System and method of advanced digital economization

Abstract

A system and method for advanced digital economization for an HVAC system having an economizer. A digital processing unit is configured to open a damper of an economizer within a dead-band range that allows for preemptive cooling prior to a call for cooling. This economization strategy allows for free cooling (outside air) without having to pay energy costs for cooled (air-conditioned) air. The system and method can be used with or without demand control ventilation (DCV). The method also includes a “self-learning” strategy with outside air and return air sensor to regularly sense past economizer damper modifications and average out recent readings to help set the dead-band range. The method can include the ability to work in conjunction with a variable supply fan speed control, provide fault detection, self-correct, auto-configure, and report system status.

Claims

1. A method to reduce energy usage of an HVAC system that provides the following functions: heating, cooling, and ventilation to an indoor building space where the HVAC system provides heating when a call for heating is received and provides cooling when a call for cooling is received, as well as an economizer function tied to the ventilation function that provides fresh air and free cooling benefit to the indoor building space; the method comprising: providing a controller that can receive sensor data, receive input data from the HVAC system that indicates an operating mode, and can send data to the HVAC system; providing an outside air sensor that is controlled by the controller, the outside air sensor is capable of sensing outside air conditions, a supply air sensor that is capable of sensing supply air conditions, and a space sensor that is capable of sensing an indoor temperature of the indoor building space; comparing, with the controller, the sensed indoor temperature with a dead-band range for an HVAC system dead-band state, the dead-band range having a heating setpoint and a cooling setpoint, the cooling setpoint being greater than the heating setpoint, the call for heating being received when the sensed indoor temperature is less than the heating setpoint and the call for cooling being received when the sensed indoor temperature is greater than the cooling setpoint; and operating the economizer function, with the controller, when the sensed indoor temperature is greater than the heating setpoint, is less than the cooling setpoint, and is increasing, to provide predictive free cooling benefit by introducing outside air through the economizer function to the indoor building space when the HVAC system is in the HVAC system dead-band state prior to the call for cooling being received when the sensed indoor temperature becomes greater than the cooling setpoint.

2. The method according to claim 1 wherein the ventilation function is modulated between a fully closed and a fully opened position to maintain a specific supply air setpoint.

3. The method according to claim 1 further comprising: establishing a minimum ventilation rate; and overriding the minimum ventilation rate when the sensed indoor temperature is within the dead-band range to allow higher levels of outside air from the economizer function based on optimum energy savings for free cooling benefit, wherein the minimum ventilation rate results in an energy penalty.

4. The method according to claim 1 wherein the HVAC system also includes a return air sensor that senses return air conditions.

5. The method according to claim 4 wherein the return air sensor is used to establish the dead-band range.

6. The method according to claim 4 further comprising a mixed air sensor.

7. The method according to claim 1 wherein the controller is capable of communicating status of the economizer function to an operator.

8. The method according to claim 1 wherein the controller further comprises fault detection to determine proper operation of the economizer function.

9. The method according to claim 1 wherein the dead-band range is calculated using a time reference.

10. The method according to claim 1 wherein the controller performs self-correction routines.

11. The method according to claim 2 wherein the HVAC system is equipped with a variable speed fan and wherein the controller is capable of controlling or sensing a fan speed of the variable speed fan.

12. A system utilizing advanced economizer strategies to reduce energy used by an indoor building space, the system comprising: an HVAC assembly configured to provide heating, cooling, ventilation, and economization functions to the indoor building space; an economizer that provides the economizer function, the economizer including at least one damper to outside air, the damper configured to operate between a closed and open position when the economizer receives a signal from a controller, wherein the open position is by percentage, the economizer being interconnected to the ventilation functions of the HVAC assembly; a space sensor configured to sense an indoor temperature of the indoor building space; the controller being configured to receive sensor data, receive input data from the HVAC assembly that indicates an operating mode, and can send data to the HVAC assembly for the purposes of operating the ventilation, heating, cooling function, or economization functions, the controller being further configured to predictively operate the economizer in a predictive cooling mode; and the controller being further configured to: compare the sensed indoor temperature with a dead-band range having a heating setpoint and a cooling setpoint, the cooling setpoint being greater than the heating setpoint; and operate the economizer when the sensed indoor temperature is greater than the heating setpoint, is less than the cooling setpoint, and is increasing, to introduce outside air through the economizer to the indoor building space and to cool the indoor building space prior to a call for cooling being generated when the sensed indoor temperature of the of the indoor building space becomes greater than the cooling setpoint.

