New Zoned System Trouble

[carestx]

Help, recently replaced 8.5 ton (3 units) with single 5 ton zone system (Amana) Located in Dallas, TX 3200 sq.ft home.
Home never reaches set temps (always 3-4 degree off), all zones calling for all all day/night long. Contractor has by-bassed air/zone sensors, moved control to thermastats. Now home not taking care of humidity and still not reaching set temps. Now they want to install an addtional 2 ton (3rd stage???)unit.
I have poor air circulation in one zone and the rooms that do get air sound like a freight train. I do have their load calc's and general data.

Looking for some suggestions/help. Will answer questions the best I can.

Thank you all in advance

[sadlier]

Just so I have a better picture of the situation, I perceive that you are the homeowner and this was obviously a remodel. When they installed the zone system did they reuse existing ducts or install new? What is the brand and model # of the zone system?

Off the bat I see one problem but need a little more info. What was the sensible and latent heat gain numbers?

You say that they want to install an additional 2 ton unit - how would this be connected to the zone system? With an additional furnace/air handler?

[carestx]

Thank you for replying

Yes I am homeowner and will try my best to answer your questions.

Show heating load at 89839 BTUH and Cooling @ 53932 Sensible and 7698 Latent or Total 61631

Hope this is what you wanted?

Unit is a Amana Prestige Ultra unit, 16 Seer, sorry all I really know.

They have placed a 14 Seer (2ton) unit outside and have hung the other half above the unit in the attic. They say they are using like the by-pass duct (they removed) when installing it.

Does this help?

[carestx]

Sorry, they also installed all new duct work!

[carestx]

Zone controller is made by ZoneX, can't tell who makes the dampers (sorry had to go to attic to find answer)

Home is a two-story currently set up with 3 zones..

All second story (zone 3) 13252 Sensible 1530 Latent 14787 total

Master Suite (zone 2) 9815 Sensible 1856 Latent 11671 total

Living Area (zone 1) 24164 Sensible 4312 Latent 28476 total

http://www.zonexsystems.com/

[sadlier]

Eeeeks! I hope that it was a misstatement when they said they are using it like the bypass duct - say 'hello' to problems if that is what they are going to do.

One problem the system has is inadequate airflow. It will take about 2,800 CFM to extract the 53,932 BTU of sensible heat out of the air conditioner. Nobody makes a residential furnace/air handler that delivers that many CFM. They would have either had to go to a commercial unit or do a "twin" on residential units. If they cannot achieve the proper airflow then they must compensate with more air conditioning but that, too, can only be taken so far. Assuming the blower is putting out 2,000 CFM of air, a 5 ton system will yield only about 39,000 sensible BTU - clearly nowhere close to the heat load calcs. Adding another 2 tons of cooling in a manner like the bypass duct will certainly make the air colder... in fact cold enough to cause the air conditioning coil to ice; Then you'll have very little cooling.

Another problem that is perceived is that the ducts are not sized properly. This is evidenced by your original statements regarding inadequate airflow, noisy airflow, and combined with the percentage of contractors that actually go through and do duct calculations to determine size. Without properly sized ducts you may end up with continual cooling problems.

Ok, I've got one more question: Are the pipes all the same size (IE 6") or only two sizes (IE 6" and 8")?

[carestx]

OK, it's nice to get some real answers.

From what I can tell there are a comnination of 6" and 8" duct. Some even looks larger then that.

Let me try to explain the second unit again, just in case. They have the unit being fed by the same return as the 5 ton and then feed it right into the supply duct used by the 5 ton.

So this is "band aid" fix to a larger issue?

So your thought is there is not enough air movement? Do the need addtional returns? Our should there be a seperate system (heat and air) to handle one of the zones.


When I fist started complaining, they came out a blew 6" of insulation in the attic. Didn't seem to do to much?

[carestx]

What do you mean by a "twin" configuration?

Also, would the indivdual zones effect airflow?

Also, will this have the same effect on heating my home?

Thanks again for the help, I feel my contractor is now only looking out for him self and hoping to get through the summer season.

Again, I hope I expalined the second unit correctly?

[mark beiser]

No way to tell for sure with the info provided, but perhaps they were off on thier load calculation, so dropping from a total of 8.5 tons of cooling to 5 tons left you short on capacity when all zones are calling.
Just a guess, but they may have figured out they made a mistake, so that is why they want to add the 2 ton unit...

I don't do any work in Dallas, but I do work in Fort Worth and the mid cities. I can't recall ever seeing a house the size of yours that was built with equipment so oversized that I would drop from 8.5 to 5 tons...

Have you considdered having an engeneering company come in and do the load calculations and zone layout? There are several in the DFW area that do that sort of work.

[carestx]

Should have considered that before I contracted the job. Right now I am trying to work through the problem with the installing company and I am in need of information that keeps me on a level playing field with them.

I think you are right and the agree they undersized the unit. This is why the added the insulation and have even suggested I change out my windows. Not going down that path.

I am concerned with the extra unit they installed. They are saying it will only kick in as a third stage, after 2nd stage has been running for x period of time.

