A little help with HVAC zone controllers

[potts.mike]

Mods if there is a better spot for this topic feel free to move it.

I am looking for a little help and information about zone controllers. currently I have an rcs thermostat that ties into cqc that I use to schedule heating and cooling for the whole house. The issue that I want to solve is that in the late afternoon our front room can really heat up causing the ac to run non stop for several hours, during this time the bedrooms can get pretty cool. this indicates to me that we are wasting a lot of energy cooling rooms that don't need to be cooled simple because the thermostat is in the front room. I know that better insulation, windows and doors would go a long way to alleviate this problem thats not really in the cards for this house.

Would a zone controller and separate thermostat for the bedroom help with this if so what should I be looking at? I know RCS makes a controller, I take it that I would also need dampers for each room?

I am totally lost on this sort of thing so any help/info is appreciated.

-Mike

 

[Ishmael]

Mike,

I had a similar issue. My son's bedroom was always substantially hotter than the rest of the house which made things pretty miserable. Here's how we solved it.

Originally, he was at the end of a duct run, and simply never got enough air. His room was also in the "perfect storm" location to take the brunt of our Arizona heat.

The first fix was to install a Honeywell zone controller and run a new, dedicated duct to his room through a damper. There was a dedicated thermostat installed in his room for his zone, and then the existing thermostat became the zone controller for everything else. This solution worked great, except my power bill went up noticeably.

I switched out the Honeywell system to a RCS ZCV4. I really only need a ZCV2, but I wanted the headroom in case I ever decide to split off another zone. I linked it to my Elk M1 and had plans of leveraging my ECM-1240 energy monitor and CQC to do load shedding to the bill back under control.

While I was planning all of this, I spoke to the original installer of the first zone system, and he pointed out that compressors have to run for several minutes to hit efficiency. He suggested that instead of driving things based on load, I might want to look at minimum run times. As it turns out, the ZCV supports minimum run time, so I set the new zone ZCV4 with a minimum run time of 9 minutes and also a minimum off time of 9 minutes, which means that once the system comes on, it must run for at least 9 minutes, and once it hits the right temperature and stops, it must stay off for 9 minutes.

With just that change, the energy monitor graph of that compressor went from this horrible constant on-off-on-off that his room was causing to more measured intervals of on and off. The total amount of time the compressor runs is down, the energy consumed is lower (and by extension my electric bill is noticeably lower), and his room is just as comfortable to his as before.

I have two air conditioners, and I switched the other one to just a RCS ZCV1 as I have no need of zones on the other side of the house, but it uses the same minimum run time and minimum off time strategy.

I really love the old RCS thermostats. I'm not as thrilled with their newer offerings as I don't trust wireless technology for something as critical as HVAC control, and I also don't see any zone controllers. Part of me keeps thinking I should but a spare ZCV2 and a TR60 just to be ready in case of failure of any of these tried-but-true models I use.

Chris

 

[tmbrown97]

OP - your problem is a common one. The part I need to warn though is that converting from a single zone to a multi-zone system takes some work, and you have to find the right HVAC partner to help you. Unfortunately, I have great disdain for the average HVAC installer (though I finally found the right one that I like working with).

To convert to a multi-zone system, you need dampers installed, possibly an extra intake, and you need to ensure that there's sufficient airflow on both zones, and you never restrict the system too much.

I do currently have a zoned house - it's a 4K sq ft house running off a single 5-ton unit, and surviving pretty well - it's split between upstairs and down. I converted to RCS and have their communicating zone controller, and it works great.

Zoning is great - and I think what Ishmael did was very smart - in fact, makes me want to double check my settings... but to do it right, you need professional assistance.

 

[potts.mike]

I have minimum run and off times set for the house but the thing is that it runs form midday until late into the night without going off. The front of the house is west facing and gets pretty warm late in the afternoon. This is only the second summer that we have had AC and I am starting to wonder if the unit is sized to small. I do find it interesting though that the second stage cooling rarely runs. I would think that it would kick on pretty quick if the temp kept climbing while the AC was running. I need to setup some runtimers to see how long it actually runs each day.

I would love to do two zones with one being the bedrooms and the other being the rest of the house but it sounds like doing that might be a little expensive.

 

[wuench]

It might be as simple as moving your thermostat closer to the "living area" (i.e. your bedrooms) and farther from those bedrooms.

 

[potts.mike]

That won't really work because we're in the living room until 10:30sh every night. And we would still be running the ac most the night to push cold air into the bedroom.

 

[tmbrown97]

So, another thing that came to mind... I'm not sure what climate zone you live in, but I live in northern California, where we can get temps up to 115 during the day and they'll drop to high 60's at night (generally there's a 25-35 degree difference between day/night). Our current system isn't zoned perfectly - there is definitely room for improvement... the thermostat is in the master, but our bedrooms are spread out in 3 separate areas of the house, each with different temperature characteristics - so the master cools first, and often the other two areas never catch up.

A few weeks ago, I installed a whole house fan - and it's been great; about the time we head upstairs, it's usually about the same temp outside as in the master; cooler than the other bedrooms. We kick on the fan and run it to cool off all the bedrooms, then once everyone is in bed and doors are closed, we open a few key windows to keep cooling the house and attic for a bit longer.

Since putting the fan in, the AC never runs once the outside temp is lower than the inside temp... last year it ran all night long, because the house would never catch up, and the building materials would hold the heat in. Now there's so much air moving, it cools everything down pretty quickly; and we can also super-cool the house in the morning and drop it down to the mid 60's, which keeps the AC from really having to work as much the next day.

So far it's been a very worthwhile investment and has made our house much more comfortable throughout. This basically also balances the temperatures throughout so when starting up the next morning, the rooms are all the same temp, vs. being a few degrees off from each other from the start, and only getting worse.