US20100170273A1

US20100170273A1 - Refrigerating and air conditioning apparatus

Info

Publication number: US20100170273A1
Application number: US12/676,244
Authority: US
Inventors: Hiroyuki Morimoto; Takeshi Sugimoto; Fumio Matsuoka; Koji Yamashita; Tetsuya Yamashita; Kouji Fukui; Takeyuki Maegawa
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2007-09-20
Filing date: 2007-09-20
Publication date: 2010-07-08
Also published as: WO2009037759A1; JPWO2009037759A1

Abstract

In a range of a wind velocity of 0.5 to 3.5 (m/s) in a refrigeration cycle, when combining absorbent having a small dependency on the wind velocity and the refrigeration cycle, it is not possible to vary dehumidification capability by changing the wind velocity and matching with an actual load is poor. In a refrigerating and air conditioning apparatus having a refrigerator 20 in which refrigerant is put, and having a compressor 20 a for compressing the refrigerant, a condenser 20 b, and a throttle device 20 c, and an evaporator 20 d, and a desiccant rotor 1, which is water adsorption means, an adsorbent is supported with the desiccant rotor 1, whose time constant at a water adsorption equilibrium becomes small as a wind velocity increases in the range of the wind velocity of 0.5 to 3.5 m/s, the condenser 20 b is disposed upwind of the desiccant rotor 1, and the evaporator 20 d is disposed downwind of the desiccant rotor 1.

Description

TECHNICAL FIELD

The present invention relates to a refrigerating and air conditioning apparatus combining a desiccant and steam compression refrigerating cycle, and more particularly to improvement of a load following capability by combining an adsorbent having an excellent matching especially with a refrigeration cycle.

BACKGROUND ART

A conventional refrigerating and air conditioning apparatus having a dehumidification function is composed of a compressor, a condenser, an expansion valve, an evaporator, and a defrost heater. In a refrigeration cycle of the refrigerating and air conditioning apparatus, refrigerant is put. The refrigerant compressed by the compressor turns into a high-temperature high-pressure gas refrigerant to be supplied to the condenser. The refrigerant flowing into the condenser is liquefied by releasing heat into the air. The liquefied refrigerant is decompressed by the expansion valve to be turned into a gas-liquid two-phase state and gasified by absorbing heat from the ambient air in the evaporator to flow into the compressor. A method is common in which water is removed by making an evaporating temperature (intake temperature of the evaporator) less than a dew point temperature.
In the case of the refrigerating and air conditioning apparatus (such as an air-conditioner) capable of controlling the rotation speed of the compressor, since a cooling load tends to be small in an intermediate period of cooling (rainy season and autumn), the compressor followed a load by reducing its rotation speed. Resultantly, a state occurs that the evaporating temperature increases to remove a sensible heat of a room, however, no latent heat is removed, so that a relative humidity of the room increases to cause discomfort to grow.
A method is disclosed in which by combining a refrigerator and water adsorption means, water in the air flowing into the evaporator (heat adsorber) is removed (removal of latent heat) in advance by water adsorption means. That is, the air dehumidified by a desiccant rotor, the water adsorption means, is supplied to the evaporator (heat adsorber). On the other hand, in order to desorb and reproduce water of the adsorbed desiccant rotor, the high temperature air heated by the condenser (radiator) is supplied to the desiccant rotor. (For example, refer to Patent Document 1)
In the method in which the refrigerator and water adsorption means is combined, it is also required to control a capability of the refrigerating and air conditioning apparatus depending on load conditions of the refrigerator and freezer and the room, therefore, a method is disclosed in which the capability is controlled by an airflow volume. (For example, refer to Patent Document 2.)

[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2001-241693 (Paragraph [0071] to [0079], FIG. 2)

[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2006-308236 (Paragraph [0020], FIG. 2)

