Zoning & Duct sizing

[Madison Mike]

I am looking to install a zoning system in my home and have a few questions after receiving three different quotes.
House is 2 year old with unfinished basement, 2800 SF (1800 ML & 1000 2nd level)
Furnace - Lennox G51MP-48C-110-06
A/C - Lennox HS29-048-5P
Supply and returns are both 12"x20" and neck to 8"x20" at end of run.
I have all 6" duct off main trunk - 14 runs on main level and 6 on upper level. All upper level runs are 'squash' pipe to run up exterior wall. There is one louver register in the trunk line for the basement.

I am looking to install 3 or 4 zones - 2nd level, main level, basement and possibly the master bedroom, which is on the main level and includes 4 registers.
Quotes
1) Install arzel zoning system in 4 zones and install bypass.
2) Would be best to install second system in attic for level 2 and could use 2 zone system for main level and basement.
3) Reconfigure and increase size of return trunk, add second supply trunk and zone trunks near furnace.

I do not like the cost associated with quote 2. What are your thoughts on the other 2 quotes? Will the arzel zoning system work adequately without lots of noise? Is the design of the existing system that poorly designed?
Thanks for any help!

[beenthere]

1. Unless both your furnace and A/C are 2 stage, your small zones are too small.

2. Is the best option for it working right, but would need to replace existing furnace and A/C also.

3. A 2 zone system might work ok. But the upstairs zone is still alittle small. Unless the equipment is 2 stage.

[Madison Mike]

It is only a single stage blower. I thought the minimum number of ducts for a zone was around 4, or is this only if you have a smaller system?

[keithman]

First I LOve the Arzel systems. You need to take into account requirements of the zones. Heat Loss & Heat Gain. If you are making a zone that is smaller than the delivery of the component you will damage equipment.

Example you have six 6" runs going up stairs if you have a 100,000 btu output furnace that zone is too small. Or if you have a four ton AC unit. Physics recomends 350-450 CFM per ton 4 ton X 400 = 1600 cfm (recomended) 6 six inch pipes cannot handle that velocity. This is why everyone is asking about variable system. Multi level or two stage. Quite often (at least in my climate) Customers are very happy with two maybe three zones

Keithman

[skippedover]

Retrofitting an existing system into a zoned system is generally a little dicey. The reason is that if the distribution system was laid out correctly at the beginning, then any attemp to zone the system will end up with incorrect duct velocities and pressures when less than all zones are calling.

Often zones are installed for all the wrong reasons. The purpose of zone controls is to increase comfort by providing even temperatures across the entire structure. Too often people try to use zone controls to create different temperature zones, which is exactly opposite to the purpose of zone controls. To properly design a distribution system for zone controls, the entire system should be oversized up to approximately 30% to accommodate the increased airflow when less than all zones are calling. A relief strategy must be incorporated into all but the most sophisticated zone control systems. First and foremost, the needs of the heating and cooling equipment must be met. If the equipment is not multi-stage, then you'll get full output no matter how many zones are calling. The designer needs to know what he/she is going to do with that excess capacity when only one zone is calling. These are the reasons you're getting so many varied opinions on how to best zone the structure. You could install equipment designed for zoning and then install that manufacturers zone controls to operate the system. I know the Carrier Infinity and Bryant Evolution systems specifically state no by-pass to be installed because their equipment is multi-staged and the zone dampers are controlled by a user interface that constantly adjusts all the dampers as necessary to maintain proper duct pressure for the stage of equipment running. Absent that type of system, you'd be best served with separate pieces of equipment for each zone and proper balancingn of the systems.

[beenthere]

It is only a single stage blower. I thought the minimum number of ducts for a zone was around 4, or is this only if you have a smaller system?

There isn't any single number of runs to a zone.

Since you have single sage equipment, it would work better having both zones require the same CFM. Would require the master bedroom and the upstairs be one zone, and the rest of the house be the other zone. It would still require a by pass large enough to bypass half of the systems air flow.(or a dump zone)

Honeywell has a zoning system that auto masters the zones.
It would work better then the Arzel in your case. It would still need the same size bypass.

2 systems is the better solution for your described set up.

[Madison Mike]

Thanks for all the replies. I now understand the issues with airflow and trying to eliminate the small zones. Does the current system seem oversized for the existing duct work? It seems as though I already have some pretty high velocities in shorter branch runs.
Currently I can adjust the dampers in the unfinished basement with fairly good results for evening out the temperature. However, I plan to finish the basement and would prefer not to install a drop ceiling in the basement, thus covering the dampers (which I am switching in the spring and fall).
Can I go with 3 zones - 1) master bed and 2nd level, 2) main level 3) basement? If this seems possible, how many branch runs would the basement require?

What is the minimum number of 6" branch runs on a zone, or more specifically what is the maximum cfm that can be effectively bypassed and what is the maximum recommended velocity of air flow?

Do both the a/c and furnace have to be replaced to dual stage, or is it simply the blower on the furnace? If the latter, can you replace the control board and motor on the existing furnace to convert it to dual stage?

If I were to upgrade to dual stage equipment, would the existing duct work be acceptable? Thanks again for all your help!

[zoneguy]

Mike:

The answer to your question is Yes. Your system will work well with an Arzel System installed.

The zone layout should be determined by how you use your space. Typically each floor should have its own thermostat. Then we look at how the load moves through the home and how you use the space; condition living spaces during the day and sleeping areas in the evening.

The layout you describe, 6 runs upstairs, 10 runs downstairs, and 1 register in the basement works well except for the basement. If you finish your basement, you will probably need more runs down there. If there are less than six you will probably need a bypass (probably an 8-inch in your case). The bypass allows some air to move from the supply to the return, alleviating any excess static pressure.

