JP7760433B2 - Air conditioning system operating method and air conditioning system - Google Patents

Description

Article 30, paragraph 2 of the Patent Act applied. September 1, 2021. Published in Proceedings of the 2021 Annual Meeting of the Society of Heating, Air-Conditioning and Sanitary Engineers of Japan, Vol. 9, pp. 53-56

The present invention relates to a method for operating an air conditioning system in an energy-saving manner, and to an air conditioning system to which this method is applied.

Energy conservation is, of course, a key issue in the field of air conditioning. While there are a wide variety of specific approaches to achieving energy conservation, in recent years in particular, various technologies have been proposed and implemented to reduce energy consumption throughout the entire system by optimizing the operating conditions of each component of the air conditioning system. For example, Patent Document 1 below describes a technology that calculates the air conditioning load based on the inlet and outlet temperatures and flow rate of chilled water in a heat source unit, estimates state variables for optimal control of the air conditioning equipment based on this, the air conditioning operating conditions (such as outside air intake volume and supply air temperature) and outside air conditions, and controls the cooling tower fan, chilled water pump, chilled water pump, and compressor on the heat source unit side to match these state variables. Furthermore, Patent Document 2 below describes a technology that monitors the measured values of the outside air wet-bulb temperature, the amount of heat generated by the heat source unit, and the chilled water outlet temperature during air conditioning operation, and then performs optimization calculations in real time to determine the control target values for the chilled water flow rate and chilled water outlet temperature for each heat source unit so that the total energy consumption of each heat source unit is minimized, thereby determining the control target values for the chilled water flow rate of the chilled water pump and the air volume of the cooling tower fan for each heat source unit.

Japanese Patent Application Laid-Open No. 2008-256258 JP 2017-101862 A

However, in the technologies described in Patent Documents 1 and 2, calculations of the operating conditions of each device are basically limited to the heat supply side (primary side); the secondary side that consumes heat is treated as the overall load from the heat supply side, which is the heat source. As a result, operation has not been optimized by taking into account the operating conditions of the secondary side devices that consume heat. This is because, in general, the secondary side of an air conditioning system has a more complex configuration than the primary side. Of course, it is in principle possible to calculate the operating conditions of the secondary side, even if the configuration is complex. However, such calculations require a much greater load than calculating the primary side, and have not been realized on a practical basis. If it were possible to calculate the operating conditions of a system including the secondary side with a practically reasonable calculation load and optimize the operating conditions of the entire system based on this, even greater energy savings could be achieved than before.

In light of this situation, the present invention aims to provide an air conditioning system operating method that efficiently calculates the operating conditions of each secondary device, optimizes the operation of each device based on these calculations, and achieves energy savings, as well as an air conditioning system that employs this method.

The present invention relates to a method for operating an air conditioning system that includes a heat source unit as the primary equipment and multiple air conditioners as secondary equipment, with chilled water circulating between the heat source unit and the air conditioners. The method sets multiple variance values as the set value for the secondary water temperature, which is the temperature of the chilled water upstream of the air conditioners, and calculates the power required for each component of the air conditioning system when the set value for the secondary water temperature is each of the variance values using a system model that hypothetically includes multiple representative air conditioners with the same performance. The method identifies the variance value for the set value of the secondary water temperature that minimizes the total power required, and operates the primary equipment so that the secondary water temperature reaches the identified variance value.

In the air conditioning system operating method of the present invention, multiple variance values are set for the secondary load heat quantity or a value related thereto, with the numerical range including the reference value, and the operating conditions for each component of the air conditioning system when the secondary load heat quantity or a value related thereto is each of the variance values is calculated. If there are multiple calculation results that are operable, the variance value for the set value of the secondary-side water supply temperature that reduces the total power is identified from the operating conditions where the variance value of the secondary load heat quantity or a value related thereto is closest to the reference value, and the primary-side equipment can be operated so that the secondary-side water supply temperature is the identified variance value.

In the air conditioning system operating method of the present invention, the value related to the secondary load heat quantity for which the variance value is set can be variance-allocated to at least one of the outdoor air load ratio and the indoor load ratio, with the other remaining at 100%.

In the air conditioning system operating method of the present invention, the value related to the secondary load heat quantity for setting the variance value is based on the sensible heat load, which is determined by the sensible heat ratio when mixing outside air and return air and introducing them into the chilled water coil, and then heat treating the target room to the set temperature. This can be determined by calculating the representative air conditioner airflow from the sensible heat load, and then calculating the secondary return chilled water temperature and required flow rate from the specified chilled water coil performance.

In the air conditioning system operating method of the present invention, the value related to the secondary load heat quantity for setting the variance value can be determined by calculating the secondary chilled water flow rate from the number of representative air conditioners in operation at any given time.

In the air conditioning system operating method of the present invention, the chiller load factor as the primary heat source is calculated using the representative air conditioner airflow calculated from the sensible heat load and the secondary return chilled water temperature and required flow rate obtained from the specified chilled water coil performance, so that the secondary supply water temperature becomes a specified variance value, and the number of chillers in operation can be calculated by receiving a signal indicating the number of chillers actually in operation.

The present invention also relates to an air conditioning system configured to be able to execute the above-mentioned air conditioning system operating method.

The air conditioning system operating method and air conditioning system of the present invention can efficiently calculate the operating conditions of each secondary device, and based on this, optimize the operation of each device, thereby achieving the excellent effect of saving energy.

1 is a block diagram showing an example of a system configuration of an air conditioning system to which the present invention is applied; 1 is a block diagram conceptually showing the concept of secondary-side operating conditions in an air conditioning system operating method according to an embodiment of the present invention. 1 is a block diagram showing an example of the configuration of a system model in an air conditioning system to which the present invention is applied. 1 is a flowchart showing an example of a calculation procedure in an air conditioning system operation method according to an embodiment of the present invention.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

Figure 1 shows an example of the system configuration of an air conditioning system to which the present invention is applicable. On the primary side (heat supply side) of the system, multiple chillers 1 are installed as heat source machines, and each chiller 1 is connected to multiple cooling towers 2 via a chilled water circulation path 3. A chilled water pump 4 is installed midway along the chilled water circulation path 3, and operation of the chilled water pump 4 circulates chilled water between the chillers 1 and the cooling towers 2. The chilled water pump 4 is equipped with an inverter-controlled motor, and its rotation speed can be changed as needed to adjust the flow rate of the chilled water (the same applies to the primary chilled water pump 8 and secondary chilled water pump 22, described below).

A primary chilled water flow path 5 is also connected to each chiller 1. Each chiller 1 uses the cold energy of a high-temperature field resulting from heat exchange between the cooling water flowing through the cooling water circulation path 3 and the atmosphere to cool the chilled water flowing through the primary chilled water flow path 5 by a phase change of the refrigerant in the case of a vapor compression refrigeration cycle, or by absorption of the low-pressure vapor of water (the refrigerant) into the absorption liquid in the case of an absorption refrigeration cycle. Multiple primary chilled water flow paths 5 extend from the primary return header 6 to the primary outward header 7, with a chiller 1 installed along each path. An inverter-controlled primary chilled water pump 8 is installed upstream of the chiller 1 in each primary chilled water flow path 5. Operation of the primary chilled water pump 8 drives the flow of chilled water from the primary return header 6 through the chillers 1 to the primary outward header 7. In addition, the primary return header 6 and the primary outgoing header 7 are connected by a bypass flow path 9, which allows cold water to circulate between the primary return header 6 and the primary outgoing header 7 when the flow rate of cold water on the primary side (primary cold water flow path 5) differs from the flow rate of cold water on the secondary side (secondary cold water flow path 16), described below, to adjust the differential pressure between the headers.

