Portable low-cost device for U-value measurement

Project abstract

Mathematical modeling of building thermodynamic processes has become an integral part of modern building performance evaluation. In business, engineering, and many other fields, mathematical models of a building play a vital role to let things run. The development of such models is often based on available construction information and thermal properties of the building materials. Unfortunately, for many buildings such data are not available or there is a significant difference between documented and actual values. Swiss company GreenTEG has developed a device for measuring the thermal properties of walls that serves to measure the U-value defining the actual thermal properties of the building elements. The operation of the device is based on a heat flow sensor. An alternative, more cost-effective method of determining the thermal properties of walls is based on the analogy of thermal processes in buildings with electrical networks consisting of capacitors and resistors (so-called RC networks).

The implementation of the device is divided into the following mini projects. They could be studied independently (only certain mini project) or sequentially (mini project by mini project), based on the students’ preferences.

Mini projects

• As a first step towards the portable device for U-value measurement, it is necessary to define and develop the hardware and software configuration which enables precise temperature measurements of wall surfaces (at least 2 measurements) and measurements of air inside and outside the wall. The measurements should be collected with time resolution of 1 min and recorded into the individual CSV file. The data should be structured in a way which enables easy data processing.

• Based on the analogy between thermal processes in buildings and electrical RC networks it is required to develop the software routines for processing the experimental data and calculating the U-value of the selected building elements (walls or windows). The developed routines should be executed on a computer. The routines take a CSV file, perform the data analysis and as an output give the calculated U-value of the building element. To have a baseline for performance evaluation, the experiments for collecting the input data with the developed device should be conducted in parallel with the experiments with the GreenTEG device available in LARES. The duration of the experiment should be at least one week. After performing the experiments and processing the collected data – the obtained results should be compared to the results of GreenTEG device and values from building documentation if such exist.

• The developed device with the accompanied software routines for data processing could be utilized to measure thermal properties of all elements forming one zone (room). Based on the analogy of thermal processes in the buildings and electrical RC-network such measurements could be utilized to create mathematical model describing the temperature dynamics in the zone with respect to the external weather conditions (temperature, solar irradiance).  The performance of the model could be validated by using real measurements from the selected zone available from the LARES Living-lab on model predictive control covering all zones in FER skyscraper building. The developed model could serve as a basis for development of advanced model-based control algorithms or estimation of unmeasurable variables influencing the zone temperature (occupancy, heating and cooling devices, etc.). There is also possibility to deploy and test the developed algorithms in on-line operation within Living-lab environment.

Additional information

• Number of students: 1
• Keywords: smart buildings, Raspberry Pi, model-based control and monitoring, U-value, wall conductivity, thermal resistance, RC-network
• Useful links:
  • https://www.greenteg.com/