DIY Geothermal heat pump trenching and plumbing.

Has anyone done a geothermal heat pump?  We dug a huge trench 30” deep X 24” wide and are wondering what supply and return lines, insulation, signal wire, power wire, etc, are required in the trench for a future system. We have plenty of space out here in the desert for the poly pipe loops and trench. The trench is 120 feet to the pond pit. I’m considering placing the loops in the hole in the ground that might be a future pond. Has anyone done this? How was your experience with DIY geothermal. Or did you decide to pay a company. We plan on adding a solar energy system also to help cover the electricity.

As we need to fill in this huge trench soon so my immediate questions are what goes in it. Do both the supply and return lines need to be insulated? Or only the supply?? Is 1” poly pipe big enough for a small house?

I’m going to build a standard cob rocket mass heater but that will not help with cooling. What website did you use for sizing and building the geothermal?

Ive read the soil type is important for the geothermal coils. Our soil is fine silty clay. No rocks. Alkaline.  Thanks.

Pipe Lenght = 600ft per 1ton (2,400ft for 4ton)
Pipe Loops = 1 loop per ton aka 600ft per loop (4loop for 4ton)
Flow Rate = 5gpm per loop(aka per ton), so 20gpm for 4ton (for 1inch pipe*)
Pipe Depth = below frost-line, 4ft usually (but less if pond/lake sourced or in a warm zone)
AC Load = 30btu/sqft (4ton for 1600sqft)
Heat Pump = 48,000BTU (4ton)
Pond Depth = 10ft (at least 6ft of water in the dry season)
Pond Size = max of 20ton of cooling per acre and or10ton of heating per acre (4ton = 0.2acres)
Pond Size = (100ft by 100ft by 10ft sounds about good for 4ton)


I am thinking food-grade gycol-water mixture so that it doesn't freeze and brust. I don't think any insulation/wiring and such is needed. Just the bare pipes. Maybe use PVC so tthat if you have to empty the system it doesn't collapse from its weight, but just regular poly for the pond.

What size house will you be cooling?
What level of insulation will you be using?
Will you use a ERV?
What temp will you keep the house at in the summer 65F or 79F or ??
Will you move most of your heat sources outside for the summer (cooking, clothes drying, showers, etc) or at least vent them?

Thanks S Benji.
I’m pretty sure we can get by with 2-3 ton GHP but will check that. House is only 1400 sq ft and well insulated. I may combine the geothermal heat pump cooling with a evaporative cooler as they are cheap. I’m going to take a screen shot of the numbers you posted and go over it. Why do you suggest PVC? I was under the impression that poly pipe HDPE is commonly used for GHP.

We don’t cook a whole lot. But it was 105 degrees here for 45 days straight last Summer. What’s a ERV?

Yes HDPE is the way to go, I wasn't too sure what type of polypipe you were thinking of using.

I also think that you can get away with a 2ton system if your space is well insulation and you work on your sources of heat(baking/cooking/shower/etc). SO all you would have to do is scale all the number I gave you down by 50%.

ERV = Energy Recovery Ventilation, it basically send cool air outside and pull hot air into the house for ventilation, but will they are passing each other, they reach equal temp and so not all of your coolth or warmth is lost. You can throw it in the bathroom so that it is always sending bathroom air outside at say 40cfm, and then dump the filtered outdoor air in a shared space say the hallway/livingroom or the air handler. https://www.supplyhouse.com/Fantech-FIT70E-SE-Series-Energy-Recovery-Ventilator-4-Side-Ports-up-to-1200-Sq-Ft

I remember now. Energy recovery ventilator. Well, the heating season is so short I’m not sure it’s worth it. And I’m not sure the ERV helps during the cooling season which is the big load. I usually am forced to go North like bird but decided to get serious and build a system to cool the house. I may paint the roof white and line the attic with silver foil and all that stuff.

