question about hooking up a VF 3000 boiler

Re: question about hooking up a VF 3000 boiler

PostBy: equipmint On: Fri May 09, 2008 12:38 pm

Freddy You have to keep in mind all the variables firing with a coal stoker during the different seasons. Your correct in that the aquastat will turn on and off the stoker mechanism to maintain your deired boiler temp settings but you need to take into consideration the pilot mode of the stoker mechanism which operates indenpentenly of the aquastat this is to maintain and keep yopur coal constantly ignited. This operates off a timer settings that you set you may also find you change these settings with the different seasons. Combine your timer settings and the adjustable feedrate which you will be adjusting for the seasons and you create conditions where you might trigger a condition that the boiler needs to give off some heat via the over heat zone. Hope this helps Curt
equipmint
 
Stove/Furnace Make: Harman VF3000

Re: question about hooking up a VF 3000 boiler

PostBy: LsFarm On: Fri May 09, 2008 1:12 pm

Hi Freddy,, let me expand on what Richard has described. Lets say your house has not called for heat for the last 20 hours, all the water in the pipes and the baseboard units is cool,, the water has reached room temperature, say 65*. The boiler's aquastat is set for 150*, and the water in the boiler IS at 150*.. Then, at 7AM, the whole house decides it needs heat, so all the baseboard zones start to circulate the water,, the 150* water in the boiler is quickly replaced by the large volume of cool water in the pipes and baseboards..

In the meantime,, for the last 20 hours, the stoker in the boiler has been in it's idle or pilot mode,with a keep-fire timer' The timer has been adding a little coal to the fire every hour or half-hour, just enough to keep the fire going. This small fire has been enough to keep the small volume of water in the boiler up to temperature, 150*. When the 7AM demand for heat comes,, the pilot or idle fire is VERY small, probably a strip of burning coal about 1"x1"x8", or about the volume of a fat hot dog.. The stoker starts adding coal to this fire,, it takes about 15-20 minutes to increase the burning coal volume to a carpet of coal that is 2" deep by 8" wide x the length of the grate,, lets say 8".. You have an 8x8x2" or 128 cubic inches of BURNING coal.. Where before you had 1x1x8" or 8 cubic inches of burning coal, just a pilot fire. A huge increase in volume of burning coal,, and remember, for the last 20 hours, the 8 cubic inches has been enough to maintain water temp in the boiler.

Once the large volume of coal gets burning, it [finally] can make lots of heat, and the temperature demands of the house and the water in the boiler are satisfied... BUT.. the fire is still going strong... your stoker will back off the combustion fan, but you still have 128 cubic inches of coal burning, so even though the stoker has stopped adding more coal to the fire,, the fire is still creating a lot of heat,, so the water temperature rises in the boiler.. and it can get hot enough to reach 220* +, and the pressure relief valve open. Even though the combustion fan has shut off, the chimney draft still pulls air through the fire.

Add to this scenario the keep-fire timer, lets say it cycles on for it's one minute run, right when the big fire was finally cooling down,, the combustion fan fires up the whole bed of coal again, and the fire and water temperatures are given a big push... here comes an overheat..

If you have a heat dump circuit, it would be set to open and circulate at say 210*, and dump the excess heat somewhere.. Either into a garage heater, a hot water resevoir, or a 'waste-it' circuit.. hopefully without A/C trying to compensate for the excess heat.

In my situation,, I have a shop that I can dump overheated water into,, but so far I've never seen an overheat, and I haven't hooked up the valves, controls and pump to use the heat dump. For the spring, I have my aquastat at 160*, and ocassionally will see overshoots up to 185*,, but well short of an overheat.

Every instalation and lifestyle is different,, you may not need a dump zone.. If you keep your target water temp low during the summer and fall, I doubt that you will need a dump zone.. but it IS a good idea..

