Can't seem to achieve proper set points on aquastat in hydronic system


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Old 12-23-14, 10:25 PM
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Question Can't seem to achieve proper set points on aquastat in hydronic system

I'll try to be as concise, yet as thorough as possible.

So here's the current setup;
-Weil-McClain gas boiler GV5 series-1, 140K BTU, set for 140-180degree
-Approx 2300sqft living space
-Zone 1 (baseboard pipes, first floor)
-Zone 2 (supplies heat exchanger in attic that provides forced warm air to 1st and 2nd floor)
-Aquastat on air handler (Honeywell L6006A) controlling fan but it seems not the circulator Aquastat set at approx 165 with 7ish degree differential


Observations:
- Sequence on call for heat; furnace/flame fires, boiler temp gauge rises to approx 160 and circulator/fan starts, warm air blows, boiler temp continues rising to 180, flame stops, circulator/fan keeps running and blowing warm air, boiler gauge slowly drops down to approx 155ish and flame fires again, boiler temp rises again to 180, warm air continues blowing. There are occasionally cycles where the fan and circulators will cycle off then almost immediately back on.

- Sequence with heat call satisfied; furnace/flame stop, circulator stops, fan continues blowing, blows warm air for approx 1-2min then air turns cold, fan stays on anywhere from 5-15min). Seems like fan stays on longer if the call for heat was satisfied when boiler temp was close to 180, and stays on for a shorter duration if the call for heat was satisfied when the boiler temp was closer to 155.

Problem(s):
- Air handler fan staying on too long (sometimes 5-15min) and blowing cold air after heat call satisfied; sometimes fan not turning-off at all before the next call for heat.
- Blowing cold air for these durations seems to be dropping the ambient room temps rapidly and leading to additional call for heat.
- I assume operating the system at a minimum of 160deg is highly inefficient and/or unnecessarily stressing the boiler


I'm going on 3 days trying to rectify this situation, but I've run out of ideas and I'm starting to confuse myself the more I try to think about a solution.
 

Last edited by TheHolyCannoli; 12-23-14 at 11:40 PM.
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Old 12-23-14, 11:11 PM
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Welcome to the forums.

I'm not the pro here but I have a few questions.....
Where is the L6006A installed.... near air handler or boiler ?
Do you have two zone valves and one circulator pump or two pumps ?


I installed a similar setup at a friends place. I used the thermostat to open the zone valve for the garage. I had a similar switch to the L6006A then monitored the temperature of the water at the coil and turned the fan on when it reached a certain temperature. When the thermostat closed the zone valve, the coil cooled off and the fan stopped.

Your system needs to be similar.
 
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Old 12-23-14, 11:30 PM
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The L6006A is at the air handler. I have 2 circulators, one for each zone.

I think I've attempted to do something similar to what I think you're describing , but perhaps in reverse. I bumped up the t-stat a few degrees, let the system run for a couple minutes, switched off the heat, and when the air started blowing cold from the vents, I turned the aquastat (large dial) down until the fan shut off. This happened to be at about 165 (with the diff set at 5). Still, the time it's taking to turn off the fan after the heat call is satisfied fluctuates greatly and eventually ends up cooling down the house.

In a perfect world, I could tell the circulators to continue running after the heat call was satisfied and until the return temp gauge on the boiler hit about 140. If I could do that, then it wouldn't matter so much when the fan shut off because I would be getting warm air blown through the vents and not wasting the remaining heat sitting in the system.

As it is now, the circulator is shutting off at whatever temp the boiler return happens to be at when the heat call is satisfied. For the aquastat to turn off the fan, I'm having to wait for the heat to simply radiate away from the pipe where the aquastat is located (at the air handler)...meanwhile the coil in the air handler has already cooled from the fan still being on and blowing air over it. And obviously, this is resulting in cold air being blown.
 

Last edited by TheHolyCannoli; 12-23-14 at 11:58 PM.
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Old 12-24-14, 01:40 AM
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It almost sounds like the temperature sensor is on the wrong side of the coil.
 
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Old 12-24-14, 06:49 AM
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Interesting you say that...A couple days ago I had noticed that the feeding(?) pipe from the boiler to the coil, is going into the opening on the coil labelled "Output-To water boiler", and the return pipe going from the coil to the boiler, is coming out of the opening on the coil labelled "Input-From water boiler".

