Navien not playing nice with Air Handler

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Rich F.

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I posted an earlier thread here trying to tune my Navien NCB-210. Dana was a huge help and I got it to a good spot where I had supply temp at 140, getting good condensation and long burns, except for my fin tube zone.

I was happy with everything, except now I'm seeing a new issue. When the basement air hander is dead cold, which now happens often this time of year, and I get a call for heat, the Navien fires at max rate to get water up to 140 but the air handler doesn't start quick enough. So the Navien shuts back down. Eventually the air handler starts but water temps in the system drop all the way down as the Navien anti-short cycle feature keeps the boiler from re-firing and getting water back up to proper temps for three minutes.

I'm trying to think of ways to get the air handler to start quicker. Ive played with the strap on aquastat position a bit (connected to an Argo ARH-1), moving it to the front, middle and back of the coil unit but no joy. Played with pump speed a bit, too. The only thing I can do fix is bump my Navien's supply temp to 150. This causes the Navien to run a little bit longer on heat call startup, juuuust enough to allow the air handler to start with the burner still firing. That is good but then puts my return temps at 125-135 which isn't great but the unit is still condensing, as evidenced by the steady drip of condensate out of the neutralizer at this temp setting. Only proper soliution I can find is perhaps a strap on aquastat that kicks on at 90 or so, not the 110 mine is rated at. But Argo only makes the one that kicks in at 110.

I suppose I could live with having to run the boiler at 150deg. supply. Like I said, Im getting return temps somewhat in the condensing zone so I'm getting decent efficiency out of the unit, just not as much as Id like. Id rather get a bit less efficiency then short cycle like crazy and beat up this Navien any more than it already is, trying to heat three zones, plus supply DHW of course.

Any ideas/suggestion though on how to run lower supply temps and get the air hander starting faster? Id rather not remove the strap on aquastat completely because of the intial cold air situation that would obviously cause.
 
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Dana

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Putting the aquastat for the air handler nearer the pump or zone valve feeding the air handler should fix the plumbing delay.

Alternatively, replacing the aquastat with a zone relay that turns on the blower at the same time as the pump/zone valve fixes it.

Either way the air handler would run cool air until the hot water hits the coil (as you correctly surmise) but moving the aquastat to an intermediate point allows you to tune that to the minimum.
 
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