solar shed is too hot, recommend efficient attic fan??

BenA

I put the solar control system in a tiny, uninsulated metal building ... the kind you see for sale at the big box home improvement stores.  Temps were getting in the 90's and I installed a box fan in one window (blowing out) and opened the other window for air intake.  Even so, temps in the building were recording up to 110 degrees F.  Definitely bad news territory.

I went in and insulated the south wall (R13), west wall (R13) and ceiling (R19).  North wall and east wall are sheltered and don't receive direct sun.  Now, with the forced box-fan ventilation, internal building temps are pretty much equal to ambient temps.  The negatives are that I have to open the windows in the morning and set the box fan in place and reverse the process at night. 

Long story short, got to thinking about an thermostatically-controlled attic vent for exhaust and a return-air floor grate for air intake (animal/insect proofed).  I found one efficient attic gable fan that claims it draws 30 watts AC for around $300 (QuietCool AFG ES-1500).  Found another attic gable fan that comes with it's own solar panel and this one looks pretty interesting for about $400 (Natural Light Energy Systems 36W).  Anyone had any experience with these two gable fans?  Are there others that are better?

Sure could use your input.

oil pan 4

Just stick a high quality ball bearing turbine on the roof and cut a hole down low to let air in, have convection do all the work.

Johann

You can also paint the outside walls and roof white to reflect the sun-rays.
A computer fan would most likely move more air than the $ 400 solar powered fan would.
Maybe use oil pan 4 idea and when the temperatures are still rising then have a thermostat turn on the computer fan. Or get a small solar panel and hook your computer fan up to that and every time when the sun is shining the fan will come on.

BenA

oil pan 4 said:

Just stick a high quality ball bearing turbine on the roof and cut a hole down low to let air in, have convection do all the work.

I sure like the energy cost of passive cooling.  Have you tried this approach or seen this approach used? 

Vic

BenA said:

oil pan 4 said:

Just stick a high quality ball bearing turbine on the roof and cut a hole down low to let air in, have convection do all the work.

I sure like the energy cost of passive cooling.  Have you tried this approach or seen this approach used? 

This Natural Convection cooling is quite common for Passively cooling attics,  and commercial metal buildings,  etc.
Works well.    Vic

BB.

Roof turbine vents don't do any more than just a covered opening in the roof.

Solar powered roof fans do not move much air (one poster here years ago found a couple of solar fans had failed, and the attic was still as cool as when the fans where running--Additional venting was enough to keep the place cool(er).

-Bill

oil pan 4

BenA said:

oil pan 4 said:

Just stick a high quality ball bearing turbine on the roof and cut a hole down low to let air in, have convection do all the work.

I sure like the energy cost of passive cooling.  Have you tried this approach or seen this approach used? 

Yes houses all around the country use this to cool the attic space. It can cool the attic space 30 to 50'F.

BenA

Johann said:

You can also paint the outside walls and roof white to reflect the sun-rays.
A computer fan would most likely move more air than the $ 400 solar powered fan would.
Maybe use oil pan 4 idea and when the temperatures are still rising then have a thermostat turn on the computer fan. Or get a small solar panel and hook your computer fan up to that and every time when the sun is shining the fan will come on.

The walls of the solar shed are white sheet metal.  The roof is a "mill" finish silver (like galvalume). 

After insulation, I'm guessing the only coating that would help would be some kind of ceramic coating.  In central Florida, they built houses out of forty foot shipping containers ..... and sprayed these containers with an expensive ceramic coating that repelled just about all radiant energy.  This was very expensive stuff a few years back, I wonder what it costs today?

A computer fan might just be the ticket as part of the solution.

littleharbor2

I put a dual 12 volt fan in my garage consisting of 2 inexpensive 12 volt, 80 watt volt automotive radiator fans hard wired  to a 12 volt 65 watt solar panel. Moves a lot of air when you need it most. These have been running every day, for 18 months now in the Baja heat and haven't skipped a beat.

MarkC

My solar equipment is in a 24x14 metal building (along with farm implements).  I covered the ceiling (sort of an "attic" space the way the ceiling supports are constructed) - and all walls with sun exposure with 1/2" Styrofoam with the reflective side toward the ceiling/walls.  The inside temps have dropped dramatically - stay close to ambient.  As I have a screened window on one end and a smaller screened window at the top of the opposite end (see my avatar), I get some natural ventilation.  I plan on adding a "gravity flow" ventilator in the "attic space" above the ceiling insulative boards that I'm sure will create quite a natural convective flow.  I did not use any insulation, except the boards themselves (minor R value).  I also left an open space around the outside of the ceiling boards to (hopefully ) "suck" air into the attic space when I put the vent hood on the roof.  I bought a "turbine" type, but took it back as it will interfere with the sun on my new set of PV panels!  I'm going to use the largest natural flow type I can find with a low profile.  I'd recommend this for any metal building for cooling.  Don't know that it'll do anything for cold conditions??  I used large plastic washers with short sheet rock screws to attach the 4x8 sheets to the studs - working great and easy to install.

jonr

If you want the most efficient reflection of heat, consider starting with a bright white paint and then adding 50% by weight barium sulfate.  The mix can be about 1/2 the heat absorption of a typical white paint.  Of course shade works even better.  Or add more insulation.

AFAIK, ceramic paints are a scam in terms of blocking heat (ie, don't expect any better than white paint).  

MarkC

An update on the use of 1/2" Styrofoam in the space between the studs inside my metal building - using an IR temperature gun:
-  With the afternoon sun on the West wall of the metal building, the outside metal skin temperature was  130 - 136 oF
-  The surface of the Styrofoam inside the building was ~97 oF the same West wall
-  The equipment inside the building was ~94 oF
-  The SMA Sunny Boy max surface temperature was 115 oF
-  The ambient temperature was slightly above  90 oF
-  The bottom surface of the PV panels was 125 oF (mounted on the roof of the metal building).
-  The areas above the ceiling panels were approx. 120 oF.

I found several areas that need the foam installed behind the metal skin.  I definitely need to install the ventilator above the ceiling panels to move more hot air out of the building.

BenA

Johann said:

You can also paint the outside walls and roof white to reflect the sun-rays.
A computer fan would most likely move more air than the $ 400 solar powered fan would.
Maybe use oil pan 4 idea and when the temperatures are still rising then have a thermostat turn on the computer fan. Or get a small solar panel and hook your computer fan up to that and every time when the sun is shining the fan will come on.

The walls of the solar shed are white sheet metal.  The roof is a "mill" finish silver (like galvalume). 

After insulation, I'm guessing the only coating that would help would be some kind of ceramic coating.  In central Florida, they built houses out of forty foot shipping containers ..... and sprayed these containers with an expensive ceramic coating that repelled just about all radiant energy.  This was very expensive stuff a few years back, I wonder what it costs today?

A computer fan might just be the ticket as part of the solution.

BenA

Lots of great info.  Thanks everyone.

After much research, I started looking at greenhouse louvered-ventilation fans.  I found an ok model (1 amp motor w/decent airflow) from a reputable vendor and placed the order.  Also ordered a fan speed control, thermostat and sheet-metal, rain-proof canopy.  I'll use standard central air conditioning return air grills for the input air source (20x20's).

I'll post some data after a meaningful time.

BoFuller

Everybody around here has a swamp cooler in their solar shed, so this year I joined them. It keeps it at 75 when its 99 outside.