European Standardisation on Indoor Air Quality

The standardisation on Indoor Air quality has mainly focused on requirements for health and requirements for ventilation. Health requirements is set by WHO and often referred to in IAQ standards. Today the most important European standard for IAQ is EN 16798-1/2. This standard was developed under CEN TC156 Ventilation and is now under revision. A similar standard ISO 17772-1/2 was developed in parallel by ISO. The standard also includes requirements for thermal comfort, acoustic and lighting. The present paper will focus on the parts dealing with IAQ. There are hundreds of substances in indoor air that may influence occupant’s health and perception of the air quality, therefore standards often prescribe a certain ventilation rate as criteria for IAQ. The paper will explain the use of the standard and give examples of criteria both using prescribed ventilation rates and criteria for individual substances.

Keywords: Indoor Air Quality (IAQ), ventilation, standards

Introduction

The first international standard that dealt with all indoor environmental parameters (thermal comfort, air quality, lighting and acoustic) was published in 2007 as EN 15251. This standard prescribed input parameters for design and assessment of energy performance of buildings and was a part of the set of standards developed to support the implementation of the Energy Performance of Buildings Directive in Europe. This standard was revised and issued as EN 16789-1. Besides the standard a Technical Report, TR 16789-2:2017 was developed to support and explain in more details the standard.

Indoor Air Quality part of EN16798-1/2

The standard is written in normative language with informative text included in the technical report. The standard does include default criteria in 3-4 categories (Table 1) for the indoor environmental parameters, as described in this paper. It is however in a series of tables in an informative annex B. Individual country can decide if they want to use these default values, only use one category, or use quite different values, which will be included in a normative national annex A with similar structure as annex B.

It is important to emphasise that the requirements and default criteria is based on the influence on the occupants and the standard do not set direct criteria depending on the type of system (mechanical or non-mechanical) used for conditioning the space.

The draft technical report TR 16789-2 will include guidance to the standard in similar sections as the standard. The TR includes also some additional sections and annexes with more voluntary concepts. In parallel two similar documents ISO 17772 and ISO-TR17772 has been published as almost identical documents.

Table 1. Description of the applicability of the categories used.

The requirements to indoor air quality is mainly expressed as a required minimum ventilation rate. The general requirements for the designer regarding the indoor air quality is the same for residential and non-residential buildings

Design parameters for indoor air quality shall be derived using one or more of the following methods:

·         Method based on perceived air quality

·         Method using criteria for pollutant concentration

·         Method based on pre-defined ventilation air flow rates

Within each method, the designer shall choose between different categories of indoor air quality and define which building category is to be used. The method used shall be documented and it must be explained why the selected method is appropriate

Method based on perceived air quality

The total ventilation rate for the breathing zone is found by combining the ventilation for people and building calculated from the following formula.

Where:

qto       is the total ventilation rate for the breathing zone, l/s;

n          is the design value for the number of the persons in the room;

qp        is the ventilation rate for occupancy per person, l/(s* person);

AR            is the floor area, m²;

qB            is the ventilation rate for emissions from building, l/(s m²).

The basic tables with default values are Table 2 and Table 3. The perceived air quality levels are set for non-adapted persons. If in special cases the design will include adapted persons (see TR 16789-2).

A criterion is that the total ventilation rate must never be lower than 4 l/s per person.

Table 2. Basic ventilation rates for diluting emissions (bio effluents) from people for different categories.

Table 3. Design ventilation rates for diluting emissions from different type of buildings.

A building is by default a low-polluting building unless prior activity has resulted in pollution of the building (e.g. smoking). In this case, the building shall be regarded as non-low polluting. The category very low-polluting requires that the majority of building materials used for finishing the interior surfaces meet the national or international criteria of very low-polluting materials.

The technical report will show tables with default values based on the two tables above and an assumed density of occupants. An example is given here in Table 4.

Table 4. Non-adapted persons. Examples of recommended ventilation rates for non-residential buildings with default occupant density for three categories of pollution from the building.

Method using criteria for pollutant concentration

The ventilation rate required to dilute a pollutant shall be calculated by this equation:

Where:

Qh        is the ventilation rate required for dilution, in litre per second;

Gh        is the pollution load of a pollutant, in micrograms per second;

Ch,I          is the guideline value of a pollutant, see Annex B6 , in micrograms per m³;

Ch,o         is the supply concentration of pollutants at the air intake, in micrograms per m³;

ev             is the ventilation effectiveness, 1.

