacuum dehumidifiers in view of the primary energy consumption. Parametric studies on the performances of the AbVD under different combinations of the hot water and cooling water supply temperatures are made. It is found that the trends for the cooling capacity variation are similar to those of the AbC. However, the situation is different for the variation of COP with the hot water and cooling water supply temperatures. Unlike those for the AbC in which the COP should reach a maximum as some hot water supply temperature, the COP of the AbVD decreases strictly with an increase in the hot water supply temperature over a range of cooling water supply temperatures considered. This can be accounted for by the fact that the rate of increase in the heating power input is greater than the cooling capacity when the hot water temperature increases.

Nevertheless, the choice of the optimal hot water supply temperature requires a compromise between cooling capacity and COP which is different from that for the AbC. The PII' s of the AbVD improved at a higher cooling water temperature and a lower hot water temperature which deems the AbVD much more suitable for use in a solar cooling system with unstable heat energy input. Accordingly, the AbVD can have much better prospect than the electrical vacuum dehumidifier, particularly in small- to medium-capacity applications for the development of sustainable air-conditioning systems. In some embodiments, the AbVD can have the utilization of thermal energy such as solar or waste heat for driving a heat source. In some embodiments, as shown in FIG. 3, the energy supply electrically connected to the heat source 130 is photovoltaic module or cell (e.g., solar module or cell).

The foregoing description of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to the practitioner skilled in the art.

The embodiments are chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications that are suited to the particular use contemplated.

NOMENCLATURE

• • CAP cooling capacity (kW)
  • COP coefficient of performance
  • c_p specific heat capacity at constant pressure (kJ/kg K)
  • h specific enthalpy (kJ/kg)
  • m mass flow rate (kg/s)
  • PII performance improvement index
  • Q thermal power (kW)
  • T temperature (° C.)

SUBSCRIPT

• • a air
  • AbC absorption chiller
  • AbVD absorption vacuum dehumidifier
  • CAP capacity
  • COP coefficient of performance
  • da dry air
  • evap evaporator
  • ew chilled waterheat heating
  • hw hot water
  • i inlet
  • outlet
  • vs vacuum section
  • w water

ABBREVIATIONS

• • AbC absorption chiller
  • AbVD adsorption vacuum dehumidifier
  • db dry-bulb temperature
  • RH relative humidity
  • VD vacuum membrane dehumidification

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Claims

1. An absorption vacuum dehumidification system, comprising: a vacuum section;an absorber connected to a permeate side of the vacuum section, wherein cooling water is input in and output from the absorber;a desorber, wherein hot water is input in and output from the desorber;a heat exchanger connected between the absorber and the desorber; anda condenser, wherein cooling water is input in and output from the condenser,wherein a weak desiccant solution is pumped to the desorber and is heated up at the desorber,wherein first water vapor is desorbed from the weak desiccant solution and is transferred to the condenser,wherein the transferred first water vapor is cooled down to become liquid water at the condenser,wherein a strong desiccant solution leaving the desorber is pre-cooled at the heat exchanger before entering the absorber, and the strong desiccant solution is diluted by absorbing second water vapor which is extracted from a moist air stream entering a feed side of the vacuum section through the hydrophilic membrane, and a dehumidified air stream is outputted from the vacuum section.

2. The absorption vacuum dehumidification system of claim 1, further comprising: a desiccant pump disposed between the absorber and the heat exchanger; andan expansion valve disposed between the absorber and the heat exchanger,wherein the weak desiccant solution is pumped to the desorber by the desiccant pump,wherein the strong desiccant solution pre-cooled by the heat exchanger is throttled by the expansion valve and fed into the absorber.

3. The absorption vacuum dehumidification system of claim 1, wherein the cooling water input in and output from the absorber is configured to facilitate absorption of the second water vapor inside the absorber into the strong desiccant solution and to dilute the strong desiccant solution, wherein the absorption of second water vapor makes the absorber maintained at a low pressure.

4. The absorption vacuum dehumidification system of claim 1, wherein pressure inside the condenser is equal to pressure inside the desorber, andpressure inside the absorber is equal to pressure inside the permeate side of the vacuum section.

5. The absorption vacuum dehumidification system of claim 1, wherein at least one of the weak desiccant solution and the strong desiccant solution comprises lithium bromide.

6. A method for absorption vacuum dehumidification, comprising: pumping a weak desiccant solution to a desorber, wherein the weak desiccant solution is heated up at the desorber by hot water input into the desorber such that first water vapor is desorbed from the weak desiccant solution and is then transferred to a condenser;inputting cooling water to the condenser, such that the transferred first water vapor is cooled down to become liquid water at the condenser;transferring a strong desiccant solution from the desorber to an absorber, wherein a heat exchanger is instructed to pre-cool the strong desiccant solution before the strong desiccant solution enters the absorber; andextracting second water vapor from a moist air stream which enters a feed side of a vacuum section through a hydrophilic membrane, so as to output a dehumidified air stream from the vacuum section, wherein the strong desiccant solution is diluted by absorbing the second water vapor inside the absorber.

7. The method of claim 6, further comprising: pumping the weak desiccant solution to the desorber by a desiccant pump; andthrottling the strong desiccant solution flowing from the heat exchanger by the expansion valve and then feeding the strong desiccant solution into the absorber.

8. The method of claim 6, wherein the absorber is with cooling water in and out so as to facilitate the absorption of the second water vapor into the strong desiccant solution and the dilution of the strong desiccant solution, wherein the absorption of water vapor makes the absorber maintained at a low pressure.

9. The method of claim 6, wherein pressure inside the condenser is equal to pressure inside the desorber, andpressure inside the absorber is equal to pressure inside a space of the permeate side of the vacuum section.

10. The method of claim 6, wherein at least one of the weak desiccant solution and the strong desiccant solution comprises lithium bromide.

11. An absorption vacuum dehumidification system, comprising: a vacuum section having a feed side and a permeate side and comprising a hydrophilic membrane that separates the feed side than the permeate side;an absorber connected to the permeate side of the vacuum section;a desorber connected to the absorber to form a desiccant solution cycle path between the absorber and the desorber;a photovoltaic energy supply configured to power a heat source that provides hot liquid into the desorber;a heat exchanger connected to the desiccant solution cycle path;a condenser connected to the desorber; anda desiccant solution flowing along the desiccant solution cycle path.

12. The absorption vacuum dehumidification system of claim 11, further comprising: a desiccant pump in communication with the desiccant solution cycle path and configured to pump the desiccant solution from the absorber to the desorber; andan expansion valve in communication with the desiccant solution cycle path and configured to throttle the desiccant solution from the desorber to the absorber.

13. The absorption vacuum dehumidification system of claim 11, further comprising: a vapor tube connecting the vacuum section to the absorber such that the hydrophilic membrane is physically free from the desiccant solution cycle path at least by the vapor tube.

14. The absorption vacuum dehumidification system of claim 13, wherein the feed side is physically separated from the desiccant solution cycle path at least by the vapor tube and the permeate side.

15. The absorption vacuum dehumidification system of claim 14, wherein the feed side of the vacuum section is configured to provide a flowing path to allow moist air entering to flow through the feed side without involving with the desiccant solution cycle path.