Heat loss for the area is about 40k btu.

My original post was a little premature.  Since then we have done some calcs and to put in a system right now is going to bust the budget.  But we will be putting in a condensing boiler to support the radiant and it will act as the backup/supplement once we do go to solar.  I have been told a glycol drain back system would be best suited for this.  I would need a larger storage tank and a good amount of collectors to support the radiant and hot water.

Has anyone on hear done solar for a radiant floor?  I would love to hear details on your system.  How does you system perform in the winter months?

 

Google 'Solar Harvest'. The guy is in Boulder and is 100% Solar(no backup).

The single biggest challenge for using solar, as I see it based on my consideration of using it, for space heating is the fact that solar energy production is lowest when the heating need is greatest, i.e., winter.

take a look at the Taco X block on our site blueridgecompany.com this is a way to start the concept, you can attach to the water heater and have an isolated heating system, not open loop. Next look at expanding the solar collection area and storage. Your water heater will still be the engine, but in a 1,000 sq ft res, you can get this by. If you were to use new SRCC certified panels and water heater/drain back system you can receive a 30% tax credit on the entire system.
his is a good thing to do, and if you have access to a hand full of 250.00 panels you are in a cost efective position.
Dan

I was watching "GREENPLANET" TV and they were discussing placing solar water heaters in new construction directly on roof sheath with out tiles or shingles under, of course with a membrane under it saving the coast of tile and labor. Has anyone done this? Product names would be much appreciated. John

Craig,

I went through the same design spiral as you trying to build, be efficient and keep costs down.  I am in the midle of building so ask me in a year how well my choices are working.  what I did was the following

1. Maximizing passive solar through good window selection, sizing and overhangs on the south side.
2.  Adding a solar powered domestic water heater.  Total installed cost is about 3300$  I did the installing.
3.  Adding a  solar air heater  www.yoursolarhome.com  I installed a 2 pannel system with a seperate PV pannel to power the fan.  The heat is  blown  into my insulated basement.  This system is up and running
4. using a propane boiler as the other heat source along with a second loop for domestic hot water. 

http://s45.photobucket.com/albums/f66/eric_anderson5193/?action=view¤t=housepic.jpg


Cheers,
Eric

Your peak load of 40KBTU/h in a house size & climate similar to mine (Worcester MA) tells me that you're NOT going to be able to supply a large fraction of your heating with solar- you need significant envelope upgrades to get there. My total finished area is about 2400', with a semi-conditioned basement to boot, and my design-day heat load is ~30K, and I still have known insulation & air sealing issues that will bring about far greater fuel reduction per dollar invested than solar. If your house isn't tight enough to need an ERV for ventilation you really should be spending it somewhere other than on active solar space heating. (And no matter what you heat with, envelope tightening is usually worth it!)

That said, if sweat-equity and the panels are cheap, if you have space for it 5-8 panels could give you something. Check out this guy's asmosheric-pressure solar-radiant retrofit:

http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm

He's using the solar radiant on an as-available basis as supplement to his existing hot-air system. Something like this may prove more cost-effective at reducing your fuel consumption than going to mod-con boiler-heated radiant and simply abandoning the hot air system. If you can, mount the panels vertically on the exising house & garage, not sloped latitude+15 on an outbuilding. In the New England snow zone you'll get better mid-winter & overall heating season performance utilizng snow-scattered light with them mounted vertically than the purely solar-geometry based theoretical latitude + 15 degree rule of thumb.

How was the 40K number derived? Manual-J overestimates- a direct or inferred actual MEASUREMENT is more accurate than any generic software modeling. Review this guy's methodology and see if you can't come up with something more precise: http://www.vonwentzel.net/HVAC/HVAC-Calculators/index.html Use a real measurement rather than manual-J or other heat-loss estimators if you can.

Going with solar for the domestic hot water may be a reasonable investment if various tax credits & other subsidies come through. But if you go through with installing a mod-con boiler for the radiant, sizing it to handle a hot-water zone with an indirect-fired hot water tank would be cheaper, and improve the carbon-footprint of your water heating immensely.

Micro-cogenerator heat source might be a good option. The only reasonably-local version available is coupled to a mod-con boiler that's too big for your heat load (and mine :-( ), but I've been told they're developing a smaller unit. See: http://www.freewatt.com/products.asp?id=172&name=Hyd They were recently acquired by ECR, but the locals in MA tell me it hasn't changed the development plans. They guy in the office next to me installed one in his 6000' house in the Boston burbs last year and is more than satisfied with it's performance.

