Using Heat from the Attic

Interesting idea. Where are you located? What kind of temperature diffrences do you get with diffrent outside temperatures.? If there are vents in the attic would you close them off for the winter. You can get booster fans to go in heating ducts. You would also need a good shut off door to stop heat escaping to the attic when you heat the shed.

Keep us informed on how it works out it could be a good idea to use in the garage to take the chill off the air in the winter.

Haven't taken time to collect good data yet but I've observed differences between attic temp and outside temp of 4-10 degrees C. I'm in eastern Canada. I installed a ridge vent in the attic so closing that off would be a problem for sure. I have perforated plastic soffit vents (I believe 5 on each side) that are about 4 x 14 inches. Right now (10 am) the outside temp is -5, the inside shed temp is -1 and the attic temp is -7. It's overcast and snowing with light wind. I haven't turned heat on in the shed for more than a week. Clearly I would want the duct shut tight with these conditions. Before installing the thermometers I checked all three and they were pretty well dead-on (with respect to each other).

Ya just don't meet many people who instrument their shed - god love you!

Taking the heat from the underside of the roof and blowing it back to the floor is commonplace in many supermarket buildings in the UK as an economic way of providing space heating to the floor area without adding a lot of new heat. It's only fans and ducts, after all, and a timeswitch or an occupancy switch to run the fan might be all that is required to heat this particular insulated shed. A simple £5GBP thermostat would be all that is required to turn the fan off.

However, consideration of the proposed arrangement begs a different question: is the ceiling between the house/whatever and the attic aequately insulated? Most attics (known as "lofts" in the UK) are thermally isolated from the rest of the house by a healthy layer of insulating material (typically 200-300mm of Rockwool in new homes, for example) and in themselves run cool. If there is heat in the attick, it might indicate that the ceiling insulation is not all that it could be, and an economic evaluation to enhance it might be a worthwhile exercise, perhaps? Check also the levels of through ventilation in the attic, lest the warm air might carry water vapour that condenses into droplets on cold nights, enhancing the deterioration of the attic structure and fittings (noted that building construction regulations vary across all parts of the world).

Great thinking about energy integration, BTW!

I constructed the building following what is pretty well common practice in Canada. The walls, starting from outside: vinyl siding, Tyvek house wrap, 1/2 inch exterior plywood, 2 x 6 studding, 6 inches of fiberglass insulation between studs (R20), 6 mil plastic vapour barrier, and, 1/2 inch exterior plywood (instead of drywall). No holes in the wall for electrical outlets - I plan to use surface mounted electrical parts. The floor starting from the earth: 4 x 4 pressure treated skids set in a shallow gravel bed, a pressure treated base consisting of 2 x 6 p.t. joists on 24 in centers, 3/4 inch p.t. plywood subfloor, 1 inch rigid foam insulation (the pink type), 1/2 inch exterior plywood. The ceiling from the inside: 1/2 inch exterior plywood, 6 mil vapour barrier, 2 x 6 rafters with R20 fiber glass between rafters, another layer of R20 on top of that, for a total of R40, and above that a standard gable roof with asphalt shingles. I used plywood for the inside so that i don't have to be concerned about mounting stuff to the walls/ceiling. The plywood also gives a nice "shed" look.

Should have said: 2 x 6 ceiling joists (not rafters) with R20...

GA! I agree completely.

Finally something I do know!

It seems this shed is very well insulated so the excess heat in the attic has to be solar gain and not heat loss from the occupied area.

An attic should remain as close to outside ambient temperatures as possible. Dark colored roofing requires more ventilation than lighter colors. If there is a temperature variation, the attic should be ventilated better by natural convection if at all possible. Some roof designs require powered ventilators connected to thermostats and humidistats.

Heat recovery should be in the form of a dedicated solar collector which can be used in the colder seasons and removed from service when not needed. Hot water or hot air are a lot more economical to construct than Photovoltaic. Hot water transfered heat is easier to collect on the roof and pipe down into the building than hot air but is a little more expensive. Hot air collectors work fine if you can mount them equal to or lower than the space to be heated. In either case, keep the Coons out.

Short answers: Work on heat sensitive solar panels is progressing using nanotech. Not there quite yet. You wouldn't get any gain if it was raining.

Temperature differential controls are available from solar supply houses.

My similar system uses an attic fan switch set for 80f, and a 4", 305cfm, 12vdc marine bilge blower that runs off battery/photovoltaics, ducted to a thermal mass. A cloths dryer vent works for a non return check. Works better than expected !

