AHS-130 Mods

AHS-130 Mods

PostBy: Joe On: Sat May 31, 2008 10:56 pm

I just joined this forum today, but I have been reading it over the past month or two. It is a fantastic resource! Thanks to all who have posted, I have learned a lot. I have been heating with an oil boiler and a radiant coal stove. The oil boiler is 37 yrs old, and I am no longer willing to pay the high price for oil. So I have been looking at coal boilers (stokers in particular). I like the AHS-130, but not the price, bumping, or documentation!
I have read on this forum that the manual is not very good. I also read that they were improving it (year old thread). I didn’t see any manual on their website. I am concerned with a unique boiler, and the lack of good documentation, how I will service it (or get it serviced). I would like to have a good set of drawings, parts list, and schematics. If these last 30+ years, something is going to need fixed in that time! If I go with the AHS-130, I would like to consider some of the modifications that Yanche has suggested.

Specify more tapings
Is the AHS-130 controlled with an aquastat? Doesn’t that sense the boiler temp? I don’t understand why I would need to sense boiler temp in more than one place. If you don’t specify the DHW coil, but want to add one later, then I would need the large tapped hole for the coil, and a plug for it since it is not installed… is that correct?

Variable Speed fan motor
I like the idea, and would like to at the same time come up with a way to thermally isolate it from the boiler. Maybe a non-thermally conductive shaft coupling? Any ideas as to what parameters you would use to control the speed? Doesn’t the boiler as it is delivered from the factory, have only two states, full on, and idle? Would the variable speed fan provide a variable burn rate, and are you trying to keep the boiler at a constant burn rate? But… doesn’t this fan aid in creating a turbulent airflow inside the boiler, so the heat transfer in to the water is better?

Reset controller
I definitely would add an outdoor temp reset control. Is there a particular controller you would recommend?

Shaker / ash removal thermal sensor control
As I understand it, there is a thermal sensor in the as path, and based on the temperature of the ashes, the shaker turns on and off. Is there any more sophistication required? What controller would you suggest if not the Fuji?

This is starting to sound like a good microcontroller application. One controller for the fan motor, ash temp control, and outdoor temp reset. Inputs would be boiler temp, ash temp, outside temp, zone thermostats, outputs would be for the fan motor speed, and ash shaker control. You could also work in a DHW priority for an indirect DHW tank, and maybe even control the DHW zone to dump heat into when the call for heat is satisfied. It would be some work for sure, but ought to increase the efficiency for the lifetime of the boiler.

Any thoughts, or interest?
Stoker Coal Boiler: AHS-130
Coal Size/Type: Pea

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Re: AHS-130 Mods

PostBy: Scottscoaled On: Sun Jun 01, 2008 8:59 am

Sure Joe, plenty of thoughts. How about supply and return temps so you could anticipate a feed rate change. How about a stack temp sensor so between that and a feed status you will know when there is an outfire. And Im sure there will be some kind of program built into this microprocessor that will track coal useage and chart it against outside air temps so that next years supply can be anticipated with greater accuracy. :lol: My thought really is that instead of all the upgrades, I will take advantage of a cost effective way to heat my house without driving the price up. :) Scott
Stoker Coal Boiler: EFM 520, 700, Van Wert 800 GJ 61,53
Baseburners & Antiques: Magic Stewart 16, times 2!
Coal Size/Type: Lots of buck
Other Heating: Slant Fin electric boiler backup

Re: AHS-130 Mods

PostBy: Yanche On: Sun Jun 01, 2008 1:44 pm

The AHS boiler comes with two aquastats, Honeywell L4081A and Honeywel L6006. The latter is used as an upper limit safety control. When the low water temperature set point is reached the L4081A will turn on the internal combustion blower. It stops when the upper set point is reached. I've suggested an additional aquastat well tapping so you can easily install an outdoor reset type aquastat. With the second measuring well you can just leave the stock aquastat in place.

My AHS S130 was not ordered with a domestic coil and had a 4" tapping for it, which was plugged. Another forum member ordered a AHS S130 without a domestic coil and later wanted to add one, but couldn't because it didn't have the tapping. I don't know what's standard. Specify what you want on your order.

I almost wish I hadn't suggested a variable speed combustion blower motor. The stock single speed direct drive or optional belt drive is just fine. Yes, the combustion blower has only on or off modes, this roughly translates to heat production or no heat production. But since you can't truly turn off a coal fire there is always some heat production. The fan shaft is what conducts heat to the direct drive motor or pillow block bearings of the belt drive option. There is also convection heat from the boiler itself. Neither design is a any problem. The belt drive is better, at questionable additional cost value. My suggestion for a variable speed motor was to match the correct amount of air to the amount needed for stoichiometric combustion efficiency. This is of no concern to the average owner, only the engineer nurds like me. Correct matching will require instruments to measure the CO and O2 gases and temperature in the flue. It's a one time measurement made at full boiler output. The ideal would be a feed back system that make adjustments automatically. That's a big engineering challenge. Nothing will will see anytime soon. Coal is still to cheap. Kind of like the auto engine carbs, run it rich, vs. electronic fuel injection, run at stoichiometric.

One reset controller is the Honeywell AQ475 aquastat. There are others, some that combine it with zone switching controls. Selecting the right one for your installation will be a research project on it's own. If you're up to it I can make some suggestions.

I have the ColdFusion X model TET-612 temperature controller. It can work with many thermocouple types plus thermistors and platinum temperature sensors. Bought new on an Ebay store for $39 with type K thermocouple. It's not clear to me the factory type K thermocouple is the correct choice. I'd pick type J. But it's an engineer type thing, the AHS choice will work just fine. I would also change the control function of the thermocouple controller, to a keep fire alive controller. Again the AHS wiring will work fine.

In my opinion any improved controls for the AHS boiler or any other boiler should be based on baseline test measurements. Want to start a thread on boiler measurement instrumentation? I'll participate. There's a lot that can be done with micro-controllers but first you need engineering data to determine what makes sense. If the fancy controller does nothing to reduce operating costs, reduce pollution, etc. it's just a science project.
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

Re: AHS-130 Mods

PostBy: Joe On: Sun Jun 01, 2008 10:16 pm

Thanks for the responses. OK, I get it that any savings will be tempered by the fact that we are already using a very cheap heat source. And now I understand the issue with having an extra tapping, so I can just add a reset controller, without changing the factory aquastats. Thanks Yanche for the info on the thermal controller you used for the ash temp sense / shaker control. What do you mean by a “keep fire alive controller”? Would you still just sense the ash temp? How would you determine when and how long to shake?

I am still confused by the variable speed combustion fan. It seems that the speed would be a balance between good combustion (as close to stoichiometric as possible), good heat transfer characteristics (turbulent vs laminar airflow, and enough speed to keep the surfaces clear of ash). Perhaps the AHS design is close to optimal? I would think that there would be only one optimal setting, for getting the most efficiency out of the boiler. Since the only variable to change is the fan speed, a variable speed fan would allow you to test different settings (while reading the flue temp and gas content), to find the optimal speed.

Please make suggestions for a reset controller, I am interested.

My goal is not a science project, but a maintainable, efficient (BTU delivered/Dollar) heating system. What I have learned so far about the control system is that there is a high temp safety aquastat, normal operating aquastat, reset controller, and ash/shaker controller. We haven’t discussed dumping the excess heat into the indirect DHW tank yet, and what to do in the summer for DHW (I was thinking about some solar preheating and perhaps point of use electric). The system will be complex (compared to what I have now), but should be much more efficient.

Thanks again for your suggestions and insight.
Stoker Coal Boiler: AHS-130
Coal Size/Type: Pea

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