Air-conditioning system

Abstract

[Problem] To provide a low-cost, energy-saving air-conditioning system that can keep the inside of a greenhouse at an appropriate temperature and humidity day or night. [Solution] The present invention uses a total heat exchanger to adjust the temperature and humidity inside a greenhouse. In a total heat exchange cooling mode, a total heat exchange is performed between outside air and the air inside the greenhouse to lower the temperature and humidity, and, as necessary, the temperature inside the greenhouse is effectively lowered by means of cooling by a cooling tower. In a dehumidifying and heating mode, the air inside the greenhouse is dehumidified to lower the humidity, and the inside of the greenhouse is heated by means of the heat of adsorption generated by the dehumidification. Switching between the two operation modes makes it possible to adjust the environment inside the greenhouse to an optimum temperature and humidity for the growth of plants day and night.

Description

Air conditioning system

[0001] The present invention relates to an energy-saving, low-cost air conditioning system that can maintain the temperature and humidity inside a greenhouse at a temperature and humidity suitable for plant growth, day and night.

[0002] In this specification, "daytime" refers to the period from sunrise to sunset, and "nighttime" refers to the period from sunset to sunrise the next morning.

[0003] In agricultural greenhouses for growing tomatoes, strawberries, and other crops (hereinafter, including plant factories and horticultural facilities, referred to as "greenhouses"), daytime temperatures inside the greenhouse often exceed 30°C (all temperatures hereafter referred to as "Celsius") due to sunlight. Even in winter, when the outside temperature is in the single digits, the temperature inside the greenhouse can exceed 30°C during the day. For this reason, from spring to autumn, or even in winter, to lower the temperature inside the greenhouse, natural ventilation equipment such as the greenhouse's entrances, skylights, and sides are opened during the day to bring in outside air and ventilate. Forced ventilation equipment such as ventilation fans is also installed to blow outside air into the greenhouse. Typically, this type of ventilation lowers the temperature and humidity inside the greenhouse or introduces carbon dioxide, creating an optimal cultivation environment for plants. However, opening the greenhouse changes the air environment inside the greenhouse, creating a stressful situation for plants. It also significantly increases the risk of pests entering from outside.

[0004] In greenhouse cultivation, maintaining a higher carbon dioxide concentration than the atmosphere promotes photosynthesis and improves yields. This is done by applying carbon dioxide from carbon dioxide supply devices such as carbon dioxide cylinders or kerosene burners. However, when the greenhouse is opened, the supplied carbon dioxide mixes with the outside air and becomes diluted, preventing the carbon dioxide concentration from increasing, meaning that much of the supplied carbon dioxide is released into the atmosphere.

[0005] Therefore, greenhouses are closed systems, i.e., completely closed greenhouses (hereinafter referred to as "closed greenhouses") or semi-closed greenhouses (semi-closed greenhouses), allowing plants to be produced while controlling the internal environment, including light, temperature, humidity, and carbon dioxide. Typically, air conditioners and dehumidifiers are used to control the temperature and humidity inside the greenhouse. A system is also used in which outside air is supplied to the greenhouse after heat exchange with the air inside. Furthermore, when actively lowering the temperature and humidity, cooling is performed using a heat pump or other cooling device. However, the temperature inside the greenhouse can easily rise above 30°C due to solar radiation, and cooling using a heat pump or other cooling device requires a great deal of energy. Another problem is that humidity is also reduced by the need for large amounts of dehumidification through irrigation and transpiration from the plants, resulting in high power consumption.

[0006] On the other hand, as the sun sets, heat escapes, gradually lowering the temperature inside the greenhouse. Closing the greenhouse at night and turning off ventilation fans prevents the temperature from dropping. However, unless some form of thermal energy is added, the greenhouse temperature will eventually reach a similar level to the outside air temperature. Furthermore, because the greenhouse is isolated from the outside air, radiative cooling is not mitigated, and depending on the weather, the temperature inside the greenhouse may drop below the outside air temperature. A large temperature difference between daytime and nighttime can actually stress plants and affect their growth. Furthermore, excessively low nighttime temperatures, especially in winter, can lead to low-temperature injury, frost damage, and other damage. Therefore, it is necessary to prevent the temperature inside the greenhouse from dropping and maintain the temperature by heating or maintaining it at night. To heat the greenhouse, fuel-oil heaters or heat pump air conditioners are installed. In addition, indoor curtains can be installed inside the greenhouse to enhance the thermal insulation effect. Furthermore, to reduce temperature variations, ventilation ducts and circulating fans are installed.

[0007] However, fuel-fired heating devices such as boilers and burners have become expensive due to the recent rise in fuel prices, resulting in particularly high heating costs in winter. They also require regular maintenance, and incomplete combustion can lead to poor combustion efficiency and the risk of carbon monoxide poisoning. Heat pumps have the advantage of being able to use several times the heat consumed for heating, but their high installation costs make them unsuitable for large greenhouses. While high thermal insulation can be achieved by using multiple layers of interior curtains, cold air can seep in through gaps, and the multi-layer coating can reduce light transmission during the day, resulting in insufficient sunlight and high temperatures and humidity. Installing ventilation ducts is both time-consuming and costly.

[0008] The factor that has the greatest impact on the temperature inside a greenhouse is changes in the outside temperature. Temperatures can change significantly even within a single day, especially in spring and autumn. In winter, the temperature inside a greenhouse can also fall below the outside temperature. Depending on the type of plant, there are variations in the optimum daytime temperature for growth and the minimum limit temperature at night. However, the cost involved in stabilizing the temperature inside a greenhouse day and night has been an issue. For this reason, there is a strong demand for the introduction of energy-saving equipment and technology.

[0009] In a prior application (Japanese Patent Application No. 2023-063461), the present applicant proposed an air conditioning system that can adjust the temperature and humidity inside the greenhouse to optimal levels for plants without opening it by installing a carbon dioxide supplying device in the greenhouse, circulating the air inside the greenhouse using the carbon dioxide supplying device, and then totally exchanging the heat of the air inside the greenhouse with outside air using a total heat exchanger before supplying it back into the greenhouse.This air conditioning system can use carbon dioxide captured from the atmosphere using DAC (Direct Air Capture) technology to adjust the carbon dioxide concentration, contributing to carbon neutrality.

