Measuring the effect of the heat flow through a chimney with different altitudes of a rescaled model and validating the results with TRNSYS, a computer-simulated model

Abstract

The thesis subject is: "Building Physics", specifically measuring the natural heat flow in an apartment building. The objective of all the measurements is to verify that, the longer a chimney gets in a building, the higher the flow through that specific chimney gets, this by adjusting different parameters from inside and outside the building, such as: wind velocity, temperature inside, surface of the window opening, etc. The flow was measured in two different ways. In the first an existing model with wooden walls of 1 cm thickness was used to do the measurements on. The model had the following dimensions: 1OO x 79 x 150 centimeters. There were 4 halogen lamps placed in the construction, and the only object that could cause the heat flow was the chimney, made of PVC. Next, the heat flow was measured when 1, 2, 3 or 4 lamps were turned on. This was measured by taking the temperature inside and outside the model and using an air velocity-meter that was placed on top of the chimney. Since there was no wind available, because the measurements were taken in a laboratory, another computer-simulated model was used to verify what happens when the wind velocity outside changes. To gauge the flow in the second method was more difficult because a new program was used, named TRNFLOW. This program is a function of TRNSYS17 and in this program we created a model that was similar with our re-scaled model. The results of the TRNSYS-program and the results of the measurements were similar. As expected, when the chimney increased in height, the heat flow also increased through the chimney. The opening of the windows didn't have a big effect on the results, but when the opening was very small the TRNSYS-program couldn't make a good simulation. What was very noticeable is that when the wind velocity outside increased above 3 m/s, the velocity through the longest chimney changed directly to the lowest flow, so the flow through the chimney is very sensitive for the wind velocity outside. Finally, for verifying the results, different methods were used: a mass balance was set up and the theory of Thermal Buoyancy was applied.