Air Cooling

Okay. I live in Toomsuba, MS. Zone 7B/8A, take your pick. It is hot and humid here. We have a reasonable risk of both tornadoes and hurricanes.

Let's just assume that I am not going to take my 7 member family, sell our home and land, find more land, and build an underground house.

Sorry - had to get that out of my system.

I love the whole rocket mass heater deal. But our problem is not that it gets cold. Instead it gets too hot and I do not have a non-electricity-using way of cooling it down. I am sure there are plenty of people that would suggest to simply get used to 100 degree heat with high humidity, but not this fella.

We also do not want trees close to the home as I have seen too many trees splitting a home in half. It is just not a comfortable feeling to have a tree swaying over the house.

Finally, our home is, by all accounts, ridiculously huge. 2,500 sqft. When we bought our home permaculture, energy savings, and so forth where not on my mind.

So - Is there any way to work with this? I am guessing that "something has to give", but I am unsure what. We are already slowly acclimating ourselves to higher temperatures, but then the humidity comes and it's pretty much a done deal - on comes the A/C. We are using up less electricity now, but I am confident we can do better.

Our home is a long rectangle, going E to W, precisely. Our wind typically comes from the NW and we do keep our windows open and encourage drafts as often as possible. While the situation of the house helps keep shade on the windows from the eaves, I would like a longer eave, but that seems like a pricey venture.

Thanks for any thoughts and constructive criticism.

Sounds like you would have a lot of south facing roof area for solar panels. Which you could then use to power an A/C unit.

There is a very small number of us here on Permies who have been talking about solar cooling, developing an absorption chiller system that can use solar energy to run an absorption refrigerator cycle, but instead of using it to cool a box down to refrigerator/freezer temperatures, have it optimized to cool (and dehumidify) large volumes of air passing across the system. If you have any do-it-yourself HVAC skills, you're welcome to kick around ideas with us and see what we can prototype.

I am afraid you are way over my head with the absorption chiller thing.

As for solar panels... I know enough about solar power to hurt somebody. If we assume I would be buying everything pre-manufactured, isn't that a fairly pricey endeavor? Or am I just spouting nonsense that other people have spouted?

John Elliott wrote:Sounds like you would have a lot of south facing roof area for solar panels. Which you could then use to power an A/C unit.

There is a very small number of us here on Permies who have been talking about solar cooling, developing an absorption chiller system that can use solar energy to run an absorption refrigerator cycle, but instead of using it to cool a box down to refrigerator/freezer temperatures, have it optimized to cool (and dehumidify) large volumes of air passing across the system. If you have any do-it-yourself HVAC skills, you're welcome to kick around ideas with us and see what we can prototype.

Solar keeps getting more and more competitive in price. If you want to play with some numbers, here is a good page with lots of information. It is a long term investment, but the only way you know if it is going to work is to calculate a lot of different scenarios, like from having just enough to keep you going (like when a hurricane knocks the power out for a week or longer) or if you want to have the whole roof covered so that you are a net producer selling back electricity to the utility.

I took some time playing around with the numbers. Loaded up my usage info on my utility website, calculated out my cost/kWh, etc., to get the most accurate guesstimate. For even a system to provide 50% of our current usage I am looking at $26k, cost at install.

Having recently made other large purchases, this is unobtainable.

Now, I am sure we can whittle down some of that if I were to use less kWh and therefore could use a smaller system and I wager the cost of installation is pricey, rather than just the cost of equipment.

Since I live in a county where I can to nearly anything I want without a permit, I wonder how much of this I can do on my own before having to bring in an electrician or the power company.

Also, what is the feasibility of doing this over time? Buying 1 piece of equipment a month over a year (or whatever it takes) so that it is paid-in-full when it is finally switched on? Is there a recommended order of buying components?

Thank you for the help.

John Elliott wrote: here is a good page with lots of information.

Those are questions that you and I are both going to have to get answers to. My plan is that after I get the roof redone (just a couple more months!) then I can think about starting to put up some panels. At first start small, and then over time, as I see how it goes, I can add capacity to the system.

