High Efficiency Single Duct Terminal Unit

This application claims priority benefit of the United States Provisional Patent Application titled, “HIGH EFFICIENCY SINGLE DUCT TERMINAL UNIT” filed on Apr. 22, 2024 and having Ser. No. 63/636,975. The subject matter of this related application is hereby incorporated herein by reference.

The various embodiments relate generally to heating, ventilation, and air- conditioning (HVAC) technologies and, more specifically, to a high efficiency single duct terminal unit.

Single duct terminal units are a component in HVAC systems, delivering and regulating conditioned air in commercial environments. Typically, these units are constructed with a sensing element that monitors the ambient or outside temperature, a heating element that warms the air within the unit, and a damper that controls the flow of the air exiting the unit. To create heated air, oftentimes these systems utilize hot water which is then circulated through the heating element, where it acts as the primary medium for transporting thermal energy. Its high specific heat capacity allows it to store and release heat efficiently. Given the prevalence of single duct terminal units, improvements in energy efficiency can lead to considerable reductions in energy consumption and operating costs. This issue is more pronounced in systems operating at lower hot water supply temperatures, where even minor variations in airflow can result in significant heating capacity losses

Conventional single-duct terminal units often employ a design where the damper is positioned upstream relative to the heating element. Such an approach regulates airflow prior to the air being heated by the heating element. Conventional construction methods have led to variability in air inlet sizes and outlet configurations. Because the ratio between the air inlet and outlet diameters directly influences airflow velocity, it becomes challenging to achieve ideal airflow conditions necessary for consistent heating performance. Fixed configurations only allow for specific airflow rates, yet a slower, more evenly mixed airflow is typically preferred for optimal heat distribution.

One drawback of conventional approaches to single-duct terminal units is that placing a damper upstream of the heating element to regulate airflow exiting the unit causes the heating element to receive an uneven mix of air, leading to potentially inaccurate temperature readings. As the damper closes, it creates air turbulence resulting in inefficient heat transfer from the heat source (hot water) to the heat sink (cold air). Moreover, to meet ASHRAE 90.1 and IECC standards, these systems are designed to operate with closed dampers during heating, which restricts airflow to only 50% of the unit's maximum capacity. This regulatory requirement, while ensuring energy efficiency, further limits the volume of air available for effective heat exchange, compounding the turbulence issues already present. This inefficiency not only increases energy consumption but also contributes to a larger environmental impact, highlighting the need for improved designs that can maintain stable efficiency under varying damper settings.

Another drawback of conventional single-duct terminal units is the fixed air inlet and outlet configuration that is typically employed, which restricts the range of airflow that can be achieved. This is coupled with the issue that traditional systems suffer from temperature stratification within the discharge ductwork, where uneven mixing of heated air leads to variable temperatures along the duct. Fixed air inlet configuration designs prevent the optimization of airflow dynamics, resulting in a system that often fails to provide the ideal air flow required for efficient heat transfer. Consequently, conventional single-duct terminal units are not only inefficient but also suffer from inconsistent performance in dynamic building environments.

As the foregoing illustrates, what is needed in the art are more effective techniques for implementing single-duct terminal units.

One embodiment sets forth a high-efficiency single duct terminal unit that improves the delivery and control of conditioned air in building HVAC systems. According to some embodiments, the unit comprises an air inlet configured to receive air from a central air handler, a heat exchanger designed to heat the incoming air, and a sensing element to monitor parameters such as airflow and ambient temperature. Notably, the unit is constructed with a damper positioned downstream of the heat exchanger to ensure uniform air distribution over the heating element. In some embodiments, the design further incorporates a configuration for utilizing an upsized outlet where the outlet diameter is greater than that of the air inlet diameter.

One technical advantage of the disclosed techniques relative to the prior art is that repositioning a damper downstream of the heat exchanger in a single-duct terminal unit allows for undisturbed and even airflow over the heating element within the unit. By having more uniform airflow to the heating element, the system minimizes the likelihood of overshooting or undershooting the desired temperature, thereby enabling more responsive and finely tuned HVAC control.

