Percentage timer converted to ash temperature measurement

Percentage timer converted to ash temperature measurement

PostBy: Yanche On: Sun Jun 17, 2007 1:17 pm

My Coal Gun boiler has the percentage timer ash grate control. Can it be field converted to the ash temperature measurement method? If yes what are the benefits and the installation modifications needed. The AHS web has a brief descriptions but I would like to know if such a conversion would permit summer operation for domestic hot water production and if there would be coal consumption savings vs. the percentage timer control.
Last edited by Yanche on Mon Jun 18, 2007 9:47 am, edited 1 time in total.
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

PostBy: Eric On: Mon Jun 18, 2007 9:33 am

It is possible to field retrofit the thermo ash monitoring control on our boilers. The major benefit to doing this is the ease of use. Really, you can get just as good performance out of the timer control if you take the time to monitor and change the settings as necessary. The automated controls basically use a thermocouple and a fuji controller to make those adjustments for you. As far as installation modifications go, you need to drill a hole in the grate base of your boiler to install the thermocouple and then do a bit of rewiring in the control box. We provide a package with thermocouple, fuji controller, a solid state relay, and instructions included for the retrofit for $489. If you wanted to do it yourself, we can provide some wiring schematics/instructions. As far as domestic water for the summer goes... the ash monitoring controls will make the boiler a little easier to operate (still nothing that frequent fine tuning of the timer can't do just as well). Keep in mind, though, that there must be some demand on the boiler just to keep the fire going during the summer. For a larger family using a good bit of domestic hot water, you probably would have no problem "keeping the boiler busy" and keeping the fire going. For small use applications... you'd probably be better served by finding another solution for summer domestic water. Also, unless you are one of those people who has their grate timer adjustments down to a science already, the ash temperature controls will probably reduce your coal consumption a bit. The thermo ash control prevents coal that is not fully burnt (i.e. coal that is still hot and buring) from being shaken through the grates and wasted. So, if you have noticed this happening, either adjust your timer or consider upgrading to the ash temperature controls.
Eric
 

PostBy: Yanche On: Mon Jun 18, 2007 6:01 pm

Based on you description of the ash temperature probe I've had a misunderstanding of it's purpose. I though it was for keeping the fire from going out under low demand conditions. I've long ago mastered the grate timer setting and never have unburnt coal in the ash. What I'm trying to achieve with the coal gun is something similar to what I have with my summer only oil boiler operation. I have a well insulated indirect hot water heater. It and my radiator and baseboard units can be heated with either my coil or oil boiler. In summer months the oil boiler only runs when the hot water heater calls for heat. This is seldom because it is large 40 gallon tank. The oil boiler is normally cold. Upon demand of the water heater thermostat the oil burner fires. There is a delay timer which prevents boiler water circulation until the boiler water temperature rises. The boiler aquastat is set low. The burner typically stops firing before the water heater thermostat is satisfied. The circulator pump keeps running transferring the BTU's to the water heater tank. By careful setting of the aquastat set point and time delay the boiler water cools just as the water heater thermostat is satisfied. The objective of all this is to minimize standby losses. I've installed a running time meter on the oil burner and it runs less than an hour per day. It's fired at 0.85 gallons/hr so I typically use about 0.8 gallons per day. Yes, I know it's not good to fire into a cold boiler. But that only applies if it's so cold that you get condensation. In summer months that's unlikely.

Now with the coal gun in summer you can turn the aquastat setting down but you still have long periods of standby loss. I was hoping the ash temperature probe system would allow the boiler water temperature to go lower than the aquastat setting. So low that the standby losses are greatly reduced. Only when the coal fire might go out the ash temperature sensor would turn on the combustion blower and then only long enough to keep the fire going. When the hot water heater calls for heat the combustion blower would come on and raise the boiler water temperature to the aquastat setting. Using my coal gun for summer domestic hot water heating only, now requires about 20 lbs of coal per day. I'm looking for a solution to cut this in half. Only then will the coal usage be equivalent to the oil usage (equivalent BTU'S). Have you ever operated the ash temperature control system in the manner I suggest?
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

Visit Lehigh Anthracite

PostBy: Eric On: Tue Jun 19, 2007 1:00 pm

The intent of the ash temperature probe as it is now is to make the Coal Gun easier to use by eliminating the need to frequently adjust the grate timer as the heating season progresses and more fuel efficient by eliminating any partially burnt coal in the ash. So far, I haven't heard of anybody doing what you propose with the thermocouple setup, but it is an intriguing idea.

