Lets start a discussion about rooftop A/C units and exposed ductwork.
The worst place to put a metal A/C unit is where? Yeah, on the roof. We are trying to keep the air inside cold and we are pushing that air through a 190 degree metal tunnel. That metal tunnel gets so hot because of what? The radiant heat from the sun. On a 95 degree day those metals can reach over 190 degrees F.
The air is one temperature when it leaves the A/C unit. The cold air absorbs that heat energy and it is warmer before it even enters the building. Homeowners pay part of their cooling costs because of those hot metals. Keep that tunnel cooler and the air enters the building at a colder temperature. The thermostat is satisfied sooner and that saves the building owner cooling energy costs.
Those are simple facts, simply explained and they make sense..
The avatar for this group is a photo of a residential rooftop A/C unit that has been coated with a radiant control coating. . This small application took about 3 pints of the coating and about 1 hours labor. The result; the air temperature coming into the home was 5 degrees colder than before.
Is this not a substantial improvement? Is this not a good bang for the homeowners buck? Yes it is!
Here are the problems with these small jobs that have a good return for the investment..
1. Most contractors are not willing to do such a small job. Not enough profit for the contractor.
2. Most contractors do not believe that such a small application of an energy saving product an possibly bring a noticeable improvement.
3. Most homeowners are under the same opinion as in #2..
4. Most A/C manufacturers give a 5-year warrany on their units. If you apply a radiant control coating to an A/C unit that is still under warranty, you just voided that warranty.
As a Home Energy professional, do you ever consider reducing the load on a rooftop A/C unit as an additional option you could offer your homeowners?
I am curious what others think about this OTHER energy saving use of a radiant barrier coating.
I'm interested in these coatings, have seen something in trade mags and know it's $$$ off the bill to apply them.
My experience was Phoenix, AZ, where the attic was 160F every day for months. The other part of moving cold with air is humidity, in deserts people have swamp coolers feeding the AC to help move more therms of cold to rooms.
It's not logical for AC+cooler to be in the attic where delta-T is huge, it should be on the shady side of the home and perhaps draw from under the homes, distributed from the basement.
For the question of other uses, thermal collection & storage is ignored in architecture passive solar or not, can these coatings be used to help preserve heat from a solar collector in piping to a tank, and the tank itself?
Seems it should ... another reaction was in the crawl space a lot of heat is lost to radiation from the floor to the ground, batting has a foil side as a radiant barrier but could be improved.
In my buildings I'm using water in pipes below the floor for thermal-mass and tear out the batting to put them in. Then closing it off with foam board, so, if you coated the pipes and/or board how much less loss would there be?
Then, if that's valid for reducing losses what if you spray it on the sheathing under the sealing layer to help reduce wall radiant losses?
It looks like I will have to start off most of my answers to questions with this statement; I am a 30 year engineering rep for the one coating I work with. I am an expert on that coating. I can tell and show you what I and a few others have proven with it. I cant speak for any of the other coatings.
Water coolers feeding A/C units. Defeats the purpose. One of the functions of an AC unit is to remove excess humidity in the air. I will give a worst case scenario type of incident. Many years ago I was called by the maintenanc manager for a large and exclusive golf course / country club. They had a problem with the AC unit above the mens shower room. Got there, the shower room was EXTREMELY humid AND they had 2 6-man hot jacuzzis in there. Got on the roof and the A/C was one big square block of ice! Never saw anything that came close to tyhat. I told him to buy a de-humidifier and our coating would not help there.
Heat energy transfers by 3 modes; Conduction, convection and Radiation. In your 160-degree attics, which of those 3 modes are affecting the attic AC unit? Answer; All 3.
1. Radiant heat from the underside of the roof deck. Radiates down and is absorbed by the A/c ub, plenum and the flex or metal ducts and the insulation on the attic floor.
2. Conduction - the attic;s R- insulation is almost always touching (sometimes piled up against or on top of the unit and ducts. THAT hot insulation is now transferring that heat energy to the cooling system.
3. Convection - the attic air passes over the hot surfaces, absorbs heat energy and transfers it to the AC equipment by convection.
I have to explain how our coating works.
Our coating is a water and ceramic based latex. It contains microscopic ceramic platelets. In the first 72 hours of curing, as the binder chemicals dissipate out, that process pulls the ceramic plateletys to the outside. This forms a thin, flexible ceramic tile. This tile is formed in the first 72 hours of curing. That ceramic tile reflects heat energy back in the direction it came from.
Now here is the hard part to believe; Just as a floor4 tile has an upper and lower side when on a floor (inner and outer side when on a wall) our coating's ceramic tile also has 2 sides. Both sides will send heat energy back in the direction it came from.
Now to the different applications that will keep the air cooler in your attic A/C systems. If an electrical outlet has no power, the electrician will star at that point ad his / her way back. I will try and do that here.
I guess I got too mlong winded ther, it cut me off.
1. Spray the coating on the ducts, plenum and A/C unit itself in the attic. They are now insulated against radiant, conductive and convective heat gain.
2. Spray thne underdecking of the roof. That same ceramic tile is going to send that heat back in the direction it came from. Cooler attic but the roof will be hotter.
When a new roof is installed, the coating can be applied to the sheathing, the black paper OR directly to the shingles *Not wood shingles.'
sorry for having to break this up but my responses I guess are too long.
You talking about the coating retaining heat inside a pipe, tank or any structure made me sit back in my chair. The answer is yes. If the inside of the pipe is hotter than the cold outsider the pipe, then yes it is going to reduce the heat loss. If the temperature outside is hotter than the temp inside the pipe, the coating will reduce the heat gain.