Zoning enhances two-stage, variable speed equipment. Changing out your current equipment could have significant operational savings and lessen the need for bypass when that basement zone calls by itself.

Mike, long and short, contractors do jobs like your hose every day using retrofit zoning. Multiple points of control will make your home more comfortable regardless of the equipment you have. Quality contractors can advise you on the appropriate equipment for your application.

Zoneguy

[Madison Mike]

I do plan to install additional branches in the basement - at least 6. It sounds like the system may not perform as well with the master bedroom on its own zone. It would probably be best zoned with the 2nd level where the remainder of the bedrooms are and this would have a total of 10 branch runs. The main level would also then have 10 branch runs.
As for the basement, would I be best off with buying a 3 (or 4) zone panel and hooking the basement to one of the other zones for now and only run 2 zones until such time I add the branch lines to the basement?
Also, could I install a large return in the basement and dump the bypass into the basement for now? Would this be beneficial?

[zoneguy]

Mike:
I personally believe that every master bedroom should have its own thermostat. In your case a small bypass will not hurt your equipment nor significantly impact effectiveness.

I would not dump air into the basement, It will just make that space uncomfortable.

The bottom line is layout the system exactly how you want it to work, make the system work for your lifestyle. There are no technical hurdles that will cannot be easily overcome.

Zoneguy

[beenthere]

Arzel is the easiest zoning system there is to install in an existing duct system.
Easy to work on too.

He'll need more then a small bypass to have his bedroom on a zone by itself.
A 110,000 btu furnace and a 4 ton A/C, when the master bedroom calls, he'll need to bypass at least 1000 CFM if not 1200.

[dash]

Arzel is the easiest zoning system there is to install in an existing duct system.
Easy to work on too.

He'll need more then a small bypass to have his bedroom on a zone by itself.
A 110,000 btu furnace and a 4 ton A/C, when the master bedroom calls, he'll need to bypass at least 1000 CFM if not 1200.

And what duct size would that be??

[beenthere]

Without a chart in front of me, about 12"
As I recall, a 10" will do about 780 CFM connected from supply plenum to near to the top of the return drop.

Installed at the return plenum might get you more. But won't allow for the 2 airs to mix right before getting to the HX, or evap coil.

[zoneguy]

For most applications, a 10" bypass can pass upto about 1000 cfm.

Calculate bypass based on velocity, not friction loss. The Bypass duct goes from the area of highset positive static to the areas of lowest negative. Also there is very little friction loss for there is very little duct work.

Therefore you get a lot of velecity through the bypass damper.
@approximately 2000 ft/min allows 1100 CFM through a 10" damper.

[Madison Mike]

So.....I can put the 2nd level on a zone (6 branch runs), the main level on a zone (10 branch runs), the master bed on a zone (4 branch runs) and the basement on a zone (1 louvre register in trunk and add 4 branch runs) and install either a 10 or 12" bypass. Is this correct?
This will then operate without excessive air noise/velocity and will not be detrimental to the heating/cooling equipment?
Just trying to get some answers from those with experience prior to installing and having a bunch of additional costs 'reworking' the duct work, etc.

[zoneguy]

Mike:
Yes jobs just like yours are done everyday.

If you decide to change to variable speed equipment or if you think you will in the future, you will need a modulating bypass damper. This is a good idea anyway because it will only open as much as you really need.

They are easily adjustable and will ensure your system remains effective and is quiet at the same time.

MAV

[beenthere]

For most applications, a 10" bypass can pass upto about 1000 cfm.

LOL.

In your earlier post, you said a small bypass.
I consider an 8" a small bypass, which is good for around 400 CFM.
So I was thinking you meant an 8" my mistake.

[dash]

Bypass needs to be sized by velocity on the ductolator.1500 to 2000 FPM.

[Madison Mike]

The 4 runs of 6" duct to the master bed will only handle 400 cfm at 500 fps. (I believe 500 fps is toward the high end of velocity) This would leave about 1200 cfm to bypass. Is this too much air to bypass? Would this not require a 12" bypass with a flow of 1500 fps? Is the bypass located on the supply trunk before any branch runs and routed to the far end of the return? If so, would this velocity get noisy over a 20 foot run?

The arzel web page has a bypass calculator and it seems to use 1000 fps for branch runs. Would this not be noisey? Would I need an automatic bypass instead of barometric? Again the arzel site says the barometric is for similar sized zones.

[pstu]

The 4 runs of 6" duct to the master bed will only handle 400 cfm at 500 fps. (I believe 500 fps is toward the high end of velocity) This would leave about 1200 cfm to bypass. Is this too much air to bypass? Would this not require a 12" bypass with a flow of 1500 fps? Is the bypass located on the supply trunk before any branch runs and routed to the far end of the return? If so, would this velocity get noisy over a 20 foot run?

The arzel web page has a bypass calculator and it seems to use 1000 fps for branch runs. Would this not be noisey? Would I need an automatic bypass instead of barometric? Again the arzel site says the barometric is for similar sized zones.

Madison Mike, one detail. The ACCA Manual D book states the upper limit for supply airfow should be 700 fpm for flex, a couple hundred higher for hard duct. 500 feet per *second* is getting too close to bullet velocity<g>.

You can buy Manual D for a few dozen dollars, here is one website which had a reasonable price just a couple days ago:
http://www.constructionbook.com/acca...-4/hvac-ducts/

While this is a lot for a slim book, it may be cheap vs. the value of getting the job done right. I believe Dash has remarked these air speed limits may be a bit archaic, perhaps under the right circumstances the limit could actually be higher with no ill effects. I'm a homeowner, he's the knowledgeable pro.

Hope this helps -- Pstu