Revision of NBR 16.401-2: Thermal Comfort

Currently, the assessment of thermal comfort in indoor environments is mainly carried out according to the American standard ASHRAE 55 (last revision published in 2017), which deals solely with environmental thermal conditions for human occupancy (ASHRAE 55 - Thermal environmental conditions for human occupancy). There are also other standards, such as the latest revision of ISO 7730 from 2005, focused mainly on the Fanger model (1970) and the calculation of PMV/PPD (ISO 7730 - Moderate thermal environments – calculation of the PMV and PPD indices) and the standard European EN 15251 revised in 2012, which in addition to thermal comfort, also addresses internal air quality, lighting and acoustics (EN 15251 - Indoor environmental input parameters for design and assessment of energy performance of buildings: addressing indoor air quality, thermal environment, lighting and acoustics). 

In Brazil, there are no specific standards for evaluating thermal comfort. The standards that involve some of the thermal comfort parameters for internal spaces are restricted to the 1990 version of Regulatory Standard NR 17 – Ergonomics (NR 17, 1990), and part two of NBR 16401 – Air conditioning installations – central and units, revised in 2006 and last published in 2008 (ABNT, 2008). Both standards do not include any mention of the adaptive model, and limit thermal comfort conditions to commercial environments that operate within restricted temperature and air velocity ranges.

This project arose from research in which the main objective was to review best practices in terms of thermal comfort standards around the world, proposing at the end an initial draft for the discussion/creation of a Brazilian thermal comfort standard. The initial ideas were presented at the Windsor 2010 conference (Cândido et al., 2010) and later expanded at the BRI (Cândido et al., 2011). The proposed text was sent to the Brazilian Committee for Refrigeration, Air-Conditioning, Ventilation and Heating (ABNT/CB-055), edited and incorporated into part 2 of NBR 16401. It is currently awaiting opening for public consultation and subsequent publication after closing revisions relating to the other parts.

About NBR 16.401 (2008), part 2 - Thermal Comfort

NBR 16401 (2008) is a revision that canceled and replaced the old NBR 6401 from 1980, focused on the design of air conditioning installations (part 1), thermal comfort parameters in conditioned environments (part 2) and air quality interior (part 3). Despite being a very detailed standard with regard to thermal comfort parameters in internal spaces, the temperature and air speed limits are restricted and, for this reason, suitable for artificially air-conditioned environments with strict speed and humidity control. relative to the air. The standard is fundamentally based on the 2005 ASHRAE Handbook Fundamentals (ASHRAE, 2005) and defines internal operating temperatures that range from 22.5°C to 25.5°C (for relative humidity of 65%), and 23.0°C at 26.0°C (for 35% relative humidity). Air speed limits are conservative, and may not adequately represent the reality of conditioned spaces that have new artificial conditioning and air circulation technologies. Therefore, for this standard, and during the hottest periods of the year (0.5 clo), the air speed must not exceed 0.20 m/s when the air distribution system is conventional (degree of turbulence from 30 to 50%), and 0.25 m/s for air distribution by displacement flow system (degree of turbulence less than 10%). During colder periods (1.0 clo), these same limits can be delineated as follows: the operating temperature and relative humidity must be within the zone delimited by 21.0°C and 23.5°C for 60% and, 21.5°C and 24.0°C for 30% humidity. The air speed in this case must not exceed 0.15 m/s for conventional air distribution, and 0.20 m/s for air distribution using a displacement flow system.


Roberto LambertsRenata De Vecchi, Maíra Afonso de André. 


ABNT. Air conditioning installations - Central and unitary systems - Part 2: Thermal comfort parameters, NBR 16401-2. Rio de Janeiro: Brazilian Association of Technical Standards, 2008.

ASHRAE. ASHRAE Handbook: Fundamentals - SI edition, Chapter 8, Thermal Comfort. Atlanta, Ga.: American Society of Heating, Refrigerating and Air-Conditioning, Atlanta, Ga.: ASHRAE, 2005.

ASHRAE STANDARD 55. Thermal environmental conditions for human occupancy. Atlanta, Georgia: American Society of Heating Refrigerating and Air-Conditioning Engineers, 2017.

CÂNDIDO, C. et al. Towards a Brazilian standard for naturally ventilated buildings: guidelines for thermal and air movement acceptability. Proceedings of 6th Windsor Conference: Adapting to Change: New Thinking on Comfort. Anais...Cumberland Lodge, Windsor, UK. 9-11 April 2010.

CÂNDIDO, C. et al. Towards a Brazilian standard for naturally ventilated buildings: guidelines for thermal and air movement acceptability. Building Research & Information, v. 39, n. 2, p. 145–153, 2011. 

EN 15251. Indoor environmental input parameters for design and assessment of energy performance of buildingsaddressing indoor air quality, thermal environment, lighting and acoustics. CEN, Brussels.

FANGER, P. O. Thermal comfort - analysis and applications in environmental engineering. Copenhagen: Darlish Techinical Press, 1970.

ISO 7730. Ergonomics of the thermal environment: analytical determination and interpretation of thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria. Geneva, Switzerland: International Organization for Standardization, 2005. 

NR 17. Regulatory Standard 17 - Ergonomics. Ministry of Labor, 1990.