Air Handling Unit Pressure Balancing Before Exhaust Air Mixing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing air handling unit systems lack control over flow direction and magnitude at the start of the mixing process due to uncontrolled pressure balance around the mixing damper, leading to potential incorrect flow direction and uncontrollable airflow.
Innovation Solution
A method that ensures a positive pressure on the exhaust air side is slightly higher than the supply air side before mixing begins, with adjustments made using either the exhaust air damper or outdoor air damper to maintain a pressure drop within a predetermined range, allowing for controlled flow direction and magnitude by synchronizing the operation of the mixing and outdoor air dampers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the mixing damper opens at the start of the mixing process without pressure control, then the mixing process can begin, but the flow direction may be incorrect and the flow magnitude becomes uncontrolled
Solution Approach 1:
The control system performs preliminary pressure balancing by adjusting the outdoor air damper or exhaust air damper before the mixing damper opens. This ensures that the pressure difference across the mixing damper is within the predetermined range (a-b to a+b Pa), thereby controlling the flow direction and magnitude before mixing actually begins.
2Stress or pressure
If the outdoor air damper is used to control pressure balance, then the pressure can be balanced, but the initial mixing flow becomes uncontrolled and potentially too large
Solution Approach 1:
The control system continuously monitors the pressure difference across the mixing damper using pressure sensors and provides feedback to the damper actuators. This closed-loop control ensures that the pressure difference remains within the predetermined range, thereby controlling the mixing flow magnitude while maintaining pressure balance.
3Stress or pressure
If the pressure difference across the mixing damper is too large, then the pressure balance is established, but the mixing flow becomes huge and uncontrolled
Solution Approach 1:
The control system changes the pressure difference parameter from a large uncontrolled value to a controlled value within the predetermined range (a-b to a+b Pa). This is achieved by adjusting the outdoor air damper or exhaust air damper to modify the pressure conditions, thereby controlling the mixing flow rate while maintaining adequate pressure difference for flow direction.
4Productivity
If the mixing damper opens quickly to achieve desired mixing ratio, then the mixing efficiency increases, but the flow direction control is lost during the transition
Solution Approach 1:
The control system performs preliminary pressure balancing and sets the outdoor air damper or exhaust air damper to appropriate positions before the mixing damper opens. This preliminary setup ensures that when the mixing damper opens quickly for efficient mixing, the flow direction remains controlled due to the pre-established pressure conditions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach ensures a controlled and soft start of the mixing process, maintaining optimal airflow direction and magnitude, preventing uncontrolled flow and ensuring a balanced mixture.
Implementation Method 1
wherein at least one first pressure sensor (18) is arranged for measurement of a first pressure drop (Δp 1 ) over the heat exchanger (8) and at least one second pressure sensor (19) is arranged for measurement of a second pressure drop (Δp 2 ) over the mixing damper (15)
Implementation Method 2
followed by a heat exchanger, after the heat exchanger a speed-controlled suction exhaust air fan
Implementation Method 3
a speed-controlled suction exhaust air fan with some kind of flow measurement device and finally an on/off-type extract air damper
Data Source
Figure 1
AI summary
Method for controlled admixture of a subset of exhaust air flow (1 ) into a supply air flow (2), at an air handling unit (3). At indicated need of exhaust air admixture firstly a positive pressure balance (Δρ2) over a mixing damper (15) is secured, i.e. that the pressure is higher on an exhaust air side (4) of the mixing damper (15) than on a supply air side (5) of the same, with the criteria Δρ2 > 0 Pa and a-b < Δρ2≤ a+b Pa, where a is a optional set value and b is a optional interval value. Balancing is performed by controlling either an exhaust air damper (6) or an outdoor air damper (12), where which damper (6, 12) regulating is determined by the actual operating point, i.e. actual pressures around the mixing damper (15). When balancing is stopped or a time for balancing has expired, the mixing process starts, whereby the mixing damper (15) and the outdoor damper (12) works in parallel and in opposite phase, until a desired value, and wherein the exhaust air fan (9) in parallel secures the correct flow in the exhaust air flow (1 ) by speed-control.