At relatively low heat loads like yours the raw economics of mod-con boilers aren't always there, even if they are more efficient. After doing a VERY careful heat load analysis, running it off a "right sized" mid-efficiency boiler and a reverse-indirect heat exchanger type buffer tank allows you to micro-zone the house without losing efficiency, roughly architected like this:

http://www.ergomax.com/New-Tanks.htm

An architecture like this is relatively insensitive to the type of heat source, making later solar or cogenerator retrofits easier, and it guarantees the boiler never short cycles on micro-zone calls: Since the boiler only serves the buffer tank, not the separate zones, it's minimum burn time is determined by the hysteresis of the buffer's aquastat and the volume of water in the buffer. Set up properly the boiler should meet or BEAT it's AFUE efficiency numbers. But since your DHW will always be 120F or higher, the tank temperature would limit the efficiency of a mod-con as the heat source to something between 90-95% combustion efficiency unless you add a separate smaller isolating buffer on the heating return water. (It's the temperature of the return water entering the boiler, not it's output temp that determines it's condensing-mode efficiency.)

This is roughly the architecture I'm committing to on my place. I'm initially going to use a sealed-combustion tankless hot water heater as the heat source, to be able to program it's modulated output for guaranteed "right sizing" as my heat load shrink. Efficiency benefits accrue from the tankless modulating down as the tank temp recovers, lengthening burn cycles too. It's very low-mass compared to a cast iron boiler, (similar to a wall-hung mod-con's mass) so it's standby & cycling losses will also be low. (I'm continuing to upgrade the performance of the building envelope- I'm better off spending the cost difference between this and a mod-con there.) I don't advise going the tankless-as-heat-source route unless you're really prepared to do the engineering, maintenance & repair yourself- most heating contractors wouldn't touch it with a 10' pole, and it WON'T last as long as a cast iron boiler by any means. But I'm figuring by the time mine craps out there will be better cogenerator options available. There are plenty of alternate combi-designs based on tankless heaters, some better than others, eg: http://dsp-psd.pwgsc.gc.ca/collection_2007/cmhc-schl/nh18-22/NH18-22-106-108E.pdf , but I wouldn't just buy anybody's on-line pre-packged partially-assembled tankless-radiant kits off the web (of which there are many.) Some may be OK in your place, but I wouldn't count on it.

The buffer tanks last pretty much forever, but if you live in a place with very hard water in the domestic water supply, plumb it such that you can give the water side of the heat exchanger a vinegar rinse every couple of years to keep it from scaling up.

Layout your radiant zones, but keep thinking about your long-term plans for a heat source to drive it and what makes the best financial return. (I'm guessing a couple grand spent on air sealing & insulation may pay better than a mod-con, but not necessarily better than even more money spent on a net-metered cogenerator.)

  I apologize for any confusion on terminology.  In the enginerd world where I spend my working life "architecture" and "system architecture" are used widely to refer to the big-picture view of a system, and have nothing to do with the forms of buildings.

The original sense of the word referred to a person, not a constructed object:  The ancient Greek was αρχιτεκτων  meaning "master builder", a compound word of αρχι (Latinized "archi", meaning head-honcho/leader/chief) and τεκτων (Latinized "tekton", meaning carpenter/builder/maker).  It took the Romans to come up with separate words for the master builder and the objects of his creation.  

But in contemporary 'mercan English "architecture" refers the overview big picture master-structure of anything,from the abstract & mathematical to the concrete & tangible- it's long since moved beyond the forms of buildings.  I'm not so convinced that this site deals much in architecture as art form/shape/function of buildings, but clearly is concerned with minutae that the αρχιτεκτων would spend his/her time contemplating, particularly when thinking about the practices & materials for sustainableprocesses & results.  There's very little here about asethetic & human factors of building design, plenty about "systems", from walls to roofs to heating/cooling/lighting etc.

Using the word "structure" to describe the system-archicture would probably be even more confusing.  (And most peops have to look it up when you start throwing around words like hydronic or hydraulic, which also have different specific meanings in different contexts.)  Language can never achieve perfection, I guess...  Language is a social contract- words mean what the users say they mean.  And they don't always agree, eh? ;-) 

Fair enough and once again, quite informative!

(OK this is even MORE thread drift but...)

If you want even more arcane reading on the subject of how buffering zoned hydronic heat this piece is a real gem:

http://www.patkelco.com/uploads/files/4bf77cff8bc8411bb00c67e962d0ef7d.pdf

It's target audience is for bigger facility physical-plants, but the math still works for residential-sized boilers and micro-zoned houses. It explains in some detail why setting up the system buffer-centric as in the Ergomax sketch ( http://www.ergomax.com/New-Tanks.htm ) works to an efficiency advantage. There is at least one vendor of small systems that has taken this approach using low mass steel boiler technology with more sophisticated controls with great success: http://www.energykinetics.com/system2000-HowItWorks.shtml http://www.energykinetics.com/productGallery.shtml

The differences between the Energy Kinetics system and a reverse-indirect/buffer using a modulating tankless hot water heater are that the EK uses a low mass steel non-modulating boiler, but sophisicated purge controls to remove remainder heat from the boiler after a firing to boost efficiency, and with the indirect as a mass to determine the minimum burn time. The tankless also uses the buffer mass to determine a minimum burn time but will also modulate based on the actual return water temp (see http://www.raypak.com/module.htm for how modulation & duty cycles affect performance) to boost output for higher load conditions.

