I got my 1200+ sf roof on my shop. It has no peak, just a slope. I was
given a HVAC study here that some organization did that said with foam
sealing, and water flowing over the outside of the roof, a 25F degree
reduction was capable. Has anyone ever used flowing water over the roof of
a building or carport or plain roof to attain cooling?

Would like to hear your stories.

Steve

On 12/17/2012 9:18 AM, Steve B wrote:
I got my 1200+ sf roof on my shop. It has no peak, just a slope. I was
given a HVAC study here that some organization did that said with foam
sealing, and water flowing over the outside of the roof, a 25F degree
reduction was capable. Has anyone ever used flowing water over the roof of
a building or carport or plain roof to attain cooling?

Would like to hear your stories.

Steve


A reputable/competent HVAC analyst will be able to understand your total
situation and give coordinated advice.
What you'll get here, based on almost zero description of your situation,
is a bunch of random input from people who've never made an actual
measurement in their life.

First question I'd ask is why didn't the people who commissioned the study
implement the recommendation?

Second question is, "do you really care what the roof temperature is?"
You really need to address the thing you care about.

If what you care about is the heat coming thru the ceiling, you might
take a broader approach.

The climate where you live is CRITICAL.
The current roof situation is CRITICAL.

If your inside is 80F and the roof is 160F, that's 80 degrees differential.
lowering that to 55 differential cuts your heat flow to 69% of what it was.
But if the R-value of your roof is 5 and you add 5 more insulation,
you halve the heat flow.
And insulation works in the winter too.
Your starting point matters a LOT.
Take the passive "low hanging fruit" first.

Are you OK with the side effects of water?
Mold/mildew/green slime/leaks/corrosion.
Frozen water system in the winter.

Then, there's the payback period on the investment. Do the math.

Google "white roof". There's a lot of info on the virtues of painting
your roof white. The supporting math will apply to any roof cooling
situation.

Steve B wrote:
I got my 1200+ sf roof on my shop. It has no peak, just a slope. I
was given a HVAC study here that some organization did that said with
foam sealing, and water flowing over the outside of the roof, a 25F
degree reduction was capable. Has anyone ever used flowing water
over the roof of a building or carport or plain roof to attain
cooling?
Would like to hear your stories.

No first hand experience, but a couple of sites deal with the question of
cooling an ATTIC while you're working there. The two best recommendations
were a water sprinkler on the roof and disconnecting one or more of the
ducts and let the house a/c cool the attic. Anyway, the watered roof is easy
enough to test.

Set up a soaker hose or sprinkler on the high side of the sloping roof and
let 'er rip. Measure the shop temperature both with and without the water
running. See if there's a significant difference.

Now for a thought experiment:

Assuming there IS a significant difference, the first thing is to find a way
to marry, in a leak-proof manner, some aluminum electrical conduit to a
water hose. Then drill itty-bitty (I'm talking really small, 1/32 or less)
holes, one every inch, along the pipe and install on the high side of the
roof. Turn on the water.

I say teeny-weenie holes because you want the water to exit the pipe the
entire length, not all coming out close to the hose connection. If you make
the holes TOO small, you can easily correct that with the next size drill
bit.

the evaporating water will deposit minerals on your roof.

this is not a problem if you do it a just few times a year.

But if you do it every summer day, there might be a problem.

Mark

"mike" wrote

If your inside is 80F and the roof is 160F, that's 80 degrees
differential.
lowering that to 55 differential cuts your heat flow to 69% of what it
was.

To me the water evaporation thing seems wasteful. I had a house where there
was enough space betwen the peaked roof and the ceiling to install a fan
with a thermostat at one end of the attic and a vent on the other end. The
fan came on whenever the temperature in the attic rose above 85. It kept
the indoors to a respectable 72 to 75 whereas before it used to easily rise
to 90+ in the summer.

On Dec 17, 9:18*am, "Steve B" wrote:
I got my 1200+ sf roof on my shop. *It has no peak, just a slope. *I was
given a HVAC study here that some organization did that said with foam
sealing, and water flowing over the outside of the roof, a 25F degree
reduction was capable. *Has anyone ever used flowing water over the roof of
a building or carport or plain roof to attain cooling?

Would like to hear your stories.

Steve

Wasn't this question asked a while ago and was answered?

On Dec 17, 7:38*pm, DD_BobK wrote:
On Dec 17, 9:18*am, "Steve B" wrote:

I got my 1200+ sf roof on my shop. *It has no peak, just a slope. *I was
given a HVAC study here that some organization did that said with foam
sealing, and water flowing over the outside of the roof, a 25F degree
reduction was capable. *Has anyone ever used flowing water over the roof of
a building or carport or plain roof to attain cooling?

Would like to hear your stories.

Steve

Wasn't this question asked a while ago and was answered?

Yup.... about a year ago



Steve B
View profile
More options Nov 3 2011, 3:31 pm
I am about to complete a metal building project. I had shown to me a
HVAC
study where large industrial sized buildings were cooled by a surface
application of plain water, sprayed on with regular PVC lines and
regular
lawn sprayers. The drainage was collected with gutters, and
recirculated.
A 25 deg. F drop was possible using this method.
Has anyone here ever used flowing water on a metal building, or any
style of
structure as a coolant? I'd like to hear of your experiences.
Steve


I'm guessing that those replies are still as good as they were a year
ago.....

It'll work, give it a try

Steve B wrote:

Has anyone ever used flowing water over the roof of
a building or carport or plain roof to attain cooling?

Would like to hear your stories.

This idea of evaporative roof-cooling has been discussed here in the
past several times.

I suggest you look up these threads:

Subject: Putting sprinkler on roof to cool shingles and attic
(July 2011)

Subject: Evaporative cooling for metal buildings
(November 2011)

Mark wrote:
the evaporating water will deposit minerals on your roof.

this is not a problem if you do it a just few times a year.

But if you do it every summer day, there might be a problem.


Good point! Yet the mineral deposits are probably light in color thereby
helping solve the problem.

On Mon, 17 Dec 2012 10:18:44 -0700, "Steve B"
wrote:

I got my 1200+ sf roof on my shop. It has no peak, just a slope. I was
given a HVAC study here that some organization did that said with foam
sealing, and water flowing over the outside of the roof, a 25F degree
reduction was capable. Has anyone ever used flowing water over the roof of
a building or carport or plain roof to attain cooling?

Would like to hear your stories.

Steve


I've seen the damage water that leaks from evap coolers and from
leaking AC condensate drains does to roofs here in AZ and I would not
purposely run water continuously over any roof I owned.