A further technical advantage is that the damper acts as an air mixing element. As noted above, the damper acts as a source of inefficiency in conventional designs for the same reason. However, in the discussed embodiment the damper provides benefit to equipment application, as the mixing element is now downstream of the heat source, the damper creates a more uniform air temperature at the discharge of the product. Better mixing of heated air as it leaves the unit promotes more accurate temperature readings of the air exiting the unit. This means single point temperature sensors will take a more accurate measurement. Improved accuracy of temperature readings yields more precise control of the heating element as well as significant energy savings and lower operational costs.

A further technical advantage is that disclosed design overcomes the limitations of conventional fixed air inlet-outlet combinations and uneven mixing of heated air within the discharge ductwork. This step increase in size was determined to cause lower velocity air exiting the unit, allowing for a more even mixing of heated air outside the discharge ductwork.

Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.

In the following description, numerous specific details are set forth to provide a more thorough understanding of the various embodiments. However, it will be apparent to one skilled in the art that the inventive concepts may be practiced without one or more of these specific details.

illustrates an orthographic view of a single duct terminal unit, according to various embodiments of the disclosure. The single duct terminal unitincludes, without limitation, an air inlet, a flow sensor, a heat exchanger, a casing, a damper(shown in later figures), an air outlet, and a control unit. At a high level, the single duct terminal unitmoves air through the system in the direction of arrow. Specifically, air is directed through the air inletin which a flow sensoris disposed. The air is then heated by heat exchangerand passes through casing. Airflow is then regulated by the damperbefore exiting via the air outlet. The flow sensorand the damperare also connected to control unit, which houses electronics that receive data from flow sensorand other sources, such as temperature sensors or thermostats. The electronics in the control unitalso control the damper. This setup establishes a feedback loop, enabling precise control of the position of the damperbased on temperature data processed by the control unit.

The air inletcomprises an inlet through which air enters the single duct terminal unit. The air inletis coupled to ducting (not shown) through which air is supplied to the air inlet. In the depicted example, the air inletis configured as a circular opening and is affixed to a casing. In certain embodiments, air is directed into the unitthrough a duct system that is coupled to the air inlet.

A flow sensor, positioned in or near the air inlet, is configured to detect the airflow. The flow sensoris able to transmit sensor readings to the control unitvia signal tubing, enabling the control unitto determine airflow characteristics based on the sensor output. The flow sensormeasures total pressure and static pressure through the single duct terminal unit. The difference between these measurements is the velocity pressure signal, which is then used by the control unitto determine the air flow rate through the air inletand adjust the damperas needed to meet performance requirements. The control of air to the occupied space allows the desired set point temperature in the environment to be maintained. In the embodiment shown, flow sensoris positioned within the air inlet. In some embodiments, a temperature sensor can be integrated into the flow sensoror installed within air inletto provide the control unitwith temperature information about incoming air to the single duct terminal unit.

Heat exchangeris installed downstream of the air inletand upstream of the air outlet. Heat exchangeris designed to heat the air flowing through the air inletand towards the heat exchanger. Notably, at this point, the air is not yet subjected to any damping. In one example, the heat exchangercomprises water coils that utilize a fin and tube construction, allowing a water-glycol mixture to be circulated through the coils to transfer heat into the body of the single duct terminal unit.

