Air humidity is one of the key factors for comfort at home, and can sometimes be unexpectedly high in a brand new “green” build. I spoke to Positive-Energy‘s Kristof Irwin and found out one method he uses – psychrometric testing – to help identify issues with discomfort in the home.
The type of comfort we’re talking here is thermal comfort, and the following factors which are most frequently controlled by your HVAC play into that:
- Air temperature
- Relative humidity – we lose heat when we perspire, and the amount of water vapor in the air determines how fast we can cool
- Air movement – moving air feels cooler
A side effect of your HVAC system is the reduction of humidity as it cools air. This is great as keeping the humidity down within an acceptable range is important for you to feel comfortable.
The challenge for builders of energy efficient homes is that building envelopes are getting tighter – there are less places for water vapor to escape. So if you’re cooking and generating steam, or taking a shower without an exhaust fan, your traditional HVAC will have to expend a great amount of energy to dehumidify the air.
There’s a sweet spot at which air temperature and air humidity feel comfortable for most of us. The interesting thing from an energy efficiency standpoint is that you don’t need to run all of your HVAC to dehumidify the air. You can simply add a lower power dehumidifier to your home, and use less energy on HVAC operations to achieve a feeling of comfort.
So what goes wrong? If your relative humidity remains high (even at a lower temperature) the combination doesn’t feel right. And if the relative humidity stays above 60% for too long, fungal spores can germinate. The EPA advises maintaining a relative humidity of 30-60%
What starts off as feeling uncomfortable can end up being unhealthy. So that’s where Kristof gets called in. He uses psychrometric testing:
“By logging humidity and temperature over time, you can learn where the air moves,” says Kristof. From there he can understand your home and figure out what needs to be addressed.
Little data loggers can be placed strategically around the home to test theories. I’m adding two in my home just to see, and I’ll report back what we learn.
Garreth Wilcock is an Austin EcoBroker®
Specializing in: New Green Homes in Austin.