Method for improving efficiency in heating and cooling systems

Info

Publication number: 20080264086
Type: Application
Filed: Apr 25, 2007
Publication Date: Oct 30, 2008
Inventor: Mingsheng Liu (Omaha, NE)
Application Number: 11/789,636

Abstract

A method for improving efficiency in heating and cooling systems which includes the steps of providing speed and pressure monitoring devices for monitoring and measuring the operational speed (OS) and the head (HR) of the fan or pump and providing a flow rate monitoring device for monitoring and measuring the fluid flow rate (Q) for fluid flowing through the fan or pump. The OS, HR and Q for the fan or pump would be periodically obtained from the speed and pressure monitoring devices and the flow rate monitoring device, and the operating S-value of the heating and cooling system would be determined by applying the formula S-value=HR/(QR)2, thereby obtaining a measurable single value representative of the overall efficiency of the heating and cooling system.

Description

Description

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates generally to systems and methods for improving the efficiency of HVAC systems and, more particularly, to a method for improving efficiency in HVAC systems which includes the steps of providing speed and pressure monitoring devices for monitoring and measuring the operational speed and head pressure of the fan or pump of the air or water-based system, providing a fluid flow rate monitoring device which will measure the fluid and flow rate of fluid flowing through the fan or pump, periodically obtaining the operational speed, head pressure, and fluid flow rate from the monitoring devices, determining the S-value of the HVAC system by applying the formula H/Q squared and applying the S-value to optimize operation of the fan or pump by adjusting the operational speed such that the measured S-value approaches the set point S-value representing optimum flow efficiency.

2. Description of the Prior Art

Fans and pumps are the major devices used to transport air or liquid in HVAC systems and through processing devices used in manufacturing concerns, such as those shown in the examples of the prior art of FIGS. 2 and 3. The basic function of such fans and pumps is to ensure enough air and water flow through the end devices. However, the required flow often changes with time and the load placed on the end devices, thus requiring some degree of flow modulation in order to permit proper heating or cooling of the end device. The required flow modulation is often achieved using the following two steps:

- 1. Modulate the fan/pump speed as the terminal load changes. The fan/pump speed would be indirectly controlled by a pressure or differential pressure set point. For example, the fan in an air handling unit is often controlled to maintain the static pressure at two-thirds (⅔) of the preset system value downstream of the main duct. In a related system, a differential pressure sensor is often installed in a liquid loop, and when the differential pressure differs from the set point, the pump speed is changed to ensure the set point.
- 2. An individual modulation damper/valve is installed for each end device and a preset damper value is assigned to each end device. The damper/valve is used to maintain the required flow when the load changes by permitting increased or decreased fluid flow to the end device.

In the majority of HVAC and industrial chilling systems, the set point of static pressure/differential pressure is often determined under the maximum load conditions. Under partial load conditions, this control approach has the following drawbacks: One, it consumes excessive fan/pump energy, approximately thirty percent more fan energy than is used for a typical variable air volume air handling unit; two, it exposes the dampers/valves in the end devices to excessive pressures which will eventually cause malfunction, thus requiring frequent adjustment of the control loop gains to maintain stable dampers/valves control, and since it is impossible to properly perform this process in many applications, the process will cause significant control device damage and unstable control; and three, excessive air leakage in the ductwork and air/water leakage through closed dampers/valves will occur due to the increased operational pressures, and consequently, thermal energy is wasted, and for example for a typical AHU, ten percent or more thermal energy is wasted.

It has further been proposed in the HVAC industry to provide a differential pressure/static pressure reset system to improve the system operation. The following approaches are often proposed: One, modulate the fan/pump operational speed to maintain at least one damper/valve at full open; or two, reset the set point based on the rule of thumb. While the first approach is ideal theoretically, it has been seldom used due to a number of practical issues. This method cannot work properly when end devices are malfunctioning. It also creates large amount of information transfer in the network, which often overloads the network and breaks down the system. The second approach would not achieve the optimum results due to the dependence of experience. There is therefore a need for a system or method which will improve and optimize the efficiency of the HVAC or industrial chilling system, yet will do so while not requiring significant modifications to the already-existing system, or which relies on outdated or non-functional system elements such as original equipment pressure sensors for reading critical system information.

It is therefore an object of the present invention to provide an improved method for improving the efficiency of an HVAC or industrial chilling or heating system.

Another object is to provide an improved method for improving the efficiency of an HVAC or industrial chilling or heating system which will obtain real-time information from the operation of the fan/pump which feeds the system, including fan/pump head and fan/pump flow rate, determine an operating S-value by dividing the head by the flow rate squared, and compare that to an optimum S-value set point initially determined for the system.

