AIR HANDLING UNIT

Abstract

An air handling unit includes an air treatment unit for treating at least a part of the fresh air via a treatment that gives rise to a pressure drop as well as a mixing damper for controlling air flow between a return air pat, and a supply air path for allowing recycling of air from a return air inlet to a supply air outlet. A supply fan sensor is used for measuring a parameter associated with air flow across the supply fan. An air treatment unit sensor is used for measuring a pressure drop across the air treatment unit in the supply air path. The air handling unit has a control system in order to determine the rate of fresh air flow, as well as optionally other control functions.

Claims

1. An air handling unit comprising: a return air inlet for receiving return air; an exhaust air outlet for expelling exhaust air to atmosphere; a fresh air inlet for receiving fresh air from atmosphere; a supply air outlet for providing supply air; an air treatment unit for treating at least a part of the fresh air via a treatment device that gives rise to a pressure drop; an exhaust fan for urging air along a return air path from the return air inlet toward the exhaust air outlet; a supply fan for urging air along a supply air path from the fresh air inlet via the air treatment unit to the supply air outlet; a mixing damper for controlling air flow between the return air path and the supply air path and for allowing recycling of air from the return air inlet to the supply air outlet; a supply fan sensor for measuring a parameter associated with air flow across the supply fan; an exhaust fan sensor for measuring a parameter associated with air flow across the exhaust fan; an air treatment unit sensor for measuring a pressure drop across the air treatment unit in the supply air path; and a control system comprising a memory for data storage and a processor for determining operating parameters of the air handling unit, wherein the control system receives input from the supply fan sensor, the exhaust fan sensor, and the air treatment unit sensor, wherein the memory comprises stored air flow data concerning a relationship between a rate of fresh air flow at the fresh air inlet and the measured pressure drop across the air treatment unit, and wherein the processor is configured to use the stored air flow data and the measured pressure drop to determine the rate of fresh air flow.

2. An air handling unit as claimed in claim 1, wherein the control system is configured to perform a calibration process to obtain the stored air flow data, the calibration process including measuring the differential pressure at the air treatment unit with the mixing damper fully closed and the supply fan speed varying.

3. An air handling unit as claimed in claim 1, wherein the stored air flow data takes the form of a look-up table stored via the memory, whereby a given measurement of differential pressure measurement, dP, at the air treatment unit is linked with a particular fresh air flow.

4. An air handling unit as claimed in claim 1, wherein the stored air flow data takes the form of parameters for a formula, optionally including the formula itself as a part of the stored air data flow.

5. An air handling unit as claimed in claim 4, wherein the stored air flow data includes parameters for a formula for determining fresh air flow, Q, where the differential pressure dP is fitted to a curve of the form:
Q=(a1×dP{circumflex over ( )}b1)+(a2×dP{circumflex over ( )}b2)+(a3×dP{circumflex over ( )}b3)+ . . . +(an×dP{circumflex over ( )}bn)+ . . . +c where c, a1, a2, a3, . . . an are constants, where any of the constants c, a1, a2, a3, . . . an can be zero, and where b1, b2, b3, bn are integer values.

6. An air handling unit as claimed in claim 1, wherein the air treatment unit comprises a treatment device including the ability for heat and/or humidity transfer between the return air and the fresh air.

7. An air handling unit as claimed in claim 6, wherein the treatment device including the ability for heat and/or humidity transfer between the return air and the fresh air is a recovery wheel or a plate heat exchanger.

8. An air handling unit as claimed in claim 1, wherein the air treatment unit includes a filter for filtering of the fresh air.

9. An air handling unit as claimed in claim 1, wherein the exhaust fan is located close to the exhaust air outlet, with the air treatment unit in between the exhaust fan and the return air inlet; and the supply fan is located close to the supply air outlet, with the air treatment unit in between the supply fan and the fresh air inlet.

10. An air handling unit as claimed in claim 1, wherein the mixing damper is located in the return air path at a point between the return air inlet and the air treatment unit and configured to provide air to the supply air path at a point between the air treatment unit and the supply fan.

