Oliver Solcher
Bibliographic info:
12th International BUILDAIR Symposium, 25-26 June 2021

Purpose of the work
In residential construction a large number of decentralized air handling units which work alternately in pairs and (thus also referred to as push/pull units) is used to serve the apartments. These ventilation systems ensure the exchange of air in residential buildings, while at the same time reducing ventilation heat losses. These air handling units are intended to ensure a regulated exchange of air but are also equipped with regenerative heat exchangers which allow for exhaust air heat recovery.
Since the air handling units work with axial fans, their resistance to pressure is very low. The building facades are subjected to indoor and outdoor pressure differentials due to wind impact and temperature differentials. As the air handling units are installed in external walls they are subjected to the same differential pressure.
These air handling units revert the direction of flow in short intervals of 1 to 2 minutes, which means that the differential pressures applied to the facade act in and against the direction of flow. Manufacturers test the air handling units in accordance with DIN EN 13141-8, which also includes a wind pressure sensitivity test of the air flow based on a pressure difference of ± 20 Pa. The air exchange rate of most units on the market exceeds the maximum of 30% under such wind pressures. The supply and extract airflow rate of the pair of air handling units under investigation does not exceed the maximum of 30 % which has been proven by the technical approval granted by the DIBt (technical authority and a service provider for the construction sector). This pair of units is used to quantify the volume flow deviation of a pair of alternating air handling units when it is subjected to the real differential pressures of a building.
Method of approach
A pair of two alternately working air handling units is built into a free-standing test bench. A continuous measurement is done of the volume flow, wind speed and direction as well as of the differential pressures on the facades where the air handling units are installed.
Content of the contribution
Presentation of the question - presentation of the measurement setup - presentation of the measurement results.
Results and assessment of their significance
The measurement took place in Spring 2021, which is why we cannot present a summary of the results just yet.

For further information please contact Dipl.-Ing. (FH) Oliver Solcher at: solcher@waermetauscher.com