Sizing circulator for a suntherm air handler

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Old 01-25-16, 06:57 PM
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Sizing circulator for a suntherm air handler

So after enduring my wife's wrath all winter because our kitchen is freezing I finally figured out the previous owners put the air handler at the end of a very long baseboard run. Luckily I have a zone that drives backup baseboards in a room with radiant. We've been down to the single digits this year and I never needed it and I figure I could repurpose that to the air handler.

The air handler has a little taco 1/40 hp circulator it (or something like that). I'd like to simply add a 3 way ball valve on the existing line to the air handler on the supply and return. This way I can rerouted to the baseboard zone in case I ever want to do that. The existing baseboard zone is powered by a taco 1/25 hp circ.

I was going to disconnect the small pump in the air handler and reuse the circ on the zone. Is that bad - do I run the risk that the zone circ is too large for the simple circuit to the air handler? I was going to do the whole head loss calculation but I can't find any specs on the air handler that would help me with that calc.

Am I overthinking and just use the existing circ?
 
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Old 01-25-16, 08:38 PM
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If the air handler was previous plumbed into a zone with baseboards, why does it have it's own circulator? Wouldn't the circulator for that zone have supplied the flow? Was the air handler in series with the baseboard run? If so, I don't see much difference between that and what you are proposing, just different zone.

Having greater than nominal flow through the air handler won't prevent the handler from doing it's thing. There will be less water temperature drop across the handler; that won't be a problem for the handler.

The downsides of too much flow in a zone are increased noise, and increased wear of the pipes. Too much overall flow through the boiler becomes an efficiency issue, but if it's only one zone out of several that has high flow, it's probably won't make a huge change in total system flow. You could always throttle the zone with a globe valve.
 
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Old 01-25-16, 09:51 PM
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Yea now that I thnk about it the speed of the water shouldn't mean anything for the air handler - the exchanger is either hot or not. If I had slower flow then perhaps that would cause a large temp drop. But if it's too much flow I guess I'm using more electricity than I need to on the pump - but otherwise it should just work.

Only thing I can't figure out is how to connect the thermostat to both the air handler and the taco 6 zone controller. I've got green, red, white, and blue (common) from the stat to the air handler. I need the control unit to turn on the zone circ and the boiler primary loop circ when the blower comes on....
 
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Old 01-26-16, 07:32 AM
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Tell us brand and model number of tstat, handler, and zone controller and we can figure it out.
 
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Old 01-27-16, 07:29 PM
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Tstat - lux tx9600TSa
Suntherm H41 air handler with both cold and hot exchangers
Taco sr506 6 zone controller
Munchkin 140s boiler

Part of what I don't understand about my system is if the zone tstats connects to the boiler in any way. I have it setup just as the munchkin manual suggests with a primary boiler loop with a circulator and the a secondary loop with individual zone circulators.

My understanding is that when a tstat calls for heat the zone circulator comes on. Independent from this the boiler continually keeps the water between 180 and 140 (I think). If the return and supply water temps are high enough the zone circulator runs but the boiler doesn't - in other words the boiler isn't controlled by the tstats but rather the water temps running through the primary boiler circuit.

But I have a feeling the boiler primary circuit circulator needs to run if any zone calls for heat. So if the air handler comes on then the taco control needs to turn on the zone circulator and tell the boiler to turn on the boiler circulator. So I assume the taco controller runs a 24v line to the boiler which has a relay on it for the boiler circulator? Or do I need to make sure the air handler is connected to the boiler outside of what the taco controller is doing? I need to add a 7th zone so I'm curious about how I'll do that as well...
 
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Old 01-28-16, 01:34 AM
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I was going to disconnect the small pump in the air handler and reuse the circ on the zone.
The pump is low-head for the potable water setup, 140 ft of 3/4" plus HX.
The heat exchanger head is: 1.9ft @4gpm or 2.3ft @4gpm.
I don't see a thermal switch so the blower will wait for the water temperature to reach +140F.
Do you have baseboard in the kitchen or just the air handler.

Suntherm_H41_17_15_Series.pdf
H15-14-41-40-17-instr.pdf
 
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Old 01-28-16, 05:20 AM
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Just the air handler in the kitchen and that is all that will be on the zone.

So the boiler fires when the water temp in the system requires it - not when a tstat calls for heat?

If so what about the boiler/primary circulator - does that fire only when the boiler fires or if any zone starts?
 
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Old 01-28-16, 10:56 AM
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The aquastat will maintain 140 boiler temperature. An outside means needs to tell it to increase to 180. Your six zone controller will have a connection to the boiler to tell it to high fire.

You'll need to add another controller to your system. A good choice would be the single zone....
Taco SR501 controller. This controller will also tell the boiler to high fire.... is so desired.
 
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Old 01-28-16, 04:04 PM
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So if a tstat calls for heat then the boiler fires high to maintain 180. Once it hits 180 it stops regardless if the zone is still on or not?

What about the primary boiler circulator? That needs to come on whenever the boiler is firing AND-OR if a zone is running?
 
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Old 01-29-16, 01:32 AM
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So the boiler fires when the water temp in the system requires it - not when a tstat calls for heat?
Call for heat; Thermostat(n)-->> activate Zone controller
Zone controller --> activate Pump for zone (n), and boiler.
The boiler does its thing: See Munchkin Boilers


When you do the math you may find that the boiler is too large for the air handler -- low fire is 43,000 BTUH.
That the system water volume is too small to prevent the boiler form short cycling.
For a condensing boiler the heating coils need to be sized much larger for a given load.

Long term see Drawing 4H [Page 36], also a smaller boiler or a buffer tank would help.

MunchkinRevision2Installation.pdf

Short term:
Raising Function 11 (Table 13.1 ) [Page 59] might help a little with the cold kitchen.
Vision 1 Program access: [Page 56-57]
You could start the heating curve at say 130F (95F default)

From Status Menu [Page 55-56)
[Record d13,d14,d15 with date and time in a log.]
Cycles/hour = d15/(d14+d13) [Ignitions/Total run Time]
Over 6 cycles per hour is bad.
 
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