Do you get your electricity from a co-op? I do, and they are always very nice to work with if there is ever a problem or if I have questions.

Yes, I am sure they will work with me when it comes time. Though you bring up another excellent point, I want to put a metal roof on before I go attaching stuff to it. Our roof line does not hang over very well and attempts to put in a drip line so we can collect rain water have been... less than outstanding. I presume using a metal roof would not only help me in avoiding the stuff in the asphalt tiles but that I could also extend the roof out the extra two inches that I need so we can collect water. Given the size of the house and the amount of water we receive we could be harvesting a whole lot of rain.

I agree that PV powered heat pumps are the most effective and appropriate technologies to consider. Reducing your loads will decrease system size and costs. With installed costs getting in the 2.00-3.00$ per watt range, simple paybacks are getting very short especially with tax credits involved. Not sure what your state offers but the federal credit alone knocks 30% off the cost of your system. NC offers another 30%, so thats a total of 60% off the total cost of the system here.

Since 10-20% of your AC load is from air leaks, air sealing is one of the most cost effective ways to have a meaningful impact.

Metal makes a great roof in most climates especially for rain harvesting. Choosing a bright white color for the roof costs nothing extra and will help decrease your cooling loads. If your insulation is at the ceiling plane, add more cellulose or fiberglass to get closer to R50 with R38 being an minimum. Always air seal the ceiling plane as much as possible before taking that step!

Your East to West orientation is ideal. Windows on the East and West contribute a great deal to your cooling loads. Consider adding deep overhangs or movable exterior shading, especially on the West.

If you ever replace the siding or cladding, consider adding exterior insulative sheathing. If you have a slab on grade, removing any floor coverings other than tile could help add thermal mass to the equation.

Consider replacing your current water heater (especially if its atmospherically vented combustion) with a heat pump water heater. Not only does this have a huge impact on your total energy costs, it will help cool and dehumidify the interior space, further reducing the loads.

We have thought to add some type of arbor over the west wall with something vining to help shade it.

I believe our insulation was blown in to the 'attic', which we have no access to. (modular home). I would have to look up the specs.

Sadly, we are not on slab on grade, I would love to use that idea.

Mississippi apparently could care less about solar. I could not find any credits for it.

Our current water heater is an electric tankless. Whole house model.

I have a recommendation to consider. Rather than cool the entire house, choose a room that can easily be sectioned off from the HVAC unit, well insulate and vapor seal the room even from the rest of the house; and use a DC powered split AC unit to cool that room independently. You can use it as a kind of "escape" room on the hottest of days, like most people use the room with the woodstove/RMH to escape to during the coldest of winter days. If you set up an East-West solar panel array properly sized for the cooling unit, you won't need all of the extra batteries and electronics required to use a solar panel array for general use, and you really wouldn't even need a thermostat as the unit would run whenever the sun was available, which also happens to be when cooling was needed most. Ideally, you could use a spare bedroom for this, if you have one available in that large house. You would have to insulate all walls as well as both the ceiling and floor of the room, and you would have to have an effective condensate drain for the water that the cooling unit condenses. This would be an ideal place to store your paper books, as they won't suffer a hot and humid bookshelf for many summers. Might also be a good place to store your boxed (not canned) shelf stable foodstuff, since items like boxed cereal last only in a relatively well climate controlled environment. Your kids could escape to that room during the hottest parts of the summer day, and then you kick them out as it cools off again.

Another possiblity, if you have an unfinished basement, is to build this room in your basement, since it's basicly an artifical root cellar. You might get a two-fer if the split unit could be set up as an ice-maker instead, and the room that it sits within simply benefits from the operations of the ice maker as the sun shines.

EDIT: BTW, my house is a 2600 sq.ft., 6 bedroom ranch with an unfinished basement. I mention this possibility because it's exactly what I'm considering doing. I'm most likely going to build the cold room in the basement, to take advantage of the natural coolness down there, but mine isn't going to be large enough for my entire family to congregate within.

