Bob wrote:I recently installed an AHS-130 boiler. I observe a substantial overshoot on the boiler water temperature to the point that the circulator override is activated. This occurs even though the override is set 35 degrees above the operating limit.
Is overshoot like this normal? If it is not normal what should I be checking to correct the problem?
If it is normal, would a PID controller for the operating limit help get more accurate regulation of the boiler water temperature? Has anyone experimented with a PID controller for operating temperature control?
Bob wrote:The operating limit is a Honeywell L4006A. A Honeywell L4081B provides the high limit and circulater override. There is no adjustable differential on either aquastat.
I have the operating limit set at 170, the high limit set at 190 and the circulater override at 205.
I too can not get an over the fire draft greater than 0.02 to 0.03. My flue is short run, about 35 inches, with an 90 deg El out of the breach and a 45 deg El turn to the thimble. Includes a 5 inch Fields RC barometric damper. Chimney draft is the same if the combustion blower is running or not. Less than 0.04. Joints are taped. Chimney is 1-2/2 stories clay tile lined and is clear. Chimney clean out is taped shut. The only thing left to do is the insulate the stovepipe. When the combustion blower is running the inspection port door gets sucked shut. I've measured the over the fire draft during this time. It measures 0.10 to greater than 0.25. Pegs my draft gauge. Higher numbers occur when is see a lot of unburnt coal in the inspection flap. Low numbers when there is a good burning fire visible. I believe there is some correlation with grate operation. Just what I haven't figured out yet.Bob wrote:I have a barometric damper installed. The AHS literature calls for an over the fire draft of .04. I have been unable to attain that--rather I run .02 to .03 with the outside temperature in the high 30s or low 40s. I have sealed the stove pipe joints.
The boiler is in a 1600 sq ft outbuilding and the building is fairly tight and reasonably well insulated. I have checked the draft with a door open and with the building closed and it really doesn't change the measured over fire draft.
The boiler has an operating limit control, a high limit, and a circulater override. If I were to install a PID controller it would replace the operating limit but be wired in series with the high limit and the circulator override would still be in the circuit.
The boiler has the AHS thermograte system installed. The AHS recommendation is for the set point for the ash temperature setting to be 140 during cold weather and 130 during times of lessor demand. I have the control set at 130--the causes the grate to operate when the sensed ash temperature drops to 120 and to stop operation when the sensed ash temperature rises to 130.
U235a4 wrote:how many circulators do you have? if more then one are they on relays? do you have zone valves? I'm looking at those controls at the moment....
U235a4 wrote:I guessing the relays are R832A's and the boilers are connected in series with the cold return water entering the coal boiler first and then the oil? I'm wrong let me know.