[0010] In this air conditioning system, in order to lower the temperature inside the greenhouse during the daytime, a total heat exchanger is used to bring the temperature and humidity inside the greenhouse closer to that of the outside air. This makes it possible to maintain the temperature inside the greenhouse at around 30°C, but for winter crops such as strawberries, lowering the temperature inside the greenhouse to around 20°C increases the sugar content and commercial value. Increasing the number of total heat exchangers and increasing the processing air volume is an effective way to further lower the temperature inside the greenhouse during the daytime, but this increases the initial cost. Furthermore, in the cultivation environment, excessive airflow from the large amount of air supplied by the total heat exchangers can stress the plants, so it is preferable to avoid installing excessive total heat exchangers.

[0011] As described above, conventional technologies can lower the temperature and humidity by using a total heat exchanger to exchange heat between the air inside the greenhouse and the outside air during the day, but there is a limit to how much lower the temperature inside the greenhouse can be during the day. Another issue is the high costs of the devices, equipment, and fuel required to heat and keep the greenhouse warm at night.

[0012] The present invention has been made to solve these problems, and aims to provide an energy-saving, low-cost air conditioning system that combines the operating method of a total heat exchanger with a cooling tower or the like to suppress increases in temperature and humidity inside the greenhouse during the day, and increases in humidity and decreases in temperature inside the greenhouse at night, thereby maintaining temperature and humidity levels suitable for plant growth both day and night.

[0013] The air conditioning system of the present invention uses a total heat exchanger to adjust the temperature and humidity inside the greenhouse. During the day, it operates in total heat exchange cooling mode, lowering the temperature and humidity by total heat exchange between the air inside the greenhouse and outside air, and effectively lowering the temperature inside the greenhouse by cooling using a cooling tower or other device as needed. At night, it operates in dehumidifying heating mode, dehumidifying the air inside the greenhouse to lower the humidity, and heating the greenhouse using the heat of adsorption generated by dehumidification. The system's most significant feature is that it can switch between these two operating modes to adjust the temperature and humidity inside the greenhouse to optimal levels for plant growth throughout the day and night.

[0014] The air conditioning system of the present invention can realize a closed greenhouse in which the temperature and humidity inside the greenhouse are maintained at optimal levels for plant growth day and night using only a total heat exchanger by switching between a daytime total heat exchanger function and a nighttime desiccant (dehumidifying) function. By using the air conditioning system of the present invention, other cooling or heating equipment is unnecessary or can be used only as a supplement, thereby reducing costs such as fuel and electricity. The air conditioning system of the present invention can lower the temperature and humidity inside the greenhouse during the day and heat the greenhouse while lowering humidity at night, promoting plant growth and reducing damage to plants caused by low-temperature damage, high-temperature damage, and pests. During hot periods, the temperature inside the greenhouse can rise above body temperature, posing safety risks such as heatstroke for workers. However, the air conditioning system of the present invention improves the environment inside the greenhouse for both plants and humans, potentially improving workability. The use of a total heat exchange rotor allows for easy switching between operating modes by simply changing the rotation speed. Since the power consumed is limited to the total heat exchanger's fan and the motor driving the rotor, significant energy savings are achieved compared to cooling methods such as heat pumps.

[0015] Furthermore, the air conditioning system of the present invention can effectively lower the temperature inside the greenhouse by using a cooling tower. The cooling tower uses natural energy and can cool the air using outside air as a heat source, so it is low cost and environmentally friendly. The cooling tower is powered only by a blower and a pump, so both the initial cost and running cost are low.

[0016] In the dehumidifying and heating mode of the total heat exchanger used in the present invention, the regeneration inlet temperature is set lower than the normal low-temperature regeneration temperature of 40 to 80°C, thereby saving energy and reducing running costs. The heat exchanger that heats the air at the regeneration inlet does not require active heating, and it can use not only hot water but also groundwater, circulating water, solar heat, geothermal heat, and waste heat from the equipment as regeneration heat, resulting in extremely energy savings.

[0017] Furthermore, because the air conditioning system of the present invention circulates the air inside the greenhouse and does not take in outside air, the carbon dioxide supply device can raise the carbon dioxide concentration inside the greenhouse to around 800 to 1000 ppm, which promotes plant photosynthesis. Since no carbon dioxide leaks into the outside air, it is only necessary to supply the amount of carbon dioxide absorbed by the plants, minimizing the operation of the carbon dioxide supply device and enabling energy-saving operation.

[0018] When greenhouses are closed systems, air flow is weak, and even if the leaf stomata are open, the carbon dioxide concentration near the leaf surface decreases, suppressing photosynthesis. However, a total heat exchanger can create air flow within the greenhouse, promoting leaf photosynthesis. Air flow also makes it possible to uniformize the temperature, humidity, and carbon dioxide concentration within the greenhouse. In this way, a closed greenhouse allows for air control of temperature, humidity, carbon dioxide concentration, and airflow, providing a space that is less stressful for plants. Furthermore, lowering the temperature within the greenhouse through cooling using a cooling tower or other device can avoid the installation of excessive total heat exchangers and provide adequate airflow to the plants.

[0019] In addition, windows and motors for opening the roof and sides of the greenhouse are either not needed or can be reduced, reducing the initial cost of the greenhouse itself. By making the greenhouse a closed system, the effects of wind and rain can be completely blocked. Furthermore, since pests and diseases cannot enter from outside, the effort of putting up insect netting is eliminated, making it possible to reduce the use of pesticides and making it possible to realize environmentally friendly agriculture such as organic farming. In recent years, extreme weather due to climate change has become commonplace, and as a result, trends in the occurrence of pests and diseases are changing, making cultivation management more difficult every year. The total heat exchanger of the present invention allows for easy switching of operating modes, reducing the burden of cultivation management.