Hope this makes sense... Greg L
LsFarm
 
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

Re: question about hooking up a VF 3000 boiler

PostBy: syncmaster On: Fri May 09, 2008 3:34 pm

I just had an idea for a heat dump.
I have a 120 gallon hot water tank for my hot water solar.
I could put a extra circulator on the vf3000 DHW coil and circulate the water in the bottom of the 120 gal tank, that way it is not wasted heat. the 120 gallon solar feeds a 30 gal superstore indirect hot water heater.

that will work!
syncmaster
 
Stoker Coal Boiler: harmanVF3000 Coal/oil option
Coal Size/Type: Rice
Stove/Furnace Make: VF3000
Stove/Furnace Model: Harman VF3000

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Re: question about hooking up a VF 3000 boiler

PostBy: Sting On: Fri May 09, 2008 4:09 pm

A correctly configured "heat dump" has an infinite ability to accept - and scrub away, the excess heat you send it! A storage tank will accept waste heat only to a point, and then become much the same problem as the over temp boiler vessel - but now you have even more mass to "blow off" via the safety.

That said - there is nothing wrong with sending "extra energy" to storage as a first stage to heat dump. But you still need a big open "dump zone" as a last safety - if the storage is full of energy (possible is some circumstances) before the pressure safety blows!
Sting
 
Other Heating: OBSO Lennox Pulse "Air Scorcher" burning NG

Re: question about hooking up a VF 3000 boiler

PostBy: Freddy On: Fri May 09, 2008 4:40 pm

*smile* I understand more now. I can see where it is a good idea to have a dump zone at the ready. It appeares that a lot has to do with variables that we don't know until "Oh, I wish I had a dump zone!"

So, how is it wired in? What tells the dump pump that it's got heat to dump?
Freddy
 
Stoker Coal Boiler: Axeman Anderson 130 (pea)
Hot Air Coal Stoker Stove: Reading piece o' junk in the barn (rice)
Coal Size/Type: Pea size, Superior, deep mined

Re: question about hooking up a VF 3000 boiler

PostBy: LsFarm On: Fri May 09, 2008 5:06 pm

An aquastat that closes it's contacts when it senses water temp over a set temperature, the contacts trigger a zone valve and a circulator pump to the dump zone... There are many variations of this.. maybe no zone valve, maybe just trigger a pump.. maybe you have a full time pump, then just a zone valve,, There are just too many varialbles.. but water temp is sensed by a close-on-rise aquastat.

My Aa boiler has a keep-fire timer, mine is set to run 1minute every 30 minutes... but there is an aquastat the opens above 210* in the timer circuit.. so if my boiler is very hot, and near a PRV protection temperature,, the timer won't trigger the fan to run and put more heat into the water..

Greg L

.
LsFarm
 
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland

Re: question about hooking up a VF 3000 boiler

PostBy: Richard S. On: Fri May 09, 2008 9:02 pm

syncmaster wrote:I just had an idea for a heat dump.
I have a 120 gallon hot water tank for my hot water solar.
I could put a extra circulator on the vf3000 DHW coil and circulate the water in the bottom of the 120 gal tank, that way it is not wasted heat. the 120 gallon solar feeds a 30 gal superstore indirect hot water heater.


Ours is set to continuously loop through the hot water tank now using a thermo siphon, probably one of the reasons this isn't a problem for us. As the temps gp up really high the extra heat is just going to increase the hot water tank temp. If I remember correctly it only ever went out once in the fall/spring. You really need all the pieces to fall into the right places for this to happen... specifically the big swing in temperature between night time and day time.

There's a couple of threads in the plumbing section that shows how to set up a loop. Might be an idea to for someone to start a hot water loop article. :D
Richard S.
 
Stoker Coal Boiler: Van Wert VA1200
Coal Size/Type: Buckwheat/Anthracite

Re: question about hooking up a VF 3000 boiler

PostBy: Yanche On: Fri May 09, 2008 10:24 pm

Boilers like the AHS S130 or A-A 130 that have a small volume of water and idle well can be safely operated in summer without a dump zone. The key is adjusting the aquastat temperature down in summer. The efficient heat exchanger design of these boiler greatly reduces the time bring the boiler water up to temperature when demand is called. That plus the small volume of water minimizes over shoot. Yes, there will be some overshoot but it will be less than the boiling point of the pressurized boiler water.
Yanche
 
Stoker Coal Boiler: Alternate Heating Systems S-130
Coal Size/Type: Anthracite Pea

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