On the secondary side (heat consumption side) of the system, multiple air conditioners 10 are installed to supply conditioned air to the target space S. Each air conditioner 10 has a chilled water coil 10a through which chilled water circulates and exchanges heat with the air passing over its surface, and an inverter-controlled intake fan 10b that exchanges heat with the chilled water in the chilled water coil 10a and sends out the air that has received the chilled heat as conditioned air. The air outlet of each air conditioner 10 is connected via an intake duct 11 to an intake port 12 of the target space S, from which conditioned air is supplied to the target space S. A damper 13 is provided in the intake duct 11 just before the intake port 12, and by changing the opening of the damper 13, the amount of conditioned air blown out from the intake port 12 can be adjusted as needed.

In addition, a return air inlet 14 for taking in indoor air is provided at an appropriate position in the target space S, and the return air inlet 14 is connected to the air inlet side of the air conditioner 10 via a return air duct 15. An inverter-controlled return air fan 15a is provided in the return air duct 15, and when the return air fan 15a is operated, a portion of the indoor air in the target space S is taken in as return air through the return air inlet 14 and returned to the air conditioner 10 via the return air duct 15. The return air returned to the air conditioner 10 is again temperature-adjusted by the air conditioner 10 and sent out as supply air. As will be described later, the return air duct 15 joins with an outdoor air duct (not shown) that introduces outside air, and the air enters the air conditioner 10 as mixed return air. It is also possible to fix the outdoor air supply ratio (OA ratio), for example, by mixing 20% of the supply air volume as outdoor air with the return air.

A secondary chilled water flow path 16 is connected to the chilled water coil 10a inside the air conditioner 10, and chilled water is supplied to the chilled water coil 10a through the secondary chilled water flow path 16. The secondary chilled water flow path 16 extends from a secondary supply header 17 and is connected to the inlet side of the chilled water coil 10a, and also extends from the outlet side of the chilled water coil 10a and is connected to a secondary return header 18. The secondary supply header 17 is connected to the primary supply header 7 via multiple communication paths 20, and the secondary return header 18 is connected to the primary return header 6 via a communication path 19. Of the multiple communication paths 20 connecting the primary supply header 7 and the secondary supply header 17, one communication path 20 is provided with a minimum flow valve 21, and the remaining communication paths 20 are each provided with an inverter-controlled secondary chilled water pump 22. The secondary chilled water pump 22 sends chilled water from the primary feed header 7 to the secondary feed header 17, and drives the flow of chilled water from the secondary feed header 17 through the chilled water coil 10a of the air conditioner 10 to the secondary return header 18. The minimum flow valve 21 is opened appropriately when the required amount of chilled water supplied from the primary feed header 7 to the secondary feed header 18 is low, adjusting the flow rate so that the required flow rate from the primary feed header 7 to the secondary feed header 18 is achieved without the secondary chilled water pump 22 operating at less than the minimum flow rate. A flow control valve 23 is installed downstream of the chilled water coil 10a in the secondary chilled water flow path 16, and the amount of chilled water flowing through the secondary chilled water flow path 16 is adjusted by the opening of the flow control valve 23.

In this way, in the air conditioning system shown in Figure 1, chilled water is circulated through the annular chilled water flow path consisting of the primary chilled water flow path 5, the secondary chilled water flow path 16, and the headers 6, 7, 17, 18 and the connecting passages 19, 20 by the action of the primary chilled water pump 8 and the secondary chilled water pump 22. On the primary side, chilled water is circulated between the chiller 1 and the cooling tower 2, cooling the chilled water in the chiller 1. On the secondary side, air is circulated between the air conditioner 10 and the target space S, cooling the air, and supplying it to the target space S.

In addition, temperature sensors that measure the temperature of the cooling water, chilled water, and air, and flow meters that measure the flow rate of these, are installed as appropriate in various locations in the air conditioning system. The operation of the above-mentioned air conditioning system is carried out by appropriately referring to the measurements of these sensors. In the example shown here, temperature sensors 24 that measure the temperature of the cooling water are installed at the inlet and outlet of each cooling tower 2 in the cooling water circulation path 3, and temperature sensors 25 that measure the temperature of the chilled water are installed at the outlet of each chiller 1 in the primary chilled water flow path 5. Temperature sensors 25 that measure the temperature of the chilled water are also installed in the secondary supply header 17 and in the communication passage 19 between the secondary return header 18 and the primary return header 6. Furthermore, a temperature sensor 26 that measures the temperature of the supply air is installed upstream of the damper 13 in the supply air duct 11.

An outside air duct (not shown) for taking in outside air is connected to the return air duct 15, and is equipped with an outside air sensor 35 that measures outside air conditions. The outside air sensor 35 is, for example, a thermo-hygrometer, and measures outside air conditions such as temperature and humidity.

Furthermore, flow meters 27 are provided in the primary chilled water flow path 5 at positions upstream of each chiller 1 and in the communication passage 19 between the secondary return header 18 and the primary return header 6 to measure the chilled water flow rate at these positions.

Each device and sensor is connected to the other devices as appropriate via a communication network 28. Information devices such as a data collection server 29, a gateway device 30, and a central monitoring device 31 are connected to the communication network 28.

The data collection server 29 is the part that collects various data related to the operation of the air conditioning system, such as the operating status of each device and the measurement values of each sensor. Various values related to the operating status are input here from the controllers (not shown) of each device, such as the chiller 1, cooling tower 2, cooling water pump 4, primary chilled water pump 8, secondary chilled water pump 22, minimum flow valve 21, and flow control valve 23. In addition, measurement values from temperature sensors 24, 25, and 26, flow meter 27, and outside air sensor 35 are also input and stored.

The central monitoring device 31 monitors and controls the operation of the entire air conditioning system, appropriately referencing data input from the controllers and sensors of each device, as well as data stored in the data collection server 29, and inputting operational commands to each device.

The gateway device 30 connects the communication network 28 to an external network (e.g., the Internet) 32. Connected to the Internet 32 is an optimization calculation unit 33, which is an information processing device such as a personal computer. This optimization calculation unit 33 has a built-in system model 34 that represents an information model of the entire air conditioning system. Based on various conditions acquired from the data collection server 29 and central monitoring device 31 via the external network 32, it calculates the operating conditions of each part of the system using the method described below, and identifies a set value for the secondary water supply temperature (the temperature of the chilled water upstream of the air conditioner 10 in the secondary chilled water flow path 16) that minimizes the total power consumed by each device. The central monitoring device 31 controls each device in real time to maintain that secondary water supply temperature.

The controller (not shown) for the heat source, primarily the chiller 1, controls the operation of various parts, such as the rotation speed of the chilled water pump 4 and primary chilled water pump 8, and the rotation speed and vane opening of the compressor within the chiller 1 via the chiller side panel, based on command signals input from the central monitoring device 31 via the network and information such as the flow rate and temperature of the cooling water and chilled water in the pipes connected to the chiller 1's condenser, evaporator, etc. Furthermore, the controller (not shown) for each cooling tower 2 controls the rotation speed of the cooling tower fan motor installed in the cooling tower 2 based on command signals input from the central monitoring device 31, information such as the outside air temperature and humidity, and measurements from the temperature sensor 24 installed in the cooling water circulation path 3.