EDIT 2: If you were to use a spare bedroom with an exterior wall, you wouldn't really even need another split unit (which is what the regular type of whole house AC unit is) but instead you could use a common window unit style AC, or one of those hotel type HVAC units. The window units are a security risk, but those that use a dedicated whole in the wall, like the hotel type units do, are not a security risk, but require that a carpenter alter your home for such a unit. This might be the best way to build a cold room if you're going to stay on the electric grid anyway. As far as I know, no one makes a window unit that can run off DC current; but an RV air conditioner could possibly still be used in this fashion with an East-West solar panel array.

Jared Stanley wrote:Mississippi apparently could care less about solar. I could not find any credits for it.

You might want to talk to a professional solar installer. I live in Kentucky, which likewise has no state credits; however the solar installers around here all seem to have subsidy agreements with coal plants in Ohio. Ohio requires coal plants purchase 'co2 credits', and you can get a deal with the installer wherein the coal operator will pay for part of your install costs if you sign an agreement that they can claim all of the 'green credits' that you would otherwise be entitled to. Which works great for a great many grid connected homesteads because we wouldn't be able to do anything with those credits otherwise. Apparently Ohio law doesn't require that the 'green credits' be produced within the state, so long as they can only be claimed by one power producer.

Our current water heater is an electric tankless. Whole house model.

Keep it. It would not only work really well with a solar hot water setup, it would also work really well as a diversion load should you ever go completely off grid with solar power.

Jared Stanley wrote:I am afraid you are way over my head with the absorption chiller thing.

Absorption chillers have the disadvantage of being quite a bit more expensive than a common AC compression unit of the same size. They are great in small form factors, such as a tiny propane refrigerator, but even these are quite expensive for what you get. If you can't consider a $26K solar array, you can't consider an absorption AC unit either.

Once upon a time, there was a natural gas/propane fired, engine driven AC unit on the market for off-grid homes (and homes in regions with rediculous electric rates but reasonable natural gas rates) but when I priced one about 5 years ago it would have been almost twice the cost of simply replacing the busted 5 ton unit on my old house. I can't remember what they were called, and I have no idea if they are still being manufactured.

One small suggestion that won't eliminate your A/C use but might reduce it quite a bit and won't cost much since you already have the AC, is to also use a fan while using the A/C. I don't often go to hot places that need AC except Delhi, which I travel through several times a year. My hotel room there has a choice of ceiling fan and AC, and I prefer to avoid using the AC, but in the hot season the fan isn't enough for me. But I can set the AC to several degrees warmer if I keep the ceiling fan on at the same time.

A solar chimney could deliver air flow on days when the wind fails. Probably not enough during the peak of summer, but a great way to move some air in other edge seasons. Early morning sun can start the flow so that an air change is achieved using the cool air of early morning.

You mentioned an aversion to trees. A row of something really strong, without large branches such as hornbeam, could be planted at a safe distance, south west of the house. This would block late afternoon sun which heats walls and shines directly into windows. On houses that have good overhangs and roof insulation, late afternoon sun is often a major contributor to heat gain, just as you return from work.

Tall foundation plantings such as rhododendron or lilac protect exposed walls from direct gain. There are many edibles that could accomplish this as well. Grapes, dwarf fruit trees ...

Upon a bit of research, I have found a company that builds solar ready DC air conditioners...

http://kingtecsolar.com/

While it's a neat unit, specificly designed to run off of a solar array and including it's own solar controller electronics, even the smallest window unit would require 870 watts of connected solar panels in order to run continuously during full sun. Since it's all but certain that one would want this thing running continuously during full sun, and likely during partial sun as well, nothing less than a full kilowatt of solar panels would likely suffice. And battery storage likely wouldn't help much in this use case. An East-West array would significantly extend the hours of useful run time for such a directly connected unit, as compared to a South facing array, but the East-West setup would require 870 watts minimum for each side of the array, for a total minimum of 1740 connected watts. One could start with a south facing array, and move to an East-West array setup or a tracking mount if the cooling time for the unit wasn't enough; but it'd probably be better to choose the smallest regular window unit available commercially, and use it in as small a room as you could manage, without leaving the electrical grid. I'm thinking a walk in closet with a reading light or two and a couple of chairs.

