AIR-CONDITIONING SYSTEM

Abstract

 The present invention provides an air-conditioning system in which, when determining a target outlet water temperature of a heat source device, a representative indoor unit is properly selected and the target outlet water temperature of the heat source device is determined in accordance with the indoor load in the selected representative indoor unit, so that high operation efficiency can be achieved without impairing comfortability.
The air-conditioning system includes a main controller 11 that determines whether a plurality of indoor heat exchangers 31 include an indoor heat exchanger 31 in which the water flow rate of water passing through the indoor heat exchanger 31 has reached its upper limit. If an indoor heat exchanger 31 is present, the main controller 11 sets a predetermined one of the indoor heat exchangers as a representative indoor heat exchanger, determines a target outlet water temperature Twsom of a heat source device 1 based on an indoor temperature Tai of the room in which the representative indoor heat exchanger 31 of an indoor unit 2 is installed, an inlet water temperature Twi of the representative indoor heat exchanger 31, an outlet water temperature Two of the representative indoor heat exchanger 31, a preset temperature Taim of the room in which the representative indoor heat exchanger 31 is installed, and an outdoor air temperature Tao, and controls the capacity of the heat source device 1 to make the outlet water temperature Twso of the heat source device 1 equal to the determined target outlet water temperature Twsom.

Description

Technical Field

[0001] The present invention relates to an air-conditioning system.

Background Art

[0002] In the related art, an air-conditioning system that generates cold water or warm water by using a heat source device, such as a heat pump, and conveys the cold water or warm water to an indoor unit by using a water pump so as to cool or heat a room is generally known. An air-conditioning system of this type generally employs a method of delivering water at a constant water temperature regardless of the load, such as supplying, to the indoor unit, cold water at 16 degrees C during cooling operation and warm water at 35 degrees C during heating operation. Since the temperatures of the cold water and the warm water in this method are determined in view of the maximum required load, if the load is small in, for example, the intervals between seasons, the operation is performed intermittently by repeating activation and stoppage by, for example, stopping a heat source device when the room temperature reaches a preset value or stopping the supply of water to the indoor unit by using a three-way valve. This leads to impaired comfortability and, in turn, to decreased operation efficiency.

[0003] As a solution for solving this problem, Patent Literature 1 discloses a control method in which a target water temperature (i.e., a target outlet water temperature of a heat source device) of water to be supplied to each indoor unit from the heat source device is reset based on a deviation between a preset temperature (i.e., a target indoor temperature) set by a user and the current indoor temperature.

Citation List

Patent Literature

[0004] 

Patent Literature 1: Japanese Unexamined Patent Application Publication No. 2007-212085 (Figs. 3 and 4)

Summary of Invention

Technical Problem

[0005] In order to achieve highly efficient operation while maintaining comfortability in the aforementioned air-conditioning system, it is necessary to set the target water temperature in view of the outdoor air temperature in addition to the deviation between the preset temperature and the indoor temperature. Specifically, for example, when performing heating operation, if the outdoor air temperature is low and the difference between the preset temperature and the outdoor air temperature is large, the indoor load for satisfying the preset temperature is large. On the other hand, if the outdoor air temperature is high, the indoor load is small because the difference between the preset temperature and the outdoor air temperature is small. Therefore, unless the target outlet water temperature is set in view of the fact that the indoor load varies depending on the outdoor air temperature, the capacity becomes excessive or insufficient, causing overshooting or undershooting of the indoor temperature with respect to the preset temperature. This leads to impaired comfortability and, in turn, to decreased operation efficiency. However, since the outdoor air temperature is not taken into account in Patent Literature 1, these problems cannot be solved.

[0006] If there are a plurality of indoor units, the amount of heat to be supplied to the rooms in which the indoor units are installed varies. Therefore, unless a representative indoor unit is properly set, the amount of heat becomes excessive in one room while the amount of heat becomes insufficient in another room, thus resulting in impaired comfortability.

[0007]  The amount of heat exchange in an indoor heat exchanger of each indoor unit can be controlled based on the flow rate of water flowing to the indoor heat exchanger. However, in an indoor unit in which the water flow rate has reached its upper limit, the water flow rate cannot be increased any further. Therefore, in order to make the indoor temperature equal to the preset temperature in the indoor unit in which the water flow rate has reached its upper limit, the outlet water temperature of the heat source device needs to be changed. However, Patent Literature 1 does not discuss this point.

[0008] The present invention has been made in view of the circumstances described above, and has as its object to provide an air-conditioning system in which, when determining a target outlet water temperature of a heat source device, a representative indoor unit is properly selected and the target outlet water temperature of the heat source device is determined in accordance with the indoor load in the selected representative indoor unit, so that high operation efficiency can be achieved without impairing comfortability.

Solution to Problem

[0009] An air-conditioning system according to the present invention includes a heat medium circuit that includes a heat source device whose capacity is variable and a plurality of indoor heat exchangers and that is configured to perform at least one of cooling and heating by circulating a heat medium through the heat source device and the plurality of indoor heat exchangers; a heat-medium conveying device configured to convey the heat medium to the heat medium circuit; a heat-source-device outlet temperature detector configured to detect a temperature of the heat medium flowing out of the heat source device; a plurality of flow control devices configured to control flow rates of streams of the heat medium individually passing through the plurality of indoor heat exchangers; a plurality of inlet heat-medium temperature detectors configured to detect temperatures of the streams of the heat medium individually flowing into the plurality of indoor heat exchangers; a plurality of outlet heat-medium temperature detectors configured to detect temperatures of the streams of the heat medium individually flowing out of the plurality of indoor heat exchangers; a plurality of indoor temperature detectors configured to detect indoor temperatures of rooms in which the plurality of indoor heat exchangers are individually installed; an outdoor air temperature detector configured to detect an outdoor temperature; and a controller configured to control the capacity of the heat source device and the plurality of flow control devices to make the indoor temperatures of the rooms in which the plurality of indoor heat exchangers are individually installed equal to preset temperatures of the rooms. The controller is configured to determine whether the plurality of indoor heat exchangers include an indoor heat exchanger in which the flow rate of the heat medium passing through the indoor heat exchanger has reached an upper limit. When the controller determines that the plurality of indoor heat exchangers have one indoor heat exchanger in which the flow rate of the heat medium passing through the indoor heat exchanger has reached the upper limit, the controller is configured to set the one indoor heat exchanger as a representative indoor heat exchanger, detect the indoor temperature of the room in which the representative indoor heat exchanger is installed by using the corresponding indoor temperature detector, determine a target outlet temperature of the heat source device based on a detection value of the indoor temperature, an inlet heat-medium temperature of the representative indoor heat exchanger, an outlet heat-medium temperature of the representative indoor heat exchanger, the preset temperature of the room in which the representative indoor heat exchanger is installed, and an outdoor air temperature detected by the outdoor air temperature detector, and control the capacity of the heat source device to make the temperature detected by the heat-source-device outlet temperature detector equal to the determined target outlet temperature.