The controller (not shown) of the air conditioner 10 controls the opening of the flow control valve 23 and the rotation speed of the supply air fan 10b and return air fan 15a based on information such as command signals input from the central monitoring device 31, the set temperature input to the operation panel in the target space S, and the temperature sensor 26 installed in the supply air duct 11. The controller (not shown) of the secondary chilled water pump 22 also controls the number of secondary chilled water pumps 22 in operation, their respective rotation speeds, and the opening of the minimum flow valve 21 based on information such as command signals input from the central monitoring device 31 and measurements from temperature sensors 25 and flow meters 27 installed in various parts of the chilled water flow path.

While simplified examples are shown here for the number and locations of each device, such as the heat source unit (chiller) 1, cooling tower 2, air conditioner 10, primary chilled water pump 8, and secondary chilled water pump 22; the number of cooling towers 2 per chiller 1; the number of air conditioners 10 and dampers 13 installed relative to the target space S; the number and locations of sensors, such as temperature sensors 24, 25, and 26 and flow meter 27; and the configuration of the cooling water circuit 3, primary chilled water flow path 5, secondary chilled water flow path 16, supply air duct 11, and return air duct 15, this configuration is merely an example, and the drawings are schematic diagrams. The specific number and configuration of these devices, sensors, piping, etc. may be modified from the illustrated configuration as appropriate depending on the actual air conditioning system. The same applies to the configuration of control and information management components, such as the data collection server 29, central monitoring device 31, optimization calculation unit 33, and system model 34. Additionally, parts that are not directly related to the spirit of the present invention or that are not considered particularly necessary to illustrate have been omitted here as appropriate (for example, the aforementioned outside air duct, the outside air conditioning unit that conditions the outside air that is taken in, and sensors, on-off valves, and flow control valves attached to various parts not shown here).

In the air conditioning system of this embodiment, the optimization calculation unit 33 calculates the operating conditions of each piece of equipment, including the secondary side. Based on this, the system determines the secondary-side water temperature that will maximize energy conservation across the entire system, and operates at that secondary-side water temperature. The concepts and calculation procedures for this optimization are explained below. Note that, in this specification, the terms "equipment" and "component equipment" refer to equipment such as the heat source unit (chiller) 1, cooling tower 2, cooling water pump 4, air conditioner 10, damper 13, return air vent 15a, minimum flow valve 21, secondary chilled water pump 22, temperature sensors 24, 25, 26, flow meter 27, outdoor air sensor 35, and data collection server 29, as well as at least some of the equipment that constitutes the air conditioning system that is not listed here (or shown). In particular, when it is stated that "equipment (system component equipment) is operated based on the set value of the secondary-side water temperature," the equipment to be operated includes at least one of the heat source unit (chiller) 1 and the cooling tower 2, and may also include other equipment as necessary.

In this embodiment, a simplified model (system model 34) is used for the secondary side, which tends to have a complex actual configuration and incurs a huge computational load when performing calculations related to operating conditions. This keeps the amount of calculations to a practically feasible level while achieving optimization of the entire system, taking into account the operating conditions of the secondary side.

In an actual air conditioning system, when multiple air conditioners 10 (see Figure 1) are installed, their type and performance often differ depending on the size and thermal load of the target space S they are responsible for. Furthermore, the configuration of the piping and ducts (secondary chilled water flow path 16, supply air duct 11, return air duct 15) and the thermal conditions of the target space S also differ depending on the location. Accurately simulating the operating conditions of each secondary device, including the air conditioners 10, requires setting and calculating these complex conditions individually for each air conditioner 10, resulting in a huge computational load.

Therefore, in this embodiment, as conceptually shown in Figure 2, a system model 34 (see Figure 1) is constructed by replacing each of the multiple air conditioners 10 installed on the secondary side with a virtual representative air conditioner 10' with the same performance. The virtual representative air conditioner 10' may be, for example, one of the air conditioners 10 actually installed in the air conditioning system, and set as an air conditioner with the same performance as that air conditioner 10. Alternatively, the virtual representative air conditioner 10' may be set as an air conditioner with the performance of that average, calculated by averaging the performance values of the multiple air conditioners 10 installed in the air conditioning system. The same number (N units) of these representative air conditioners 10' are then assumed to be installed in place of the actual air conditioners 10. By constructing the system model 34 based on such a hypothetical assumption, it is no longer necessary to perform calculations for each air conditioner 10 with different performance when calculating the operating conditions of the secondary system, thereby significantly reducing the computational load. Note that, for components other than the air conditioner 10, appropriate omissions, averaging, approximations, and other processing may also be performed. For example, similarly, it may be assumed that there are multiple representative spaces S' with the same heat load, volume, set temperature, etc. for the target space S. Furthermore, the number of representative air conditioners and representative spaces is not limited to one type per system model, and representative air conditioners and representative spaces with multiple performance and specifications may be assumed. For example, if 10 air conditioners are installed, a configuration may be adopted in which one type of representative air conditioner is assumed for five units with similar performance, and a different type of representative air conditioner is assumed for the remaining five units.

Using the system model 34 created based on these settings, the operating conditions of each component of the air conditioning system are calculated based on the operating status of the primary heat source unit (chiller) 1, the operating status of the secondary air conditioner 10, the outdoor air conditions, and the secondary heat load. Using the operating status of the chiller 1 and air conditioner 10, the outdoor air conditions, and the secondary heat load as given conditions, the operating conditions of each piece of equipment that can achieve an appropriate air conditioning state in the target space S are calculated. The energy consumption of each piece of equipment under those operating conditions is then calculated, and these are summed to calculate the energy consumption of the entire air conditioning system.

This calculation is performed for each secondary water temperature, using the temperature of the chilled water sent out from the secondary feed header 17 (i.e., the temperature of the chilled water upstream of the air conditioner 10; hereafter referred to as the "secondary water temperature") as a parameter, with multiple secondary water temperatures set. That is, for example, for five secondary water temperature settings of 7°C, 8°C, 9°C, 10°C, and 11°C, the operating conditions are calculated for each setting, and the energy consumption of the entire system is calculated for each setting (for convenience, multiple values set for this calculation are referred to as "variance values" below). Then, from the calculated operating conditions, the variance value that minimizes energy consumption for the entire system is identified, and each piece of equipment that makes up the system, particularly the primary-side chiller 1 and cooling tower 2, is operated so that the secondary water temperature becomes the identified variance value.

Generally, the higher the secondary water temperature (i.e., the higher the target temperature of the chilled water to be cooled), the lower the energy consumption in the chiller 1 and cooling tower 2. Because the evaporation temperature in the chiller's evaporator increases, the temperature difference with the condenser in a vapor compression chiller decreases, reducing the compressor's workload. On the other hand, if the secondary water temperature is increased, the chilled water coil in the secondary air conditioner cannot compensate for the temperature difference between the chilled water going back and forth to cool the air. This increases the amount of chilled water required to circulate on the secondary side to meet the heat load on the secondary side for transporting the same amount of heat, resulting in increased energy consumption by equipment such as the primary chilled water pump 8 and secondary chilled water pump 22. In other words, setting the secondary water temperature too high or too low can lead to increased energy consumption. Therefore, the secondary water temperature that minimizes the total energy consumption is determined, and the air conditioning system is operated to achieve the specified secondary water temperature.