A further object of the present invention is to provide an improved method for improving the efficiency of an HVAC or industrial chilling or heating system in which the operating speed of the fan/pump is increased or decreased to bring the operating S-value into accordance with the S-value set point representing the optimum efficiency for the system.

Still another object is to provide an improved method for improving the efficiency of an HVAC or industrial chilling or heating system which does not require system information obtained from previously installed gauges and sensors which may be damaged or non-functional or may be unavailable due to their location being unknown within the building in which the HVAC system is installed.

Finally, an object of the present invention is to provide an improved method for improving the efficiency of an HVAC or industrial chilling or heating system which is relatively simple and straightforward in design and construction and is safe, efficient and effective in use.

SUMMARY OF THE INVENTION

The present invention provides a method for improving efficiency in HVAC systems, the HVAC system having at least one of a fan and a pump, a motor for driving the pump, at least one air handling unit (AHU), and a heating/cooling system, the method comprising the steps of providing speed and pressure monitoring devices for monitoring and measuring the operational speed (OS) and the head pressure (H_R) of the at least one of a fan and a pump and providing a flow rate monitoring device operatively associated with the at least one of a fan and a pump for monitoring and measuring the fluid flow rate (Q) for fluid flowing through the at least one of a fan and a pump. The OS, H_Rand Q for the at least one of a fan and a pump is then periodically obtained from the speed and pressure monitoring devices and the flow rate monitoring device, and by utilizing those readings, the operating S-value of the HVAC system is obtained by applying the formula: S-value=H_R/(Q_R)², thereby obtaining a measurable single value representative of the overall efficiency of the HVAC system. The operating S-value is then utilized to optimize operation of the at least one of a fan and a pump by adjusting the operational speed (OS) of the at least one of a fan and a pump such that H_R/(Q)²approaches the S-value set point of the HVAC system thereby increasing the operational efficiency of the HVAC system.

The present invention thus provides a substantial improvement over those systems and methods found in the prior art which are designed to provide for adjustment to HVAC systems for increasing efficiency. Specifically, because the method of the present invention does not require use of the remote pressure sensor already installed in the HVAC system in order to determine the most efficient operating speed for the pump or fan, it is not necessary for a user of the present invention to determine the location of the originally installed pressure sensor, determine if it is working correctly, and provide preventive maintenance to maintain the pressure sensor in its properly operating condition. Furthermore, because the system and method of the present invention generally reduces efficiency determinations to the proper operation of the fan or pump in connection with the HVAC system, it is far easier for a user to implement the method of the present invention as compared to those intricate and failure-prone systems and methods found in the prior art. Finally, because the present invention is usable not only with HVAC systems, but with any cooling or heating system which includes a fan or pump for driving fluid through the system, it may be adapted and used with many industrial chilling or heating systems which bear little if any resemblance to HVAC systems yet, because they include a pump or fan which can be controlled by an implementation of the present invention to increase efficiency, improvement in the efficiency of those industrial systems may be achieved through implementation of the present invention.

In the preferred embodiment, the proposed S-method will provide optimal and reliable fan and pump control, which will:

1. Maximize the fan/pump efficiency and save electrical energy consumption.

2. Provide stable damper/valve control.

3. Eliminate excessive thermal energy waste.

4. Eliminate the need of the static pressure sensors in fan systems and the differential pressure sensors in pump systems.

It is therefore seen that the present invention provides a substantial improvement over those systems and methods found on the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the HVAC system outfitted with the system and method of the present invention to increase the efficiency of the HVAC system;

FIGS. 2 and 3 are schematic diagrams showing air and water flow systems of the prior art illustrating the disadvantages of these systems;

FIG. 4 is a schematic diagram of the various modules of the present invention; and

FIGS. 5-11 are flow chart diagrams which disclose in detail the various modules of the system and method of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The S-value determination method is an intelligent control algorithm/system for optimally controlling fan/pump speed in heating ventilation and air-conditioning (HVAC) systems, such as those shown in FIG. 1, and in industrial chilling and heating systems having fans and/or pumps therein. This method intelligently modulates the fan (pump) speed to satisfy the desired flow, to maximize the energy system efficiency and to warrant stable end user device control. This method can be applied to variable air or water volume systems in HVAC systems for fan and pump speed control, and to industrial processes as well. FIG. 1 presents the schematic diagram of the S-value determination method, and in the preferred embodiment, the present invention would include the following sensors or signal sources: A differential pressure sensor or signal source is connected to the fan/pump to measure the fan head or pump head pressure, and a fluid flow meter is provided in the system to measure fan airflow or pump flow. There are many different methods and devices which can be used to obtain this data, including using the fan airflow station or pump flow station as disclosed in U.S. patent application Ser. Nos. 11/498,539 and 11/491,767, or by using conventional flow measurement meters such as those commonly used in fluid flow applications. Furthermore, the present invention would provide a power meter or signal source, which can be a built-in meter in a Variable Frequency Drive (VFD) which is designed to measure the true power output of the motor.

