HVAC arrangement

[sepefrio]

I have never seen an arrangement like this before. I have a bunch of pictures, but I tried to draw a picture instead to give a more complete look without all the other junk in the way. This is in the attic. There are two condensers and two thermostats as well.

Dark blue are supply line

Light blue return

the red is a damper

Why would it be hooked up this way? If you can't make out what I mean I'll post more of the pictures.

Click to Enlarge

48.4Â KB

Click to Enlarge

13.53Â KB

Edit - This is suppose to be a zoned system, but the way I am looking at it, with the supply connected, no matter which unit us running, it goes to the entire house. Also, why would a supply be connected to the return plenum (even with a damper valve). Is this set up just fubared that bad or am I missing something?

[Jim Katen]

I have never seen an arrangement like this before. I have a bunch of pictures, but I tried to draw a picture instead to give a more complete look without all the other junk in the way. This is in the attic. There are two condensers and two thermostats as well.

Dark blue are supply line

Light blue return

the red is a damper

Why would it be hooked up this way? If you can't make out what I mean I'll post more of the pictures.

Edit - This is suppose to be a zoned system, but the way I am looking at it, with the supply connected, no matter which unit us running, it goes to the entire house. Also, why would a supply be connected to the return plenum (even with a damper valve). Is this set up just fubared that bad or am I missing something?

I think you've got the supplies and the returns mixed up.

Is the damper in your drawing a barometric damper? Does it open & close by itself as the pressure in the duct changes?

- Jim Katen, Oregon

[Richard Moore]

I think you've got the supplies and the returns mixed up.

Yeah, it doesn't make any sense that supply and return ducts could be connected at the same end of a furnace/air handler. Your diagram must be off. Everything between the two units should be returns. Was the damper at the tee motorized? If so it could be a fresh air intake for the VIAQ system.

More photos please.

[Phillip]

In some zone systems there is a supply that goes back to the return. This is a by pass supply line. This supply is also on a zone damper. It is needed when there are not enough of the supply zones opened for proper airflow of the system. That is when it will open and let the supply air go to the return.

I have seen when there is a supply line run to a humidifier which is in the return.

I have no ideal if any of this fits your systems, just food for thought.

[Terence McCann]

In some zone systems there is a supply that goes back to the return. This is a by pass supply line. This supply is also on a zone damper. It is needed when there are not enough of the supply zones opened for proper airflow of the system. That is when it will open and let the supply air go to the return.

There is the Carrier VVT system (Variable Volume Variable Temperature) and the Trane Vari-Track system (among others). These systems turn a single zone system into a multi-zone system by adding zone dampers and zone thermostats to the system. If only 3 out of the 5 zones are open then the bypass damper (the damper that dumps supply air back into the return air) opens up to keep a load on the system. It measures current to the blower motor and when the current starts to drop it opens up the bypass damper to "load" the system. There is a temperature low-limit thermostat which will kill the air conditioning to prevent freeze ups. There is a hi-limit as well for the heating side of the system.

The system in the pictures is not a VVT system.

[sepefrio]

The damper was mechanical, as in you had to manually open/close it.

And no, the supply's and returns are not backwards. I thought the same thing at first and actually walked each line to make sure where it went and drew up my first sketch while in the attic with it.

I gave it to a HVAC buddy of mine. He first started laughing then said yeah this is a simple case of massive over engineering (and over cost)a good thing. The two units are in fact inline units. The 2.5 ton fires first and cools the whole home. When more is needed, the 1.5 ton kicks in to assist. He said the biggest problem is you would never know if one unit is dieing and the other is just taking up the slack or what. There were 2 zone control panels all "Bubba" wired in, as well as sensor valves at the duct openings. Had to be a dozen of them. Two thermostats as well. Everything was Trane.

It is still the craziest set-up I have ever seen.

These are at each duct.

Click to Enlarge

30.02Â KB

The zone control panels.

Click to Enlarge

56.4Â KB

It's hard to see the damper here so I circled it. It really just looks like a gear shift sticking out. No wire or other connections seen, This is at the center T BTW.

Click to Enlarge

33.75 KB

[Thor]

Picture 3 is of a barometric by-pass. You are looking at a zone system, the purpose of the by-pass is to relieve excess static pressure when all zones are not calling. It does this by dumping supply air back into the return air. The gearshift thing that you talk about is a balancing rod for the barometric damper.