CR4 - The Engineer's Place for News and Discussion®

Previous in Forum: Intersection Design - Bypass or Stoplight   Next in Forum: Cracks in Reinforced Cocrete Slab
Close

Comments Format:






Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







24 comments
Associate

Join Date: Dec 2010
Posts: 44
Good Answers: 1

Roof Cooling?

04/19/2012 11:54 PM

I'm sure it's been tried but has anyone water cooled a roof for summer cooling savings?

Since the cooling load of a building is mostly from the exterior and mainly the attic what better than to cool the roof?

I am thinking of circulating water from the eves to the peak with an efficient sump pump and letting the evaporative effect do the cooling much like a cooling tower.

Also a possibility would be evaporative cooled water from the north side of the roof to circulate through a 4" pan holding the air conditioner outside condenser unit.

All electrical raised above the water level of course.

Water treated for bacteria.

Would this do any effective cooling?

Norm

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
2
Guru
Australia - Member - New Member

Join Date: Feb 2008
Location: Australia
Posts: 1376
Good Answers: 155
#1

Re: Roof Cooling?

04/20/2012 2:07 AM

This idea does work but requires a little bit of infrastructure and owner involvement.

I've seen an industrial roof cooled that way using irrigation sprinklers. The effect was dramatic and almost instantaneous, even in a high humidity situation. The radiant heat inside the building from the underside of the metal roofing was the issue there. We used an IR thermometer to measure the interior roof temp and teh drop was around 20 degrees C on hot summer days.

Collecting and recycling the water has significant benefit, especially if you have rainwater storage capability instead of buying it from the water authority.

HOWEVER, a scientifically designed and manufactured system should give you greater efficiency and reliability and is easily "sold" to the next purchaser, while an ad hoc (home made) system might be less attractive.

We eventually installed good insulation. Once the insulation is in place, external cooling impact is significantly reduced and the use of internal cooling becomes even more effective.

__________________
Just an Engineer from the land down under.
Register to Reply Good Answer (Score 2)
2
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 22909
Good Answers: 591
#2

Re: Roof Cooling?

04/20/2012 3:29 AM

Before doing this, lag the ceiling to the thickness required for new buildings under local building regulations. For example, in the UK, it would be minimum 250mm of Rockwool (usual disclaimer - other insulation materials are available). This will keep the building cooler in Summer and warmer in Winter in the 50-60deg latitudes.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply Good Answer (Score 2)
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 9877
Good Answers: 541
#3

Re: Roof Cooling?

04/20/2012 8:09 AM

Wasting water like this is prohibited...Insulation is much cheaper, and just as effective...

__________________
Life is like riding a bicycle. To keep your balance you must keep moving. A.E.
Register to Reply
Participant

Join Date: Jan 2013
Posts: 1
#24
In reply to #3

Re: Roof Cooling?

01/08/2013 10:57 PM

it's not really a waste per se but I would agree on improving your insulation first before doing your water cooling plan. It's not a common one, which means you might end up spending more.

Register to Reply
Guru

Join Date: Aug 2009
Location: Glen Mills, PA.
Posts: 2389
Good Answers: 115
#4

Re: Roof Cooling?

04/20/2012 9:10 AM
__________________
In a time of universal deceit, telling the truth is a revolutionary act. George Orwell
Register to Reply
2
Power-User

Join Date: Jun 2008
Location: Kentucky Lake
Posts: 392
Good Answers: 25
#5

Re: Roof Cooling?

04/20/2012 9:13 AM

There are several roof coatings that are white. The highly reflective coating keeps the roof from getting so hot in the first place. Then insulate and ventilate.

Adding water the roof and building in general could host a multitude of other problems such as algae, mold, decay, termites etc. Pumps get stopped up with leaves, pipes leak and and it would cease to function if the power went out.

Although in principle it would work, it just sounds like a lot of work. Keep it simple, paint it white.

Register to Reply Good Answer (Score 2)
Guru

Join Date: Jun 2008
Location: Oman
Posts: 565
Good Answers: 12
#6

Re: Roof Cooling?

