What Relative Humidity means for indoor air quality

H2O is probably the most common yet most potent chemical known to humankind. The substance is capable of everything from the most boring (ruining basements) to the most grandiose (creating enormous caves). Most importantly, it serves as the building block of all life. . Even the tiniest percent of water evaporates from the surface of the Earth, as practically all water here is either ice or liquid. 0.001% of the water on our planet remains suspended in the air continuously. The concentration of water in the air (humidity) strongly depends on the altitude and air temperature locally. Usually, it varies from a warmer region to a colder one, and the difference between regions may reach as much as 25%. 
Many people are aware of the ways that humidity (a relevant amount of water suspended into the air) influences our bodies and lifestyles. Nevertheless, most public places ignore the humidity of air, what we call “relative humidity,” entirely... 

How relative humidity is measured

Relative humidity (RH) is defined as a percentage figure. It varies depending on the air temperature. Hotter air is capable to contain more water, while colder air can only hold smaller amounts. For example, when the air temperature reaches 69 degrees, a cubic meter of air is capable of holding 19 grams of water. But when it gets to 77 F, the air is able to hold a total of 22 grams of water,  and the RH at that point reaches an absolute 100%. So, as it  gets hotter, humidity drops. The opposite thing happens when it gets colder. 

The Physics Behind Relative Humidity

In order to realize how cool relative humidity can be, imagine that when it drops to zero percent,  the air is absolutely dry. Once relative humidity rises to a hundred percent, there is so much water in the air that it either solidifies or liquifies, depending on how hot or cold it is. You see, one reason that relative humidity is “relative” is because a single room can include warmer and cooler areas. Thus since some of the parts have older air, the air in the same room contains a different amount of water. This way, air in a colder climate and air in a warmer climate can be of the same relative humidity (for example, 70%), and retain different amounts of water. This is the main reason that  you can literally sense water in the air with your skin in a very hot and humid climate. 

Thermometer vs Hygrometer

The perfect combination of ambient indoor temperature and humidity is 64.4 F with 40% to 60% humidity. In order to know for sure the humidity of your own environment, you’ll need to get a hygrometer. Normally, a hygrometer includes a thermometer: this way you’ll know for sure how humidity and temperature balance together. 

Indoor Humidity in Everyday Life

Everyone is familiar with how relative humidity impacts human beings: it affects the overall comfort the most. ASHRAE’s standards and guidelines for efficiency, health, and safety have shown that general comfort for a human being is composed of the following:

  • air freshness
  • airflow intensity
  • ambient air temperature
  • relative humidity
  • metabolism speed
  • the number of clothes on at the time.

With all of these combined, it is clear that to feel comfortable in a room, it is necessary to get somewhat lower humidity with relevantly high temperatures. 

The normal body reaction to high heat is sweat, which evaporates, causing your body to cool off. But that process cannot be maintained in case ambient air is already saturated with water 100% (relative humidity rate). Sleeping in high relevant humidity may be a way of explaining how it’s impossible to sweat and cool off, which may interfere with your good night’s sleep. 

Everyone may have seen these word combinations within their local weather forecast: apparent temperature vs “heat index.” This fact relates to the relative humidity issue: with hotter air, the temperature that actually shows on the thermometer feels way much different from what actually you can sense with your skin. The perceived temperature really differs from what your weather forecast says. 

Image courtesy: https://www.wpc.ncep.noaa.gov/

NOAA's National Weather Service provides hourly surface data for the North American region. Thanks to this kind of data, you can assess the potential impact of the weather on a family outing.

Did you know that relative humidity not only impacts humans but everything around them? Apparently, some allergens are activated as the ambient air becomes more humid; this, for instance, promotes the number of mites living in the dust of your home. So, if your relative or a family member is suffering from asthma or severe respiratory allergies, you should keep the humidity levels in your home below 50%. One more group of household hazards thrive at 80% and higher humidity levels: fungi, also known as “mold.” These microscopic fungi appear whenever there is little ventilation and a lot of moisture. These impact human health similarly to mites: prompting allergies and asthma to act up. To be honest, just keeping the humidity down is not a way to solve the issue. You have to eliminate mold infestations altogether and to keep any residual spores out of your household air; you should therefore consider a high-quality multi-stage air purifier for every room. 

Dry air and its Impact on Human Health

Humidity at lower ranges can prompt considerable discomfort. If you do not have any device indicating humidity in your home, the signs that may point to lower humidity levels, like 30% and lower, are super-dry tight skin, heel fissures, dry eyes, and dry-nose sensations. The drier air gives your entire body stress by parching out your mucous membranes and making it more susceptible to viruses of all sorts. This way, you either have to take care of a proper home’s atmosphere, or you’ll need to try to regulate the amount of stuff floating in your household air by installing a purifier of some sort within your HVAC system or a stand-alone appliance.

Where does humidity come from?

Let’s imagine that you’ve got this hygrometer at home and it indicates that humidity levels at your place are not even close to what you want them to be. What do you do?

First, let’s evaluate the relevant humidity throughout  your home. If you find that colder rooms are doing better on humidity, solve the overheating problem: set the regulator to a milder temperature. Most humans do not need 82F and up to feel comfortable at home. You may consider sacrificing your favorite pair of pajama shorts for a nice pair of cozy sweatpants and a sweater. This way your body will keep its comfort while your lungs and nostrils will be saved from drying out as well. 

Secondly, consider ventilating your room more often than you used to. Outside air rarely gets super dry, unless it is summer. So giving a good old draft a whirl may actually help. Ventilating every room regularly will aid the overall better living atmosphere for your home, 

A Humidifier or dehumidifier may be one way around normalizing the living conditions. The best combination is an air purifier with an ozonator that has a display with all of the important air quality indicators: humidity, temperature, cleanliness. Remember that keeping air humidity in your home between 40% and 60% is optimal. 

Air conditioners usually work against you by drying the air they cool off. Keep in mind there is a multitude of other factors that impact the indoor air you and your family are breathing. Some of those are as follows: house plants, home pets, cooking fumes, perfumes, bathroom odors, junk buckets, aerosols, household dust—you name it!

In the olden days, they hung wet cloths onto heaters or mopped floors incessantly in order to bring humidity levels up. These days you do not have to try so hard, except to keep the clean water going in your humidifier and open your windows on a regular basis.

As you can see, understanding air quality and relative humidity, in particular, helps undertake simple actions in order to increase the quality of life for the entire family.

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