S Bengi wrote:Yes HDPE is the way to go, I wasn't too sure what type of polypipe you were thinking of using.

I also think that you can get away with a 2ton system if your space is well insulation and you work on your sources of heat(baking/cooking/shower/etc). SO all you would have to do is scale all the number I gave you down by 50%.

ERV = Energy Recovery Ventilation, it basically send cool air outside and pull hot air into the house for ventilation, but will they are passing each other, they reach equal temp and so not all of your coolth or warmth is lost. You can throw it in the bathroom so that it is always sending bathroom air outside at say 40cfm, and then dump the filtered outdoor air in a shared space say the hallway/livingroom or the air handler. https://www.supplyhouse.com/Fantech-FIT70E-SE-Series-Energy-Recovery-Ventilator-4-Side-Ports-up-to-1200-Sq-Ft

If the house needs more than 2 tons cooling I’m moving ahah. The concept of a sand battery is a fun idea. Imagine being able to store much of the heat pumped out of the house all summer then reuse that heat in the winter. Of course it won’t be 100% efficient so would need some energy input.

ERV unlike HRV 100% helps in the summer AC season. I recommend getting one.

Yes, insulation and dealing with heat source will be a major help. Have you thought about a green roof. You could plant all your veggies up there, the plants and water will keep your house cool, and it will be a cool garden spot to hangout in. You probably only need  3inch of growing media (think hydropnic), with the water recirclulating so it uses less water and it cools the roof and it produces a harvest.  

Whats your average winter temp for me it is 30F for the coolest month (Jan) so if its even warmer for you, It's possible that just winter solar gains is all you need.

S Bengi wrote:ERV unlike HRV 100% helps in the summer AC season. I recommend getting one.

Yes, insulation and dealing with heat source will be a major help. Have you thought about a green roof. You could plant all your veggies up there, the plants and water will keep your house cool, and it will be a cool garden spot to hangout in. You probably only need  3inch of growing media (think hydropnic), with the water recirclulating so it uses less water and it cools the roof and it produces a harvest.  

I wonder if a green roof would work on this house. I’ve grown succulents on a small shed roof before. But I didn’t care about the resale value of the shed. I thought about building a shade structure around the south and west side of the house. It’s blazing hot there and the walls heat up. And misting but dont like using the extra water.
 Ive read your posts going way back in years. Thanks for all the positive input. I’ll consider these ideas.

Please describe the "pond pit." I assume this is a water-filled dugout? How much volume, and how deep?

Douglas Alpenstock wrote:Please describe the "pond pit." I assume this is a water-filled dugout? How much volume, and how deep?

Hi Douglas. The pond pit is a borrow pit we got the soil from to place our shop/barn on as this is floodplain. It is silty clay. Presently it’s 20’x50’, and slopes down like swimming pool to 7’ deep.  I calculated it at about only 50,000 gallons presently but I might dig it out further. I was trying to stack functions by using the borrow pit for something. Also I wanted to see what the soil horizons are here. I’m considering making Adobe blocks and could use more of the soil for that. This would make the pit bigger. I was also having fun with the thought of a natural swimming pond. The edges of the pit are excavated  about 20” deep X 7 feet wide for gravel as filtration medium. Also as terraces to grow aquatic plants on sides of the pond One major issue is it will not seal without pond liner because the steep sides would not hold bentonite clay. If we bevel out the sides then bentonite or glaying might work.

I’ve had other fun ideas such as floating solar panels. Floating plants, a floating cabin, etc. Ponds and water can be fun.

I’ll add it’s currently completely dry presently as are all the cattle pits here that do not have water pumped to them. I’m channeling a swale to the pit and the roof runoff. I’m curious to see what it does during the monsoon. Im in the observation phase of the design. I’m going to fence it off to keep the cows from trashing it when it does have water. Our perimeter fence might get breached lol. Thanks for asking, what are you thinking ?

S Bengi wrote:ERV unlike HRV 100% helps in the summer AC season. I recommend getting one.

