CN111094882A

CN111094882A - System and method for reducing energy consumption of a chilled water distribution system

Info

Publication number: CN111094882A
Application number: CN201880053806.3A
Authority: CN
Inventors: 本·魏贝定; 伊恩·登普斯特
Original assignee: Optimum Energy LLC
Current assignee: Optimum Energy LLC
Priority date: 2017-08-21
Filing date: 2018-08-21
Publication date: 2020-05-01
Also published as: WO2019040435A1; EP3673218A4; EP3673218A1

Abstract

A chilled water distribution system includes a chilled water loop in fluid communication with a plurality of building sites and also in fluid communication with a plurality of chiller stations. A monitoring and control system communicates with one of the chiller stations, which will be referred to hereinafter as a "controlled" chiller station because the chiller station is configured with one or more variable frequency drives that are controlled by the monitoring and control system for regulating the speed of at least one chiller station component such as, but not limited to, a pump or a fan. By this regulation process, the pressure difference of the cooling water circuit can be maintained in an "optimum range" in order to minimize the energy consumption of the chiller station while optimizing the output of the chiller station.

Description

System and method for reducing energy consumption of a chilled water distribution system

Cross Reference to Related Applications

This application claims priority from us patent application No. 15/682,320 filed on 8/21/2017, which is incorporated herein by reference in its entirety as if fully set forth herein.

Technical Field

The present invention generally relates to a system and method for reducing energy consumption of a chilled water distribution system by monitoring and controlling a variable speed drive within a base chiller station or a controlled chiller station.

Background

Conventional cooling water systems typically include a cooling circuit having a return line and a supply line, both of which are in fluid communication with at least two cooling stations and at least two buildings. In such conventional systems, the water supply pressure generated at the cooling station is relatively high, which in turn may lead to any number of undesirable consequences. For example, even if a standard maintenance schedule is followed, higher pressures may reduce the useful life of the system. Alternatively or additionally, higher pressures may require more frequent maintenance, which in turn leads to higher costs. Further, higher pressures may require the installation of pressure relief valves, but while such valves may reduce the pressure of the incoming cooling water, their installation also increases capital costs and system control complexity. In addition, the pressure relief valve may not seal adequately against the higher pressures and subcooling may be a problem.

Disclosure of Invention

A chilled water distribution system includes a chilled water loop in fluid communication with a plurality of building sites and also in fluid communication with a plurality of chiller stations. A monitoring and control system communicates with one of the chiller stations, which will be referred to hereinafter as a "controlled" chiller station because the chiller station is configured with one or more variable frequency drives that are controlled by the monitoring and control system for regulating the speed of at least one chiller station component such as, but not limited to, a pump or a fan. By this regulation process, the pressure difference of the cooling water circuit can be maintained in an "optimum range" (sweet spot) in order to minimize the energy consumption of the chiller station while optimizing the output of the chiller station.

In one aspect of the invention, a distributed process cooling water system includes a supply line having a supply line pressure sensor; a return line having a return line pressure sensor, the supply line pressure sensor and the return line pressure sensor cooperating to provide a pressure differential between the supply line and the return line; a plurality of buildings, each building having a building automation system controller, each building in fluid communication with the return line and the supply line, the controllers communicatively networked together; a plurality of cooler stations including at least one base cooler station, each cooler station in fluid communication with the return line and the supply line, the cooler stations communicatively networked together, at least one of the cooler stations in communication with at least one of the buildings; and an operating system operable to process machine readable instructions, the operating system in communication with at least the base cooler station, the operating system configured to receive a signal indicative of the pressure differential, the operating system further configured to determine whether to adjust a pump speed of the base cooler station, bring another cooler online, or take another cooler offline based on the pressure differential to maintain the pressure differential within a desired range.

