Coal Boiler Buffer Tank, Any Success or Failure Stories ?

If you have ever tried using a buffer tank in conjunction with a coal (or wood) boiler (OK, any solid fuel), what has been your experience? Did it save energy? Were there any other benefits (or downsides)? Was it worth the expense? Or did you feel afterwards that it was a waste of money?

What is a 'buffer tank' ?? Do you mean a large storage tank to hold heated water for the system??

If so, that is fairly common with wood burning boilers since they cannot sit and idle like a coal fire,, they smoke and stink badly.. once a wood fire is burning hot it is fairly clean.. So the wood burners fire up their boilers, heat up a huge quantity of water, usually 1-2000 gallons of water to ~180*, then shut down the wood fire..
The stored water's heat is used untill it is ineffective to heat the building then the wood fire is started again..

A storage tank is realy not needed or desired with a coal stoker boiler.. maybe with a coal hand fired boiler, but even there, a hand fired coal fire will idle with some control, and not smoke out the neighborhood..

There is a lot of room and money needed to install a storage tank, I'd not connsider it unless you are burning wood.

Greg L

Thanks! Consider it unconsidered.

But on the other hand, what if it is a very small boiler buffering tank that doubles as an indirect hot water tank? This unit came up recently in another thread. It is called the Ergomax E23, and it is an indirect hot water tank with a tiny capacity of only 27 gallons of water. What makes it uniquely different from most (to perhaps all) other indirect hot water tanks is that the E23 (and its bigger brothers) is in effect a "reverse indirect hot water tank". Instead of having 27 gallons of domestic water sitting in a tank that is heated by an internal coil, the Ergomax has 27 gallons of "boiler water" inside of it, and its internal coil only holds 1/3 of a gallon of domestic water. The boiler and the Ergomax are looped together via a primary circulator, and then the Ergomax also has outlets and returns that are where you make the tie-ins that go out to and return from the homes zones via multiple zone circulators or a single secondary circulator and zone valves. In effect this thing is just an unfired external extension of your boiler, adding water capacity to it (I.E., buffering it). In my case, since the AHS S130 and the Ergomax E23 both hold 27 gallons of boiler water it would double my boilers water capacity to 54 gallons.

Is there any possible benefit to this oddity of a buffer tank and indirect hot water combination unit in conjunction with coal? In the other thread I questioned its benefit.

http://www.ergomax.com/

I just read the FAQ's...
I think you should get one and install it and then you could update us all to how well it works.

lsayre wrote: Instead of having 27 gallons of domestic water sitting in a tank that is heated by an internal coil

Is there any possible benefit to this oddity of a buffer tank and indirect hot water combination unit in conjunction with coal? In the other thread I questioned its benefit.

There is a gallon or less in your boiler's coil.
If you are looking for an engineering exercise, this would be a good one to throw a lot of time and money at. You just bought one of the best boilers on the planet, you are not going to fix anything it has to make it work for you. Forget this other stuff, you don't need it.

I have a 500 gallon buffer tank I installed on my wood boiler. The purpose is to even out the wood fire and keep it burning hot. It also provides storage to provide heat to get you through the night without having the backup system kick on.

The tank will not make a coal boiler burn more efficient.

When I start using coal to heat my house, I will use the buffer tank in the summer as a heat source for domestic hot water. I will fire the coal boiler once or twice a week to heat the tank up and then let the coal boiler go out to minimize standby losses. I'll let people know how it works.

coaledsweat wrote:

lsayre wrote: Instead of having 27 gallons of domestic water sitting in a tank that is heated by an internal coil

Is there any possible benefit to this oddity of a buffer tank and indirect hot water combination unit in conjunction with coal? In the other thread I questioned its benefit.

There is a gallon or less in your boiler's coil.
If you are looking for an engineering exercise, this would be a good one to throw a lot of time and money at. You just bought one of the best boilers on the planet, you are not going to fix anything it has to make it work for you. Forget this other stuff, you don't need it.

After thinking this through I agree that in conjunction with a coal boiler the Ergomax E23 is clearly a solution without a problem. The Coal Gun already has a DHW coil within it, so why add an outside boiler water storage tank that only brings the exact same thing to the table. The outside buffer tank tank does not create energy, and can only lose energy with time, ultimately costing money rather than saving money. Not to mention that it is expensive.

If you are trying to squease every last bit of energy out of the ahs, then why not just insulate the boiler and pipes better, you would achieve the same thing without all the added water and need for a bigger expansion tank. Ever notice the axeman doesn't have ANY insulation on it, keeps my basement at 71 and reduces the need on the dump zone. Are you going to heat the room where the ahs resides ???