DISCLOSURE OF INVENTION

Problems to be Solved by the Invention

Like Patent Document 1, in an air conditioner having desiccant, zeolite and silica gel are employed as a solid adsorbent provided on a surface of a desiccant rotor. In the case of using zeolite for the solid adsorbent, FIG. 13 shows water equilibrium adsorption characteristics of zeolite. It is found from FIG. 13 that in order to effectively desorb and reproduce water adsorbed by the zeolite, it is necessary to supply the air of the relative humidity of several percent or less. In order to reduce the relative humidity of the air, the air has to be heated to a high temperature, so that zeolite and silica gel cannot be reproduced by a waste heat generated by the compressor in the refrigeration cycle using refrigerant such as HTC (Hydrofluorocarbon) that operates at a critical temperature or lower.
FIG. 14 is a graph showing a relation of dehumidification capability of zeolite, an adsorbent used for conventional water adsorption means, and wind velocity.
According to our research, it is found that dehumidification capability (adsorption capability) of zeolite, which is widely used as the adsorbent, saturates at the wind velocity of approximately 1 [m/s]. On the other hand, since in a heat exchanger of the refrigeration cycle, heat exchange capability (evaporation capability, condensation capability) linearly increases up to approximately 4 [m/s], the wind velocity in which an adsorbent capability (dehumidification capability) becomes appropriate (approximately 0.5 to 1.5 [m/s]) does not correspond to that in which the heat exchanger capability becomes appropriate (0.5 to 3.5 [m/s]). For example, when the wind velocity is set for 2 [m/s], an average wind velocity of the refrigeration cycle, the adsorbent can not obtain dehumidification capability to match the wind velocity. As a result, while it is possible to obtain a sufficient sensible heat capacity in the heat exchanger, a latent heat capability is poor in the adsorbent, causing a problem that an SHF (=sensible heat capability/[sensible heat capability+latent heat capability]) becomes large. Under such a state, since an input amount of a blower does not contribute to humidification capability (latent heat capability), a COP (=[sensible heat capability+latent heat capability]/[input of compressor+input of blower]) becomes worse.
To the contrary, when setting for a suitable wind velocity (approximately 0.5 to 1.5 [m/s]) of the adsorbent, a sufficient dehumidification capability may be obtained, however, since the airflow volume (wind velocity) is small in the heat exchanger, a problem occurs that the sensible heat capability becomes small and the SHF becomes small. Further, since the airflow volume (wind velocity) is small in the heat exchanger, an evaporation temperature in the evaporator is lowered. Resultantly, the input to the compressor becomes large and the COP is deteriorated.
Since the dehumidification capability of the adsorbent does not linearly change with the increase of the wind velocity, the dehumidification capability (latent heat capability) cannot be controlled by the wind velocity. As a result, the SHF (latent heat capability/[sensible heat capability+latent heat capability]) becomes large and a phenomenon occurs that it does not match the load.
Further, the latent heat in the adsorbent is not sufficiently removed and in the evaporator installed at a downstream of the adsorbent, a frost deposition occurs to lower the reliability of the refrigerating and air conditioning apparatus.
The present invention is made to solve such a problem and its purpose is to improve a load following capability and to obtain a high reliability refrigerating and air conditioning apparatus by combining the adsorbent well suited for the refrigeration cycle in the refrigeration cycle.

Means for Solving the Problems

In a refrigerating and air conditioning apparatus having a refrigeration circuit in which a refrigerant is put and provided with a compressor for compressing the refrigerant, condenser, throttle device, and evaporator, and water adsorption means which adsorbs water in an air-conditioned space to release it outside, the refrigerating and air conditioning apparatus according to the present invention employs an adsorbent as the water adsorption means whose time constant of water adsorption equilibrium becomes small as the wind velocity increases. In other words, an adsorbent is employed whose dehumidification capability becomes large as the wind velocity increases.

Effect of the Invention

With the refrigerating and air conditioning apparatus according to the present invention, in the refrigerating and air conditioning apparatus having a refrigeration circuit in which refrigerant is put and provided with a compressor for compressing the refrigerant, condenser, throttle device, and evaporator, and water adsorption means which adsorbs water in the air-conditioned space to release it outside, since an adsorbent is employed whose time constant of water adsorption equilibrium becomes small as the wind velocity increases, it becomes possible to change dehumidification capability and latent heat capability by changing the wind velocity, so that load following capability is enhanced and reliability of the refrigerating and air conditioning apparatus is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a configuration of a refrigerating and air conditioning apparatus according to an embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating driving conditions of water adsorption means, which is a principal configuration of the refrigerating and air Conditioning apparatus according to the embodiment of the present invention.

FIG. 3 is a phsychrometric diagram illustrating operation of the refrigerating and air conditioning apparatus according to the embodiment of the present invention.

FIG. 4 is a characteristic diagram illustrating adsorbent characteristics of the adsorbent provided with water adsorption means which is a principal configuration of the refrigerating and air conditioning apparatus according to the embodiment of the present invention.

FIG. 5 is a graph showing a relation between a type of an air conditioning apparatus and wind velocity.

FIG. 5 is a graph showing the relation between a weight change of the adsorbent and time.

FIG. 7 is a graph showing the relation between a time constant and wind velocity.

FIG. 8 is a diagram showing an internal structure of a cylinder of a dehumidification rotor.

FIG. 9 is the diagram showing the relation between an adsorbent/desorbent time and adsorption/desorption amount.

FIG. 10 is a graph showing the relation between the wind velocity and time constant of the adsorbent.

FIG. 11 is the graph showing the relation between the refrigeration capability and wind velocity.

FIG. 12 is the graph showing the relation between the humidification capability of the adsorbent used in the present embodiment and wind velocity.

FIG. 13 is a characteristic diagram illustrating adsorbent characteristics of zeolite, which is the adsorbent used in conventional water adsorption means.

FIG. 14 is the graph showing the relation between the humidification capability of zeolite, which is the adsorbent used in the conventional water adsorption means, and wind velocity.

REFERENCE NUMERALS

- 1 desiccant rotor
- 2 driving means
- 3 a, 3 b, fan
- 4 a the first air
- 4 b the second air
- 5 rotation direction of desiccant rotor
- 6 desiccant rotor
- 7 driving means
- 20 refrigerator
- 20 a compressor
- 20 b condenser
- 20 c throttle device
- 20 d evaporator
- 20 e temperature detection means
- 20 f, 20 g, 20 h temperature and humidity detection means
- 20 i control and operation means
- 30 inside of cylinder
- 31 bulk air layer
- 32 boundary layer
- 33 adsorbent layer
- 34 adsorbent pores
- 35 midgap between bulk air layer and boundary layer
- 36 midgap between boundary layer and adsorbent pores
- 37 adsorbent layer thickness
- 100 a open air side
- 100 b refrigeration room (air-conditioned space)