Advantageous Effects of Invention

[0010] According to the present invention, since the target outlet water temperature can be set in accordance with the load of the entire system, control with high operation efficiency can be achieved without an excessive or sufficient capacity of each indoor unit and also without impairing comfortability.

Brief Description of Drawings

[0011] 

[Fig. 1] Fig. 1 illustrates the configuration of an air-conditioning system according to Embodiment of the present invention.

[Fig. 2] Fig. 2 illustrates the relationship between the outdoor air temperature and the capacity (i.e., the heat pump capacity) required in a heat source device in the air-conditioning system according to Embodiment of the present invention.

[Fig. 3] Fig. 3 illustrates the relationship between the difference between a preset temperature and the outdoor air temperature and the rate of change (i.e. the rate of increase) in inlet water temperature of an indoor heat exchanger when making an indoor temperature equal to the preset temperature at that temperature difference, based on Fig. 2.

[Fig. 4] Fig. 4 is a flowchart illustrating a method for controlling the air-conditioning system according to Embodiment of the present invention.

[Fig. 5] Fig. 5 illustrates another configuration example of the air-conditioning system according to Embodiment of the present invention.

[Fig. 6] Fig. 6 illustrates the relationship between the amount of heat exchange and the AK value of the indoor heat exchanger.

Description of Embodiments

Schematic Configuration of Air-Conditioning System

[0012] Fig. 1 illustrates the configuration of an air-conditioning system according to Embodiment of the present invention. As shown in Fig. 1, an air-conditioning system 100 includes a heat source device 1 and a plurality of indoor units 2(N) connected in parallel with the heat source device 1. The number N in parentheses is given to each indoor unit 2 for differentiation and ranges from 1 to N (N is the number of connected units). If it is not necessary to differentiate between the indoor units, they will simply be referred to as "indoor units 2" hereinafter. Furthermore, a temperature detected by a device or a detector, which will be described later, installed within each indoor unit 2 in Fig. 1 will be expressed in a similar manner.

[0013] The air-conditioning system 100 includes a water circuit 50 that has a water pump 3, the heat source device 1, water pumps 4, and indoor heat exchangers 31 connected in this order and that serves as a heat medium circuit through which, for example, water as a heat medium circulates. The water pumps 4 and the indoor heat exchangers 31 are disposed in the respective indoor units 2. The water pump 4 in each indoor unit 2 controls the amount of water passing through the indoor unit 2. The amount of water circulating through the entire water circuit 50 is controlled by the water pump 3.

[0014] The indoor units 2 are installed in respective rooms and each include an indoor temperature detector 22 that detects an indoor temperature Tai of the room in which the indoor unit 2 is installed, an inlet water temperature detector 23 that detects an inlet water temperature Twi of the indoor unit 2, and an outlet water temperature detector 24 that detects an outlet water temperature Two of water flowing out of the indoor unit 2. Values detected by the indoor temperature detector 22, the inlet water temperature detector 23, and the outlet water temperature detector 24 are read into an indoor control device 12 within the indoor unit 2 in which the detectors are provided.

[0015] The air-conditioning system 100 further includes an outdoor air temperature detector 21 that detects an outdoor air temperature Tao, a heat-source-device outlet water temperature detector 25 that detects an outlet water temperature Twso of the heat source device 1, and a heat-source-device inlet water temperature detector 26 that detects an inlet water temperature Twsi of the heat source device 1. Values detected by the outdoor air temperature detector 21, the heat-source-device outlet water temperature detector 25, and the heat-source-device inlet water temperature detector 26 are read into a main controller 11.

[0016] The indoor control devices 12 installed in the indoor units 2 and the main controller 11 are capable of exchanging the detected values and perform cooperative processing so as to control the entire air-conditioning system 100. As an alternative to the configuration for performing cooperative processing, a configuration in which the main controller 11 has all functions of the indoor control devices 12 is also possible.

[0017] The main controller 11 uses the aforementioned detectors installed inside and outside the indoor units 2 to detect the indoor loads in the rooms in which the indoor units 2 are installed. Then, the main controller 11 controls the water pump 3 and the water pumps 4 in accordance with the indoor loads in the rooms or controls the outlet water temperature Twso by controlling the capacity of the heat source device 1, thereby making the indoor room temperatures Tai of the rooms equal to preset room temperatures Taim of the rooms.

[0018] The devices constituting the air-conditioning system 100 will be described below in sequence.

Heat Source Device

[0019] The heat source device 1 supplies warm water during heating operation and cold water during cooling operation to the indoor units 2. The heat source device 1 may be a heat pump capable of supplying warm and cold water, or may be a device capable of supplying warm water only, such as a gas or oil boiler.

Indoor Heat Exchanger

[0020] Each indoor heat exchanger 31 exchanges heat between water circulating through the water circuit 50 and indoor air so as to heat or cool the room. For example, a radiator is used as the indoor heat exchanger 31, such that the room can be heated or cooled by the temperature of water flowing into the radiator. As an alternative to a radiator, for example, a fan coil unit or a floor heating panel may be used.