[0020] The air conditioning system of the present invention is particularly suitable for strawberry cultivation. If the temperature inside the greenhouse exceeds 32°C, the fruit will sunburn, resulting in unsalable strawberries that will have to be discarded. Therefore, measures are needed to ensure that the temperature inside the greenhouse does not exceed 32°C, preferably 30°C. Depending on the variety, the optimum daytime temperature for strawberries is 18-23°C, and nighttime temperatures must be maintained at a minimum of 5-7°C. Strawberries are cold-tolerant, but are susceptible to frost damage in prolonged freezing temperatures or temperatures below -5°C. Furthermore, if the temperature inside the greenhouse is suddenly raised while strawberry plants are cold from nighttime temperatures, the temperature difference will cause condensation on the cold plants. Condensation not only makes it difficult for stomata, which are responsible for transpiration, to open, but also hinders harvesting and increases the risk of disease.

[0021] According to test results, strawberries perform well when grown in a greenhouse with a temperature between 15 and 30°C. It has also been reported that while yields are high at greenhouse temperatures of both 20°C and 30°C, 20°C is superior in terms of quality, such as sweetness. The air conditioning system of the present invention can effectively lower the daytime greenhouse temperature from 30°C to approximately 20°C during the winter, spring, and autumn seasons by operating in total heat exchange cooling mode during the day and using a cooling tower or other cooling device. Since the greenhouse can also be heated at night, the strawberries are not damaged by high or low temperatures. Thus, the air conditioning system of the present invention is particularly effective for cultivating strawberries, a winter crop, and enables the production of high-quality strawberries at high yields.

[0022] Fig. 1 is a diagram showing a closed house using the air conditioning system of the present invention, in which a carbon dioxide supply device and a total heat exchanger are installed separately. Fig. 2 is a flow diagram of a total heat exchanger used in the air conditioning system of the present invention. Fig. 3 is a psychrometric chart showing the results of dehumidification performance calculations assuming that adiabatic dehumidification occurs in Example 2 of the present invention. Fig. 4 is a psychrometric chart showing the results of dehumidification performance tests in Example 3 of the present invention. Fig. 5 is a psychrometric chart showing adiabatic dehumidification and isothermal dehumidification.

[0023] In the air conditioning system of the present invention, a carbon dioxide supplying device is provided in the greenhouse, which makes the carbon dioxide concentration of the air inside the greenhouse higher than that of the outside air, and a total heat exchanger is provided to exchange total heat between the air inside the greenhouse and the outside air, so that the environment inside the greenhouse can be adjusted to the optimum temperature and humidity for plant growth.

[0024] (Closed House) The air conditioning system of the present invention can realize a closed house. As shown in FIG. 1, a closed house using the air conditioning system of the present invention includes a carbon dioxide supplying device 2 and a total heat exchanger 3. The interior of the house 1 is controlled to maintain a constant environment suitable for plant growth, such as a temperature of 20-30°C, a humidity of 55-85% RH, and a carbon dioxide concentration of 800-1000 ppm. The carbon dioxide supplying device 2 supplies air with an increased carbon dioxide concentration into the house 1, thereby increasing the carbon dioxide concentration within the house 1. As a result, it is possible to achieve a carbon dioxide concentration of approximately 1000 ppm, which promotes plant photosynthesis. The total heat exchanger 3 performs total heat exchange between the air within the house 1 and outside air and supplies the air back into the house 1. This reduces the temperature and humidity of the air within the house 1, which has become hot and humid, without reducing the carbon dioxide concentration within the house. In this way, the air conditioning system of the present invention can adjust the temperature and humidity within the house to an optimal temperature and humidity for plants without opening the house.

[0025] (Carbon Dioxide Supply Device) While the carbon dioxide supply device used in the air-conditioning system of the present invention is not limited, a device using an adsorption rotor 4 and DAC technology to separate, capture, and concentrate carbon dioxide from the atmosphere and supply it to plants is preferred, as shown in Figure 1. The carbon dioxide supply device 2 takes in air from the greenhouse 1, which has a higher carbon dioxide concentration than the outside air, and supplies the air with an increased carbon dioxide concentration back into the greenhouse 1, thereby increasing the carbon dioxide concentration within the greenhouse 1. In Figure 1, the carbon dioxide supply device 2 equipped with the adsorption rotor 4 is installed within the greenhouse 1. The adsorption rotor 4 is a honeycomb rotor made by corrugating a non-flammable sheet such as glass fiber or ceramic fiber paper and wrapping it around a rotor, and is supported with a carbon dioxide adsorbent such as a weakly basic ion exchange resin or an amine-supported solid adsorbent. Alternatively, the adsorption rotor 4 has a hollow cylindrical shape and is filled with granular or pellet-shaped carbon dioxide adsorbent.

[0026] The adsorption rotor 4 is driven to rotate at a constant speed around its central axis by a geared motor (not shown) or the like. The adsorption rotor 4 has an adsorption zone that passes at least outside air in the direction of rotation of the rotor, adsorbs carbon dioxide from the outside air, and exhausts the adsorption zone to the outside. The adsorption rotor 4 also has a desorption zone that passes air from the house 1 heated by a regeneration heater (not shown) or the like, desorbs the carbon dioxide adsorbed in the adsorption zone, and returns the air to the house 1. This allows the carbon dioxide concentrator 2 to concentrate the carbon dioxide in the house 1 and circulates and supplies the high-concentration carbon dioxide within the enclosed house 1. The adsorption rotor 4 may also have other zones, such as a purge zone or a pre-purge zone, in addition to the adsorption zone and desorption zone. Furthermore, the desorption of carbon dioxide from the adsorption rotor 4 is not limited to a temperature swing due to heating, but may also be a pressure swing due to reduced pressure.

[0027] The carbon dioxide supplying device 2 is not limited to one that uses an adsorption rotor, and may also be a carbon dioxide cylinder or a kerosene burner. Also, a carbon dioxide supplying device that uses a chemical absorption method, a physical absorption method, a membrane separation method, or the like may be used. In this way, the present invention can be implemented by simply installing a total heat exchanger (described below) in a greenhouse that already has a carbon dioxide supplying device installed.

[0028] (Total heat exchanger) In the total heat exchanger 3 used in the air conditioning system of the present invention, part of the air inside the house 1 is sent to the total heat exchanger 3, where it exchanges total heat with outside air, and then the air is returned to the house 1. This reduces the temperature and humidity of the air inside the house 1, which has become hot and humid, but does not reduce the carbon dioxide concentration inside the house.

