I've been ruminating over how to heat a 2200 sq ft farmhouse in the finger lakes region of new york.

I wanted to float an idea about using the concept of a water wall in conjunction with active solar hot water heating.  The idea would be to install several 9 foot steel or fiberglass containers between widely spaced studs in my central wall, which I would use as massive low temp radiators.  I do not have the architectural set up to do this passively, so I'm considering an active approach.

Mounting x number of collectors to the roof, using a drainback closed loop system, with the living room "tanks" as both storage and radiation.  One way to control them would be to play with the temp point where the pump turns on.


What I don't understand is how much radiation would they offer at what temp...and how many panels I would need to heat them to x temp.   I would aim to keep the house at say 55-60 degrees with this system and supplement this with my wood stove.


I'm not anywhere near doing this but trying to imagine options.  Although I am a diyer, geothermal is still really expensive and want to avoid gas and coal.  

That kind of tankage and plumbing and solar panels could cost you as much or more than doing a geothermal system yourself.

The problem I see with your system is that with no other storage, you are going to have to stop collecting heat when the storage and radiator tanks are making the place comfortable. You won't be able to store any heat past that point, they will start cooling off and once the sun goes away, you will need to employ the backup system anyway.

Before going to geothermal or any type of solar it's worth air-sealing the hell out of the place with blower-door verification. Even $1000 of spot foam and spot-insulation can easily reduce the mechanical requirements by ten grand- these old farmhouses were uninsulated wind-tunnels. Getting a significant fraction with solar usually requires R30+ walls in that region- the sunnier winter days tend to correspond with the bitterest of cold nights, and the rest of the time the sun is a bit weak.

Assuming you air seal it to under 3ACH/50 and have at least R10 whole wall values (2x4 studwall with cellulose or open cell foam), a better 2-3 ton ductless mini-split air source heat pump can probably handle the load at 55F interior temps down to about -5F and will run at near-geo efficiencies for well under 10 grand. Some of the Mitsubishis & Daikins are rated to still run with 70% of rated output at temps a bit below -10F, others crap out at 0F. The better Fujitsus are good to at least -5F, maybe lower. While the efficiency at +5F outdoors & lower are pretty crappy with a 70F indoor temp, at 55F you'll do OK- a COP of about 2.0. At the mean January temps of ~20-23F the COP will be just shy of 3.0.

If instead of spending 20 grand on a minimalist geo system you spent 6 on a mini-split and 14 on photovoltaics the PV input would handle much of your heating costs if net-metered, and at higher average solar efficiency than an active solar system. Assuming a seasonal average of 2.5 (a conservatively low estimate) Mini-split COP x 15% PV efficiency= 37.5%, which would take an ultra-low panel temp to achieve with a drainback after discounting for pumping power.

I also live in the Fingerlakes region of NY in an old timber frame farm house. That wood stove is your friend in these houses, especially with our supply of firewood in this part of the state. As has already been stated, air sealing and insulation is key in these old places. I've been working on mine for the last 25 years and finally have it comfortable, a far cry from the wind tunnel we started out with, but I doubt I'll ever be able to get mine down to the 3ach/50 mentioned above.

I've also done some experimentation with solar thermal via an air heater. It's definitely worth doing, but honestly, in our area, consider its heat as a bonus, but don't depend on it being a reliable source. We just don't normally have a good location for sun. Don't be fooled into using this fall and winter as an example, as it's been uncharacteristically sunny this year Hydronic solar applications where you can store a couple of days heat work pretty well, though, as we seem to get 2 (or 3) cloudy days for every decent sunny day here in the winter months, and solar water heating makes a lot of sense as you can use that year round.

We personally just went the geothermal route and we're really happy with the system so far. Our wet soils and cold winters are ideal for geo. I didn't look at mini splits, though. Most of these farm houses don't have a very open floor plan so I suspect it would take several units to do the whole house.

Until either our electric rates go way up (currently around $.11 /kwh for me including supply charges and tax), solar pv install prices come down more, or NY state starts some sort of SREC program, I don't personally see the payback for pv here yet. No matter how I look at the numbers, I'm calculating about 20 years at best., in my case for break even. That could easily change soon, especially as outfits such as Solar City make their way to our area.

I really am a solar advocate, but trying to make one of these old farm houses mostly solar heated in our area might be a lesson in frustration. Bags of cellulose, cans of Great Stuff, and the wood stove are the most cost effective heating strategies. (but the geo system really is sweet).

Specifically, on your design, how about instead...Really simple would be an air heater for bonus heat.  More complicated, but cost effective would be a hydronic active water heating system for DHW.  Then if that works, add to it with more storage and collector area, and put in some radiant heaters for added heat.  You'll still need some sort of a main heating system though.  I successfully used wood for years and had the oil furnace just as a backup when we went away, or needed to heat the house up quickly.

There are multi-splits available with HSPFs > 8 that can handle up to 8 interior units, at a cost-adder of ~$1500 per head- don't rule them out even for old farmhouses even if it's not an open floor plan. Worst case a single $5K 2-ton mini-split in a larger common area that you intentionally over-heat a bit isn't much different from having a wood stove in the same room.

If you're serious about air-sealing an old farmhouse it's worth buying a foam gun and using the 20oz+ cans of can-foam rather than buying cases of Great Stuff available at box stores with the cheezy plastic-straw applicator and the breakable valve tips. You can leave can-foam cans on the gun for months without it setting up, and the adjustability of the flow is a great benefit. Dense-packing the walls can be tricky in some of these houses with oddball framing elements creating hidden pockets, but that's worth doing too.

Going with low-E storm windows can be cheaper/better than replacement windows, if the old windows aren't totally trashed. It's worth breaking out the sash weights and either dense-packing cellulose or insulating those pockets with low-expansion foam though. See:

http://www.ornl.gov/sci/buildings/2010/Session%20PDFs/22_New.pdf

http://low-estormwindows.com/resources/ (<<< read the documents in these links- there's some very good stuff in there.)

 

Until either our electric rates go way up (currently around $.11 /kwh for me including supply charges and tax), solar pv install prices come down more, or NY state starts some sort of SREC program, I don't personally see the payback for pv here yet. No matter how I look at the numbers, I'm calculating about 20 years at best., in my case for break even. That could easily change soon, especially as outfits such as Solar City make their way to our area.

I really am a solar advocate, but trying to make one of these old farm houses mostly solar heated in our area might be a lesson in frustration. Bags of cellulose, cans of Great Stuff, and the wood stove are the most cost effective heating strategies. (but the geo system really is sweet).

 

I would be interested in how you are calculating a 20 ROI on your solar system in the finger lakes.  Send me an email at [email protected] and we should chat. I live and work right in your area!

Posted By ACES-Energy on 28 Dec 2011 08:49 PM

 

Until either our electric rates go way up (currently around $.11 /kwh for me including supply charges and tax), solar pv install prices come down more, or NY state starts some sort of SREC program, I don't personally see the payback for pv here yet. No matter how I look at the numbers, I'm calculating about 20 years at best., in my case for break even. That could easily change soon, especially as outfits such as Solar City make their way to our area.

I really am a solar advocate, but trying to make one of these old farm houses mostly solar heated in our area might be a lesson in frustration. Bags of cellulose, cans of Great Stuff, and the wood stove are the most cost effective heating strategies. (but the geo system really is sweet).

 

I would be interested in how you are calculating a 20 ROI on your solar system in the finger lakes.  Send me an email at [email protected] and we should chat. I live and work right in your area!

Done.