Single and central air conditioning

What is the impact of relative humidity on human productivity?

Why air conditioning is no luxury:

  • air conditioning in Germany is as useful as a central heating system in the Congo
  • air conditioning systems are noisy
  • air conditioning systems cause draught

That’s all wrong!

We’ll tell you why

When discussing air conditioning systems in Germany, you always hear the argument that the few hot days can be survived without air condition devices.

People often forget two important facts. In the first place, the outdoor climate is not the same as the indoor climate, and secondly, heat is not the only crucial point. Humidity in combination with high temperatures can especially cause discomfort.

We want to give you a simple explanation as to the reasons why.

The human body is a heat producer

The human body is a very complex system which only works properly at temperatures of 36 – 37°C (97°F). With an adequate diet and mild ambient temperatures it is not a problem. However, if you are surrounded by cold temperatures, you have to increase your heat generation with a high-calorie diet and/or compensate the loss of heat via the skin with adequate clothing.

You cannot stop your food intake when temperatures are too high and shedding layers at the workplace has its limits.

At a room temperature of 20°C (68°F) about 20 to 30% of excess body heat is transferred to the surroundings via sweat evaporation. With rising temperatures, the skin’s reflex is to intensify perspiration. None of this poses a problem for the body given a low relative humidity and is hardly noticeable.

DHowever, relative humidity is normally over 40% in the summer and so we feel the air as muggy and heavy and it strains the cardiovascular system. It is important to keep indoor temperatures and relative humidity as low as possible so that the body can transfer excess heat to the environment.

At our latitudes, the relative humidity in combination with high temperatures is above the optimal range for well-being. Therefore, air conditioning is imperative if you want to promote human productivity and health.

It is not for nothing that the guideline for workplaces restricts the maximum reasonable room temperature to 26°C (79°F), which actually can be quite tolerable when the relative humidity is appropriate.

It is the combination of high temperatures and high humidity that limits the performance of the human body.

Let’s not forget the indoor temperature

As mentioned above, there is a crucial difference between indoor and outdoor temperatures. When debating about the pros and cons of air conditioning people usually consider the outdoor temperature. Actually, indoor temperatures should be taken into consideration because even in the winter, the temperature inside can be quite high due to sunlight shining in and heat loss from humans and electronics.

Outdoor temperatures of 18°C to 19°C (64°F to 66°F) plus direct sunlight without adequate air exchange can cause room temperatures of 26°C to 27°C (78°F to 80°F) even with solar protection devices.

In addition, high humidity strains the circulation. In a field trial in Stuttgart (Baden-Württemberg) the relative humidity was between 62% and 94% for 27 days. The maximum temperatures ranged between 24°C and 32°C (75 and 90°F).

VThose are no conditions for high productivity. In addition to the circulation straining climate, the ozone level is usually too high, so the body needs a climate to regenerate. In Frankfurt am Main, for example, the amount of sunlight according to the German norm DIN 4170 during office hour ranges between 550 and 950 hours per year according to the German norm DIN 4170.

Measurements that were taken from April to September 1992 in Stuttgart revealed that the sun shone on 92 days. Outdoor temperatures ranged from 19°C to 32°C (66°F to 90°F).

For rooms situated on the west side of buildings air conditioning is practically a must because even airing out a room at night, temperatures will not drop more than 2.5°C (36.5°F).

Furthermore, airing rooms out is not always possible or advisable, especially in areas with high air pollution such as in inner-cities. The temperatures in offices, shops, department stores, surgeries and flats located in such areas depend on how solar energy reaches through the windows and other heat-permeable external building components. The specified maximum temperature can be exceeded quickly. High humidity in combination with high temperatures can also negatively influence the well-being and health of building occupants.

If an air conditioning system is installed in such rooms, the temperature cools down and the air is also simultaneously dehumidified. This brings humidity to normal levels and also has the benefit of binding and removing pollutants via the condensation. This process not only affects dust particles but also carbon dioxide and sulphur oxides.

The cooling and dehumidification process in the air conditioning unit thus enhances the air quality.