Backup boiler heating thermal storage?

[EricO]

Hello everyone. This is my first post. I've been reading the forums for a while now and it's been a HUGE source of help, but I have a question that I haven't really found a direct answer too.

Ok, so please don't laugh if this is a dumb question, but I'm wondering if it's common practice to have your back up heat system also heat the thermal storage tank?

I'm working on putting my system together right now and thinking through everything. Setup will be an EKO 40 with 500+ gallons unpressurized storage, hydronic baseboard heat, and a LP boiler backup.

The primary thought was that the EKO would heat the baseboards and charge the thermal storage when running, and then the baseboards would draw from thermal storage between burns. Mainly I'm trying to figure out, I want the backup boiler to heat the baseboards, but should it also heat the thermal storage?

Thank you in advance for your help. Direction to diagrams are always welcomed too!
Eric

P.S. - Thought was to have the EKO and LP boiler as part of a pressurized system for the baseboard, and use a heat exchange for the thermal storage tank since it's unpressurized. (I know the benefits of the pressurized storage,but dont really have room for one.)

 

[velvetfoot]

I personally think it would be a waste to heat that tank if the scenario could be something like, you're working late or something and the oil dumps a lot of heat into that tank, where you could be filling the boiler when you got home.

I'm putting in a pellet boiler with a 119 gallon buffer tank, but I will heat it with backup oil because I like the thought of less cycling on the boiler, esp. since there are two zones involved. The pellet boiler can probably go a couple days though even with just the onboard hopper and even more if I build a box, so unwanted oil boiler firings won't be as much of a factor..

 

[EricO]

I personally think it would be a waste to heat that tank if the scenario could be something like, you're working late or something and the oil dumps a lot of heat into that tank, where you could be filling the boiler when you got home.

Thanks for the reply velvetfoot. I agree that it would probably be a waste. Ideally, I'd figure out how to run plumb the system so that the backup wouldn't feed the storage tank, but don't have any good ideas yet. Have an idea how to keep the two separate? Thermal mixing valve?

 

[Coal Reaper]

it was much simplier for me to just allow my system to move water to/from storage. this accurs at the rate of 3GPM as my storage circ runs whenever there is a call for heat. my initial thought was "great, now there is not a chance for storage to potentially freeze or my lines running to the barn." in addition, what i actually found is that it kept storage warm enough that it then didnt take me forever to charge the tanks back up when i did go back to burning wood. probably the OB fires longer and uses a bit more oil but then i dont go through so much wood in order to bring the storage tanks back up to temp. wood firing time would also be greatly lengthened if there was a high demand for heat in the house. i am happy with it like this and also i didnt need to mess around with all the valving.

 

[alaskawild]

Eric... It would be a waste to do it that way. Is your LP boiler a mod-con? Your backup boiler using a small 25 gallon buffer tank so you don't heat the thermal storage is the way to go. Works great with radiant heat because your thermal storage would last longer but this setup will work just the same for baseboard. You will need to make the appropriate heat setting changes for the higher heat output but it gives you the general idea. Take a look at the attachment.

 

[maple1]

My backup does not heat my storage, just puts water to the zones.

But - I have a check valve in one spot that helps accomplish that. Next opportunity I get, I will be taking the flapper out of that valve & drilling a small hole in it to let some storage water into that picture. As is, the electric backup boiler short cycles a lot when heating, and, if all the zones stop calling for heat at about the same time the boiler reaches setpoint, the backup circ will deadhead for a while because the heat can't get out. Part of those issues is that the electric boiler is bigger than it had to be - but I did discover that it does help to have a bit of buffer, so might as well let the storage be that bit of buffer.