The control unithouses the necessary circuitry to process both atmospheric temperature and flow sensor readings required to determine the optimal position of the damper. The control unitcontains the necessary mechanisms to adjust the damper position, thereby controlling the amount of heated air passing through the single duct terminal unit. The damper position represents the degree to which the damper is open or closed, i.e., the extent to which airflow is permitted through the air outlet. In the event that no air is to flow past the damper, the control unit rotates a rod connected to the damper such that the damper is oriented perpendicular to the airflow, thereby sealing the air passage. The control unit allows maximum airflow by rotating the rod such that the damper is parallel to the direction of airflow. In the case where a variable amount of air is required to control the temperature, the control unitrotates the rod to adjust the damper position to a state ranging from fully open to fully closed. The control unit may utilize various control methods, such as a feedback loop or other control mechanisms (but not limited thereto), to achieve a specified temperature or airflow, wherein the damper is dynamically adjusted as the control unitdetects the room temperature approaching the desired temperature. In the illustrated embodiment, a control unitis coupled to the casing. The control unitcontrols whether the heat exchangerheats air entering the air inletthat flows through the single duct terminal unit. Control unitalso controls the degree to which heat exchangerheats air passing through the unit depending upon the heating needs of a space to which air flows from single duct terminal unit. Control unitreceives temperature and/or airflow data from flow sensoras well as temperature data from one or more temperature sensors that can be positioned in air outletor downstream of the air outlet. Control unitcan also receive a requested temperature from a thermostat control that obtains temperature data from an environment receiving airflow from single duct terminal unitand allows for users to set a requested temperature for the environment.

The casingprovides an exterior shell in which the heat exchangeris installed and through which air flows from the air inletto the air outlet. In some embodiments, the casingis provided with thermal and acoustic insulation to minimize noise generation and reduce undesired heat transfer between the interior of the single duct terminal unitand the exterior environment. Moreover, the casingis designed to be substantially airtight, thereby directing airflow from the air inletto the air outlet, as will be described in greater detail in subsequent figures. The depicted casinghas a generally rectangular cross-section, although alternative geometries for both the air inletand the casingcan be employed.

shows an opposing side of single duct terminal unitrelative to. Specifically, arrowshows the direction of air flow, as it is exhausted by the air outlet. The air outletdischarges air that has passed through the single-duct terminal unit. The quantity of airflow is partially controlled by the damper, which is illustrated inand further described in the corresponding discussion. The exhausted air from the air outletcan either be released into the room's ambient environment or directed into another duct for further transport to a designated heating area.

Terminal unitis designed to accommodate a wider range of air inlet and outlet configurations. This is advantageous because manufacturers often provide only specific sizes for these components, limiting flexibility. The illustrated embodiment of the single-duct air terminal unitcan accommodate an outlet diameter that is 12.5% to 25% larger than the air inlet diameter. By sizing the air outletlarger than the air inlet, the air velocity at the air outletis reduced compared to the air inlet. By upsizing the air outletrelative to the air inlet, the air exiting the single duct terminal unitis more thoroughly mixed than in embodiments that have similarly sized inlets and outlets. As air moves more slowly through the unit, the air has more time to mix uniformly, resulting in more homogeneous mix of air as it leaves the system. This slower flow is a direct result of the ratio between the air inletand the air outlet: as the cross-sectional area of the fluid increases at the air outlet, the air velocity decreases (per the continuity principle), allowing the air molecules more time to interact and mix together before exiting the system.

illustrates a partially transparent orthographic view of a single duct terminal unit, according to examples of the present disclosure. In the depicted view, the casingis rendered as partially transparent to reveal the interior of the single duct terminal unit. Air entering the air inletfollows the direction indicated by arrow, passes through the flow sensor, and is subsequently heated by the heat exchanger.

After passing through the heat exchanger, airflow is then regulated by the damper, which is positioned downstream of the heat exchanger. The damperis configured to rotate about an axis, with its rotational position controlled by the control unit. The damperis operatively connected to the control unitvia a rod whose position is adjusted by the control unit, enabling the position of the damperto vary continuously from a fully closed configuration, wherein the damper is oriented substantially perpendicular to the direction of airflow, to a fully open configuration, wherein the damper is aligned parallel to the airflow through the single duct terminal unit.