Figure 3 is a block diagram illustrating the configuration of the system model 34 and the calculation procedures used by it. The system model 34 includes calculation modules corresponding to each piece of equipment that makes up the air conditioning system, allowing it to calculate the operating conditions for each piece of equipment.

The system model 34 includes a secondary-side calculation unit 34a that calculates the operating conditions of each secondary-side device, and a primary-side calculation unit 34b that calculates the operating conditions of each primary-side device. The secondary-side calculation unit 34a includes, as calculation modules, a room model 34c that calculates the thermal conditions in each target space S, an air volume calculation unit 34d that calculates the supply air volume for each air conditioner 10, a coil inlet air calculation unit 34e and a coil outlet air calculation unit 34f that calculate the air conditions upstream and downstream of the chilled water coil 10a, respectively, a coil chilled water calculation unit 34g that calculates the chilled water flow rate in the chilled water coil 10a and the chilled water temperature at the outlet of the chilled water coil 10a, a piping model 34h that calculates the amount of chilled water circulating on the secondary side, and a secondary pump model 34i that calculates the operating conditions of the secondary chilled water pump 22. Here, each module performs calculations for each part that makes up the air conditioning system, but the modules related to air conditioners 10 (air volume calculation unit 34d, coil inlet air calculation unit 34e, coil outlet air calculation unit 34f, coil chilled water calculation unit 34g) assume the performance of the same representative air conditioner 10' and perform calculations for N units based on this (i.e., the calculation results from the representative air conditioner 10' are multiplied by N). Similarly, when a representative space S' is assumed for the target space S, a room model 34c with the same heat load, volume, set temperature, etc. is also assumed for the room model 34c, and calculations for N rooms are performed using this.

The primary-side calculation unit 34b includes, as calculation modules, a heat source number control unit 34j that selects the number of operating chillers 1, which are heat source machines, and a heat source calculation unit 34k and a cooling tower calculation unit 34l that calculate the operating conditions of each chiller 1 and each cooling tower 2. The heat source calculation unit 34k and the cooling tower calculation unit 34l perform calculations for each chiller 1 and cooling tower 2 provided in the air conditioning system.

The system model 34 as described above is as follows:
- Heat load (sensible heat load and latent heat load) in the secondary room (target space S)
- Set temperature and humidity in the target space S (room dry-bulb temperature set value, room relative humidity set value)
- Outside temperature and humidity (outside dry bulb temperature, outside relative humidity)
・Air supply temperature and humidity settings (air supply temperature setting value, air supply humidity setting value)
・Exhaust air volume setting (exhaust air volume setting value)
- Operating status of heat source equipment (number of operating chillers 1 and power of each unit)
Operating status of air conditioners (number of operating air conditioners 10)
The secondary water supply temperature setting is used as a given condition, and the calculation modules corresponding to each component of the air conditioning system calculate values related to the operating conditions of each component (load, energy consumption, etc.), thereby calculating the power consumption of the entire system. Among the given conditions, the room dry-bulb temperature setting and the room relative humidity setting are values set in the target space S. Measurements from the outdoor air sensor 35 are used as the outdoor dry-bulb temperature and outdoor relative humidity. The supply air temperature setting, supply air humidity setting, and exhaust airflow setting are generally fixed values (although they can be changed manually) and can be obtained from the central monitoring device 31. The operating status of the heat source unit and the air conditioner can also be obtained from the central monitoring device 31. As mentioned above, the secondary water supply temperature is set to an appropriate value, for example, between 7°C and 11°C, and used in the calculation. The secondary latent heat load and sensible heat load will be described later.

In the system model 34, first, the air volume calculation unit 34d calculates the value of the supply air volume V _S (m ³ /h) in the air conditioner 10 using the following formula.
V _S =3,600ν・Q _S /(1.006+1.805X _S )・(T _R sp - T _S )

where ν is the air specific volume (m ³ /kg DA), Q _S is the sensible heat load (kW), X _S is the supply air absolute humidity (kg/kg DA), T _R sp is the room dry-bulb temperature setting value (°C), T _S is the supply air temperature setting value (°C), 1.006 is the constant pressure specific heat of air (kJ/kg·K), and 1.805 is the constant pressure specific heat of water vapor (kJ/kg·K).

The room model 34c calculates the temperature and humidity of the indoor air, and the return air volume using the value of this supply air volume V _S. The indoor air temperature (indoor temperature T _R (°C)), absolute humidity of the indoor air (indoor absolute humidity X _R (kg/kgDA)), and return air volume V _R (m ³ /h) can be calculated using the following equations.
T _R =T _S +3,600ν・Q _S /(1.006+1.805X _S )・V _S
X _R =X _S +3,600ν・Q _L /(2,501+1.805T _R )・V _S
V _R = V _S - V _E

where Q _L is the latent heat load (kW), V _R is the return air flow rate (m ³ /h), and V _E is the exhaust air flow rate setting value (m ³ /h).

The indoor sensible heat load _QS and latent heat load _QL can be calculated using the following procedure. First, the load heat quantity of the air conditioner 10 is calculated as the product of the temperature difference of the chilled water upstream and downstream of the chilled water coil 10a and the flow rate. The load heat quantity calculated in this way is the sum of the indoor load and the outdoor air load.

The air to be conditioned is a mixture of indoor air taken in as return air and outdoor air. The proportion of outdoor air can be determined from the settings in the central monitoring device 31, the operating status of the air conditioner 10, return air fan 15a, and outdoor air conditioning unit (not shown), the opening degree of the damper 13, etc., and is, for example, 20% of the air introduced into the air conditioner 10. The outdoor air load per volume can be calculated from the difference between the outdoor air conditions (outdoor dry-bulb temperature, outdoor relative humidity) measured by the outdoor air sensor 35 and the supply air conditions (supply air temperature set value, supply air humidity set value). The indoor load can be calculated by subtracting the outdoor air load calculated in this way from the load heat quantity calculated based on the product of the temperature difference and flow rate of the chilled water in the chilled water coil 10a.

The indoor load is further divided into sensible heat load and latent heat load, and the sensible heat ratio (the proportion of sensible heat load in the indoor load) SHF is assumed to be, for example, 70%. This ratio is merely an assumption and is not necessarily a strictly accurate value, but it allows us to calculate the values of the sensible heat load _QS and the latent heat load _QL .

The power of the supply air fan 10b and the return air fan 15a can be calculated based on the supply air volume V _S and the return air volume V _R calculated above. For example, the following approximate formula, which is a quadratic approximation of the P-Q diagram of the fan, can be used as the calculation formula.
P=a・Q ² +b・Q(n/N)+c・(n/N) ² ...(1)
Pw=(ρ・g・Q・P/60,000)×η

where a, b, c are coefficients calculated from the P-Q diagram, P is pressure (Pa), Q is flow rate ( ^m3 /min), n is rotation speed, N is rated rotation speed, ρ is fluid density (1.2 kg/ ^m3 ), g is gravitational acceleration (9.8 m/ ^s2 ), η is efficiency, and Pw is power (kW). The flow rate Q in this formula is a different value from the sensible heat load _QS and latent heat load _QL described above, and the supply air volume _VS and return air volume _VR are substituted here to determine the power Pw of supply air fan 10b and return air fan 16a.