Attic ventilation fans are common products in the US. They usually come with a simple built in thermostat that turns them on when temperature rises to a resetable level and off when it falls. Put a duct, maybe 10-12 inch diameter from the attic fan to the shed. A second similar fan near the ceiling of the shed will control the temperature in the shed and a manual damper bypass will allow you to redirect the hot air away from the workshop when the seasons change. In the coldest weather you will probably want to cover the opening of the fan in the shop. A simple sliding cover with an actuating rod you can reach from below should work fine.

Ed Weldon

On further thought ........ If the run of ductwork to the shed is long you may need a squirrel cage blower instead of an ordinary fan to get enough air flow through the duct. Add a simple thermostat and a relay to handle the current of the fan and that should work.

Ed Weldon

Nice idea! I would suggest to insert a dust filter in the intake of the duct system to prevent collection of dust and other contaminants there.

As an option you might also condsider to reverse the air flow so that you could draw colder air from the ground to the ceiling for better temperature control in the summer.

Also you might consider to use a kind of latent heat storage (e.g. phase changing material) and insert it into the ducting system (maybe, a kind of by-pass system?). So you could "store surplus" latent heat during daytime and release it during evening / night time to smothen temperature variations. Of course, this principle could also be used for cooling, if appropriate.

Ther are some paraffin materials which have melting points which make them useful for latent heat storage. As a "low-cost-DIY" solution, I would think about filling them into a heat exchanger (for a first try an old radiator from a hydronic heating system should do) and route the air through it.

Just some results of my personal brainstorming, perhaps the other contributers would like to work this out into a little more detail!

good luck!

nudnik

Paraffin phase change packages up over head? How much heat would you get considering that heat will rise away from your living area, and more importantyly, how would you make them conform to fire code? I don't know that I like the idea of a living under a napalm bomb.

I dod not speak about putting the paraffin (or other phase changing materials) over your head. rather I suggested to put it into a heat exchanger and then route the air stream through the heat exchanger! By the way, here in Europe pretty much research work is being done on phase changing material and there are several techniques under investigation, including the incorporation of small paraffin holding spheres into plaster. So you will definetely not create a "napalm bomb". By the way: Does the National Fire Code say anything about use of candles?

nudnik

Nudnik, I like the suggestion about using a dust filter... don't want fiberglass particles drawn from the attic and blown around the "living" area of the shed. Thanks, Bob

Good day,

I live in quite a sunny country (semi-arid) where in our short winter of about three months it gets nice and cold. Sunshine though the day heats the air in the roof creating a 10ºc difference between there and indoors. I put a duct inside the gable and down to the passage, introduced 4 old 12v computer cooling fans switched by a cheap thermostat and powered by a small solar panel on the roof. I can now walk around in winter wihtout a shirt in the house.

regards,

Leon

The most inexpensive way would be to do it manually. Its warm up here and cold down there so I'll turn on a fan and circulate the air.

Otherwise you need some sort of microprocessor (PLC) which has a range of parameters between two temp sensors (maybe three along with inside and outside humidity sensors). Alright so now its getting more and more expensive, but what the heck it is kind a fun.

You might try to search for Home Automation sites on the web. There are several sites that sell some-such.

The greatest savings is likely bringing in outside air when the outside temperature is higher than the temperature in the shop. This is often the case in the morning when the shop is cold and the insulation is keeping it colder than the ambient temperature.

A forced air duct with an insulated damper to bring in outside air or close once the shop's temperature exceeded the ambient temperature would be simple and cost effective. A second damper would have to be connected to a second vent since you can't have flow without an in and an out. A/C Dampers and controls from the autowreckers would make a cheap test project.

I would suggest that if you see the oportunity to include your electric heater in the plan, don't fasten ducting to a conventional heater. It is likely not approved for it and if you void UL/CSA certification and create a fire hazard, your insurance may not cover any loses.

As for the attic one could scavenge the heat from it by creating a heat exchanger but the costs would likely outweigh the savings. A second option would use the attic space as a transition from the outside when bringing resh air in. The extra Btu's in the attic may be short lived and the risk of bringing in moisture laden air would likely result in frost problems. Like mentioned in post#5.

