Solar heat for garage slab

hot_rod

without storage is one of the methods used by cedar Mountain. check out their article in the Nov. dec. PHCNews.

Bob Ramlow also proposes tube in a 12" sand bed storage below slabs for homes. Temperature control may be an issue in the fall when the slab is warm and no sizeable heating load. Opening windows is the method he prefers to control the temperature. That may work for a shop, but not an idael comfort system for most homeowners.

hr

Greg_35

Solar heat for garage slab

I am looking for some feedback on a radiant slab fed by solar thermal panels.
The job is a 1200 sq.ft. garage/storage/workshop, well insulated with R19 walls, R-40 ceiling, 2"-rigid insulated concrete 4" slab). There are 1200 ft of 3/4 he-pex in the slab and there will be total daily solar ratings of 80KBTU (max). Excellent, unobstructed solar-south exposure, and near vertical mount that will do very well for winter and late fall/early spring. Design temp is -20deg F.
The owner is not concerned about an even heat, just to get some btus from the sun. There is a wood stove for when more heat is needed.

The aspect we are discussing is whether to use a storage tank or not. We will probably use PV powered DC circs.

I'd appreciate any thoughts you might share from your experience, or directions to specific resources, on similar design strategies.

Thanks, Greg

Mark Custis

Solar Radiant

Sounds to me you have done your home work. We have yet to design and install a system like you describe, but I am sure if I keep asking folks about them someone will say yes.

How about a small wood fired boiler?

We have a geothermal radiant system here in northern Ohio. The building is about 2200 Square feet with 7 300' x 1/2" loops off a manifold. We used a water to water heat pump connected to 5 300' x 5/8" slinky loops sunk in the pond.

We poured about a five inch slab and it acts as storage. Winter in Cleveland has been cold early this year and the customer, who I talked to yesterday says with the thermostat set at 62* he washed and changed the oil in his truck in a tee shirt.

We added glycol to both sides of the heat pump so the building can be shut down without damage. We could easily add some solar, if we can "hide" the collectors, the customers wife thinks they are ugly. My wife thinks collectors will soon become a fashion statement.

I envy your project, good luck.

Greg_35

I should clarify that the wood stove is not providing heat to the radiant loops, just heating the space directly when needed.

Greg

Greg_35

Thanks for the response Mark. We aren't considering an additional, or back-up heat source for the slab radiant. Just trying to weigh the pros and cons of storage tank or not.

Yes, we will be seeing a lot more panels - both thermal and PV. They are being integrated directly into new structure designs. And well planned retrofits can look quite nice, though site, orientation, style of existing, pre-solar, homes often present difficult esthetic 9and mechanical) install challenges.

Best wishes for your projects.

Greg

hot_rod

where are you located?

use data available online or one of the solar design software programs to get "in the ballpark'

RET Screen is a free downloadable solar design program. FChart and Valentin all have demo version available

Here is an example of one 4X6.5 panel in Milwaukee. Remember the output is per day, not per hour. So determine the load and add up how many panels it would take to cover that.

hr

Mark Custis

Hot Rod makes a good point

and he has more hands on than I do. You may want to add a pool or spa to "dump" extra heat in the summer. Callffi's #3 Idronic's is an excellant primmer.

Retscreen, is very good too, (thanks Hot Rod, I will miss you on a monthly basis, and I get the scheduling issue of a small business) we are working our way through it. It is very powerful.

Why no back up to the slab? Too bad it is poured, you could have used it as your storage.

Better antifreeze the floor as well as the collector system. I do not worry too much about glycol, as I tend to read the directions on the container and buy the test strips.

Send us a picture if you can.

Mike Dunn

solar storage

I would suggest you utilize storage for a strictly space heating application. 2 gallons of storage for every square foot of panel. I don't know how many panels you have but let's say you install 3 120 gallon storage tanks and you can get these tanks up to 150 degrees. You have usable store down to at least 90 degrees. That's a difference of 60 degrees * 360(gallons) * 8.33(lbs per gallon) or approximately 180,000 btu's. If your heat loss is around 30K at design this gives you approximately 6 hours of heat with no supplement.

Mike

Larry Weingarten

Greg

The only thing I see about your design that could be a concern is overheating in summer. Even with vertical collectors, summer sun could make for an overly toasty garage. If it never gets so hot in summer, you probably don't need to worry about it. A possible solution to overheating might be to make some sort of venetian blind (fixed or movable) to shade the collectors from high sun.

I like the simplicity of the design ;~)

Yours, Larry

Greg_35

circulator specs.

Thanks Mark, HR and Larry for your comments and suggestions. We are in VT. I do have RET screen and have been familiarizing myself with its considerable contents.

