TLDR – HVAC Humidity Control
- Keeping the humidity in your home balanced equals higher temperatures that are more comfortable for people.
- Proper HVAC system design will result in more comfort for the homes occupants and less money wasted on electricity.
- If your home is humid, do not buy a portable dehumidifier for 24/7 use. Find and fix the underlying cause of the humidity. These portable units are band-aids that can double your electric bill.
- Spending a day to seal and caulk air leaks, can do wonders for your homes comfort, health, and energy efficiency.
When cooling inanimate objects like cars or electronics (for the most part) the only concern is temperature. However, with human beings that sweat and feel, it is a more a complicated subject that brings humidity and psychology into the mix. To keep things simple, I have broken this down into four sections.
This is the temperature where the water starts coming out of the air. Just like a cold glass of iced tea outside on a humid summer day, where the water begins dripping off of the glass. Or, when a cold front moves in on a hot, humid day and the result is a rainstorm. In both of these examples, you have hot, humid air that was cooled below the dew point. What factors determine dew point? Well, to keep things simple, the warmer the atmosphere is, the more water vapor that it can hold. The dew point is the critical temperature where the air cannot hold any more water. It is the temperature where the air becomes saturated with water.
Our skin excretes water which then evaporates, taking heat or energy with it, and this is how we cool ourselves. If the dew point rises, sweat doesn’t evaporate as quickly as it should, and this is a problem of concentration. A general property of the universe is that things want to expand and equalize. And the greater the concentration difference between two areas, the greater the pressure will be to equalize. If you have a bunch of sweat on your body (water) and there is already a bunch of water in the air, the strength of the forces behind the evaporation (cooling) process will reduce.
This effect is easily felt when you wipe rubbing alcohol on your skin, and it immediately feels cool. What is happening is that the molecules of your skin are running into the liquid particles, just like in a car accident. Car one hits car two, then car number one stops and its energy is transferred to car number two. Car two then continues moving with the momentum of car one. The molecules making up your skin are running into the liquid particles on your skin, giving the liquid molecules just enough energy to break free and join the atmosphere as a vapor. Your skin is then left with less energy or less heat.
Types of Heat
Heat is energy and it can never be destroyed, only transferred from one area to another. When you move heat away from an object, the temperature of that object is lowered, and this is known as Sensible Heat. When you transfer out enough Sensible Heat, you will reach a temperature where a phase change occurs. For example, when cooling liquid water to make ice, you remove enough Sensible Heat to bring the temperature down to 32 degrees Fahrenheit. Once there, you then remove what is called Latent Heat to cause the phase change to occur. This process is the same with all phase changes. Liquid water to steam, liquid ammonia to a gaseous ammonia, etc.
How a human feels can vary. We are not digital machines that are always content at the same temperature. Our mood, our metabolism, our immune system, our brain, all control many factors that are still not well understood to this day.
What does that mean for my home?
If the humidity inside your home is maintained at a lower level, human occupants will then have the same level of comfort at a higher temperature setting. This can mean a lower electric bill when the proper balance is obtained. The ideal indoor humidity is 55% with the ideal temperature being 75 to 78 degrees Fahrenheit. If your home isn’t comfortable within this range, the possibility exists that the humidity in your home is too high. It is also important to keep in mind that everything needs to be in balance because insulating against temperature and humidity are two different things. This is important to note because some homes just aren’t able to hold lower humidity levels and trying to force lower levels, can be a waste of money.
Common causes of humidity in your home
Do not buy a portable dehumidifier from a local big box store and run it 24/7, because they can easily double your electric bill. These are only for drying out areas after water damage or assisting with humidity-related health issues on a temporary basis. Every time that I come to a home that bought a small dehumidifier due to there being high humidity issues, they had a deeper underlying issue. By buying a dehumidifier, you end up fighting the issue from the wrong end by just treating the symptoms. If you have an oil leak on your car, do you fix the leak or do you just keep putting more oil in the engine?
- Dryer vent or some other exhaust vent is open in the walls and dumping humidity into the home.
- Leaky HVAC ductwork is pulling in hot humid air from outside.Improperly designed and/or configured HVAC system.
- Broken HVAC system that isn’t able to cool the attic coil below the dew point.
- A home with inadequate insulation and/or improperly sealed. Check everything, windows, doors, exterior walls, and all ceilings that touch the attic.
- Electric attic vent fans that overpowering and/or the soffits are clogged, resulting in air being sucked out of the house.
How do I manage the humidity in my home?
The number one way to control the humidity in your home is to keep it from entering in the first place. And the best way to do this, in my opinion, is to seal your home with closed cell spray foam insulation. And, yes, this is expensive to do BOTH after the fact and as new construction. However, using the small spray cans of foam and silicone sealant are good ways to seal up gaps in your home that let in humidity. If you are serious about building a new home, spray foam is the only way to go. If you have an existing home, spending a Saturday to fill in air gaps with caulk and replace weather strips on windows and doors, can do wonders for comfort and energy savings.
Bigger isn’t always better!
An equally important factor is having a properly designed AC system. If your HVAC contractor channeled their inner “Tim the Toolman Taylor” by implementing a “bigger is better” attitude, you will have humidity issues in your home. An over-sized AC system will turn on, lower the temperature in your home, and then turn off. Removing humidity takes a little more AC system run time than these rapid on and off cycles can provide, resulting in a cold, damp home, that gives mold a nice hospitable environment to grow as well. To remove humidity, the coil in your attic needs to be so cold that it drops below the dew point.
To understand this portion, let us go back to that scenario above with the cold glass of iced tea sitting outside on a hot summer’s day. The water that is dripping off the glass is humidity condensing out of the air, due to the surface of the glass being below the dew point. Now, envision a fan blowing on the side of that glass. With the fan blowing across the glass, it is mixing the air around the glass, moving anyone molecule out of the way before it has a chance to drop below the critical dew point temperature.
With an HVAC system that is both designed and configured correctly, it does two things. Number one, it varies the fan speed that moves the air across the evaporator coil and, number two, it is appropriately sized so that it will run for longer intervals. Both of which, results in a more comfortable and a more energy efficient home.
By practicing everything above, you can not only save a little more money on your electric bill; your home will be a lot more comfortable as well.
If you have any questions, please feel free to contact me, Anthony, at 33 Solutions LLC!