My pastor writes a weekly blog, and recently he mentioned a life experience where he was completing the wiring of a new Nest thermostat as part of a DYI project to make his home more energy efficient. He said he was feeling self-assured as he connected the power wire to the thermostat from “the heater,” but later that night awoke to a cold house. While I found it interesting how he made the connection between an HVAC project and the Almighty, that is not the subject of this blog. I did find a part of it worth discussing however, and that is the topic of terminology.
I responded to my pastor that it was a great article, but that as a member of the HVAC community, I had to let him know that from a terminology perspective, the wire was actually coming from his furnace, not the heater. Similarly, have you ever had someone walk into a room, look up at the ceiling and say something like, “Wow, those grills are really dirty. They need to change them.” That statement is just wrong on many levels.
Let’s first address the term “grilles.” A grill is something you cook on and a grille is an air outlet or inlet device. You would not want to cook on a grille, as it would leave funny looking sear (not to be confused with seer) marks and likely impart the taste of cooked paint to your food. While we are on the topic of grilles, let’s clarify once and for all what the differences are are between air inlet and outlet devices. (ASHRAE’s term) Grilles can be used on both the supply and return air side of the system, and are technically described as a device whereby the inlet and outlet area, size and shape are generally the same. In general, a grille is also a device where the general direction of the air coming from the ductwork is not changed after passing through the grille. Adding a damper to a supply air grille makes it a register.
A diffuser is a supply air (only) device that is used to achieve specific objectives related to airflow patterns and mixing. More specifically, a diffuser is an air outlet device in which the inlet and outlet area size and shape are generally not equal. In addition, the direction of air leaving a diffuser usually changes from the direction in which it is traveling when it leaves the ductwork.
Whew, I’m glad we cleared all that up. What about the comment related to dirty grilles and the need to change them? Read next week’s blog and we will tackle that statement. Meanwhile, I need to go check the setting on that automatic ambient air setpoint control device!
Picture courtesy of homeandgardenware.com