I dismissed this because the aquastat is indeed located downstream from the coil, on the return pipe going to the boiler. I had to have the coil replaced/retro-fitted because it froze and burst on the previous homeowner (no glycol in system).

Also, maybe worth noting is that the aquastat at the air handler is located approx 2ft downstream from the beginning of the return pipe coming out of the exchanger. Could this be too far away to accurately control the fan based on water temps inside the coil?
 
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Old 12-24-14, 07:02 AM
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I would try to get that sensor bulb as close to coil as you can.
Wil the water off and no flow, the pipe leading to the coil may be staying hotter that the coil is. There are way the you can keep a pump running to purge the system of heat, but with a CI boiler of that size you would tend to overshoot the fan coils target setpoint.
You might want to trade the mechanical aquastat for something electronic that allows a smaller differential, as this is what you need. Something that will kick the fan on at 165 and off at 164. or of similar values.
 
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Old 12-24-14, 08:03 AM
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Moving the aquastat closer would definitely require an HVAC visit...I just don't feel comfortable cutting/removing/adding to the current piping.

Could you elaborate on how to keep the circulators running for a few minutes after the heat call has been satisfied?
 
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Old 12-24-14, 09:58 AM
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Moving the aquastat closer would definitely require an HVAC visit...I just don't feel comfortable cutting/removing/adding to the current piping.
It's not a model that simply straps onto the pipe with a clamp?
 
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Old 12-24-14, 10:06 AM
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It's definately an aquastat location issue. My brother had the same issue at his new house. Moving the aquastat solved the problem.
 
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Old 12-24-14, 12:03 PM
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Once the flow stops and the coil cools off, it would still take a bit of time before the pipe two feet away cooled off... by that time, you're blowing cold air... but you knew that already!
 
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Old 12-24-14, 12:35 PM
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(can't find the "quote" button)

NJ Trooper:
Based on the stock photos of this particular aquastat, it looks like there is a metal bulb that inserts into a "T" shaped pipe that would then be connected in-line with the return pipe.

I thought maybe I could replace it with an air temperature sensing model such as this, but still, I would be required to drill a hole somewhere in the air handler near the coil. And I don't even know if the radiant heat near the coil would be enough to heat the air and trigger the switch quick enough to avoid the same situation I'm having now.

I didn't know there were models that simply clamp on the pipe. Although I would assume an air temp sensor would be the most accurate in preventing cold air from blowing, it sounds like clamping something to the pipe would be the quickest/easiest solution. Any particular clamp-type model recommendations?


Thanks to everyone thus far for all the help, it is very much appreciated. Hope everyone has a great holiday and good luck in the new year.
 

Last edited by TheHolyCannoli; 12-24-14 at 01:01 PM.
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Old 12-24-14, 01:05 PM
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(can't find the "quote" button)
All the way to the right on the tool bar above the compose window.

Based on the stock photos
Never trust the stock photos... what 'flavor' of 6006 do you have? What are the last four digits of the number? i.e. the FULL part number for your aquastat, L6006A is a 'family'.

I thought maybe I could replace it with an air temperature sensing model
Won't work. You would have delayed turn ON in that case because with a hot coil and no air flow, it would take a long time for the heat radiated from the coil to turn the fan on.

You need to sense the water temp in the coil.

Any particular clamp-type model recommendations?
Not yet... take a close look at the one you have already. Are you SURE that the bulb is in a 'well'?
 
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Old 12-30-14, 12:01 PM
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Pics of aquastat:
https://www.dropbox.com/s/k4xd7181up...31920.jpg?dl=0

https://www.dropbox.com/s/5ri74648z6...32135.jpg?dl=0

Appears to be the immersion bulb type. Full model number is L6006A1145
 

Last edited by TheHolyCannoli; 12-30-14 at 12:18 PM.
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Old 12-30-14, 05:07 PM
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If I'm not mistaken, that is mounted on a 'well'.

You may be able to simply remove the aquastat from that location and if you are clever, devise a way to strap the bulb onto the pipe right next to where it exits the air handler.
 
 

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