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If you’ve been reading Trees Full of Money for a while, you are probably aware of how passionate I am about the use of geothermal energy to heat and cool your home. Using energy stored in your own back yard, Geothermal Heat Pumps can save consumers 70% or more on their yearly heating and cooling bills, and best of all ground source heat pumps have a minimal impact on the environment.
Unfortunately, the cost of a professionally installed geothermal system is prohibitive to most homeowners including myself. Until such time that geothermal systems become less expensive (or I get a significant windfall of cash) I would like to share my tips on an alternative way to harvest geothermal energy to “partially” cool your home during those sweltering summer days.
This method has been utilized by many homeowners in the northern states for years without them ever realizing that they were tapping into a source of renewable energy. I have simply perfected the process to get the most efficient use out of the cool air that is stored inside your home’s basement.
If your home doesn’t have a basement or suitable crawl space beneath it, you will not be able to utilize this technique but you may be interested in reading about it anyway.
What You Will Need:
1) A “below ground” basement or crawl space with direct access from inside your home, it also helps if your basement or crawl space has a small window that can be opened to add air flow.
How it Works
2) A small portable fan.
3) Optional: A portable dehumidifier
During hot summer days and cold winter nights, basements in our homes stay relatively mild when compared with the outside temperatures and the temperatures in the main part of your house. This is a classic example of how geothermal energy works.
The temperature of your basements exterior walls are regulated by the relatively constant temperature of the radiant heat trapped only a few feet down beneath the ground adjacent to your home’s foundation walls. These temperatures radiated through your basements walls and cool (or heats) the air volume inside your basement. The trick is getting this usually damp and musty cool air distributed throughout the rest of your home.
After some experimenting, I have finally come up with the most efficient method for achieving this goal.
I place a small dehumidifier in my basement the night before to bring the relative humidity down from over 80% to less 60% by the following morning. I also ensure that all of the window shades are drawn on the “sunny side” of my house to minimize the effect of the suns “solar” heating. If your has a relatively low humidity then the use of a dehumidifier may not be necessary.
If the outside temperature gets below 75deg during the night I will leave most of the upstairs windows open in my house with fans sucking in the “cool” air until the outside temperature gets above this level.
As the sun comes up and the inside temperature of the house begins to rise I wait until the inside temperature of the house gets above 77deg. At this point I “turn on” my geothermal system by doing the following:
I crack open one of the small windows in my basement just enough to let a little bit of airflow through. Then (with all of the other windows closed in the house) I crack open another window in one of my homes upstairs bedrooms with all doors open between the two windows so that air can flow through (tip: opening the highest window you have in your home will vent out the most hot air in your home [heat rises!]). You can also close of other areas of the house that you do not wish to cool to maximize the cooling effect in the areas of the house you frequent during the day.
I then place a small window fan in an upstairs window with the flow of air pointing out the window. This technique effectively suck air up from the basement through the house and then out the window.
The trick is to monitor the temperature of the air on the suction side of your fan as it is being pushed outside. Close the windows (and the basement door) and shut the fan down when the drop in the rooms temperature begins leveling off.
It usually takes between 30 minutes to an hour for all of the cool air to be circulated through depending on your fan’s power and how large your home is. If all has gone to plan, the temperature inside your home should have dropped a more tolerable 4-5 degrees. This may buy you a couple of hours time that you don’t need to run your air conditioner.
Caution: If you run the fan too long, all of the cool air that was trapped in your basement will be displaced by the warmer outside which will then be sucked up into the rest of your home negating the whole process. You generally only get one shot at this cool air during the day since it will take at least 6 hours for your cool basement walls to regulate the temperature of the new mass of warm air that has been displaced into your basement.
It may seem like a lot of work but you really get the hang of it after a weekend of testing and if nothing else this DIY geothermal energy project is a fun experiment to share with your family! Thanks for reading and be sure to check out some of my other articles on personal finance, and alternative energy! I am also curious to hear how this technique works for you, be sure to comment below with any successes, failures, or criticisms of this method!
Related Articles:
An Explanation of how Geothermal Heat Pump Systems Work
Insulated Concrete Forms (ICF): Green Building Technology
Do It Yourself (DIY) Geothermal Cooling System
Should You Pre-Buy Your Home Heating Oil This Year?
Do It Yourself Home Energy Audits
36 Ways to Reduce Your Home’s Energy Use
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Dude, Ben…That is Genius! I wonder how it will work in my house since I have a multi-level and all four levels are staggered. In other words, my house looks like a flight of staircases in a tall building. You go up one flight, you are on a landing, you turn and go up another flight, you are on a landing, you turn and go up another flight, etc. etc.