At 11:30 am today with sun and a wind speed of about 40 km/h the outside temp was -3.6 c with RH 37%, inside was -3.0 with RH 77% and attic -0.2 (don't have RH sensor in the attic. I believe that during the winter (maybe all seasons?) the ideal attic temp should equal the outside temp. I think those conditions will reduce or eliminate condensation. So any control system would have to take in consideration all three temps to make an attic heat system worth while. I would like to have the system automatic. I have observed inside temp lower than the temp as you indicated. And as someone else mentioned I will probably have to get into into some sort of microprocessor system to get this to be most effective. And, yes, I want this all combined with my electric heater (that will most like be a parabolic radiant heater that I have on hand). Now if I was into microprocessors I would be on my way - maybe.

Ferget microprossers, expensive attic fans, and complicated ducting. All the stuff I mentioned earlier is cheap, off the shelf, $130.00 total. The last time I bought a temp. differential switch it was a mere $40, microprocesser included. Though that was a while back. Thumb through Solar Age mag., West Marine catalog, then hit your building supplier. Take you half a day max.

Get a wired thermostatic switch. Set it in the attic and use it to turn your fan on when it gets warm enough in the attic. If you buy it on line probably 5 to 10 bucks. If you have to replace it after 4 to 5 years, thats OK. Or you can over-engineer the hell out of it, make it satellite controlled from some remote atmospheric monitoring station and turn it into a nightmare. It's a shed and you are trying to save a couple of bucks on the heating costs. It is important not to forget that.

Well I have to say it's not really about saving money re heating the shed. The shed started out as an ordinary shed but as I got more into it I decided to do a pretty good job in terms of minimizing air leaks, insulating to recommended standards, etc. So I am must interested in how the building will perform with regards to heating and cooling. As I mentioned earlier I will surface mount the electrical fixtures to further minimize the possibility of air leaks. I will be doing a minimally involved analyses as time goes on... but this is just at the hobby level. I eventually want to tie a home made wind turbine into the shed. My login name (vgsdvawt) stands for Variable Geometry Vertical Axis Wind Turbine

One other thought about heating the shed. Do you have a decent southern exposure of one of the shed walls where you could locate a "lean to" greenhouse? With the right interconnections the shed and the greenhouse could act to each moderate the temperature of the other at appropriate times with some automated shutter controls. Use of your wind turbine to supply power to charge a battery for electronic control would be a neat adjunct and could prove the value of your system for locations away from reliable connections to the power grid.

BTW are you ready to share any details of your wind turbine design with the rest of us? I have an interesting possible application unrelated to comments above that I'd be willing to share for no obligation on your part.

Ed Weldon

Ed, The long axis of the shed is aligned roughly se-nw. Two house-type steel doors with about 75% glass each; one on the south end and one on the east end. Two small windows; one on the east and one (smallest) on the north end. I think I'm getting a reasonably good solar gain from this glass, but it could be better and your idea re lean-to greenhouse might be possible. The variable geometry savonius darrieus vawt is a machine that I experimented with back in 1981. I just dug up an old, but very poor, photo of the turbine and it is now my avatar for CR4. Here's a quote from a report at the time: "The buckets are connected to the straight Darrieus blades in a manner that cause the buckets and blades to change geometry under the influence of centrifugal forces. The peak aerodynamic operating efficiency is achieved when the buckets reach a cylindrical configuration. The cylindrical configuration is a quasi-stable mode that is maintained over a range of operating speeds. Overspeed control is obtained by the buckets toggling to the extreme high-drag configuration."

I Googled "savonius darrieus" and came up with quite a few interesting and informative links. Now I see what it is all about. I can understand your interest in the technology. The failure of that technology to win out in the race to build wind farms has likely dropped it into a corner of mechanical curiosities not to be taken seriously anymore. But for the creative inventive mind? A motherload.

Ed Weldon

A "Motherload" sounds terrible....

You probably meant to write "mother lode"......

My online Dictionary at http://www.thefreedictionary.com/Mother+lode gave out:-

mother lode

n.1. The main vein of ore in a region.2. An abundant or rich source: "the kind . . . who makes Boston the mother lode of advance men" David Nyhan.

I hope this helps you with your spelling!!

I still enjoyed your post, though that word would pass better when one looks in the Toilet before using the handle I feel!!

What we old computer engineers called a "Core dump" about 40 yeras ago!!!

Your attic is the highest point. It will have the lightest (and hence the hottest) part of the air as also the most CO₂ rich portion ? which you want to push back into circulation ?