[0029] 2 is a flow diagram of the total heat exchanger used in the air conditioning system of the present invention. The total heat exchanger 3 is equipped with a total heat exchange rotor 5. The total heat exchange rotor 5 is made of an aluminum sheet or the like formed into a honeycomb shape, with a moisture adsorbent carried on the sheet, ultimately forming a rotatable rotor. Examples of moisture adsorbents include calcium chloride, diatomaceous earth, silica gel, zeolite, ion exchange resins, and polymer adsorbents.

[0030] The total heat exchange rotor 5 has at least a treatment zone 6, which passes air from within the greenhouse 1 in the direction of rotation of the rotor and returns the air to the greenhouse 1, and a regeneration zone 7, which passes outside air and exhausts it outside the device. In the present invention, the total heat exchanger 3 has two operating modes: a total heat exchange cooling mode and a dehumidifying heating mode. It operates in the total heat exchange cooling mode during the day to reduce the temperature and humidity inside the greenhouse, and effectively lowers the temperature inside the greenhouse by cooling using a cooling tower as needed. It operates in the dehumidifying heating mode at night to dehumidify the greenhouse and heat the greenhouse using the heat of adsorption generated by dehumidification. Switching between the total heat exchange cooling and dehumidifying heating operating modes of the total heat exchanger can be easily achieved by simply changing the rotation speed of the total heat exchange rotor, which rotates at a high speed in the total heat exchange cooling mode and a low speed in the dehumidifying heating mode. This realizes a closed greenhouse that can maintain a temperature and humidity suitable for plant growth throughout the day and night.

[0031] (Daytime: Total Heat Exchange Cooling Mode) During the daytime, the temperature inside the greenhouse rises due to solar radiation, and the humidity inside the greenhouse also rises due to watering and plant transpiration, resulting in a higher temperature and humidity inside the greenhouse than outside. Therefore, the total heat exchanger is operated in total heat exchange cooling mode. That is, the total heat exchange rotor is operated at a high speed of several tens of rpm (rotations per minute, the number of rotor rotations per minute), for example 20 rpm, to exchange total heat between the air inside the greenhouse and outside air and lower the temperature and humidity.

[0032] As shown in FIG. 2 , on the treatment side, a portion of the air inside the greenhouse 1 is passed through an air filter (AF) by a blower 8 and sent to the treatment zone 6 of the total heat exchange rotor 5, where it undergoes total heat exchange with outside air. The air that has passed through the treatment zone 6 and has reduced temperature and humidity is further cooled by a first heat exchanger 10 using a cooling tower as needed to lower its temperature and is then supplied back into the greenhouse 1. On the regeneration side, outside air is passed through an air filter by a blower 9 and sent to the regeneration zone 7 of the total heat exchange rotor 5, where it undergoes total heat exchange with the air inside the greenhouse 1. The air that has passed through the regeneration zone 7 and has increased in temperature and humidity is exhausted outside the device. In the total heat exchange cooling mode, the second heat exchanger 11 provided before the regeneration zone 7 is not used.

[0033] Here, to further lower the temperature of the air that has passed through the treatment zone 6, a heat pump unit, chiller, or evaporative cooler may be used as the first heat exchanger 10. However, in the present invention, a heat exchanger using cooling water cooled by a cooling tower is particularly used. The first heat exchanger 10 is used as needed when it is necessary to more effectively lower the temperature inside the greenhouse, such as when the temperature inside the greenhouse exceeds 30°C or when it is necessary to supply air that is cooler than the outside temperature into the greenhouse. In this specification, "chilled water" refers to water cooled by a refrigerator (chiller), and "cooling water" refers to water cooled by a cooling tower. Furthermore, "circulating water" is synonymous with cooling water and refers to water circulating between the cooling tower (heating tower) and the main unit, and is particularly referred to as "circulating water" when used in a heating tower.

[0034] (Cooling Tower) A cooling tower lowers the temperature of cooling water by directly or indirectly contacting a heat transfer medium, such as water, with the atmosphere, partially evaporating the water and providing the cooling water with the latent heat of evaporation resulting from the enthalpy difference with saturated air. In principle, cooling water can be obtained at temperatures close to the wet-bulb temperature, which is lower than the outside air temperature. Due to the heat exchange principle of the cooling tower, it is affected by natural phenomena such as atmospheric temperature, humidity, and season. The lower the air temperature, the greater the temperature difference with the surrounding environment and the evaporation rate, and the greater the cooling tower's capacity. In other words, a lower atmospheric wet-bulb temperature allows the cooling water temperature to be lowered, so cooling water at lower temperatures can be obtained in spring and autumn compared to summer. Furthermore, the cooling tower's capacity is even greater in winter, estimated to be 2.4 times that of summer. In the present invention, air that has passed through a total heat exchanger is cooled as needed by a first heat exchanger 10 using a cooling tower. For example, by installing a coil through which cooling water cooled by a cooling tower flows on the treatment outlet side of the total heat exchange rotor 5 as the first heat exchanger 10, it is possible to further lower the temperature of the air (treatment outlet) that has passed through the treatment zone 6.

[0035] Cooling towers are not used alone in air conditioning applications; they are generally used in combination with heat pumps, chillers, and other heat-source equipment that requires heat dissipation. For this reason, even those skilled in the art would not easily imagine using a cooling tower alone to cool the outlet air of a total heat exchanger. For example, central air conditioning systems in air conditioning facilities typically use chilled water, and cooling towers are used to regulate the temperature of this chilled water. Cool air for cooling indoor spaces is generated by heat exchange with chilled water within the air conditioner. Heated chilled water is sent to a chiller, where the refrigerant absorbs heat through evaporation in the evaporator, and the absorbed heat is then released to the chilled water in the condenser. The cooling tower serves to dissipate the heat released to the chilled water in the chiller's condenser to the outside air. Therefore, this air conditioning cooling tower constitutes part of a central air conditioning system together with the air conditioner and chiller, and is used as an auxiliary unit for the chiller, completely different from the use of a cooling tower alone in the present invention.