Using our coating;
We have coated boilers and steam pipes in a hospital and rfeduced the surface temnperature of those metals from 267F down to 155F. A 35% reduction in heat loss per the hospital engineering chief. I have his statement if you want it.
Employees of the East Bay Regional Park District coated the unbderside of a 33 foot mobile home in one of their parks. They also coated the the metal heater duct than ran the full length of the unit. They documented the results. An 84% reduction in heater run time. I have that statement also.
One of the simple sales tools I came up with for our sales people was so simple and believeable and worked eery time. I took stitchbond polyester roofing cloth and coated it with our coating. I cut it into 8 inch by 2 inch strips. Our coating is an elastomeric. I would turn on the hot water water in the kitchen and let it run very slowly. I would let the faucet get good and warm, wrap the coating strip around and pinch it tiht. Gave it about 20 and asked them to touch the the strip. Then I had them touch the the bare faucet. V ery noticeable difference. Then we went to the water heater and I uncovered a little of the hot pipe. Wrapped the strip around that pipe and repeated that test. They touched the strip, cool. Then they touched that very hot pipe, normally yelled or cursed. Had one one little old lady yell at me while shaking her hand "I CANT BELIEVE YOU LET ME DO THAT!"
You let them burn their hands and they will NEVER forget you.
Used as eithar an interior or exterior paint or roof coating, it retains heat in the cold months and keeps it out in the hot months.
Sounds like the perfect, thin insulator adding enough thermal inertia to separate two masses and/or mediums a lot better than most insulation.
For my use I'd spray it on the downward or exterior side of the board, it helps delay changes a lot for so little, this adds a lot of help moving more wall or floor mass into thermal-mass to help maintain comfort zone.
Do you have tables of q or R-factor for it online?
Products like these dont have an R-rating. You still have to have the R-rated insulation to meet codes. Cant substitute this coating for that.
However, tests can be performed to give a material like this an equivalent R-rating.
Several years ago a controlled terst was conducted on our product vs standard white paint. It was done by the engineering department of UNLV under the supervision of Dr. Semir Moujaes, Associate Professor. It was done as a Master’s Thesis for (Now Dr.) Arnel Ruffy. It was a 2 year study.
Two clone buildings were built on top of one of the campus buildings. One was coated with standard paint, the other with our coating.
The walls, floor and roof were rated at R-25 with standard insulation. The results proved the building with coating used 52.02% less energy to maintain the same temperature inside.
I have one of the executive abstracts of that project. It is as big as a New York phone book!
We asked Dr. Moujaes how much more R-rated insulation would have had to be added to achieve that same energy saving result. He did the calcs and said a level of R-32.6 would have te added to achieve the same energy savings. Now, that is what our ‘equivalent R-rating’ was for that specific application
Right, that reinforces my understanding of how it works, I was after what to plug in for values in this small thermal modeling app MIT did, this is a 400-minute run with the standard wall on top vs adding exterior insulation board on the bottom, has furring strips then replace the siding, cuts conduction by 2/3 ... I'll try to find a ballpark value from the 52.02%.
So, same as under the floor, this coating is added to the exterior of the board under the furring strips & should chop a worthwhile hunk out of losses for the cost of adding that step in a remodel.
For wood-frame homes I prefer hemp-mortar stucco now in place of the foam board used without a vapor barrier over the sheathing for moisture transfer at 1-1/2" thick, this fits here on the wet side of the Cascades, it breathes moisture slowly and doesn't allow fungal growth yet like your coating slows heat-transfer down beyond what pure insulation can do.
This also makes the rooms quieter.
Hey again Tom,
"your coating slows heat-transfer down beyond what pure insulation can do."
That is one way to explain how our coating works. I prefer this way, "Our coating allows the R-rated insulation in buildings to perform it's function on a greatly reduced temperature scale."
If you have furring strips in a wall system, wouldnt that leave an air space in the wall ? Would that air space be what results in your conductive heat reduction? Even with that air gap, one side will be warmer than the other and you will still have a radiant heat gain / loss through the air gap.
Radiant heat can travel through a perfect vaccuum.
This discussion has certainly got off the main track here about AC units but it has brought up some interesting points.
I would be remniss in my obligations if I did not point out something about the wall system you described. Anytime there is an air space in a wall system, it is considered a fire hazard. It allows a fire to spread much faster through that wall if a fire occurs.
OK Tom, I think I am on the last question now,,,I think. LOL
Going under the building and applying (Spraying) the coating to the underside of the wood floor. Yes, it makes a very noticeable difference in the temperature of very cold floor tiles or linoleum in the cold months.
Concrete floor? Apply it to the concrete, give it a week and then lay your carpets. Very noticeable improvement.
Here are few examples of residential AC and the results from coating them with our Radiant Control Coating.
Reduced air temperature coming into the house by 5-degrees on a 90-degree day. Elk Grove, Cal.
Dropped air temp 12-degrees on 90 degree day, 61 to 49 degrees per the AC contractor. Porterville, Cal.
All readings taken at the closest and furthest ceiling registers from the unit. The least I have ever dropped the air temperature on small residential units is 5 degrees. The most I have ever dropped the air temperature, on a mid sized commercial unit and duct, was 25-degrees.
When making a presentation to a prospective customer; I would quote them a price to paint the exterior of their house. I had absolutely no quallms about saying "If I coat your AC unit on your roof and that LITTLE job can bring the air temperature down by 5-degrees or more, will you let us paint your whole house? If our insulating coating can drop the temperature by 5-degrees just by painting a few square feet on your AC unit, how much better will your house be if we painted the entire thing?"
Any time I had to do that free demonstration, we never failed to convince the customer that it was an excellent investment.