13. The system according to claim 12 wherein the controller is configured to communicate a status of the economizer function to an operator.

14. The system according to claim 12 wherein the controller further comprises fault detection configured to determine proper operation of the economizer.

15. The system according to claim 12 wherein the controller further comprises auto-configuration.

16. The system according to claim 12 wherein the controller further comprises self-correction routines.

17. The system according to claim 12 wherein the controller is configured to modulate the ventilation function between a fully closed and a fully opened position to maintain a specific supply air setpoint wherein the HVAC assembly is equipped with a variable speed fan; and wherein the controller is configured to control the variable speed fan.

18. A system that uses advanced economizer strategies to reduce energy used by an indoor building space, the system comprising: an HVAC assembly configured to provide heating, cooling, and ventilation functions to the indoor building space, wherein the HVAC assembly includes a variable speed fan; a controller configured to receive sensor data, receive input data from the HVAC assembly that indicates an operating mode, and send data to the HVAC assembly to operate and monitor the heating, cooling, and ventilation functions; an economizer configured to provide an economization function, wherein the economizer includes at least one damper to outside air; and an outside air sensor configured to sense an outside air temperature and transmit data representing the outside air temperature to the controller; and an inside air sensor configured to sense an inside air temperature of the indoor building space and transmit data representing the inside air temperature to the controller; wherein: the controller is further configured to compare the sensed indoor temperature with a dead-band range having a heating setpoint and a cooling setpoint, the cooling setpoint being greater than the heating setpoint; and when the controller determines that the sensed indoor temperature is greater than the heating setpoint, is less than the cooling setpoint, and is increasing, the controller is configured to: (i) operate the economizer in a predictive cooling mode to introduce outside air to the indoor building space prior to a call for cooling being received when the sensed indoor temperature becomes greater than the cooling setpoint and (ii) maintaining a determined target airflow through the economizer by (i) increasing an opening of the at least one damper and (ii) decreasing a speed of the variable speed fan.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Like reference numerals are used to designate like parts throughout the several views of the drawings, wherein:

(2) FIG. 1 is a schematic diagram of a prior art HVAC system illustrating a fan and fan motor, heating, cooling, and an economizer dampers;

(3) FIG. 2 is a schematic diagram illustrating the base version of the present invention;

(4) FIG. 3 is a schematic diagram illustrating an alternate embodiment of the present invention including a sensor to determine space occupancy;

(5) FIG. 4 is a schematic diagram illustrating an alternate embodiment of the present invention including occupancy and return sensors;

(6) FIG. 5 is a schematic diagram illustrating an alternate embodiment of the present invention including occupancy, return, and space sensors;

(7) FIG. 6 is a schematic diagram illustrating the block diagram control logic for the present invention;

(8) FIG. 7 is a schematic diagram illustrating the control logic for sensor selection;

(9) FIG. 8 is a schematic diagram illustrating the control logic for the ventilation dead-band determination; and

(10) FIG. 9 is a schematic diagram illustrating the control logic for the economizer fault detection.

(11) FIG. 10 is a chart illustrating energy required to condition outside air; and

(12) FIG. 11 is a chart illustrating free cooling benefit.

DETAILED DESCRIPTION OF THE INVENTION

(13) Referring to FIGS. 1-9, and 11, the present invention is directed to a system and method for utilizing advanced digital control economizer strategies that reduce energy usage by employing outside air as a cooling asset when the building space has not triggered a call for cooling. Essentially, a building space is preemptively cooled (or “pre-cooling”) in optimum dead-band ranges that are established.

(14) According to one aspect of the invention, the system utilizes an advanced digital economizer (ADE) that consists of a computerized processing unit, environmental sensors, and an interface to an HVAC system. The ADE includes the ability to connect to the HVAC conditioning control points, fan command and fan speed, and an economizer actuator. It has the ability to provide standard low voltage thermostat type control signals to HVAC equipment and modulating resistive or voltage signal to the economizer actuator. The ADE can be used with either new or existing equipment. The ADE can be implemented in a commercially available controller (like an Easy IO 32), a PLC (like an ABB AC500), or embedded directly on a programmable chip (like a MicroChip PIC24). At its core is the ability to store instructions, accept commands, retain setpoints, and react to sensor inputs.