[0036] Cooling towers utilize natural energy and can cool air using outside air as a heat source, making them low-cost and environmentally friendly. Cooling towers are powered by a blower and a pump, resulting in low initial and running costs. Considering factors such as the cooling water temperature setting, required pump capacity, heat load fluctuations, and seasonal variations in cooling tower capacity, power consumption can be further reduced. Forced-draft, open-type cooling towers allow for a compact tower body, reducing costs. However, cooling towers are relatively large, require a large installation area, and installation is limited, so those skilled in the art would not normally consider using them in total heat exchangers. However, since the present invention targets greenhouses, the cooling tower can be installed outside the greenhouse, occupying only a portion of the vast agricultural land, making the installation area virtually insignificant.

[0037] (Nighttime: Dehumidifying Heating Mode) At night, the temperature inside the greenhouse gradually drops and the relative humidity rises. Although the amount of transpiration is lower than during the day, plants still transpire at night. This causes the humidity inside the greenhouse to rise, resulting in a higher humidity level than the outside air. Therefore, the total heat exchanger is operated in dehumidifying heating mode. By reducing the rotation speed, the total heat exchange rotor can be used as a dehumidifying rotor that exhibits desiccant function. That is, the total heat exchange rotor rotates at a low speed of several to several dozen rph (rotations per hour), for example, 10 rph, and dehumidified air is supplied into the greenhouse to reduce humidity. In addition, the adsorption heat generated by dehumidification increases the temperature of the air that passes through the treatment zone (treatment outlet), allowing heated air to be supplied into the greenhouse. Note that operating the total heat exchanger in cooling mode at night sends cold air into the greenhouse, further lowering the temperature inside the greenhouse.

[0038] As shown in Figure 2, on the treatment side, a portion of the air inside the greenhouse 1 is passed through an air filter by a blower 8 and sent to the treatment zone 6 of the total heat exchange rotor 5, where it is dehumidified and its temperature rises due to the heat of adsorption associated with the dehumidification. The air that has passed through the treatment zone 6, with its humidity reduced and warmed, is then supplied back into the greenhouse 1. On the regeneration side, outside air is passed through an air filter by a blower 9 and sent to a second heat exchanger 11, such as a hot water coil, where it is heated. The air that has passed through the second heat exchanger 11 is sent to the regeneration zone 7 of the total heat exchange rotor 5 where it is humidified, and the humidified air is then exhausted outside the device.

[0039] In a temperature swing using a conventional adsorption rotor, the treatment side is generally operated at a low temperature and the regeneration side at a high temperature. In other words, the regeneration inlet temperature is typically higher than the treatment inlet temperature. For example, in a typical dehumidification device, if the required dew point temperature is low, the treatment inlet temperature is pre-cooled to 7 to 15°C, and the regeneration inlet temperature is heated to 100 to 140°C or higher. However, since the present invention aims to create an energy-saving device, high temperatures are not required, and the regeneration temperature is lower than the 40 to 80°C generally considered to be low-temperature regeneration. Normally, a regeneration temperature below 30°C is not practical and is therefore not even considered. In the present invention, the regeneration inlet temperature may be 40°C or lower, 30°C or lower, or even 20°C or lower. The regeneration inlet temperature may also be lower than the treatment inlet temperature. To prevent freezing and condensation in the device, it is preferable that the air exiting the second heat exchanger 11 (regeneration inlet temperature) be at a temperature that will not freeze the regeneration outlet side, such as 5°C or higher.

[0040] In the present invention, dehumidification can be performed even at a regeneration temperature lower than normal. The driving force is the difference in relative humidity between the treatment inlet and the regeneration inlet. In other words, dehumidification is achieved by a "relative humidity swing." That is, in the dehumidifying heating mode of the present invention, the relative humidity at the regeneration inlet is set lower than the relative humidity at the treatment inlet. The greater this difference, the greater the driving force for dehumidification. At night, the relative humidity inside the greenhouse increases as the temperature drops, but transpiration from plants promotes an increase in relative humidity compared to daytime, resulting in a higher relative humidity than daytime. Meanwhile, the relative humidity of the outside air also increases as the outside temperature drops, but the increase is smaller than the increase in relative humidity inside the greenhouse. Furthermore, the absolute humidity also decreases at night as the outside temperature drops compared to daytime. Therefore, depending on weather conditions, the relative humidity difference between the inside and outside air tends to be larger at night compared to daytime. In the present invention, the treatment inlet uses indoor air with a high relative humidity, while the regeneration inlet uses outdoor air with a lower relative humidity than inside the greenhouse, which is favorable for relative humidity swing.

[0041] Furthermore, in the present invention, the relative humidity at the regeneration inlet is further reduced by heating the outside air using the second heat exchanger 11. However, because the regeneration inlet temperature is low, the second heat exchanger 11 does not require active heating; simply using groundwater or circulating water as regeneration heat is sufficient, resulting in extremely energy-efficient systems. Geothermal, underground heat, and solar heat can also be used. If a heat source is available, even waste heat from devices and machinery, such as the exhaust heat from outdoor units or control panels, can be utilized. By providing the second heat exchanger 11 with a coil through which water heated by these heat sources flows, the regeneration inlet temperature can be increased and the relative humidity can be reduced.

[0042] Furthermore, the cooling tower used to cool the first heat exchanger 10 during the day can be used as a heating tower (heating tower) at night as a heat source for the second heat exchanger 11, using circulating water to heat the outside air at the regeneration inlet. In this case, a cooling tower (heating tower) with specifications that allow it to function as both a cooling tower and a heating tower is selected. The heating tower absorbs heat from the atmosphere to raise the temperature of the circulating water. This utilizes air energy without using fuel, resulting in energy savings and low costs. Since the outside air temperature is low at night, it is preferable to use the relatively warm air inside the greenhouse as a heat source. For example, a coil is installed inside the greenhouse, and the circulating water used to heat the heating tower is passed through the coil inside the greenhouse. The relative humidity inside the greenhouse is higher than that of the outside air, making condensation more likely to occur on the coil surface. This allows heat to be obtained without lowering the dry-bulb temperature inside the greenhouse (without lowering the temperature inside the greenhouse). The circulating water heated by the resulting condensation heat is circulated to the heating tower, where it heats the outside air. If the first heat exchanger 10 can increase the treatment outlet air temperature, a heat source such as geothermal heat may be used for nighttime heating operation only, similar to the heat source for the second heat exchanger 11. For example, if groundwater is used as the heat source for the first heat exchanger 10, the temperature of the groundwater remains approximately constant at 16 to 18°C ​​throughout the year, and therefore it can be used for cooling during the day and heating at night. In this case, a switching valve or separate coil is required to switch between the cooling water supplied by the cooling tower for daytime cooling operation and a heat medium from a different heat source.