BEST MODE FOR CARRYING OUT THE INVENTION

Descriptions will be given to the refrigerating and air conditioning apparatus according to the present embodiment. In FIG. 1, the refrigerating and air conditioning apparatus is provided with water adsorption means and refrigerator 20. In addition to a desiccant rotor 1, which is water adsorption means; motor, which is driving means 2 for driving the desiccant rotor 1; fan 3 a for supplying a first air 4 a to the desiccant rotor 1, which is the air of an open air side 100 a; and fan 3 b for supplying a second air 4 b to the desiccant rotor 1, which is the air in a refrigeration room 100 b, R404A, HFC system refrigerant, is sealed, and the apparatus is composed of the refrigerator 20 including a compressor 20 a, condenser 20 b, expansion valve 20, which is a throttle device, and evaporator 20 d. The refrigerant can be R134a, R407c, R41aA, ammonia, BC, and so on. Since CO₂is refrigerant operating at a critical point and over, its characteristic is that a high air temperature is easily obtained at the time of condensation. As a result, a reproduction temperature of the adsorbent can be made higher, so that the desiccant rotor 1 can be made small. With the rotation of the fan 3 a, a first air 4 a performs heat-exchange with the condenser 20 b and forms an air flow so as to pass the desiccant rotor 1. With the rotation of the 3 b, a second air 4 b passes the desiccant rotor 1 and is further supplied to the evaporator 20 d to form the air flow to perform heat exchange with the evaporator 20 d. The condenser 20 b is located upwind of the first air 4 a against the desiccant rotor 1, which is water adsorption means. The evaporator 20 is located at the downwind side of the second air 4 b against the desiccant rotor 1, which is water adsorption meahs. As shown in FIG. 2, the desiccant rotor 1 is columnar, rotates in the direction of an arrow 5 by the motor 2, located in a space of the open air side 100 a and refrigeration room 100 b, and rotationally transfers with time.
Descriptions will be given to behavior of the refrigerator 20: The refrigerant compressed by the compressor 20 a turns into the high temperature and pressure refrigerant to flow into the condenser 20 b. The refrigerant flowing into the condenser 20 b discards heat to an ambient air to turn into liquid refrigerant. The discarded heat (condensation waste heat) to the ambient air is reused for reproduction of water adsorption means. The liquefied refrigerant is decompressed by the expansion valve 20 c to become a gas-liquid two-phase refrigerant to be delivered into the evaporator 20 d.
The gas-liquid two-phase refrigerant delivered into the evaporator 20 d become gaseous by absorbing heat from the ambient air to be sucked by the compressor 20 a. Since the air flowing into the evaporator 20 d is the dewatered air by the desiccant rotor 1 subjected to absorption of heat, its characteristic is no frost formation on the surface (fin, heat transfer tube) of the evaporator 20 d.
Next, descriptions will be given to behavior on a psychrometric (a1) diagram. FIG. 3 is a psychrometric diagram illustrating behavior of the refrigerating and air conditioning apparatus according to an embodiment of the present invention. In FIGS. 1 and 2, for the second air 4 b passing the desiccant rotor 1 on the side of the refrigeration room 100 b, it is specified that the state of the air before passing the desiccant rotor 1 is (1), the state of the air right after passing the desiccant rotor 1 is (2), and the state of the air right after performing heat exchange with the evaporator 20 d is (3). For the first air 4 a passing the desiccant rotor 1 on the side of the open air side 100 a, the state of the air on the upwind side of the condenser 20 a is (4), the state of the air right after performing heat exchange with the evaporator 20 b is (5), and the state of the air right after passing the desiccant rotor 1 is (6).
Firstly, descriptions will be given to behavior of the desiccant rotor 1 to adsorb water in the refrigeration room 100 b. The air in the state (1) is the dry-bulb temperature −10[° C.], relative humidity 60[%], and absolute humidity 0.96[g/kg]. The air in the state (1) supplied to the desiccant rotor 1 turns into the air in the state (2) to proceed toward the evaporator 20 d, in which the relative humidity is dehumidified along an equi-enthalpy line from 60[%] to 20[%], the absolute humidity is dehumidified from 0.96[g/kg] to 0.36[g/kg], and the dry-bulb temperature increases from −10[° C.] to −8.5[° C.]. As shown in FIG. 4, since the adsorbent provided in the desiccant rotor 1 has a larger adsorbable water content in the area of the relative humidity 30[%] or more, it can dehumidify the air in the state (1). The air in the state (2) is subjected to heat exchange in the evaporator 20 d, only the sensitive heat is removed and cooled with the absolute humidity being a constant, and turned into the air in the state (3) whose relative humidity is less than 100[%] and the dry-bulb temperature being −20[° C.]. To prevent a frost formation on the evaporator 20 d and defrosting operation of the refrigerator 20, an opening of the expansion valve 20 c, rotation speed of the compressor 20 a, rotation speed of the fan 3 b, and so on, are adjusted, so that an evaporation temperature of the evaporator 20 d is higher than the dew point: temperature (−25.7[° C.] in the present embodiment) of the air in the state (2). The air in the state (3) is spread into the refrigeration room 100 b to keep the dry-bulb temperature therein at −10[° C.]. The area that adsorbed the water of the desiccant rotor 1 is moved to the open air side 100 a by the motor 2 and the water adsorbed by the desiccant rotor is desorbed at the open air side 100 a to be mentioned later.
Next, descriptions will be given to the behavior in which adsorbed water by the desiccant rotor 1 is desorbed at the open air side 100 a. The air in the state (4) is the dry-bulb temperature 32[° C.], which is the outside temperature, relative humidity 60[%], and absolute humidity 18.04[g/kg]. The air in the state (4), supplied by the condenser 20 b is subjected to heat exchange in the condenser 20 h and heated, only the sensible heat being added under a constant absolute humidity, with the dry-bulb temperature increasing up to 53[° C.], and turning into the air in the state (5), in which it is dehumidified down to the relative humidity 20[%], to be supplied to the desiccant rotor 1. The opening of the expansion valve 20 c, rotation speed of the compressor 20 a, rotation speed of the fan 4 a, and so on, are adjusted so that a condensation temperature of the condenser 20 b becomes 55[° C.]. The air in the state (5) supplied to the desiccant rotor 1 is humidified along an equi-enthalpy line from the relative humidity 20[%] to 60[%], the absolute humidity 18.04[g/kg] to 24.38[g/kg] and turning into the air in the state (6) with the dry-bulb temperature being decreased from 53[° C.] to 37.3[° C.] to be released to the open air side 100 a. When the air in the state (5) whose relative humidity is 20[%] is supplied to the desiccant rotor 1, since, as shown in FIG. 4, the water content that can be preserved by the adsorbent provided by the desiccant rotor 1 becomes extremely smaller than that in the area where the relative humidity is 30[%] or more, water can be released into the air at the open air side 100 a. The dewatered area in the desiccant rotor 1 is moved into the refrigeration room 100 b again by the driving force of the motor 2. By repeating this behavior, the refrigeration room 100 b is dehumidified.
