need help with gasification wood boiler installation with oil burner

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Old 10-19-14, 07:19 PM
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need help with gasification wood boiler installation with oil burner

so i am running my greenwood 1oo wood gasification boiler as manual designated and with greenwood supplied AIC flat plate heat exchanger(mod.#br-hexr6-07. my gw 100 is set as primary heat source for my hot water baseboard( 1500sf ranch) and my 40 gal indirect hot water tank, my hot water therm. is set at 125 degrees and my oil burner 's honeywell L8124a aquastat control is set at 140 degree low limit and 160 degrees at the high limit threshold with a 10 degree differential. my gw furnace (only 5 ft away from the oil burner), has no problem heating its side of the loop water to 180+ degrees, however the oil burner continues to cycle on every 5 to ten minutes to i 'm assuming, handle the low oile burner thermostat need, as there is no call for house heat, all the while and each time this happens, the gw damper stays shut and never seems to open, because the gw temp does not seem to ever really go much below 180 degrees.requiring the damper to open. i know the three taco pumps, the gw circulator, the baseboard circulator, and the hot water circulator all are functioning properly and are moving 10gpm or better. the heat exchanger seems to be working properly based on temp readings and touch( the heat exchanger is brand new) and this is the first ten days of my installation and operation. the other thing that is evident is, that because the gw never seems to open the tamper for more than 30 seconds at a time and usually only when there is little wood remaining in the gw, the gw door is almost glued shut with creosole as the fire never seems to burn that hot. i have of course limited the amount of wood i feed based on the heat demand and even still the gw fire keeps it loop temp. constant(the gw does not seem to ever fall below 180degrees), but does not seem to exchange enough heat or enough heat fast enough to either keep the furnace temp. hot enough or open its own damper. are my oil burner limits set wrong? should i have different threshold temperature settings? i am at a loss. please help. thanks much.
 
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Old 10-20-14, 05:04 PM
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A wood gasification boiler should operate at high fire all the time there is wood in the gas generator and the heat produced needs to be stored , usually in a 500 gal. insulated tank. the oil boiler and storage tank need to be piped and controlled so that when the oil boiler water needs to be heated as determined by out door reset ( best method ) IMO or by the oil boiler aqua stat, the pump between the storage tank and the plate heat exchanger will come on with the pump between the oil boiler and other side of the plate heat exchanger . The oil burner will be kept off by the temperature in the storage tank. When the storage tank water temperature is below the temperature of usable heat the oil burner will be allowed to come on .The wood boiler will burn at high fire until the wood is gone or the storage tank reaches it high limit . A dump zone large enough to prevent system from reaching a dangerous temperature must be incorporated into system. The wood boiler is dedicated to heat the storage tank and the storage tank heats the oil boiler .I have read that paraffin wax put in the storage tank will increase the capacity of the water to store heat and provide a cap to keep the water from evaporating.The detail of how to pipe and control the system requires a good understanding of how system should operate and how boiler controls work.
 
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Old 10-20-14, 05:45 PM
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when i bought the gwood boiler(the company has since been sold) i was told specifically that a storage tank was not necessary as i did not have indoor space available. it has been difficult to get specific help from the manufacturer, but is there any way to keep the oil boiler from firing by turning on the house circulator at a temp just higher than the oil boiler's low limit threshold, or another way to delay the oil firing while still allowing the house circulator to run thereby allowing effective heat exchange?
 
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Old 10-20-14, 07:31 PM
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To keep the oil burner from firing the water temperature in the oil boiler must be kept above the setting of its aqua stat. When there is a heat call from a room thermostat or the indirect DHW the terminals TT of aqua stat will be shorted and the burner will fire to raise the boiler water temperature to the high limit setting, usually 180f. The circulator pump will receive power from aqua stat terminal c1 to circulate water to emitters. Since you have an indirect DHW heater the low limit can be turned off or better yet the aqua stat can be configured for cold start and now the burner will only fire on a call for heat ,TT shorted. Since there is no storage tank the wood boiler must be able to deliver that 180f water to the plate heat exchanger and it must be big enough that the btus delivered can be carried away and deposited into the water of the oil boiler which will increase in temperature to be near the same as the wood boiler. When this happens the pump circulating the oil boiler water through the plate heat exchanger will shut down as will the wood boiler pump. The wood boiler control must be capable of shutting off the air to the wood to keep water temperature in a safe range usually 220f before the dump zone is activated .
 
