Any tips for fine tuning a hydro-air unit?


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Old 11-30-12, 05:53 AM
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Any tips for fine tuning a hydro-air unit?

My current setup uses an oil fire boiler to heat two hydro-air air handlers. One for the first floor and one for the 2nd floor. The sequence of operation is as follows:

Room thermostat calls for heat & opens zone valve @ supply header. Circulator pump turns on followed by firing of the boiler. Hot water circulates through the coils of the air handler and an aquastat mounted on the pipe of the return side turns the blower on.

Whats happening is after the thermostat is satisfied, the blower continues to blow air, which after a couple seconds starts turning cold. I've timed the blower and this lasts almost 2 minutes. With cold air blowing, it almost brings the room temperature back to the thermostat set point. And the process repeats itself. I've tried adjusting the setpoint indicator & differential adjustment and I've been somewhat successful in reducing the cold air scenario. Any lower of a setting and the aquastat shuts the blower down before the thermostat is satisfied.

Is this the desired setup for hydro-air units? Are there any tricks in fine-tuning or is it all in the aquastat?
 
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Old 12-05-12, 05:27 PM
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I just realized there were no replies to this!

What's the aquastat on the blower fan set at? Should be somewhere around 110-120 I believe.

I don't think I would go for a high differential... probably something around 10 would be a starting point.

You don't want that blower coming on until that coil is good and warm, and you want it to shut off while it's still warm enough that it doesn't blow cold.
 
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Old 12-26-12, 06:17 AM
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There has to be a better way. I've tried for weeks to set it correctly. The blower is controled by a line mounted aquastat (on the return piping). L6006 to be exact.

It seems that 140degF setpoint with a 10 degree differential is the best I can get it. Anymore of a differential, it begins to blow cold air after satisfying the thermostat. Any less, I'm wasting a longer run-time of the AHU blowing warm air. However, on some occasions, the transfer across the coils cools the return water so fast that it shuts off the blower before the thermostat is satisfied.

The problem I think I'm having is the thermostat is satisfied quickly and closes the zone valve resulting in the ambient temperature on the copper piping to keep the blower running. However, without hot water flowing through, the coil quickly cools off and ebgins blowing cold air.

There has to be a controller (maybe a "smarter" t-stat) that would work better for my situation. Is there a t-stat that not only controls a zone valve but also controls AHU's to keep running for a programmed period of time? I would LOVE to have something that keeps the zone valve open for 30 seconds or so after the t-stat is satisfied and raise the room temperature a couple degrees higher than the set-point.

Is this the only way to power hydro-air units?
 
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Old 12-26-12, 07:30 AM
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Is the AH aquastat hard-wired to the AH ? Im wondering if you can power the AH aquastat from the same control circuit as the circ pump.. that way the air wont turn on until the aquastat is up to temp, but it will kill the power to everything once the t-stat is satisfied. The disadvantage would be abandoned heat in the AH at the end of heat call.
Or.. perhaps your AH motor is multi-speed ? If so, try it with the blower at a slower speed.. it wont be robbing the btus as quickly at the end of call. The disadvantage would be slower heat up of rooms, of course.
 
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Old 12-27-12, 09:07 AM
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I thought of that but I would most likely be short cylcing the AHU.
 
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Old 12-27-12, 12:54 PM
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the transfer across the coils cools the return water so fast that it shuts off the blower before the thermostat is satisfied.
You may not have enough flow ... with a lazy flow the water can't stay hot enough on it's way through the coil.
 
 

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