I really cannot see a window unit working in our home. It has a very open floor plan. That poor little window unit would freeze up quick with how hard we would be trying to run it. I stand to be corrected, but I don't think that is the solution. That's an awful lot of panels, isn't it? Sounds like it would increase the cost of my system by - a lot.

Creighton Samuiels wrote:Upon a bit of research, I have found a company that builds solar ready DC air conditioners...

http://kingtecsolar.com/

While it's a neat unit, specificly designed to run off of a solar array and including it's own solar controller electronics, even the smallest window unit would require 870 watts of connected solar panels in order to run continuously during full sun. Since it's all but certain that one would want this thing running continuously during full sun, and likely during partial sun as well, nothing less than a full kilowatt of solar panels would likely suffice. And battery storage likely wouldn't help much in this use case. An East-West array would significantly extend the hours of useful run time for such a directly connected unit, as compared to a South facing array, but the East-West setup would require 870 watts minimum for each side of the array, for a total minimum of 1740 connected watts. One could start with a south facing array, and move to an East-West array setup or a tracking mount if the cooling time for the unit wasn't enough; but it'd probably be better to choose the smallest regular window unit available commercially, and use it in as small a room as you could manage, without leaving the electrical grid. I'm thinking a walk in closet with a reading light or two and a couple of chairs.

Jared Stanley wrote:I really cannot see a window unit working in our home. It has a very open floor plan. That poor little window unit would freeze up quick with how hard we would be trying to run it. I stand to be corrected, but I don't think that is the solution. That's an awful lot of panels, isn't it? Sounds like it would increase the cost of my system by - a lot.

Indeed, any air conditioner is going to be an energy hog. But I mentioned the window unit as a reference to my earlier post about sectioning off a small room as a 'cool room' that is air conditioned independently. But with this kind of requirement, a solar powered ice maker and/or an air conditioned walk in closet is about all that you're going to be able to do short of that $26K solar power system.

Jared Stanley wrote:
We also do not want trees close to the home as I have seen too many trees splitting a home in half. It is just not a comfortable feeling to have a tree swaying over the house.

I also find this statement funny. I now live on 13 acres, all but our 2 acre yard is thickly wooded. Thick enough that the dog has trouble getting through the brush. Even my 2 acres of yard has scattered trees across it, and there is no space large enough to build a 2 car garage without cutting down at least one tree. The majority of these trees are 50+ years old and 70+ feet tall. I've lived in Kentucky most of my life, and trees grow everywhere. I've literally never heard of a tree "splitting a home in half". Maybe homes are just built sturdier here, but I doubt that.

Jared Stanley wrote:Okay. I live in Toomsuba, MS. Zone 7B/8A, take your pick. It is hot and humid here. We have a reasonable risk of both tornadoes and hurricanes.

I love the whole rocket mass heater deal. But our problem is not that it gets cold. Instead it gets too hot and I do not have a non-electricity-using way of cooling it down. I am sure there are plenty of people that would suggest to simply get used to 100 degree heat with high humidity, but not this fella.

We also do not want trees close to the home as I have seen too many trees splitting a home in half. It is just not a comfortable feeling to have a tree swaying over the house.

Finally, our home is, by all accounts, ridiculously huge. 2,500 sqft. When we bought our home permaculture, energy savings, and so forth where not on my mind.

So - Is there any way to work with this? I am guessing that "something has to give", but I am unsure what. We are already slowly acclimating ourselves to higher temperatures, but then the humidity comes and it's pretty much a done deal - on comes the A/C. We are using up less electricity now, but I am confident we can do better.

Our home is a long rectangle, going E to W, precisely. Our wind typically comes from the NW and we do keep our windows open and encourage drafts as often as possible. While the situation of the house helps keep shade on the windows from the eaves, I would like a longer eave, but that seems like a pricey venture.

Thanks for any thoughts and constructive criticism.