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Old 10-21-14, 05:08 AM
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Not 100% clear on your piping, but...
I would pipe the system so that the cooler return water goes into the wood boiler heat exchanger, from that heat exchanger go into the oil boiler, from the oil boiler go back to the system circulator to the house.

If... you have closely spaced tee's and each boiler has it's own circulator injecting into those closely spaced tees, then things are a little more complicated.
Your oil boilers control TT should be wired to a strap on aquastat (or imersion would be prefereable), this would be set to say 140 F or so. basically the minimum you want the system to drop to before firing the oil burner.

An upgrade would be to use an outdoor reset instead of this new aquastat, and wire it back to the oil boilers TT. Set it to a heat curve that would keep the water temps 5 or so degrees lower than what is required to heat the house.
This will save oil, and will also notify you that your out of wood.

Some boiler do not require a mass storage tank, some do. Best to talk to the manufactorer, or rep about it. They will know what they sell best.

You do not need elaborate controls, but the better controls you have the more flexible your system becomes.
 
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Old 10-21-14, 02:53 PM
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I always keep the systems separate , the oil boiler was the first heating unit therefor the heat emitters would return to the oil boiler . The storage tank through a plate heat exchanger will heat the oil boiler . If there is no storage tank the wood boiler would heat the oil boiler through the plate heat exchanger if the wood boiler is open , if it is closed the plate heat exchanger is eliminated .This allows the oil boiler to heat when there is trouble with wood boiler.
 
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Old 10-21-14, 03:50 PM
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The system return should not go to the oil boiler.
The system return should go to the wood boiler / heat exchanger / storage tank.
From there it can go and get heated by the oil boiler if needed.
This way at least the wood boiler can attempt to heat some of the return water if not all of it. Even better, add VS injection from the wood boiler / storage to the system loop with ODR...
If the oil boiler see the return water then it might try to heat it up, thereby doing the work of the wood boiler.

Really there are a number of ways to do things, as long as the cheapest fuel source does most of the work then it's all good.
 
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Old 10-21-14, 04:03 PM
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to everyone who has replied thus far, thank you, much appreciated, but still in need of further insight.
if i understand you correctly, maybe this will help.
i have tried reducing the oil boiler's low threshold all the way and that certainly keeps the boiler from firing constantly, but what results is low water temp on the house side of the system, lower that the temp necessary to keep the hw tank up to temp. so then i get a call for the hw and the hw circulator starts, but because the water temp in the boiler loop is so low it triggers the oil boiler to fire yet again. same thing when there is suddenly a house call for heat. could my problem be essentially this:
my house loop is essentially stagnant when there is neither a call for house heat or hot water, each call necessary for their circulators to run, and thus bring the house loop thru the h/e to pick up the 180 degree heat, now essentially allowing the heat exchanger to effectively transfer its ready and waiting 180 degree heat. also, because the gw boiler can not effectively transfer its heat it burns ever so slow, as it is always at 180 degree high limit temp keeping the damper closed, and building the inside full of creosote the h/e manufacturer assures me its capacity is more than enough to work effectively, but the process is not instantaneous, and requires consistency. do i have to plumb a dedicated h/e loop, with its own circulator, tee'd off from the feed and return oil boiler lines, bypassing both the hw loop and the house loop to keep this circulation process effective? is ther another way to do this? do i need different controls? what are your thoughts?
 
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Old 10-21-14, 04:29 PM
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Toheating I understand your reasoning and if the oil boiler aqua stat is left to turn the oil burner on even though the wood boiler is up to temperature then pipe return to wood boiler. I always have wood boiler aqua stat interrupt the firing of oil boiler as long as wood boiler is hot. Your right there are many ways to set these systems up and it is probably best to follow manufactory instructions, not as much fun but safer as you don't have to take the blame when things go south.
 
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Old 10-21-14, 04:34 PM
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if your actively killing the TT to the oil boiler than you have flexibility.
I try to design for simplicity and failsafe operation.
Too many aquastats all over the place make for a complex system to troubleshoot and fix if your not the designer
 
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Old 10-21-14, 04:47 PM
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I try also to keep it simple but do to the high cost of fuel we are encouraged to come up with more efficient systems and thus high teck such as out door reset indoor sensors , gasification wood boilers , therefore if you install a one of a kind system make good electrical drawings and lots of explanations or you risk having your system modified or even torn out .
 
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