Arkansas HVACR NewsMagazine November 2024

HVACR NewsMagazine November 2024

Tech News

Back to the supply RH, there will be dehumidification whenever the coil is cold enough for moisture to condense on its surface. You'll just see high relative humidity in the supply because the supply air is cooler than the return air. A high supply RH reading should not be a sign that the coil isn't dehumidifying as it should. (On that note, aim for long runtimes and slower fan speeds for the best possible dehumidification.) All that said, RH can be confusing when you consider how the same amount of moisture can translate to very different RH values depending on the temperature. Just remember that the temperature tells us how much moisture the air can hold before we start seeing wet surfaces everywhere — hot air holds more, and cold air holds less. For that reason, relative humidity is useful for our diagnostic purposes because it can tell us a lot more about the air as it relates to the safety of the air around us than absolute humidity can. Absolute humidity won't let us know how close we are to the dew point or our relative risk level for IAQ threats like bacterial and fungal growth. But if you're ever curious about the absolute humidity, you're more than welcome to plot the dry-bulb temperature and relative humidity on a psychrometric chart to see the exact amount of moisture in the air. It might not be that useful for our purposes, but it's still neat. Conclusion

Chapter Meetings Look at All Things Foam In October, the Association provided 8 Continuing Education classes during the regular chapter meetings. Seven of them were on the subject of SPF, spray polyurethane foam. Most of us have been to classes on closed cell on duct and have seen more and more houses turn to SPF encapsulation. Done right SPF is an excellent insulation. Done wrong it can create humidity problems that we may get blamed for. Done right: the heat loss and gain is dramatically reduced, especially when our duct is in the attic. It can be as much as 30%. That means our equipment needs to be resized from our typical thinking of 500 square feet per ton. That also means our duct must be reduced to accommodate the reduction in AVF. Sometimes it is a little hard to get our head around it. Done wrong: SPF improperly installed can increase humidity levels that are difficult to solve. Open cell on the deck must have a impermeable layer to prevent vapor from migrating to the deck at night and “ ping ponging ” back to the attic in the day — increasing the humidity. The class was an eye opener that made most of us scratch out heads. It certainly opened us to the need to cooperate with other trades. After all, the House is a System.