The coil inlet air calculation unit 34e calculates the mixing point from the outdoor air conditions (outdoor dry-bulb temperature and outdoor relative humidity), the return air volume V _R and state (which can be understood as the indoor temperature _TR and indoor absolute humidity X _R ), and the supply air volume V _S and state (supply air temperature set value and supply air humidity set value), and calculates the temperature and absolute humidity of the air upstream of the chilled water coil 10a.

The coil outlet air calculation unit 34f calculates the temperature and absolute humidity of the air downstream of the chilled water coil 10a from the supply air volume _VS and state (supply air temperature set value and supply air humidity set value).

The coil chilled water calculation unit 34g uses the number of coil rows (known value) to calculate the flow rate of chilled water flowing through the chilled water coil 10a and the temperature of the chilled water at the outlet side of the chilled water coil 10a from the upstream air conditions (temperature and humidity) calculated by the coil inlet air calculation unit 34e and the downstream air conditions (temperature and humidity) calculated by the coil outlet air calculation unit 34f. The amount of heat exchanged between the chilled water and air can be calculated from the difference in air conditions between the upstream and downstream sides. Specific calculation procedures are, for example, as follows. First, the amount of heat exchanged qt (W) can be calculated as follows, assuming it is the same as the heat balance on the air side:
qt=V _S ×1.2×(hc _ai・hc _ao )

where hc _ai is the enthalpy of the air at the coil inlet side (J/kg), and hc _ao is the enthalpy of the air at the coil outlet side (J/kg). On the other hand, the amount of heat exchanged qt can also be expressed by the following formula.
qt=Row×Kf×dtlm×Af×WSF

where Row is the number of coil rows, Kf is the heat transfer coefficient (W/m ² ·°C·Row), dtlm is the logarithmic mean temperature difference (°C), Af is the coil front surface area (m ² ), and WSF is the wetted surface coefficient.

The heat transfer coefficient Kf, the logarithmic mean temperature difference dtlm, and the wetted surface coefficient WSF can be expressed as follows:
WSF=C ₁ ×SHF ² +C ₂ ×SHF+C ₃
Kf=C4/{1/( _C5 +uf ^C6 + _C7 )+1/( _C8 +vw ^C9 + _C10 )}
dtlm= _dt1・_dt2 /ln( _dt1 / _dt2 )
dt ₁ = tc _ai・tc _wo
dt ₂ = tc _ao・tc _wi

where SHF is the sensible heat ratio, _C1 to _C10 are coefficients provided by the manufacturer, uf is the supply air velocity in front of the coil (m/s), vw is the flow velocity of the chilled water passing through the coil (m/s), tc _ai is the air temperature upstream of the coil (°C), tc _wo is the water temperature at the outlet of the coil (°C), tc _ao is the air temperature downstream of the coil (°C), and tc _wi is the water temperature at the inlet of the coil (°C). The front air velocity uf can be determined from the supply air volume _VS , and the passing air velocity vw can be calculated from the coil specifications based on the front air velocity uf. The air temperatures upstream and downstream of the coil tc _ai and tc _ao and the chilled water temperature at the inlet of the coil tc _wi are known values, while the water temperature at the outlet of the coil tc _wo is an unknown.

The above formula allows the temperature tc _wo of the chilled water at the outlet side of the chilled water coil 10a to be calculated, and furthermore the flow rate Q (L/min) of the water in the chilled water coil 10a can be calculated using the following formula.
Q=60×qt/{Cw×(tc _wi −tc _wo )}

where Cw is the mass specific heat of water (kJ/kg·°C). Note that the water flow rate Q in this formula is a different value from the above-mentioned sensible heat load _QS and latent heat load _QL , and the fan flow rate (air volume) Q in the previous formula.

The piping model 34h multiplies the chilled water flow rate per air conditioner 10 calculated in this way by the number of operating air conditioners 10 obtained from the central monitoring device 31 to calculate the total chilled water flow rate on the secondary side.

The secondary pump model 34i and heat source number control unit 34j calculate the number of operating heat source units (chillers) 1 from the total flow rate of chilled water on the secondary side, and calculate the power of the secondary chilled water pump 22 and primary chilled water pump 8 based on the chilled water return temperature on the secondary side (which is the same as the coil outlet water temperature) and the set value of the secondary side supply water temperature.

Specifically, first, the flow rate in the bypass flow path 9 between the primary headers (primary supply header 7 and primary return header 6) is calculated from the total secondary chilled water flow rate calculated by the piping model 34h, taking into account the minimum flow rate of each heat source unit 1. Furthermore, the chilled water temperature in each primary and secondary header is calculated from the chilled water return temperature on the secondary side and the set value of the secondary side supply water temperature. The heat load calculated from the chilled water temperature and flow rate is allocated to the rated capacity ratio of each heat source unit 1, and the number of operating heat source units 1 is determined. The number of operating secondary chilled water pumps 22 is determined from the secondary chilled water flow rate, and the primary side return water temperature (chilled water temperature in the primary return header 6) and secondary side supply water temperature (result value, not the set value) are calculated based on this water volume balance. The power of the secondary chilled water pumps 22 and primary chilled water pumps 8 can be calculated based on this using a formula similar to equation (1) above.

The heat source calculation unit 34k and cooling tower calculation unit 34l calculate the power of the heat source machine 1, the cooling tower 2 fan, and the cooling water pump 4. As an example, we will explain the calculation procedure when the heat source machine 1 is a centrifugal chiller.

The power consumption amount E _ref in the heat source unit 1 is the product of the power consumption rate e _ref and the rated power consumption amount E _{ref_r} , as shown in the following equation.
E _ref = e _ref × E _{ref_r}

As shown in the following equation, the power consumption rate e _ref can be expressed as the product of a partial load rate influence coefficient C1, which is a function of the load rate _q , a coolant temperature influence coefficient C2, which is a function of the coolant inlet temperature _Td , a coolant flow rate ratio influence coefficient C3, which is a function of the coolant flow rate ratio vd, a coolant outlet temperature influence coefficient C4, which is a function of the coolant outlet temperature _Tc , and a coolant flow rate influence coefficient C5, which is a parameter of the coolant flow rate ratio _vc . Under rated conditions, the values of C1 to C5 are all 1.0, and e _ref = 1.0.
e _ref = C1 x C2 x C3 x C4 x C5
C1=a ₁ q ² +b ₁ q+c ₁
C2=a ₂ T _d ² +b ₂ T _d +c _{2
C3 = a3vd3 + b3vd2 +} ^c3vd ₊ ^d3
_{C4 = a4Tc2} + _{b4Tc +} ^c4
_C5 = _{a5vc2 + b5vc +} ^c5

Here, the chilled water outlet temperature _Tc is the temperature of the chilled water at the outlet of the chiller 1, and the resultant value of the secondary side water temperature calculated above can be used when the flow of chilled water in the bypass flow path 9 is not taken into consideration. Also, the chilled water inlet temperature _Td is the temperature of the chilled water at the inlet of the chiller 1, and when the bypass of the chilled water circulation path 3 is not taken into consideration, it can be considered to be the same value as the temperature of the chilled water at the outlet of the cooling tower 2 (cooling tower outlet temperature).