Make sure the check out the recent thread "Efficient Air Conditioning" in this forum. Beyond the suggestions offered in that thread, it is also possible to dry the air with a desiccant that is regenerated with heat. There are some commercial systems available, but I don't know about them (search "desiccant wheels").

Here's the link --- https://permies.com/t/27465//Efficient-Air-Conditioning

If you put a metal roof on (insulated well), you could extend the south eave more than the 2 inches (the exact formula for how much is in Brad Lancasters water harvesting books, I think), to shade the south windows and walls from sun in summer and let it shine in winter

How about harvesting water and cooling your home with misters on the roof top?

Here is an interesting discussion. http://ecorenovator.org/forum/solar-power/3053-diy-9-2kw-solar-array-2.html

An individual recently installed an Enphase off grid solar system. Since he did the installation (which does not seem terribly difficult) he was able to avoid a lot of expense. He got a 12,500 watt system for $1.72 per watt before rebates! Folks, the price on solar has been falling so very rapidly in recent years. A grid tie solar system combined with installing a highly efficient split ductless a/c system, and doing what you can to reduce the cooling load, is probably the most practical and cost effective solution.

Actually, if you already have a central a/c system, then it makes sense to add a grid tie solar system large enough to provide most of the electricity consumed by the a/c system, then operate the a/c system continually while the solar array is producing. Even better if net metering is available.

http://www.builditsolar.com/Experimental/RoofCooling.htm

A roof sprinkler system http://www.builditsolar.com/Experimental/RoofCooling.htm

Evaporative cooling for your air-conditioner's coils that won't foul the coils: http://www.builditsolar.com/Projects/Cooling/ACEvapCool/ACEvapCool.htm


Earth tubes could also be useful...

The point is that if you only intent to use the solarpanels for the A/C you really don't need very much battery, because you use the electricity while the solar panels are producing most energy.

A solar chimney is a good idea, esp. if it is combined with an air intake that is water cooled (could be as simple as a terracotta pot full of water or taking the air intake In from a water tank outside.

A pergola is useful too - with a vine or kiwis, which loose their leaves in the winter. Here in Spain many people grow annuals like cucumber and squash on their pergolas.

Insulation of the entire house and roof helps, shutters in front of windows, painting the house white. Making sure you don't have heat-bridges.

Dawn Hoff wrote:The point is that if you only intent to use the solarpanels for the A/C you really don't need very much battery, because you use the electricity while the solar panels are producing most energy.

In fact, you don't need batteries at all, if you intend to set up a solar array specificly for the A/C. Better would be to oversize the AC, and use some method of cold storage. Which can be as simple as an icemaker running during the peak solar power output whenever the AC is keeping up with the cooling demand. Sort of like using an icemaker as a diversion load, whenever the primary load does not call for power.

I don't know how to quote Exactly - you don't need batteries, so I don't quite understand the price quoted $23.000).

We have just gotten a quote for a 5 kWh off the grid system, with 4 days batteries backup at €36.000 (incl. installation). A 3 kWh system with 1 day backup we can buy for less than €15.000, if we install it ourselves. Now we use about 4 kWh a year, but don't use AC (last year we did and I think we used 6 kWh). The largest cost is definitely on the batteries. Without batteries I think we could get a 3kWh for €9-10.000 incl installation. I don't know what they cost in the states but $23.000 seems very expensive.

OK - a desert rat is going to enter the fray!

