Measuring energy loss in buildings

Energy loss through walls

The effective measurement of heat flow through exterior walls is crucial to understanding the energy consumption and efficiency of any building. Environmental conditions determined by location, design, structural conditions, and the materials used in construction can all contribute to heat loss; influencing energy efficiency, and consequently, costs. Today it is well known that large discrepancies can occur between expected and actual energy loss through heat transfer, revealing flaws, or areas for improvement and re-design. With heat-flux sensors, it is possible to take on-site measurements, accurately and efficiently, for quality control and long-term monitoring.

MF-Series Heat flux sensors

EKO's MF-Series Heat flux sensors are perfectly suited for building thermal efficiency research, thanks to a flat thin design, optimised for minimum interference in most test conditions and areas. With some flexibility, they can also be applied to semi-curved surfaces. And with models available in different sizes and thicknesses, the MF-Series is suitable for indoor and outdoor applications.

HOW-TO Application Guide

1

Suitable Sensors

Select the right heat flux sensor for your application. The sensor must be chosen according to the conditions (e.g. required sensitivity) and the geometry (e.g. required size and shape). A smaller sensor can be selected when the surface space is limited; while larger sensors can be thinner, with a lower thermal resistance. Our largest sensor is extra sensitive, capable of capturing very small values of heat flux that are invisible to ordinary heat flux sensors. It's an ideal option when the surface size allows, and the surface structure or heat distribution is less uniform. It is important to note that for larger sensors, full contact with the surface is more critical. All EKO sensors are incredibly flat and thin, a significant advantage for minimum interference, but make sure you use a contact medium (e.g. thermal compound or conductive tape).

2

Thermal Properties

The thermal properties of construction materials are often unknown; however, they can be determined through on-site measurements using heat flux sensors. When the sensor is placed on top of a surface, heat flow as the sum of conduction, radiation, and convection heat fluxes are measured. Using physical models, properties such as thermal resistance, thermal transmittance, and thermal conductivity can be estimated. When the sensor is placed in between two surfaces inside an object with full contact, heat conduction can be measured.

3

Thermal Contact

When using heat flux sensors, the contact area between the sensor and the measured area is critical. If a heat flux sensor does not make good thermal contact with the surface, it will cause a local hot spot to form (or a cold spot in the case where the heat flux is negative) due to small airgaps. This hot spot will alter thermal gradients and change the overall heat transfer coefficient. Flat, layered sensors are usually mounted with a thermally conductive adhesive or paste to minimise contact resistance. Simply putting a sensor against a surface may still result in a heat flux reading, but the contact resistance will keep the reading from being accurate and meaningful.