Using the power consumption E _ref , the cooling water outlet temperature (the temperature of the cooling water at the outlet of the refrigerator 1) T _dr can be calculated using the following equation.
q _cd = q _c +E _ref = q _c (1+1/ _{COP_qc} )
V _d = q _cd / (T _dr - T _d )

where q _c is the heat amount of chilled water, _{COP_qc} is the coefficient of performance for each operating load factor, q _cd is the heat amount of cooling water, and V _d is the flow rate of cooling water.

On the other hand, on the cooling tower 2 side, the cooling tower outlet temperature _Td can be calculated as follows using _Tds , a function of the outside air wet-bulb temperature _WB , a cooling tower inlet temperature influence coefficient C7, which is a function of the cooling tower inlet temperature (the temperature of the cooling water at the inlet of the cooling tower 2) Tdr, and a first cooling water volume influence coefficient C8 and a second cooling water volume influence coefficient C9, which are functions of the cooling water flow rate _Vd .
T _d = T _ds × C7 × C8 × C9
T _ds =a ₆ WB ² +b ₆ WB+c _6
C7 = _{a7Tdr2 +} ^b7Tdr _{+ c7}
C8=f(C9, T _dr , WB)
^C9 = _{a9Vd2 + b9Vd + c9}

The coefficients _a1 to _a5 , _b1 to _b5 , _c1 to _c5 , and _d3 are calculated from the diagrams provided by the manufacturer. The coefficients a6 to _a9 , _b6 to _b9 , and _c6 to _c9 can be determined experimentally. Note that the coefficients _a1 to _a9 , _b1 to _b9 , _c1 to _c9 , and C1 to C9 are different values from a to _c and _C1 to _C10 in the above formulas.

Using the above formula, the heat source calculation unit 34k calculates the cooling water outlet temperature _Tdr using the cooling tower outlet temperature (cooling water inlet temperature) _Td calculated by the cooling tower calculation unit 34l, and the cooling tower calculation unit 34l calculates the cooling tower outlet temperature _Td using the cooling water outlet temperature (cooling tower inlet temperature) _Tdr calculated by the heat source calculation unit 34k. This calculation is repeated (this calculation simulates the circulation of cooling water between the heat source machine (chiller) 1 and the cooling tower 2). This is repeated until the cooling tower outlet temperature (cooling water inlet temperature) _Td matches the set value (or approaches within a certain tolerance range (e.g., the value matches to the first decimal place)). If the cooling tower outlet temperature _Td does not reach the set value even after repeated calculations, this means that the cooling water cannot be cooled to the set value. In this case, the calculation is repeated until the cooling tower outlet temperature _Td matches the previous value (or approaches within a certain tolerance range (e.g., the value matches to the first decimal place)).

The above procedure can be used to calculate the power of each heat source unit 1. Based on this, the power of the cooling water pump 4 can be calculated using a formula similar to the above formula (1). Furthermore, the power of the fan of the cooling tower 2 can be calculated using the following formula.
Pw=CT _pw +Pw _rating
CT _pw = (T _dr - T _d sp)/(T _dr - T _d )

where CT _pw is the cooling tower fan power ratio, T _d sp is the cooling tower outlet temperature lower limit set value (°C), and Pw _rating is the cooling tower fan rated power (kW). Note that the power Pw of the cooling tower 2 fan calculated here is a different value from the power Pw of the supply air fan 10b and the return air fan 15a in the above formula.

By adding up the power of each part calculated by each calculation module in this way, it is possible to calculate the power of the entire air conditioning system, including the primary and secondary sides, under specific given conditions. Note that the calculation procedure described here is merely an example, and the formulas and parameters used in each calculation module, as well as the order of calculations between calculation modules, may be changed as appropriate.

The optimization calculation unit 33 then performs similar calculations using the system model 34 under multiple different given conditions, selects operating conditions from the multiple calculation results that will reduce the power consumption of the entire system, and inputs the set value for the secondary water supply temperature under those operating conditions to the central monitoring device 31. The central monitoring device 31 operates the components of each part of the system (particularly the primary-side heat source unit 1 and cooling tower 2) based on the set value for the secondary water supply temperature input from the optimization calculation unit 33.

The selection of these operating conditions will now be explained. Above, we first explained how five variance values, for example between 7°C and 11°C, were set for the set value of the secondary water supply temperature, and the operating conditions were calculated for each case. In this embodiment, multiple variance values are also set for the outdoor air load rate and indoor load rate, and the operating conditions are calculated. The reason for calculating multiple cases for the secondary water supply temperature setting is to determine the set value for the secondary water supply temperature that minimizes the power consumption of the entire system, while the reason for calculating multiple cases for the outdoor air load rate and indoor load rate is to increase the likelihood of obtaining calculation results that are feasible for the system.

Each component in an air conditioning system has its own set of achievable operating conditions. For example, a pump can only operate between maximum and minimum flow rates. If these practical limitations were ignored, it would theoretically be possible to calculate the operating conditions under any given set of values for the secondary water temperature and other variables. However, operation under these calculated conditions may not actually be possible. For example, increasing the secondary water temperature requires a higher chilled water flow rate to meet the secondary load heat demand. However, if the required flow rate exceeds the pump's rated output, such operation is not possible in reality, making it unsuitable for simulating the operation of an air conditioning system. Similarly, depending on the given conditions, calculations performed using a certain calculation module based on certain values may produce results that are inappropriate for the operation of the corresponding equipment. Or, if calculations using the results output by one calculation module are performed using another calculation module, the results may also be inappropriate for operation. To simulate the operating conditions of a real air conditioning system, it is necessary to exclude these incompatible calculation results and focus on realistically possible operating conditions.

In this embodiment, therefore, multiple variance values are set for the outdoor air load ratio and the indoor load ratio, and the above calculation is performed for each case where the outdoor air load and indoor load are at each of these variance values, with incompatible calculation results being eliminated. The remaining calculation results represent operating conditions that are compatible with the air conditioning system (that are actually operable). From these, first, those with variance values for the outdoor air load ratio and the indoor load ratio that are closest to pre-determined reference values are extracted. Of the extracted operating conditions, the secondary side water supply temperature for the operating condition that results in the smallest total power for the entire system is identified, and the system is operated at that secondary side water supply temperature setting.

In addition, incompatible calculation results can be excluded by completing all calculations in the system model 34 as described above, then determining whether the calculated operating conditions are possible for each piece of equipment, and discarding the calculation results if even one part is not possible. However, for example, if each of the calculation modules above sets a compatibility range for the calculation results it outputs, and the system model 34 is configured to output an error judgment and stop subsequent calculations if the calculation result is outside the compatibility range, unnecessary calculations can be eliminated, reducing the amount of calculation and the time required for calculations.

The variance and reference values for the outdoor air load ratio and indoor load ratio in the above calculations will be explained below. In the calculation example above, the ratio of outdoor air intake to supply air was set to 20% of the total, and the outdoor air load and indoor load were calculated based on this (note that the value of 20% is based on the outdoor air intake volume in the actual air conditioning system. If the outdoor air intake volume or its set value in the air conditioning system is different from 20%, then the load calculation should naturally also be based on that value). The outdoor air load and indoor load values calculated in this way are used as their respective reference values.