[0043] In the following, as Example 1, in the total heat exchanger of Fig. 2, the total heat exchange rotor 5 is operated in total heat exchange cooling mode during the daytime in spring or autumn, and the temperature is further lowered by the first heat exchanger 10 using a cooling tower before being supplied again to the house 1. The symbols in Table 1 correspond to the state of the air at the positions indicated by the numbers in parentheses in Fig. 2.

[0044]

[0045] During the day, the total heat exchange rotor 5 rotates at high speed and operates in total heat exchange cooling mode. On the treatment side, high-temperature, high-humidity greenhouse air (4) with a temperature of 30.0°C and an absolute humidity of 21.6 g / kg (DA) is heated to 33.0°C by a blower 8 to produce air (5). This air passes through the treatment zone 6 of the total heat exchange rotor 5 and undergoes total heat exchange with outside air, resulting in air (6) whose temperature and humidity have been reduced to 23.9°C and 12.6 g / kg (DA). The air is then further cooled to 19.4°C by a first heat exchanger 10 using a cooling tower to produce air (7), which is then returned to the greenhouse. On the regeneration side, outside air (1) at a temperature of 20.0°C and an absolute humidity of 8.7 g / kg (DA) passes through the regeneration zone 7 by the blower 9 and undergoes total heat exchange with the air inside the greenhouse, becoming air (3) whose temperature and humidity have increased to 29.2°C and an absolute humidity of 17.7 g / kg (DA).The air then leaves the blower 9 and is exhausted outside the device.

[0046] When the temperature is lowered by the first heat exchanger 10 using a cooling tower, the relative humidity increases. Therefore, the temperature is set so that the air passing through the first heat exchanger 10 will not condense. Even if this air has a high relative humidity, the absolute humidity itself is low, and when it is supplied into the greenhouse, the temperature rises, causing the relative humidity to decrease.

[0047] In winter, when the outside temperature is too low, performing total heat exchange during the day will send cold air into the greenhouse, causing the temperature inside the greenhouse to drop excessively. However, even during the daytime in winter, humidity inside the greenhouse rises due to plant transpiration and irrigation. In this case, the operation of the total heat exchanger 3 and cooling tower is stopped, or they are operated in dehumidifying heating mode at night. By operating the total heat exchanger 3 in dehumidifying heating mode, it is possible to adjust the humidity without lowering the temperature inside the greenhouse while dehumidifying the air inside the greenhouse even during the day.

[0048] As Example 2, Table 2 shows the results of calculations for the dehumidifying and heating mode in the total heat exchanger shown in Figure 2, in which the total heat exchange rotor 5 is operated in the dehumidifying and heating mode during winter nighttime, and the inside of the greenhouse is heated by the heat of adsorption generated by dehumidification. A psychrometric chart showing the results of these calculations is shown in Figure 3. The symbols in Table 2 and Figure 3 correspond to the air conditions at the positions indicated by the parenthesized numbers in Figure 2.

[0049]

[0050] At night, the total heat exchange rotor 5 rotates at a low speed and operates in dehumidifying and heating mode. On the treatment side, indoor air (4) at a temperature of 15.0°C, absolute humidity of 9.6 g / kg (DA), and relative humidity of 90% RH leaves the blower 8 and passes through the treatment zone 6 of the total heat exchange rotor 5. Moisture is adsorbed, and the temperature rises due to the heat of adsorption, becoming dehumidified air (6) at a temperature of 17.5°C and absolute humidity of 8.6 g / kg (DA). This dehumidified air is then returned to the greenhouse. On the regeneration side, low-temperature, low-humidity outdoor air (1) at a temperature of 1.0°C and absolute humidity of 2.1 g / kg (DA) is heated to a temperature of 5.0°C by the second heat exchanger 11, becoming air (2) with a relative humidity of 38.7% RH, and entering the regeneration zone 7. The air passing through the regeneration zone 7 is cooled to 2.5°C by the heat of desorption, and becomes air (3) with an absolute humidity of 3.1 g / kg (DA).The air then leaves the blower 9 and is exhausted to the outside of the device.

[0051] In Example 2, calculations were performed assuming that adiabatic dehumidification occurs. As shown in Figure 5, in "adiabatic dehumidification," it is assumed that no energy is exchanged during the dehumidification operation of the desiccant, and transitions occur along isoenthalpy lines on a psychrometric chart. In the psychrometric chart of Figure 3, the air states at the inlet and outlet of both the treatment side and the regeneration side transition along the isoenthalpy line of the inlet air. Note that in actual dehumidification operations using temperature swings, dehumidification performance is reduced compared to adiabatic dehumidification due to an increase in enthalpy of the treatment outlet gas caused by sensible heat transfer from the regeneration side to the treatment side via the rotor, heat of adsorption greater than the latent heat of vaporization of water, and mass transfer resistance.

[0052] In Example 3 below, a dehumidification performance test was conducted under test conditions simulating a nighttime dehumidifying and heating mode, using a rotor carrying silica gel as the total heat exchange rotor 5 of the total heat exchanger 3 in Figure 2. The test results are shown in Table 3. A psychrometric chart illustrating the test results is shown in Figure 4. The rotation speed of the adsorption rotor 1 was 10 rph. The symbols in Table 3 and Figure 4 correspond to the air conditions at the positions indicated by the bracketed numbers in Figure 2. The temperature and humidity conditions at the treatment inlet and regeneration inlet in the dehumidification performance test of Example 3 were adjusted to be as close as possible to the values ​​calculated in Example 2.