FIG. 5 shows a suitable wind velocity range for each application in the refrigeration cycle (refrigerating and air conditioning apparatus). From FIG. 5, it is found that the wind velocity range for the refrigeration cycle is 0.5 to 3.5 [m/s]. The larger the wind velocity, the larger an air duct pressure loss in the heat exchanger. As a result, the size of a fan motor becomes so large that cost is boosted. Therefore, an upper limit of the wind velocity is about 3.5[m/s]. That is, when the wind velocity is about 3.5[m/s] or more, it is more advantageous in cost to improve heat transfer capability by increasing an heat transfer area of the heat exchanger than by increasing the wind velocity.
(1) Since an indoor unit performs cooling or heating a space where people stay, when the wind is strong (wind velocity is large), users feel, discomfort and noises become large, so that the air velocity is set comparatively small, 0.5 to 2 [m/s] (including low notch). Being used indoors, so that the unit has to be as compact as possible. Since there is no frost formation, a fin pitch is made small (approximately 1 to 2 rum).
(2) An air conditioner for equipment cools a large space such as a factory, so that it is necessary to have a large range and a large airflow volume is required. Because of these restrictions, the wind velocity of the air conditioner for equipment is set for approximately 3 to 3.5[m/s].
(3) Outdoor units of refrigerators (heat source side, outdoor units) and air conditioners are installed outdoors. Because dusts attach to the heat exchanger and degradation over time is significant, in place of improving heat transfer capability by increasing the wind velocity, they cope with degradation with age by increasing the heat transfer area. Because of these restrictions, the wind velocity of outdoor units of refrigerators and air conditioners are set for approximately 1.5 to 2 [m/s]
(4) Unit coolers (indoor unit side of the refrigerator) are installed in the cold storage warehouse and refrigeration warehouse and frost formation tends to occur, however, since they have wide fin pitches (4 to 10 mm) and are tolerant of noises, they are used under comparatively large wind velocities 1.5 to 3 [m/s].
Next, descriptions will be given to a method for selecting the adsorbent having an excellent matching with the refrigeration cycle. A method is conceivable for measuring the dehumidification capability by rotating the desiccant rotor 1 with the wind velocity being a parameter. However, since there are the “optimal rotation speed” and the “optimal division ratio for adsorption and desorption”, a great amount of time is required for measurement. Therefore, with the desiccant rotor 1 being stopped, time variation of weight of the desiccant rotor 1 is measured. FIG. 6 shows an example. FIG. 6 shows the relation between water adsorption amount (weight of the adsorber) and time under a certain wind velocity. A static characteristic of the adsorbent is a first-order lag system as shown in FIG. 6. From FIG. 6, a time constant (time needed to reach 0.63 times of the equilibrium adsorption amount) is obtained.
Next, the time constant is measured by changing the wind velocity in the range of the wind velocity (0.5 to 3.5 [m/s]) in the refrigeration cycle. FIG. 7 shows the time constant measured by changing the wind velocity. In FIG. 7, material A is the adsorbent not suited for the combination with the refrigeration cycle. Material B is the adsorbent suited for the combination with the refrigeration cycle. Regarding the material A, the time constant does not change when the wind velocity is 1.5 [m/s] or more in the range of the wind velocity (0.5 to 3.5 [m/s]) in the refrigeration cycle. The time constant represents the adsorption velocity, and the smaller the time constant, the larger the adsorption velocity. That is, since the time constant of material A shows almost no change in the range of the wind, velocity (0.5 to 3.5 [m/s]), it means no change in the dehumidification capability. On the other hand, regarding material B, in the range of the wind velocity 0.5 to 3.5 [m/s], as the wind velocity increases, the time constant becomes small. That is, it means that in the range of the wind velocity in the refrigeration cycle, the dehumidification capability can be varied by increasing the wind velocity.
Material B in FIG. 7 satisfies a relation represented by formula (1) in 0.5 to 3.5 [m/s].
T=√{square root over ( )}Ta/(C1×Xa×v) (1)
Where, T: time constant [s], Ta: air temperature [K], C1: constant (obtained by experiment), Xa: absolute humidity [kg_H2O/kg_air], and v: wind velocity
It is found that the time constant of material B is in inverse proportion to the wind velocity. That is, the larger the wind velocity, the smaller the time constant of Material B, and the smaller the wind velocity, the larger the time constant of the adsorbent.
Next, descriptions will be given to a method for deriving formula (1) above.
FIG. 8 is a diagram showing a structure of the portion where adsorption and desorption are performed in the dehumidification rotor 11 and its flat plate model. The inside of the cylinder of the desiccant rotor 1 has a honeycomb structure like FIG. 8( a) and can be expressed like 8(b) when substituted by a simple flat plate model. In the flat plate model, the structure of the inside of the cylinder 30 is expressed by a bulk air layer 31, boundary layer 32, and adsorbent layer 33, and further, on the adsorbent layer 33, unevennesses are formed created by adsorbent pores 34. A midgap 35 between bulk air layer and boundary layer is between the bulk air layer 31 and boundary layer 32 and a midgap 36 between boundary layer and adsorbent pores being between the boundary layer 32 and adsorbent pores 34. A thickness of the adsorbent layer 33 is expressed by a adsorbent layer thickness 37.
An adsorption velocity and desorption velocity are determined through a steam of a H₂O molecule of two stages in the midgap 35 between bulk air layer and boundary layer and the midgap 36 between boundary layer and adsorbent pores. Here, when adsorbent and desorbent velocities are expressed using an integrated mass-transfer coefficient kt, formula (2) is obtained based on a first-order Langmuir type adsorption/desorption formula. As an analytic solution of formula (2), formula (3) is obtained, which is a response of a first-order lag system. A time constant T expresses the time until the water amount in the air adsorbed/desorbed by the dehumidification rotor 11 reaches (1−e⁻¹) times (about 63.2%) of an equilibrium adsorption water amount q* against 1 kg of adsorbent.

