Solar Hot Water with a wood fired water boiler

[NW Island]

Does anyone have any experience using solar heated water in conjunction with a wood fired water boiler?  I'd like to combine these two heating sources for hydronic heating and domestic hot water.  I'm thinking the solar collectors would be the primary source of heating the water, and the wood fired boiler would supplement that source when there in not enough sun or the heating water demand exceeds the capacity of the solar collectors.  Question is whether both the solar collectors and the wood fired boiler would heat water in a separate hot water storage tank (through the use of heat exchangers immersed in the tank), or whether the solar collectors would "pre-heat" the return water to the wood fired boiler (in the case where the wood fired boiler has a integral water storage tank). Or perhaps there is another, better idea I'm not aware of.

[StorminN]

NW Island,

Are you talking about an outdoor wood boiler like the Central Classics and such?

Check out the animations on Thermomax's web site... these guys are in Victoria, BC and distribute Thermomax and SolarMax vacuum tube solar collectors for western North America. I've met Patrick before and he's a nice, knowledgeable guy.

DHW combined with woodstove

Solar Hot Water applications

More locally, you could also call Larry Owens at Northwest Mechanical in Seattle... he's a very knowledgeable guy and a great resource... (he's a co-founder of the Shoreline Solar project, too). NW Mechanical has done tons of solar hot water installs, including hydronic heating... not sure if they have combined SHW with a wood fired boiler, but it would be where I started asking questions if I was going to do it...

You might also ask the folks who manufactured your boiler... they might have a drawing already.

I think if it were me, I'd probably have an 80-100 gallon super-insulated hot water tank in the house, with multiple heat exchangers in it... glycol from the solar collectors, loop from the wood boiler, loop to the hydronic heating, and the domestic hot water... to meet code, the tank would probably need an electric element in it, too (because we can't "rely" on wood or solar). This tank would be the central point for all the hot water made. With this setup, in the summertime, you wouldn't have to heat all the water in the boiler just to get domestic hot water...

-N.

[NW Island]

Stormin N;

Thank you for that good information.  I hadn't yet seen that data on the Thermomax site, so I'll study it.
I do know Larry Owen, and perhaps I should contact him about this but I suspect he may not have any direct experience with this type of a combo system.
I have not yet purchased my OWB boiler.  Yes, I am thinking of an OWB (like Central Boiler E-Classic 2300).  Problem is (as you probably know living in WA) that these types of units are technically not allowed.  Am I misunderstanding this restriction, or do you have any insight on how an OWB can be used in WA?

J

[StorminN]

Hi NW Island,

I don't know the specifics as to what is allowed and what isn't. It might be by county? I DO know that I see a few OWB's out here in Clallam County... and my friend's Dad owns one... I'll see if I can ask him if he knows the specifics.

OK, I just did a quick Google search and came up with this:

http://apps.leg.wa.gov/WAC/default.aspx?cite=173-433-100

(3) Solid fuel burning devices. After January 1, 1995, a person shall not advertise to sell, offer to sell, sell, bargain, exchange, or give away a solid fuel burning device in Washington unless it has been certified and labeled in accordance with procedures and criteria specified in "40 CFR 60 Subpart AAA - Standards of Performance for Residential Wood Heaters" as amended through July 1, 1990, and meets the following particulate air contaminant emission standards and the test methodology of the United States Environmental Protection Agency in effect on January 1, 1991, or an equivalent standard under any test methodology adopted by the United States Environmental Protection Agency subsequent to such date:

     (a) Two and one-half grams per hour for catalytic woodstoves; and

     (b) Four and one-half grams per hour for all other solid fuel burning devices.

     (c) For purposes of this subsection, "equivalent" shall mean the emissions limits specified in this subsection multiplied by a statistically reliable conversion factor determined by ecology that relates the emission test results from the methodology established by the United States Environmental Protection Agency prior to May 15, 1991, to the test results from the methodology subsequently adopted by that agency.

So I guess you'd have to contact Central Boiler and ask them if the E-Classic 2300 meets this standard... which is more stringent than the Federal standard...

-Norm.

[logwalker]

Hello, At this time any boiler below one million btus is not allowed to be used in the state of WA. None have been certified at this time. Above that threshold they have very specific rules and restrictions and have to be certified in any case. There is some hope that next year may bring a change in the regs. The EPA website has some info and a contact number for a guy named Tom. He will take phone calls and does know a lot about the issue. Call him and Call him and let him know how you feel on this. He does listen well. Joe

[Karl_N.]

This was a project I was supposed to do back in June. I am going to do just what you are talking about. I would run the return through to the cold inlet of the boiler and heat the resevoir then have the regular line from the boiler run through a flat plate heat exchanger and then a closed loop through a hot water tank with two tanks in it, that way as you are heating your hydronics while heating your domestic. Two tanks in one is nice just cause you get to work from a large resevoir but I suppose other resevoirs can be made pretty easily. I'm rambling but yes I think it can be done effectively. I'm running my radiant floor off of the boiler and using 1/2 d.c. pumps that run off of their own solar panels.

[rowerwet]

Hi NW Island,

I don't know the specifics as to what is allowed and what isn't. It might be by county? I DO know that I see a few OWB's out here in Clallam County... and my friend's Dad owns one... I'll see if I can ask him if he knows the specifics.

OK, I just did a quick Google search and came up with this:

http://apps.leg.wa.gov/WAC/default.aspx?cite=173-433-100

(3) Solid fuel burning devices. After January 1, 1995, a person shall not advertise to sell, offer to sell, sell, bargain, exchange, or give away a solid fuel burning device in Washington unless it has been certified and labeled in accordance with procedures and criteria specified in "40 CFR 60 Subpart AAA - Standards of Performance for Residential Wood Heaters" as amended through July 1, 1990, and meets the following particulate air contaminant emission standards and the test methodology of the United States Environmental Protection Agency in effect on January 1, 1991, or an equivalent standard under any test methodology adopted by the United States Environmental Protection Agency subsequent to such date:

     (a) Two and one-half grams per hour for catalytic woodstoves; and

     (b) Four and one-half grams per hour for all other solid fuel burning devices.

     (c) For purposes of this subsection, "equivalent" shall mean the emissions limits specified in this subsection multiplied by a statistically reliable conversion factor determined by ecology that relates the emission test results from the methodology established by the United States Environmental Protection Agency prior to May 15, 1991, to the test results from the methodology subsequently adopted by that agency.

So I guess you'd have to contact Central Boiler and ask them if the E-Classic 2300 meets this standard... which is more stringent than the Federal standard...

-Norm.

The Eclassic is cleaner than the EPA standards and even meets the next level of standards according to the sales rep from CB I saw this past sumer.