bebster, In a typical solar electric vs direct solar heat comparison the direct heat is only about 10 times as efficient at a much lowercost. Rich Californians making a GREEN statement aren't swayed by such comparisons.
[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]
"I'm not from your planet, monkey boy!"
Let the buyer beware indeed! Living here in northwestern Wisconsin one can really appreciate having a warm floor to habitate or perform compensated servitude upon! However neither my employer nor my homestead have such extravagance. I have however ordered a American Steel Span building for a hobby garage. I now know that I do not want the "sprayed on insulation". I do want radiant in-floor heat though,and everybody knows everything about them,especially salesmen! The building is to be a 30ft. by 50ft. with 8ft. sidewalls and 16ft. center height. The foundation is to be a concrete trough type. Since the foundation outer perimeter has to be installed first could the "inside" actual cement floor be insulated (isolated) from the outer perimeter? Wouldn`t this be beneficial to reduce heat loss? I will have a closed heating system with a electric hot water heater. I have never heard of a tankless hot water heater,would this be a viable option for my application?
Hunyuc. Not extravagant (look up the word) but possibly luxurious!
You need to do or have someone do for you some heat loss calcs. Input data include:
1. worst case outside temp when you'll use the shop,
2. desired inside temp,
3. Number, size, location, and performance specs of windows,
4. R-value of walls, ceiling, and floor insulation.
5. space dimensions
6. estimate of infiltration
This will determine the Btu requirement to achieve the desired inside temp with the worst case outside temp. This will likely be more than the electric hot water heater will provide and even if you could find a large enough electric water heater, you better have really low electric rates.
The thermal time constant is so loooong that you have to anticipate usage well in advance to get the slab warm. This is NOT the way most of us work. Heating the slab 24/7 is the practical approach, expensive but bractical. A hedge against 24/7 heating cost is to go for floor warming not complete space heating, i.e. heat the slab enough to make it comfortable to be on/near but not enough to supply all the heat required to maintain the Btu ballance. Supplement the slab heat with another heat source. I like radiant, I went with forced air to share duct cost with A/C and it was easier in my situation.
In your climate there should be lots of concrete guys with experience putting in insulated foundations and floors. You need insulation betseen the foundation and the dirt on the outside. I prefer at least R-11 insulaton under the slab here in south central Oklahoma, you'd do better with more. Design the footers, stem walls, and foundation such that you can put in the desired isulation prior to the pour. I think the DoE has design info on this if you draw a blank with local concrete guys. IF you go with a floating slab then yo can have a thermal break between the slab and foundation or stem wall.
The advantage of a tankless DHW heater is virtually no standby losses, i.e. the heat lost through the tank types tank insulation between firings. Since you need to heat a slab 24/7 the heater runs a lot so standby loss is not a real consideration. Besides, you wouldn't put the DHW heater outside in your climate so the standby losses just help heat the room (no heat is actually lost considering winter time.) You cold put the tank in a water heater closet vented to the inside during winter and the outside during summer, especialy if you plan on A/C. Go with the most cost effective solution which is likely the tank type. Surely you have room for the tank so space is not a driver.
I'd be shopping around for the most Btu for the buck before I decided on using an electric DHW tank. Places where electricity is very high often see heat pumps used to heat DHW. You can buy a water heater with a small heat pump mounted on it but I would be looking at a small geothermal installation, a water to water heat pump or a high SEER air to air heat pump with gas (natural or propane) backup for when outside temps go below about 40 F.
If you pay 3-4 cents per KWh then my system suggestions may not prove to be so wonderfully cost competitive.
In-floor hydronics doesn't care where the heat in the water came from just so you get some. You could burn hair trimings from a barber shop or corn cobs if it were practical.
If you don't like the 24/7 aspect of in-floor hydronic heat then consider insulating the slab but heating the ceiling. I have 3 rooms with in-ceiling hydronics. Works fine. A potential advantage is that the response time is much much faster so you don't have to heat the space 24-7. With a slab, even boiling water in the tubing won't heat the floor fast enough to allow you to only run the heat when you use the shop. The ceiling will respond much faster.
Hydronic heat in the ceiling could be the "OTHER" supplemental heat source to make up the short fall of the slab which is warmed for comfort but not hot enough to supply all the heat needed. A ceiling will heat and cool fast enouh to make "set back" strategies work whereas a slab will not. If you have or can get gas (propane or natural) then radiant ceiling heat is a good consideration. These heaters work very fast to make you comfortable and as they supply a high percentage of radiant heat as opposed to convective they mostly heat objets not the air.
[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]
"I'm not from your planet, monkey boy!"
The same thing only diferent. We built 4500 sq. ft. of home in northern MN. 2 years ago. It has a basement and main level. Somewhere between the two levels, we have a commercial greenhouse attached to the southern wall (like the ones you see attached to fast food places). There are french doors from the dining room to the greenhouse. The best I've done so far is to heat the house all day long when the outside temp was -27 with the wind howling. Of course no sun, no heat. We are still kinda new to all this, but learning. I started saving all our 1-gal and 1/2 gal jugs (with caps) and fill them with water and store them in the greenhouse. I also put all my bags of potting soil in there. After the sun goes down, these items still radiate a little heat. I'm getting the hang of things. The intention of the greenhouse was for planting, and my theory said I could heat my house with it too (it worked.) and to use it some day as a hot tub room. It is 11' x 26' with the South wall, East wall and roof all glass. I have to shade it in the summer though. The floor joists are on 12" centers to support anything I'll ever do. The 'other' heat source is a propane fired boiler, that heats water for; the concrete floors (basement and garage), domestic water and makes hot forced air. If I live long enough, I want to figure out how to preheat the water in the closed loop system, before it goes through the boiler, via the sun. That's another chapter.