Yes, insulation and dealing with heat source will be a major help. Have you thought about a green roof. You could plant all your veggies up there, the plants and water will keep your house cool, and it will be a cool garden spot to hangout in. You probably only need  3inch of growing media (think hydropnic), with the water recirclulating so it uses less water and it cools the roof and it produces a harvest.  

Whats your average winter temp for me it is 30F for the coolest month (Jan) so if its even warmer for you, It's possible that just winter solar gains is all you need.

I’m inspired by these ideas to make this house habitable without being a big energy liability and food desert. We are currently still burning propane for heat. The average winter temperature is about 45 degrees. It’s frosty then sunny and warm to about 60 most winter days. So passive solar gain could work well here. I’m now inspired to make this a envelope house and build Adobe walls around the E,, W, and South with solariums to gain warmth. A hybrid Earthship sort of house. It would probably never perform as well as a Earthship but we are in mild southern New Mexico not cold northern New Mexico.

Winter Temp = 45F Daily swings of (30F to 60F)
Summer Temp = 95F Daily swings of (80F to 110F)

House Size = 1400sqft
Roof = Moist Green Roof at 95F and R20+
Walls = R20+, with a summer greenwall (vines growing on a lattice?)
Floor = R20+, high thermal mass to store coolth(summer) and warmth(winter)
Heating = Radiant Floor Heating + Chiller (easily transfers heat from solar gains + heat pump + RMH)
Ventilation = ERV (doubles as bathroom vent), so that it tempers the air and filters it
AC = 2-4ton, multi-zone minisplit, could be a chiller so less toxins in the house, with the low humidity you can also chill the floor, could make Hot Water too.

Heatpump/Mini-split
Pipe Lenght = 600ft per 1ton (1,200ft for 2ton)
Pipe Loops = 1 loop per ton aka 600ft per loop (2loop for 2ton)
Flow Rate = 5gpm per loop(aka per ton), so 10gpm for 2ton (for 1inch pipe*)
Pipe Depth = below frost-line, 4ft usually (but less if pond/lake sourced or in a warm zone)
AC Load = (usually 30btu/sqft so 4ton for 1600sqft, but with all your thermal mass+insulation only 2ton)
Heat Pump = 24,000BTU (2ton)
Pond Depth = 10ft (at least 6ft of water in the dry season)
Pond Size = max of 20ton of cooling per acre and or 10ton of heating per acre (2ton = 0.1acres)
Pond Size = (70ft by 70ft by 10ft sounds about good for 2ton)

Jeremy Baker wrote:

Douglas Alpenstock wrote:Please describe the "pond pit." I assume this is a water-filled dugout? How much volume, and how deep?

Hi Douglas. The pond pit is a borrow pit we got the soil from to place our shop/barn on as this is floodplain. It is silty clay. Presently it’s 20’x50’, and slopes down like swimming pool to 7’ deep.  I calculated it at about only 50,000 gallons presently ...

Thanks Jeremy. I just wanted to make sure I understood the system design you were proposing -- the heating/cooling capacity does not come from piping in the trench that contacts soil, but from the mass of water in the pond.

What typical soil temperatures would you expect in your trench, summer and winter?

Douglas Alpenstock wrote:

Jeremy Baker wrote:

Douglas Alpenstock wrote:Please describe the "pond pit." I assume this is a water-filled dugout? How much volume, and how deep?

Hi Douglas. The pond pit is a borrow pit we got the soil from to place our shop/barn on as this is floodplain. It is silty clay. Presently it’s 20’x50’, and slopes down like swimming pool to 7’ deep.  I calculated it at about only 50,000 gallons presently ...

Thanks Jeremy. I just wanted to make sure I understood the system design you were proposing -- the heating/cooling capacity does not come from piping in the trench that contacts soil, but from the mass of water in the pond.

What typical soil temperatures would you expect in your trench, summer and winter?