But without the smart boiler-purge controls, the tankless loses some post-burn heat to standby that would have been retrieved with a System 2000. A tankless being even lower mass than a steel boiler (it's basically a very tiny water-tube copper boiler) it's hard to say how much of a performance hit that really is. It's literally an order of magnitude lower mass than a cast-iron boiler, so the standby losses will be low (which is how they can perform better than 80% efficiency on hot-water heater EF tests.) The fact that the tankless will modulate up under high load (like when somebody is taking a shower when it's 10F outside and the system is calling for heat) may give it some advantages if the system is set up reasonably. If the flow rates, buffer temp and boiler output temps are set up to provide exactly the "design day" heat load for the heating system, it'll still be able to deliver higher burn rates for continuous domestic hot water loads as well (for low/moderate heat load houses.) The tankless also inherently low-temperature and thermal-shock tolerant where a steel boiler is less so, and needs special plumbing & design details to deal with water temps below 140F returning from radiation during fire.

Still the EK System 2000 does extremely well. Check out the seasonal and partial-load performance of #3 (almost certainly a System 2000), compared to several other combi-systems tested at the Brookhaven Nat'l Labs

http://www.nora-oilheat.org/site20/uploads/FullReportBrookhavenEfficiencyTest.pdf

Note how well is does even at 3-5% of full load (see the partial load curve on Appendix 3 page 3)- it can outperform even more sophisicated modulating/condensing boiler systems(!). By making the buffer mass the center of the heating system universe rather than a separate "priority zone" to be served with it's own burn as most indirect-fired tanks are configured, all thermostat calls are created equal as far as the burner is concerned (since it is agnostic of the thermostat calls, only serving the aquastat on the tank), and the minimum burn times can be designed-in, set by the hysteresis of the aquastat, the mass of the central buffer, and the flow/output temp on the boiler loop. According to other data most tankless heaters reach full thermal-efficiency in draws of 5 gallons or more, so bringing up even a 25 gallon buffer tank/indirect up 5-10F it will tend perform as well as in a hot water heater EF test provided the buffer is still a reasonably low temp (120-130F) and reasonable delta-Ts & flows on the tankless loop. A well-designed and configured version should be able to beat any cast-iron+ indirect setup, and may approach mod-con or Energy Kinetics System 2000 type annual performance.

There are alternatives to Ergomax as the DHW heat-exchanger/buffer:

http://www.thermo2000.com/pdf/en-US/specs/turbomax.pdf
http://www.thermo2000.com/pdf/en-US/manu/turbomax.pdf

http://www.tfi-everhot.com/pdfs/TFI_EAseries.pdf

For lower temp heating systems (water temps under 140F) it's probably better to get use a somewhat larger heat exchanger in the indirect, but also bump the output temp of the tankless to at least 15F higher than the aquastat temp to be able to deliver the full DHW load.


(steering the topic at least vaguely back on-thread...)

Creative designers will find ways of including solar inputs to such a system, but storage for solar heating systems will require more buffer than a 25-50 gallon tank, and will work with higher (solar) efficiency using purpose-built stratifying tanks etc. But as long as the primary heating system is based on hydronic boilers, boosting the real world in-system performance by 15-50% with buffering is worth the time spent designing it.

Craigsward,

Danal1 wrote
"He's using the solar radiant on an as-available basis as supplement to his existing hot-air system. Something like this may prove more cost-effective at reducing your fuel consumption than going to mod-con boiler-heated radiant and simply abandoning the hot air system. If you can, mount the panels vertically on the exising house & garage, not sloped latitude+15 on an outbuilding. In the New England snow zone you'll get better mid-winter & overall heating season performance utilizng snow-scattered light with them mounted vertically than the purely solar-geometry based theoretical latitude + 15 degree rule of thumb."

He is right. Using a reflector sized by taking a near vertical collector and runing a line south a 22.5° angle of reflectance from the TOP of the collector until it intersects a horizontal line projected south from the BOTTOM of the collector will increase performance of a flat plate collector by 40%.
Raysun
[email protected]

One point I would like to make is that you need multiple pex loops in your floor. If you do just one looong loop you accumulate too much friction resistance, and your fluid (propylene glycol/water probably) won't flow fast enough to have heat left at the far end of the loop.

A friend made this mistake and her floor isn't even warm at the end of the loop. This is why the vendors sell manifolds, so it's easy to have several short loops, and they all stay warm from start to finish.

JR