The company has been great in responding, I am just tired of seeing them. And I spent a lot of money to upgrade the system and want to make sure I get the proper system config.

[carestx]

Everyone, I really do apprecaite the information. It is an equalizer for us homeowners. We have focused on the AC side of the system, so is it safe to assume everyone thinks the heat will work (it was a matched Amana heat) fine.

Right now I am taking everthing you share with me and using it to red between the lines of what they are telling me or doing. Only time will tell.

Does anyone see any long term problems with the so called 3rd stage design??

[mark beiser]

Originally posted by carestx
Does anyone see any long term problems with the so called 3rd stage design??

Again, no way to really answer that with certainty without knowing far more about the system. It does sound very odd though.

You would probably be better served if the added unit took care of a zone by itself, with its own ductwork and all.

I don't have any experience with the equipment or the zone system they used in your house. All of my experience is with Trane, Lennox, EWC and Honeywell.

[johnsp]

You seem to have a large home with a large cooling load. I'd have been suspicious hearing a single 5 ton unit replacing 8.5 tons of capacity. Zoning 2 floors is very common, but going 3 or more is a very complicated balancing act. A step down to between 7 and 8 tons with 2 seperate systems with two zones off the larger unit seems more logical and simpler to install and maintain. They should to be able to simplifiy the ductwork and isolate one of the zones onto its own supply plenum. I would not let them put the 2 ton in (you might need more) until I saw a plan that would support the new cooling load and ductwork.

[beenthere]

Not a good idea to twinn 2 different size units.

[mark beiser]

Originally posted by beenthere
Not a good idea to twinn 2 different size units.

Yeah, having a 5 ton blower and a 2 ton blower sharing the same return and supply is BAD mojo.

[wormy]

I also agree with putting the 2 ton on a zone by itself.

Lemme explain twinning to you to be a little more edumacated hehe
by twinning, we mean putting two furnaces parallel to each other. The furnaces share the same return and share the same supply.
I've seen this alot in commercial applications.
The furnaces have to specially set up for twinning though.
Most furnaces have a 'Twin' terminal that you connect from one furnace to the other, and there are also special kits that provide the additional safeties required for problems that can arise in the future.
All twinning that I've ever seen has had two furnaces that match sizes.

In the application you are describing...
Using the 5 ton to come on first then bring on the 2 ton as a second stage if needed...
The 5 ton can 'recirculate' air through the two ton equipment. This can cause the blower wheel of the 2 ton unit to start rotating backwards. When the 2 ton unit does come on... the motor will have a hard time reversing and going the other direction. There's a chance that the motor will actually start up and run backwards too.
Not good on the furnace, blower, or AC equipment.

Also, by recirculating the air... the air will get colder and colder and eventually freeze the unit up.
Or if your in the heating season, the air will get hotter and hotter and will end up tripping safety switches.

I would re-figure the loads on the house again.
Once using zoning and then a regular load calculation on each zone. There are different considerations when figuring the heat loads with a zone system, so the numbers will end up different.

(havent' payed much attention to the numbers you give so take it for what its worth)
I'd try to put the downstairs as a zoned system and the upstairs as an individual unit.
The upstairs would need a filter grille of its own upstairs.
The downstairs would need a filter grille of its own downstairs.

Wished I was there to really diagnose the system though.
There's alot I would check for.
Load calculations
Duct sizing calculations
House design considerations
etc

[sadlier]

Wormy described the twinning well. It looks like the configuration is basically as a twinned unit; I agree that it isn't a good idea to mix different sizes of units in a twinning setup.

The ductwork was apparently not sized according to the International Mechanical Code, either. The IMC requires a Manual D calculation to be done (or other recognized method) and a Manual D calculation usually gives different pipe sizes, not just two. Granted that your house may be a rare exception, but I doubt it. Zoning is not intended to make up for improper duct design and zoning will only go so far in compensating for improper duct design.

Options vary and some were already suggested. A whole system analysis by someone else would be the best bet so that all options could be explored and actual system sizing can be analyzed. Fixing the system so that the proper airflow can be achieved so as to maximize the efficiency of the cooling equipment may require something that all of us contractors hate to do.

[carestx]

Thanks again to everyone. I think the next step for me is to get an professional out to evaluate what is here and tell me what should be here.

I would guess the best person would be an independent Mech. Eng. firm?

Someone had mentioned there are firms in the DFW area that do this?

If my contractor would only tell me what/why he is doing things this might be easier. They are happy playing hit or miss with the system and my money.

Thank you

[sadlier]

One place to check for a contractor is on this website. Otherwise when checking around ask them how they determine duct sizing. Don't go with a contractor that doesn't know the Manual D or sets it aside for an easier method.

[Edited by sadlier on 09-08-2004 at 12:03 PM]

[carestx]

Sadlier,

Looking for a third party (nutral party) not sure where to look.

I have requested general design info from current, will see what I get.

All in all, the system is not doing the job but the season has turned. Not sure what I will manage to achieve.

Did you see my zone breakdowns on sensible & latent loads, how would you recommend I use the existing 5 ton and where should I request a seperate system ?