Replacing with Carrier 5-zone system, tech says may not work

[craig-drip-tx]

Hi thanks in advance for any advice or commentary you can offer. I have a 20-year history of suffering from poorly installed residential HVAC while living in Houston, TX where it is miserable having bad A/C. Around 2007 I retrofitted the house I was in with a commercial zoning system and it was a fantastic improvement. However it was still not perfect. For example one zone was assigned to 2 bedrooms across from each other and the thermostat for that zone was in the hallway between the 2 rooms. I could be in the hallway and the thermostat is reading 74 degrees and then walk 10 feet inside one of the rooms and it would be 80. I swore at that time that if I ever built a house it would have proper zoned HVAC from the start.

In 2018 I contracted with a national builder to build a house from dirt. They refused my request to add a zoning system at the time of construction due to policy. I ended up with 2 Lennox systems:

• UP 14ACXS030-230 Lennox Merit Series, Air Conditioner Condensing Unit, 2.5 Ton, 14 SEER, 1 Stage, R-410A
• DOWN 14ACX-060-230 Lennox Merit Series, Air Conditioner Condensing Unit, 5 Ton, 14 SEER, 1 Stage, R-410A (Aprilaire 8126X fresh-air ventilation system 15 minutes/hour)

The house is 2-story 6BR 6BA ~5300 square feet and of course it has just the 2 thermostats, one on each level. Downstairs is mostly acceptable although we do have one room (guest room) that is usually freezing. Upstairs however is awful with its one thermostat. There are 3 bedrooms, a game room and a media room upstairs. It gets so hot at times that my son in his bedroom will have a box fan 2 feet from his face blasting at full speed and he is still sweating. However over at the single thermostat it thinks things are fine so it does not call for cooling. The game room is similarly hot at times. I have not even attempted to setup the home theater in the media room because I know as soon as the AV equipment is on, projector, etc and 4 or 5 people are in that room, it will hit 85 degrees. I was told that while adding zoning to the upstairs is straightforward since it has better attic access, adding zoning to the downstairs could be more difficult. Since I am mostly happy with the downstairs, I decided to tackle upstairs only first.

The home came with a 2-year warranty on mechanical and I did not want to void that warranty so I have been waiting patiently for 2 years to upgrade the upstairs to a zoned system. From reading this forum I knew that my single-stage Lennox unit was not going to work well with zoning so I anticipated a major overhaul. I am in the Austin area and after some searching I found a great A/C contractor/owner who seemed to know about zoning systems. I told him I would love to have one of the Jackson, EWC or Arzel systems that I read about on this forum. I had a notion that the big name HVAC equipment companies had inferior options when it came to zoning. The contractor however only installs Carrier equipment and he convinced me that using all Carrier components would be the smartest choice since they are all designed to communicate with one another. That made sense to me and since my current equipment is not that great just replacing it all made sense. So he spec'd out a top-of-the-line system:

• 3.0 ton Infinity Greenspeed (variable speed) SEER 21.5 (cooling variable 25% to 100%)
• Modulating furnace (variable 40% to 100%), blower motor Variable Speed Constant airflow
• (5) thermostats w/touch screen smart sensors (Wifi enabled)
• Surge protectors
• UV Lamp
• REME-HaloLED
• removal and replacement of all existing ductwork (current ones are improperly sized)
• some larger supply grills and a 2nd supply air grill on the media room.
• 4" Honeywell media cabinet filter

I asked for 5 zones, 1 for each of the 3 bedrooms, the media room and the gameroom. He had to order a special order modulating variable speed furnace that takes about 10 weeks to get in. I know talk of pricing is not allowed here but I can tell you that this is not an inexpensive project. However I feel like it is a good investment that will allow us to enjoy our home in comfort.

