Page 6 - proposallinks

DEMONSTRATION DETAILS

Heat Flux Principle & Method to Accurately Measure U-Value
Heat Flux Sensors are based on the Seebeck effect. When heat passes through the
sensor, the sensor generates a voltage signal. This voltage signal is proportional to
the heat passing through the sensor. greenTEG Heat Flux Sensors can resolve heat
fluxes < 0.01 W/m2.

In the field of building physics, U-Value is the term used to describe the
heat transfer coefficient of a building element (e.g. wall or window).
U-Value describes the insulation quality of a building. The unit of the
U-Value is W/(m²K). The smaller the U-Value, the better the insulation
quality of the building element.

How to measure U-value? The greenTEG measurement-approach uses a
heat flux sensor and two temperature sensors. 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. Placing sensors inside and
outside of a building, transmitting the data to nodes connected to the internet via a secure
gateway and then performing analytic calculations to convert to energy billing costs will provide a
convenient way for building owners to cost-justify investments that will reduce energy waste.
Why Is This an Advantage?
Energy audits that provide accurate information on ways to reduce waste are required to validate
subsidies, rebates and financing of energy saving improvements. Currently the time and expense
required, as well as personnel, certifications and equipment needed to conduct reliable audits limits

the number of audits that can be completed. Furthermore, the methods now being used do not
provide reliable real-time data. For example:

1. Thermography (i.e. infrared imaging) shows thermal radiation of an object as an image showing spots with
higher and lower radiation. Thermography helps to understand overall quality of a building envelope and
identify thermal bridges and sections with inadequate insulation. However, it does not produce quantitative
data (e.g. U-value in W/m2K) that can be used to interpret energy loss. Therefore, this method can only be used
to roughly approximate the U-value.

2. Multiple temperature measurements - By synchronizing three or more temperature sensors inside and outside
of a building element, it is possible to calculate the heat flux indirectly, and from this information, derive the U-
value of a building element. While this method generates quantitative data, it is not usable for in-situ
measurements. To apply this method, a minimum temperature difference of 10 °C between the inside and
outside temperature is required. Such temperature differences do not occur very often in most regions, and are
most likely not achieved continuously throughout the year. Moreover, both the inside and outside conditions
must be constant during the measurement period and no solar radiation is allowed. These requirements make it
very hard to obtain reliable data.

6