Which storage option would you choose?

[gorsuchmill]

I heat with radiators and hydronic coils which, I estimate, could all work down to 140* or so. My storage alternatives are a non-pressurized system with an EPDM liner and a pressuirized storage tank. The benefit of the non-pressurized system would be its location, in the boiler room approx. 20' from the new Tarm. However, I've been reading the maximum temp. for EPDM is approx. 170*, which provides a relatively modest delta T. On the other hand, I would try to drive the pressurized system to 190* or so, thereby increasing the delta T. The downside is the tank would need to be located in an unheated garage approx. 80 lineal feet from the wood boiler, 50' of which would require buried pipe.

What would you do?

By the way, I take delivery of a Solo 40 within the next month and appreciate everyone's input in helping me with my decision to gasify.

Thanks,

Lee

 

[Nofossil]

Based on my experience, you'll be hard pressed to get either type of storage closer than ten degrees to your boiler outlet temperature. Is there anything you can do to get usable heat out of water down to 120 or so? I added a bit more baseboard and I'm adding a radiant zone for that purpose.

You want your storage close to the point of use, especially if you're ever going to use it for heating DHW.

 

[gorsuchmill]

Nofo - I'm not sure if I can reduce the usable water temp. Adding a radiant area would require a lot of piping in a crawl space at a hefty price.

If the 10* spread is common, then 180* outlet water would be indifferent to either the EPDM or pressurized systems. However, is it possible to deliver 190* or possibly 200* water which, after the loss you indicated, would still give a more favorable delta T? Assuming that to be the case, would you recommend pressurized at 180* located 80' from the boiler (50' underground piping) in an unheated garage or 170* non-pressurized approx. 20' from the boiler in an indoor application? What if the pressurized could be driven to 190*?

Thanks again.

 

[WoodNotOil]

I would suggest perhaps oversizing the storage tank and going with un-pressurized. A larger tank would take longer to drop in temperture. I am sure someone could do the math and tell you how much bigger it would need to be to not drop below 140* between burns. I have the solo plus 40 and they suggest 800 gallons for it. I am going to put in 800-1000 gallons of storage this summer in an unpressurized tank with EPDM liner using a hx plate. I think 80' is a long way and it would take a lot of insulation if the tank is in an unheated space. I am not a professional, but that is what my gut tells me. I'll be interested to hear what others have to say.

 

[Nofossil]

Nofo - I'm not sure if I can reduce the usable water temp. Adding a radiant area would require a lot of piping in a crawl space at a hefty price.

If the 10* spread is common, then 180* outlet water would be indifferent to either the EPDM or pressurized systems. However, is it possible to deliver 190* or possibly 200* water which, after the loss you indicated, would still give a more favorable delta T? Assuming that to be the case, would you recommend pressurized at 180* located 80' from the boiler (50' underground piping) in an unheated garage or 170* non-pressurized approx. 20' from the boiler in an indoor application? What if the pressurized could be driven to 190*?

Thanks again.

My personal preference would be inside for these reasons:

1) Much less transmission loss
2) Much less standby loss and/or much less money and space cunsumed by insulation.
3) For intermittent loads (DHW), you don't have to push 160' of ice cold water through the system every time you start circulating.
4) Any standby loss heats the house. Not so good in summer, but you'll likely have it much cooler then if you use it at all.

Pressurized would make the plumbing and heat exchanger situation simpler and cheaper, but probably more than offset by the buried line costs.

You mention radiators and hydronic coil. Are these the old fashioned cast iron freestanding radiators? Does 'hydronic coil' mean a water-to-air heat exchanger in an air duct?

 

[gorsuchmill]

Woodnotoil - Your suggestion is a good one. I was thinking of approx. 1000 gallons of unpressurized, but the 30* delta T seems like it might not have enough benefit. By the way, what type of implements do you use (i.e. radiators, baseboard, radiant)?

Are others out there using radiators with unpressurized storage and receiving good function out of the setup?

 

[gorsuchmill]

Nofo -

Yes, old timey cast iron rads on my first floor and water-to-air exchangers on my second floor. I just completed a home renovation/addition project which included adding central air to my upstairs and a 2-story addition. I'm heating the addition and upstairs with heat pumps, backed up with the hydronic coils. My first floor is not ducted, and therefore is heated only by the cast iron rads.

 

[WoodNotOil]

gorsuchmill - I have baseboards on both the 1st and 2nd floor and a retrofitted radiant floor in the 1st floor. The 1st floor actually has two baseboards, a radiator, and a toe-kick. I use the radiant floor all winter and the baseboards etc. come on if it is really cold and I can use them in the fall and spring when the floor is overkill.

I don't know a lot about the math involved in delta T etc., but I say oversize everything a little and it should work fine. For instance, the solo 40 puts out 140,000 BTU and I plan to use a 225,000 BTU plate hx. I can probably deliver more BTUs to the house than I would ever need. I oversized things at the suggestion of my heating contractor who worked along side me to install the tarm. He said doubling what you think you need isn't a bad idea. The house had a steam system originally and I converted the steam boiler to hot water, took all of the cast iron radiators out, and put in a whole new delivery system.

As far as adding radiators/baseboards, what about using the existing pipes and adding more along side or replacing the existing with larger. I got my living room radiator from houseneeds.com.
(broken link removed)

 

[jebatty]

While I agree it would be difficult to accomplish less than a 10* temp spread between boiler and storage, keep in mind that boiler peak supply easily could be 180-200, going into the top of the tank, although the bottom of the tank will be less. My boiler on cycling will hit a high of about 195 and a low of about 170, assuming full-time heat draw to storage. The low will creep up as the tank temp rises, but generally the top end won't go over about 195.