Do You Ever Charge Up Your Large Heat Storage Tank With Oil?

[velvetfoot]

Disclaimer: I only have a 117 gal buffer tank, but I can see the possibilities with a wood boiler/oil backup and big storage.

Having many different zones coming on and off at different times would be no problem with a large heat storage tank (500-1000 gal). You wouldn't have to think about an oil boiler cycling on and off a lot. It's just that when it would come on, it would run for a long time. Sure, there'd be heat loss through the tank, but many people insulate the crap out of them, heat loss would be within the building envelope, and there wouldn't be any boiler startup/shutdown/flue losses while the system is operating off the tank

What do you think? Oil is pretty cheap right now.

 

[maple1]

Sounds OK with the way the price of oil is right now, and if you're paying for wood or are in short supply.

Would definitely be more efficient than just running off the oil in the traditional way - I think. With storage water coming into the boiler that is quite a bit cooler than would be coming back from heating zones, there might be potential to recover more heat before it hits the chimney too - not sure if condensation would be an issue or not though.

 

[velvetfoot]

Boiler protection would be involved of course.

 

[peakbagger]

I have considered turning my two oil tanks into direct storage but expect that keeping 550 gallons of oil heated to 180 degrees is not a great idea . There are low mass oil boilers like the System 2000 units that have very low thermal mass I expect that that's the better option.

 

[velvetfoot]

So, your storage is not well insulated? You don't have an oil boiler? Either one would knock you out of my scenario.

 

[hobbyheater]

At one time I did heat the storage tank using the oil boiler. The boiler was a cast iron sectional weighing 375 lbs and holding 3.5 gallons of water and maintaining a temp between 170 F/185F for DHW coil. The nozzlel on the burner was 1.1 GPH.
An hour meter was connected to the burner to record its running time and over a 3 day period, with no house heat or DHW water drawn from the boiler over this time, the boiler ran for 9 hours over this 72 hour period just to maintain stand by water temperatures. When house heating and DHW load was added, the hour meter recorded 6 - 7 hour of burn time a day.
The oil boiler was then plumbed to heat the storage tank (1045 imp gallons) and would run for 5 hours every second day to heat the storage.

 

[velvetfoot]

Very interesting. That's quite a difference. How is your tank insulated? Have you ever figured out how much heat it loses just sitting there?

The ultimate setup that seems to proffered is a heat source that can modulate down to match load, condensing flue gasses while constantly providing relatively low temperature water to a radiant emitter. But, as I said at first, what if there is a different heat distribution system with loads are coming on and off, here and there, reacting to occupancy, time of day, etc? Or, what if the load is less than the lowest level of heat that the modulating source can provide? The boiler turns off, and then has to start up again, maybe shortly thereafter.

Anyway...

 

[hobbyheater]

Very interesting. That's quite a difference. How is your tank insulated? Have you ever figured out how much heat it loses just sitting there?.

Tank is very well insulated, with a heat loss of 1,300 BTU's per hr.

 

[Rory]

My system has a 670 gallon passive storage tank, and my oil furnace is equipped with a set point controller to heat the tank if it drops below the "set point". My heat exchanger didn't seem to dump the heat into the tank quickly enough and my boiler short cycled a lot until I raised its maximum internal temp to 200F. It's funny that you think it may be more efficient than direct heating, though - I've been contemplating changing it to use one of the valves that allows either/or operation. If I go that route, I'm going to add a heat pump/water heater on my DHW line downstream of the storage tank and stop having fires in the summer.

 

[tom in maine]

This thread seems to be about two different things. Didn't it start out asking about storing heat in oil, or am I confused.
In keeping with the first part of this thread: if you think your insurance company is pissy about wood burning, they would love to hear you have hundreds of gallons of hot oil.

Water is a cheap date. You can use new oil tanks to store hot water, but they will corrode and they are not made to hold pressure.

 

[maple1]

I thought it was pretty plainly about heating storage (water) with an oil boiler.

 

[JP11]

I get some 'ghost flow' because my wood boiler input comes into 'closely spaced Ts' in an injection loop on the out leg of my boiler.

I'm impressed how this setup very rarely heats up the boiler jacket in the oil boiler. However... the way it's plumbed, if I let the oil run unplanned (temp in the wood boiler tanks just goes below 140) then when the oil boiler runs I get some inadvertent heat going back out my injection loop piping to the tanks.

If I PLAN to be away and let it run on oil.. I just shut my valves to eliminate the flow to wood storage. I don't think there is enough of a benefit to letting the oil run. Disclaimer.. With a large house, my oil boiler never short cycles. The indirect DHW tank is about a 15 to 20 minute call on the boiler.

 

[tom in maine]

My bad. Re-read it again. I guess my head was someplace else.
I actually heat our tank with oil when not burning pellets if necessary for back up.
I do not think it is the best way to do things, but it was a simple system to do and provides DHW through a hx.
If it was not for the dhw, I would not heat the tank with oil.
I use a Toyotomi and the tank does eliminate some short cycling of these units.

All that being said, I fired up the latest pellet boiler we are working on last night. No more oil unless I go away.
Pics to come soon.

 

[velvetfoot]

am I confused

Yes, you are.

 

[velvetfoot]

I get some 'ghost flow' because my wood boiler input comes into 'closely spaced Ts' in an injection loop on the out leg of my boiler.

I'm impressed how this setup very rarely heats up the boiler jacket in the oil boiler. However... the way it's plumbed, if I let the oil run unplanned (temp in the wood boiler tanks just goes below 140) then when the oil boiler runs I get some inadvertent heat going back out my injection loop piping to the tanks.

If I PLAN to be away and let it run on oil.. I just shut my valves to eliminate the flow to wood storage. I don't think there is enough of a benefit to letting the oil run. Disclaimer.. With a large house, my oil boiler never short cycles. The indirect DHW tank is about a 15 to 20 minute call on the boiler.

Plus, you have radiant distribution smoothing things out.

 

[velvetfoot]

All that being said, I fired up the latest pellet boiler we are working on last night. No more oil unless I go away.
Pics to come soon.

Cool! Or, Hot!