In another aspect of the invention, a method for controlling a chilled water distribution system includes the steps of: (1) determining a real-time pressure differential at a selected location within a cooling water circuit of the distribution system; (2) monitoring a real-time pump speed of a base chiller station, the base chiller station including a variable frequency drive coupled to a cooling water pump; (3) determining energy loads of a plurality of buildings served by the cooling water circuit; (4) adjusting the pump speed of the base chiller station to maintain it substantially within a desired range of a predetermined set point pressure differential of the cooling water circuit; and (5) determining whether to change the capacity of the distribution system by bringing a chiller of another chiller station online or offline.

Drawings

Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings:

FIG. 1 is a schematic system diagram of a cooling water distribution system having an operating system in communication with at least one controlled chiller station to adjust pump speed within the chiller station and/or bring other chillers online or offline in accordance with an embodiment of the present invention;

FIG. 2A is a schematic system illustration of a controlled chiller station having at least one variable speed drive coupled to at least one cooling water pump, according to an embodiment of the present invention;

FIG. 2B is a schematic system diagram of another cooling water distribution system in accordance with an embodiment of the present invention;

FIG. 3 is a flow chart of a method for determining an operating mode of a controlled chiller station according to an embodiment of the present invention; and is

FIG. 4 is a chart indicating an optimal range of operating a controlled chiller station according to an embodiment of the present invention.

Detailed Description

In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details. In other instances, well-known structures associated with cooling water distribution systems, the operating components used in the cooling water distribution systems, chiller stations, pumps, sensors, cooling water circuits, various computing and/or processing systems, various system operating parameters, and methods for operating cooling water distribution systems that supply one or more buildings have not necessarily been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments of the invention.

In conventional chilled water distribution systems, the chilled water supply pressure generated at each cooling station is relatively high, which in turn has several consequences for the building served by the chilled water loop. For example, the higher cooling water supply pressure of a building near a cooling station may require the installation of a pressure relief valve to reduce the incoming cooling water supply pressure, which may increase capital costs and system complexity in terms of control, installation, and maintenance. A higher cooling water supply pressure may mean that some types of control valves cannot be closed against a higher pressure and, in combination with a lower cooling water temperature, this may create a sub-cooling situation requiring heat compensation. Further, higher cooling water supply pressures may result in increased maintenance costs and maintenance frequency for all components in the system that are affected by the higher pressures.

To address at least some of the above-noted shortcomings of conventional systems, at least one aspect of the present invention is directed to a chilled water distribution system for supplying one or more buildings. For purposes of this specification, a building may generally include any structure that utilizes the cooling water supply lines of the system and requires a non-zero load. Likewise, the term "load" may generally refer to the flow demand required by a cooling unit of a building, which may take the form of a rooftop cooling unit. Flow demand typically means that in terms of tons of water, for example, a particular building may require 5,000 tons of water from the system to meet its current cooling and/or heating needs. Also, the load required for a particular building fluctuates even throughout the day due to temperature changes, weather changes, time of day (e.g., primary hours of operation), and the like.

The cooling water distribution system may be controlled by monitoring the cooling water circuit pressure differential between the supply line and the return line to maintain a minimum pressure that still allows the chiller station and the building's cooling units to function adequately. Reducing the cooling water circuit pressure differential (i.e., the pressure differential between the cooling water supply and the cooling water return) may achieve a number of advantages. For example, the chilled water distribution system and method for operating the same of the present disclosure may advantageously reduce the overall energy usage (i.e., energy consumption) of the overall system, and reduce the energy usage of at least two networked cooling stations, which in turn will reduce chilled water production costs and chilled water prices. The reduction in cooling station energy usage may not only offset any increased power consumption in one or more loads. Further, maintenance costs of the cooling water circuit, the chiller station and the load associated with problems related to higher pressures may be reduced.

Fig. 1 shows a schematic system diagram of a cooling water distribution system 100 having a cooling water circuit or conduit 102 in fluid communication with a plurality of buildings 104 (individually illustrated as buildings 104 a-104 d) and also in fluid communication with a plurality of chiller stations 106 (individually illustrated as chiller stations 106 a-106 d). The monitoring and control system 107 is in communication with one of the chiller stations 106, and in particular with the chiller station 106a, which is the chiller station 106a that is specifically configured with one or more variable frequency drives (not shown) to variably control the speed of at least one chiller station component, such as but not limited to a pump or fan.