Where,

q: water adsorption/desorption amount at an arbitrary time (kg_H2O/kg_ads)
t: arbitrary time (s),
q*: equilibrium adsorption water amount against 1 kg of adsorbent (kg_H2O/kg_ads),
kt: integrated mass-transfer coefficient (1/s), and
T: time constant (s) (Tad: adsorption time constant (s) or
Tde: desorption time constant (s)).
$\begin{matrix} Formulas \\ \frac{\partial q}{\partial t} = kt \cdot (q^{*} - q) & (2) \\ q = q^{*} \cdot (1 - e^{- kt \cdot t}) T = \frac{1}{kt} & (3) \end{matrix}$
The integrated mass-transfer coefficient kt, which is a factor determining adsorption and desorption velocities, originates, as shown in FIG. 8, in a two-stage mechanism of a mass transfer resistance in the midgap 35 between bulk air layer and boundary layer and that in the midgap 36 between boundary layer and adsorbent pores caused by a surface tension in the adsorbent layer, being represented by the formula (4) as follows.

Where,

kt: integrated mass-transfer coefficient (1/s),
ka: mass transfer coefficient in the midgap between bulk air layer and boundary layer 35 (1/s),
kb₁: mass transfer coefficient in the midgap between boundary layer and adsorbent pores 36 (1/s), and
1/kt=1/ka+1/kb1 (4)
A water movement amount Mad of the midgap 35 between bulk air layer and boundary layer per unit time and unit area at adsorption and water movement amount Mde at desorption are expressed by formula (5) as follows. The mass-transfer coefficient ka of the midgap between 35 bulk air layer and boundary layer is in proportion to a mass-transfer coefficient αm of the H₂O molecule of the midgap 35 between bulk air layer and boundary layer.

Where,

Mad: water movement amount at adsorption (kg_H2O/(m²·s)),
Mde: water movement amount at desorption (kg_H2O/(m²·s))
Xa: bulk air layer absolute humidity (kg_H2O/kg_air),
Xc: boundary layer absolute humidity (kg_H2O/kg_air),
ρa: bulk air layer air density (kg_air/m³),
ρc: boundary layer air density (kg_air/m³), and
αm: mass-transfer coefficient of the H₂O molecule of the midgap between bulk air layer and boundary layer (m/s).
At adsorption: Mad=αm×(xa−xc)×ρa(xa>xc)
At desorption: Mde=αm×(xc−xa)×ρc(xc>xa) (5)
The mass-transfer coefficient αm of the H₂O molecule of the midgap 35 between bulk air layer and boundary layer is in proportion to a product of a condensation frequency Jin, expressed by the number of molecules coming in per unit time and unit area, and wind velocity v. The condensation frequency Jim is calculated by formula (6) as follows. Formula (7) can be obtained based on formula (6).

Where,

αm: mass-transfer coefficient of the H₂O molecule of the midgap between bulk air layer and boundary layer (m/s),
Jin: condensation frequency (number of molecules/(m²′ s)),
V: wind velocity (m/s),
M: mass of water molecule (kg)=3×10⁻²⁶,
k: Boltzmann constant (J/K)=1.38×10⁻²³,
T: absolute temperature (K),
P: vapor partial pressure (N/m²),
C1; coefficient (obtained based on a static characteristic experiment, etc.), and
Ta: air layer absolute temperature (K).
$\begin{matrix} Formulas \\ α m \propto Jin \times v = \frac{p}{\sqrt{2 π mkT}} \times v & (6) \\ ka \propto α m \propto Jin \times v = \frac{p}{\sqrt{2 π mkT}} \times v \propto c 1 \times \frac{xa \cdot v}{\sqrt{Ta}} & (7) \end{matrix}$
On the other hand, adsorption/desorption velocities of the midgap 36 between boundary layer and adsorbent pores by a surface tension in the adsorbent pores 34 is calculated by formula (8) as follows.

