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Requirements for thermal comfort study material

2. Requirements

European standard EN 16 798-1 (with national translation STN EN 16 798-1) "Input parameters of the indoor environment for designing and evaluating the energy efficiency of buildings - addressing indoor air quality, thermal environment, lighting and acoustics" specifies how design criteria can be established and is used for sizing systems. It defines how to establish and define the main parameters to be used as input for building energy calculation and long-term assessment of the indoor environment. It also identifies parameters for monitoring and displaying the indoor environment as recommended in the directive on the energy performance of buildings (EN 16 798-1).

The purpose of the international standard EN ISO 7730 "Moderate thermal environment - Determination of PMV and PPD indices and specification of conditions for a thermal environment" is to present a method for predicting the thermal sensation and degree of discomfort (thermal dissatisfaction) of people exposed to a moderate thermal environment and to specify acceptable environmental conditions for comfort. It applies to healthy men and women and was originally based on studies of North American and European subjects, but also agrees well with recent studies of Japanese subjects and is expected to apply with good approximation to most parts of the world. It refers to people exposed to indoor environments where the goal is to achieve thermal comfort, or indoor environments where there are slight deviations from comfort.

European Technical Report CEN CR 1752 "Ventilation of buildings - Design criteria for indoor environments" covers criteria for indoor air quality, ventilation, thermal comfort and noise.

Critical issues such as adaptation, effect of increased air velocity, humidity, type of indoor pollution sources, etc. are still being debated, but in general these standards can be used worldwide. Nevertheless, it is important to consider people's clothing related to regional traditions and the season (Olesen, 2004).Criteria for an acceptable thermal climate are specified as requirements for general thermal comfort (PMV‐PPD index or operative temperature, air velocity, humidity) and for local thermal discomfort (draught, vertical air temperature differences, radiant temperature asymmetry, surface temperature of the floor). Such requirements can be found in standards and guidelines such as EN ISO 7730, CR 1752 and ASHRAE 55.

 

Table 1: Acceptable thermal environment for general comfort (ASHRAE Handbook, EN ISO 7730)



An equation in EN ISO 7730 calculates the PMV index based on the six factors clothing, activity, air and mean radiant temperature, air velocity and humidity. Even if a PMV value of 0 is obtained, there will still be at least 5% of the occupants who will be dissatisfied with the thermal environment (EN ISO 7730).

Table 2: Example design criteria for spaces in various types of building (EN ISO 7730)

 

Different labeling is used in the new CEN standard STN EN 16798-1. There are four categories indicated by numbers from I to IV. The categories I, II and III correspond to categories A, B and C in tables above. The category IV accounts for short deviations (for example exceeding the noise level when opening window for a short period of time, etc.) This category can be accepted only certain period of time. Moreover, unlike in previous standards, STN EN 16798-1 sets values also for residential buildings/spaces. The four categories are described in the following Table 4.

Table 3: Description of applicability of individual categories in STN EN 16798-1



Recommended values for the acceptable range of the indoor temperature for heating and cooling are based on a range for the PMV‐index. An example is shown in Table 5.

Table 4: Default design values of the indoor operative temperature STN EN 16798-1:2019



Indoor environmental parameters, which directly affect the heat balance of human body and are directly related to the thermal comfort:

  • Insulation of clothing
  • Metabolic rate
  • Air temperature
  • Mean radiant temperature
  • Relative air velocity
  • Relative humidity

No uniformity of the thermal environment (vertical air temperature differences, radiant temperature asymmetry, warm or cold floors and draft) may cause local thermal discomfort. The limits for vertical air difference and radiant temperature asymmetry corresponds to approximately 5% dissatisfied, while the limits for floor temperature correspond to 10% dissatisfied and for draft to 15% dissatisfied. The higher percentage of dissatisfied is allowed for draft, since air movement is most difficult to control in practice. The percentages of dissatisfied are not additive, as it may be the same people who are feeling discomfort due to draft, radiant asymmetry, air temperature differences, and floor temperatures (Ashrae, 1997). The people with higher activities are able to accept also higher values.