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Aquastat for hydro air setup

giantsean
giantsean Member Posts: 65
Hey All,

Thanks for everyone's help thus far. I know this is more of a multi-disciplinary question but I figured it fit here best. Hopefully it's appropriate for the forum. I have the below setup for the purpose of my question:

1 x Navien CH240 combi boiler
2 x Trane TAM7 air handler w/ hydro coils (1 zone up, 2 zones down w/ Honeywell HZ211 zone controller)

Problem is that the Navien has fixed DHW priority (no way to change) and BOTH AH's are not cycling down / continue to blow the fan with cold water circ'ing during a long DHW call. The TAM7's have supply aquastats but they don't seem to do too much... per the startup (and my testing) cold water will only delay - but not prevent - startup. Similarly, if they are already running, it will not stop them.

My plan is to pick up a couple of third party strap-on aquastats to sever the heat call during times of cold water. What I am unsure of is where exactly to wire them. Is it as easy as splicing it into W?

If so the only other question is, if I went to a multistage stat/ZC, would severing W1 also disable W2/W3 or would I need to cut them at the proper time as well? It seems that for full fan speed the AH needs all three engergized (hence needing to jumper W1-W3) though I have not tested it extensively.

Finally, assuming this all works, I'm open to any suggestions on which model/brand aquastat to purchase. Thanks again!

Comments

  • njtommy
    njtommy Member Posts: 1,105
    Are you using outdoor reset or is the combi boiler set for a fixed supply water temp?
  • unclejohn
    unclejohn Member Posts: 1,833
    Is the DHW a sensor or T'stat? And is the A/H a variable speed or PSC? Sounds like VS. If DHW uses T'stat control you can run a relay off the call for heat and break The "R" circuit to the A/H and that should stop the fan. If your using a sensor for DHW you could run a line voltage relay off the pump and do the same thing.
  • giantsean
    giantsean Member Posts: 65
    Tommy - I left the ODR on but crank the K factor down in summer and up in winter. At K=6 the supply is about 160.

    John - the boiler itself senses a DHW demand (I guess via water flow) and immediately prioritizes it. During the call it will not send hot water to the heating loop at all. It is a VS handler. You may have come up w/ the backup solution though... if I can't get W to work I can just interrupt R. Just need to make sure to disable this setup when it's cooling season :)
  • giantsean
    giantsean Member Posts: 65
    Welp as it turns out I don't need an aquastat at all. For giggles I took another look at the Navien manual and found a few terminals on the board that referred to "A/H". Called Navien and they confirmed it was a fan break. I was able to test routing W through the board and lo and behold, during a DHW call the boiler cuts the connection. Works like a charm! Figured I'd update this post in case anyone else ever did a search for a similar issue.
  • njtommy
    njtommy Member Posts: 1,105
    edited November 2015
    I knew the new NCB combi had that feature. Was not sure the old one did or not.
    It would be nice to be able have the fan speed on the ahus change to a higher speed as the water gets hotter to deliver more btus following the odr curve. I Know the tam7 are pretty advanced having installed a few before. But never with hydro air.
  • giantsean
    giantsean Member Posts: 65
    If you've done any time with Navien you probably know that their manual creation skills leave a lot to be desired :wink:

    Yeah with you on the TAM7... it seems like it can do so much but the hydrocoil install option seems like almost an afterthought. It is becoming hugely popular in my area so you'd think it would behoove them to dial in some more options.

    Interestingly speaking of ODR, someone suggested on another thread I modulate heat performance via the ODR on the Navien. Trouble is that unless it's supplying 150+ to the coil it will not satisfy the heating needs (or take forever to do so). It would indeed be nice if the boiler, stats, and A/H could talk to each other in more of an integrated solution. Maybe some day !
  • njtommy
    njtommy Member Posts: 1,105
    edited November 2015
    Have you watched the navien run at all with one zone calling? Does it run the whole time for a call for heat or does it short cycle( turns on and runs for a few mins then cycles off for 2 mins)? If the boiler is short cycling it will take forever to try and heat your house along with killing the boiler and its efficiency.