Where,

q: adsorbed water amount at an arbitrary time (kg_H2O/kg_ads),
t: arbitrary time (s),
dp: adsorbent average particle size (m),
Ds: surface diffusion coefficient in the adsorbent pores 34 (m²/s),
q*: equilibrium adsorption water amount against adsorbent of 1 kg (kg_H2O/kg_ads),
kb: mass transfer coefficient of the H₂O molecule in the boundary layer and adsorbent layer pores, and
ab: adsorption layer thickness (m).
$\begin{matrix} Formula \\ \frac{\partial q}{\partial t} = \frac{15}{{dp}^{2}} \cdot D_{s} \cdot (q^{*} - q) \approx \frac{kb}{ab} \cdot (q^{*} - q) & (8) \end{matrix}$
A surface diffusion coefficient in the adsorbent pores 34 in formula (8) is calculated by formula (9) called an Arrhenius equation as follows. Since an absorbent layer absolute temperature Tb turns into an air layer absolute temperature Ta in a short time period, it is assumed that Tb≈Ta.

Where,

Ds: surface diffusion coefficient in the adsorbent pores (m²/s),
Ds0: 2.54×10⁻⁴(m²/s)
Ea: activation energy (j/mol)=4.2×10⁴,
R0: gas constant (J/(mol·K)), and
Tb: adsorbent layer absolute temperature (K)
$\begin{matrix} Formula \\ D_{s} = D_{s} 0 \cdot \exp (\frac{- Ea}{R 0 \cdot Tb}) & (9) \end{matrix}$
The mass transfer coefficient kb₁in the midgap 36 between boundary layer and adsorbent pores by a surface tension in the adsorbent pores 34 is in proportion to the surface diffusion coefficient Ds in the adsorbent pores 34. Therefore, formula (10) as follows is obtained.

Where,

kb₁: mass transfer coefficient in the boundary layer and adsorbent pores (1/s),
kb: mass transfer coefficient of the H₂O molecule in the boundary layer and adsorbent layer pores (m/s),
ab: adsorbent layer thickness (m),
c2: coefficient (obtained based on a static characteristic experiment, etc.), and
Ds: surface diffusion coefficient in the adsorbent pores 34 (m²/s).
Kb ₁ =kb/ab∝c2×Ds (10)
From formulas (3), (7), and (10), the time constant T is expressed by formula (11) as follows. An adsorption time constant Tad and desorption time constant Tde are determined based on formula (11).