Water Pumps: Water-Flow Control Devices

[0021] The water pump 3 serving as a primary water conveying device supplies water to the water circuit 50. The water pumps 4 serving as secondary water conveying devices supply water to the respective indoor units 2 from the water circuit 50. Fixed-speed pumps or pumps whose rotation speeds are controlled to be variable using, for example, inverters are used as the water pump 3 and the water pumps 4. The water pump 3 and the water pumps 4 serve as water-flow control devices that control the flow rate of water circulating through the water circuit 50. The water pump 3 can control the flow rate by using in combination a fixed-speed pump and a capacity control valve whose opening degree is variable and adjusting the opening degree of the capacity control valve. If the head of the water pump 3 is sufficiently large, the flow rate of water flowing through the indoor units 2 is sometimes controlled by using flow control valves in place of the water pumps 4.

Parameters for Determining Amount of Heat Exchange

[0022] A method for determining a target outlet water temperature Twsom of the heat source device 1 in the air-conditioning system 100 according to Embodiment will be described next. The following description assumes heating operation as an example.

[0023] An amount of heat exchange Qw(N) in the indoor heat exchanger 31 (N) of a certain indoor unit 2(N) can be expressed by Expression (1) based on a water flow rate Gw(N), a specific heat Cpw(N) of water, an inlet water temperature Twi(N) of the indoor heat exchanger 31 (N), and an outlet water temperature Two(N) of the indoor heat exchanger 31 (N).

[0024] [Math. 1]

[0025] Specifically, the amount of heat exchange Qw(N) of the indoor heat exchanger 31 (N) can be increased by increasing the water flow rate Gw(N) or by increasing the inlet water temperature Twi(N).

[0026] When a heat pump is used as the heat source device 1, since the operation efficiency normally decreases if the outlet water temperature Twso (i.e. the inlet water temperature Twi(N) when viewed from the indoor unit 2) of the heat source device 1 is increased, it is desirable that the water flow rate be increased as much as possible for increasing the capacity.

[0027] However, in the room equipped with the certain indoor unit 2(N), if the current indoor temperature Tai(N) is low relative to a preset temperature Taim(N) and there is a need to increase the amount of heat exchange of the indoor heat exchanger 31 (N), the water flow rate of the water pump 4(N) included in the indoor unit 2(N) may have already reached its upper limit. In this case, it is necessary to deal with the indoor load by increasing the amount of heat exchange Qw(N) of the indoor heat exchanger 31 (N) by increasing the inlet water temperature Twi(N) of the indoor heat exchanger 31.

[0028] Accordingly, when it is necessary to increase the inlet water temperature Twi of each indoor heat exchanger 31, a target value for the inlet water temperature Twi is determined in view of the outdoor air temperature Tao in Embodiment. This prevents an excessive or insufficient capacity in each indoor unit 2, and moreover, appropriate control can be performed in view of the load of the entire system, thus allowing for increased operation efficiency.

[0029] Increasing the inlet water temperature Twi(N) of the indoor heat exchanger 31 amounts to increasing the capacity of the heat source device 1. Therefore, the relationship between the capacity of the heat source device 1 necessary for making the indoor temperature Tai equal to the preset temperature Taim and the outdoor air temperature Tao will be first described below. Then, the relationship between the outdoor air temperature Tao and the rate of change (i.e. the rate of increase) in the inlet water temperature Twi of each indoor heat exchanger 31 will be described.

[0030] Fig. 2 illustrates the relationship between the outdoor air temperature Tao and the capacity (i.e., the heat pump capacity) required in the heat source device 1 in the air-conditioning system according to Embodiment of the present invention. Fig. 2 illustrates an example in which the preset temperature Taim is set at 20 degrees C for heating operation, and includes (a) illustrating a case where the indoor temperature Tai is 20 degrees C, which is equal to the preset temperature Taim, and (b) illustrating a case where the indoor temperature Tai is 18 degrees C, which is lower than the preset temperature Taim. In the case of (b), the water flow rate of the water pump 4 has reached its upper limit.

[0031] As shown in Figs. 2(a) and 2(b), the capacity of the heat source device 1 necessary for making the indoor temperature Tai equal to the preset temperature Taim decreases with increasing outdoor air temperature Tao. Furthermore, as shown in Fig. 2(b), when the indoor temperature Tai is 18 degrees C, which is lower than the preset temperature Taim, the capacity is insufficient by an amount indicated by an arrow in Fig. 2. As is clear from the length of the arrow in Fig. 2, this insufficient amount is larger when the outdoor air temperature Tao is high (e.g., 10 degrees C) than when the outdoor air temperature Tao is low (e.g., 0 degrees C).

[0032] In Fig. 2(b), since the water flow rate of the water pump 4 has reached its upper limit, as described above, the insufficient amount of capacity is compensated for by increasing the inlet water temperature Twi of the indoor heat exchanger 31. Thus, when the indoor temperature Tai of 18 degrees C is to be increased by 2 degrees C to the preset temperature Taim of 20 degrees C, the water-temperature increment for the inlet water temperature Twi of the indoor heat exchanger 31 needs to be larger when the outdoor air temperature Tao at that time is high (i.e., when the difference between the preset temperature Taim and the outdoor air temperature Tao is small) than when the outdoor air temperature Tao at that time is low (i.e., when the difference between the preset temperature Taim and the outdoor air temperature Tao is large).

[0033] Therefore, when the water-temperature increment for the inlet water temperature Twi of the indoor heat exchanger 31 is determined solely based on the difference between the preset temperature Taim and the indoor temperature Tai without taking into account the outdoor air temperature Tao as in the related art, the following problem occurs. Specifically, if the outdoor air temperature Tao is high, as described above (i.e., if the difference between the preset temperature Taim and the outdoor air temperature Tao is small), the water-temperature increment for the inlet water temperature Twi is set to be smaller than the required water-temperature increment regardless of the fact that the water-temperature increment needs to be large. In this case, the capacity becomes insufficient, leading to undershooting. In contrast, if the water-temperature increment is set to be larger than the required water-temperature increment, the capacity becomes excessive, leading to overshooting.

[0034] Next, Fig. 3 illustrates the relationship shown in Fig. 2 in which the indices are replaced with other indices.

