Temperature Measurement in Air Ducts - An Optimized Method for Solar Air Heaters
Abstract
Facing the fact that a growing number of companies are pushing the market for solar air heaters Fraunhofer ISE is developing and improving well defined and precise measuring methods to characterize such solar air heaters. This work is done within the project Luko-E1 with the aim to standardize tests not only regarding performance measurements but also regarding reliability testing. The thermal efficiency of the solar air heater depends mainly on the factors mass flow, irradiance, and temperature lift. One key element of high quality test results is an accurate measuring method of the temperature which are quite quite complicated to achieve within airstreams because of many influencing variables. In this paper the problematic of temperature measurements in air channels is discussed and two different air temperature measurement methods are compared. In the first method, the air temperature layers in the channel are mixed by an air blender, generating a uniform temperature profile according to the recommendations of ANSI ASHRAE 93. The second method determines the temperature using a net to homogenize the airstreams velocity in front of a temperature sensor which measures a mean value by integrating the temperature over its sensors length.