Aquastat wiring question

[Giantsean]

Thanks for everyone's help thus far. I think I am now down to my final question, and hopefully it's not too tough. Let me describe my setup again:

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!

 

[Jadnashua]

You might splice the aquastat into the fan 24vac control line. Only when the temperature of the water flowing was at least warm, would the fan then be enabled. This would need to be switched out with a bypass when cooling season came around.

 

[Sponsor]

 

[Giantsean]

You might splice the aquastat into the fan 24vac control line. Only when the temperature of the water flowing was at least warm, would the fan then be enabled. This would need to be switched out with a bypass when cooling season came around.

Thanks. In my setup the fan works via the G from the thermostat. Interrupting it by itself does not actually stop the fan in the AH (making me question what it does in the first place, but that's another matter entirely ). I was thinking of just interrupting 24V to the AH entirely but I would then need the bypass for summer. Someone suggested to interrupt W but I needed to test whether power applied directly to W2 or W3 would still amount to a heat call (even without W1 energized).

 

[Jadnashua]

On most forced air systems, there are often two ways for the fan to turn on: manually forced via the thermostat switch, or internal to the heating plant itself, often when it detects the heat exchanger is warm (and it will run until it cools off). Most of the time on cooling, since you aren't worrying about a cold blast like you might during the heating season, they start the fan up as soon as a call for cooling comes. IN those 'automatic' situations, the G wire has nothing to do about it.

 

[Giantsean]

On most forced air systems, there are often two ways for the fan to turn on: manually forced via the thermostat switch, or internal to the heating plant itself, often when it detects the heat exchanger is warm (and it will run until it cools off). Most of the time on cooling, since you aren't worrying about a cold blast like you might during the heating season, they start the fan up as soon as a call for cooling comes. IN those 'automatic' situations, the G wire has nothing to do about it.

Got it, and I had kinda already figured that's what G did (reacts to the "fan" setting on the stat). That said, I am still unaware of how to splice into the fan control of the TAM7 properly (I'm sure there is a way... whether or not it nullifies the warranty is another matter ). It just amazes me that Trane never thought of this problem. They do in fact have an aquastat which mounts to the coil inlet but all that does is at best delay startup until temp is reached or 60 seconds (probably to allow the coil to heat up on startup, which is fine but doesn't fix my problem)

Another potentially much easier solution would be to place a relay directly in the path of the air handler power. This way nothing would run including the circulators. Maybe a relay with some sort of timer to prevent the whole thing from cycling up/down for a quick turn on/off of the water. Then again I guess a quick on/off would not be cold enough to cut it off in the first place.

 

[Jadnashua]

This was a duplicate, sitting there, and since it won't let me delete it, I'm just mentioning it.

When the system is in DHW heating mode, see if you could tap into that control line and use it to power a relay that breaks the fan motor control of the heating system. Again, though, in the summer, when you are running a/c, you'd want to bypass that as, at least then, a/c and hot water are independent.

 

[Giantsean]

Yeah there is a wiring diagram which seems fairly straightforward. However I am trying to avoid splicing into the wiring of the air handler itself it at all possible, to avoid any warranty issues.

 

[Jadnashua]

You could use a relay to break the white (call for heat - I think that's the white wire!) when the water is being heated.