View Full Version : Closed Loop Returns on HVAC?
09-19-2011, 04:28 PM
Does this sound right..... Again, I have to say I'm refrigeration not HVAC.
That being said I visit my aging parents several time a year in Florida. As I passed the gigantic Plenum in the hallway I heard dripping sounds. Turned out the condensation drain at the air handler backed up because of some jack asses who didn't glue them properly during construction. The plenum flooded and I got left with a huge job and a insurance claim because of the mold. I digress.... upon further inspection I noticed no other return heading into this plenum that sits directly under the air handler. I went into the attic and noticed 3 returns in the front of the house and 2 returns in the back of the house were "closed loop". I'm not proficient in HVAC but I was under the impression all the returns go to the Plenum to blend and distribute the air back into the air handler.
So my question........ is closed loop returns a practice that i'm unaware of or just lazy installers?
thanks for any input.
09-19-2011, 04:56 PM
What does closed loop mean. Are they not ducted back to plenum? They should be.
09-19-2011, 05:09 PM
Maybe he is referring to what we call a "jump" duct which is a duct from a bedroom to the open area of the home nearby. This is so bedrooms have a proper return airflow open area of the home which is served by the main return duct that feeds into the plenum.
09-19-2011, 05:15 PM
x2 on the Transfer Return Duct.
What is this jumpduck you speak of?:whistle:
09-19-2011, 05:22 PM
I guess you can call it a "jump duct" but nothing returns to the air handler except the big plenum that has a vent into the hallway about 24" x 24"
closed loop meaning the bedroom return is connected to the den return and that's it they are connected to each other but not to the plenum. I took a visual in the attic and also followed up with the ribbon test. Nothing stuck to the return vents (yes while the system was running).
09-19-2011, 05:25 PM
re:This is so bedrooms have a proper return airflow open area of the home which is served by the main return duct that feeds into the plenum.
there is no "main" return duct. the only thing feeding the Air handler is the giant plenum witch the only source of air is from one main vent from the hallway 24 x 24 into the air handler.
09-19-2011, 05:26 PM
I should note that the house is about 2300sq. ft. single level with 9 ft ceiling.
09-19-2011, 05:29 PM
His other return ducts going into the atic space kind of through me off a little.
09-19-2011, 07:44 PM
I saw something similar in a commercial building with a Trane Voyager RTU. The return air went directly into the unit by way of one large return opening and it had a similar design. I think they called it "open plenum" Anyone know of this?
09-19-2011, 09:27 PM
I saw something similar in a commercial building with a Trane Voyager RTU. The return air went directly into the unit by way of one large return opening and it had a similar design. I think they called it "open plenum" Anyone know of this? Rob, This sounds like a "return air ceiling". The entire space above the drop ceiling is open to the duct that draws air from that space to the unit on the rooftop. If the building construction were air tight, the idea would be OK. Of course, in the real world the idea sucks because the return air ceiling is not constructed airtight and sealed. It is cheap construction and wasteful of energy.
09-23-2011, 07:17 AM
Rob, This sounds like a "return air ceiling". The entire space above the drop ceiling is open to the duct that draws air from that space to the unit on the rooftop. If the building construction were air tight, the idea would be OK. Of course, in the real world the idea sucks because the return air ceiling is not constructed airtight and sealed. It is cheap construction and wasteful of energy.
You're right about being air tight Lynn, I learned about it at my last job as a maintenance man at a facility, I was in school and tagged along with the HVAC guy who serviced the place. The complaint was the Voyager unit wasn't heating very well and they could feel cold air blowing out the returns. Turns out there was a sheetrock ceiling above the drop ceiling that separated the conditioned space from the unconditioned attic with vented soffit and someone working on the wiring in the building had cut out huge areas of the sheetrock out and when the wind blew it blew in through the returns near the cut out area and it was also pulling a large amount of 30 *F air into the unit instead of air from the conditioned space.
09-23-2011, 09:23 AM
Laurance - The way I read it there is a RA grill in the ceiling of the den and another in the ceiling of the bedroom. Then there is a duct connecting these grills, not connected to anything else? Is the den open to the hallway - no door that can be closed?
The RA inlet to the blower only gets air from the hallway 24 X 24?
If I understand correctly you have what others have described as jumpducts. Air would be expected to move from the bedroom to the den when the bedroom door is closed through this duct. Air will take the path of least resistance. Since the air in the bedroom is cooler than the attic, it will likely leak anywhere else it can (such as under the door if there is an undercut) until there is enough pressure to move it up through the ceiling grill. If there is a door between the den and the hallway, this return strategy fails when the den door is closed, unless there is another jumpduct from the den to the hallway. With that in mind you will likely not be able to detect air movement through this duct unless the bedroom door is closed.
There are two options - design the return duct system correctly and replace, or if the temps are fairly even and your parents have no comfort complaints leave it alone. If it were my parents I would do it to squeeze as much capacity and efficiency from the system as I could. If it was a customer and they were not complaining about comfort, I would present the options and let them decide. For the customer there is a benefit vs investment decision to make.
09-23-2011, 10:27 AM
Re: to answer your questions, and now i know the terminology.
front of the house: den, bedroom are jumped to the hallway.
Back of house: bedroom is jumped into the hallway.
BTW: most of the time all the doors are kept open.
So the hallway and down into the kitchen is acts like one big plenum because it's one big open area?
I could without incurring much cost do the job myself: put a coupling on these two jumps and run it down the wall into the plenum. If I'm doing would anyone recommend:
1.add another return in the kitchen/2nd den which is the other side of house of course away from the cooking area.
2. cut the return hallway intake by 1/2 to increase pull from the other returns that would now be routed directly to the plenum. this would allow the warmer air (return registers in the ceiling) to return to the plenum an equal amount as the lower air (vent on wall close to floor in hallway).
09-23-2011, 01:13 PM
...BTW: most of the time all the doors are kept open. Good.
So the hallway and down into the kitchen is acts like one big plenum because it's one big open area? Yes. ...Making the changes you suggest will decrease capacity and efficiency. Don't do it.
09-23-2011, 02:01 PM
If you are going to make changes, the ducts need to be designed as a part of the system. As Lynn said you can make things worse.
Be careful with returns near kitchen areas. Odor and grease can be pulled into the duct.
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