Syncing HVAC Zones

[ano]

I installed a three zone HVAC system controlled by three OmniStat2's.  It works great, but I discovered one problem with a zoned AC system; there is no synchronization between zones. What happens is this, one zone will call for AC, the AC will start and the zone will be cooled and the AC will shut off. Then maybe a minute later another zone calls for AC, the AC starts and cools that zone, etc. While it all works great, I'm worried that all that on and off will shorten the AC life and decrease efficiency. 
 
So I am thinking of some ways to sync multiple zones so they work together assuming they all need AC at the same time. So my first idea is to detect when one thermostat is calling for AC, then drop the temp setpoint on the other two thermostats by one degree. Maybe all three.  That way if they were close to going on they would. 
 
Maybe a second idea would be this; I wait until all thermostats are in the off state with no OmniStat calling for AC. At this point I turn all Omnistats to OFF for say 10 minutes. After 10 minutes I turn all the Omnistats back on, so any that Omnistat that would have gone on in this 10 minute period now turns on, and zones are synced.  The benefit here is no tweaking the temps. If its really hot, the AC will never stop so the 10 minute break won't go into effect.
 
Does anyone else do something similar?  Does it work? 

 

[tmbrown97]

I just set minimum run times and minimum off times.  Once the A/C turns off, I leave it off for 9 minutes.  Once it comes on, I leave it on for a minimum of 6.
 
That said, I do this through the RCS Communicating Zone Controller, which sadly was discontinued.  It's awesome because all the keypads and zones talk to each other, so if you're downstairs wondering why the air is on, you can see that the upstairs triggers MRT.
 
For something comparable, you'd probably need to set some jumpers on the zone controller board itself if it has anything like that.
 
Absent of that I suppose you'd need some pretty crazy rules.

 

[ano]

I am using the Honeywell HZ432, which seems pretty full-featured, but surprisingly, I don't see a setting for minimum off time or on time.  The Omnistats have this, but that doesn't help much.  I'm not opposed to replacing the zone controller if I find a better one, because that is the cheapest part of this all.  I see Smarthome still sells the RCS 001-00250 ZC4 4-Zone HVAC Controller, but sadly it doesn't support a 2 Stage AC.

 

[tmbrown97]

And I'm pretty sure that's the non-communicating version... they OEM that for a lot of companies so I'm sure it'll be around for a while - but the communicating version that uses special proprietary wall display units instead of standard thermostats was confirmed discontinued.
 
I'm afraid I'm out of ideas.

 

[sic0048]

And I'm pretty sure that's the non-communicating version... they OEM that for a lot of companies so I'm sure it'll be around for a while - but the communicating version that uses special proprietary wall display units instead of standard thermostats was confirmed discontinued.
 
I'm afraid I'm out of ideas.

 
But you can use communicating thermostats (like the RCS TR-45, TR-65, etc) with the non-communicating zone controller and get control of the system that way.  The end effect should be about the same which is probably why RCS discontinued the smart zone controller/dumb thermostat version.  They get the same functionality without having to manufacture a whole different set of components.

 

[apostolakisl]

The trouble with "syncing" zones is it is the opposite of having zones.  The whole idea of zones is to "unsync" the different sections of your house.  Now I understand how limited syncing of zones maintains the zoning concept in a general sense, but I suspect the reason that it isn't readily available is because it partially undoes what it is you were trying to do in the first place.

 

[ano]

The trouble with "syncing" zones is it is the opposite of having zones.  The whole idea of zones is to "unsync" the different sections of your house.  Now I understand how limited syncing of zones maintains the zoning concept in a general sense, but I suspect the reason that it isn't readily available is because it partially undoes what it is you were trying to do in the first place.

 
I don't disagree with you.  In some ways.
 
What I have discovered is this. I keep my house at about 80, which is normal here in Phoenix.  When its around 95 out or below, all my zones run about equally, which implies I didn't really need a zoned system.  This is also the time I think I need to "sync" zones to reduce the AC from starting and stopping so much. 
 
When it gets over 100 outside (which it can do for 6 months of the year), then the AC has a much harder time at keeping the house a good temp. and this is where the zoning really helps.  Since its hotter out, the AC also blows hotter, and parts of my house get much more sun exposure then other parts, so the zoning really helps.
 
In the process of writing this I got another idea.  How about if I installed a relay in the attic by the zone controller that would effectively disconnect all the dampers and this relay would be controlled by my Omni Pro II?  When it was cool (below 95) I would activate the relay, deactivating the dampers, and I'd basically have a unzoned system. Over 100 degrees out I deactivate the relay so the dampers work like normal and the zoning would be back?  I think this could work.  With the switch of a relay, I could go from zoned to unzoned and back. I like it.

 

[apostolakisl]

I don't disagree with you.  In some ways.
 
What I have discovered is this. I keep my house at about 80, which is normal here in Phoenix.  When its around 95 out or below, all my zones run about equally, which implies I didn't really need a zoned system.  This is also the time I think I need to "sync" zones to reduce the AC from starting and stopping so much. 
 