NOTE. Ch,i and Ch,o may also be expressed as ppm (vol/vol). In this case the pollution load Gh has to be expressed as l/s.

To calculate the design ventilation air flow rate from Eq. (2), the most critical or relevant pollutant (or groups of pollutant) shall be identified and the pollution load in the space shall be estimated. When this method is used it is required that CO₂ a tracer for the emission from people (bio effluents) shall be used as one of the gases. Table 5 shows the CO₂ levels corresponding to the recommended ventilation rates in Table 4.

Table 5. Examples of CO₂ levels corresponding to the ventilation rates from Table 4.

Method based on pre-defined ventilation air flow rates

This is a method to determine certain pre-defined minimum ventilation air flow rate estimated to meet requirement for both perceived air quality and health in the occupied zone.

Design ventilation rates in residential buildings

Pre-defined ventilation air flow rates can be given on national level based on one or more of the following criteria: total air change rate for the dwelling, supply air flows for specific rooms, exhaust air flows from specific rooms. In an Annex to the standard, the default values for the three criteria are shown (see Table 6). It is assumed that air is supplied in living rooms and extracted from wet rooms. Both the total air flow rate for the entire dwelling and the exhaust air flow rate from wet rooms shall be calculated. The higher of the two shall be used. In the technical report several examples on default ventilation rates in residential buildings are presented.

The standard is also describing concepts for naturally ventilated building, where the criteria based on CO₂ could be used. In an annex a methodology for defining default design opening areas for natural ventilation systems in dwellings is presented (see Table 7). The opening areas must be provided as supply/extract grilles, stack ducts, window grilles, or similar system.

Table 6. Criteria based on pre-defined supply ventilation air flow rates for residential buildings: Total ventilation (1), Supply air flow (2) and (3).

Table 7. Default design opening areas for dwellings. Values for bedrooms and living rooms may be given per m² floor area or as fixed values per room.

Filtration and air cleaning

The standard is also setting up some requirements regarding the use of filtration and air cleaning. The influence of position of outdoor air intakes, filtration and air cleaning shall be considered according to prEN 16789-3 (revised EN 13779) and the draft technical report TR 16789-2. If filtration and air cleaning is used the following points shall be considered:

·         Reducing the amount of airborne pollutants (pollens, molds, spores, particles, dust) from the outdoor air intake by circulating the air through a filter.

·         Circulating secondary air through a filter or other air cleaning technology to reduce the amount of pollutants in the air

·         Reduce the concentration of odors and gaseous contaminants by circulating the secondary air or recirculating the return air (gas phase air cleaning)

Design guidelines on air cleaning and filtration are given in EN 16789-3 and ISO DIS 16814. How to partially substitute outside air-by-air cleaning is described in draft TR16789-2.

Conclusion

The standard present values for design of mechanical ventilation systems by recommended ventilation rates. For natural ventilation systems the design can be based on recommended CO₂ levels.

There is a need for updating the standard. For method 2 there is only a reference to WHO-criteria for individual substances. Other indices or substances could be used in method 2. One of the most critical pollution sources, particles, are not dealt with in the standard.

Finally, the use of air cleaning need to be extended and part of the normative part.

Bibliography

EN 16798-1:2019, Part 1: Indoor Environmental Input Parameters for Design and Assessment of Energy Performance of Buildings Addressing Indoor Air Quality, Thermal Environment, Lighting and Acoustics, CEN, 2019.

CEN/TR 16798-2:2019, Guideline for Using Indoor Environmental Input Parameters for the Design and Assessment of Energy Performance of Buildings, Draft for Working Group Red, CEN, 2019.

ISO 17772-1:2017. Energy performance of buildings - Indoor environmental Quality - part 1: Indoor environmental input parameters for the design and assessment of energy performance of buildings. ISO 2017.

ISO TR 17772-2:2017. Energy performance of buildings — Part 2: Guideline for using indoor environmental input parameters for the design and assessment of energy performance of buildings. ISO 2017.

B.W. Olesen et. al. :2020. The use of CO₂ as an indicator for indoor air quality and control of ventilation according to EN 16798-1 and CEN/TR 16798-2. Roomvent2020.

D. Khovalyg, O. B. Kazanci, H. Halvorsen, I. Gundlach, W.P. Bahnfleth, J. Toftum, B.W. Olesen, 2020, Critical review of standards for indoor thermal environment and air quality, Energy and Buildings 213, pp. 109819, https://doi.org/10.1016/j.enbuild.2020.109819.