Midlifew, Solar preheat works better when working at lower input temps like if you were preheating your cold water supply before passing it through a DHW tank to finish the job. Some of thos e thermos botle type vacuum bottles would probably get hot enough for your preheat needs. Have to do the math to see what the breakeven, if any, would be.
How do you shade yoiur green hoiuse in summer? My sis-in-law just had to have a sun room with all glass roof, this right after I put in a glass room with insulated roof. Hers of course looks much nicer until they had to put a tarp over it to keep the summer temps below 100+ and then the algae grew on the tarp and they got tired of rolling and unrolling it...
Both her husband, another engineer, and I tried to tell her it would seriously overheat to the point it would be unuseable but she went ahead with a versiion with opening skylights and ceiling fans. It still overheats so bad they had to just put a tarp over it.
Regarding your greenhouse floor. Since you mention joists it clearly is not a slab. This is one of the reasons it does such a good job heating in the daytime. Unfortunatley your floor doesn't have the heat storage capacity of a slab so the room will go cold pretty quickly when the fire in the sky gows away. You could check the load bearing capacity of the floor and put a layer of gypcrete on the floor and then tile over it or patern the crete and stain it. This would give you a little less heating in the day time but retain a lot more heat into the evening. How about some large aquaria to get you some thermal mass?
Without heating doesn't the room tent to freeze at night during extreme conditions? Curious what sort of visual transmittance, U factor, and E did yo get in your glass?
Sounds like it is a neat room as is and yoi will only improve it over time.
[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]
"I'm not from your planet, monkey boy!"
o.k. a little more detail. We have a split entry with attached garage. The basement has 9' ceilings. The greenhouse floor is about 2 1/2' lower than the main floor. There are double doors off the dining room entering the greenhouse. The greenhouse also has sliding doors on the West wall to the future deck and a man door on the East wall, which is also the garage wall. Got all that? The greenhouse floor has hot water tubing for aux. heat and 2 floor vents for forced air heat/a.c.
I cut pieces of f/b/f (foil/bubble wrap/foil) to fit each piece of insulated, low E, glased roof glass. As Spring turns to Summer, I cover more and more pieces of glass (on the inside) until I only have the vertical South wall open. I also have a thermostat on the ridge vent for when it gets too warm. The garage has 12' ceilings, and stays fairly cool so I can open the man door for additional ventilation. The garage also has a fully functional cupola with an air shaft from the garage ceiling that exits through the louvers in the cupola. We are coming up on our third Summer here, so we will do fine tuning as needed. Hope this helps sis. Also, a shade cloth, say 50, 60 or 70% would do much better than a tarp.
midlife, About the tarp. I can't argue with any feelings you may have with regard to looks. The tarp is butt ugly but even letting 20% of the light through would overheat their room in summer. If you haven't been to SOCAL in the summer more than a few miles from the beach you might not appreciate the situation. It was a BAD idea from the beginning. The room was added on out of wishful thinking, not proper engineering. A bandaid is a bandaid whether it is color coordinated, has stars and stripes, or has happy faces on it.
I get it as regards your layout. If it works for you then that is the main thing. I wouldn't get away with aluminized bubble wrap going up and down in a patch work. I would be required to put some pretty cloth on the inside of the bubble wrap or hang up a large solar shade to extend and retract as needed in stead. The fancy version would not perform one whit better than your solution but it would be required to keep peace in the family.
Out in the desert a lot of folks use solar shades to cover the windows in addition to whatever traditional window treatments are used. The ones my mom had at Sun City CA were made of solar bronze colored plastic with partial aluminization on the "outside" surface. There were also versions with only aluminization and clear plastic material. I don't know the % transmission of the particular ones my mom had but I'd guess they reflected at least 90% back out the window and passed less than half of what wasn't reflected due to the degree of shading in the plastic. You could look at the sun through the shade comfortably.
I have a fairly large dormer on the south side of my great room and knew while designing the room that I would need some light control for its windows. This dormer's south wall is essentially all windows (including the gable end) and I chose to not have one of those typical extended "V" shaped overhangs to shade it.
I designed an inverted window shade with a counter weighted roller (instead of a spring) that is raised and lowered like a sail by pulling or slacking a halyard that is lead around two turning blocks and down to a comfortable height for the operator where you cleat it off to hold the "sail" in the desired position. The counter weight rolls up around the tubular drum on which the sail furls. To keep the counter weight from being too ugly, I decided on weights like you see on grand father and cuckoo clocks.
The sail shape is a triangle atop a rectangle and it is hoisted by a gromet at the top of the triangle.
[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]
"I'm not from your planet, monkey boy!"
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