When it gets over 100 outside (which it can do for 6 months of the year), then the AC has a much harder time at keeping the house a good temp. and this is where the zoning really helps.  Since its hotter out, the AC also blows hotter, and parts of my house get much more sun exposure then other parts, so the zoning really helps.
 
In the process of writing this I got another idea.  How about if I installed a relay in the attic by the zone controller that would effectively disconnect all the dampers and this relay would be controlled by my Omni Pro II?  When it was cool (below 95) I would activate the relay, deactivating the dampers, and I'd basically have a unzoned system. Over 100 degrees out I deactivate the relay so the dampers work like normal and the zoning would be back?  I think this could work.  With the switch of a relay, I could go from zoned to unzoned and back. I like it.

 
If you did this, than any of your thermostats that call for cooling will result in the entire house getting cooled.  I am not sure you want that to happen, maybe you do.  The way around that would be to use a relay to switch control from your zone control board to one particular thermostat.  This would have to have quite a few poles as there are at least 4 wires on your thermostat and probably more.

 

[ano]

Remember, my three thermostats are OmniStat2's, so turning two of them to off is a simple programming command.  If they are off, they won't call for AC and the zone control won't be the wiser. 
 
O.K. I did more thinking. (I know, that always gets me in trouble. :unsure: )
Here is what I'll try first, because its easy and just software and requires no attic work. (It gets toasty up there, you know. )
 
I'll use my Omni Pro II to monitor all three thermostats for the AC being on in any zone. After it sees that, it will check for when the AC is OFF on all three zones. Once that occurs, it will turn all three thermostats OFF for 10 minutes.  When the 10 minutes is over, turn the thermostats back to Auto. 
 
If its hot, most likely multiple zones will now call for AC and it will be as synced as its going to be. 
 
I have the thermostats set for a minimum AC ON time of 9 minutes. This with the 10 minute OFF time means the AC will, at most, start 3.15 times per hour.  An AC unit is rated to start up to 4 times per hour, so this should work perfectly. You DON'T want your AC to start more than 4 times per hour.

 

[tmbrown97]

But you can use communicating thermostats (like the RCS TR-45, TR-65, etc) with the non-communicating zone controller and get control of the system that way.  The end effect should be about the same which is probably why RCS discontinued the smart zone controller/dumb thermostat version.  They get the same functionality without having to manufacture a whole different set of components.

It's definitely not the same though - in that scenario, each of the thermostats would have their own minimum off time or minimum run time - but what if one tstat turns off and starts its 9 minute MOT, but the next one starts to call?   There's no way the controller or other tstat knows that the whole system should be down for 9 minutes (but I know there's some sort of lockout to prevent overcycling - it must be on the board somewhere).  Having a system where all zones talk to each other allows all the components to work together better.

 

[sic0048]

It's definitely not the same though - in that scenario, each of the thermostats would have their own minimum off time or minimum run time - but what if one tstat turns off and starts its 9 minute MOT, but the next one starts to call?   There's no way the controller or other tstat knows that the whole system should be down for 9 minutes (but I know there's some sort of lockout to prevent overcycling - it must be on the board somewhere).  Having a system where all zones talk to each other allows all the components to work together better.

 
I hadn't thought about that, but as you suggest, there is probably something on the zone board to prevent short cycling.  You may not be able to access that from the automation system, but the reality is that you don't need to access min run/rest times as part of the automation scheme.  Stuff like that is set up once and forgotten about.  So while the current option may work a little differently, I think the end result is close enough to the smart zone controller system that it works for the vast majority of people out there.

 

[IndyMike]

Ano,
 
I had a look at the HZ432 installation manual - you are correct that there doesn't appear to be a user adjustable min run/min off setting to prevent short cycling.  I would be amazed if the panel didn't offer some type of protection for this (maybe not user adjustable).  It's the panels job to protect the equipment.
 
You do have a number of options for controlling the 2nd stage compressor: Thermostat control, % Zones calling, Timer, off.
 
If you are using the thermostat(s) to control the second stage you may have more capacity than your small zones can handle.  Personally, I'd try the % zones setting and ensure that at least 2 zones are calling for cooling before engaging the second stage.
 
The "timer" option is a delay before engaging the 2nd stage.  Default is 5 minutes, which may be too short.  While you could use this option, and adjust the time upward, it will likely become a headache when summer comes.
 
2nd stage control setting are on page 10 (flow chart).  Timer (Advanced settings) on page 11: http://www.forwardthinking.honeywell.com/related_links/zoning/truezone/install/69_2070_01.pdf
 
If you have a DATS (Discharge Air Temperature Sensor) I would also enable the "Multistage DATS inhibit".  This will allow the panel to downstage the compressor if you are nearing the low temp limit on the DATS (rather than shutting down the entire system when the limit is hit).