By positioning the damperdownstream of the heat exchanger, air flows evenly over the heat exchangerin contrast to prior art configurations where the damperis positioned upstream of the heat exchanger. In prior art configurations, the damper deflects the airflow prior to reaching the heat exchanger, resulting in uneven distribution of heated air across the surface of the heat exchanger, inaccurate temperature measurements, and reduced efficiency in thermal control. The air inlet, air outlet, and damperare depicted with a circular cross section in one embodiment. One or more of the air inlet, air outlet, and dampercan be implemented with a different cross-sectional shape, such as an elliptical, square, rectangular, or other cross-sectional shape.

illustrates an alternative view of a single duct terminal unitwith the casingremoved, according to various embodiments of the present disclosure. In this view, another perspective of the damperis provided.

illustrates a front view of the single duct terminal unit, with the flow sensorshown located within the air inlet. As shown in the other figures and corresponding descriptions, the flow sensorprovides data used by the control unitto calculate the airflow to the unit.

illustrates a rear view of the single duct terminal unit, showing the damperlocated within the outlet. In this view, the damperis closed, restricting the airflow and controlling the volume of air delivered to the space served by the single duct terminal unit.

illustrates a method according to various embodiments of the disclosure. The method can be implemented using the single duct terminal unitdiscussed with reference to. According to one embodiment, the methodbegins at step, where the control unitreceives a requested temperature associated with an environment to which single duct terminal unitdelivers heated airflow. For example, the environment includes a room to which air outletof single duct terminal unitis connected via ducting. The requested temperature can be received from a thermostat or another control system that determines whether the single duct terminal unitshould deliver heated air to the environment. In one embodiment, control unitreceives temperature data associated with an environment, and the control unitdetermines whether and to what extent single duct terminal unitshould deliver heated air to the environment.

At step, control unitdetermines a measure of airflow into the single duct terminal unitvia air inlet. The control unitobtains data from flow sensorto determines how much air is flowing into the single duct terminal unit. The airflow can be provided by an air handler or another unit tasked with providing airflow to the single duct terminal unitin the HVAC system associated with the environment.

At step, control unitdetermines a temperature of the airflow into the air inlet. Flow sensorcan be equipped with a temperature sensor, or a separate temperature sensor can be disposed within or adjacent to air inlet. At step, control unitdetermines a setting for heat exchangerthat determines to what extent the heat exchanger heats airflow that has entered air inletand the casing. The control unitdetermines the setting for heat exchangerbased on the temperature of the air entering air inlet, the volume or velocity of airflow into the air inlet, and the requested temperature associated with the environment. At step, control unitdetermines a damper setting for damperbased on the heat exchanger setting and the requested or desired temperature in the environment to which single duct terminal unitis configured to deliver heated airflow. As noted above, the damperis downstream of the heat exchanger, which is downstream of the air inlet. In some embodiments, damperis disposed within or integrated within air outlet.

In sum, the various embodiments shown and provided herein set forth a high-efficiency single duct terminal unit that addresses the limitations of conventional systems. In one embodiment, the unit incorporates a damper positioned downstream of the heat exchanger to promote uniform airflow over the heating element, thereby enhancing heat transfer and reducing temperature discrepancies. In addition, the unit is designed with an optimized air inlet and outlet configuration, where the outlet diameter exceeds the inlet diameter, to lower airflow velocity and foster more thorough mixing of heated air. These design features collectively yield improved temperature accuracy, more precise control of the heating element, and significant energy savings.

One technical advantage of the disclosed techniques relative to the prior art is that repositioning a damper downstream of the heat exchanger in a single-duct terminal unit allows for undisturbed and even airflow over the heating element within the unit. By having more uniform airflow to the heating element, the system minimizes the likelihood of overshooting or undershooting the desired temperature, thereby enabling more responsive and finely tuned HVAC control.

