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Upgraded HVAC 2-Zone system to an RCS Communicating system

Posted by Work2Play , 28 October 2011 · 2460 views

HVAC RCS Thermostat
For those following along, this is my second automated home.  The last home was a single story ranch house on a raise foundation with easy attic access, prewired for security, and nothing worked when I moved in, so it was easy to get sprinklers, HVAC, doorbell, sprinklers, and everything else up and running with one good day of wire running.

In this house I'm taking things further, but it's a much larger home, not prewired for anything, 2-story on a concrete slab, and it was finished/working when I bought it.  That said, I've got 90% of my lights converted, security up and running, but many other things at 70%.

In April when I took on wiring the house, I also bought bought a new RCS ZCV4 Communicating Zone Controller along with 3 WDU's (Wall Display Units) and some remote temp sensors.  It was my hope I could take my existing 2-zone system and convert it to a 3 or 4 zone system.  Because of the layout and different characteristics, it really needs 4 separate zones.  However, after talking to a couple HVAC companies, we decided we weren't ready to take on rezoning the house just yet - so instead I'm using only 2 of the zones of the ZCV4 to mimic the same 2-zone behavior I already had.

So - after a long hot summer and a few $800+ electric bills, I finally decided to venture into the attic this week.  I intentionally waited until less-critical temperatures in case anything went wrong and we were left without HVAC for any period of time... this of course was a wise choice.

Everything was actually pretty straightforward - for the most part it was just a matter of matching up wire colors and functions on the old zone controller with the new one - with only some minor differences.  The main one being that the instructions said that a separate 24VAC transformer is required but not included (to handle the load of up to 4 zone dampers and extra tstats).  Well, I wasn't expecting that, but it just so happened that I had a 24VAC 40VA Elk transformer sitting around from my previous house's sprinkler controls - so I grabbed that and headed up.  

When I went to power things up, the tstats came online just fine but there was no control of the HVAC system.  It was just dead.  Luckily previous experience (from when I installed the HAI system in my last house and blew the fuse - that time by swapping out thermostats while the system was powered up and letting wires touch/short) I learned that there's an automotive-style fuse inside the blower on the control board... so I opened that up, and sure enough, it was blown.

Well, I called it a night since I had no idea what was wrong, had no fuses, and it was time to pick up the kids... but after an email to RCS (they couldn't tell what I did wrong, but did tell me how to avoid needing the separate transformer) - and a trip to autozone for more fuses, I poked around and figured out what I did wrong... I basically directly shorted out the power and was blowing fuses.  Ironically if I'd looked at the wiring diagram for the 2-zone controller it made a whole lot more sense!

So - now all is well - the system is back up and running and working great.  All in all, a pretty boring story actually (as you've surely noticed by now) - but I will say I'm pretty pleased with the system now that it's up and running.  I got the system talking to the Elk on the first shot - and immediately showing in eKeypad - even before I figured out the short issue - so by the time I was in the attic troubleshooting, I was able to use my iPhone to set/change the HVAC and make sure everything was working correctly - quite a handy feature.

As I mentioned, in my previous house I had HAI - and I was pretty happy with the RC80 controlling my heat pump... but I didn't want to try to wire Cat5 to my existing thermostat locations if I didn't have to... Otherwise I would've gone with the Omnistat2 in a heartbeat because I think they look great.  I went with the RCS platform because you only have one new wire to run, and that's from the Elk's XEP to the zone controller - which is about 10ft above my Elk in the attic - so it was an easy run.  It's not compatible with normal thermostats, but instead uses WDU's or Wall Display Units.  They hook up with the existing wiring and only require 4 conductors so existing wiring should be no problem.  For me this made it a no brainer.  

I didn't care much for the overly plain look of the thermostats, but once I powered them up and the soft buttons and dot matrix display are on, it actually looks pretty nice.  There are user controls on each tstat for screen brightness, screen timeout, things like that... so you can have the screen go completely to sleep, or just dim down after a period - however you like.  

Now that all is up and running, I saw one cool feature where the WDU can display outside temperature - either from a probe plugged into it, or you can send it the outside temp from the controller - very cool!  I figured I could tell the Elk to send the outside temp to it over the serial port based on a custom value - that Elve would update based on the weather service... would be pretty cool, but it turns out the Elk protocol doesn't send raw ASCII commands, but instead sends the text string in a text message format "TM=" so it's always interpreted like normal text to display in messages, and the command doesn't go through.  Disappointing - so hopefully I'll come up with a way around it... If you can get to the direct ascii commands, you can control any aspect of the tstat vs. just the most basic command set that's part of the M1.

The RCS controllers are pretty versatile - they can handle heat pumps or conventional furnace/AC.  They support 2 stages of cooling and 2-stages of heating (3 stages on a heat pump), plus they support a fresh-air vent.  They have inputs for remote temperature sensors and outside temp sensor. There are two WDU's available, though documentation on their website is sorely lacking... one's basic display with no frills; the other is a full featured unit like any traditional tstat.

I don't have pictures because there's nothing exciting about it - but if you have any questions about the system, just ask.

Oct 29 2011 08:56 PM
I have been happy with the RCS therms as well. When I got the two tstats I thought I was going to use the messaging feature a whole lot. Outside of testing the messaging capability upon installation I have not used it since. I think I am moving away from wall controlled devices, outside of wall switches, on the whole. I could really care less now about my tstats being visible or not. Now I probably would prefer hiding them in the wall because I am mainly controlling them via pc, phone, tablet, etc... Ps: I am going to miss my $800 electric bills too. I hate summer!
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Todd, I just saw this write-up, sorry I overlooked it!


Thermostats are pretty far down the road for me, but this is inspiring.
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That is funny - I wrote it specifically because you asked about it!

I should also note - with a little help from others on the board, I figured out the right way to send the outside temperature to the unit to be displayed on the thermostats. I had it working very nicely, where Elve would set a counter in the M1 based on the NOAA weather data... was great, for about a week... then they turned off the NOAA feed! One of these days I'll upgrade Elve and get the new driver; it was a pretty cool feature.
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iostream - i'm not sure if you're following this, but I found a useful purpose for the Messaging feature - whenever there's a message waiting, it flashes the red light on the thermostat. It's quite noticeable from anywhere in the house where you can see a thermostat, even without my glasses on.

I since upgraded Elve and have wunderground.com's outside temperature integrated to show as the outside temp. Conveniently, I was able to pull the feed from one of my neighbors about 5 houses over so as long as his weather station is properly installed, it's more accurate than the temps over at the airport (it cools down much faster over there - no concrete/stucco holding the heat).

So now - whenever it cools down to where outside is a lower temperature than the upstairs, a message gets sent to the thermostats which makes the red light flash. The message is just "Use the Fan!" but nobody reads it anyways. Once conditions reverse, I send a "Clear all messages" which stops the flashing.

Whenever we see the red light flashing, we know it's time to kill the A/C, open some windows, and kick on the Whole House Fan that we put in at the beginning of summer. It's been a great money saver!
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