Adding zones to system

We have a 2 story house built in 1993 that is approximately 2500sf. Upstairs is 1000 and downstairs is 1500sf. 2 returns upstairs and 2 returns downstairs. My heatpump is a tempstar T4H736GKD200 (3 ton, 2 stage) and the airhandler is FVM4X4800A (variable speed). We have only 1 thermostat in the family room that runs the whole house. We have a lot of trouble keeping consistent temps between up and downstairs. It can be up to 4-8 degrees warmer upstairs.

I had 3 companies come out today for options on how to fix the issue. The first 2 suggested making zones with my existing setup. 1 damper in the main run to upstairs and 1 in the main run for downstairs and then installing a zone control unit near the airhandler and a second tstat upstairs. Neither said anything about needing a bypass or a dump. They seemed to indicate I had plenty of airflow and returns that there wouldn't be an issue.

Company 3 stated that it would be a bad idea to install a zone system. He said if only one zone running the 3 ton unit would be forcing to much air through and would result in damage to the compressor. The only way around it would be to install a dump for when the pressure got to high. This would dump conditioned/heated air into the crawl space of garage resulting in a waste of money. His first suggestion was to install a ductless mini split with 2 head units upstairs and his alternative suggestion would be to install a second heat pump and airhandler.

Cost for company 1 and 2 suggestions would be around 2100 cost for the zoning setup. Cost for company 3 would be 6-7k depending on the option.

Company 2 actually suggested that I set my fan to run 24/7 and see if that helps before doing anything. I've been doing that all day and its brought the upstairs 1 degree closer to downstairs so I'm not sure it's going to work but I'll give it a few more days while we try to decide on which if any of the other options to pursue.

So whose right? any suggestions?

 

Your 2 stage 3 ton unit is only 2 tons with only stage 1 running.

If you get a Honeywell zone control and configure it to control stage 2 with the number of zone demanding cooling you would be running a 2 ton unit if only one zone has a demand.



Not all zone control systems run fully open or closed.
The Carrier zone system can partially open the closed dampers if the leaving air temperature sensor starts detecting temperatures that are too low.
It uses power open/ power closed dampers and a timed signal to the dampers to control position.


The guy that invented mini split units has horns. Your service techs will require tech support to repair it the day it fails. Any parts required will probably need to be ordered.

 

Houston-thanks for the feedback. Neither company has said what brand equipment they would be using yet- still waiting on the full proposals to come back. If I understand you correctly, I might not need a bypass or dump if they use the right equipment then?

 

If I installed a barometric bypass I would set the weights to a high static pressure.

Do you know your existing external static pressure?

I think Carrier has the best zone control option available but the less expensive Honeywell might be sufficient for your application. I would avoid the Harmony zone control.

 

The idea of zoning is wonderful in theory but never seems to work like promised.

It sounds like you have a split level house like mine. With a gas furnace and the A/C added to it. The ductwork was sized and located for the best heat delivery.... not cooling.

Whatever you do....you need to try to reduce the heat load in the second floor. Attic insulation and better attic venting are two positive steps.

 

The only guaranteed solution is two add the second unit.

 

I had a home energy audit last year and was told we had excellent insulation in the attic and it would not be worth the money to add additional. The hvac companies also committed on how well insulated it was.

 

I have seen a minisplit cause the indoor humidity to reach 83% in the house.
Tech support kept me on hold for several hours until I gave up and left the jobsite. They called me back 2 service calls later when I was at someone else's home servicing their unit.

The blower would never fully turn off on a Mitsubishi air handler and tech support tried to explain to me that this was by design since the remote control doesn't actually sense temperature. ( On the following day after another wait on hold for tech support)

After ordering the Honeywell 6000 looking stat and receiver and cutting a jumper in the air handler the problem was resolved. Tech support seemed amazed that I didn't want the fan to always run. I suspect that they are in a very dry climate.

That was 3 service calls and many many hours on hold. Of mini splits Mitsubishi is probably the most popular but they do not employ enough people to support their product.

They have made an improvement in that they now schedule an appointment with me when they call me back two service calls later. It is tough to wait for hours on hold when you are charging someone $99 an hour.

LG Tech support answered the phone every time that I have called and assisted me in located the faulty components. (though I have called them much less often)

My company has installed hundreds of Carrier zone control systems. It is a very reliable product.
It would definitely be my choice for that application if the duct work allows it.