[0035] Fig. 3 illustrates the relationship between the difference between the preset temperature Taim and the outdoor air temperature Tao and the rate of change (i.e. the rate of increase) in inlet water temperature of the indoor heat exchanger 31 when making the indoor temperature Tai equal to the preset temperature Taim at that temperature difference, based on Fig. 2. The rate of change in inlet water temperature is equal to the quotient of the water-temperature increment for the inlet water temperature Twi of the indoor heat exchanger 31 divided by the product of the current inlet water temperature Twi multiplied by 100.

[0036] It is clear from Fig. 3 that the rate of change in inlet water temperature decreases as the difference between the preset temperature Taim and the outdoor air temperature Tao increases. When the difference between the preset temperature Taim and the outdoor air temperature Tao is large, it can be said that the indoor load for satisfying the preset temperature Taim is large. Therefore, by reducing the water-temperature increment for the inlet water temperature Twi of the indoor heat exchanger 31 as the indoor load increases, control free from overshooting or undershooting becomes possible. In this regard, an example in which the current indoor temperature Tai is 18 degrees C and the preset temperature Taim is 20 degrees C will be described below in detail.

When Indoor Load is Large: Low-temperature Outdoor Air

[0037] A capacity ratio P of a capacity B of the heat source device 1 at the current point of time (i.e., when the indoor temperature Tai is 18 degrees C) to a capacity A of the heat source device 1 when the indoor temperature Tai and the preset temperature Taim are equal to each other at 20 degrees C at an outdoor air temperature Tao of 0 degrees C can be calculated in the following manner. Specifically, the capacity A is replaced by the difference between the preset temperature Taim and the outdoor air temperature Tao as another index, and the capacity B is similarly replaced by the difference between the indoor temperature Tai and the outdoor air temperature Tao. Thus, the capacity ratio P is (18 degrees C - 0 degrees C)÷(20 degrees C - 0 degrees C)×100=90%. Therefore, the indoor temperature Tai can be made equal to the preset temperature Taim by increasing the inlet water temperature Twi by an amount equivalent to about a 10% increase in capacity relative to the current capacity B of the heat source device 1.

When Indoor Load is Small: High-temperature Outdoor Air

[0038] The current capacity ratio P of the heat source device 1 when the outdoor air temperature Tao is 10 degrees C is calculated in a manner similar to the above and is (18 degrees C - 10 degrees C)÷(20 degrees C - 10 degrees C)×100 =80%. Thus, the indoor temperature Tai can be made equal to the preset temperature Taim by increasing the inlet water temperature Twi by an amount equivalent to about a 20% increase in capacity relative to the current capacity B of the heat source device 1. As is obvious, the current capacity of the heat source device 1 corresponding to low-temperature outdoor air and the current capacity of the heat source device 1 corresponding to high-temperature outdoor air are different from each other; the current capacity of the heat source device 1 corresponding to high-temperature outdoor air is the smaller. Therefore, in order to increase the indoor temperature Tai by the same degrees C, that is, 2 degrees C, the capacity ratio needs to be increased by a larger amount in the case of high-temperature outdoor air than in the case of low-temperature outdoor air. Moreover, with regard to the increment for the inlet water temperature Twi of the indoor heat exchanger 31 necessary for increasing the indoor temperature Tai by 2 degrees C, although the increment itself is larger in the case of high-temperature outdoor air than in the case of low-temperature outdoor air, the increment is smaller in the case of high-temperature outdoor air in terms of an absolute value of a target inlet water temperature Twim.

[0039] The foregoing reveals that the rate of change (i.e., the rate of increase) in the inlet water temperature Twi of each indoor unit 2 necessary for making the indoor temperature Tai equal to the preset temperature Taim varies in accordance with the outdoor air temperature Tao even when the difference between the indoor temperature Tai and the preset temperature Taim is the same. In other words, the rate of change (i.e., the rate of increase) in the inlet water temperature Twi of each indoor unit 2 varies in accordance with the temperature difference between the indoor temperature Tai and the outdoor air temperature Tao. More specifically, the rate of change (i.e., the rate of increase) in the inlet water temperature Twi of each indoor unit 2 has an inversely proportional relationship with the temperature difference between the indoor temperature Tai and the outdoor air temperature Tao. This point is also clear from Expressions (6) to (8) (to be presented later).

[0040] The water-temperature increment for the inlet water temperature of each indoor heat exchanger 31 necessary for making the indoor temperature Tai equal to the preset temperature Taim is also affected by the current inlet-outlet water temperature difference in the indoor heat exchanger 31. More specifically, the increment for the inlet water temperature Twi of each indoor unit 2 needs to be larger when the inlet-outlet water temperature difference is large than when the inlet-outlet water temperature difference is small. This point will be described later.

[0041] Accordingly, the temperature difference between the indoor temperature Tai and the outdoor air temperature Tao and the inlet-outlet water temperature difference in each indoor heat exchanger 31 affect the water-temperature increment necessary for making the indoor temperature Tai equal to the preset temperature Taim. Thus, by determining the water-temperature increment and by extension the target inlet water temperature Twim of the indoor heat exchanger 31 in view of this point, overshooting and undershooting of the indoor temperature Tai with respect to the preset temperature Taim as described above are prevented more reliably, as compared with the case where the water-temperature increment is determined solely based on the difference between the indoor temperature Tai and the preset temperature Taim, thereby allowing for control with high operation efficiency while maintaining comfortability.

[0042] Next, a specific method for determining the target inlet water temperature Twim will be described. Since the inlet water temperature Twi of each indoor heat exchanger 31 is the same as the outlet water temperature of the heat source device 1, a method for determining the target outlet water temperature Twsom of the heat source device 1 will be described below.

Method for Determining Outlet Water Temperature

[0043] An amount of heat exchange Qio between the air inside a room and the outdoor air can be expressed by Expression (2) based on a heat exchange performance AKio(N) of the building, the indoor temperature Tai(N), and the outdoor air temperature Tao.

[0044] [Math. 2]

[0045] If the capacity Qw(N) of the indoor heat exchanger 31 (N) and the amount of heat exchange Qio(N) between the air inside the room and the outdoor air are balanced, the relationship among the inlet water temperature Twi(N) of the indoor heat exchanger 31 (N), the outlet water temperature Two(N) of the indoor heat exchanger 31 (N), the indoor temperature Tai(N), and the outdoor air temperature Tao can be expressed by Expression (3) based on Expressions (1) and (2).