This geothermal is fun to design. I understand the heating/cooling capacity comes from the pond but the trench from the house to the pond will only be 30” deep so I do not want the chilled or heated water to be affected by the soil temperature as it goes for the house to the pond or the pond to the house. Also I’m not sure if the heat pump reverses the direction it’s pumping the water when it switches from heating to cooling. It’s different concepts than I’m used to. I’ll look for soil temperature maps. I’m told the soil gets very warm in Summer so I’m thinking of floating solar panels to shade the pond (and reduce evaporation) and make it deep like at least 10 feet. Fun design challenges.

Jeremy Baker wrote:Fun design challenges.

Indeed! But I think you're asking the right questions.

Lets focus on your Outside Loop (GHX)
Seperating Distance = 24inches (not the usual 48inch or 120inch)
Pond Temp = 95F (average daily air temp = average temp of 10ft deep pond)
AC Exiting Water Temp = 105F ( you will now have to turn up your flow rate to 10gpm per ton vs the usual of 5gpm/ton)
Usual Temp Delta = 10F (this is the usual temp delta, but your entering water temp will not be the pond temp sadly)
AC Entering Water Temp = 100F (it picked up some heat along the 110ft run from the exiting piping in the tiny 24inch trench, so your flow rate will have to double)
Flow Rate = 10gpm per ton (not the usual 5gpm due to hotter entering water temp)

Pond Issues
I am however concerned about the water levels in your 100ft by 100ft by10ft deep pond in the desert.
Evaporative Loss = ??
Irrigation Loss = ??
Animal Hydration Loss = ??
Leakage Loss = ??
Swale Inflow = ??
Rainfall Inflow= ??
Well pump Inflow = ??
Greywater Inflow= ??
Creek Inflow = ??

S Benji. The numbers help place the design in perspective. I was hoping a body of water might have a lower average temperature due to night time to cool down and if it has a small surface area exposed to sunlight but is deep. The deep ponds I’ve experienced are cold in the deep part and only warm in the shallow areas. Also I was considering burying the loops under the pond liner and deeper than 10 feet but that might reduce conductivity.
Evaporative loss is a concern here in the sunny windy low humidity desert. A small but deep pond might help with that. Also a wind berm might help.

Pumping 10 gallons or higher per minute sounds like a lot! I’d prefer to keep it lower than that. But I’m concerned that the size and investment of the geothermal loops might just be too much.

The cooling season is also the monsoon season with a average of 15” precipitation. So I’m curious to see how a swale and roof catchment  works.

I’m considering building a Adobe walled room around the E, W, and South side of the house and growing food in a passively conditioned space. With a high mass floor this might temper the house temperatures passively thus reducing the need for active cooling. The performance depends largely on night time temperatures.

Also, a green wall and perhaps green roof as are design possibilities as  you suggested. Thanks.

To help give you better info can you supply the summer average temp for the location. I use this website.
https://lookups.melissa.com/home/zipclimate/zipcode/?zipcode=87123

If I were to change your location to Albuquerque NM, the average summer temp is about 75F.
Pond Temp = 75F
Adobe Wall/Floor Temp = 75F
ERV incoming Air temp = 78
Courtyard/GreenWall air temp = 81F (up to 10F cooler than outside)
Outside Air Temp = 90F
(with this setup you might not even need AC and if you do a simple 1ton window unit would be good enough. With the low humidity, I would just cycle the pond water thru the floor.

Winter
Outside Air Temp = 23F
Attached Greenhouse = 33F (57F during the day)
ERV Incoming Air Temp = 51F (halfway between indoor and greenhouse, 63F during daytime)
Room Temp = 70F (5F lower than the floor temp)
Radiant Floor Temp = 75F (15F lower than the water in the pex pipe)
Radiant Water Temp = 90F (really this could just be from solar gain or heatpump or instant HW tank or RMH)
Pond Water Temp = 35F