In the preferred embodiment, the method of the present invention includes seven modules, as shown best in FIG. 4. The first module is the start module, which ramps up the fan/pump speed from zero to a predetermined level (for example, to fifty percent speed) within the given time period (for example, over thirty seconds).

When the first module function is completed, the second module is engaged. The sampling module processes the signals from the sensors, devices and resources to obtain real time values for the fan/pump head, fan/pump speed, airflow or water flow and the motor power consumption. In addition, the sampling module may also receive the static pressure signal for a fan system, and differential pressure signal for a pump system. In the preferred embodiment, the static pressure sensor is typically installed downstream of the fan to measure the duct static pressure or total pressure, with the typical locations being approximately two-thirds downstream of the main duct or at the end of the main duct. Likewise, the differential pressure sensor is typically installed downstream of the pump. The typical location is often at the end of the loop. It should be noted, however, that the static pressure sensor and the differential loop pressure sensor are optional. The preferred sampling system for each of the sensor and devices would involve processing all signals using a moving average, and the time period between periodic sampling would preferably be in a range of five seconds to several minutes.

The third module is the fan/pump flow station module, which determines the fan/pump flow based on measured fan/pump speed, fan/pump head and fan/pump curves. As was stated previously, this module would preferably be based on U.S. patent applications No. 11/498,539 and 11/491,767. The fan airflow/pump water flow can also be obtained from the conventional flow meters which are stationed within the HVAC system.

The fourth module is the S-value set point module, which determines the set point of the S-value. S is the system resistance factor. Two options exist depending on the selection of the pressure or the differential pressure signals. The first option is to define the S-value as the ratio of the fan/pump head and the square of the fan/pump-flow. The second option is to define the S-value as the ratio of the static pressure (static pressure reading) and the fan airflow, or as the ratio of the differential pressure (differential pressure sensor reading) and the pump flow. The details of selecting S-value set points are discussed in the next section.

The fan/pump head module determines the set point of the fan/pump head or the static pressure set point or differential pressure set point depending on the selection of the S-values. The set point of the fan/pump head, static pressure, or differential pressure is as the product of the set point of S and the square of the fan/pump flow.

The speed control module is a PI loop, which modulates the fan/pump speed to maintain the actual fan/pump head, or fan static pressure, or differential pressure at its set point, which is determined by the fan/pump head module.

The output module produces the following information: fan/pump efficiency, equivalent pump working point (percentage of fan/pump flow, percentage of fan/pump head at one hundred percent speed), and fan/pump power. The fan/pump efficiency is determined as the ratio of the useful mechanical work and the actual power consumption. The useful work input is the product of the fan/pump flow and head, which shall be converted into proper units. The output module may include standard network communication port or standard analog output port. The method of the present invention may also include standard interfaces to communicate with other controllers.

The set point of the S-value, which sets the optimal level of efficiency for the system with which the present invention is being used, is preferably determined using one of the following method. First, the S-value set point may be determined as the product of a coefficient and the ideal S-value which is determined as the ratio of the design fan/pump head and the square of the design airflow/water flow. The coefficient can be in a range of 1 to 1.5, with the resulting equation appearing as follows:

S_{set point}=α(H_D/(Q_D)²)

where α is a safety factor, which can be a function of the fan/pump flow to prevent overloading of the fan/pump, H_Dis the design fan or pump head and Q_Dis the design fluid flow.

Second, the S-value set point may be determined using the experimental trial method which involves the following steps. First, the fan/pump is run at its low speed limit and the measured airflow/water flow and fan/pump head are recorded. Determine the first operating S-value (S₁) as the ratio of the recorded head and the square of the recorded flow. The fan/pump would then be run at ten percent higher operating speed than its low limit, and again the measured airflow/water flow and fan/pump head would be recorded. Determine the second S-value (S₂) in the same manner as the first S-value (S₁) using the newly acquired recorded head and recorded flow. If S₂is five percent (5%) greater than S₁(this ratio being adjustable depending on the specific system, but generally five percent is the preferred percentage to be used for the calculation), then determine the minimum S-value set point as S₂or the average of S₁and S₂. If it is not, the fan/pump speed would be increased at an interval of ten percent (adjustable) until the current S-value (S₂) is five percent (adjustable) greater than the previously obtained S value (S₁). This method is best suitable for systems which monitor the control damper information or control valve position when pneumatic controllers are used in the terminal boxes or the control valves.