04/21/2012 4:25 AM

Effective roof insulation & water proofing is one of the better options to reduce roof load. Roof Gardening is another suggestion to reduce roof load on A.C system.

Register to Reply
Guru

Join Date: Dec 2007
Location: Mumbai, India
Posts: 1790
Good Answers: 23
#7

Re: Roof Cooling?

04/21/2012 7:26 AM

Central Building Research Institute in India had conducted experiment in this regard. They had covered the roof of R.C.C building with Jute Bags and sprinkled water on these bags. There was significant drop in temperature due to evaporation on the water. It was cheaper alternative to expensive air conditioning of the buildings.

__________________
"Engineers should not look for jobs but should create jobs for others" by Dr.Radhakrishnan Ex President of India during my college graduation day
Register to Reply
2
Associate

Join Date: Apr 2011
Posts: 45
Good Answers: 4
#8

Re: Roof Cooling?

04/21/2012 10:06 AM

Do a search on the internet for Ceramic Powder. You can buy this powder to mix with your roof paint. It will cut approximately 70 to 80 % of the heat from coming through your roof. You can also paint the inside and the outside of your house the same way and stop 80% of the heat from coming into and stop the air conditioning from leaving your house. I have used a pre-mixed ceramic paint on 400 degree F. steam pipes at a thickness of 7 to 10 mils and you can lean against them and not feel discomfort. Don't take my word for it - Just do a search for ceramic powder.

Register to Reply Good Answer (Score 2)
Guru
Hobbies - DIY Welding - New Member Hobbies - Target Shooting - New Member Engineering Fields - Civil Engineering - New Member United States - Member - New Member

Join Date: May 2009
Location: Red Hook, New York (Mid-Hudson River Valley)
Posts: 3896
Good Answers: 144
#10
In reply to #8

Re: Roof Cooling?

04/21/2012 10:28 AM

I've used this ceramic paint additive in our house, applied to the ceilings and exterior walls with a minimum of 2 coats. There was a marked decrease of inside air temperature of about 25% less then the previous year, using nearly identical outside ambient air temps, humidity and amount of sunshine. It's expensive and a PIA to apply, but it does work! The stuff was originally developed for NASA.

I would have applied it to the roof shingles, but alas I could not.......first there's solar panels on the southern half of the roof. Second, applying the paint would have voided the 30-year asphalt shingle warranty on a roof that was installed 2 years prior.

__________________
"Veni, Vidi, Vici"; hendiatris attributed to Gaius Julius Caesar, 47 B.C.
Register to Reply
Guru
Engineering Fields - Mechanical Engineering - Ever Changing United States - Member - From the Redwoods to the Valleys Engineering Fields - Control Engineering - Building blocks or writing code - to keep you comfortable

Join Date: Apr 2008
Location: 38th Parallel
Posts: 682
Good Answers: 16
#21
In reply to #8

Re: Roof Cooling?

04/24/2012 7:25 AM

Painting the roof or ceiling?

Too much maintenance if you are painting the roof.

__________________
"It has been my experience that folks who have no vices have very few virtues." - Abraham Lincoln
Register to Reply
Power-User

Join Date: Apr 2008
Location: Baltimore
Posts: 121
Good Answers: 3
#9

Re: Roof Cooling?

04/21/2012 10:19 AM

1) use the collected heat for something (hot water preheat?)

2) don't waste the water (recirc or garden plot?)

3) how much does the evaporation (if any) increase water cost (or electricity to pump in makeup well water)

4) how much energy cost does the pump require?

5) how much heat does the pump generate if in the house (counterproductive?)

6) consider unintended consequences (does it shorten life of the roof?, etc)

7) consider other approaches to success (plant fast-grow shade trees, reflective roof, collect solar energy and make electricity, roof vents to move hot air out by convection, air vent fan, air condition the house, roof-top deck or garden, insulate attic, etc etc etc)

just a few thoughts

Register to Reply
Power-User
Engineering Fields - Engineering Physics - New Member

Join Date: Oct 2006
Location: MSP, MN
Posts: 419
Good Answers: 4
#11

Re: Roof Cooling?

