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Purpose of the work
The study presented in 2019 on paired, alternating air handling units (push/pull units) found that wind load peaks can have an impact of up to 100 Pascal of differential pressure on air handlers. Yet, these units can only be tested up to a pressure sensitivity of 20 Pascal. The building authority DIBt specifies in its technical approvals that the range of application is set to a differential pressure of 0 Pascal of for these devices. During the follow-up investigation, we captured the characteristic curves of the air handlers at all speeds under simulated wind loads. In addition, we analyzed how often wind-induced differential pressures occurred and used these findings to estimate the ventilation efficiency of air handlers running at different speeds under wind load. Ultimately, we are seeking an answer to the question as to whether a pair of alternately operating air handling units is fit for energy-efficient ventilation of residential buildings due to its sensitivity to wind.
Method of approach
Two push/pull unites working in pairs are installed in a stand-alone specimen. The air flow of the pair of push/pull units is continuously measured while simulating constant wind loads at all air handler speeds. The frequency of the wind-induced differential pressures is then used to draw conclusions on the ventilation efficiency of these air handlers.
Content of the contribution
- Present the issue
- Present the measurement setup
- Present the test results
- Evaluation of results and conclusions
Results and assessment of their significance
Air handling units operating in pairs will only be able to maintain an air flow deviation of 30 % at a wind-induced differential pressure of 20 Pascal when running at the highest speed. At 75%, 50 %, and 25 % of maximum air flow, their pressure stability drops to nearly 0 Pascal. Since the evaluation of the wind load frequency hasn’t been carried out yet, we are not yet able to state how often the air handlers are unbalanced.
Conclusions
Nevertheless, we can make the following statement: Since these devices generally run at the lowest speed due to their noise emissions, a differential pressure of 2 Pascals is sufficient to seriously disrupt an energy-efficient operation of this ventilation system.
For further information please contact Oliver Solcher at: mail@oliversolcher.de