The revision of EN 15 251 with indoor environmental criteria is on!
August 21, 2012

The revision of EN 15 251 with indoor environmental criteria is on!

This is a collection of some important thoughts from the article about EN 15 251 by Professor Bjarne W. Olesen in REHVA Journal (Vol 48). EN 15 251 is all about indoor environmental input parameters for the design and assessment of the energy performance of buildings addressing indoor air quality, thermal environment, lighting and acoustics.  EN 15 251:2007 will be revised to consider and the development of buildings and a need for improved requirements, in particular adapted/non-adapted occupants, personalized system, air cleaning, ventilation effectiveness and illumination, and many others.

Thermal comfort criteria for indoor environment are needed for personalized systems, where occupants can set their own preferences. The personalized systems are in testing in several research and industrial buildings.  This would lead to increased ventilation effectiveness in personalized ventilation systems, and probably this will allow relaxing of the requirements for the general environment, thus saving energy.

Local thermal comfort parameters are not included in the standards, but they have an impact on the design and dimensioning of HVAC systems, thus influence on the energy performance of buildings. These parameters are for example asymmetric radiant temperature from surfaces, draught, vertical stratification of air and surface temperatures.

The main differences in ASHRAE and EN recommendations are that ASHRAE requirements deals with the minimum code requirements for adapted people, while the EN requirements focus on non-adapted people (visitors). It is said that after 15 min people adapt to the air quality in the room, especially to the odour from bio effluents, yet there is slower adaptation to emissions from building materials and smoke. It turns out that only 1/3 of ventilation rate would be sufficient to provide an acceptable perceived air quality for occupants if using an adapted approach!

The possibility of using air cleaning is of great interest as partly used air cleaning can substitute for the outside air, thus you can reach a higher class without any additional outdoor air, and thus save energy. Air cleaning is taken into account in ASHRAE using the analytical procedure, yet nothing in EN recommendations. The implementation of the new factor Clean Air Delivery Rate (CADR) could help with measuring of air cleaning efficiency.

Ventilation rates in standards are often based on full mixing of air and that might cause that the different ventilation effectiveness in summer and winter is neglected. The air distribution effectiveness needs to take into account how effectively the outside air is transported and distributed in space. Leakage means that the amount of ventilation must be increased, yet this is not included in EN 15 251 and only briefly in ASHRAE 62.1.

In EN 15 251 is stated only one level of illumination, yet more levels of daylight factor (DF) should be included together with recommended criteria for direct sunlight availability or percentage of probable sunlight hours (SAD = seasonal affective disorder).

The occupant behavior is in great need of mapping and specification of some “standard” patterns for occupant behavior is highly desirable because it has been proven in dynamic analysis that the energy consumption is influenced by certain occupant behavior (such as temperature set-point, time of occupancy, solar shading, etc.).

Image by Petra Vladykova