04/21/2012 12:03 PM

I tried this some years ago. Made a manifold of PVC pipe that straddled the roof peak. Then used "leaky" hose to dribble water down the roof. Water that made it off the roof was really hot. The tradeoff would be what the water costs versus HVAC savings. But the wife didn't like it and I took it down before I could get any data.

Register to Reply
2
Power-User
United States - Member - US Navy Veteran

Join Date: Mar 2007
Location: Nothing sucks more than that moment during an argument when you realize you're wrong.
Posts: 305
Good Answers: 22
#12

Re: Roof Cooling?

04/21/2012 12:29 PM

I cooled a (-40F internal) freezer roof by 40F (external surface temp) at a food plant by rolling on a white thermoplastic product. White roofs became the standard in all 13 of our plants located in the SE Unites States.

I also worked in a warehouse in south Florida (HOT) that had a metal roof where we had a 3" foam layer sprayed on with a white coating sprayed on top of the foam. The inside second level loft temperature dropped by 60F!

Summary:

1. Reflect all the heat that you can. ( any color as long as it's white)

2. Insulate attic from the heat that gets through. (spray foam, blown or roll insulation)

3. Ventilate / exhaust the heat that is left over.

4. Don't use water.............

http://roofcalc.com/index.shtml
http://www.ornl.gov/sci/roofs+walls/facts/CoolCalcEnergy.htm

__________________
You never know when it will strike, but there comes a moment when you know that you just aren't going to do anything productive for the rest of the day.
Register to Reply Good Answer (Score 2)
Power-User

Join Date: Sep 2011
Posts: 164
Good Answers: 1
#13

Re: Roof Cooling?

04/21/2012 3:06 PM

I like the idea. I've been tempted to do this myself using a hose from time to time. But long term I think it could be trouble. Maybe it would be something to use only in extreme circumstances.

Register to Reply
Power-User
United Kingdom - Member - New Member

Join Date: Oct 2010
Location: Torquay England
Posts: 184
Good Answers: 3
#14

Re: Roof Cooling?

04/21/2012 5:18 PM

In Arizona they use a foam spray about 6 inches and then paint it white.. works very well

__________________
Torque is not cheap
Register to Reply
Power-User

Join Date: Jul 2007
Posts: 459
Good Answers: 24
#15

Re: Roof Cooling?

04/22/2012 2:42 PM

Near where I live, the unthinking politicians demanded wooden shake roofs on houses, thinking it would make the neighborhood look classier. The unintended (?) consequences were larger fire depts. and higher insurance premiums. In that context, or in places where brush or forest fires are a problem, a roof wetting system might really pay off. Locally, water conservation is not a big issue; Kansas City advertises itself as the "city of fountains" and the grass median strips are irrigated by sprayers.

Register to Reply
Power-User
United States - Member - US Navy Veteran

Join Date: Mar 2007
Location: Nothing sucks more than that moment during an argument when you realize you're wrong.
Posts: 305
Good Answers: 22
#16

Re: Roof Cooling?

04/22/2012 4:59 PM

I pulled this off the net as an example..................

Whether you are currently planning new construction or reroofing an existing roof, Spray Polyurethane Foam Roofing and Lapolla White Reflective Coatings are for you. This is because it lends itself well to all types of roofing situations, from traditional flat roofs to unusual designs. Foam roofing systems can be applied rapidly, with little or no disruption to the facilities. In most reroofing situations there is not even a need to remove the existing roof.

Spray Polyurethane Foam has been used as a roofing and insulation material for over 40 years. At one time it was considered to just be an alternative to built-up roofing; foam roofing now protects a wide range of buildings. During this time, foam roofing systems have proven themselves through comprehensive, independent studies to be dependable, long lasting, and very affordable. Today there are foam roofs that have been in place for over 4 decades, and by all appearances they should be able to last indefinitely as long as they are properly maintained.