Alternatively, the experimental trial method may involve analysis of the damper/valve positions in the following manner. The fan/pump speed would be modulated until a certain percentage of the dampers/valves in the system are near full open while all zone temperatures or discharge air temperatures of the coils are maintained at the preferred set point. At this point, the fan/pump head and the air/water flow would be recorded and this would represent the optimal operational values for the system. For either of the experimental trial methods, however the maximum S-value obtained would be used as the S-value set point for the system, and this ratio would provide the basis for adjustment of the operating characteristics of the fan/pump during operation of the system.

It should be noted that the safety factor α referred to previously will vary due to fluctuations in the load placed on the system. For example, at partial load conditions, the load ratios vary from end device to end device and consequently, the safety factor should increase as the fan/pump flow decreases. Therefore, in the preferred embodiment, the safety factor would generally be expressed as the following formula:

α=(Q/Q_D)⁻ⁿ

where η is a constant which varies between 0 to 0.5, depending on the flow rate and pump or fan operational characteristics.

The operational elements of the method of the present invention are best shown in the flow charts of FIGS. 5-11 as including numerous steps which, when applied to an HVAC system or industrial chilling or heating system, will invariably improve the efficiency of the system over time, barring any unforeseen circumstances or system failures. A detailed discussion of each of the elements of flow charts found in FIGS. 5-11 is not deemed necessary, as the flow charts are self-explanatory and would generally be implemented via a computer program or the like which executes the various steps and includes interfaces with each of the operative elements of the HVAC system or industrial chilling or heating system, as shown in FIG. 1. However, it should be noted that FIGS. 9 and 10 disclose what may be deemed “the heart” of the present invention, in that modulation and control of the fan/pump operational speed is performed via the implementation of the fan/pump speed control module. Specifically, it should be noted that once the fan/pump head and the fan/pump fluid flow rate have been established via sampling by the speed and pressure monitoring device and the flow rate monitoring device, the operating S-value formula is applied to obtain a specific ratio based on current operation of the system. This ratio is then compared to the S-value set point obtained from the system which represents the optimum operating efficiency of the system, namely, when the pump or fan is operating at one hundred percent capacity and all of the various dampers or other resistance factors in the system are open to provide the least resistance through the system for the air or liquid flowing therethrough. If the ratio of fan/pump head to fan/pump fluid flow squared obtained from the actual operation of the fan/pump is approximately equal to or close to the optimum ratio obtained previously, the system is functioning at or near optimum efficiency and adjustment to the operating speed of the fan/pump is not absolutely necessary. However, if the ratio obtained is significantly higher or lower than the optimum ratio, the system determines this and the operating speed of the fan/pump is consequently increased or decreased to increase or decrease the fan or pump head in order to bring the ratio closer into accordance with the preferred optimum ratio which was initially determined by either application of the design head and flow rate formula or the experimental trial formula as applied to the system. The system periodically checks the operating S-value and performs the same comparison with the optimum ratio and, in this manner, the system of the present invention optimizes the operation of the HVAC system or industrial chilling or heating system with which it is connected, thereby significantly increasing the efficiency with which the system is being operated.

The present invention provides many advantages over those efficiency improvement systems and methods found in the prior art. For example, elimination of the static pressure sensor and differential pressure sensor in the ductwork and liquid loops will further ensure reliable system operation. As was discussed previously, in real-life engineering projects, the locations of these sensors are often hard to find. Consequently, repair and replacement of damaged or non-functional sensors is rarely, if ever, performed. Due to these malfunctions of the sensors, it causes significant amount of energy waste as well as poor comfort in the HVAC system. Also, the present method and system maximizes the fan/pump efficiency by minimizing the fan/pump head and reducing air leakage through the ductwork and end devices, and also reduces water leakage through closed valves. Finally, the overall system stability is significantly improved and damper and actuator damage is minimized.

It is to be understood that numerous additions, modifications and substitutions may be made to the present invention which fall within the intended broad scope of the appended claims. For example, the specific steps disclosed in the flow charts of FIG. 5-11 may be modified or changed so long as the intended general function of comparing the operational S-value to the optimum S-value set point initially obtained by the system is periodically performed. Furthermore, implementation of the operational elements of the present invention may be modified or changed, as, for example, the speed and pressure monitoring devices and flow rate monitoring devices may be of any appropriate type so long as accurate readings of those speeds, pressures and flows may be obtained from the HVAC system or industrial system with which the invention is being used. Finally, although the present invention has been described with some particularity regarding obtaining of the initial S-value set point for the system, it should be understood that any appropriate method or system may be used to determine the S-value set point so long as the S-value set point obtained through the alternative methods generally conforms to the values expected when the methods disclosed above are applied to the same HVAC system or industrial system.

