Zoning questions

GrizmulJuly 24, 2014

Hi all. I am planing a new HVAC system and have a few questions on zoning. Planned equipment:

A/C Bryant 187B 4 ton two-stage and variable speed
Heat Bryant 987M modulating variable speed gas furnace
ERV - not sure on which one.
Whole house de-humidifier aprilaire 1830

3 zones -
zone 1- ~690 CFM
zone 2 - ~620 CFM
zone 3 - ~290 CFM

1. Is there a way to tell what the minimum air flow is needed for this equipment? How can I tell what the range of workable CFMs would be?

2. When a zone closes does it close the supply, return or both?

3. How would a whole house de-humidifer work when returns or supplies are closed? Normal attachment for the de-humidifier is both intake and exhaust on the return line.

I think one of my biggest concerns is the ability to de-humidify a zone w/o cooling it. If possible, one solution I could think of, would be to turn on all zones at the lowest fan speed and half tonnage to allow the a/c and de-humidifier to de-humidify but it seems like the possible solutions could get complicated.

Any ideas or help here?


This post was edited by Grizmul on Thu, Jul 24, 14 at 9:52

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Do U actually need a 4-Ton system?

It is easier to zone with less total airflow requirements, especially with a mere 290-CFM zone..

Here is a link that might be useful: free whole house load-calc

    Bookmark   July 25, 2014 at 8:28AM
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I hope this is Infinity/Evolution zoning controls.

Location please.

What size home?

What size is existing system?


    Bookmark   July 25, 2014 at 8:50AM
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@udarrell 3 ton was slotted if we didn't use an ERV other wise 4ton with one. We were right on the edge and these don't come in 1/2 ton increments it is 2 stage. So I assume 2ton or 4 ton with variable speed fan.

@tigerdunes Washington dc, 3000 sq/ft home, no existing system (new construction)

I haven't picked out the controls yet but will make sure they are the wi-fi enabled evolution controls and zoning controls.

    Bookmark   July 25, 2014 at 9:44AM
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No more than 80 KBTU Evolution furnace!


    Bookmark   July 25, 2014 at 9:58AM
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Oh sorry forgot to put that, 60K furnace.

Do you guys have any technical insight on the 3 questions in the original post? I am a bit unclear on how those concepts work.


This post was edited by Grizmul on Fri, Jul 25, 14 at 12:21

    Bookmark   July 25, 2014 at 12:17PM
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Did the HVAC contractor do a load calculation? I am curious as to why adding an ERV increases the cooling load.

If the heating load is less than 60K BTU, then I would think 3 tons for cooling would be fine for Washington, DC. Something does not seem right.

Very few 2-stage condensers have a an even split between the high and low stages. The low stage is typically 70% of the high stage. Therefore the air flows for a 4 ton 2-stage would be 1400-1600 CFM for the high stage, and 980 - 1120 CFM in the low stage. These numbers are approximations using 350-400 CFM per ton of cooling.

Zone 3 may be too small to handle the air flow even in the low stage. You need to find a contractor who is very good at zoning. The other choice is to get independent furnaces and AC condensers for each floor. They would be smaller units and you would not be spending money on zoning controls and wiring.

    Bookmark   July 25, 2014 at 1:27PM
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I would look into Bryant's new 5 stage var capacity AC condenser. This has just been introduced. But it seems this would solve the issues with your 3 zones particularly the small zone. The downside is I doubt dealers know very much about this and of course there is no history on the unit.

Mdl 189 BNV

Link attached.

Here is a link that might be useful: Mdl 189 BNV

    Bookmark   July 25, 2014 at 1:34PM
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The 2-stage comes in 2, 3, 4 & 5-Ton sizes.

Therefore, by making your home & the duct system more efficient U could probably go with the 3-Ton; which would work better in a zoned situation.

Never oversize because U have a 2-stage zoned system.

Here is a link that might be useful: Free Whole House Loads-Calc

    Bookmark   July 25, 2014 at 1:36PM
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@MIke Yes, a Man-J and D calcs were done. w/o and ERV the req. total capacity at .80 SHR was 3.2 tons and he was thinking a 3 ton unit would work. Adding in the ERV ups it to 3.3 or 3.4 tons and he feels that would push us into the next level up at 4 tons.

@Tiger wow- that might be the solution. Depending on the price that seems like the ideal fit and hoping this new model isn't buggy :)

@udarrell yes if they can somehow make it more efficient that would work. I'm just using an independent person for the Man-Js so he takes certain things into consideration. I may just opt for the 3 ton unit regardless but this 5 stage unit sounds like the solution. 25-100% capacity.

Thanks for the two links. Those may be very useful!

    Bookmark   July 25, 2014 at 2:45PM
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I am very surprised that none of the posters on this thread have not raised the question of the 60 K modulating furnace paired with the Evolution 4 ton AC condenser. Not only that, but how come the dealer has speced out this combination and pairing.

To the OP. you need to verify the qualifications and experience of dealer with both Bryant and Evolution zoning controls.

I would want to see a comprehensive load calculation both heating and cooling with agreed upon design temperatures broken out by each zone.

Does a 60 K modulating furnace carry a 4 ton blower rating for the 4 ton AC condenser?


    Bookmark   July 25, 2014 at 7:51PM
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Tiger, I am getting a bit worried now :) I have a 20 page detailed Manual J document where I had asked the person to pair the modulating furnace with the multi-stage A/C. The design came back and specified 53K BTUH for heating and 36000 btuh for cooling.