Where,

T: time constant (s) (Tad: adsorption time constant (s) or
Tde: desorption time constant (s)),
ka: mass transfer coefficient in the midgap between bulk air layer and boundary layer 16 (1/s),
kb₁: mass transfer coefficient in the boundary layer and adsorbent pores (1/s),
Ta: air layer absolute temperature (K),
C1: coefficient (obtained based on a static characteristic experiment, etc.),
Xa: bulk layer absolute humidity (kg_H2O/kg_air),
V: wind velocity (m/s),
C2: coefficient (obtained based on a static characteristic experiment, etc.), and
Ds: surface diffusion coefficient in the adsorbent pores 34 (m²/s)
$\begin{matrix} Formula \\ T = \frac{1}{kt} = \frac{1}{ka} + \frac{1}{{kb}_{1}} \propto \frac{1}{\frac{c 1 \cdot xa \cdot v}{\sqrt{Ta}}} + \frac{1}{c 2 \cdot D_{s}} & (11) \end{matrix}$
FIG. 9 is a diagram showing the relation between the adsorption/desorption time and adsorption/desorption amount. hen actually applying to an air conditioning apparatus, for example, a static characteristic experiment using the dehumidification rotor 11 is performed and values such as the adsorption time constant Tad and desorption time constant Tde are determined based on the above mentioned formulas.
Here, formula (11) is considered.
When an internal diameter (hereinafter, referred to d) of the pore becomes an order of nm, since as the pore internal diameter d becomes smaller, a bonding strength (conservative force) becomes stronger between water (H₂O) molecules accommodated in the pore and molecules constituting the pore wall, the water molecule is hard to be separated and diffused from the pore. That is, an activation energy Ea in formula (9) is dependent on the internal diameter of the pore d. In the case of zeolite, the pore diameter is about 0.5 mm and the activation energy of the zeolite becomes relatively large. When the activation energy becomes large, the surface diffusion coefficient Ds becomes relatively small according to formula (9). It shows that in the zeolite, water in the pore becomes difficult to move. When the surface diffusion coefficient Ds becomes relatively small, mass transfer resistance 1/kb₁between boundary layer and adsorbent layer pores becomes relatively large. Thereby, the integrated mass-transfer resistance 1/kt is rate-limited by the resistance inside the pore according to formula (11) and does not decrease less than a certain value.
Accordingly, regarding the time constant T expressed by formula (11), when the wind velocity is increased, a first term on the right-hand of formula (11) becomes small. However, the value of a second term on the right-hand is large, the time constant is rate-limited by the second term on the right-hand and does not decrease less than a certain value.
On the other hand, when the pore internal diameter d>1 nm, the activation energy Ea is smaller than the zeolite. So that, the influence of the second term on the right-hand becomes small and the time constant T strongly depends on the first term on the right-hand of formula (11). As a result, formula (1) is derived and as the wind velocity increases, the time constant becomes small.
When expressing the relation between the wind velocity and time constant of the adsorbent by a graph, FIG. 10 is obtained. Based on the above investigation, it is theoretically confirmed that there is a dependence property among the pore diameter, time constant, and wind velocity. From experiments (FIGS. 7 and 12) supported data can be obtained that the theory is appropriate, as well. It is found that the pore diameter of the adsorbent having an excellent matching with the refrigeration cycle is 1 nm or more. Specifically, it is found that mesciporous silica is well suited typical material with the refrigeration cycle having pores of 1 nm or more and whose pore distribution is small (homogeneous).
Like the present invention, when the wind velocity is in the range 0.5 to 3.5 [m/s], by applying the absorbent whose time constant decrease as the wind velocity increases to the refrigeration cycle, the power of a blower can be effectively used.
FIG. 11 shows the relation between the wind velocity and heat exchanger capability. FIG. 12 shows an example of the relation between the wind velocity and dehumidification capability (adsorption capability).
As is found from FIG. 11, when the wind velocity (the wind velocity of the air passing the heat exchanger) is increased, the heat transfer coefficient front a fin to the air in the heat exchanger becomes large, so that heat exchanger capability is improved. By using the characteristic, control and operation means to be described adjusts refrigeration (condensation) capability by varying the wind velocity against load change in the refrigeration cycle. Specifically, when increasing the refrigeration (condensation) capability, the control and operation means accelerate the rotation speed of the blower to make the wind velocity larger. When reducing the refrigeration (condensation) capability, the control and operation means decelerate the rotation speed of the blower to make the wind velocity smaller. To control the wind velocity (airflow volume) is effective means to control capability of the refrigeration cycle.
As is found from FIG. 12, when the wind velocity is increased, since the amount of the air passing per unit time in contact with the adsorbent carried by the desiccant rotor 1 increases, the dehumidification capability of the adsorbent is enhanced.
In a common environment, since most of loads are occupied by ingress of the outside air, a sensible heat load and latent heat load (dehumidification load) simultaneously increase and decrease. That is, when a large latent heat capability (dehumidification capability) is needed, a large sensible heat capability is required as well. Like the present invention, in the wind velocity range (0.5 to 3.5 [m/s]) needed by the refrigeration cycle, by applying the adsorbent whose dehumidification capability increases with the increase of the wind velocity to the refrigeration cycle, the dehumidification capability and sensible heat capability can be adjusted by the wind velocity (rotation speed control of the blower). As a result, an operation range of the system is expanded and load change following capability is improved. Further, since latent heat is properly removed, frost formation onto the evaporator located at the downstream of the desiccant can be stably prevented, so that reliability of the system can be improved.
Next, descriptions will be given to an example of a method for controlling the present invention. As shown in FIG. 1, the present system has evaporation temperature detection means 20 e, means 20 f for detecting an evaporator suction air temperature and relative humidity, means 20 g for detecting the air temperature and relative humidity at an inlet of the desiccant (adsorption side), means 20 h for detecting condenser blowoff air temperature and relative humidity. A temperature sensor 20 e, temperature and humidity sensors 20 f, 20 g, and 20 h, control and operation means 20 i are also provided.
By the temperature and humidity sensor 20 g, the temperature (T0) and relative humidity (RHO) inside are detected. The measured T0 and RH0 are converted into an enthalpy H of the air by the control and operation means 20 i. A table of air enthalpy and wind velocity as shown by table 1 is determined by such as a test in advance, and the table is made to be stored in storage means (not shown) in the control and operation means 20 i. When needed, based on the table in the storage means, by controlling the voltage of the blower motor, the air volume is controlled. Basically, when the air enthalpy H is large (a large load), the air volume is made large. When the air enthalpy H is small (a small load), the air volume is made small.

TABLE 1

Table of air enthalpy H and blower motor voltage (wind velocity)

