System and method for determining duct leakage in a HVAC system

A system and method of determining duct leakage in an HVAC system including an HVAC unit assembly operably coupled to a system controller, the method including operating the system controller to determine system leakage data, operating the system controller to determine supply leakage data, and operating the system controller to determine a duct leakage measurement based in part on the system leakage data and the supply leakage data.

TECHNICAL FIELD OF THE DISCLOSED EMBODIMENTS

Technical Field of the Disclosed Embodiments

The presently disclosed embodiments generally relate to heating, ventilation and air conditioning (HVAC) systems, and more particularly, to a system and method for determining duct leakage in a HVAC system.

Background of the Disclosed Embodiments

Generally, a duct leakage tester is a diagnostic tool designed to measure the airtightness of forced air heating, ventilating and air-conditioning (HVAC) ductwork. A duct leakage tester typically consists of a calibrated fan for measuring an air flow rate and a pressure sensing device to measure the pressure created by the air flow. The combination of pressure and fan flow measurements is used to determine the ductwork airtightness. The airtightness of ductwork is useful knowledge when trying to increase energy conservation within a building such as a residential home.

Generally, a typical duct leakage testing system includes three components—a calibrated fan, a register sealing system and a device to measure air flow pressure and building pressure. Supply registers or return air grills are sealed using adhesive tapes, cardboard, or non-adhesive reusable seals. One register or return is left unsealed, and the calibrated fan is then connected to the unsealed register. Pressure is monitored in one of the branches of the ductwork while the calibrated fan delivers air into the system. As air is delivered into the ductwork, pressure builds and forces air out of any holes in the various ductwork connections or through the seams and joints of the furnace or air-handler. The tighter the ductwork system (e.g. fewer holes), the less air required from the fan to create a change in the ductwork pressure.

This method of duct leakage testing requires administration by a certified person; therefore, this method is time consuming, and increases the overall cost of installation. There is, therefore, a need for a method to determine duct leakage that reduces the required time to perform the test.

SUMMARY OF THE DISCLOSED EMBODIMENTS

In one aspect, an HVAC system for determining duct leakage is provided. The HVAC system includes a system controller, and an HVAC unit assembly in communication with the system controller, the HVAC unit assembly comprising a blower compartment door and a blower system. The system controller is configured to determine system leakage data, determine supply leakage data, and determine a duct leakage measurement based in part on the system leakage data and the supply leakage data.

In an embodiment, the HVAC system further includes at least one supply conduit coupled to the HVAC unit assembly and at least one return conduit coupled to the HVAC unit assembly.

In an embodiment, the blower system is configured to operate at a plurality of motor parameters to generate system static pressure data and system airflow data, and operate at a plurality of motor parameters to generate supply static pressure data and supply airflow data. In an embodiment, the plurality of motor parameters includes at least one of a plurality of motor torques and a plurality of motor speeds.

In an embodiment, the system controller is further configured to determine a leakage supply airflow value at a pre-determined leakage static pressure value, determine a leakage system static pressure value based on the leakage supply airflow value, determine a leakage return static pressure based on the leakage supply airflow at the pre-determined leakage static pressure value, determine a return flow constant based on the leakage return static pressure and the leakage supply airflow at the pre-determined leakage static pressure value, determine a leakage return airflow at the pre-determined leakage static pressure value based on the return flow constant, and determine a system leakage value based on the leakage return airflow and the leakage supply airflow. In an embodiment, the pre-determined leakage static pressure value is approximately 0.1 inch water column.

In one aspect, a method for determining duct leakage is provided. The method determine duct leakage in an HVAC system including an HVAC unit assembly including a blower compartment door and a blower system, at least one supply air conduit coupled to the HVAC unit assembly, at least one return air conduit coupled to the HVAC unit assembly, and a system controller operably coupled to the HVAC unit assembly. The method includes operating the system controller to determine system leakage data, operating the system controller to determine supply leakage data, and operating the system controller to determine a duct leakage measurement based in part on the system leakage data and the supply leakage data.

In an embodiment, operating the system controller to determine system leakage data includes restricting airflow in at least one supply air conduit and the at least one return air conduit, and operating the blower system at a plurality of motor parameters to generate system static pressure data and system airflow data. In one embodiment, the plurality of motor parameters comprises at least one of a plurality of motor torques and a plurality of motor speeds.

In an embodiment, operating the system controller to determine supply leakage data includes opening the blower compartment door, and operating the blower system at a plurality of motor parameters to generate supply static pressure data and supply airflow data.

In an embodiment, determining a duct leakage measurement includes operating the system controller to determine a leakage supply airflow value at a pre-determined leakage static pressure value, operating the system controller to determine a leakage system static pressure value based on the leakage supply airflow value, operating the system controller to determine a leakage return static pressure based on the leakage supply airflow at the pre-determined leakage static pressure value, operating the system controller to determine a return flow constant based on the leakage return static pressure and the leakage supply airflow at the pre-determined leakage static pressure value, operating the system controller to determine a leakage return airflow at the pre-determined leakage static pressure value based on the return flow constant, and operating the system controller to determine a system leakage value based on the leakage return airflow and the leakage supply airflow. In an embodiment, the pre-determined leakage static pressure value is approximately 0.1 inch water column.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

FIG. 1illustrates an exemplary HVAC system10constructed in accordance with the present disclosure. In one embodiment, the HVAC system10includes an HVAC unit assembly12including a blower compartment door13. The blower compartment door13is configured to provide access to the motor28and blower30(as shown inFIG. 2). In the embodiment shown, the HVAC unit assembly12is located inside a structure, but it will be appreciated that the HVAC unit assembly12may be located outside of a structure. At least one supply air conduit14is coupled to the HVAC unit assembly12to deliver conditioned air to the interior space15, and at least one supply register vent16is coupled to each supply air conduit14to direct the flow of the conditioned air. Three supply register vents16A-C are shown in the illustrated non-limiting embodiment.

The HVAC system10further includes at least one return air conduit18coupled to the HVAC unit assembly12, and at least one return register vent20coupled to the at least one return air conduit18. The at least one return air conduit18is configured to extract air from the interior space15and direct the extracted air to be re-circulated through the HVAC unit assembly12.

The HVAC system10includes a system controller22operably coupled to the HVAC unit assembly12. The system controller22is configured to control the operation of the HVAC unit assembly12to deliver conditioned air to the interior space15. The system controller22is further configured to provide a determination of duct leakage according to the method disclosed herein.

In one embodiment, as shown inFIG. 2, the HVAC unit assembly12includes an HVAC unit assembly control24, and a blower system26which includes a motor28and a blower30. The system controller22is shown in direct communication with the HVAC unit assembly control24, and the HVAC unit assembly control24is shown in direct communication with the motor28of the blower system26. The system controller22may be in wired or wireless communication with the HVAC unit assembly control24and motor28.

In one embodiment, the HVAC unit assembly control24includes an HVAC unit assembly controller32, which includes a first microprocessor34and a first memory36for storing certain operational characteristics particular to the given HVAC system10. As shown, the HVAC unit assembly controller32can be in communication with a model control and feedback circuit38and with a motor control and feedback circuit40. The feedback circuit38serves to connect the HVAC unit assembly control24to the system controller22via a system bus42, and allows signals to be communicated between the HVAC unit assembly control24and the system controller22. Feedback circuit40connects the HVAC unit assembly control24to the motor28, and serves to transmit commands to, and receive operation feedback from, the motor28via a motor bus44.

The blower system26includes a motor28configured to operate at a plurality of motor parameters. In an embodiment, the plurality of motor parameters includes at least one of operational motor torque and operational motor speed. The blower system26further includes a blower30, which has a blower diameter and an operational blower speed. The motor28serves to rotate blades or other means of the blower (not shown) to move air through the at least one supply air conduit14and the at least one return air conduit18associated with HVAC system10.

In one embodiment, the motor28includes a variable speed motor. The motor28receives operation requests in the form of an operating airflow volume, or operational motor torque, over the motor bus44from the HVAC unit assembly control24, and reports back its operating speed, or operational motor torque via the motor bus44to the HVAC unit assembly control24.

In one embodiment, the system controller22includes a computing element46that further includes a second microprocessor48and a second memory50, and may be, for example, capable of storing and reading input data, performing calculations, and reporting the results of calculations. In one embodiment, the system controller22includes a user interface element52, such as a graphical user interface (GUI), a touch screen display, a LCD display, or other means by which a user of the HVAC system10can be apprised of system status and/or particular characteristics of the system (such as static pressure). The system controller22also optionally has a user input element54, such as a keypad, keyboard, touch screen or other data input means, which allows a user of the HVAC system10to change the operation of the HVAC system10. In one embodiment, the system controller22may in communication with a remote device, such as a mobile phone, and the user interface element52and user input element may be located on the remote device.

FIG. 3illustrates a method100for determining duct leakage in an HVAC system10. The method100includes the step102of operating the system controller22to determine system leakage data. In an embodiment, as shown inFIG. 4, operating the system controller22to determine system leakage data includes step202of restricting airflow in the at least one supply air conduit14and the at least one return air conduit18, and step204of operating the blower system26at a plurality of motor parameters to generate system static pressure data and system airflow data. In an embodiment, the plurality of motor parameters includes at least one of a plurality of motor torques and a plurality of motor speeds.

Airflow may be restricted in the at least one supply air conduit14by closing or sealing each of the at least one supply register vents16A-C, and airflow may be restricted in the at least one return air conduits18by closing or sealing the at least one return register vent20. The system leakage data in a section of the HVAC system10external to the HVAC unit assembly12is determined by the system controller22in one embodiment, although the determination of the system leakage data could be performed at any number of locations in the HVAC system10that include processing devices, such as at the HVAC unit assembly control24, or a remote device in communication with the HVAC system10, such as a mobile phone.

In order for system controller22to determine the system leakage data in the illustrative embodiment shown inFIG. 2, system controller22first receives a value for system volume airflow rate (of air flowing through the HVAC system10), and values for blower diameter and blower speed from the HVAC unit assembly control24over the system bus42. In one embodiment, the HVAC unit assembly control24commands the blower system26to operate at a plurality of motor parameters (e.g., three different operational motor torques or three different airflow rates to name a couple of non-limiting examples) to determine the system leakage data across the HVAC system10.

The values for system volume airflow rate, blower diameter, and blower speed could be stored in the second memory50of the system controller22long before calculation, though in some embodiments, these values, especially for system volume airflow rate and blower speed, are received at the system controller22from the HVAC unit assembly control24contemporaneously, or nearly contemporaneously, with the determination of the system static pressure data by the system controller22. As is known in the art, the system controller22employs an algorithm including unit characteristic constants from the HVAC unit assembly control24to determine the system static pressure data external to the HVAC unit assembly12.

The method100further includes the step104of operating the system controller22to determine supply leakage data. In an embodiment, as shown inFIG. 5, operating the system controller22to determine supply leakage data includes step302of opening the blower compartment door13and step304of operating the blower system26at a plurality of motor parameters to generate supply static pressure data and supply airflow data.

Opening the blower compartment door13allows the system controller22to determine the leakage flow rate of the at least one supply conduit14because the airflow from the at least one return conduit18is allowed to escape through the blower compartment door13. After the system controller22completes step102of determining the system leakage data, the HVAC installer may open or remove the blower compartment door13, and operate the system controller22to direct the blower system26to operate at different operational motor torques to determine the supply static pressure data and supply airflow data.

The method100further includes step106of operating the system controller22to determine a duct leakage measurement, for the system10, based in part on the system leakage data and the supply leakage data. In an embodiment, as shown inFIG. 6, determining a duct leakage measurement includes step402of operating the system controller22to determine a leakage supply airflow value at a pre-determined leakage static pressure value. In an embodiment, the pre-determined leakage static pressure value is approximately 0.1 inch water column. It will be appreciated that the pre-determined leakage static pressure value of approximately 0.1 inch water column was chosen based on the present standard for measuring duct leakage; however, the pre-determined leakage static pressure value may be greater than or less than approximately 0.1 inch water column.

Determining a duct leakage measurement further includes step404of operating the system controller22to determine a leakage system static pressure value based on the leakage supply airflow value, step406of operating the system controller22to determine a leakage return static pressure based on the leakage supply airflow at the pre-determined leakage static pressure value, step408of operating the system controller22to determine a return flow constant based on the leakage return static pressure and the leakage supply airflow at the pre-determined leakage static pressure value. The flow constant is derived from a flow and system pressure curve as a function of power-law. Determining a duct leakage measurement further includes step410of operating the system controller22to determine a leakage return airflow at the pre-determined leakage static pressure value based on the return flow constant, and step412of operating the system controller22to determine a system leakage value based on the leakage return airflow and the leakage supply airflow.