I don’t know about “genius”, but it is pretty cool to experiment with! I would pick which level of your house you spend the hottest part of the day in. Close off the other sections from that room and the basement and give it a shot!
This is a very creative tip. My parents have a basement that is the perfect place to hang out in the summer, sometimes you even need a blanket. Fortunately, it is a finished basement, so they can be down there during the day, and even sleep down there at night.
Wow! You’re like a mad scientist! I have this crazy picture in my head of you taking temperatures and readings all over your house. Very helpful and entertaining!
This is genius! I love it. I don’t have a basement, unfortunately, but I would try it at my parents’ house. One question though – will it work in reverse? Ie, heating the house? My guess is not, since the basement would still be cooler… ?
There will not be enough heat in the basement for this system to effectively work in “reverse” in the winter time.
And even in the summer time, you only have one shot to get it right. You should be able to keep your house cool for a couple hours longer without running the AC, but of course that depends on your home’s insulation properties, and the temperature outside your house!
Let me know how it works for your parents!
My husband really wants to do the geothermal heating, I will show him this post.
Another idea would be to close all the cold air returns in your house and open the ones in the basement. The basement walls and floor will cool the air as it passes through and the furnace will blow the cooled air into the house just run your furnace fan only.
This will change your basement into the cooling device for your home instead of the A/c
also this doesnt allow any hot air from the outside in and it recirculates the air you already have cold.
You may need extra cold air inlets in your basemnet most new homes are ducted with efficiency and cold spots in mind so you need to help it along with some extra cold air intakes in the basemnt
I just did this in my house about an hour ago my crawlspace temp is maintaining at 68.9 degrees my house is 75 degrees and it is 86 outside i will give an update as to any temp changes indoors and outside it is about 4 oclock now so its the hottest part of the day here in central illinois
ok its been a few hours the sun is really coming in our two front windows and front door but with just the fan running i am maintaining 75 degrees i think it is still 82 degrees outside
What you are doing is called “passive solar cooling” and homes could (actually should) be designed to take advantage of this. We are currently building a home in Florida which uses 600 linear feet of buried pipe to create underground airspace similar to the use of your basement for storing cool air. We are going a bit further with the use of thermal chimneys to create a gentle negative pressure inside the home which slowly draws cool air in from the underground tubes. This maintains a comfortable inside temperature even when blazing outside.
I’m going the other way. Trying to get the Heat out of that basement floor, using a makeshift heatpump.
http://forum.doityourself.com/showthread.php?t=361014
If I can get 25,000 BTU out of my basement for a few hours and then let it recover for 6 hours, it might be worth the $399
Hey Ben… I have considered doing something similar in a new construction. Using PVC pipe of 6″ or so size around the foundation then pipe it into the void beneath the AC closet so the negative pressure created by filtering will suck the air through the burried pipe from a wall vent hooked to the PVC pipe. Run the pipe as far as you can afford around the foundation and up into a wall then attach it through a duct box and cover with a decorative vent cover. possibly use light filtering material to prevent bugs or trash being sucked into the pipe.
What does anyone think about that?
Here is a link to a very complete site on all you need to know about Geothermal
Geothermal Heat Pump at Home
And if you browse the archives , you will find around 100 FAQs about geothermal (ground source) heat pumps
I have a 150 foot deep abandoned well on my property, I was thinking about using it as a shaft for passive geo cooling for a workshop area in my barn. It would draw in up to 100 degree air from outside (here in Texas), pass down the 150 foot shaft, then back up the shaft (in a separate 2″ tube) and into my 12×16 insulated room in the barn. If it doesnt work, I may add a cold water drip to allow evaporation to assist the cooling of the air down the hole. My concerns are wether I will be able to suck enough air back up through a 2″ pipe to cool a room that size – it is very well insulated. Would PVC be OK to use? Is 150 feet (300 feet total, since the air will go down the 4″ casing, then up thru the 2″ PVC) enough distance to achive ground temerature? If this works I may dig a trench 3′ deep around my property and make it about 300 ft long, and drop a 6″ pipe into the ground and simply cool the outside air with the ground and pump it into my house. Step 1 is to try the well, then step 2 would be to build the trench and shut down my AC units. I may have to create several trenches in order to cool the entire home, but, it will never wear out, never need repair -except for replacing the whole house fan on occasion. Probably cost me a couple grand if I do it myself. Much cheaper than a whole dual AC system, and the summer cooling bills should be pretty low. – it would just be the cost of fans to draw in enough air to keep the house cool.
Any thoughts on if just a passive system will work?
