…but so much more. In our previous blog post we described what a good indoor climate and good indoor air is, and we introduced a number of parameters that are important to follow. Time has now come to dig into how temperature affects indoor climate and us humans.
When it comes to temperature, we all know what it is. But why is there a need to write a blog post about it? Well, 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.
In our world of indoor climate we often use 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 more common words – the situation where people are satisfied with the temperature and do not want a warmer or colder climate.
And when do we reach that? Well, humans originate in tropical climates, which means that the temperature we find comfortable is relatively high compared to the average temperature outdoors for us Nordic people. For offices and housing, 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.
What happens when the temperature is not optimal?
At too high temperatures we get tired and have difficulties concentrating. And at too low temperatures, we find it difficult to do things physically.
To make it even more complex, each person is unique and the surrounding temperature is therefore perceived differently depending on factors, such as body temperature, operating temperature (how you experience the temperature more precisely), clothing, activity level and personal traits. This means that we can never reach 100% satisfaction. 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. So, the goal must be to reach as few dissatisfied as possible.
In general, when there is complaints the complainant often exaggerates the importance of one single factor, e.g. air temperature or humidity. So it’s important to understand that there are actually a number of different factors that may affect the indoor climate. Test data show that the following parameters provide how warm you feel:
– Air temperature
– Relative humidity
– The average radiation temperature
– Insulation, clothing
Temperature is not just temperature
Within indoor climate we speak about air temperature, operating temperature, and radiation temperature. Air temperature is a general measure of temperature, and it doesn’t take into account radiation or temperature difference. In practical application, the term operating temperature is used. The operating temperature is a summary measure of air temperature and radiation temperature. Finally, radiation temperature is a measure of the radiation exchange with surrounding surfaces in all directions.
Impact on people
People lose heat through the radiation to all surfaces that are colder than the bare skin or the surface temperature of the clothes, e.g. for winter windows but also for 20-degree interior walls. Skin temperature varies across the body between 30 degrees and 34 degrees when comfortable heat balance. The temperature of the skin averages 33 degrees when resting. One of the important functions of the air is to cool the body. The cooling should be as great as the heat generated in the body to give a complete heat balance.
We mentioned activity as one of the individual factors above. People who sit still a lot need a higher temperature. For example school children. They would need a temperature of 22 degrees in classrooms.
Ok, now we have made an introduction to the area temperature and thermal comfort. When designing an indoor climate system there are quite a few things to consider to get a good indoor climate. And in a coming blog post we will dig deeper into the terms thermal comfort and thermal indoor climate.