Testing decentralized, alternating ventilation units
With the purge air method, the heat recovery for balanced air mass flows can be determined for alternating, decentralized ventilation units. The uncertainties of the previously used ‘direct method’ due to inhomogeneous speed and temperature profiles at the outlet of the ventilation Units are bypassed by the purging air method and the measuring accuracy is higher. In addition, with the optional humidity conditioning, the humidity recovery can be determined. Further thermal characteristics are the air flow rate in alternating operation and the balance, which can also be determined with the test bench. The test bench is equipped with an auxiliary blower so that even continuously operating ventilation units can be measured with the direct method.
|Volume flow purge air||20…200 m³/h |
(± 1.0 % EV)
|Temperature purge air||7…21°C|
|Humidity purge air||10…92 % r.h.|
|Measurement accuracy volume flow||± 1 % MV|
The challenge – ‘alternating operation’
- Direct methods inaccurate
- Heat recovery not measurable
In decentralized split ventilation units, 2 units each work in pairs in an opposite, alternating operating mode. The opposite operation ensures the balance of incoming and outgoing air flows in the room. Alternating Operation allows regenerative storage in the ventilation units to be used for heat and humidity recovery.
Direct measuring methods for determining the temperature and speed directly at the outlet of the ventilation units are very inaccurate in the case of inhomogeneous temperature and flow conditions.
The solution – purge air method
- Conditioned purge air
- Measurement of thermal characteristics in alternating operation
The German research project EWWALT has evaluated the weaknesses of the direct measuring method for alternating ventilation units, which has been used approximately up to now, and proposed the scavenging air method as the test method of choice for the revised version of the standard based on the results. These results and calculations have already been considered and implemented in the scavenging air test bench of EP Ehrler Prüftechnik.