The Evolution models that came back were furnace: 987MA60060V21 , A/C: 187BNA048****D w/ a coil of CNPV*4821AL*

Now this is purely from the Man-J s w/ my input on using Bryant and variable speeds. The dealer is working over the data now but are there questions or things I should bring up regarding the integrity of this setup? Are you saying the blower module will not work with a 4 ton a/c?

Is this combination a bad combo? What combo would work well?

    Bookmark   July 26, 2014 at 9:17AM
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Here is a link for the Bryant 987 product data manual. Page 3 describes what the model number means. Digits 6 and 7 (60) means the furnace has a 2000 CFM blower which would be fine for a 4 ton AC. You only need 1600 CFM blower so you could also use furnaces which have the 1600 and 1800 CFM blower.

I question the Manual J calculation. Only 53K BTU of heating for a 3000 sq. foot house seems low. If the cooling load is 36,000 BTU, then why is the contractor recommending a 4 ton AC?

Here is a link that might be useful: Bryant 987 product data

    Bookmark   July 26, 2014 at 9:49AM
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I appreciate all the help and hope I am not screwing up the translation of Man-j info. -- thanks for that link mike .

@ Mike the Equipment total load is 36302 but the line below it says Req. total capacity at 0.80 SHR = 3.3 ton.

He said because there are no 1/2 ton increments he thinks going up to 4 ton is probably best.

The CFMs I listed were what I added up from looking at the duct drawings. For example I will see a red line to a window with a 99 cfm marking....I am a newbie so I just used the sum of all those numbers. Maybe this is the wrong way to do it. Looking at the cooling equipment summary he has:
sensible coolign: 30800
laten cooling: 7700
total cooling 38500
actual air flow : 1200 cfm
air flow factor: 0.040 cfm/btuh
static pressure 0.70 in H20
load sensible heat ratio 0.86

for heating:
Heating in 60600, heating out 60000
temp rise: 50
actual air flow 1094
air flow factor 0.022 cfm/btuh
static press 0.70 in h20

he then has a table with data like this:

family / kitchen 599 sq/ft, htg load 11346btuh, cooling load 5630, htg avf (cfm) 248, clg AVF (cfm) 227

he does this for each room and the sum of all those rooms comes up to 1200 CFM. This is a Man-j using the wrightsoft software which I bet some of you are familiar with. It looks very detailed. If it didn't have personal info all over it I would attach it.


    Bookmark   July 26, 2014 at 10:08AM
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I would like to see the AHRI matching number that says the 987 mod furnace 60 K size can support a 4 ton 187 Evolution AC condenser. I looked and couldn't find confirmed documentation. Maybe I overlooked it.

I find the load calc highly suspect and suggest you have it independently confirmed by another party. And I would look into the new 189 5 stage condenser. Along with the mod furnace, it could solve a lot of sizing issues concerning zoning.


This post was edited by tigerdunes on Sun, Jul 27, 14 at 5:25

    Bookmark   July 27, 2014 at 4:55AM
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Tigerdunes makes a good point. The Bryant product data sheet lists several models with varying blower sizes, but all of them may not be available.

    Bookmark   July 27, 2014 at 7:43PM
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Talked with the HVAC guy this morning. He seems to think the 4ton variable speed system with 60k btu would work fine. With the 60k furnace and blower that is 1200CFMs that will put me around 300 CFM per ton for the 4ton system and @70% for the second stage it would be about 2.8 tons. This is still an issue for a 290 CFM zone...

He seemed to think the multi-zone will work fine because he will use a bypass duct on the multi-stage variable speed blower!!!! I thought this was a big no-no in general and here we are working with a completely variable system. Wouldn't it be smarter to just partially open another zone ?

I am a bit tied to this HVAC company for various reasons but at this point I would like to find someone is is good with zoning and variable system up in northern VA. I don't know how to find this said company or person though.

    Bookmark   August 4, 2014 at 1:01PM
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Also, tiger talked about the pairing of the furnace with 4ton ac, and the model furnace is 987MA60060V21. According to the PDF http://literature.cwgoodguys.com/987M-Spec.pdf the blower on this model handles 2000CFM clg. The pdf has a chart for the model number to clg capacity conversion (model number nomenclature) on page 3. Does that look correct?

    Bookmark   August 4, 2014 at 1:50PM
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Even with new construction, I would want to see in writing a load calc supporting a 60 K mod high eff furnace for a 3000 sq ft home in DC area. This needs independent confirmation.


    Bookmark   August 4, 2014 at 2:06PM
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Oh, you are thinking the furnace is either too large or too small? Let me see if I can attach the Man-J pics maybe that would be useful.

    Bookmark   August 4, 2014 at 3:20PM
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Hmm there could be a lot of pages. Not sure what is of value.

    Bookmark   August 4, 2014 at 3:24PM
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There are 17 pages of this. Unless these are of value I won't post anymore. This is a third party who created the Man-js. You are thinking I should go to yet another person to get more info?

    Bookmark   August 4, 2014 at 3:28PM
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I was thinking the furnace was too small plus did not have a 4 ton rated blower to support the 4 ton rated AC condenser.

However both fears have been alleviated by your man J plus the matching AHRI number. I think the only question as far as equipment goes is the use of the 189BNV var speed AC condenser. I certainly would discuss the benefits with your dealer.


    Bookmark   August 5, 2014 at 6:51AM
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