Put house in the shade for the summer

[valterra]

Now that we're going to start heating up, I'm already dreading the large utility bills for my AC in the summer time.

I've looked on the board for "solar cooling," hoping there was some way to use the sun to cool the house.  Spraying the roof with water seems like a good idea.  Nebraska can be VERY humid during the summer, so I don't think an evaporative cooler would work so well.

Keeping solar energy off of the house seems to be the best thing.  If the sun is beaming energy in the order of Megawatts, it seems silly to try to cool it using the smallest number of kilowatts.  Better to avoid the sun altogether, in my way of thinking.

So I got to thinking that I could put some kind of mounts on my roof, and then simply extend a tarp of some kind that would sit a few inches above the roof.  Then I don't have to try building (or planting) something large adjacent to the house that would block the sun in the winter time.

Crazy?  I see these guys want to sell a 14 x 20 foot thermal blanket for $249.

We've been considering making a solar-powered attic fan.  But this kind of solution would keep (some of) the solar energy off the house in the first place.  I realize that the area immediately around the tarp would be hot.  But that's a hot spot several inches ABOVE the roof, instead of the roof itself.

I was thinking that with some spiked mounts and some use of elastic and eyelets, you could make something that could be easily put up in the summer and taken down in the winter.

Anyone done this?  

[Stonebrain]

How long will this stuff survive in sun and rain and wind.

If it regularly flies to pieces,You'll ffind this nice stuff all over in the trees,and on the plastic-ilands that are growing in the oceans.

A good isolation of the roof might be more cost effectif and more effectif in general without all the hussle to put it up and down

cheers,

Jaap

[etownlax]

In the United Arab Emirates there is this Ski resort that is indoors. Outside temperatures can easily reach 100 F. Their best form of insulation is acutally air. It was on TV(think it was the Travel channel maybe Discovery) that they showed around the place. Then they showed how they kept it best insulated, and that was a gap of air between the inside and the outside of the resort. Air is a VERY good insulator. Air does not transport heat very well. However the way this works best is if that air doesn't get replaced by the hot air on the outside. Think of it this way. A cooler is a good insulator. If you put steak in it with ice, it should last a good while. Now if you Allow the Cooler to "Change"(like allowing the air to move bringing hot air in and removing cool air) By replacing it with a cooler that has been heated inside and out, it really totally defeats the purpose and makes the steak go bad quicker. Thats prety much what your attic is alreay for.

So sure the sun isn't helping but, if you were to "enclose" an additional part even beyond your attic and roof. That would help a whole lot more, But it would cost a GREAT deal. Also if you just used a reflective "paint"(if thats even legal) that would shield a good amount of sun too.

Just some thought to ponder. I figure more ideas the better, cause it couldn't hurt.

-Randy

[richhagen]

I believe that most common types of insulation actually work by trapping air spaces so there is little or no convection, then the trapped air conducts poorly and radiates poorly, so less heat is lost.  Rich

[valterra]

So in the case of my house (regular split-level), I can use your ideas like this:

• better insulation in the attic to seal in the living space of the house.  That living space would be like the cooler you mentioned.
  
• an attic fan that would remove stale, hot air from the attic area, so the air adjacent to the "cooler" isn't  burining hot?
  
• or are we saying that actually trapping the air in the attic would be better because it can't exchange?  that doesn't sound right for some reason.  I always thought attics were like ovens, trapping hot air.
  

[richhagen]

I would say that adding insulation between the attic space and the living space would be very worthwhile thing, especially in winter where escaping heat rises.  

Ventilating the attic is a good thing because of the heat gained by the air in this space by the sun light baking the roof above.  If the temperature in the attic is higher than the ambient outdoor temperature then ventilating it would be beneficial.  Heat is transferred by convection, conduction or radiation.  Things that aid in heat transfer away from the living space, or minimize heat transfer into it will be good things in general.  Most convection, the movement of material is hot air moving upward, not down from the attic to the house unless pressure differences occur (why top opening freezers tend to be more efficient).  Conduction is a function of the cube of the temperature difference if I recall correctly, so minimizing this would be beneficial, which means that cooling a hot attic would be to some extent beneficial in this regard, and keeping surfaces cooler means that they will radiate less energy as well.  

Having a light colored roof which reflects more of the light striking it would also help - or just build a shade of solar panels above it :-)  Rich

[ghurd]

I can't imagine why a CmeBrew style fan used as an attic fan wouldn't save more than it cost to make in a warm region in a year or 2.

This is a 20" box fan blade on a $20 treadmill motor, run straight from a 17W or 32W solar panel, no battery.  I know it's a huge difference, but I don't remember.

G-

[valterra]

Is this the "1000% percent more efficient" something fan that I've seen on here?  I thought that was interesting when I saw it.

You know - my parents' treadmill just died, and craigslist seems to be "treadmill-heavy" right now.

[TheCasualTraveler]

The 2 ideas I like best and am doing on my Florida home, like ghurd said,

DC ventilating fans run by a solar panel and battery. I just added a ridge vent along the peak of my roof and this summer I will tear open the gables and build two large vents with DC fans that run slow and quiet. Thermostat controlled and much larger than the tiny all in one solar vents you can buy. On the cool shady side of the house the fan will draw air in and the other end will exhaust.