[0046] [Math. 3]

[0047] In this case, C1 (N) is a constant determined from the water flow rate of the indoor heat exchanger 31 (N) and the heat exchange performance of the building in which the system is installed.

[0048] If the relationship between the inlet water temperature (i.e., the target inlet water temperature) Twim(N) of the indoor heat exchanger 31 (N) and the preset temperature Taim(N) when the indoor temperature Tai(N) is equal to the preset temperature (i.e., the target indoor temperature) Taim(N) is expressed by using the relational expression presented in Expression (3) above, Expression (4) is obtained.

[0049] [Math. 4]

[0050] Based on Expressions (3) and (4), the relationship among the current inlet-outlet water temperature difference in the indoor heat exchanger 31 (N) (i.e., the difference between the inlet water temperature Twi(N) and the outlet water temperature Two(N)), the indoor-outdoor temperature difference (i.e., the difference between the indoor temperature Tai(N) and the outdoor air temperature Tao), the preset temperature Taim(N), and the inlet water temperature (i.e., the target inlet water temperature Twim(N)) of the indoor heat exchanger 31 corresponding to the preset temperature Taim(N) can be expressed by Expression (5).

[0051] [Math. 5]

[0052] Expression (5) can be rewritten as Expression (6).

[0053] [Math. 6]

[0054] Similarly considering the case of cooling operation, the relationship among the current inlet-outlet water temperature difference in the indoor heat exchanger 31 (N), the indoor-outdoor temperature difference, the preset temperature Taim(N), and the inlet water temperature (i.e., the target inlet water temperature Twim(N)) of the indoor heat exchanger 31 (N) corresponding to the preset temperature Taim(N) can be expressed by Expression (7).

[0055] [Math. 7]

[0056] Specifically, based on the heat-balance relationship between the amount of heat exchange Qw in the indoor heat exchanger 31 and the amount of heat exchange Qio between the inside and the outside of the room, a deviation ΔTwim(N) (which corresponds to the aforementioned water-temperature increment) between the target inlet water temperature Twim(N) and the current inlet water temperature Twi(N) for making the indoor temperature Tai(N) equal to the preset temperature Taim(N) can be determined.

[0057] For clarity, Expressions (6) and (7) can be collectively expressed as Expression (8). Specifically, the deviation ΔTwim(N) can be determined from the indoor-outdoor temperature difference, an inlet-outlet water temperature difference ΔTw in the indoor unit 2, and the temperature difference between the preset temperature Taim and the current indoor temperature Tai. These temperature differences can be determined by using the values detected by the temperature detectors installed in the air-conditioning system 100.

[0058] [Math. 8]

[0059] The target outlet water temperature Twsom of the heat source device 1 can be determined based on Expression (9) by using the deviation ΔTwim(N) determined from Expressions (6) and (7) and the current outlet water temperature Twso of the heat source device 1.

[0060] [Math. 9]

[0061] In actual control, the outlet water temperature Twso of the heat source device 1 gradually changes to the target outlet water temperature Twsom. Specifically, a target outlet water temperature Twso(i+1) in the next step i+1 is determined at every predetermined control interval i, and is given by Expression (10).

[0062] [Math. 10]

[0063] As presented in Expression (10), the deviation ΔTwim(N) is multiplied by a relaxation coefficient α, and the target outlet water temperature Twso(i+1) of the heat source device 1 is gradually changed at every control interval i, so that overshooting and undershooting are suppressed. The heat source device 1 is controlled to ultimately make the indoor temperature Tai(N) equal to the preset temperature Taim(N).

Control Method

[0064] Fig. 4 is a flowchart illustrating a method for controlling the air-conditioning system according to Embodiment of the present invention. The method for controlling the air-conditioning system 100 will be described below with reference to Fig. 4.

[0065] The heat source device 1 starts its operation, the water pump 3 is driven, and the main controller 11 and the indoor control devices 12 provided in the respective indoor units 2 perform room temperature control (STEP 1).

[0066] Each water pump 4 is controlled based on a rotation speed and a voltage command from the corresponding indoor control device 12, and the main controller 11 determines the operational state of the water pump 4, that is, the water flow rate in the corresponding indoor unit 2, based on a signal from the indoor control device 12 (STEP 2). Then, the main controller 11 determines whether at least one water pump 4 is present in which the water flow rate has reached its upper limit (STEP 3). The upper limit may be sent from the main controller 11 to each indoor control device 12 or may be set by each indoor control device 12.

[0067] If the main controller 11 determines that even a single water pump 4 is absent in which the water flow rate has reached its upper limit, the main controller 11 controls the indoor control devices 12 so as to continue with the current control. Specifically, each indoor control device 12 controls the water flow rate by using the corresponding water pump 4 so as to continue with the control for making the indoor temperature Tai equal to the preset temperature Taim (STEP 4).

[0068] On the other hand, if at least one water pump 4 is present in which the water flow rate has reached its upper limit and the number of water pumps is one (No in STEP 5), the target outlet water temperature Twsom of the heat source device 1 is corrected (STEP 7). Specifically, the deviation ΔTwim(N) in the indoor unit 2(N) having installed therein the water pump 4 in which the water flow rate has reached its upper limit is calculated by using Expression (6) described above. Then, the target outlet water temperature Twsom of the heat source device 1 is obtained from Expression (9) described above based on the calculated deviation ΔTwim(N) and the current outlet water temperature Twso of the heat source device 1. The main controller 11 controls the capacity of the heat source device 1 such that the outlet water temperature Twso of the heat source device 1 detected by the heat-source-device outlet water temperature detector 25 becomes equal to the corrected target outlet water temperature Twsom.

[0069] If the water flow rate is at the upper limit in two or more water pumps 4 (Yes in STEP 5), an indoor unit 2(N) with a largest deviation ΔTwim(N) is selected as a representative indoor unit from the indoor units 2 having reached its upper limit (STEP 6).