Jim,
The nature of your question goes beyond my level of expertise in the area! However, perhaps some other readers on this site will be able to answer your question! Let me know how your DIY geothermal system works out!
Ben
to bryan and jim j
mother earth magizine from the early 80’s had an article on this exact use. I have been wanting to try it for years but did not have the nerve. I think 6 feet was required depth and I think 300 feet in length, but not sure. ie the temperature is the same from 6 feet or lower. Not sure of the size of the diameter of the tube. I live on 3 acres with plenty of room to dig but don’t want to spend the money for failure. I would appreciate any input.
fred
I don’t understand the pre-occupation with buried or subterranean air-vent pipes.
It would be much cheaper and healthier in the long run to run PEX water pipes underground in the back yard, in a closed-loop system. Caution: pipes have to be buried at least SIX feet deep; going deeper appears to provide a little cooler environment at a much higher cost. Use a small pump (low watt) to circulate the water through a large radiator (new or old), and blow air through the radiator. Be prepared to pipe condensate from the radiator into a drain, either outside or into the sanitary sewer.
If you have a well, fine. But please don’t go for the excessive cost (we were offered) to bore THREE thirty-inch wells 100′ deep to cool your piping, to provide 3-ton AC capacity…..this by a NW Florida geo-thermal “expert” company.
The air-movement fan and pump can be thermostatically c0ntrolled. The radiator can be enclosed in a foam-board plenum (use dry-wall screws and good duct tape to construct and seal) and air can be distributed by existing (or new) air ducts. Filter the air where it goes into the plenum to keep the radiator clean.
Or, you can build (new) a super-insulated home with AAC (Aerated Autoclaved Concrete) walls and and insulated roof (poly-iso), like we are doing in Southern Alabama. We will simply install the radiator in the attic and air-cool the entire structure, with bleed air (from the plenum) to cool the hurricane room and garage. No duct-work, except to the hurricane room and garage. Radiator will be mounted high in the attic, in an open-ended plenum, and, guess what, cool air will drift down through ceiling vents into the house. There will be two return air vents installed (at either end of the house), near the ceilings where some stratified warmer air will collect to return air back to the radiator plenum. There will also be a “fresh-air” vent from the outside into the return air duct to the plenum. These will provide the needed air “circulation feeling”, as well as the use of exhaust fans in the kitchen, two bathrooms and laundry room.
We’re building a 1700 square foot home with attached 400 square foot garage. On a warm Summer day of 90+ degrees, ground temperature at -6 feet is 58-64 degrees here (depending on accuracy of my measuring equipment (64) versus local wisdom (58). Insulated chases have been built into the back walls of the house to minimize coolth loss. Best estimates from much internet searching look for 100′ buried 3/4″ PEX per ton of conditioning. Our super-insulated home requires a “normal” two-ton HVAC system. We are going to be very conservative and bury 500′ of PEX, which is probably over-kill.
We also are using radiant floor heat, so we are not concerned about “mixing” systems, although the 58-64 degrees sure does give one a leg up on a “basic” warming source, if you were using a “normal” ducted air system. But, our basic premise is this: cool air falls (so we’ll start high in the attic with this source) and warm air rises (so we’ll have Pex hot water in the floor). This type of split operation is the most efficient use of normal air circulation.
For those of you who may doubt the value of super-insulating a building, consider these facts: We have completed the 400 square-foot garage walls with AAC block and (so far) R-30 built-up roof, with steel shingles.
On June 5, 2009, at 1PM CDT, sky was clear with 86-degree outside (shaded, protected) temperature (sunlight actually measured 110 degrees). Inside the garage, with no doors and no windows installed (basically an open structure with NO roof vents), the temperature measured 79 degrees (outside and inside measurements were taken about 3′ above the floor). These temperatures were confirmed by a visiting building contractor. We personally have observed similar measurements in two other open AAC buildings (no windows or doors installed).
But, try and find information for this type of installation on the internet! Good luck! The whole geo-thermal idea has been hi-jacked by companies who want to sell you heat-exchangers and add-on hot water equipment, all at big-bucks prices.
Good luck with your project. Just watch out for mold and fungus in those air-tube circulation systems!
Are you really saving anything? Seems to me running a dehumidifier for 7 hours the night before in the basement and a fan all night long is simply a trade off for running the A/C.
Even if you do cool the house by 4 or 5 degrees as you say, leaving the windows open and pulling the air up from the basement(dehumidifier or not) when the A/C does come on it has to deal with the responsibility of removing the humidity from the air before comfortable temperature change can occur. Seems to me your just robbing Peter to pay Paul.