White roof. I just reshingled my roof with white shingles. They are supposed to reflect about 35% of the light. I am looking into elastomeric roof coatings that can reflect up to 85% of the light. The paint is for resurfacing older roofs but I plan to do it to my new roof. It's very simple and it works. In the sunbelt, white is the new green for roofs.

Other things I have done,

Sycamore trees to shade the house, they grow fast, have big leaves and lose their leaves for the winter after the heat is gone.

Insulation and caulk to keep conditioned air in.

Solar film on the windows. This reflects light but what I didn't know was the glass absorbs a LOT of heat due to the film. On a hot day you can touch the glass and it is HOT. So...

I added awnings above the windows for 2 reasons. It keeps the rain away so I can leave windows open more and it also keeps the sun off the glass. These awnings I made myself and it was a really simple and strong design, and cheap. I can do a tutorial if anyone is interested.

Another good idea is to replace window screens with solar (sun blocking) screens that cover the whole window, not just the part that opens.

Last, I plan to experiment with spraying water on the roof. Also, you can now get tiny little misting nozzels in the irrigation dept at home depot. These are often used to cool the air in outdoor restaurants and cafe's and are really neat.

Personally I would not try the tarp or thermal blanket idea. To sum up, a light reflective roof with good ventilation underneath is the way to go.

[vawtman]

Hi Valterra

 A little more info on the structure would be helpfull.

 Insulated glass windows?

 Wall thickness and is a barrier on the inside?

 Insulation depth in the attic and is a vapor barrior separating the two airmasses?

 Full basement?

 Vented soffits with ridge vents?

 If you have cooling problems during the summer you likely have heating issues also.

 I'm studying to be a Home Inspector when i retire.Passed the internet test so far LOL

 Mark :v)

[spinningmagnets]

A "whole house fan" is about $280 from Home Despot, and it is located in the ceiling near the center of the house. It can be run from a thermostat, or bypassed with an on/off. It pulls cooler ambient air from inside the house up into the attic (gravity closing vent slats when off) and the ambient temp air flows evenly out the vents around the perimeter of the attic, taking with it the accumulated attic heat. Obviously, DON'T run this when the AC is on, but it can cut down on the hours the AC is run.

What I actually tried is, I installed a small $70 thermostat-run attic fan that pulled air from inside the attic out the vent screen at one end of the attic. It used the amount of electricity that an incandescent bulb would use, and cut my AC bill from $160 to $80 (in the summer). I installed it with a switch so I could de-power it 7 months a year.

Once, while I was in the attic, I learned a little about fluid air flow characteristics. The fan was on one end of the attic, and it drew air in from the soffet vents located around the entire edge of the attic, so only half the attic air was cool. By sheer dumb luck it was the half over the house, and not over the garage. If I had stayed, I would've added a second fan on the other end.

These attic evacuation fans can be run while the AC is running inside the house, thats why I chose it first instead of the whole house fan (which I may have added later).

Any windows that get hot, shade them on the outside (instead of just blinds or shutters inside). I honestly feel I got a good result for about 5 months a year by stapling loose weave cloth onto the eaves of the entire south wall, it hung down 3/4ths to the ground, and shaded the wall and windows. The cloth was stored in the garage the other 7 months.

For a cabin, I have considerd adding a second roof attached one foot above the common roof. It would put the entire house in the shade, and an exit slot on the ridge would allow rising hot air to flow up. A patio shading the east, south, and west sides would keep all the walls and windows cool. Just some ideas...

[valterra]

I'm encouraged by your report that you cut that heating bill way down by using the attic fan!

I was going to make sure that the incoming air would be from a single source on the opposite side of the attic.

[scottsAI]

Hello valterra,

As you noticed there are many things you can do. Some more cost effective than others.

Check out the options, consider your situation and skills to determine what works for you.

Many good suggestions already made so will not repeat many of them.

Vent the attic with sufficient air, the goal is to keep as close to outside temp as possible.

Even with good venting the HOT roof radiates heat down to the house.

Reflective radiant films above the insulation is more or as effective as a second roof with ventilation.

Wind induced ventilation can do a great job without requiring power, even with low winds.

A cool attic is more cost effective then more insulation.

Whole house fans are effective only if the evening air temperature drops low enough to make use of it.

If the evening air temperature is low enough then store the "cool" in a thermo mass, maybe eliminating AC run time.

Fans

Fan power is a cubic function, twice the air flow 8 times the power. Air foil shaped blades improve air flow 26% or more, in cubic functions this is half the power. Ceiling fans, air blowers, while house fans use less power with air foil blades. Slow moving air for a long time will use less total power than a high speed fan running for a short time.

Ground Water cooling, if your ground source water is below 60 deg then use it to cool house not AC. Discharge water can be used for watering the lawn or to fill a pond.

ICE block cooling, freeze a large block of ICE in the winter, use to cool Fridge and AC for house.

My home in MI needs 15 foot cube of ICE. Bury it in the ground.

Keep sun off AC condenser.

Keep sun out of home.

Consider pure water misting on AC condenser.

Desiccant to reduce humidity, assuming 60% humidity half the energy to cool is the latent heat of condensing the humidity out. Use AC condenser heat to dry desiccant.

Ground source heat pump.

As mentioned www.builditsolar.com has many inexpensive cooling ideas.

Have fun,

Scott.