[0070]  In this case, the deviation ΔTwim(N) is a value obtained by taking into account the effect the outdoor air temperature Tao has on the indoor load. Of the plurality of indoor units 2, an indoor unit 2 with a larger deviation ΔTwim(N) requires a larger amount of heat exchange of the indoor heat exchanger 31. Therefore, in STEP 6, the indoor unit 2(N) that requires the largest amount of heat exchange in the indoor units 2 is selected as a representative indoor unit. Then, the target outlet water temperature Twsom of the heat source device 1 is corrected as described above based on the deviation ΔTwim(N) in the selected indoor unit 2(N) (STEP 7). The main controller 11 controls the capacity of the heat source device 1 such that the outlet water temperature Twso of the heat source device 1 detected by the heat-source-device outlet water temperature detector 25 becomes equal to the corrected target outlet water temperature Twsom.

[0071] As a specific example, it is assumed that the water flow rate has reached its upper limit in two of the indoor units, that is, the indoor units 2(1) and 2(2). Moreover, ΔTwim(1) = 2.0 degrees C, ΔTwim(2) = 1.0 degree C, α = 0.2, and Twso(1) = 45 degrees C. In this case, the indoor unit 2(N) with the largest deviation ΔTwim(N) is the indoor unit 2(1), and the target outlet water temperature Twsom is corrected based on the deviation ΔTwim(1). Specifically, Twsom = 45 degrees C + 2 degrees C = 47 degrees C. In actual control, as described above, a target outlet water temperature in the next step is as follows: Twso(2) = 45 degrees C + 2.0 degrees C × 0.2 = 45.4 degrees C. Moreover, a target outlet water temperature in the step after next is as follows: Twso(3) = 45.4 degrees C + 2.0 degrees C × 0.2 = 45.8 degrees C.

[0072] In this case, the target outlet water temperature Twsom is too high for the indoor unit 2(2). Therefore, in the indoor unit 2(2), the water flow rate is controlled by controlling the water pump 4 by referring to the deviation between the current indoor temperature Tai(2) and the preset temperature Taim(2).

[0073]  The following description assumes a specific example of how the water-temperature increment necessary for making the indoor temperature Tai equal to the preset temperature Taim is affected by the inlet-outlet water temperature difference ΔTw in each indoor heat exchanger 31.

[0074] First, the reason why the inlet-outlet water temperature difference ΔTw in the indoor heat exchanger 31 varies from one indoor unit 2 to another indoor unit 2 will be described. For the sake of simplicity, it is assumed that the water flow rate, the inlet water temperature Twi, and the indoor temperature Tai are the same in the indoor units 2.

[0075] In this case, as is clear from Expression (1) described above, the inlet-outlet water temperature difference ΔTw in the indoor heat exchanger 31 varies from one indoor unit 2 to another indoor unit 2 due to differences in amount of heat exchange in the indoor heat exchangers 31. As shown in Fig. 6, the amount of heat exchange of each indoor heat exchanger 31 is proportional to an AK value indicating the performance of the heat exchanger, which is the product of a heat exchange area A and a heat transfer coefficient K. Specifically, as in the above-described condition, when the inlet water temperature or the indoor temperature is the same, the amount of heat exchange increases with increasing heat transfer area or heat transfer coefficient.

[0076] The reason why the inlet-outlet water temperature difference ΔTw in the indoor heat exchanger 31 varies from one indoor unit 2 to another indoor unit 2 is not limited to the heat exchange performances of the indoor heat exchangers 31. As presented in Expression (1), if the amount of heat exchange is the same in the indoor heat exchangers 31, the inlet-outlet water temperature difference ΔTw in the indoor heat exchanger 31 varies from one indoor unit 2 to another indoor unit 2 due to differences in water flow rate in the indoor heat exchangers 31. This means that the inlet-outlet water temperature difference ΔTw increases with decreasing water flow rate, whereas the inlet-outlet water temperature difference ΔTw decreases with increasing water flow rate.

[0077] As described above, there are various reasons why the inlet-outlet water temperature difference ΔTw in the indoor heat exchanger 31 varies from one indoor unit 2 to another indoor unit 2. Next, an effect such differences in inlet-outlet water temperature differences ΔTw in the indoor heat exchangers 31 have on the water-temperature increment necessary for making the indoor temperature Tai equal to the preset temperature Taim will be described with reference to a specific example.

[0078] Expression (11) represents the relationship among the inlet water temperature Twi, the outlet water temperature Two, and the target inlet water temperature Twim when making the indoor temperature Tai equal to the preset temperature Taim by using Expression (8). As described above, since it is assumed that the indoor temperatures Tai, the outdoor air temperatures Tao, and the preset temperatures Taim are the same, the ratio of the difference between the preset temperature Taim and the indoor temperature Tai to that between the indoor temperature Tai and the outdoor air temperature Tao is constant and is expressed as β.

[0079] [Math. 11]

[0080] [Math. 12]

[0081] The reason why the inlet-outlet water temperature difference ΔTw in the indoor heat exchanger 31 varies from one indoor unit 2 to another indoor unit 2 is not limited to the heat exchange performances of the indoor heat exchangers 31, and may additionally include, for example, the following reason. Specifically, if the heat exchange performances of the indoor heat exchangers 31, the indoor temperatures Tai, the inlet water temperatures Twi, and the preset temperatures Taim are the same, that is, if the amounts of heat exchange of the indoor heat exchangers 31 are the same, the inlet-outlet water temperature difference ΔTw in the indoor heat exchanger 31 varies from one indoor unit 2 to another indoor unit 2 due to differences in water flow rate in the indoor heat exchangers 31. This means that the inlet-outlet water temperature difference ΔTw increases with decreasing water flow rate, whereas the inlet-outlet water temperature difference ΔTw decreases with increasing water flow rate.

[0082] As described above, there are various reasons why the inlet-outlet water temperature difference ΔTw in the indoor heat exchanger 31 varies from one indoor unit 2 to another indoor unit 2. Next, an effect such differences in inlet-outlet water temperature differences ΔTw in the indoor heat exchangers 31 have on the water-temperature increment necessary for making the indoor temperature Tai equal to the preset temperature Taim will be described with reference to a specific example.