Air enthalpy	H < H1	H1 ≦ H < H2	H2 ≦ H < H3	H3 ≦ H

Blower motor	V 0	V 1	V 2	V 3
voltage

The suction temperature (T1) and relative humidity (RH1) of the evaporator 20 r are detected by the temperature and humidity sensor 20 f. The measured T1 and RH1 are converted into a dew point (Td) by the control and operation means 20 i. When an evaporation temperature (Te) is controlled to be the dew point or over, no frost is formed in the evaporator and no defrost operation is required, so that efficiency is significantly improved. In the present embodiment, the “dew point Td (° C.)” is made to be a target evaporation temperature Tem. The control and operation means 20 i adjust the frequency of the compressor 20 a and opening of the expansion valve 20 c so that the evaporation temperature be Tem or more. For example, when Te>Tem, the control and operation means 20 i increases the frequency and decrease the opening of the expansion valve 20 c. To the contrary, when Te<Tem, the control and operation means 20 i decreases the frequency and increase the opening of the expansion valve 20 c.
Next, descriptions will be given to the control of the condenser side. By the temperature and humidity sensor 20 h, a blowout temperature (T2) and relative humidity (RH2) of the condenser 20 d are detected. The control and operation means 20 i adjusts the frequency of the compressor 20 a and opening of the expansion valve 20 c so that the relative humidity of the condenser side becomes a target relative humidity (RHm, 20% in the present embodiment). When RH2>RHm, the control and operation means 20 i increases the frequency and reduce the opening of the expansion valve 20 c. To the contrary, when RH2<RHm, the control and operation means 20 i decreases the frequency and in-creases the opening of the expansion valve 20 c.
In addition, in order to secure dehumidification performance, since it is necessary to sufficiently reproduce the adsorbent, to make the relative humidity of the condenser side be the target relative humidity or less becomes a prioritized item of control for the most part of the operation range.
FIG. 4 is a configuration diagram of an essential part of the refrigerating and air conditioning apparatus according to the embodiment of the present invention. At the same time, water adsorption characteristic is shown of the adsorbent provided in the desiccant rotor, which is water adsorption means. The adsorbent is a porous silicon material with a number of pores of about 2 nm (nanometer) being prepared and adsorbs water through a capillary condensation phenomenon. In FIG. 4, a horizontal axis is the relative humidity in an air-conditioned space and vertical axis is an equilibrium water adsorption amount. It is found from FIG. 4 that a feature of the adsorbent employed in the present embodiment of the present invention is that an inclination which is a rate of change of equilibrium water adsorption against the relative humidity in the range of 20 to 30% is greater than that in the range of less than 20% or 30% or over. According to our study, mesoporous silica having homogeneous pores of 1 to 10 nm is the adsorbent having a strong dependency on the wind velocity and being especially well suited with the refrigeration cycle in the range of the wind velocity of the refrigeration cycle.

Claims

1. A refrigerating and air conditioning apparatus comprising;

a refrigerant circuit in which a refrigerant is put, having a compressor for compressing the refrigerant, a condenser, and a throttle device, and an evaporator, and

a water adsorption portion which adsorbs water in an air-conditioned space to release into the open air,

wherein an adsorbent is employed for the water adsorption portion whose time constant of water adsorption equilibrium decreases as a wind velocity increases.

2. The refrigerating and air conditioning apparatus of claim 1, wherein the adsorbent is mesoporous silica having homogeneous pores of 1 to 10 nm and passing wind velocities of the water adsorption portion, the evaporator, and the condenser being set for 0.5 to 3.5 m/s.

3. The refrigerating and air conditioning apparatus of claim 1, wherein the adsorbent satisfies a relation

T=√Ta/(C1×Xa×v)

provided that a time constant is T [s], air temperature Ta [K], constant C1, absolute temperature Xa [kg_H2O/kg_air], and wind velocity v.

4. The refrigerating and air conditioning apparatus of claim 1, wherein the water adsorption portion is a rotor type in which said adsorbent is supported, being disposed downwind of the condenser and at the same time being disposed upwind of the evaporator.

5. The refrigerating and air conditioning apparatus of claim 1, comprising:

a blower provided in the air-conditioned space for the evaporator making the water adsorption portion ventilate the air therein;

storage means for storing a table making an enthalpy of air correspond with a control voltage of driving means for driving the blower;

temperature and humidity detection means for detecting a temperature and a relative humidity of air in the air-conditioned space prior to passing the water adsorption portion; and

control and operation means for converting detection results of the temperature and humidity detection means into enthalpy to obtain a control voltage corresponding to the enthalpy by referring to a table stored in the storage means and controlling the driving means based on the control voltage.

6. The refrigerating and air conditioning apparatus of claim 1, comprising:

a blower provided in said air-conditioned space for the evaporator making the water adsorption portion ventilate air therein;

temperature and humidity detection means for detecting a temperature and a relative humidity of the air in the air-conditioned space after passing the water adsorption portion and prior to passing the evaporator by a force of the blower; and

control and operation means for converting a dew point temperature of the evaporator based on detection results of the temperature and humidity detection means to control the frequency of the compressor and opening of the expansion device so that an evaporation temperature of the evaporator becomes equal to or larger than the dew point temperature.

7. The refrigerating and air conditioning apparatus of claim 1, comprising:

a blower provided at the outside of the air-conditioned space and making the water adsorption portion ventilate the air passing the condenser;

temperature and humidity detection means for detecting a temperature and a relative humidity of air at the outside of the air-conditioned space after passing the condenser and prior to passing the water absorption portion by a force of the blower; and

control and operation means for controlling the frequency of the compressor and opening of said expansion device based on detection results of the temperature and humidity detection means so that the relative humidity becomes a predetermined value.

8. The refrigerating and air conditioning apparatus of claim 2, wherein the adsorbent satisfies a relation

T=√Ta/(C1×Xa×v)

9. The refrigerating and air conditioning apparatus of claim 2, wherein the water adsorption portion is a rotor type in which said adsorbent is supported, being disposed downwind of the condenser and at the same time being disposed upwind of the evaporator.

10. The refrigerating and air conditioning apparatus of claim 3, wherein the water adsorption portion is a rotor type in which said adsorbent is supported, being disposed downwind of the condenser and at the same time being disposed upwind of the evaporator.

11. The refrigerating and air conditioning apparatus of claim 2, comprising:

12. The refrigerating and air conditioning apparatus of claim 3, comprising:

13. The refrigerating and air conditioning apparatus of claim 4, comprising:

14. The refrigerating and air conditioning apparatus of claim 2, comprising:

15. The refrigerating and air conditioning apparatus of claim 3, comprising:

16. The refrigerating and air conditioning apparatus of claim 4, comprising:

17. The refrigerating and air conditioning apparatus of claim 2, comprising:

18. The refrigerating and air conditioning apparatus of claim 3, comprising:

19. The refrigerating and air conditioning apparatus of claim 4, comprising: