Hey all,
Just recently had a Mitsubishi Heavy Industries, ducted and zoned air con installed. There's the main zone which covers the living areas and has the return air grill (RAG). Then there's 4 other zones which are just bedrooms and a study.
We have an AirTouch 2 controller which lets us set the airflow to each zone as a percentage out of 100. At night we close the master bedroom door, turn on the zone for only that room and set it to 40% airflow (any higher and it causes the air to whistle as it escapes the door frame).
I recently stumbled across some articles (all for American HVACs) that claimed that turning on only one room can cause extra stress on the air con due to pressure and if you're going to you should leave the door slightly ajar and give the air a pathway back to the RAG. Is there any truth to this? I now worry that having only one zone on with the airflow set so low (40%) is effectively giving little options for the air to escape the duct and potentially causing undue stress on the whole thing.
I'd have initially thought the system would be smart enough to compensate for this and decrease its "air force" but I now assume the air flow setting is just for the zone vent itself and doesn't actually tell the aircon to decrease its force.
Thanks!
ANSWER BELOW:
Ok, I spoke with one of the engineers for Polyaire, the people that make the AirTouch controllers.
He confirmed that yes, running it the way we are is an issue. Running only one room with the door closed will cause a lot of pressure in the system which has to escape somewhere which "at worst could cause things to pop off" I assume he meant ducting/grills. It will also cause extra wear on the fan as it's "like it's running into the wind" (the analogy he gave).
He confirmed that the smartest idea would be to run with all the ducts open but certainly at least the "main house" that has the RAG in it. Given the return air grill is the thing that determines how hard the system runs (and that isn't in our master bedroom) the grill at the moment would be sucking warm air from the rest of the house causing the air con to run harder and so opening vents to the rest of the house and cooling more of the house down will actually cause the air con to be MORE efficient than just trying to cool one room.
So there you go. I learned today.
there should be Constant Zone(s) that are automatically opened.