Now we are about 3 weeks away from the furnace arriving so we can begin the installation, and I get an email from the contractor stating that after speaking to a technical supervisor (at Carrier or maybe the distributor?) they have some concerns about the system as designed. Basically they say that if only one of the 5 zones is calling for cooling, the system may "think" it has "lost control" and ramp all the way up to 100% and attempt to blow all 3 tons of cooling into that one room.

"Remember this system is at all times maintaining 1/16th of a degree of its set temp. That means something as simple as a one or two degree drop will "force" the machine to go to 100% capacity. The Technical supervisor has concerns that when this situation occurs you might be unhappy with the sound level exiting the vents on the ceiling in that one zone. In an effort to maintain customer satisfaction, he thinks that you should seriously consider reducing the amounts of zones from 5 to 2. He recommends putting all 3 bedrooms on one zone and then the game room / media room on a second zone. This would reduce the issue of a sound nuisance as more vents would be available to distribute the airflow when the temperature is dropped just a few degrees in any particular zone"

"You fully understanding what this system will do in the event of a temperature drop when no other zones are calling runs the risk of "sound" with installing of a 5 zone system. We know it will work, we know it will heat and cool but I do have concerns about sound. So as long as you are on the same page with the potential nuisance sound issue that can / will occur at times then we can proceed with the 5-zone install but I seriously want you to consider reducing the amount of zones"

This was not what I wanting to hear. Having only 2 zones for all 5 rooms will put me right back in the position of having unbalanced cooling. The media room is all turned off and empty 98% of the time but when it is occupied it needs lots of cooling to counter the BTUs from the people and equipment. Not having thermostats in each bedroom means once again my kids will need that box fan to keep them cool. Actually I need to check with him to see if he is proposing 2 zones with 2 thermostats/sensors or still have 5 thermostats/sensors but if any one is calling for cool, then all the rooms on that zone group will get cooling. The 5-thermostat 2-zone solution is not ideal but at least I would be ensured no one room could be hot. Worst case is some rooms in the zone group would be over-cooled which is way more manageable than being too hot (you can always put on a sweater).

Is it just me or does the explanation of the 5-zone system blowing 100% capacity / 3 tons of cooling into one room sound wrong? What is the purpose of the variable speed 25% to 100% cooling if it can't dial down to 25% when only one zone is calling? Either they don't understand how the system works or that is one poorly designed system.

I saw this in another thread:

"It has been my experience that anything less then 20% for a zone is going to cause trouble. Already been said. Got to question why it was set up that way to begin with. When zoning and some small zones are to be designed, two stage equipment is important for the longevity of the system, and your comfort. You will need to set up some load shed, or dump zone to help with the overload."

That to me implies that for small zones, a 2-stage or even variable speed unit (like the one I am getting) ought to be able to perform.

Going with a 2-thermostat 2-zone solution is a non-starter for me. No way I can spend that kind of money and still have the original problem. It is hard for me to know how bad this noise problem will be but if what they say is true and the system will blast 100% into only one zone I imagine that the sound would be unbearable. I can't have children being woken at night by the HVAC. To my simple mind it does not seem difficult for a system like this to be intelligent and instead of all or nothing for each zone, it could send a higher percentage of cooling to the room calling for it but still send some cooling to the other zones. Or, if it would simply run at 25% when only one room is calling, then there ought not be a noise problem.

I'm really bummed because I liked this contractor and it is really hard to find someone that is knowledgeable about zoned residential. If anyone knows someone they would recommend in the Austin area please let me know. I need to find out what my liability is with regard to the special order furnace but it seems like if the system I requested is now considered unworkable by the manufacturer then I ought not be held responsible for anything should I decide to cancel the whole project.

[Restaurant Mech]

I'd reccomend just installing a mininsplit in the rooms you want as ZONED.
Frankly for running 5 zones I'd be doing it with 2 separate systems anyway. I'm finding anything more than 3 zones on a system just confuses everything.
Because with zoning really each zone needs to be sble to handle 75% of the ENTIRE airflow of the unit to work properly. Otherwise you run into problems.
So I'd leave the current system as is snd add extra capacity with a couple of mini splits.