11. A HVAC system comprising the air handling unit of claim 1.

12. A method of use of an air handling unit of claim 1 to provide supply air within a HVAC system, wherein the use of the air handling unit comprises performing a calibration process to obtain the stored air flow data, the calibration process including measuring the differential pressure at the air treatment unit with the mixing damper fully closed and the supply fan speed varying.

13. The method as claimed in claim 12, comprising using an output of the supply fan sensor to determine a rate of air flow at the supply fan, varying the supply fan speed with the mixing damper closed, and thereby mapping known rates of air flow across the air treatment unit against the pressure drop measured by the air treatment unit sensor.

14. The method as claimed in claim 13 including determining a relationship between the pressure drop at the air treatment unit and the air flow through the air treatment unit and thereby determining air flow data to store at the memory as the stored air flow data; and optionally comprising repeating the calibration process during later use of the air handling unit in order to update the stored air flow data.

15. A computer programme product comprising instructions that, when executed on an air handling unit as claimed in claim 1, will cause the control system of the air handling unit to perform a method including a calibration process including measuring the differential pressure at the air treatment unit with the mixing damper fully closed and the supply fan speed varying.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Certain embodiments of the present concept will be now be described by way of example only and with reference to the accompanying drawing in which:

[0032] FIG. 1 shows an air handling unit with mixing damper and air treatment unit.

DETAILED DESCRIPTION OF THE INVENTION

[0033] As seen in FIG. 1, an air handling unit 100 comprises a return air inlet 10 for receiving return air; an exhaust air outlet 12 for expelling exhaust air to atmosphere; a fresh air inlet 14 for receiving fresh air from atmosphere; and a supply air outlet 16 for providing supply air. A return air path 18, 20 extends from the return air inlet 10 toward the exhaust air outlet 12 and a supply air path 22, 24 extends from the fresh air inlet 14 via the air treatment unit 26 to the supply air outlet 16. The air paths may be within ducts separated by a wall.

[0034] Within the air handling unit 100 there is an air treatment unit 26 for treating at least a part of the fresh air via a treatment device that gives rise to a pressure drop. The air treatment unit 26 can include treatment device(s) for providing one or more of: heat and/or humidity transfer between the return air and the fresh air, filtering of the fresh air, or other treatments leading to a pressure drop for the fresh air. In the example of FIG. 1 this is a treatment device in the form of a recovery wheel 26 including the ability for heat and/or humidity transfer between the return air and the fresh air. The recovery wheel 26 is hence fluidly connected to the return air path 18, 20 and also fluidly connected to the supply air path 22, 24.

[0035] An air treatment unit sensor 38 is included for measurement of a pressure drop (e.g. differential pressure) over the air treatment unit 26, i.e. over the recovery wheel 26 of FIG. 1. This is used in order to determine air flows within the air treatment unit 26 as discussed further below.

[0036] In the return air path 18, 20 there is an exhaust fan 30 for urging air along the return air path 18, 20 toward the exhaust air outlet 12. In the supply air path 22, 24 there is a supply fan 28 for urging air along the supply air path 22, 24 from the fresh air inlet 14 and via the air treatment unit 26 to the supply air outlet 16. A supply fan sensor 32 can measure a parameter associated with air flow across the supply fan 28 and this measurement may be used to determine the rate of air flow at the supply fan 28. Similarly an exhaust fan sensor 34 can measure a parameter associated with air flow across the exhaust fan 30 and this measurement may be used to determine the rate of air flow at the exhaust fan 30. In this way, as is known in the art, data can be obtained concerning the air flow in the supply air path 22, 24 and the return air path 18, 20.

[0037] If the two air paths were sealed from one another, as is the case in some prior art systems, then the data from the fan sensors would be sufficient to know all of the air flows in the air handling unit 100. However, in this case the air handling unit 100 also includes a mixing damper 36 for controlling air flow between the return air path 18, 20 and the supply air path 22, 24 and for allowing recycling of air from the return air inlet 10 to the supply air outlet 16. With the mixing damper 36 open then air flow from the return air path 18, 20 to the supply air path 22, 24, such as for heat retention or to meet other user requirements. The result of this is that when using only the fan sensors it is not possible to determine all of the air flow rates, and for example the air flow rate for the return air 10 is no longer known, and neither is the air flow rate at the fresh air inlet 14.