(15) The ADE can use temperature and humidity sensors to monitor environmental conditions. The sensor will provide a varying electrical signal based upon the conditions. For example, the temperature sensor could be a 10K NTC thermistor that changes the resistive value based on temperature changes. For humidity measurements, the sensor could be a 0-10 VDC sensor, where the voltage output changes based on changes in the humidity. It is also required for the ADE to receive indication of the space conditions. This can come either from a variable resistive or voltage signal, but it can also be transmitted to the controller through on/off or digital inputs.

(16) The prior art for demand control ventilation provides energy savings when the outside air temperature is extreme. The reduction in outside air results in energy savings. The outside air that is brought into the space has to be treated to reach proper occupant comfort level. This is demonstrated in FIG. 10. The darker shade bar shows the energy that would be required to treat the outside air in the standard condition (baseline usage), and the lighter shade bar represents the energy required to treat the air when DCV is used. As the temperature gets more extreme, the energy savings increase because the temperature difference between the outside air and the space comfort levels is greater.

(17) During mild conditions when the outside air could be used for free cooling. DCV would result in an energy penalty. DCV provides a reduction in outside air. As demonstrated in the chart in FIG. 11, the reduction in outside air during mild conditions reduces the amount of free cooling that is provided by a traditional system. The present invention overcomes the limitation of prior art, and when the system enters the dead-band mode, the invention will allow the free cooling benefit to be provided to the space. As further defined the specific dead-band mode for each unit can be set using setpoints [8.4 and 8.7] or the dead-band range can be learned based on the actual system performance [8.3 and 8.6] in FIG. 8. FIG. 11 illustrates typical savings that can be achieved through free cooling.

(18) Referring to FIG. 2, in the base control mode the ADE will only use the outside air [2.1] and the supply air [2.4] environmental sensors to manage the economizer [2.3] and ventilation [1.5] (fan) functions. A space balance point and space high economizer cut out will be used to determine the operating mode. If space is satisfied, the outside air is greater than the balance point and it is less than the high economizer cut out, the unit will enter the advanced ventilation mode. During the advanced ventilation mode the economizer damper [1.2] will be opened and modulated to maintain a supply air setpoint as determined by the controller. The default supply air setpoint is 59° F. The controller will have default settings of 50° F. for the balance point and 70° F. for the high economizer cut-out. When the outside air is outside of the advanced ventilation band, the economizer will be controlled to minimum position. The minimum position will either be set by the DCV strategy as defined above, or it will be controlled to a fixed outside air volume, typically 25%.

(19) Referring now to FIG. 8, and still in the base mode, the controller will have the ability to learn the balance point of the space [8.1-8.9]. The controller will log [9.9] the outside conditions when the system transitions into the heating mode. It will store previous logged values, typically up to 10 values, and average the logged values together. To reduce the potential for the advanced ventilation to drive the system into heating mode, the learned balance point will be the average value plus one degree. Advanced ventilation will not be allowed when the outside air conditions are lower than the learned balance point [8.3]. The controller will store the learned balance point in the event of a power failure, a calibration or relearn request [8.11] will be sent to the controller to reset the learned balance point.

(20) Referring also to FIGS. 4 and 7, another embodiment of the invention is when the ADE is equipped with a return air sensor [4.2]. The return air sensor will be used to determine the advanced ventilation mode initiation point [7.8], and related process 7.1-7.10. Instead of a fixed high economizer lockout, the advanced ventilation mode will be enabled when the outside air will take less energy to cool than the return air [8.3]. The advanced ventilation mode activation can still be based off of the balance point referencing outside air or it can be based off return air. The self-learning process for the return air will work similar to the outside air self-learning process, as described above [FIG. 8]. Instead of the outside air conditions being logged on a call for heating, the return air conditions are logged when the HVAC system transitions into heating. It will store previous logged values, typically 10, and average the logged values together. The advanced ventilation mode can be enabled when the return air [4.2] temperature is 2° F. greater than the average [8.6] logged values. The economizer damper [1.2] actuator can be modulated to maintain a consistent return air [4.2] temperature at 2° F. greater than the averaged values.

(21) When the ADE is equipped with a space sensor, the space conditions will be used to determine when the controller will use the advanced ventilation control [FIG. 5]. When the space temperature is in the dead-band, the unit will be in the advanced ventilation mode. The dead-band is the period when the HVAC system is satisfied and the space conditions are in between the heating and cooling setpoints. Advanced ventilation is an energy saving technique that is designed to prevent over-cooling of the space. If the advanced ventilation mode drives the HVAC system into heating operation, the energy savings that are achieved by advanced ventilation pre cooling will be offset by the wasted heat energy. To prevent over cooling, the economizer actuator can be modulated to maintain the space temperature, for example, at 1° F. above the heating setpoint [8.3].

