What is U-value?
U-value insulation

Building Insulation Quality Indicator: What is U-value?


This short review aims to answer the following question: What is U-value? Discover the U-value definition, working principle, applications and how to measure it in 6 steps!


Introduction


This short article presents how to perform an accurate and reproducible U-value measurement with greenTEG’s U-value development kit.


What is the U-value?


U-value is the term used to describe the heat transfer coefficient of a building element (e.g. of a wall). The U-value describes the insulation quality of a building. The unit of the U-value is W/(m²K). The lower a U-value, the better the insulation quality of the building element.

What is the equipment required to perform this measurement?


The following equipment is required to measure the U-value of a building or the building envelope energy performance:

U value kit
greenTEG’s U-value kit
goms II
gOMS II – Wireless U-Value Measurement

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Want to understand more about greenTEG’s U-Value measurement solutions? Explore more about our products and their features by clicking on the image to the right!


For which use cases can this measurement can be employed ?


U-value measurement

Typical applications include measurement of building insulation, windows, and various industry driven R&D fields.

Thermal energy enters buildings mainly from the heating system and from solar irradiation.

The energy exchange between the building and the outside is focused through the roof, walls, windows, and thermal bridges e.g. balconies, into the soil, and through exchange of ambient air.

Every building is a complex thermal system and to optimize these systems (for example to reduce heating costs), precise data is required.

As the measurement set up for glass differs due its low thermal capacity to the influence of radiation for opaque materials.


  • Assessing the status quo : A precise status quo assessment of the U-value before a refurbishment increases the quality of the overall planning.
  • Check before project handover : In case of dispute between project partners, a non-invasive U-value measurement can increase the transparency between the project partners.
  • Heat bridge and mold detection : Dew point assessment via room humidity and surface temperature measurement. Quantitative assessment of heat bridges via U-value measurement.
  • Applications in R&D, quality control : Exact measurement tool for U-value measurement in R&D of new insulation materials. Tool for quality control in the production of insulation materials

Discover our full set of application notes, case studies and whitepapers in our download & PDF section available here.


How to measure the U-value of a building?


Building performance evaluation with greenTEG’s U-value kit


Advantages

  • Easy to mount: with normal adhesive tape to fix the sensor to any wall or window.
  • Easy to transport with its transportation box.
  • Real-time measurement directly on your laptop.
  • Fast measurement: without following the ISO guidelines, the measurement is performed in less than an hour.
  • Easy analysis with our user-friendly software!
  • Versatile equipment various applications.
U value kit

Our measurement-approach uses a heat flux sensor and two temperature sensors (see image below). This approach is standardized in ISO 9869, ASTM C1046 and ASTM C1155. This is the only method which delivers reliable quantitative in-situ information about a building envelope. Read about a U-Value measurement with our gSKIN® U-Value KIT in a case study from ETH Zurich. In a study sponsored by the Swiss Federal Office of Energy and conducted by Hässig Sustech, the gSKIN® U-Value Kit was used to measure the insulation quality of walls in older buildings. The English abstract is available on page 3 of the study which can be accessed here. We also offer a cloud-based, wireless solution for U-value, R-value, and temperature measurements.



Six-step protocol to measure your building insulation performance


U-Value-Measurement
U-Value-Measurement
U-Value-Measurement

Choose an optimal measurement spot on the building element of interest.

On the inside of this spot, place the heat flux sensor, and one temperature sensor.

On the outside of this spot, place the second temperature sensor.

U-Value-Measurement
U-Value-Measurement
U-Value-Measurement

Connect all three sensors to the data logging unit.

Start the measurement process (via your Laptop).

Evaluate the U-value of the wall element with the software included .


They trusted our equipment for their project


The Swiss Federal Office of Energy supported us with its expertise during the development of our technology. In 2010, greenTEG got certified by the Commission for Technology and Innovation (CTI). Together with our partner Climate KIC we exhibit our technology at the Umweltarena Spreitenbach.


Other measurement techniques reviewed


To differentiate our measurement-approach from other often applied approaches we reviewed the most common ones:


Table Look-up (Building Catalogue)
There are complex databases containing λ-Values of generic building elements ordered by element material and/or year of construction. With these databases, the U-value of a building envelope (e.g. wall) is calculated by adding all materials contained within the specific element (e.g. specific wall = 20cm concrete + 20cm glass wool). While this method is very simple and quick, it does not produce an accurate U-Value, only an approximation.


Thermography (i.e. Infrared imaging)
This approach shows the thermal radiation of an object and produces an image showing spots with higher and lower radiation. An infrared image gives only qualitative results, hence an U-value cannot be determined.


Multiple Temperature Measurement
This approach is based on three or more temperature measurements on both inside and outside of a building element. While this approach produces a U-Value, it needs a minimum temperature difference of 10 °C between the inside and outside to work and it is assumed that the thermal boundary resistance is constant.


Old Wall

Want to obtain the U-value for your Project?

Your measurement conditions may never be perfect. Our guide will give advice for your project’s unique set of circumstances.