Residual Air in zones not calling- What is normal?

RAMerr

Looking for advice. We have a new home built a year ago, 3000 sq feet in New England. Builder's contractor put in 5 ton, single stage, 3 zone system. Zone 1 is the first floor (approx 1200 sq ft). Zone 2 and zone 3 make up the 2nd floor (approx1700 sq feet). We have had multiple issues since day 1 that the contractor has worked with us to try and resolve. Biggest 2 issues are: (1) the compressor turning on for 6 minutes where it gets really cold really fast, then its off for 15 min where it gets warm until the system kicks back on (2) cold air coming out of vents in zones not calling and zones cooling below the set temp (mostly Zone 1- first floor). Contractor checked dampers and they are working. He just installed a static bypass in order to try and fix both problems -so the 5 tons of air would have somewhere to go when only one or two zones are calling. The bypass did seem to help some with comfort (ie: not freezing us out in that 6 minutes), however, its' still cycling on for approx 6 minutes and off for approx 15 and we still can't seem to achieve a consistent comfortable temp. We also still seem to get a good amount of air blowing through zone 1 when zone 2 or 3 is calling. I'm being told that's normal residual air? But it seems like too much air- enough air to cause the curtains to move. Is there a way to test the air that is coming out of the vents not calling to see what the air flow is? And what should we accept as normal residual air flow from vents in a zone not calling?
And is it normal for a system to cycle on for 6 min and off for 15min ? or should it be more consistent, like on for 10, off for 10?
Thanks for any advice!

Big Ed_4

My first thought is the system over sized .. I would like to see the heat gain calculation to know for sure ...

SuperTech

Definitely sounds like its an oversized system on an undersized and badly designed ductwork.  

Three zones on a 5 ton unit? I hope this is modulating variable speed equipment or at least two stage.

It's rare to see a two zone setup work properly.  Its really best for the equipment and the comfort of the occupants if each zone has its own dedicated system.

unclejohn

all zone systems should have a freeze stat on the coil and a discharge air sensor. That is what is shutting you down for fifteen minutes most likely. Also if you are trying to get 2000cfm through one 12" damper somethings gotta give. Seems to be a very poor design.

DeBow

Systems short cycle when the equipment is way over sized. The thermostat sensible temperature is satisfied while the latten heat has not been removed. These installations tend to be cold and damp feeling. If the equipment is properly sized the equipment cycles on and runs for quite a while and stays off. It has a longer run time because it is sized properly and running to remove all of that humidity. The opposed blade dampers of a zoned system should prevent air from passing through when the zone is close. All dampers are open. when one calls the others close shut. If this is not the case, the ductwork is wrong.

RAMerr

Thank you everyone We've had 2 other contractors come out at this point to help us diagnose. Both thought possibly oversized, but needed to see load calculations. Also, one of the contractors found that the discharge air temp sensor had been incorrectly wired and put in the wrong location. (might be why our coil froze twice). So they moved it and wired it correctly. We bought free standing thermostats to let us know the wetness in the air and it seems to be around 45% most times. Ive been asking the contractor who installed the system from day 1 re: it possibly being oversized an he said it was sized to meet the entire need of the house when all zones are calling (which he said is the right way to do it). Unfortunately- not all zones ever call at once. Both contractors that came in to help us evaluate and diagnose the system said the ductwork was done very nicely and looked good (it's decent sized ductwork). In my research, what Ive uncovered is that a single stage unit should never be zoned, it causes a lot of problems. At this point, we are thinking that we get rid of Z3 and just have 2 zones, or talk to the contractor about getting a smaller unit (after he provides the heat load calculations)- but that will entail alot of heartache and conflict because I would imagine he's not going to bear the financial cost of that and put it on us.
We really appreciate everyone's recommendations and open to any more feedback or suggestions. We just want to be comfortable in our home.

ratio

45% RH sounds pretty dry for this time of the year.

What brand/model of zone panel? I'm familiar with Honeywell TrueZONE® panels, they will actually stage down based on discharge air temps & can stage up based on a timer, number of zones calling, or pass through a 2^nd stage call from a thermostat.

RAMerr

We were surprised that the RH was 45% when we got the thermostat. You can feel the cold air when you walk in the house. Ive had many people walk in and say how frigid it was in the house.
The zone panel is a Honeywell HZ432 TrueZONE, with T4 PRo Thermostats and the TrueZONE damper assemblies.
Is stage down- to reduce the air flow when only one/two zones calling? And Stage up to increase air flow? Is that a separate timer we would have installed on the system? It sounds like that would help and maybe mimic what a dual stage compressor would have done? Do I understand that correctly? Or do I have that backwards? Thanks!

ratio

It's to drop to stage one cooling, or off if it's already on low. I forgot that you said you have a single stage unit. The DS/BK terminal is to slow the fan down, but that's generally only present on units with variable speed fans.

It sounds to me like too much air most of the time. A five ton single stage unit puts out 2000 CFM (more or less) of air when the fan is on & zero when the fan is off. You've got to have somewhere for that air to go. The bypass will help with that, but brings it's own problems. (You can't bypass much air back into the return or the temps crater (cooling) or skyrocket (heating).) It's pretty unlikely that any one zone will be able to take all that air.

The TrueZONE panel has a checkout feature. I'd test each zone individually & fiddle with the bypass setting to get the downstairs zone to take all the air; then tie the two upstairs zones together & see how they operate together. & give some thought to changing out the single stage unit for a two stage variable speed unit. IDK if I'd reduce the size, maybe watch it though the heating & cooling seasons & think about a 4 ton multi stage.

Also, I've been pretty disappointed with the Honeywell dampers—they can't seem to hold back the air if the air pressure is anything above negligible. I think you're seeing this with the overcooling you're experiencing.

RAMerr

Thank you ratio. One of the other contractors that came in to test the system also told us he has had a lot of issues with the honeywell dampers malfunctioning- but ours were functioning when he checked them. But clearly even though they are functioning, they arent holding back the air. Is there an acceptable amount of air that we should see coming through first floor zone when its not calling? Quite honestly, it feels like we dont have a zoned system at all because we get a ton of air in Z1 when Z1 isn't calling.

ratio

I can't recall offhand if the TrueZONE dampers have a minimum position (keeps them from going completely shut) but it's possible that it is set too high. More likely (having never seen the install, mind you) is that the blower air pressure is too high for the dampers to hold back. An air balance should have been performed as part of the commissioning of the system, that would tell you how much is flowing through each zone. If it's significantly less than the nominal 2000 CFM the unit makes whenever it's running, that would raise the pressure in the duct & force air out wherever it could—like leaky zone dampers. A bypass can help some, but like I mentioned before bypassing too much air causes other issues.

motoguy128

5 tons for 3000sqft on new construction in temperate New England? Should be a 4 ton 2 stage system. Zoning should almost always use multistage. Or better yet modulating.

4 tons cools my 3600sqft 1903 Brick Victorian in much hotter SE Iowa.

unclejohn

The honeywells do have a min. set of zero to 30% open if I remember correctly.