[0038] To address this issue the present air handling unit 100 can make use of added data from the pressure drop over the air treatment unit 26. If this can give a measure of air flow at the air treatment unit 26 in the supply air path 22, 24 then the fresh air flow is known and then all of the air flows in the system can be derived. However, a problem arises in that the relationship between the pressure drop measured by the air treatment unit sensor 38 and the fresh air flow may vary for different air handling unit 100s and/or may change over time, e.g. as components wear or become dirty from use.

[0039] The air handling unit 100 proposed herein comprises a control system 50 comprising a memory for data storage and a processor for determining operating parameters of the air handling unit 100, wherein the control system 50 receives input from the supply fan sensor 32, the exhaust fan sensor 34, and the air treatment unit sensor 38. Advantageously, the memory includes stored air flow data concerning a relationship between a rate of fresh air flow at the fresh air inlet 14 and the measured pressure drop across the air treatment unit 26. This stored data can relate specifically to the unit in question and since the processor can be configured to use the stored air flow data and the measured pressure drop to determine the rate of fresh air flow then it becomes possible to derive all of the air flow rates for all of the inlets and outlets. This then allows for improved control of the speed of the exhaust fan 30 and/or the supply fan 28, even when the mixing damper 36 is fully or partly open.

[0040] The stored air flow data can be data that has been obtained by a calibration process including measuring the differential pressure at the air treatment unit 26 with the mixing damper 36 fully closed and the supply fan speed varying. Known rates of air flow across the air treatment unit 26 can be mapped against the pressure drop measured by the air treatment unit sensor 38. The calibration process can be performed quickly and easily to give air flow data that is specific for the air handling unit 100 and for its air treatment unit 26. The calibration process may be repeated periodically, e.g. during maintenance or inspection of the air handling unit 100, and/or when components are replaced or cleaned.

[0041] The calibration process can provide stored air flow data in the form of a look-up table stored via the memory. In this case then during use the control system 50 can use the look-up table to map given differential pressure measurement at the air treatment unit 26 with a particular fresh air flow rate.

[0042] The stored air flow data may alternatively involve fitting measurements of differential pressure, and the known air flow at the supply fan, to a curve or to a suitable predefined form of formula, and then storing the formula or parameters of the formula at the memory.

Q=(a1×dP{circumflex over ( )}b1)+(a2×dP{circumflex over ( )}b2)+(a3×dP{circumflex over ( )}b3)+ . . . +(an×dP{circumflex over ( )}bn)+ . . . +c [0043] where any of the constants c, a1, a2, a3, . . . an, etc. can be zero, such that the relevant term does not contribute to the end value of the air flow, Q, and where b1, b2, b3, bn are integer values, e.g. 1, 2, 3, . . . , n, or more generally may be any floating point value. In a simple example the stored air flow data may provide that:

Q=a×dP2+c

[0044] It will of course be appreciated that 2 may be replaced with any point value larger than zero.

[0045] A use for the air handling unit 100 is for air in a building. With this example the return air is from the building, e.g. from a conditioned space in the building, and the supply air is for the building, e.g. for the conditioned space in the building. The return air inlet 10 and supply air outlet 16 are connected to the conditioned space in building suitable ducts or other air flow passages. This can be a part of a building HVAC system. The air handling unit 100 can hence be used to provide supply air within a HVAC system such as a building HVAC system, with the control system 50 giving better control by ensuring that all the air flow rates are known, even when the mixing damper 36 is open. The calibration process to obtain the stored air flow data may be performed during first use of the air handling unit 100, e.g. upon installation/commissioning, and the calibration process can then be repeated during later use of the air handling unit 100 such as during maintenance or inspection of the air handling unit 100, and/or when components are replaced or cleaned.

[0046] The control system 50 includes a processor and memory and within the control system 50 software products can be used to configure it to operate as required herein. With an air handling unit 100 having the sensors and so on described herein then the control system 50 can be advantageously configured via a computer programme product to enable the air handling unit 100 to perform the calibration process and to thereafter use the stored air flow data as set out above.