# Adding Energy Effeciency To Existing Mexican Construction



## flybeech (Jun 9, 2011)

In an effort to keep our house of Merida and our house of Chicxulub Puerto under the 1C requirements by the commission and remain somewhat comfortable, I need to insulate the houses and replace the windows and doors. I want to be able to use air conditioning and remain under the dreaded DAC electricity usage rate.

Being of typical Mexican construction of solid concrete, I am thinking about various ways I can improve the effeciency of my houses, both for increased comfort and lower energy usage. I thought about constructing interior walls of sheetrock over a wood framework and placing fiberglass insulation between the concrete interior walls and the fured-back sheetrock. This will also allow me to add various electrical outlets and related wiring.

Has anyone got ideas of ways to increase the r-value of the Mexican concrete house?


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## tepetapan (Sep 30, 2010)

You can find R values of anything with an internet search, finding fiberglass insulation in Mexico could be a problem. Styrofoam panels can be had but even then 2 x 4 studs are not cheap by any means. 
To be honest, it would be best to rent for a couple years, look around, see how things are done and then start to make plans. They solve problems a different way than you are probably use to but that does not make it wrong, just different.


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## conklinwh (Dec 19, 2009)

We were having this discussion last night at a party. The guys that I talked to looked at multiple options and decided to look at solar which really surprised me. They said that they were quoted a 12kW system installed and network connected for $8KUS. This is $.67/W installed which is really good. There goal is to avg 6hrs or 72kWh/day, about 440kWh per period. This would get them under DAC rate. BTW, I've heard PV modules approaching this rate but never an installed/interconnected system.


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## RVGRINGO (May 16, 2007)

Solar electric and solar water are becoming more and more popular in the Chapala area; enough so that we now have local dealers with installation capabilities. Some folks have made almost total conversions. Of course, they had the disposable income and were young enough to be able to foresee a payback over time.


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## conklinwh (Dec 19, 2009)

RVGringo you are right with PV in the $3-5/watt as normally quoted, it has a long payback. If truly $.67/watt, this is a whole different story if you are paying the DAC rate. BTW, solar thermal is easier to justify, especially if jacuzzi or heated pool.


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## Guest (Jul 5, 2011)

flybeech said:


> In an effort to keep our house of Merida and our house of Chicxulub Puerto under the 1C requirements by the commission and remain somewhat comfortable, I need to insulate the houses and replace the windows and doors. I want to be able to use air conditioning and remain under the dreaded DAC electricity usage rate.
> 
> Being of typical Mexican construction of solid concrete, I am thinking about various ways I can improve the effeciency of my houses, both for increased comfort and lower energy usage. I thought about constructing interior walls of sheetrock over a wood framework and placing fiberglass insulation between the concrete interior walls and the fured-back sheetrock. This will also allow me to add various electrical outlets and related wiring.
> 
> Has anyone got ideas of ways to increase the r-value of the Mexican concrete house?


Solar is fine, but it's not fixing the problem, it's just sourcing the energy from somewhere else. And it is an expensive option, no matter what the cost/Kwhr.

In a home in a hot climate, electricity usage runs something like this: A/C 30-50%, refrigerator 10-12%, electric water heating 10-15%.

In a past life, I lived in a place that was hotter than the Yucatan, and everyone had concrete houses there too. The difference is that most of the houses had Dryvit installed on the outside, which consists of a board insulation stuck to the concrete with adhesive, with a thick, textured colored coating applied over the board. It wasn't cheap, but the trade off was that they never had to paint the house again. Much more energy efficient than adding insulation inside the house.

If you've got electric hot water, switch it out to a gas water heater, mounted outside. Another option is to put a clock timer on an electric hot water heater so that it fires up about an hour before your normal shower time, then off, and then on again for an hour before your normal dishwashing or shower time in the evening.

Don't want to sound like a moron, but do you keep the coils in the back of your refrigerator clean? I'm not talking about dusting off the outside - I mean unplug the frig, take the back guard off and get all of the dust and gunk off everything there, the coils, the condensor , the works. Twice a year. Keep the freezer full. If it's half empty, fill 1 gallon ziplock plastic bags with plain old water, leave a little airspace inside, and put them in the freezer. It will make the frig run less often if the freezer is full, and costs nothing to do.

If your A/C condensor units are sitting in direct sun during the day, figure out a way to shade them - this will add about 10% efficiency. Just make sure the exhaust air flow from the A/C condensor fan is unobstructed for the first 5 feet.

What is your house like? OK, the walls are concrete. Do you have a flat roof? Is it concrete? Is it sealed in white, or did the last people who did it opt for the cheaper dark red sealant, which will just sit there and absorb heat all day, and raise the cooling demand all night. If it's bare concrete, then coat the roof with white sealant, or figure out a way to shade the roof during the hottest part of the day.

Another thing you can add are timers on the A/C splits. If you start the timer an hour before bedtime, and then program it to shut off the A/C at about 1 or 2am, the cool will coast and allow you to sleep the rest of the night.

How is your house oriented - windows to the south, or to the west? If the house is not shaded on the west side getting the afternoon sun, fix it with either trees or something else to provide shade there and avoid the heat gains.