[0083] In this case, it is assumed that the inlet water temperature Twi is 40 degrees C in both an indoor heat exchanger 31 with a large inlet-outlet water temperature difference ΔTw and an indoor heat exchanger 31 with a small inlet-outlet water temperature difference ΔTw, the outlet water temperature Two is 30 degrees C in the indoor heat exchanger 31 with the large inlet-outlet water temperature difference ΔTw, and the inlet-outlet water temperature difference is 10 degrees C. It is furthermore assumed that the outlet water temperature Two in the indoor heat exchanger 31 with the small inlet-outlet water temperature difference ΔTw is 35 degrees C, and the inlet-outlet water temperature difference is 5 degrees C. Specifically, the water-temperature increment in each of the indoor heat exchanger 31 with the inlet-outlet water temperature difference ΔTw of 10 degrees C and the indoor heat exchanger 31 with the inlet-outlet water temperature difference ΔTw of 5 degrees C will be discussed.

[0084] Letting TwimH be the inlet water temperature (i.e., the target inlet water temperature) when the indoor temperature Tai becomes equal to the preset temperature Taim in the indoor heat exchanger 31 with the large inlet-outlet water temperature difference ΔTw, the relationship between the current inlet and outlet water temperatures of the indoor heat exchanger 31 and the target inlet water temperature TwimH is given by Expression (13) based on Expression (11) above.

[0085] [Math. 13]

[0086] Also, letting TwimL be the inlet water temperature (i.e., the target inlet water temperature) when the indoor temperature Tai becomes equal to the preset temperature Taim in the indoor heat exchanger 31 with the small inlet-outlet water temperature difference ΔTw, the relationship between the current inlet and outlet water temperatures of the indoor heat exchanger 31 and the target inlet water temperature TwimL is given by Expression (14) similarly based on Expression (11) above.

[0087] [Math. 14]

[0088] Since the inlet water temperatures Twi are the same, the target inlet water temperatures have a relation TwimL < TwimH. Thus, the target outlet water temperature Twsom of the heat source device 1 needs to be corrected to an extent larger for the indoor heat exchanger 31 with the large inlet-outlet water temperature difference ΔTw than for the indoor heat exchanger 31 with the small inlet-outlet water temperature difference ΔTw.

[0089] Accordingly, even when the difference between the preset temperature Taim and the indoor temperature Tai is the same, the target outlet water temperature Twsom in the indoor heat exchanger 31 with the large inlet-outlet water temperature difference ΔTw becomes higher than that in the indoor heat exchanger 31 with the small temperature difference ΔTw. Therefore, the target outlet water temperature Twsom of the heat source device 1 is determined in accordance with the indoor heat exchanger 31 with the larger inlet-outlet water temperature difference ΔTw in the indoor heat exchangers 31.

[0090] Referring back to Expression (8), a deviation ΔTim (i.e., the water-temperature increment) between the target outlet water temperature Twsom and the current inlet water temperature Twi is proportional to the inlet-outlet water temperature difference ΔTw in each indoor heat exchanger 31. As described above, when selecting a representative indoor unit 2, an indoor unit 2 with a largest deviation ΔTim is selected. This amounts to determining the target outlet water temperature Twsom in view of the inlet-outlet water temperature difference ΔTw in each indoor heat exchanger 31 as well.

[0091] Accordingly, in Embodiment, the indoor unit 2 in which the water flow rate has reached its upper limit is selected as a representative indoor unit for determining the target outlet water temperature Twsom of the heat source device 1, and the target outlet water temperature Twsom is determined by using the deviation ΔTwim in the representative indoor unit 2. Specifically, the target outlet water temperature Twsom is calculated by using the water temperatures (Two and Twi) of the indoor unit 2 in which the water flow rate has reached its upper limit and the indoor temperature Tai, and the obtained target outlet water temperature Twsom is preferentially used so that the capacity of the representative indoor heat exchanger 31 in which the water flow rate has reached its upper limit can be controlled. Therefore, the comfortability in the room in which the representative indoor heat exchanger 31 is installed is not impaired. With regard to the other rooms, room temperature control need only be simply performed therefor by adjusting the water flow rates so that comfortability therein is similarly not impaired.

[0092] Specifically, since the target outlet water temperature Twsom can be set in view of the load in the entire air-conditioning system 100, the capacity of each indoor unit 2 can be prevented from being excessive or insufficient. Thus, overshooting or undershooting can be prevented, thereby achieving control with high operation efficiency without impairing user's comfortability in each room.

[0093] If the water flow rate has reached its upper limit in a plurality of indoor units 2, the deviation ΔTwim is calculated for each indoor unit 2. An indoor unit 2 with a deviation ΔTwim largest of the calculated deviations ΔTwim is selected as a representative indoor unit for determining the target outlet water temperature Twsom of the heat source device 1. Therefore, because the target outlet water temperature Twsom can be set in view of the amount of heat exchange Qio between the air inside the room and the outdoor air in each indoor unit 2, that is, in view of the load in the entire air-conditioning system 100, the capacity of each indoor unit 2 can be prevented from being excessive or insufficient. Thus, overshooting or undershooting can be prevented, thereby achieving control with high operation efficiency without impairing user's comfortability in each room.

[0094] Furthermore, since the target outlet water temperature Twsom of the heat source device 1 is determined based on the indoor temperature Tai in the room in which the indoor heat exchanger 31 of the representative indoor unit 2 is installed, the inlet water temperature Twi of the representative indoor heat exchanger 31, the outlet water temperature Two of the representative indoor heat exchanger 31, the preset temperature Taim of the room in which the representative indoor heat exchanger 31 is installed, and the outdoor air temperature Tao, the target outlet water temperature Twsom can be set in accordance with the indoor load while taking into account the effect of the outdoor air temperature Tao. Therefore, an advantage similar to that described above can be achieved.

[0095] The refrigerant circuit is not limited to the configuration in Fig. 1 and may be provided with a bypass 60 between the heat source device 1 and the indoor units 2 in the water circuit 50, as shown in Fig. 5. In this case, the heat-source-device outlet water temperature detector 25 is disposed downstream of the bypass 60 so that an advantage similar to that described above can be achieved. In Fig. 5, components that are the same as those in Fig. 1 are denoted by the same reference numerals.