The outdoor air load ratio and indoor load ratio values are distributed based on this reference value, and multiple variance values are set for each. For example, for the outdoor air load ratio, 11 variance values are set in 1% increments from 95% to 105% of the calculated reference value. For the indoor load ratio, 5 variance values are set in 2.5% increments from 95% to 105% of the calculated reference value.

In this way, m variance values _x1 to _xm are set for the outdoor air load ratio, and n variance values _y1 to _yn are set for the indoor air load ratio. The numerical ranges of _x1 to _xm and _y1 to _yn (95% to 105% in the above example), the number of variance values (m and n values; 11 or 5 in the above example), and the intervals between variance values (1% or 2.5% in the above example) can be set as appropriate, without being limited to the examples described above. However, the numerical ranges should include the reference value (i.e., for example, if _x1 ≦ _xm , then _x1 ≦reference value ≦ _xm ). It is also recommended that one of the variance values be set to the reference value (in the above example, the variance value at 100% corresponds to the reference value). For the secondary-side water supply temperature setting, l variance values _z1 to _zl (five variance values from 7°C to 11°C in the above example) are set. Then, m variances for the outdoor air load ( _x1 to xm ₎ , n variances for the indoor load ( _y1 to yn ₎ , and l variances for the secondary-side water temperature setting ( _z1 to _zl) are given as given conditions, and the system model 34 performs a brute-force calculation of the above operating conditions. That is, m x n x l calculations are performed (in the above example, 11 x 5 x 5 = 275 brute-force calculations are performed). From these calculation results, feasible operating conditions are extracted whose outdoor air load ratio and indoor load ratio are close to the reference values. (Note that it is possible that the "operating condition whose outdoor air load ratio is closest to the reference value" and the "operating condition whose indoor load ratio is closest to the reference value" differ. In such cases, priorities can be assigned to these values, and the operating conditions can be narrowed down in order accordingly. For example, the "operating condition whose outdoor air load ratio is closest to the reference value" is first extracted, and then, if there are multiple such operating conditions, the "operating condition whose indoor load ratio is closest to the reference value" can be further extracted from those.) From among these, an operating condition with the smallest total power is selected, and the set value of the secondary side water temperature for that operating condition is identified.

In addition to the secondary water supply temperature, the example described here sets variance values for two values related to secondary load heat quantity: the outdoor air load ratio and the indoor load ratio, in order to ensure the most feasible calculation results. However, when setting variance values as a given condition other than the secondary water supply temperature, it is also possible to set variance values for only one of the outdoor air load ratio or the indoor load ratio, and treat the other as 100%. Alternatively, a variance value can be set for the secondary load heat quantity (the sum of the outdoor air load and the indoor load) itself, and the operating conditions can be selected by performing calculations similar to those described above. Furthermore, the variance value can be set for any value related to secondary load heat quantity. For example, variance values can be set for sensible heat load, latent heat load, the ratio of outdoor air load to indoor load, or the ratio of sensible heat load to latent heat load in the indoor load. Variance values can be set for only one of these, or for three or more.

The procedure for calculating these operating conditions can be summarized, for example, in a flowchart such as that shown in Figure 4. First, the secondary load heat quantity is calculated from the operating status of the air conditioning system input to the central monitoring device 31, and based on this, the outdoor air load ratio and the indoor load ratio are calculated, and using these values as reference values, multiple variance values ( _x1 to _xm , _y1 to _yn ) are set for each (step S1). Also, variance values ( _z1 to _z1 ) of the set value of the secondary side water supply temperature are set.

Next, from the variance values of the outdoor air load, a variance value to be used in the initial calculation is selected (step S2). In the initial calculation, for example, _x1 is used. Furthermore, from the variance values of the indoor load, a value to be used in the initial calculation is selected (step S3). In the initial calculation, for example, _y1 is used. For the set value of the secondary side water supply temperature, a variance value to be used in the initial calculation (for example, _z1 ) is also selected (step S4).

After selecting the variance values to be used in the calculation for the set values of the outdoor air load ratio, indoor load ratio, and secondary water temperature, the operating status of the heat source unit 1 and air conditioner 10, as well as the outdoor air conditions measured by the outdoor air sensor 35, are obtained from the central monitoring device 31 (step S5). Using these as given conditions, the operating conditions are calculated using the system model 34 (step S6).

Once the calculation of the operating conditions based on one given condition setting has been completed in this way, it is determined whether there are any uncalculated secondary-side water temperature variances under the current outdoor air load and indoor load conditions (step S7). After the initial calculation using outdoor air load _x1 , indoor load _y1 , and secondary-side water temperature _z1 has been completed, the variances of _z2 to _z1 have not yet been calculated. If there are any uncalculated variances, the process returns to step S4, where another variance is selected (if _z1 was used in the previous calculation, the next variance would be _z2 , for example), and the operating conditions are calculated again (steps S5 to S6). This process is repeated up to the lth time, and when there are no more uncalculated variances, the process proceeds to step S8.

In step S8, it is determined whether there are any uncalculated indoor load variance values under the current outdoor air load conditions. Once calculations using outdoor air load _x1 and indoor load _y1 have been completed, the variance values for _y2 to _yn remain uncalculated. If there are any uncalculated variance values, the process returns to step S3 and another variance value is selected. Using the newly selected indoor load variance value, the operating conditions are again calculated based on each variance value of the secondary side water temperature (steps S4 to S6). This process is repeated n times, and when there are no more uncalculated variance values, the process proceeds to step S9.

In step S9, it is determined whether there are any uncalculated outdoor air load variance values. After the calculation for outdoor air load _x1 is complete, the variance values for _x2 to _xm remain uncalculated. If there are any uncalculated variance values, the process returns to step S2 and selects another variance value. Using the newly selected indoor load variance value, the operating conditions are again calculated based on the variance values for the indoor load and secondary water temperature (steps S3 to S6). This process is repeated m times, and when there are no uncalculated variance values, the brute-force calculation of m x n x l operating conditions has been completed. At this stage, the process proceeds to step S10, where appropriate operating conditions are selected from the calculation results as described above, and the set value for the secondary water temperature that minimizes the total power is identified, and the air conditioning system is operated based on this.

Note that the procedure shown here is merely an example, and the content of each step and the order of the steps may be changed as appropriate. For example, the operating status may be acquired (step S5) before step S2, or the order of the brute-force calculations (steps S2-S4, S7-S9) may be reversed. The variance value for the secondary-side water temperature may be set in advance rather than being set together with the other variance values in step S1.

As shown in Figure 2, if the air conditioning system is equipped with N representative air conditioners 10' on the secondary side and the calculations described above are performed, this calculation can be performed, for example, at intervals of 15 to 20 minutes. In this way, the set value for the secondary water supply temperature that will result in energy savings for the entire air conditioning system can be calculated automatically in real time, and operation can be performed automatically based on this.

It is generally known that raising the secondary water temperature can reduce the power consumed by heat source equipment and cooling towers, leading to energy savings, under conditions when the secondary heat load is not high, such as during the transitional season, winter, nighttime, or rainy weather. Conventionally, energy savings have been achieved by manually adjusting the secondary water temperature setting depending on the situation. However, such manual operation relies heavily on the operator's experience and intuition, and depending on the operator's level of proficiency, it is not always possible to set the secondary water temperature to the optimal value each time. As a result, it cannot be said that energy-saving operation through adjustment of the secondary water temperature is fully achieved. As in this embodiment, the secondary side operating conditions are calculated in real time, a secondary water temperature that requires less power for the entire system is calculated, and each piece of equipment (particularly the primary side heat source equipment 1 and cooling tower 2) is operated based on this. The system automatically calculates and executes appropriate operating conditions as needed. Compared to conventional manual operation, the system can determine the secondary water temperature that is most advantageous for energy savings at the appropriate time and change it as needed while operating each piece of equipment, thereby achieving further energy savings.