(22) Referring now to FIG. 1, the ADE will also have the ability to monitor the outside [1.1], return [1.3], mixed [1.10], supply [1.8], and space environmental conditions. The outside [1.1] air is ambient air that the surrounds the building that the space is contained within. The return [1.3] air is the air coming back from space to the HVAC system. The mixed [1.10] air is a blend of outside and return air before it is treated by the HVAC equipment. The supply [1.8] air is the air that is leaving the HVAC system being supplied to the space. A supply sensor [5.1 in FIG. 5] will reflect any conditioning that is provided by the HVAC system. The space sensor detects the environmental condition of the space that is treated by the HVAC system.

(23) The ADE will support multiple configurations. Changes will be either configured on the controller through dip switches, potentiometers, or through a user interface which can be a local LCD with push buttons, a hand held tool, or a computer interface. The configuration will allow the user to change the application, configure sensors, adjust setpoints, and initiate calibration.

(24) The ADE will control the quantity of outside air that is being supplied to the space by controlling the economizer [1.2], commonly expressed as the economizer position. When the economizer position is indicated in this document, it is referencing the percentage of the outside air in relation to the total air handling capacity of the unit. For example, a 20% economizer position means 20% of the air delivered by the air handler comes through the outside air dampers. Therefore, 80% of the air is being recirculated from the space as return air. If the HVAC system has a constant volume fan, the outside air flow will be adjusted by making changes to the economizer actuator position. If it is a variable volume system, the ADE will control the volume of outside air by controlling both the fan speed and the economizer actuator position. The ADE will modulate the outputs to find the corresponding values that can produce the required air mixture using the lowest amount of energy to achieve the desired outcome. By default, the ADE will first increase the damper position before increasing the fan speed, which results in higher energy use.

(25) Referring to FIG. 6, the ADE will utilize a central processor [6.10] to control the economizer and HVAC unit. The central processor will coordinate information from the inputs [6.1-6.9] and stored setpoints or data [6.15] to the logic, math, and control algorithms [6.16] so the ADE can affect the desired action of the HVAC system [6.11-6.14]. The central processor will be able to accept inputs from the HVAC system: occupied command [6.1], heating call [6.2], cooling call [6.3], and fan call [6.4]. It will also process environmental sensor data: outside sensor [6.5], return sensor [6.6], supply sensor [6.7], mixed air sensor [6.8], and space sensor [6.9]. It will be able to send commands to the HVAC system components: economizer [6.11], heating function [6.12], cooling function [6.13], and the fan [6.14].

(26) The ADE can accept signals from the existing temperature controller [1.9] or new temperature controller [2.5]. The most common interface will be though digital inputs. The existing control system will send an on/off command that will be monitored by the ADE. It will be able to accept Stage 1 Heat, Stage 2 Heat, Stage 1 Cool, Stage 2 Cool, and reversing valve commands. The existing control will be routed to the ADE, and the ADE will connect to the HVAC system control terminals. Alternately the ADE can become the temperature controller and replace the existing controls. When the ADE is the temperature controller it will store occupied and unoccupied heating and cooling setpoints [6.15] and it will monitor the space temperature. It will provide the control signals for the fan [1.5], and it will enable the fan to run in the occupied mode. When the space temperature is less than the heat setpoint, heating [1.6] will be enabled. When the space temperature is greater than the cooling setpoint, the unit will go into the cooling mode. When the ADE is in the cooling mode the economizer [1.2] or mechanical cooling [1.7] can be used to meet the demands of the space. The heating or cooling output will increase based on the deviation from setpoint and how long the deviation has existed. It will use proportion, integral, and derivative (PID) control loop and a sequencer [6.16] to stage the conditioning functions. In either connection when the space is occupied and there is no call for heating or cooling, the system is determined to be in the ventilation mode.

(27) Another embodiment of the ADE involves an HVAC system with modulating heating and cooling valves. In this application, the ADE will operate the heating and cooling functions with a varying analog output signal.