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## conklinwh (Dec 19, 2009)

GringoCarlos, all good stuff, especially if you live in hot climate. We don't so no air conditioning but still DAC rate. You would normally be right on solar but point that I was making is that if truly $.67/W installed is that this could have a reasonably short payback when consider the drop in usage under DAC rate plus the fact that the rest falls back to Tarifa 01(I asked person not under DAC here for rate) and that .713p/kWh for 1st 150kWh, 1.189/kWh for next 100kWh and 2.513p/kWh up to 500kWh versus 3.060p/kWh flat plus Cargo fijo under DAC. I did some quick math. If someone were at 900kWh/period which is about where they & I are and solar could get them to 499kWh/period which is just under the DAC rate here. The saving in usage rate plus cargi fijo would be about 2000p/period and about 2500p with IVA(16%) and DAP(8%). This would payback the $12KUS in 60 periods or 10years and I used very conservative solar yield rates. Also, electricity will continue to rise and thus the payback even shorter. This compares to typical solar that never pays back without subsidy.
I'm only saying that if this cost is true, I would compare to significant construction costs 1st.
In either case, there are many other tricks to save such as unplugging electronics when not in use.


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## makaloco (Mar 26, 2009)

My house is a remodeled Mexican "low income" type home, brick with a flat concrete roof, in an urban residential neighborhood in Baja California Sur (strong sun 300+ days of the year and loads of concrete to absorb heat). I live here year around without AC, though I do have a small pool.

With proper preparation, spray polyurethane can be applied to an existing roof and west exterior wall. The downside with a wall is that stucco applied over the polyurethane tends to crack. Best to finish with a rustic surface (e.g., "chino") so that any cracks are less visible.

In addition to the polyurethane, I had a product called "Plasticool" applied to my roof, and it made a significant difference in the indoor temp. It reflects as well as insulates (when first installed it was blinding white).

My remodeling contractor erroneously ordered tinted window glass called "Filtrosol" that does a decent job of screening out the sun. It's not cheap and I have large windows, so I grumbled at the time, but now I'm glad I have it.

Ceiling fans are useful whether or not you have AC. With AC, you can set the temp higher and it "feels" cooler because of the moving air. Also, the fans help distribute the cooler air through the house.

Any kind of shade helps a lot. I had a 1-meter overhang built on the west side of the house, and it made a noticeable difference. Ditto for trees, as someone else mentioned. I "adopted" a small mandarin orange tree that a neighbor had to remove and placed it between the summer afternoon sun and the large bedroom window. It has grown into a lovely efficient shade tree.Take care not to shade the house so much that you need lights during the day.

My electric bills average about 400 pesos every two months (Tarifa 1D). I've never been anywhere near the DAC, even with the pool and running fans 24/7 during parts of the summer.


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## dongringo (Dec 13, 2010)

Conklinwh - Thanks for bringing up solar power as a DAC killer (maximum Mex electric rate). I was stuck weighing either or, not both, on a new construction. Incidentally, I was quoted about 16K US for a 750kw solar/wind installation.


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## flybeech (Jun 9, 2011)

dongringo said:


> Conklinwh - Thanks for bringing up solar power as a DAC killer (maximum Mex electric rate). I was stuck weighing either or, not both, on a new construction. Incidentally, I was quoted about 16K US for a 750kw solar/wind installation.


750kW production is a pretty big electric plant. Could that $16k quote for the solar/wind installation have been for 7.50kW or 0.750kW?


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## flybeech (Jun 9, 2011)

Since our casitas are poured concrete, the roof and walls have an R-value of NOTHING. In the night, the concrete holds all the heat captured during the day like a brick oven. It's really not that bad, but I just don't feel like installing AC until I can greatly improve the thermal characteristics of the houses. 

With a tarifa of 1C, I've got 850kWh to work with every month in Merida, which should be plenty. Chicxulub Puerto will be tougher with a tarifa 1B and only 400kWh per month.

What I need is INSULATION!

Should I just give up on the idea of having a a house with a thermal resistance greater than ZERO?


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## RVGRINGO (May 16, 2007)

Be careful in changing the construction in Mexican homes; they've only had some 490 years experience with it in this climate. Others have tried NoB methods & you won't be the first to learn the differences.


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## flybeech (Jun 9, 2011)

RVGRINGO said:


> Be careful in changing the construction in Mexican homes; they've only had some 490 years experience with it in this climate. Others have tried NoB methods & you won't be the first to learn the differences.



You've certainly got a point RVG. The lifetime construction of our casitas is hard to beat.

Others have suggested I install a solar and wind generation plant for thousands of $$$, but I'm just interested in having some AC and staying out of DAC territory at the same time. I have no desire to structurally modify the house, or cover the outside with some foam that will fall apart in a few years.

I just want to find a reasonably-priced way to insulate the walls and roof from the inside of the house, that doesn't really change the structure. I'm thinking of a slightly dropped acoustic ceiling and furring on some sheet rock walls with fiberglass batts in between. Really, anything is an improvement over the R-0.01 that I have now.

I suppose the best solution is forget it all and just tolerate the 36 - 37 degree summer days, like everyone else does.


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## conklinwh (Dec 19, 2009)

We are in a much different situation as in the winter have cool/cooler nights and warm sunny days while in the summer, other than May, we still have cool nights and warm days. The insulation of choice is adobe and has been for hundreds of years. When we built our place, they set up an "adobe factory" on site which consisted of one person and a two block form. Adobe on the outside of block does a great job of holding and equalizing temperatures. In the mornings in the winter, we sometimes use our gas logs to cut the chill and some nights, we turn on a timed fan. Only real problem with adobe is protection as needs be sealed every year or someway else protected.


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## dongringo (Dec 13, 2010)

kWh (kilowatt hour), obviously


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## RVGRINGO (May 16, 2007)

Flybeech,
You've chosen a difficult place to live comfortably. Insulating from the inside will not provide protection from the heat collected by the mass of your concrete walls and roof, which will still be inside the structure and force the AC to deal with it at high cost. Insulating from the outside would have some benefit, but only a minor effect unless you built an vented air space between the insulation wall and the masonry wall. Best to move to a better climate! The only other option is complete shade to protect you from the sun, but you'll still have to deal with the humidity and ambient air temperature.


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