Solar Add Compatibility with new Wood Boiler

[rickh1001]

I am in the final planning stages of getting ready to install a new wood boiler, along with about 1,000 gal of pressurized water storage. My wife wants to add solar hot water into the mix as soon as possible. In some ways, it makes no sense ecologically, since wood is "condensed sunshine". However, I like the concept, but have trouble figuring out how to make the the two work well together. If I have a large thermal storage tank, it would dwarf the contribution of the solar panels. In the summer, there would be too much water for the panels to heat. In the winter, the solar would have to add heat to the storage system which is already at +180 deg, and would seem a minor contribution for a whole house heating system. DHW will already be taken care of by HX with the wood boiler. I suppose I could simply add a parallel system with its own smaller 80-100 gal storage tank for the DHW, and use that in the summer, but this seems an expensive duplication of effort.

My general question is, what is the best design approach to adding solar water heating in with a wood boiler, or is solar not really that relevant once a good wood boiler system is in place?

 

[webbie]

My opinion is that the solar should be isolated from the system and used for DHW only. The theory with thermal solar is that the most efficiency is gained in raising the coldest possible water only a few degrees at a time. When one attempts to raise water to over 140 degrees on a regular basis - especially in the middle of winter in the northern cloudy climates - there is a point of diminishing returns.

My opinion only, of course.

Another option if you really want to experiment with solar thermal is to install a relatively small array - maybe 4 panels, and hook it to it's own tank and then use a potable water kickspace heater - in addition to the DHW. This would help you heat one particular room - and some kickspace heaters can work on 120 degree water.

So I am in some agreement with you that the best use of thermal solar - in your case and figuring economics into the equation - is DHW only.

 

[steam man]

I am currently installing a good size solar system that will heat DHW and then switch to a storage tank which will provide DHW preheat (like Nofossils) and radiant floor heating. The boiler will also heat the tank. I would like to get 9+ months of heat out of the solar panels. My pool is set up to act as a heat dump in the summer. The economics for me is pretty good though it would be pricey for others. Even being in northern Maine I get great heat gain. Hopefully I'll get enough data to make a good evaluation. My wife gets pretty sick of handling wood right about February. Solar for DHW would be a nice touch though.

Mike

 

[Jim K in PA]

This is something I am wrestling with as well. My plan was to have a couple of panels heating one or two 80 gallon non-energized electric HW tanks. My GARN dealer suggested I use the storage capacity of the GARN to better utilize the collected solar energy in the summer. I can also have 4-6 panels (home made 3x6 enclosed 1" black poly ~120' per panel) feeding the GARN due to it's location behind the garage (I have better exposure and more roof area to mount more panels). I don't expect much contribution from the solar panels from November-March.

Has anyone found a good means of determining energy input from passive panels based on temp, fluid capacity, flow rate and panel size?

 

[steam man]

This is something I am wrestling with as well. My plan was to have a couple of panels heating one or two 80 gallon non-energized electric HW tanks. My GARN dealer suggested I use the storage capacity of the GARN to better utilize the collected solar energy in the summer. I can also have 4-6 panels (home made 3x6 enclosed 1" black poly ~120' per panel) feeding the GARN due to it's location behind the garage (I have better exposure and more roof area to mount more panels). I don't expect much contribution from the solar panels from November-March.

Has anyone found a good means of determining energy input from passive panels based on temp, fluid capacity, flow rate and panel size?

If your trying to just get DHW, the separate solar preheat tanks would be perfect. Hooking it up to the Garn as storage bothers me, especially with homemade panels with unknown output capacity. Typically certified panels have a rated output to make an educated guess based on the location and amount of panels for design purposes. After that collected data based on flow, temp in/out would give you accurate numbers. The Garn storage may work if you have radiant heating which requires lower temps but I am doubtful. To use the Garn as storage for solar and then to provide only DHW would seem to be inefficient. Put it this way, solar for DHW and the garn for cold season heating sounds like the best bang for the buck for you. Your seasonal oil bill should be minimal. I think it is diminishing returns after that. IMO.

Mike

 

[Jim K in PA]

If your trying to just get DHW, the separate solar preheat tanks would be perfect. Hooking it up to the Garn as storage bothers me, especially with homemade panels with unknown output capacity. Typically certified panels have a rated output to make an educated guess based on the location and amount of panels for design purposes. After that collected data based on flow, temp in/out would give you accurate numbers. The Garn storage may work if you have radiant heating which requires lower temps but I am doubtful. To use the Garn as storage for solar and then to provide only DHW would seem to be inefficient. Put it this way, solar for DHW and the garn for cold season heating sounds like the best bang for the buck for you. Your seasonal oil bill should be minimal. I think it is diminishing returns after that. IMO.

Mike

Thanks Mike. You have described what I am concerned about, however it may still work out. Given the large storage volume of the tank (almost 2000 gals) and the relatively small level of output, it would take a while to heat the GARN up to a useable temperature. However, if I get enough Btus out of the panels that meets or exceeds our DHW needs, I can certainly send that energy into the GARN as I pull it out as long as the GARN is at or near 140* F.

Based on a daily usage of 60 gallons of 110* F water, with an incoming water temp of 45*F, I would need ~32k Btu per day. IF I can get that much (or more) out of my panels, I should be able to keep up with the draw out of the GARN. This would surely simplify my setup too.

 

[verne]

depending on where your 1000 gal tank is located, and your boiler. maybe building a fire once every week or two is an option. I put my boiler and tank in my barn for that purpose . I think if Im going to invest that much money into solar its going to take me off the grid.

 

[Jim K in PA]

depending on where your 1000 gal tank is located, and your boiler. maybe building a fire once every week or two is an option. I put my boiler and tank in my barn for that purpose . I think if Im going to invest that much money into solar its going to take me off the grid.

Not sure to whom you were addressing this, but I am installing a GARN with integral water storage of approximately 2000 gallons. You are correct, for my setup I may need to have a single burn during the summer once a week or so, depending on how much sun we get, ambient temps, and standby losses.

My solar investment will be fairly low, as I will be building my panels myself using cheap black poly pipe. Pump, controls, and sensors will likely add up to more than the materials for the panels. I should be able to do it all for under $150/panel. I have no need or desire to get off the grid, as having that backup or supplement certainly makes life less stressful. I have a stream for pico-hydro, enough wind for a small amount of generation, and may invest in PV if the state or Feds come up with a decent incentive to do so. But doubt I will replace 100% of my electrical needs with all of it combined.