[pacnw]

Unless the bedroom are HUGE, they are all but guaranteed to be too small for proper zoning!!!!

While you may think zoning is the way to go, unless it is done by a true professional in zoning it will ALWAYS be a disaster!!!!!

[Mr Bill]

While you may think zoning is the way to go, unless it is done by a true professional in zoning it will ALWAYS be a disaster!!!!!

I agree 100%! And because you never know how it’s going to work out, or the customers expectations, you could be going back and tweaking for months. 5 zones? Yes, mini-split in some rooms would be better. Sometimes I wonder if the old school manual dampers, once adjusted for the comfort needed in each room were a better way, seems we had a lot less complaints. :-)


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[kdean1]

It sounds like a distribution issue to me. Have measurements of air flow been taken with a flow hood? Do the bedrooms have returns or just supplies? Has the house been tested with a blower door and zonal tests for the problem rooms?

Zoning is NOT a cure-all. It can be a source of problems rather than a solution.

[craig-drip-tx]

old school manual dampers, once adjusted for the comfort needed in each room were a better way

It sounds like a distribution issue to me. Have measurements of air flow been taken with a flow hood? Do the bedrooms have returns or just supplies? Has the house been tested with a blower door and zonal tests for the problem rooms?

My issue with this is that these zones have wildly varying heat loads at different times. Depending on where the sun is shining, how many people are in a room, how much A/V equipment, popcorn machine, etc is running each zone either needs a whole lot of cooling or very little. So everything could be "tuned" to work perfectly for one scenario, and in another it performs badly. Zoning with a thermostat in each area (combined w/ a variable speed cooling unit) sounds on the surface like it should solve the problem of wildly varying heat loads.

Do the bedrooms have returns or just supplies?

Each of the 5 zones has return and supply. The media room will be getting a 2nd pair of return/supply.

Unless the bedroom are HUGE, they are all but guaranteed to be too small for proper zoning!!!!

What I can't understand is if my cooling unit is variable speed down to 25%, and assuming I am happy to get ~20% flow to each room that is calling, why would 1 zone calling with the variable running at 25% not work? Also it would seem smart if the zoning system would not be all or nothing, i.e. in the case 1 room is calling, still pump cool air to all zones but just open the calling room damper more than the others.

While you may think zoning is the way to go, unless it is done by a true professional in zoning it will ALWAYS be a disaster!!!!!

Yep, now if I could just figure out how to find that true zoning pro!

I am going to give the minisplit idea for the media room (it is has the highest variable cooling needs) some thought. In my old HVAC-nightmare house we actually did install a Fujitsu minisplit in one room but it gave us so many headaches with burned out control boards and other electronics issues that we ended up tearing it out and going back to the central HVAC for that room. A few years after that we installed a HighSEER minisplit in a garage apartment and I was very happy with its reliability and performance.

[dan sw fl]

My issue with this is that these zones have wildly varying heat loads at different times.

Depending on where the sun is shining,
how many people are in a room,
how much A/V equipment, popcorn machine, etc
is running each zone either needs a whole lot of cooling or very little.


So everything could be "tuned" to work perfectly for one scenario, and in another it performs badly.
Zoning with a thermostat in each area (combined w/ a variable speed cooling unit)
sounds on the surface like it should solve the problem of wildly varying heat loads.

Each of the 5 zones has return and supply. The media room will be getting a 2nd pair of return/supply.

Yep, now if I could just figure out how to find that true zoning pro!

.

THE ROOM LOADS NEED TO BE PRECISELY QUANTIFIED
so the range of room air flow rates are reasonable and sufficient.

__________ ___ ___ ___ KEEP IT SIMPLE.!
so it actually works.

Zone 1 : Bedrooms
Zone 2 : Other

ATTACHMENT