At $.22 peak vs $.07 off peak, I would use a water tank to store heat/cold. Payback is quick if you have space for one.

Running the 220W pump & air handler all day with a COP of less than 2 at on 22 cent electricity for a miniscule amount of sensible cooling makes little financial sense if you can be running the compressor with a COP north of 5 at a much lower duty cycle to achieve the same or better cooling. (What flow rate on the loop do you get out of your 100 watts of pump?)

You can still use a set-back strategy to pre-cool the place when the rates are low.

Hi everyone,

I'm new to the forum. I'm currently a student in my last year of a technologist diploma. I have done work in the construction industry for quite a few years in a few different areas. I have been doing a research project on earth tubes and their potential for cooling throughout the summer. I have a blog where I have been posting my progress and results. I am very interested in passive technologies and incorporating them into residential construction. I have only looked at the temperature potentials. I did not have the funding to look into issues of contaminated air, water drainage or offgas, radon gas concerns. My results have been interesting and I think this type of system has good potential to reduce energy demands for cooling, and heating. My climate is an interior desert in British Columbia. I would love anyone's feedback or ideas. I'm new to this part of the building industry(residential and mechanical design). My blog and research can be viewed at http://aret2220carrier.blogspot.com/. I have lots to learn, but feel this small system would go a long way towards reducing energy use if used as a fresh air intake for HVAC systems.

I am an engineer and have worked with earth tubes for heating and cooling of self heated structures for 30 plus years. What is it you want to know or learn?

Brian

jonr I have 16k gallons of hot water storage in our indoor pool I do only use the geothermal off peak, very rarely on peak only if we need to heat up the hot tub with guest over.

Dana I do use setbacks I gain about 6F in summer with nothing and about 4F when circulating the geo field. About 1/2 the reason is to keep the house cooler on peak, but warming up the field for use later doesn't hurt either. I also have extra solar PV power, more than enough to run the circ pump and furnace fan without drawing from the grid. I don't know what the smaller pump moves, but it is 1/2 the size of the two units on the main geo unit, so I am sure it is much less.

Quote: I am an engineer and have worked with earth tubes for heating and cooling of self heated structures for 30 plus years. What is it you want to know or learn?

I am very interested in this technology. I have had very limited exposure to cool tubes.

The cool tube sys( CTS ) was on a 1800sf house insulated with 3 layers aluminum foil ceil'g and walls. I don't know how many lineal ft was used but the sys performed very well. Worked well until mold started to grow in the tubes. Seems the contractor digging the channels made them level and after a while the tubes settled down away from the house allowing water to pool. My feeling was that if the tubes had sloped towards the house and had a run off tube that it would be working today, 20 yrs later. Seems to me the tubes were 8 ft down. This was a closed circuit sys.

By the way this house also had a sun porch that fed hot air to a rock bin in the basement. Last contact I had with owner was about 5 yrs after construction. That sys was still heating the house.

I have wanted to see another air tube sys but I'm concerned that even with slope to house that mold could still grow. PVC is notorious for mold growth. Any suggestions?

There is a website that has a tube configuration that is more complex than the straight line sys I saw. I believe the web site is: freeairconditioning.com.

Do you have a web site or could suggest some where I could get more insight on these sys?

I believe that as the ZPE devices come on line for home use that the ZPE units along with foil insulated homes equipped with CTS and solar heat will be a big boon. The foil, CTS and solar heat will mean a smaller ZPE for the home owner.

The gov, oil companies and utilities have been suppressing foil insulation for over60 yrs in this country. I believe the same will, is happening, with the ZPE technology. Things could get messy if the public really becomes aware of what is going on.

I custom design self-heated zero energy homes and systems. I often use earth tubes, if they are the most economical solution. Using earth tubes requires knowing the max BTUs of cooling, max BTUs of heating, humidity drying needs, thermal buffering needs, total thermal storage needs, required air movement, climate, solar aptitude, solar insolation, building design, wind exposure, flora situation, etc. Understanding the interactions of all of the above is needed to adequately design the earth tube system.

A few simple rules of thumb:
1. No corrugated pipe, no areas where water can puddle.
2. Planned drainage is a must for the condensate.
3. Dirt thermal conductivity is limited to 0.5 BTUs /ft. hr. ºF
4. Dirt thermal capacity is limited to 0.20 BTUs per pound per ºF
5. You need to design in a minimum of a working safty factor of 2 or 3 when sizing.
6. Typically the design has multiple tubes that with at least 1/2 the tubes can be reversible.
7. 1/2 tubes to top of thermal loop, 1/2 to bottom of thermal loop.
8. If 50 feet of rise can be designed into the loop it can be driven with convection.
9. Due point has to be monitored and air velocity needs to be understood.
10. You can design in thermal recharge of cold field with water field soak.
11. If pipes are dried out by air movement once a day they will never mold.
12. 4 inch PVC tubes can be drag cleaned with a rope and a bleached rag easily.


Yes, I have a web site, is http://www.zehtalk.com/. It is about home design and building, not specifically earth tubes. If you have additional questions you can call me at (360) 567-6681.

Brian