The cooling water circuit 102 includes a supply circuit 102a and a return circuit 102 b. Pressure sensors 108 are in communication with the supply and

return circuits

102a and 102b, respectively, and the pressure differential between the sensor readings provides the cooling water pressure differential. Although two pressure sensors 108 are shown, the system 100 may include multiple sensors for taking pressure readings at various locations around the cooling water circuit 102.

Each building 104 includes a Building Automation System (BAS) 110 (individually, 110a to 110 d). The BAS 110 receives and exchanges operational information with a heating, ventilation, and cooling (HVAC) system of a respective building. In one embodiment, the BAS may take the form of a BAS as described in U.S. patent application nos. 12/609,452 and/or 12/874,607, both of which are incorporated herein by reference in their entirety. In the illustrated embodiment, the BAS may be connected together by a network so they can receive information and exchange information between each other, with the chiller stations, and with the monitoring and control system 107. In another embodiment, the BAS 110 may operate independently of each other while each communicates with the monitoring and control system 107.

In the illustrated embodiment, each cooler station 106 communicates with at least one other cooler station to provide a networked communication link. The chiller station 106a communicates directly with the monitoring and control system 107. As will be described in more detail below, the cooler station 106a operates as the primary cooler station in the group in response to the load requirements of the building and in conjunction with the output and processing capacity of each cooler station.

In one embodiment, the monitoring and control system 107 takes the form of an operating system having a relational control algorithm that automatically calculates the most efficient operation of the cooling water distribution system 100 to include various components or subsystems within, such as, but not limited to, chillers, pumps and cooling tower fans, based on real-time building cooling loads. As described herein, the in-operation monitoring and control system 107 may advantageously provide an overall approach to maximize energy efficiency while providing stable operating performance not achievable with conventional proportional-integral-derivative control.

Fig. 2A shows a close-up schematic system illustration of the chiller station 206 in fluid communication with the cooling water circuit or conduit 202. The chiller station 206 includes a plurality of variable speed drives 212 that are respectively coupled to a supply pump 214, a return pump 216, and a cooling tower fan 218. Accordingly, it is an aspect of the present invention to monitor and control the variable speed drive 212 to quickly respond to real time building load changes without the need for the chiller 215 to run at full or zero power as occurs in conventional, prior art systems.

Fig. 2B shows a system schematic of a chilled water distribution system 200 having a chilled water circuit or conduit 202 in fluid communication with a plurality of buildings 204 and also in fluid communication with a plurality of chiller stations 206 (which may take the form of the chiller stations 206 described in fig. 2A). The cooling water circuit 202 includes a plurality of pressure sensors 208 for monitoring the pressure differential between the return line and the supply line. In the illustrated embodiment, the BAS of the building is not shown. In the present embodiment, each chiller station 206 includes one or more variable frequency drives 212 for variably controlling the speed of a supply pump 214, a return pump 216, and/or a cooling tower fan 218. A monitoring and control system (not shown) communicates directly with at least one of the chiller stations 206. For the purposes of this description, the chiller station 206 in communication with the monitoring and control system is the chiller station shown on the right side and will be referred to hereinafter as the "controlled" chiller station.

In operation, the pressure differential of the cooling water circuit 202 may be monitored at several locations, and the speed (i.e., power) of at least one of the supply pumps 214 of the main cooler station may be continuously monitored. Each of the pressure differential locations will have a minimum pressure differential required for the building to function properly (e.g., temperature, humidity, etc.). The speed of the cooling water supply pump 214 at the primary cooling station will be adjusted to maintain a minimum pressure differential at all of these pressure differential locations. In addition, information from the building's cooling water pumps (e.g., pump speeds obtained from the BAS) will allow the monitoring and control system to analyze in real-time or at least simultaneously, which ensures that any pressure drop at one or more of the cooling stations 206 will not adversely affect the operation of the building. For example, if the pressure differential at one or more locations becomes too low, this may result in an overall increase in energy consumption within the building 204 as a whole.