First, I have to ask...You say that you currently use .8 gallons of fuel oil per day to heat your domestic water. At $3 per gallon, this is roughly $2.40 per day. You also say that you are using 20 lbs of coal, which even at $200 per ton (assume delivered), this costs you about $2.00 per day. I see what you're saying about equivalent BTU usage, but what exactly are you looking for here?

Your setup sounds very well planned out. I think what you want to do with using the thermocouple to control the fan instead of the grates will work. From a technical standpoint, its as simple as switching a wire, giving the Fuji controller control over a different motor. Actually, you might even look into getting a dual input/dual output controller where you could control both the grates and the fan with the same controller. To my knowledge, the controllers we install are only single input or single output limited (not sure which one right now without checking). But then, the problem becomes where do you want to place the thermocouple to trigger the fan. Currently, we place the thermocouple in the bottom of the coal pile (right on top of the grate) so that as the coal pile burns, the thermocouple is sensing the ash temperature at the bottom of the pile. This is a great way to sense when to shake the grates, but is it going to be sufficient to tell us when to give the fire more air? We use a type K thermocouple for ash monitoring, so it isn't really suited for measuring temperatures much further up in the coal pile. You could upgrade to a type N (a good bit more expensive), but then we run into the problem of where to mount it on our machine. We mount the ash monitoring thermocouple in the grate base where we don't have to worry about going through the water wall. To mount it higher, we would have to find some way of going through the water wall (something that we would have to do during manufacturing as opposed to something you can do yourself). I'll look into it further, but I can't think of a way around this right now.

That leaves us with the question of whether we can get an idea of how the coal fire is doing just from sensing the ash temperature. The best answer I can give is that it might work if you take enough time to experiment and tweak the temperature settings just right. It's worth a shot though... Let us know how it turns out if you do try it.

Also, this is a minor tidbit of info... On the aquastats, if you take the cover off, you'll notice a little tab of metal that prevents the aquastat from going below a certain temperature. You can bend that tab back and go lower if you want. We do it all the time to test the aquastat operation at room temperature. (I don't know what this does as far as the UL listing of the aquastat goes, so if anybody is thinking of doing this in a commercial application or is worried about their insurance, realize that this tip is unofficial. AHS does not condone or support any action not in accordance with the guidelines established in our operator manual.).
Eric
 

PostBy: Yanche On: Wed Jun 20, 2007 10:20 am

My interest in an optimum summer coal burning is somewhat an academic. I already know heating domestic hot water with my coal boiler is cheaper than using oil. But for a "coalgun" installation that is in a central air conditioned home the standby losses contribute significantly to the heat load the air conditioner must remove. Depending on the A/C equipment efficiency and electric costs this would make heating with coal a bad idea.

I will be installing an indoor/outdoor aquastat on my S-130, a Honeywell AQ475A this summer. This has a setting for maintaining summer boiler temperature when used for domestic hot water. I'm still considering my control options for keeping the fire burning and minimizing standby losses.
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

PostBy: Yanche On: Fri Jun 29, 2007 10:56 pm

The AHS boiler with the ash temperature control option uses a Fuji brand PID temperature controller. The PID stands for Proportional (P), Integral (I), Derivative (D). These controllers are much more sophisticated than the simple on-off type thermostat. I'm planning on retrofitting my S-130 with this type of controller. In my search for the right kind of controller I've come across a very complete explanation of PID controllers. See: http://newton.ex.ac.uk/teaching/CDHW/Feedback/

The reference site appears to be part of a college course on feedback systems. The PID controller is used as an feedback example and is explained in detail. There is an oven controller simulation which shows the effects of changing the control parameters. None of this applies to the Coalgun ash controller however, because it is just used in the classic on-off thermostat mode. On the other hand if you want to know how the PID controllers really work, check out the site.
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

Visit Lehigh Anthracite