Late summer and early fall in Southern California is characterized by hot, dry air, frequently accompanied by those “Santa Ana” high winds. Dry air thins out our mucous membranes, weakening our defense against infection by bacteria and viruses. How do we keep our air healthy when the outdoor humidity drops to less than 10%?
Fortunately, air conditioning can be a big help
As air cools the amount of moisture it can hold falls. This is why cold fronts frequently become storm fronts; excess moisture in the air precipitates out as rain. In your home, keeping the air cooled also reduces its ability to absorb moisture, preventing the dryness and risks we experience around low humidity conditions. Our recommendation is to set the thermostat to 75º and let the air conditioner run as consistently as possible in hot, dry weather. If that’s low enough to get the coil below dewpoint, you’ll get close to the preferred human range of 45% to 55% for humidity levels. Even if you don’t reach dewpoint, relative humidity will still rise when the temperature falls, getting you closer to the humidity sweet spot.
On the other hand, sometimes we get a wave of tropical moisture coming up from the Gulf of California, resulting in unusually high rather than low humidity levels. That poses its own health risk because too much humidity promotes the growth of mold and mildew, neither of which are good for human health. If the coil gets below dewpoint, the excess moisture in the air condenses out and drains away as liquid water. Once again, our air is closer to our comfort zone as well as dry enough to cut the risk of mold.
Much of today’s HVAC equipment is variable-speed
This means the equipment can automatically and silently ramp up and down depending on the load. This is ideal for humidity control. The ability of air conditioning systems to maintain optimal humidity levels depends less on system capacity and more on runtime, so the continuous operation of variable-speed systems is perfect for controlling humidity. Another benefit is that more runtime means more air circulation, which prevents stagnant pockets where air can get too dry or too humid. And running continuously isn’t necessarily more expensive or energy-intensive than the short-cycling we usually see with traditional single-speed equipment. Compressors and furnace fans obey the Fan Law, meaning a 50% reduction in rotational speed means a 75% reduction in energy use. Variable speed systems spend nearly all their runtime at the lower, energy-efficient speeds while single-speed equipment always runs at full speed.
As always, bringing in outside air (once it cools off outside, of course) has health benefits, too. Provided you don’t have dust or pollen allergies, you will find the air in your home fresher and more pleasant once you open the windows. The Federal EPA rates outdoor air as four to six times cleaner than indoor air, so take advantage of this “free indoor air quality” upgrade whenever you can.
If you have more questions about HVAC or humidity, feel comfortable reaching out to the air pros at Air-Tro. Call us at (626) 357-3535 whenever you need help with your indoor comfort needs.