An example of the method100may be such that an HVAC installer closes or seals the at least one supply register vents16A-C and the at least one return register vent20. The HVAC installer operates the system controller22and blower system26to determine system leakage data (e.g., system static pressure and system airflow data) by operating the blower system26at three different operational torques.

As shown in the illustrative chart ofFIG. 7, with airflow shown on the x-axis, and static pressure shown on the y-axis, system leakage data points60,62, and64are created from operating the blower system26at three different operational torques with restricting airflow in the at least one supply air conduit and the at least one return air conduit with the blower compartment door13closed. Data point60shows an airflow of approximately 60 SCFM at an ESP of approximately 0.84 inch water column, data point62shows airflow of approximately 50 SCFM at an ESP of approximately 0.62 inch water column, and point64shows an airflow of approximately 46 SCFM at an ESP of approximately 0.44 inch water column.

The HVAC installer opens or removes the blower compartment door13, and operates the system controller22and blower system26to determine supply leakage data (e.g., supply static pressure and supply airflow data) by operating the blower system26at three new operational torques. The system controller22determines a leakage supply airflow value at approximately 0.1 inch water column by using the supply static pressure and supply airflow data, and fan law and system curve principles.

As shown in the illustrative chart ofFIG. 7, with airflow shown on the x-axis, and static pressure shown on the y-axis, supply leakage data points50,52, and54. Data point50shows an airflow of approximately 95 standard cubic feet per minute (SCFM) at an external static pressure (ESP) of approximately 0.57 inch water column, data point52shows an airflow of approximately 80 SCFM at an ESP of approximately 0.42 inch water column, and data point54shows an airflow of approximately 60 SCFM at an ESP of approximately 0.25 inch water column. Line56is derived from data points50,52, and54using the equation:
P=K×Qn

Where P is the external static pressure, K is the flow constant, Q is the airflow. Using best fit techniques with data points50,52, and54, K and n are computed to be 1.91×10−4and 1.775, respectively. In an embodiment, n may be a value greater than or equal to approximately 1.5 and less than or equal to approximately 2.5. It will be appreciated that n may be a value less than approximately 1.5 or greater than 2.5. Line56is used to determine data point58indicating a leakage supply airflow value (e.g., approximately 34 SCFM) at an external static pressure of approximately 0.1 inch water column. It will be appreciated that the order of determining system leakage data and supply leakage data may be reversed.

The system controller22determines a leakage system static pressure value based on the pre-determined leakage static pressure value and the leakage system static pressure. Using the aforementioned equation, line66is derived from data points60,62, and64to determine data point68indicating a leakage system static pressure value at the same airflow as the leakage supply airflow (e.g., approximately 34 SCFM). In this instance, the leakage system static pressure value is approximately 0.26 inch water column.

It will be appreciated that in a balanced HVAC system10the total system static pressure is equal to the static pressure on the supply side plus the static pressure on the return side, or illustrated by the equation:
PT=PS+PR

Therefore, to have an airflow of approximately 34 SCFM in the at least one return conduit18, the static pressure in the at least one return conduit18, PR, would need to equal approximately 0.16 inch water column (0.16=0.26−0.1).

The system controller22determines a return flow constant based on the leakage return static pressure and the leakage supply airflow at the pre-determined leakage static pressure value. The return flow constant may be determined by the equation:
KR=PR/QS0.1n=0.16/341.7775=3.06×10−4

The system controller22further determines a leakage return airflow at the pre-determined leakage static pressure value based on the return flow constant. The leakage return airflow may be determined by the equation:

Therefore, the leakage return airflow at 0.1 inch is approximately 26 SCFM. Now that the leakage return airflow has been established, the system controller22can determine a system leakage value based on the leakage return airflow and the leakage supply airflow. The system leakage value is may be determined by the equation:
QTOT0.1=QS0.1+QR0.1

Therefore, the determined system leakage for the HVAC system10is approximately 60 SCFM at an external static pressure of approximately 0.1 inch water column in the at one supply conduit14and the at least one return conduit18.

It will be appreciated that the system controller22may perform an autonomous test to determine the duct leakage measurement of the HVAC system10without the need of external equipment; thus, reducing the time to verify the system leakage of the HVAC system10.