A further technical advantage is that the damper acts as an air mixing element. As noted above, the damper acts as a source of inefficiency in conventional designs for the same reason. However, in the discussed embodiment the damper provides benefit to equipment application, as the mixing element is now downstream of the heat source, the damper creates a more uniform air temperature at the discharge of the product. Better mixing of heated air as it leaves the unit promotes more accurate temperature readings of the air exiting the unit. This means single point temperature sensors will take a more accurate measurement. Improved accuracy of temperature readings yields more precise control of the heating element as well as significant energy savings and lower operational costs.

A further technical advantage is that disclosed design overcomes the limitations of conventional fixed air inlet-outlet combinations and uneven mixing of heated air within the discharge ductwork. This step increase in size was determined to cause lower velocity air exiting the unit, allowing for a more even mixing of heated air outside the discharge ductwork.

1. In some embodiments, a single duct terminal unit comprises an air inlet coupled to a casing that allows air to enter the casing, a heat exchanger disposed within the casing and downstream of the inlet relative to airflow entering the casing, a damper disposed downstream of the heat exchanger relative to the airflow entering the casing, the damper controlling airflow through an air outlet, and a control unit in communication with the damper, wherein the control unit adjusts a positioning of the damper based upon airflow through the air inlet and a requested temperature of airflow through the air outlet.

2. The single duct terminal unit of clause 1, wherein the air inlet is sized smaller than the air outlet.

3. The single duct terminal unit of clauses 1 or 2, wherein the air inlet and air outlet comprise a circular cross section.

4. The single duct terminal unit of any of clauses 1-3, wherein a diameter of the air outlet is approximately 12.5% to 25% larger than a diameter of the air inlet.

5. The single duct terminal unit of any of clauses 1-4, wherein the air outlet is disposed downstream of the heat exchanger relative to airflow entering the casing.

6. The single duct terminal of any of clauses 1-5, wherein the air outlet comprises a cylindrical outlet coupled to the casing, and the damper is disposed within the air outlet.

7. The single duct terminal unit of any of clauses 1-6, further comprising a flow sensor disposed within the air inlet or the casing, the flow sensor communicatively coupled to the control unit and configured to detect airflow through the air inlet.

8. The single duct terminal unit of any of clauses 1-7, further comprising a temperature sensor disposed within the air inlet, wherein the temperature sensor provides inlet temperature data to the control unit.

9. The single duct terminal unit of any of clauses 1-8, further comprising an outlet temperature sensor disposed within the air outlet or downstream of the air outlet, wherein the temperature sensor provides outlet temperature data to the control unit.

10. The single duct terminal unit of any of clauses 1-9, wherein the heat exchanger comprises a plurality of water coils that utilize a fin and tube construction.

11. The single duct terminal unit of any of clauses 1-10, wherein the control unit adjusts the positioning of the damper in response to a requested temperature from a thermostat associated with an environment receiving airflow from the air outlet.

12. In some embodiments, a method comprises receiving, in a control unit, a requested temperature associated with an environment, determining, in the control unit, a measure of airflow into an air inlet of a single duct terminal unit based on data from an airflow sensor, determining, in the control unit, a temperature of airflow into the air inlet, determining, in the control unit based on the measure of the airflow and the temperature, a setting for a heat exchanger disposed downstream of the air inlet and upstream of a damper, determining, in the control unit based on the measure of the airflow, the temperature, and the setting for the heat exchanger, a damper position of a damper located downstream of the air inlet and the heat exchanger, and causing, by the control unit, the damper to be position at the damper position and the heat exchanger to activate according to the setting for the heat exchanger.

13. The method of clause 12, wherein the damper is positioned within an air outlet of the single duct terminal unit.

14. In some embodiments, a method of clauses 12 or 13, wherein the control unit determines the damper position and the setting for the heat exchanger based on temperature data from a temperature sensor in the air outlet or downstream of the damper.

Any and all combinations of any of the claim elements recited in any of the claims and/or any elements described in this application, in any fashion, fall within the contemplated scope of the present invention and protection.

The descriptions of the various embodiments have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.