[0096] Also, because the target outlet water temperature Twsom is determined such that the difference between the target outlet water temperature Twsom and the current outlet water temperature Twso of the heat source device 1 is inversely proportional to the difference between the indoor temperature Tai in the room in which the representative indoor heat exchanger 31 is installed and the outdoor air temperature Tao, an advantage similar to that described above can be achieved.

[0097] Furthermore, because the target outlet water temperature Twsom can be set in accordance with the current capacity of the heat source device 1 by determining the target outlet water temperature Twsom of the heat source device 1 such that the difference between the target outlet water temperature Twsom and the current outlet water temperature Twso of the heat source device 1 is proportional to the inlet-outlet water temperature difference in the representative indoor heat exchanger 31, an advantage similar to that described above can be achieved.

[0098] The main controller 11 calculates the deviation ΔTwim by multiplying, by the difference between the preset temperature Taim and the indoor temperature Tai, a value obtained by dividing the inlet-outlet water temperature difference in the indoor heat exchanger 31 by the indoor-outdoor temperature difference, and sets a value obtained by adding the current inlet water temperature Twi to the determined deviation ΔTwim as the target outlet water temperature Twsom. By performing the calculation in this manner, the target outlet water temperature Twsom can be set in accordance with the current indoor load and the capacity of the indoor heat exchanger 31, whereby a similar advantage can be achieved.

Reference Signs List

[0099] 1 heat source device 2 indoor unit 3 water pump 4 water pump 11 main controller 12 indoor control device 21 outdoor air temperature detector 22 indoor temperature detector 23 inlet water temperature detector 24 outlet water temperature detector 25 heat-source-device outlet water temperature detector 26 heat-source-device inlet water temperature detector 31 indoor heat exchanger 50 water circuit 60 bypass 100 air-conditioning system

Claims

1. An air-conditioning system comprising:

a heat medium circuit that includes a heat source device whose capacity is variable and a plurality of indoor heat exchangers and that is configured to perform at least one of cooling and heating by circulating a heat medium through the heat source device and the plurality of indoor heat exchangers;

a heat-medium conveying device configured to convey the heat medium to the heat medium circuit;

a heat-source-device outlet temperature detector configured to detect a temperature of the heat medium flowing out of the heat source device;

a plurality of flow control devices configured to control flow rates of streams of the heat medium individually passing through the plurality of indoor heat exchangers;

a plurality of inlet heat-medium temperature detectors configured to detect temperatures of the streams of the heat medium individually flowing into the plurality of indoor heat exchangers;

a plurality of outlet heat-medium temperature detectors configured to detect temperatures of the streams of the heat medium individually flowing out of the plurality of indoor heat exchangers;

a plurality of indoor temperature detectors configured to detect indoor temperatures of rooms in which the plurality of indoor heat exchangers are individually installed;

an outdoor air temperature detector configured to detect an outdoor temperature; and

a controller configured to control the capacity of the heat source device and the plurality of flow control devices to make the indoor temperatures of the rooms in which the plurality of indoor heat exchangers are individually installed equal to preset temperatures of the rooms,

wherein the controller is configured to determine whether the plurality of indoor heat exchangers include an indoor heat exchanger in which the flow rate of the heat medium passing through the indoor heat exchanger has reached an upper limit, and when the controller determines that the plurality of indoor heat exchangers have one indoor heat exchanger in which the flow rate of the heat medium passing through the indoor heat exchanger has reached the upper limit, the controller is configured to set the one indoor heat exchanger as a representative indoor heat exchanger, detect the indoor temperature of the room in which the representative indoor heat exchanger is installed by using the corresponding indoor temperature detector, determine a target outlet temperature of the heat source device based on a detection value of the indoor temperature, an inlet heat-medium temperature of the representative indoor heat exchanger, an outlet heat-medium temperature of the representative indoor heat exchanger, the preset temperature of the room in which the representative indoor heat exchanger is installed, and an outdoor air temperature detected by the outdoor air temperature detector, and control the capacity of the heat source device to make the temperature detected by the heat-source-device outlet temperature detector equal to the determined target outlet temperature.

2. The air-conditioning system of claim 1,
wherein a deviation between the target outlet temperature of the heat source device and a current outlet temperature of the heat source device is inversely proportional to a difference between the preset temperature of the room in which the representative indoor heat exchanger is installed and the outdoor air temperature detected by the outdoor air temperature detector.

3. The air-conditioning system of claim 1 or 2,
wherein a deviation between the target outlet temperature of the heat source device and a current outlet temperature of the heat source device is proportional to a difference between the inlet heat-medium temperature of the representative indoor heat exchanger and the outlet heat-medium temperature of the representative indoor heat exchanger.

4.  The air-conditioning system of any one of claims 1 to 3,
wherein a deviation between the target outlet temperature of the heat source device and a current outlet temperature of the heat source device is calculated by multiplying, by a difference between the preset temperature and the indoor temperature of the room in which the representative indoor heat exchanger is installed, a value obtained by dividing an inlet-outlet water temperature difference in the representative indoor heat exchanger by a difference between the indoor temperature of the room in which the representative indoor heat exchanger is installed and the outdoor air temperature detected by the outdoor air temperature detector, and the target outlet temperature of the heat source device is determined based on the deviation.

5. The air-conditioning system of any one of claims 1 to 4,
wherein if the plurality of indoor heat exchangers include a set of indoor heat exchangers in which the flow rates of the streams of the heat medium have reached the upper limit, a deviation between the target outlet temperature of the heat source device and a current outlet temperature of the heat source device is determined for each individual heat exchanger of the set of indoor heat exchangers by multiplying, by a difference between the preset temperature and the indoor temperature of the room in which the indoor heat exchanger is installed, a value obtained by dividing an inlet-outlet water temperature difference in the indoor heat exchanger by a difference between the indoor temperature of the room in which the indoor heat exchanger is installed and the outdoor air temperature detected by the outdoor air temperature detector, and the indoor heat exchanger with a deviation largest of the determined deviations is set as the representative indoor heat exchanger.

Drawing