Fig. 3 shows a flow chart of a process 300 for controlling a chiller station based on pressure differential readings at desired locations throughout a cooling water circuit. At 302, various buildings obtain information through respective BASs. At 304, information regarding the operation of the primary cooler station is obtained. At 306, the monitoring and control system analyzes the

information

302, 304 to determine the mode of operation as indicated by decision gate 308.

In the first mode of operation (mode 1), the chiller stations are each online, but none reach full power. At 310, the monitoring and control system simply continues to monitor the incoming information, as indicated at block 310.

In the second mode of operation (mode 2), one or more of the chiller stations are operating at full power, or may soon reach full power, based on information from the building BAS. At 312, the monitoring and control system determines whether one of the chillers at one of the chiller stations should be brought online, or if the chiller is already online, whether its capacity should be increased by signaling the variable speed drive of the corresponding pump.

In the third mode of operation (mode 3), one or more of the chiller stations are operating well below full power, or may soon operate well below full power, based on information from the building BAS. At 314, the monitoring and control system determines whether one or more coolers at one of the cooler stations should be taken offline and/or which cooler should be derated.

Control of one or more variable frequency drives coupled to the cooling water pump can significantly reduce the overall energy consumption of the building as a whole. For example, the cooling water distribution system shown in FIG. 2 may be used for various buildings on a university campus. In this example, the main cooler station may need to meet an average load of about 12,000 tons of cooling water, and this condition is accomplished with three on-line coolers in the main cooler station. Once the campus load exceeds 12,000 tons, the monitoring and control system determines which cooler or coolers at one or more of the other cooler stations are to be brought online. Preferably, the monitoring and control system determines when one or more additional chillers are brought online as needed to minimize fluctuations in steady state operation of the chiller station and thereby reduce overall energy consumption.

Referring back to fig. 1, the pump speed at the chiller station 106a controls the pressure differential of the cooling water circuit 102 to maintain the desired minimum pressure differential. The pump speed at chiller station 106c is responsive to the total output at chiller station 106a, and only provides flow/output control. The monitoring and control system 107 monitors the pump speed at the

chiller stations

106a and 106c, the chiller flow/output of the

chiller stations

106a and 106c, the total flow/output of the

chiller stations

106a and 106c, and the pressure differential at selected locations throughout the cooling water circuit 102. The monitoring and control system 107 then calculates the pump speeds of the pumps at the

chiller stations

106a and 106c, and also determines the total number of pumps to operate at the

chiller stations

106a and 106 c.

The monitoring and control system 107 may be preprogrammed to store all operational set points for flow, output capacity (e.g., tonnage of chilled water), pump speed, number of pumps in operation for one chiller station, and desired pressure differential at various locations in the chilled water loop 102. Further, each of these set points may be adjusted as the building load changes for various reasons.

In one operating embodiment, the cooling water circuit pressure may be controlled and a minimum energy level (e.g., kilowatts per ton) of the overall system is achieved by controlling the speed of the pump at the chiller station 106a and bringing the other chiller stations on-line or off-line to maintain a minimum pressure differential in the cooling water circuit.

Preferably, the monitoring and control system 107 can determine the operational sequence of the entire system even when the various chillers are of different sizes and flow control is performed for different evaporator pressure drops using a variable frequency drive on the cooling water pump rather than using an evaporator flow control valve as has been conventional in the past. Thus, in fig. 1, the chiller station 106c may be referred to as a "flow controlled" chiller station because it is the only chiller station having a variable speed drive on its cooling water pump in addition to the chiller station 106 a.

