Effects of humidity at our homes

By Adam Ziagi

Humidity is the amount of moisture or water vapour in the air. In everyday usage, humidity is commonly referred to as relative humidity, expressed as a percent in weather forecasts and on household.

The amount of water vapour in the air at any given time is usually less than that required to saturate the air. 
Relative Humidity =

Actual vapour density

  X 100%
                      Saturation vapour density

You and your family produce moisture when you breathe or perspire. Even your indoor plants produce moisture. We add water vapour to indoor air through routine household activities such as cooking, showering, bathing, doing laundry, and dishwashing. More moisture can enter your home from the surrounding soil through a basement or crawl space.

How the relative humidity is controlled

Unlike temperature, humidity is somehow complicated in controlling and monitoring at family level. To control relative humidity we need a dehumidifier that will actually heat a room just as an electric heater which draws the same amount of power as the dehumidifier. A regular air conditioner transfers energy out of the room by means of the condensor coil, which is outside the room (outdoors).

This is a thermodynamic system where the room serves as the system and energy is transferred out of the system. Conversely with a dehumidifier, no energy is transferred out of the thermodynamic system (room) because the dehumidifier is entirely inside the room.

Therefore all of the power consumed by the dehumidifier is energy that is input into the thermodynamic system (the room), and remains in the room as heat. In addition, if the condensed water has been removed from the room, the amount of heat needed to boil that water has been added to the room. This is the inverse of adding water to the room with an evaporative cooler.

Only few people can manage to install dehumidifiers at their homes as they do for air conditioners. But people need to know about humidity for their comfort and health. Too much or too little humidity can produce difficulties for householders. Some of the problems are no more than nuisances; others could be far more serious.  They often occur during the heating season when our windows are closed, and indoor air circulation and ventilation are reduced.

Diagnosing the humidity problem

Typical symptoms - Too much humidity - Too little humidity
• condensation on windows
• wet stains on walls and ceilings
• moldy bathrooms
• musty smells
• allergic reactions
• chapped skin and lips
• scratch nose and throat
• breathing problems
• static and sparks
• problems with electronic equipment

Long-term effects
• damage to the house and its contents
• ongoing allergies
• other health problems
• continuing discomfort
• damage to furniture and other items

Instead of guessing whether or not you have a humidity problem inside your house, why not find out for sure?

A small, inexpensive and easy-to-use instrument called a hygrometer (sometimes known as humidity sensor or relative humidity indicator) can measure the humidity level in your house and confirm whether the house has too much or too little humidity. Once you know for sure, you can decide whether any action is required and, if so, what action to be taken. But you will do it confidently if your hygrometer is calibrated.

Calibration made simple

All hygrometers should be calibrated. Some are not properly set when they leave the factory. Others, even the best models on the market, may experience what is known as drift, which means that they do not hold their accuracy over long periods and need to be re-calibrated.

Calibration is easy. The intention of this article is to give you knowledge on how you can calibrate your hygrometer using everyday household at your own home. The basic principle is to create a small-scale environment where the relative humidity is known. You place your hygrometer in this environment and compare its reading to the known humidity level.

Once you have calibrated your hygrometer, you can be confident that you are getting accurate readings. Even so, you should re-calibrate your hygrometer once a year, especially if it is a mechanical instrument, to make sure that it continues to work properly.

Step by step on how to calibrate your hygrometer

Ingredients needed:
- 125 ml (about ½ cup) of table salt
- 50 ml (about ¼ cup) tap water

- Hygrometer to be calibrated
- a coffee cup
- a 5 l plastic bag or well-sealed pressure cooker

Step 1: Get to know your hygrometer

If your hygrometer has a pointer, look for screws or knobs on it that will allow you to move the pointer. If there are none, or if you have an electronic hygrometer, physical adjustment will not be possible, but you can still calibrate.

Step 2: Prepare the mixture

Place the tap water and the table salt in the coffee cup and stir for a several seconds.

Step 3: Set up

Put the coffee cup and your hygrometer inside the plastic bag or pressure cooker, and seal tightly. Note that salty water can damage your hygrometer if it comes in direct contact with it. Put the bag or pressure cooker in a draft-free place and out of direct sunlight, where the room temperature is likely to remain constant.

Step 4: Check your RH reading

After 8 to 12 hours, note your hygrometer’s RH reading. Your hygrometer should read about 75 per cent. If it does, you do not need to adjust it. If it does not read close to 75 per cent, note the difference between your hygrometer reading and 75 per cent.

Step 5: Correct to the standards

If your hygrometer is adjustable, immediately adjust the reading to 75 per cent. If your hygrometer cannot be adjusted, record the difference you noted in Step 4. In the future, each time you take a reading from your hygrometer, you will need to add or subtract that difference. After that, you will have calibrated your hygrometer.

Experts have developed rules to help homeowners make decisions regarding humidity levels in their house. The limits should be used as guides only. Acceptable or comfortable humidity levels will actually vary from season to season, from house to house, and even between rooms in the same house.