EcoRenovator  

Go Back   EcoRenovator > Improvements > Geothermal & Heat Pumps
Advanced Search
 


Blog 60+ Home Energy Saving Tips Recent Posts Search Today's Posts Mark Forums Read


Reply
 
Thread Tools Display Modes
Old 09-24-19, 04:41 PM   #1
menaus2
Apprentice EcoRenovator
 
Join Date: Feb 2011
Location: Driftless Region, North America, Earth, Solar System, Orion Arm, Milky Way Galaxy,Virgo Supercluster
Posts: 116
Thanks: 13
Thanked 35 Times in 25 Posts
Default Earthtube-fed air conditioning?

I have an idea that I haven't been able to find really discussed elsewhere online, so I thought I'd throw it out here.

Basically, instead of using earth tubes to directly condition a space, you would use it to feed cooled air to a 2-hose portable air conditioner.

Potential advantages:
1. Increased efficiency for the air conditioner
2. Eliminates mold concerns associated with earth tubes since heat exchange air and
3. Portable A/Cs are relatively inexpensive ~$400, can easily be upgraded/swapped out.
4. Earth tube design and materials could be simplified since mold isn't so much of a concern.
5. Simplicity/fail-safe nature of air as a fluid. No leaks, special fluids to worry about.

Potential Disadvantages
1. Alternative GSHP, or A/C's could be inherently more efficient with less work.
2. Static pressure in earth tubes, need for booster fans
3. Cost/work involved in excavation for tubes.

Questions:
1. How much of an efficiency gain would the air conditioner see from pre-cooled air?
2. What sort of depth of pipe would be necessary? (a/c only) and in what kind of climates?
3. Thermodynamic effect of condensation in the earth tube?

Cheers!

menaus2 is offline   Reply With Quote
Old 10-09-19, 11:24 AM   #2
menaus2
Apprentice EcoRenovator
 
Join Date: Feb 2011
Location: Driftless Region, North America, Earth, Solar System, Orion Arm, Milky Way Galaxy,Virgo Supercluster
Posts: 116
Thanks: 13
Thanked 35 Times in 25 Posts
Default

Hard to dig up solid information on the impact of outside air temperature and air conditioner efficiency. The closest study I've been able to find is here:

https://aceee.org/files/proceedings/...193-000015.pdf

Figure 3 & 4 show massive power consumption differences (0.2KW at -5 to 0 deg. F difference to inside building vs 2.5-3KW at 30-35 deg. F difference) Basically, 15 times less power used.

The question is teasing out how much of that is simply the difference in building cooling load.
If the air tubes can cool 90 deg. F outside air to 65 deg. F (pretty average summer soil temp for only a few feet underground in Wisconsin) and the air conditioner reduces that to say 50 deg. F then could we say that the earth tubes are doing roughly 63% of the cooling? My totally uneducated, ignorant calculations would suggest the A/C would have to work about 3x less.

So would a 11 SEER $400 portable A/C combined with earth tubes perform similar to a 33 SEER $1,600 minisplit?
menaus2 is offline   Reply With Quote
Old 10-09-19, 06:42 PM   #3
MN Renovator
Less usage=Cheaper bills
 
MN Renovator's Avatar
 
Join Date: Nov 2010
Location: Minneapolis, MN
Posts: 940
Thanks: 41
Thanked 117 Times in 91 Posts
Default

The entering air of an AC condenser being 65 degrees instead of 90 degrees doesn't reduce the power consumption by that much. My compressor uses about 2200 watts with a 90 degree entering temperature and 1900 or so with a 65 degree entering temperature and the output capacity at the evaporator is more but the total likely doesn't end up being more than about 15%.

The best source of information for entering condenser temperature, power usage, and output with a TXV driven unit can be found from HVAC manufacturers information. Goodman has a solid product specification sheet for their units.
https://www.goodmanmfg.com/pdfviewer....pdf?view=true

One more important factor - An AC condenser requires unimpeded airflow, they can't handle much static pressure without losing flow, if you are adding a blower to push air through an earth tube, you MUST add that power back in, which could cause a net loss in efficiency.
MN Renovator is offline   Reply With Quote
Old 10-13-19, 01:20 PM   #4
Ron342
Apprentice EcoRenovator
 
Join Date: Feb 2010
Location: Maryland
Posts: 120
Thanks: 26
Thanked 12 Times in 8 Posts
Default

If i remember correctly some did on this blog built one of these a couple yrs ago for his air coupled outside unit. Maybe do a search and i’ll also see if i can find my bookmark
Ron342 is offline   Reply With Quote
Old 10-23-19, 12:13 PM   #5
menaus2
Apprentice EcoRenovator
 
Join Date: Feb 2011
Location: Driftless Region, North America, Earth, Solar System, Orion Arm, Milky Way Galaxy,Virgo Supercluster
Posts: 116
Thanks: 13
Thanked 35 Times in 25 Posts
Default

If the 15% reduction turns out to be accurate, it would seem to be the final nail in the coffin for the idea. It looks like a high SEER mini-split would be the far more economical choice, and a D/C solar one could make it completely off-grid.

I like the fail-safe simplicity of earth tubes, but extracting the cooling while isolating a potentially contaminated air stream in an efficient way might not be doable. It would be interesting to see some real world results from that Blog Ron342!

menaus2 is offline   Reply With Quote
Reply


Tags
a/c, air conditioner, earth tube, geothermal, portable ac

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 08:01 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Ad Management by RedTyger
Inactive Reminders By Icora Web Design