[0053]

[0054] Example 2 (Table 2, FIG. 3) is compared with Example 3 (Table 3, FIG. 4). In Example 2, assuming that adiabatic dehumidification occurs, with the treatment inlet air (5) having a temperature of 15.0°C and a relative humidity of 90.0% RH and the regeneration inlet air (2) having a temperature of 5.0°C and a relative humidity of 38.7% RH, based on Table 2, the amount of dehumidification on the treatment side (the absolute humidity of the treatment inlet air (5) minus the absolute humidity of the treatment outlet air (6)) was 1.0 g / kg (DA), and the temperature rise on the treatment side (the temperature of the treatment outlet air (6) minus the temperature of the treatment inlet air (5)) was 2.5°C. On the other hand, in Example 3, when the treatment inlet air (5) had a temperature of 21.9°C and a relative humidity of 71.0% RH and the regeneration inlet air (2) had a temperature of 9.3°C and a relative humidity of 48.5% RH, the dehumidification amount on the treatment side was 0.9 g / kg (DA) and the temperature rise was 1.1°C when tested with an actual total heat exchange rotor.

[0055] As in Examples 2 and 3, in the present invention, the relative humidity at the regeneration inlet is set lower than the relative humidity at the treatment inlet, and the dehumidification operation is performed using the relative humidity swing as a driving force. Therefore, the regeneration inlet temperature can be set lower than the 40 to 80°C typically used for low-temperature regeneration. Furthermore, a reversal phenomenon in which the regeneration inlet temperature is lower than the treatment inlet temperature can occur, which is unthinkable with normal temperature swings. This is an idea for adsorption / desorption operation that even a person skilled in the art would not easily come up with.

[0056] When adiabatic dehumidification occurs, theoretically, heat of adsorption is generated when 1 g of moisture is dehumidified, resulting in a temperature rise of 2.5°C. While the calculated (theoretical) values ​​in Example 2 and the experimental values ​​in Example 3 show the same dehumidification rate, the experimental temperature rise is only 1.1°C, less than half the theoretical value of 2.5°C. In other words, the difference between the treatment outlet temperature and the treatment inlet temperature is small, resulting in a steeper slope than the adiabatic dehumidification shown in Figure 3, as shown in the psychrometric chart in Figure 4, and dehumidification closer to isothermal dehumidification as shown in Figure 5. In Example 3, the temperature on the regeneration side is low, so the rotor rotates from the regeneration zone to the treatment zone while still cold, and the cold heat storage effect suppresses the temperature rise due to heat of adsorption in the treatment zone. However, when the ambient temperature is higher than in Examples 2 and 3, for example, at 10 to 20°C, the temperature difference between the treatment side and the regeneration side is gentler, and dehumidification progresses from isothermal dehumidification to adiabatic dehumidification. For example, strawberry cultivation is popular in Fukuoka Prefecture, where the applicant is located, and the conditions in winter, spring, and autumn are suitable for this purpose. Therefore, the dehumidifying heating mode of the air conditioning system of the present invention is particularly useful in areas where the outdoor temperature does not drop extremely low even in winter. Furthermore, by performing a dehumidifying operation that approaches adiabatic dehumidification, such as by rotating the rotor as slowly as possible, and adjusting the rotation speed while considering the balance with the amount of dehumidification, it is possible to effectively utilize dehumidifying performance and temperature rise due to heat of adsorption.

[0057] As described above, the air conditioning system of the present invention is characterized by having a total heat exchange cooling mode during the day, which exchanges heat between the air inside the greenhouse and outside air and cools the air at the treatment outlet using a cooling tower or the like, thereby reducing the temperature and humidity inside the greenhouse, and a dehumidification heating mode during the night, which dehumidifies the air inside the greenhouse and heats it using adsorption heat. The total heat exchanger's operating mode can be easily switched by changing the rotation speed of the total heat exchange rotor, realizing a closed greenhouse that can maintain a temperature and humidity suitable for plant growth throughout the day and night, enabling plant production in a stable internal environment. The dehumidification operation in the nighttime dehumidification heating mode is characterized by driving a relative humidity swing by lowering the regeneration inlet humidity below the treatment inlet humidity, thereby allowing the regeneration temperature to be in a lower temperature range than normal low-temperature regeneration. As a result, the regeneration inlet temperature may be lower than the treatment inlet temperature.

[0058] In normal dehumidification, indoor spaces are generally dry in winter, so humidified air that has passed through the regeneration zone is supplied into the room, and dehumidified air that has passed through the treatment zone is exhausted. However, the present invention uses the exact opposite idea of ​​dehumidifying the indoor space (inside the greenhouse).

[0059] The total heat exchanger 3 is not limited to a total heat exchange rotor, but two or more stationary cross-sectional total heat exchangers may be installed, and the processing (ventilation of indoor air) and regeneration (ventilation of outdoor air) may be switched in a batch manner, and the total heat exchange cooling mode and the dehumidifying heating mode may be switched by controlling the ventilation time, etc.

[0060] In FIG. 1 , the carbon dioxide supplying device 2 is installed inside the house 1 and the total heat exchanger 3 is installed outside the house 1, but this is not limiting and both may be installed inside or outside the house 1. Alternatively, the carbon dioxide supplying device 2 and the total heat exchanger 3 may be installed between the indoor and outdoor areas of the house 1, with the adsorption zone of the carbon dioxide supplying device 2 located outside the house 1 and the desorption zone located inside the house 1, and the regeneration zone of the total heat exchanger 3 located outside the house 1 and the treatment zone located inside the house 1. In this way, it is possible to eliminate ducts connecting the carbon dioxide supplying device 2 and the total heat exchanger 3 to the house 1. Furthermore, the total heat exchange rotor 5 may have zones other than the treatment zone and the regeneration zone.

[0061] The carbon dioxide supplying device 2 and the total heat exchanger 3 may be combined into an integrated device (unit). In this case, the overall device becomes compact, but the carbon dioxide supplying device and the total heat exchanger process significantly different amounts of air, making it difficult to separately control the carbon dioxide concentration and the temperature and humidity inside the greenhouse.

[0062] In controlling the carbon dioxide concentration in the greenhouse by the carbon dioxide supplying device 2 and controlling the temperature and humidity by the total heat exchanger 3, the volume of air processed by the total heat exchanger is overwhelmingly large. Therefore, it is preferable to install the carbon dioxide supplying device 2 and the total heat exchanger 3 separately as shown in Figure 1, as this makes it easier to control the carbon dioxide supply concentration and the temperature and humidity in the greenhouse separately. Installing the total heat exchanger 3 separately is also preferable because it allows various devices to be used as the carbon dioxide supplying device.

