Temperature – cold facts on a hot topic
Well, maybe we exaggerated a bit calling indoor temperature a hot topic, but it’s an important part of the indoor climate when it comes to comfort and productivity. And to feel comfortable is a prerequisite for performing without hindrance. Both high and low temperatures can affect mental ability, work capacity, strength and mobility. This in turn can affect the frequency of accidents, work performance and comfort.
Thermal comfort
In the world of indoor climate we often hear the term thermal comfort. It is defined as “that condition of mind that expresses satisfaction with the thermal environment” in the globally recognized ASHRAE 55 and ISO 7730 standards for evaluating indoor environments. In other words – the situation where people are satisfied with the temperature and do not want a warmer or colder climate.
So, when do we reach that level of satisfaction? There is no exact answer to this question as there is no exact science. It all depends on the occupants age, clothing, health and their highly subjective opinion on what feels good. If a larger number of people are staying in a building with optimal conditions at least 5 percent of people are dissatisfied with the indoor climate. The aim should be to reach as few dissatisfied people as possible. But in general terms, for offices and schools, a suitable indoor temperature in the summer is 23-26°C, in the winter 20-24°C. The fact that it should be warmer in the summer is because the difference between outside and indoor temperature becomes too great otherwise, light summer clothes mean that we would freeze indoors if we did not raise the temperature slightly.
Calculating thermal comfort
Lindabs online calculation tool LindQST Indoor Climate Designer is updated with the method for analytical determination and interpretation of thermal comfort. It uses calculation of the predicted mean vote (PMV) and percentage of dissatisfied (PPD) indexes and the local thermal discomfort criteria DR (Draught Rate). The PMV index predicts the mean response of a large group of people on a 7-point thermal sensation scale, while PPD is directly linked to PMV and estimates the percentage of people who would be dissatisfied with a particular thermal environment. All based on the EN/ISO 7730 standard. Categorization of the thermal comfort calculations are according to EN 16798.
What happens when the temperature is not optimal?
At too high temperatures we get tired and have difficulties concentrating. It can also aggravate any pollution that is already present. At too low temperatures, we find it difficult to do things physically. In general, when there are complaints, the complainant often exaggerates the importance of one single factor, e.g. air temperature. There are actually a number of different factors that may affect the thermal comfort:
Environmental factors
– Air temperature
– Airspeed
– Relative humidity
– The average radiation temperature
Individual factors
– Activity
– Insulation, clothing
Sources:
https://www.ashrae.org/file%20library/technical%20resources/standards%20and%20guidelines/standards%20addenda/55_2017_d_20200731.pdf
Ergonomics of the thermal environment - Analytical determination and interpretation of the thermal comfort using calculation of the PMV and PPD indices and local thermal comfort criteria (ISO 7730:2005)