I definitely agree with trying to do things to cut energy consumption before thinking of installing solar power - mostly because it will give you a truer solar array size if you end up going that way:
--insulate up to your correct R Value
--metal roofs with reflective coatings can save some serious $$ and are great for rain catchment
--duct sealing is also a big energy saver
--shade will keep you cool - I'm going to ditto planting trees in a solar arc around your home to shade it in the summer time. Around here, we're told by the experts to plant trees approx. 15 ft away from the east, west and south sides of the house (but our desert trees tend to be shorter than other places so maybe you could plant them further away). There is an EXCEPTION to this rule. IF YOU ARE PLANNING TO INSTALL PV PANELS - DON'T PLANT TREES ON THE SOUTH SIDE - they will shade your panels and need to come out.
--if you are tree adverse, use EXTERIOR blinds on your windows to stop heat transfer from sun hitting the glass of your windows (25% of your heating and a/c energy bill is lost through windows - either by heat gain in the summer or heat loss in the winter). Dual pane windows with wooden frames are also an option. Trellises with thick vines are another good option - they won't damage your house in a storm. Low sun is going to hit the East side of your house in the morning, and the West side in the afternoon. Thick, deciduous vines will act as a baffle for this low angle sun in the summer (the NW afternoon sun in the summer is particularly bad). Here in Phoenix, I have multiple shade layers comprised of overstory trees, tall shrub "solar baffles" strategically located to block that low morning and evening sun, vines on trellises and exterior shades. All help greatly!
--Paint your house white or another light color to reflect light and heat away from it (albedo effect).

All those things (and probably a bunch of others) will lower your AC bill. There are FEDERAL tax credits still available for most of those projects for another couple of years. Check out this site to find rebates: http://energy.gov/savings

Some things that might NOT work in your HUMID climate:
--"Leaky pot" cooling - usually you need dry air for this to work as the cooling comes from evaporation.
--Solar chimney - these are often used in conjunction with water - like a fountain (middle east/north Africa), the aforementioned leaky pot or even just a tub of water located on the cool side of the house. While a solar chimney may move some air, it probably wouldn't feel all that much cooler in the really humid temps.
--if you have a wind corridor that goes through your property, you can seek to enhance it by NOT planting foliage in the path of the prevailing summer breezes.
--which begs the question - is your area appropriate for wind energy??

I'm going to bump this old thread, because I had an idea I wanted to share that would be useful to the original poster. I already shared my "cool room" idea, although I admit that I never followed through with it myself. However, I've been taking hints from Paul Wheaton's old "hot spot" video (the one where the assistant is the test subject, and is using a heated keyboard, spot lamp, etc to keep warm in a *really* cool room). I've bought a set of electric mattress pads (much better than heating blankets) for my wife, myself and my kids old enough to not pee on it. It not only made for great brownie points with my wife, it permitted me to set the programmable thermostat down to 64 degrees overnight without my wife having trouble sleeping. They worked great for two winters. Recently (because it's been hot here, and my central air is slowly dying and repeatedly freezes up these days) I've been thinking of other ways to keep my wife cool overnight sans central air. My wife, like many wives, will complain about being too hot in the daytime; but she *must* be comfortable enough to sleep well, or everyone suffers later.

So I started doing some research. I've seen the videos about how some guys make a 'spot cooler' by cutting a fan & flexible dryer vent into a bucket lid, and then place a frozen jug of ice into the bucket. Quick, simple...check. Sure, it requires the use of freezer space (so off grid is still probably out of the realm of realistic possibilities) but it's also very localized. But the fan is too loud, and the air volume too high, to work as a cooling unit at night. Then it hit me. I'll use one of those 'silent' aquarium air pumps inside of a styrofoam cooler, and push the air to a large airstone under the sheet at the foot of the bed. With the sheet tucked properly at the foot and sides of the bed, cool air would be (slowly, depending upon the size of the pump) pushed towards the head of the bed. In this case, faster is not better; since too much air flow would not only consume your ice before morning, but make Momma upset. I would expect that, with a slow air flow, condensate would be contained inside the cooler, and air moving through the tubing would be both cool and fairly dry, but I'm likely to loosely wrap the air stone inside a small towel just in case. The hum from the 'silent' air pump would be muffled by the styrofoam cooler first, and more so by placement under the foot end of the bed. I've ordered a 1.7 liter-per-minute (really small) air pump and an oversized air stone from Amazon, and intend to test it on my oldest daughter during the next hot night; because her room has the greatest temp swings (coldest in winter, warmest in summer; the heated mattress pad made her *so happy*) and I can boss her around. Depending upon her reports, I might then sneak it into my bed and use it on a muggy night that the AC can't keep up (which is often these days).

If nothing else, it would be a wise tool to keep around should the AC finally die.