In another embodiment, the variable frequency drive may be mounted on other cooling water pumps in other cooling water stations. In such an embodiment, the monitoring and control system would control the sequence of operations to operate the controlled chiller station in the "best range" (see fig. 4) of the controlled chiller station in terms of energy efficiency, and then bring one or more individual pumps and chillers of the other chiller stations online. FIG. 4 is a schematic diagram showing how a reference or "controlled" chiller station operates at a range of capacities or flow rates. For example, the controlled chiller station may operate at a maximum flow rate to generate a maximum pressure differential 402 in the cooling water circuit, or the controlled chiller station may operate at a minimum flow rate to generate a minimum pressure differential 404 in the cooling water circuit. Preferably, the monitoring and control system 107 (FIG. 1) functions to control the flow rate of the controlled chiller station to maintain the difference in the chilled water loop between the maximum set point pressure differential 406 and the minimum set point pressure differential 408, and thus within the "optimal range" 410. When above or below the actual maximum or minimum pressure differential, respectively, the monitoring and control system will then determine whether the second individual chiller at one of the other chiller stations should be brought online or offline to move back into the "optimal range" 410 and still adequately meet the building's current chilled water load demand.

Referring back now to fig. 2B, when the cooling water load demand of the building 204 is sufficiently low, the cooling station 206 (controlled chiller station) can handle the full load. The specific pressure differential measurement from around the cooling water circuit 202 will be continuously monitored. The monitoring and control system 207 will determine which pressure differential location should be used for control purposes. For example, if the minimum set point of one of the buildings 204 (e.g., the upper left building in fig. 2B) is 6 pounds force per square inch gauge (psig) and the other building (e.g., the lower right building in fig. 2B) has a minimum set point of 2psig, but the actual pressure at the upper left building is 6psig and the actual pressure of the lower right building is 5psig, then the pressure differential of the upper left building is used for control. Because the actual pressure meets the minimum set point for building indication control, the monitoring and control system 207 will command the speed of the cooling water pump and the rate of cooling flow at the controlled chiller station 206 to remain constant.

As the building load demand, such as one or more buildings, increases, the pressure differential across the cooling water circuit 202 may decrease and one or more of the measured pressure locations may fall below its desired set point. In this way, the monitoring and control system 207 will then begin to increase the cooling water pump rate at the controlled chiller station 206, which will also increase the pump flow rate until the desired set point pressure differential is again achieved. In one embodiment, the cooling water pump speed is incrementally increased until a desired set point pressure differential is achieved.

During some different period of operation when the building cooling water load has decreased, the pressure differential across cooling water circuit 202 will increase accordingly, which may cause one or more of the measured pressure locations to rise above its desired set point. In turn, the monitoring and control system 207 will begin to reduce the chilled water pump rate at the controlled chiller station 206, which will also reduce the pump flow rate until the actual pressure differential in the chilled water loop 202 is at the desired set point pressure in the chilled water loop. In one embodiment, the cooling water pump speed is incrementally decreased until the desired set point pressure differential is achieved.

The process of adjusting the pump speed at the controlled chiller station 206 to maintain the cooling water circuit pressure differential may continue as long as the output of the controlled chiller station 206 is expected to remain within the limits of its minimum and maximum outputs and flow rates. Once the controlled chiller station 206 has reached the maximum flow rate or the minimum flow rate, additional actions, such as bringing other pumps and chillers at one or more of the other chiller stations on-line or off-line, will likely be required.

For example, when the controlled chiller station 206 reaches its maximum output, depending on the expected building cooling load for the time remaining in the day, it may be desirable to bring one or both of the other two chiller stations online. Conversely, when the controlled chiller station 206 reaches its minimum output, the monitoring and control system 107 (fig. 1) will no longer control the pump speed at the controlled chiller station 206, but will maintain the pump speed at its minimum speed while temporarily ignoring the high circuit pressure differential. Depending on the expected building load requirements for the time remaining in the day, it may be desirable to take the controlled cooler station 206 offline.