To do this, it is necessary to calculate the operating conditions on the secondary side. In air conditioning systems, the secondary configuration is generally complex, and calculating this requires a large amount of calculation, making real-time calculations difficult. However, in this embodiment, a representative air conditioner is assumed as the air conditioner in the calculations, and calculations are performed on a virtual system equipped with multiple identical representative air conditioners, thereby significantly reducing the calculation load. While this does result in a slight decrease in the accuracy of the operating conditions calculations, it does make it possible to calculate operating conditions in real time, and it is possible to reduce energy consumption by selecting the secondary side water supply temperature setting each time to be more energy-efficient.

In addition, to avoid a situation where feasible operating conditions cannot be calculated, multiple variance values are set for each of the secondary load heat quantity values (outdoor air load and indoor load) used as given conditions in the calculation, and a brute force calculation is performed, allowing for a certain degree of calculation error to be tolerated and allowing for the calculation of feasible operating conditions. In this way, real-time energy-saving operation based on the secondary side operating status can be carried out without difficulty.

As described above, this embodiment relates to an operating method for an air conditioning system that includes a heat source unit 1 as the primary-side equipment and multiple air conditioners 10 as secondary-side equipment, with chilled water circulating between the heat source unit 1 and the air conditioners 10. Multiple variance values are set as the set value for the secondary water temperature, which is the chilled water temperature upstream of the air conditioners 10. Using a system model 34 configured by assuming that multiple representative air conditioners 10' with identical performance are installed, the power of each component of the air conditioning system when the set value for the secondary water temperature is each of the variance values is calculated. The variance value for the set value for the secondary water temperature that minimizes the total power is identified, and the air conditioning system is operated so that the secondary water temperature is at the identified variance value. In this way, the secondary water temperature that is advantageous for energy conservation can be determined at the appropriate time, and each component can be operated at the identified secondary water temperature, thereby achieving energy conservation in the operation of the air conditioning system.

Furthermore, in this embodiment, multiple variance values are set for the secondary load heat quantity or values related thereto, with the reference value included in the numerical range, and the operating conditions for each component of the air conditioning system when the secondary load heat quantity or values related thereto are each of the variance values is calculated. If there are multiple calculation results that are operable, the variance value for the set value of the secondary-side water supply temperature that reduces the total power is identified from the operating conditions where the variance value of the secondary load heat quantity or values related thereto is closest to the reference value, and the primary-side equipment is operated so that the secondary-side water supply temperature is at the identified variance value. In this way, feasible operating conditions can be calculated, allowing for calculation errors.

In addition, in this embodiment, the value related to the secondary load heat quantity for which the variance value is set is balanced and allocated to only one of the outdoor air load ratio or the indoor load ratio, with the other remaining at 100% (in the example described above, both are allocated).

In addition, in this embodiment, the value related to the secondary load heat quantity for setting the variance value is based on the sensible heat load, which is determined by the sensible heat ratio when mixing outside air and return air and introducing them into the chilled water coil 10a, and then heat-treating them to the set temperature of the target room. This can be determined by calculating the representative air conditioner airflow from the sensible heat load, and then calculating the secondary return chilled water temperature and required flow rate from the specified chilled water coil performance.

In addition, in this embodiment, the value related to the secondary load heat quantity for setting the variance value can be obtained by calculating the secondary chilled water flow rate from the number of representative air conditioners in operation at any given time.

In addition, in this embodiment, the chiller load factor on the primary heat source side is calculated using the representative air conditioner airflow calculated from the sensible heat load and the secondary return chilled water temperature and required flow rate obtained from the specified chilled water coil performance, so that the secondary supply water temperature becomes the specified variance value, and the number of chillers in operation can be calculated by receiving a signal from the number of chillers actually in operation.

Furthermore, the air conditioning system of this embodiment is configured to be able to execute the air conditioning system operating method described above, and can therefore achieve the same effects as those described above.

Therefore, according to the above embodiment, the operating conditions of each secondary device can be efficiently calculated, and the operation of each device can be optimized based on this, resulting in energy savings.

The air conditioning system and operating method of the present invention are not limited to the above-described embodiment, and various modifications can of course be made without departing from the spirit of the present invention.

1 Heat source machine (refrigeration machine)
10 Air conditioner 10' Representative air conditioner 10a Chilled water coil 34 System model

Claims (7)

An operating method for an air conditioning system including a heat source unit as a primary side device and a plurality of air conditioners as secondary side devices, and configured so that chilled water circulates between the heat source unit and the air conditioners,
A plurality of variance values are set as a set value of a secondary water supply temperature, which is the temperature of chilled water on the upstream side of the air conditioner;
Using a system model configured assuming that multiple representative air conditioners with the same performance are installed, calculate the power of each component of the air conditioning system when the set value of the secondary water supply temperature is each of the variance values,
Identify the variance value of the set value of the secondary water supply temperature that reduces the total power,
An operating method for an air conditioning system, characterized by operating a primary-side device so that the secondary-side water temperature is a specified variance value. Regarding the secondary load heat quantity or values related thereto, multiple dispersion values are set so that the numerical range includes the reference value,
Calculating the operating conditions of each component of the air conditioning system when the secondary load heat quantity or a value related thereto is each of the variance values;
If there are multiple calculation results that are operable, identify the variance value of the set value of the secondary side water supply temperature that reduces the total power from the operating conditions in which the variance value of the secondary load heat quantity or a value related thereto is closest to the reference value;
2. The method for operating an air conditioning system according to claim 1, further comprising the step of operating a primary-side device so that the secondary-side water temperature is set to the specified variance value. The method for operating an air conditioning system according to claim 2, characterized in that the value related to the secondary load heat quantity for which the variance value is set is a variance allocation for at least one of the outdoor air load ratio and the indoor load ratio, and the other is treated as 100%. 4. The method for operating an air conditioning system according to claim 2 or 3, wherein the value related to the secondary load heat quantity for setting the variance value is based on the sensible heat load, which is determined by the sensible heat ratio when mixing outside air and return air and introducing them into the chilled water coil, and then heat treating the mixture until it reaches the set temperature of the target room, and the representative air flow rate of the air conditioner is calculated from the sensible heat load, and the secondary return chilled water temperature and required flow rate are calculated from the specified chilled water coil performance. The method for operating an air conditioning system according to any one of claims 2 to 4, wherein the value relating to the secondary load heat quantity for setting the variance value is obtained by calculating the secondary chilled water flow rate from the number of representative air conditioners in operation at each time. An operating method for an air conditioning system as described in any one of claims 2 to 4, characterized in that the chiller load factor as the primary heat source is calculated using the representative air conditioner air volume calculated from the sensible heat load and the secondary return chilled water temperature and required flow rate obtained from the specified chilled water coil performance, so that the secondary supply water temperature becomes a specified variance value, and the number of operating chillers is calculated by receiving a signal from the number of units actually operating. An air conditioning system characterized by the air conditioning system operating method described in any one of claims 1 to 6.