Because of its light weight, Sprayed Polyurethane Foam Roofing can be applied over already existing roof installations. It can be applied directly over asphalt, shingles, built-up roofs, clay tile, concrete, metal, and wood. This saves the need for tear-off, reducing the amount of time, disruption to the business, even the debris in landfills. The roof has to be properly prepared by cleaning off any loose debris and aggregate, and by making sure that it is completely free of moisture.

__________________
You never know when it will strike, but there comes a moment when you know that you just aren't going to do anything productive for the rest of the day.
Register to Reply
Guru

Join Date: Sep 2008
Location: Where the sun sets on OZ
Posts: 728
Good Answers: 9
#17

Re: Roof Cooling?

04/22/2012 8:31 PM

Here hot weather is also fire season. I have simply put a submersible pump in my raimwater tank and a sprinkler system on the roof. The runoff goes back into the tank. due to the high volume there is little evaporation and good cooling.

__________________
Where's the KaBoom? There should be a KaBoom!
Register to Reply
Associate

Join Date: Dec 2010
Posts: 44
Good Answers: 1
#18
In reply to #17

Re: Roof Cooling?

04/22/2012 9:18 PM

Quote: Here hot weather is also fire season. I have simply put a submersible pump in my rainwater tank and a sprinkler system on the roof. The runoff goes back into the tank. due to the high volume there is little evaporation and good cooling.

Thats what I had in mind!

Norm

Register to Reply
Guru
Australia - Member - New Member

Join Date: Feb 2008
Location: Australia
Posts: 1376
Good Answers: 155
#19
In reply to #18

Re: Roof Cooling?

04/23/2012 3:02 AM

Good thoughts, but careful!!!!

When there is a fire large enough to think to use this system, there is usually significant wind and the water is blown away from the building. Sprinklers at the perimeter of the yard might be more effective in cooling the incoming embers and the air stream also.

If you want to use it for fire suppression, then you will need to get sprinklers that do NOT have rubber seals or similar components and the hose will need to be repalced with hard pipe.

Fire control is serious stuff and it needs to be VERY carefully thought through.

__________________
Just an Engineer from the land down under.
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 22909
Good Answers: 591
#20
In reply to #17

Re: Roof Cooling?

04/23/2012 5:15 AM

Beware of concentrating and cultivating air-borne bacteria in that lovely warm water tank with such a system, particularly legionella pneumophila.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply Score 1 for Good Answer
Guru
Engineering Fields - Mechanical Engineering - Ever Changing United States - Member - From the Redwoods to the Valleys Engineering Fields - Control Engineering - Building blocks or writing code - to keep you comfortable

Join Date: Apr 2008
Location: 38th Parallel
Posts: 682
Good Answers: 16
#22

Re: Roof Cooling?

04/24/2012 7:36 AM

How about a Solar powered attic fan. Zero energy costs the same result. No mold, or maintenance required. When it breaks throw it away and replace it. We have used this company below on our projects in the past for warehouse ventilation along with some good fans from the Bigass fan company.

http://www.atticbreeze.net/zephyr.htm

http://www.bigassfans.com

No piping just one hole and go!!!!!

__________________
"It has been my experience that folks who have no vices have very few virtues." - Abraham Lincoln
Register to Reply
Guru

Join Date: Jan 2011
Posts: 668
Good Answers: 3
#23

Re: Roof Cooling?

04/28/2012 7:23 PM

you "MUST" have ventilated soffit with a roof vent "ridge cap". the air flow between the soffit and vent can't be blocked by insulation. never insulate the the roof. turbine ventilators might also be needed. make sure the attice floor insulation is about r-30.

Register to Reply
Register to Reply 24 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

Barchetta (1); CaptMoosie (1); durtieduck (1); esbuck (1); HaroldJ (1); JIMRAT (1); Just an Engineer (2); Mag (1); markar (2); merc600sec (1); mrswamy (1); normnet (1); passingtongreen (1); PWSlack (2); snatr (1); SolarEagle (1); SSCpal (1); Stedou73ish (2); suresh sharma (1); valkyrierider (1)

Previous in Forum: Intersection Design - Bypass or Stoplight   Next in Forum: Cracks in Reinforced Cocrete Slab

Advertisement