ByPass Zoning tech question.

[easybend]

I read all the manuals (mastered Manual J unabridged version) for HVAC and 90% of my questions were answered. Unfortunately, few of my concerns were not clearly explained in the Manual D.

The book tells you to use a bypass duct for the "extra" air when you implement multiple zone sections. That makes sense. The book also tells you that the bypass in not necessary if the equipment can be controlled (can adjust the airflow for the equipment).

This is what I am speculating. Tell me if I am wrong: If one is using a single speed or multiple speed furnance/airhandler, the bypass is required, because the equipment cannot dynamically change the rate of air going through. Now if the solution incorporates a variable speed furnance/airhandler the bypass is optional or not required, because the machine somehow (I do not know how) adjusts the airflow.

Can someone please tell me if I am correct in my assumptions? In addition, if I am correct how the furnace does know to adjust the airflow when one zone is closed for example. I cannot figure this out, because I have never done this part of HVAC and my situation cries for no bypass, because there is no space.

[eberrong]

Carrier Infinity zoning systems require no bypass. This system is fully intgrated...the condenser, air handler, thermostats, and zone controller all talk to each other. That is how the the airhandler knows to adjust the flow based on the thermostats and what zones are calling for cooling/heating. You can also set limits for the amount of flow (CFM's) in each zone based on the noise level it produces.

[beckservmngr]

Zoning can be a great thing, and can be very disasterous all at the same time, depends on the installer. with thaqt said, you are right, and you are wrong. The zoning required depends a lot on the ductwork itself, and how many zones. if you only have two zones, and the ductwork can be adequetly sized, you do not need a bypass.(it also depends on the zone dampers used.) if three or more zones are there, u must have a bypass, along with freeze protection, and temperature limit controls installed.

It all goes off of CFM, no matter what, whether you have a 3 ton variable drive, or multi speed, you still have to meet that 1200 cfm requirement.

[easybend]

eberrong
That's a smart approach. Are they well document when it comes to installation? I don't know much about Carrier.

beckservmngr
"if you only have two zones, and the ductwork can be adequetly sized, you do not need a bypass." - I have hard time agreeing with this. If we agree that the adequetly sized ductwork for two zones is 1.25 times the regular size. Both zones require almost equal amount of air. The 25% of air will go to the open zone, but where will the rest of the 75% air from the closed zone go?

[jrbenny]

Well, a bypass damper is not a must. It depends not only on your duct size but the zone controller. Trane zoning as well as Carrier Infinity zoning does not require a bypass. A bypass is prohibited on Carrier Infinity zoning. They both use a relief and staging strategy to ensure proper airflow through the equipment.

A bypass only ensures the register noise is minimized. Dumping hot/cold air into the return does nothing but put you closer to an equipment temperature limit. Airflow may be increased through the equipment, but you are dropping/lowering your entering air temperature. In turn, your discharge temperature is pushed closer to an equipment limit.

You should not be using a bypass to maintain airflow through the system. Your ducts need to be sized properly to ensure correct airflow through the system.

[beckservmngr]

Originally posted by easybend
eberrong
That's a smart approach. Are they well document when it comes to installation? I don't know much about Carrier.

beckservmngr
"if you only have two zones, and the ductwork can be adequetly sized, you do not need a bypass." - I have hard time agreeing with this. If we agree that the adequetly sized ductwork for two zones is 1.25 times the regular size. Both zones require almost equal amount of air. The 25% of air will go to the open zone, but where will the rest of the 75% air from the closed zone go?

That is where the adequatly sized ductwork comes into play. you have to size each zone to be able to handle 75% of the cfm. please, do research, the zoning system we use has the documentation for what I have posted. We do not agree that 1.25 is adequatley sized, if not haveing a bypass.

[easybend]

Hmmm, I'm lost here. According to Manual D the bypass has to handle 80% of the extra air if the closed zone is fully closed. If the zone does not fully close the bypass should handle the difference.

My 1.25 was a rough number according to Manual D guide. It seems incorrect to size a duct to handle additional 75% of air. That would throw off everything else.

[easybend]

"You should not be using a bypass to maintain airflow through the system. Your ducts need to be sized properly to ensure correct airflow through the system."

I'm not saying you guys are incorrect, but that is the opposite of what the Manuals are saying.

[beckservmngr]

one of those things, go by the book, or go by experience?

Good luck with what you decide. Peace easybend

[easybend]

Cool. Thanks. One thing I just learned, I love Carrier Infinity. Seems very nice and I like the fact that it does not need a bypass.

[jrbenny]

Originally posted by easybend
"You should not be using a bypass to maintain airflow through the system. Your ducts need to be sized properly to ensure correct airflow through the system."

I'm not saying you guys are incorrect, but that is the opposite of what the Manuals are saying.

Apply the mixed air equation to this design. What happens to the mixed air temp with each pass through the heat exchanger?

[easybend]

So what you saying it the air will heat up to the point where it will reach some limit that the exchanger has and possibly damange the exchanger. Makes sense.

Funny thing. I just called like 5 distributors for Carrier Infinity in New Jersey and 4 of them would not sell me anything anyway. I thought capitalism was the advantage of N. America. Look at XXX. They will sell you anything.

<<<Don't link or put DIY sites in your post.>>>

[Edited by jrbenny on 10-18-2006 at 02:45 PM]

[jrbenny]

Infinity is only sold to program dealers in my market. It's not unusual practice.