For the example where only a single chiller station is online, as the building load changes (e.g., increases or decreases, respectively), the monitoring and control system will adjust the pump speed (flow) to generate a corresponding change for maintaining the chilled water circuit setpoint pressure differential. Since there are multiple pressure differentials across the circuit and there are multiple minimum set points, the monitoring and control system can also determine which pressure differential is the "controlling pressure differential" at any one point in time. In addition to adjusting the pump speed, the monitoring and control system may also determine the optimum number of cooling water supply pumps that should be in operation at any given time. When a pump is added or removed, the monitoring and control system notifies the operator to start or stop the pump, and once accepted by the operator, the BOP system will start or stop the pump as it is. Thus, the monitoring and control system attempts to maintain the chilled water distribution system within an "optimal range" where the controlled chiller station is sufficient to meet the desired capacity of the building load by bringing other chillers within the other chiller stations on-line or off-line. Thus, the pump speed, and therefore the output, of the controlled chiller station is adjusted to maintain the desired chilled water circuit pressure differential selected by the monitoring and control system.

In embodiments where the controlled chiller station continuously performs pressure control, the monitoring and control system adjusts the pump speed of another chiller station online to maintain the output of the controlled chiller station in a desired "optimal range". In this embodiment, the cooling water pump at the uncontrolled chiller station will not react to the circuit pressure unless the output of the controlled chiller station is outside the desired "optimal range" and a constant flow will be maintained.

While the preferred embodiments of the invention have been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiments. Instead, the invention should be determined entirely by reference to the claims that follow.

Claims

1. The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

a distributed process cooling water system comprising:

a supply line having a supply line pressure sensor;

a return line having a return line pressure sensor, the supply line pressure sensor and the return line pressure sensor cooperating to provide a pressure differential between the supply line and the return line;

a plurality of buildings, each building having a building automation system controller, each building in fluid communication with the return line and the supply line, the controllers communicatively networked together;

a plurality of cooler stations including at least one base cooler station, each cooler station in fluid communication with the return line and the supply line, the cooler stations communicatively networked together, at least one of the plurality of cooler stations in communication with at least one of the plurality of buildings; and

an operating system operable to process machine readable instructions, the operating system in communication with at least the base cooler station, the operating system configured to receive a signal indicative of the pressure differential, the operating system further configured to determine whether to adjust a pump speed of the base cooler station, bring another cooler online, or take another cooler offline based on the pressure differential to maintain the pressure differential within a desired range.

2. The system of claim 1, wherein the base chiller station comprises at least one cooling water pump coupled to a variable frequency drive.

3. The system of claim 1, wherein the operating system adjusts the pump speed of the base chiller station by transmitting a command to the variable speed drive.

4. The system of claim 1, wherein the base chiller station comprises at least one chiller unit operable to supply water to and receive water from at least one cooling tower.

5. The system of claim 1, wherein the operating system includes one or more relational control algorithms for determining whether to adjust the pump speed of the base chiller station.

6. The system of claim 1, wherein the operating system determines to bring another chiller online when the actual pressure differential exceeds the maximum set point pressure.

7. The system of claim 1, wherein the operating system determines to take the other cooler offline when the actual pressure differential is below the minimum set point pressure.

8. A method for controlling a chilled water distribution system, the method comprising:

determining a real-time pressure differential at a selected location within a cooling water circuit of the distribution system;

monitoring a real-time pump speed of a base chiller station, the base chiller station including a variable frequency drive coupled to a cooling water pump;

determining energy loads of a plurality of buildings served by the cooling water circuit;

adjusting a pump speed of the base cooler station to substantially maintain it within a desired range of a predetermined set point pressure differential of the cooling water circuit; and

a determination is made whether to change the capacity of the distribution system by bringing the chiller of another chiller station on-line or off-line.

9. The method of claim 8, further comprising calculating a desired pump speed for at least one other chiller station based on the real-time pressure differential, real-time pump speed, and energy loads of the plurality of buildings.

10. The method of claim 8, wherein adjusting the pump speed of the base chiller station is performed substantially simultaneously with bringing a chiller of another chiller station on-line or off-line.

11. The method of claim 8, wherein adjusting the pump speed of the base chiller station comprises providing a command to a variable speed drive coupled to the cooling water pump.

12. The method of claim 8, wherein adjusting the pump speed of the base cooler station to approximately remain within a desired range comprises maintaining an output capacity of the base cooler station within an optimal range.