We are at the stage of specifying the circulators for the system. We are planning on using PV powered circs. To get sufficient head of 18+ ft, since the circuit includes 300 ft 3/4" pex and ~60 ft of supply/return piping and panel resistance as well as a 50/50 glycol mix, we are considering two pumps in parrallel. Any special issue I need to consider here and more basically, will I actually get twice as much flow by doubling similar circs.

Thanks to all for your time and thoughts. I'll post pictures after next time at the job site.

Greg

Mark Custis

Check the web sites

of the pump manufaturers. You can only move so much water through a pipe. You only want to pump what you need the rest of the capacity is wasted.

I know Wilo makes a PV powered pump. You might take a look at the pump curves for that unit and compair it to your system.

hot_rod

Laing D5 strong

has a pretty good pump for solar. It available in the single and dual pump stations from Caleffi, I hear.

hr

Bob Gagnon plumbing and heating

Solar Collectors as a Fashion Statement

Mark, your wife is REALLY COOL! Thanks, Bob Gagnon

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Bob Gagnon plumbing and heating

I wonder if a slab is the best application

for solar? I know the it works with the lowest temperature water for radiant heating, and I think it will work great in the fall, but I'm worried that in the winter the limited amount of BTU'S for only 6 or 8 hours a day may just get absorbed onto the ground. Remember with a boiler you send heat down into that slab 24 hours a day to charge it up, sending 75 or 80 degree water for 6 or 8 hours a day, might be barely noticable, I would also run a radiant panel on an inside wall or ceiling with aluminum plates, then all those limited amount of BTU'S in the winter will be within the heated envelope.

Thanks, Bob Gagnon

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Mark Eatherton

Garage solar story...

I had a student who attended one of my early RPA studies who lives just south of Denver. He asked me to come see his "project". He had retrofitted his whole house with RFH. He had also built a new garage. It was an oversized 21/2 car garage, about 30 feet wide, and long enough for a car, plus some extra. His walls had similar R value and his slab was thicker in the middle (12" if my memory serves me correctly) and 6" on the edge with 1/2" PEX @ 12" O.C.. He also had the northern exposure of the garage (garage door side) tubed outside of the garage for snowmelt, for the length of a car and the width of the garage in front of the garage door..

He had 7 each 4 X 10 collectors ground mounted, lean to style on the southern exposure of the garage at approximately a 55 degree angle. Control was quite simple. If the collectors were more than 70 degrees F, he started his circulator and moved glycol between the 6 gallon electric water heater/expansion tank on the floor of his garage and the slab. Once the garage was up to temp (70 degree F setting) any residual energy was diverted to his snowmelt system via a diverting 3 way valve. There was no aux. system in his garage. He was raising red earth worms in his garage. He said if the garage dropped below 45 degrees F, all of his worms would die. The system had been running for 2 years, and he'd not lost a worm, and he'd never had to shovel snow off the north side of his garage.

I was impressed.

ME

Greg_35

Are you saying

Hi HR,

that the Caleffi dual station 255 seriesuses a Laing D5? Or that they have an option to use a WILO DC circ? My Caleffi idronics 3 catalog shows the station uses a WILO Star S-16U15 AC circ.

Also, where can I get information on how much additional head resistance is applied with an increase in glycol percentage of the HTF. For example, Laing's head figures are good up to a 20% glycol mix, but give no specs or formula for increasing it to 50% glycol (our target)?

Thanks again for your time and insights.

Greg

Greg_35

We were considering

having some wall mounted fin-tube on the supply from the panels before the manifold to the radiant. Of course, a radiant panel would be much more effective in that case.

As to the heat in deeper winter just being absorbed into the ground through downward heat-loss (even with the well-insulated slab?) we figure that would be just that much less load on the supplemental wood stove heater, wouldn't it

As I mentioned before, the owner wants to just bring as many BTU's into the garage slab as available in the fall, winter and spring. And as long as we can do that in as simple and effective manner as possible then the project parameters will be met.

Thanks so much for taking the time to think this through with me.

Greg

hot_rod

An option

is the Laing D5 strong, also a Star 21 for a bit more head. I've not seen the Wilo DC, although I have questioned Wilo NA and Germany about it?

hr

Mark Custis

Saw the Wilo

here in Cleveland at the 2007 solar show.

Maybe they went back to the drawing solar board.

Greg_35

Thanks for that story

Mark,

I really appreciated your story of a good design and its good results.

Thanks,

Greg Durgin

Wayco Wayne_2

Sorry I didnt read all the responses. MY ADD is acting up. :Z

but in response to the original inquiry, my first response is no storage tank. Use it or lose it. The slab will act as a storage anyways. Use flat plates and a drainback system so you can use more panels and drain back when no heat is needed in the Summer and provide protection from freeze up during power outages. KISS method rules. WW

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