There has therefore been shown and described a method for improving efficiency in HVAC and industrial chilling and heating systems which accomplishes at least all of its intended objectives.

Claims

1. A method for improving efficiency in HVAC systems, the HVAC system having at least one of a fan and a pump, a motor for driving the pump, at least one air handling unit (AHU), and a heating/cooling system, said method comprising the steps:

providing speed and pressure monitoring means for monitoring and measuring the operational speed (OS) and the head (HR) of the at least one of a fan and a pump;

providing flow rate monitoring means operatively associated with the at least one of a fan and a pump for monitoring and measuring the fluid flow rate (Q) for fluid flowing through the at least one of a fan and a pump;

periodically obtaining the OS, HR and Q for the at least one of a fan and a pump from said speed and pressure monitoring means and said flow rate monitoring means;

determining the operating S-value of the HVAC system by applying the formula; S-value=HR/(QR)2

thereby obtaining a measurable single value representative of the overall efficiency of the HVAC system.

2. The method of claim 1 further comprising the step of determining the S-value set point of the HVAC system, said S-value set point representing the optimum operating efficiency of the system

3. The method of claim 2 wherein said step of determining said S-value set point comprises providing the design head (HD) and design fluid flow rate (QD) for the at least one of a fan and a pump in the HVAC system and entering the HD and QD values into the equation: S-value set point=HD/(QD)2, thereby obtaining a value for the S-value set point for the HVAC system.

4. The method of claim 2 wherein said step of determining said S-value set point comprises the steps:

running the at least one of a fan and a pump at its low speed limit;

measuring the fluid flow rate and head of the at least one of a fan and a pump;

determining the initial operating S-value (S1) as the ratio of the head and the square of the fluid flow rate;

increasing the operational speed of the at least one of a fan and a pump approximately ten percent;

measuring the second fluid flow rate and second head of the at least one of a fan and a pump;

determining a second S-value (S2) as the ratio of the second head and the square of the second fluid flow rate;

comparing S2 to S1 to determine S2 is approximately five percent (5%) greater than S1,

assigning S1 the value of S2 and repeating said increasing, measuring, determining and comparing steps if S2 is not approximately five percent (5%) greater than S1; and

setting said S-value set point as the average of S1 and S2 if S2 is approximately five percent (5%) greater than S1.

5. The method of claim 2 further comprising the step of applying said operating S-value to optimize operation of the at least one of a fan and a pump by adjusting the operational speed (OS) of the at least one of a fan and a pump such that HR/(Q)2 approaches said S-value set point.

6. The method of claim 2 further comprising the step of multiplying the S-value set point by a factor of α, where α is a safety factor which is a function of the fan/pump flow to prevent overloading of the fan/pump and is calculated by the formula α=(Q/QD)−n, where η is a constant between zero (0) and 0.5.

7. A method for improving efficiency in heating and cooling systems, the heating and cooling system having at least one of a fan and a pump, a motor for driving the pump and a heating/cooling system, said method comprising the steps:

providing speed and pressure monitoring means for monitoring and measuring the operational speed (OS) and the head (HR) of the at least one of a fan and a pump;

providing flow rate monitoring means operatively associated with the at least one of a fan and a pump for monitoring and measuring the fluid flow rate (Q) for fluid flowing through the at least one of a fan and a pump;

periodically obtaining the OS, HR and Q for the at least one of a fan and a pump from said speed and pressure monitoring means and said flow rate monitoring means;

obtaining an S-value set point for the HVAC system representing generally the optimum efficiency value for the HVAC system;

determining the operating S-value of the HVAC system by applying the formula; S-value=HR/(QR)2

thereby obtaining a measurable single value representative of the overall operating efficiency of the HVAC system; and

comparing said operating S-value with said S-value set point to optimize operation of the at least one of a fan and a pump by adjusting the operational speed (OS) of the at least one of a fan and a pump such that said operating S-value (HR/(Q)2) approaches said S-value set point.

8. The method of claim 7 wherein said step of determining said S-value set point comprises providing the design head (HD) and design fluid flow rate (QD) for the at least one of a fan and a pump in the heating and cooling system and entering the HD and QD values into the equation: S-value set point=HD/(QD)2, thereby obtaining a value for the S-value set point for the heating and cooling system.

9. The method of claim 7 wherein said step of determining said S-value set point comprises the steps: