Building Envelope blog posts
Superior energy efficiency through radiant heating and redimensioning of fresh air
| May. 5, 2020
Every schoolboy knows that air is a poor heat transfer medium, but it is still used for heating many supermarkets and halls. Ruukki was keen to make a serious study of the overall energy efficiency of large cavernous buildings. The apparent underlying reason for preferring air heating is that it can be set up in an easy and cost-effective way, as air conditioning units must be dimensioned for large ventilation volumes anyway.
Redimensioning of airflow in ventilation systems
HVAC designers generally determine air volumes by selecting the shortest route and applying standard guiding values instead of a demand-controlled approach. This leads to massive over-dimensioning of the outside airflow. Assuming that one person requires six litres of air per second, for example, the 2 l/s/m2 guideline value for retail outlets will provide enough fresh air for more than 3,300 people in a space of 10,000 square metres! Of course these fresh air volumes are immediately rationalised in practice by the carbon dioxide control that is often fitted in modern ventilation systems, but the capacity of the equipment itself is still inexplicably designed on the assumption of standard guiding values. It can even be greater in practice to make sure that there will also be enough heat on the coldest days.
Energy-efficient radiation-based heat distribution
We were keen to challenge this established practice and develop a system of radiation-based heat distribution that would be substantially more energy-efficient. The air conditioning equipment could then also be dimensioned simply to match the true need for fresh air. In practice this would mean that we could manage with air conditioning machines of no more than half the current size!
The benefits of a radiation-based heating approach seemed to grow as we studied this option in greater detail, and we were also keen to try it out in a new hall with an energy rating of almost zero constructed for HAMK Häme University of Applied Sciences. The radiation profile that we developed for integration into the roof structure of the pilot building was not only energy-efficient, but also aesthetically pleasing. We have been thoroughly satisfied with the trial, and hopefully we shall also have a heat wave this summer to be able to test its use with a geo-cooling system.