I'm replacing a 30 year old furnace with a new one. My house is about 1600 SF in Bay Area. Since this house is not really energy efficient I'm planning to use a two zone (bedrooms, living area) system. One of the contractors gave me an estimate for a Carrier performance 2 speed, 2 stage 94% with two thermostats, dampers, and a control board. Another one gave me an estimate for Carrier infinity (costs about $X more) and is telling me that infinity is the only system that works well for a zoned system. Do you have any opinions about the suitablity of the two models for zoning and the value proposition?
[Edited by jrbenny on 11-04-2006 at 01:38 PM]
The Infinity modulating zoning system is probaly the best resi zoning sysytem out.
I recommemd making your house more energy efficient before upgrading your HVAVC system.
You save money everyday that way.
There are quite a few after market zoning products to choose from. Of the after markets, I prefer EWC but they are all comparable for the most part. The Infinity Zoning system is far superior to anything else out there and is well worth the extra money when used in conjunction with the Infinity furnace and 2 speed condensing unit. The Infinity system is much like plug and play technology and takes alot of the burden out of the hands of the installer. The after-market models are much less forgiving and you should seek out an installer who has a good amount of experience installing such systems. Good luck...
Dave in NJ
Thank you Dave and beenthere for your replies. If my understanding is correct, you are saying that there's a matching zoning control board that comes with the Infinity furnace, but for the Performance, a third party control board will be used and it could work fine if properly set up. What are the main points that the installer needs to be careful about (or I should make sure done properly)?
Becarefull not to have too small of a zone.
EG: a bathroom as its own zone is trouble on a standard zoning system.
The zoning panel should have the ability to lock out second stage if only 1 zone is calling, if no zone is more then 60% of unit capacity.
It is correct that there is a Infinity Zoning Board (however it does not come with the furnace, you have to purchase it separately) that is designed to work with the infinity system. If you are to go with the comfort or performance series, then you will need to use an after market zoning system (I believe carrier does make one for that application as well). The installer will have to make sure the zones (ductwork) are sized properly and if a by-pass is to be used then that too needs to be sized and designed properly. A supply air sensor should always be used to protect the equipment. A poorly designed system can allow the supply air to reach temperatures that are too high or too low for proper operation and the SAS (supply air sensor) would shut down the equipment should this condition occur. The biggest issue with zoning is what do you do with the extra air? For example, lets say you are doing a small two story house, 1200 sq ft up and 1200 sq ft down. Lets say for arguments sake that you have 4 tons of A/C. Now when both zone are calling no problem, but when say the upstairs satisfies a damper closes and now you have 4 tons worth of air going to the first floor. The problem here is that your trying to stuff 10 pounds of crap into a 5 pound bag. So you need a way to get rid of the extra air. One way of handling this problem is to install a by-pass. A by-pass uses a damper that will sense the extra air pressure and open allowing the air to go somewhere else. Now you have to decide where the extra air will go. You can do what is called a dump and just let the air go into a non-critical space (attic, garage, etc) or you can pipe the air back into the return duct where it gets recycled in a sense. This where the supply air sensor comes into play, because once you start recycling conditioned air it can easily freeze up your coil, but you can avoid this if it is done properly. Same goes with the heating cycle. The furnace is designed to operate within a certain temperature range, once you start recycling the hot air, it can go outside that range and start tripping limit (safety) switches. I purposely over-simplified this so that I could give you a taste of what we do as professionals. It is actually much more involved than this and that is why I recommend you find someone with a good amount of experience with zoning. Again, I also recommend the Infinity zoning because a computer controls everything, for example the computer constantly monitors the pressure in the ducts. When one zone closes the computer can see that and will ramp down the blower speed to send just enough air to the open zone, thus eliminating the need for a by-pass damper. Awesome!!!
Hope this helps....
Dave in NJ
Thank you beenthere for the points and Dave for the detailed explanation. It looks like this should be achievable with a 2 stage 2 speed system if designed so that when only one of the 2 zones needs to be on, force the furnce to low speed and low heat.
2 zone system Installed, found issues
I finally decided to use a Carrier performance 93% 2 stage furnace and selected a contractor after speaking with a few companies. They installed the furnace along with a Honeywell controller and dampers the other day (while I was away). Initially when I talked with their sales rep and brought up the extra air issue and asked whether the controller can take care of it (i.e. force the low stage when only one zone is active), he insured me that the controller will do that. When I checked the controller, I found out that not only there's no logic in this contoller to handle such a case, they have also used the controller suitable for a single stage (Honeywell EMM-3). I have not checked, but it does not look like they have used a bypass either. After reviewing several controller manuals, I found that Honeywell TZ-4 can actually be setup to control which stage comes on based on percentage of zones calling. So one option is ask them to use TZ-4, but the drawback is it never turns on the 2nd stage for one zone only. Since my zones are not the same size (zone 1 is 600 SF, zone 2 is 1000 SF), I'm thinking of limiting the furnace to stage 1 for the case of zone 1 calling and let the thermostat on zone 2 or combination of the two enable the 2nd stage.
The question I have is what are the problems when the furnace running on high and only one zone (zone 2 as I plan) is active? Does it damage the furnace due to increased pressure or is it mainly generating more noise?
The TZ4 will allow you to control staging by time if you want.
What will happen when the furnace goes to second stage with only zone 2 calling depends on how well the furnace was sized, and the duct size. The DAT sensor will protect the furnace from over heating. You may get noise.
Did they put the same size furnace in as you had, or did they do a load calc and put in the right size.
The Zonex 2 stage panel bases staging on time and temp. It times to high after so many minutes but only if supply temp allows. If the small zone is calling, chances are the supply air will be plenty warm and the furnace will stay on low. If the big zone calls and moves more air, the furnace will likely time to high. We use this panel ourselves. My office is a small zone but needs heat so much more than the rest. If only it calls, the furnace runs on low. If a 2nd zone calls or a larger zone calls alone, the furnace can time to high if needed.
> Did they put the same size furnace in as you had, or did
> they do a load calc and put in the right size.
We had a very old 100K BTU Fraser system, so I guess it may have been 60-70% efficient. They put an 80K BTU, so the actual heat going inside the building should be the same.
>What will happen when the furnace goes to second stage with
> only zone 2 calling depends on how well the furnace was
> sized, and the duct size. The DAT sensor will protect the
> furnace from over heating. You may get noise.
They have not even connected the DAT on the zone control system! Maybe they know or assumed the carrier furnace itself has a DAT and internal protection.
The Totaline thermostats used can turn on the 2nd stage based on adjustable time and adjustable separate dead zone for the 2nd stage, so I'm thinking of setting the small zone to longer time and higher dead zone to reduce the instances it calls the 2nd stage. I think you can program this to works fairly satisfactorily in most cases. It won't be optimal in all cases for example when both zones are calling for 1st stage only, but the temprature is low enough to benefit from 2nd stage. As you said an integrated system like Infinity or just slightly smarter controller could handle this.
You don't want your furnace cycling on the high limit.
Have them install the DAT, and set it lower then the high limit.