It will be in a utility room that shouldn't require much to heat it.

I've never heard of these, but assuming that the Ergomax is well-insulated, wouldn't it let the uninsulated coal boiler rest at a lower temperature? The boiler would only crank up when hot boiler water is needed; the rest of the time less heat would be lost to the room and up the flue?

Mike

If you desire....someone will create an outlet for you to dump cash into. You can buy a TT load of coal a year and utilize the technology that we have had for 100 years and still never come close to breaking even in your lifetime with many of the "new green technologies" we have today. I do admire your resolve in searching for the "Magic Bullet", and if you find it, share it with the world. You have in your possession the most cost effective solution for your family's heat and hot water, so hook it up, relax and enjoy. I guess folks here all want to see pictures, so don't forget that.
Your postings have sure gotten folks thinking, and that is an excellent way of making progress. I live where we have all sorts of folks from the cities with 'impressive degrees' and 'worldly ideas' for their second homes, so geo, high temp solar extractors, $250,000 solar arrays, bio boilers, super insulated homes are all over the place.......while the rest of us use wood, pellets, oil, propane, and a few old timers who burn coal.

Not because I'm an old timer, but I would advise you to do a competent install of your AHS, and enjoy the comfort year-round.
With all the uncertainty in the middle east, the only certainty is that it will never change in our lifetime.
If you were building a new home, you could incorporate many new features to make the heating and cooling much better, but we unfortunately live in a 'wooda, coulda, shuda world. Hook it up, spark it up, enjoy. .....sounds like a Cheech and Chong moment.....

The main benefit that the manufacturer touts for the Ergomax buffer tank (aside from its dual use as an indirect hot water tank) is its ability to reduce or eliminate a boiler phenomenon called "short cycling" (which of course they claim is an energy wasting and very bad thing to let happen to your boiler).

I guess if I knew more of what "short cycling" really was, and if in fact it is a very bad thing, and then finally if it relates to solid fuel (and specifically coal fired) boilers, that would go a long way in assisting in a final determination of its potential value.

My current thinking is that short cycling is mainly a phenomenon of oil, gas, and propane boilers whereby the fire goes completely out (cycles off) when the 180 degree (or high limit) set-point is achieved. If the boiler is then constantly being drawn down by zones that are rapidly calling for heat and then calling for the heat to stop, then calling again, calling off again etc..., the boiler must fire up, stop firing, fire up again, etc.... in a rapid cycle that is what I assume to be known as short cycling, and (somehow, not well explained by Ergomax) this might not be the most energy efficient way to fire (cycle) a boiler (at least of this type).

A coal boiler however will not be turning on and off endlessly, since it will inherently run continuously, so perhaps the entire theory of the buffer tanks benefit is completely lost on the coal boiler (although it will have to ramp up the fire and then ramp down the fire , so perhaps this can be considered its form of cycling, and perhaps this can also be classified as "short cycling"). The opinions I've heard here so far seem to agree with the assessment that it is not relevant to coal boilers.

At roughly $1,050 for the smallest model of Ergomax it would be one expensive hot water tank if that is all it wound up being good for, and as I have concluded already, if a boiler has an internal DHW coil, it doesn't even have a use for that purpose.

To lower the operating costs of any boiler you must have a control system that keeps it off when it is not needed. With coal this is difficult because of the "keep the fire alive" requirement. The AHS and the similar A-A boiler are unique because they have relatively low water volume. The internal combustion fan forces the gases against the boiler vessel resulting in a "quick" recovery. Naturally there are long thermal time constants with coal. I would expect a control system could be engineered for the AHS & A-A boiler that would substantially reduce standby heat losses, especially for summertime domestic hot water production. This would be done by allowing the fire to all but go out and then quickly ramping up the fire when a demand occurs. The control would also have to anticipate when the demand will be satisfied and turn off the blower before the demand is actually satisfied. There would be multiple control loops and only electronics could do it.

BUT, the complication necessary would likely not be worth it for the coal saved. Just accept that some coal will be burned that doesn't really need to be burned.

Pacowy wrote:I've never heard of these, but assuming that the Ergomax is well-insulated, wouldn't it let the uninsulated coal boiler rest at a lower temperature? The boiler would only crank up when hot boiler water is needed; the rest of the time less heat would be lost to the room and up the flue?

Mike

Reguardless, you need to maintain enough temperature in the boiler to stop it from condensing, there will always be a heat loss at the boiler, NOT as great if the temperature is lower. Insulate the boiler better if you want to save, adding more square footage (more water and area produced by the buffer tank) will increase the loss, reason they insulate the tank. THE BIGGER THE SQUARE FOOT AREA, the greater the loss.