(28) Any variation of the ADE can also be configured for demand control ventilation (DCV). DCV is a common practice that is supported by the ASHRAE 62.1 standard. It is used to determine the proper ventilation rate for a building based on occupancy. The most common way to monitor the occupants in a space is by using a CO2 sensor [3.1]. The CO2 sensor provides a voltage output that increase as the CO2 levels in the space increase. The DCV control sequence will be overridden whenever the controller initiates the Advanced Ventilation mode as described below. When DCV is engaged, the minimum ventilation settings will be reset based on the occupancy levels. The minimum and maximum ventilation rates will be set based on ASHRAE 62.1 guidelines, commonly the minimum ventilation rate will be set to 5-10% outside air volume and 20-40% for the maximum rate. As the CO2 in the space increases, the economizer output will increase to maintain the appropriate ventilation rate.

(29) An alternate embodiment would allow ADE to use a timing method to determine when the advanced ventilation mode can be utilized [7.5]. The ADE would consider the space satisfied and to have a cooling disposition when a period of time, such as 45 minutes, has elapsed following the termination of the last heating call [2.7]. The ADE would then modulate the economizer [2.2] to maintain a supply air [2.4] temperature setpoint (such as 60° F.) to prevent overcooling. If no heating calls have happened for the selected time period following the beginning of occupancy, the ADE would then enter the advanced economizer mode and modulate the economizer [2.2] to achieve a supply air temperature such as 65° F. The occupied period is assumed to have occurred when the supply fan command [2.6] transitions from off to on.

(30) When one or more valid environmental sensor is connected to the ADE, the ADE may automatically select the application mode that is used to determine the dead-band range. [FIG. 7.] The sensor is considered to be valid if there is a proper electrical reading and if the value is changing at regular intervals. The valid sensor with the highest priority is used to establish the setpoints and the measured variable that will determine advanced economizer mode. The space sensor would typically have the greatest priority [7.2], the return sensor will typically have the next highest priority [7.3], and the outside air sensor will typically have the lowest priority [7.1].

(31) For example: if the space sensor is valid [7.2], the dead-band range will be the occupied heating and cooling setpoints [7.7]. If the sensor goes invalid, the ADE will transition to the return air sensor [7.3], and the return air high economizer lockout and balance point setting is used to establish the dead-band range [7.8].

(32) If the ADE is controlling based on the outside air sensor and if either of the supply outside air sensors returns an invalid reading, the ADE would be disabled from operating [7.6].

(33) Referring now to FIGS. 4 and 9, the ADE has the ability to verify proper economizer operation. When there is at least a 10° F. difference between the outside air and the return air, the conditions are acceptable to verify the economizer performance. The first step is to establish a baseline for the economizer effectiveness. If the ADE is equipped with a mixed air sensor [4.1], the mixed air sensor would be used. If there is no mixed air sensor [4.1], the supply air sensor [2.4] will be used. The supply air sensor value will be adjusted to compensate for the heat from the supply fan motor. The user will set the motor horsepower in the controller, and the controller will automatically calculate the heat output. The controller will be able to calculate the heat from the motor by factoring in different motor speeds. The controller will take readings of the Outside [2.1], Return [4.2], and Mixed [4.1] or Supply [2.4] air sensor(s), and a mass air flow calculation will be used to determine the actual percentage of outside air to return. The economizer efficiency is the measure of the actual performance of the economizer (as determined by the mass flow calculation) expressed as a percentage when it is compared to a theoretical perfect economizer. The economizer efficiency value is stored in the controller [9.9]. The process is completed again at regular intervals or it can be manually initiated at the controller [9.1-9.6]. Newer samples are compared to the baseline value [9.2]. If the economizer efficiency has increased or improved [9.4], it would likely indicate a sensor drift or sensor failure [9.7]. If the economizer efficiency has decreased [9.5], it could indicate a sensor failure or a problem with the economizer damper and actuator assembly [9.8]. These problems can be indicated by a flashing LED on the controller or through an external user interface [9.10]. The baseline economizer efficiency can be reestablished at any point by triggering a recalibration procedure.

(34) The illustrated embodiments are only examples of the present invention and, therefore, are non-limitive. It is to be understood that many changes in the particular structure, materials, and features of the invention may be made without departing from the spirit and scope of the invention. Therefore, it is the Applicant's intention that its patent rights not be limited by the particular embodiments illustrated and described herein, but rather by the following claims interpreted according to accepted doctrines of claim interpretation, including the Doctrine of Equivalents and Reversal of Parts.