[0063] In FIG. 1 , one carbon dioxide supply device 2 and one total heat exchanger 3 are installed, but this is not limited thereto, and multiple units of either or both may be installed. For example, if the greenhouse 1 is large or if the temperature and humidity increase within the greenhouse 1 is significant, attempting to control temperature and humidity with a single total heat exchanger would require a larger rotor diameter and a larger device. However, by installing multiple devices, each device can be made smaller while maintaining redundancy, which is effective when there is a problem with the installation space of the device. Also, in FIG. 2 , the blower 8 is located on the treatment inlet side and the blower 9 is located on the regeneration outlet side, but this is not limited thereto. For example, by installing the blower 9 on the regeneration inlet side, the heating effect on the regeneration side can be enhanced by the temperature increase caused by the blower.

[0064] To keep the greenhouse warm, sliding or roll-up curtains are often deployed to block light and heat, maintain heat, and adjust the amount of sunlight. By using these curtains to reduce the size of the air-conditioned space, daytime cooling and nighttime heating can be enhanced, and the supply air flow rate can be reduced, further reducing costs. In this case, it is preferable to use airtight sheets. Since the humidity is regulated throughout the day and night by a total heat exchanger, the relative humidity inside the greenhouse does not increase and condensation does not occur. In addition to the air-conditioning system of the present invention, other cooling or heating equipment may be used as a supplement. When tunnel cultivation is performed, air from the air-conditioning system of the present invention may be supplied to the tunnel.

[0065] As described above, airflow is generated within a closed greenhouse by using a total heat exchanger to exchange heat or dehumidify. As mentioned above, if a greenhouse is simply treated as a closed system, the airflow will be weak, suppressing photosynthesis even if the stomata in the leaves are open. However, a total heat exchanger can create airflow within the greenhouse, making it possible to promote leaf photosynthesis. In addition, airflow makes it possible to uniformize the temperature, humidity, and carbon dioxide concentration within the greenhouse.

[0066] In the air conditioning system of the present invention, when the greenhouse is closed, the temperature and humidity are adjusted using a total heat exchanger, and carbon dioxide is supplied using a carbon dioxide supply device, it is possible to maintain a high carbon dioxide concentration of 800 to 1000 ppm.

[0067] The above describes the case of adjusting the temperature and humidity inside a house, but the present invention is not limited to a house and can be applied to any indoor space where temperature and humidity need to be adjusted. In this case, the term "house" in this embodiment is read as "indoor space."

[0068] The air conditioning system of the present invention can maintain the temperature and humidity inside a greenhouse at a level suitable for plant growth throughout the day and night, making it particularly effective for cultivating strawberries, a winter crop, and enabling the production of high-yield, high-quality strawberries. It can be applied not only to greenhouses where plants are grown, but also to controlling the internal environment of indoor spaces such as buildings that require a constant indoor environment and reactors that house chemical reaction systems that are sensitive to humidity. It can be used for a variety of purposes, as long as the purpose is to adjust the temperature and humidity inside an indoor space during the day and prevent a drop in temperature at night. In rooms isolated from the outside air, the carbon dioxide supply device of the present invention can be used for other purposes by replacing it with a supply device for other gases such as oxygen or nitrogen. Furthermore, because the regeneration temperature is lower, various heat utilization is possible, making it a highly energy-efficient device.

[0069] REFERENCE SIGNS LIST 1 House 2 Carbon dioxide supply device 3 Total heat exchanger 4 Adsorption rotor 5 Total heat exchange rotor 6 Treatment zone 7 Regeneration zone 8, 9 Fan 10 First heat exchanger 11 Second heat exchanger

Claims

1. An air conditioning system comprising a total heat exchanger having two operating modes, a total heat exchange cooling mode and a dehumidification heating mode, wherein in the total heat exchange cooling mode, the air in the indoor space is subjected to total heat exchange with outside air to reduce the temperature and humidity and then returned to the indoor space, and in the dehumidification heating mode, the air in the indoor space is dehumidified to reduce the humidity and the air whose temperature has been increased by the heat of adsorption generated by the dehumidification is returned to the indoor space, and the temperature and humidity of the indoor space are adjusted by switching the operating modes.

2. The air conditioning system according to claim 1, characterized in that in the total heat exchange cooling mode, the air that has passed through the total heat exchanger is further cooled by a first heat exchanger and returned to the indoor space.

3. An air conditioning system according to claim 2, wherein the first heat exchanger is a cooling tower.

4. An air conditioning system according to any one of claims 1 to 3, characterized in that a total heat exchange rotor is used for the total heat exchanger.

5. An air conditioning system as described in claim 4, characterized in that the total heat exchange rotor rotates at a high speed in the total heat exchange cooling mode and at a low speed in the dehumidification heating mode, and the operating mode is switched by adjusting the rotation speed.

6. The air conditioning system described in claim 4, characterized in that the total heat exchange rotor has at least a treatment zone and a regeneration zone, the air in the indoor space passes through the treatment zone and is supplied to the indoor space again, and the outside air passes through the regeneration zone and is exhausted.

7. An air conditioning system as described in claim 6, characterized in that a second heat exchanger is provided before the regeneration zone, and the outside air is heated by the second heat exchanger and sent to the regeneration zone.

8. The air conditioning system according to claim 6, wherein in said total heat exchange rotor, the relative humidity at the regeneration inlet is lower than the relative humidity at the treatment inlet.

9. The air conditioning system according to claim 6, wherein in said total heat exchange rotor, the temperature of the regeneration inlet is lower than the temperature of the treatment inlet.

10. The air conditioning system of claim 1, wherein the indoor space is a house.

11. An air conditioning system according to claim 10, further comprising a carbon dioxide supply device.

12. The air conditioning system described in claim 11, characterized in that the carbon dioxide supplying device is equipped with an adsorption rotor having at least an adsorption zone and a desorption zone, the outside air is passed through the adsorption zone to adsorb carbon dioxide and then exhausted, and the air inside the house is heated and passed through the desorption zone to desorb carbon dioxide, thereby supplying high concentration carbon dioxide into the house.

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