Recently, some areas of the country have been experiencing dangerously high discomfort levels. Many men regularly find themselves struggling with open windows, and women seemingly intent on cooking them. This article is intended to bring clarity to this mixture of misunderstanding and ignorance between the genders when it comes to climate control, and points towards a workable solution.
Humans generate heat
Humans (live ones particularly) generate considerable heat as a result of the myriad of chemical reactions, the friction due to muscular action and fluids moving around in them. If this heat is unable to escape, body temperature begins to rise, bringing on heat exhaustion and death, in extreme situations.
Human temperature regulation
Even while sitting still the average human body needs to lose roughly the same amount of heat that is given off by a 100 W incandescent light bulb, which it does largely through evaporating water (perspiration) and by radiating infrared energy. Even when not visibly sweating, a live human is constantly losing water via the pores in their skin. By regulating the rate at which this water is allowed to evaporate, the body is able to keep its operating temperature within safe limits.
Body mass affects temperature regulation
As a person's mass increases, their skin area does not increase at the same rate, so persons having a larger body mass possess less skin area per kilogram than their thinner co-workers. This means that thin people generally keep cool far easier than fatter people. It also means that thinner people get cold easier than fatter people.
Gender affects regulation
News for some: Hey, girls and boys ARE different!
Generally, men exhibit a faster metabolism than women, which means, for their mass, they generate more heat - that is, were a man and woman to have identical mass, the man would give off more heat, and evaporate more water than the woman. You can of course get fat women and thin men, in which case the effects cancel out, or even reverse the more common trend. Generally, men generate more body heat, women less. The biggest difference will be between a fat man and a thin woman. This is generally - you do get uncommon exceptions.
Humidity
Air contains water that has evaporated from rivers, lakes, seas, plants and animals. The hotter the air, the more water it can hold. Once the air is 'full' of water, obviously it becomes difficult, or impossible, to get more water to evaporate. The amount of water in the air is commonly referred to as humidity, and most often expressed as a percentage of the maximum that the air could hold at a particular given temperature.
Dew point
That stuff that runs down the sides of your ice-cold beer mug is dew (water from the air, that has condensed on the outside of the glass). This happens because the glass is at a lower temperature than the dew point. The dew point temperature rises as the relative humidity rises, until the air reaches saturation. At this point the dew point is the same temperature as the air - which means that everything that is not hotter than the air... will be wet! The higher the relative humidity (and dew point), the harder it is to evaporate more water into the air, and the harder it is for a human to keep their body temperature within safe limits.
Discomfort index
It is possible to feel just as comfortable (or uncomfortable) at 23°C as at 28°C, provided that the humidity level at the higher temperature is sufficiently lower than that present at the cooler temperature. Ultimately the level of comfort depends on both temperature and humidity.
Airconditioners both cool and remove moisture
The airconditioner passes room air over its icy-cold heat exchanger, which absorbs heat from the room air. Since the heat exchanger is so cold, it is often colder than the dew point, which means that water from the air in the room will condense on the heat exchanger, run off of it, and be piped out of the building. This means that the room air begins to get both cooler and dryer.
Diffusion of moisture and open windows
Now, there is a law of physics (The law of Entropy), which says that the water held in the air will naturally spread out evenly, and it is not possible to maintain a low humidity level in a body of air that is exposed to another body of air at a very high humidity level.
Simply put: If you open that window you are going to let all the water in!
It will be as humid inside as outside. If it is humid inside, it means that the air needs to be even colder to achieve the same comfort level. Moisture is continually entering through the open window, which gives the airconditioner an impossible task. This wastes power and causes unnecessary wear on the airconditioner.
What a thermostatic controller does
As the word implies, a thermostat is intended to keep the room at a preset, static temperature. If the room is hotter than the set temperature, the airconditioner's compressor starts up and the air is cooled until the temperature has dropped to this pre-set level, at which point the compressor turns off. As the temperature slowly rises, it will again cause the compressor to start, and so the temperature will go up and down within a narrow band - if left alone!
The only thing the thermostat setting does is tell the compressor when to turn on and when to turn off - so please note:
* Lowering the temperature setting DOES NOT make the room cool any faster!
* Raising the temperature setting DOES NOT make the room cool down any slower, or make the air coming out of the airconditioner less icy!
While some fancier airconditioners do allow you to adjust the fan speed, and some may have a 'turbo' mode, where the thing can cool quicker - adjusting the thermostat setting does nothing to change how fast or how slow the airconditioner cools the room.
What fans can and cannot do
The reason a fan can make you feel cooler, is that the increased flow of air over your skin speeds up the evaporation process, making the conditions feel cooler. This effect is known as wind-chill factor, and can only be working if there is somebody sitting in the draught of the fan.
Fans do not make the room cooler. In fact, their motors give off heat, and by stirring the air around they actually slightly raise the temperature in the room. So unless the fan is blowing on you, it is not helping you at all.
Men and women compromise
All that remains is striking a fair compromise between the optimum levels for male versus female.
If men like 23°C and woman like 26°C, then the rule is that the room sits at 24,5°C and an accurate thermometer at a central point in the room is used to settle any disputes.
Since guys are the hotter creatures, if anybody should be in the path of the air vent, it should be the men and not the women. Positioning of work areas and male and female staff should take airconditioning into consideration.
Company policy
Working from a purely economic perspective, when theair conditioner is running, the windows must be CLOSED - for the same reason that you put the plug in before you attempt to fill your bath. And just as you do not stick your head under the taps when filling your bath, you should avoid having the airconditioner blowing on any employee - if at all practically possible.
John Gibbs,
Associate Editor:
SA Instrumentation & Control [email protected]
© Technews Publishing (Pty) Ltd | All Rights Reserved
printer friendly version