Homebrew "passive"? Geothermal

[Dan M]

ok, I want to replace the 1500 watt submersible heater that I have to use to keep the horse trough from freezing.  Seems this is a great place to use ground heat, since I'm just aiming for "not frozen", rather than "room temperature".

We pay about $0.09/kwh, so a 1500 watt heater, that bareley keeps up when it's really cold and/or windy, costs me about 13.5 cents per hour to run, or in a 24 hour day could cost around $3.25 per day.  A month of really cold weather can really start to add up.

I need to rent a trencher for another project anyway.  I'm told it will go down about 5 1/2 feet.  I'm looking at burying tubing, recirculating it through the trough.  It appears that 100w pump can transfer as much heat into the tank as a 1500 watt heater.

The numbers I have at this point:

2 gallons per min, 5 degree F delta T ----->   1408 watts

linear with respect to both gpm and delta T.

I think I'll need to insulate the tubing from around the frost line up to the tank.  The question I have are:

Will black ABS tubing work?  I assume copper would be much better for the heat transfer, but how much better? and it is worth the $, when I could use twice as long a run of ABS for less than the same $.

Also, I assume more surface area is better.  Should I consider 2 parallel runs of 1/2" tubing, as opposed to, for example, a single run of 3/4" ?

Rather than trial-and-error my way through this are there any recommendations for tubing size, length, flow rate, etc?

Thanks in advance,

Dan M

[SparWeb]

You need one of these!

Sorry I don't know anything about geothermal works.  My approach was to use FLOATING deicers but insulate all around to keep in as much heat as possible.  There are several other insulated trough boxes on the BuildItSolar website.

If you don't have much sun in the area, you can build the box without the window.  I have one like that, too.

[spinningmagnets]

Having an insulated lid on the tub with a hole just big enough for the horses snout would be a big improvement. Insulate the tub on all sides and the bottom too. They will be suspicious of the new set-up, but when they get thirsty, warm water will overcome their apprehensions.

For geothermal, I would borrow/rent a well-auger (one-foot diameter?) and dig as deep as is convenient. Drop in a loop of plastic pipe and back-fill with smooth mud.

The down-flow leg should be insulated (cold sinks) and the upflow leg should be exposed to the 50F-degree soil (warm rises). Cold sinking leg should draw from the bottom of the tub, and the warm rising leg should spill to a level under the water-line near the top.

Put a Small savonius VAWT inline with the warm water exhaust, with the bottom of its shaft spinning a tiny crude propellor inside the up-tube to help boost circulation. Google image search "VAWT", and you could make one from a 5-gallon bucket.

If you trench the pipe run (instead of a vertical well), make sure it slopes up to the tub, so no air gets trapped at the end. VAWT is optional for a proper vertical well, but for a horizontal trench-run, I'd definitely include a mini-VAWT circulation pump.

I've never done this, if you do it, please post how it turns out.

[Dan M]

Thanks for the comments, but:

Passive solar MIGHT average 6 hours/day useful output.  Between the short days, and so much lake effect snow, I'm gonna have to be running electric heat the other 18 hours/day.

Also, I'm already renting a trencher for another project, if 5 1/2 ft will get me to a reasonable temp, I think I'll avoid having to rent the well digger (which I found to be impossible anyway.....when I wanted to put in a new well).

The insulating thing might be good, but I'd like to be able to eliminate the electric heater completely.  The barn (which also contains my office) is fed by a single 20 amp breaker, and I have to un-plug the silly heater to make coffee....which is not a big deal, except when I forget to plug it back in.

Thanks again.

[ghurd]

Insulating is a big step to eliminate the electric heater.

Where are you?  It will make quite a difference in deciding if 5.5' is deep enough.

Lake Effect, and 6 hours of solar in the winter, don't mesh.

G-

[GaryGary]

Hi,

Some solar heated (or not solar heated) insulated tanks that people have tried are described here:

http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm#Animals

Some of these have a season or more of use on them, and generally the results are good.  The tanks heat up enough during the sunny periods to store heat and not freeze for quite a while -- days, depending on the temperatures.  The insulation and small open water surface help this.

This is the one I made for my neighbors horses -- it worked well enough last year that we made no changes to it for this winter -- she thinks its great:

http://www.builditsolar.com/Projects/WaterHeating/SolarHorseTank/SolarHorseTank.htm

It seems to me that the geothermal should work.  You would need to get down far enough to get to dirt that stays far enough above freezing to make a difference.  Around here, the ground at 3 ft down in mid winter is at or near freezing, so it would have to be deeper than that to do much good (for our locations).

If you do the geothermal, please report on how it comes out.

I think that just insulating the tank well and limiting the open water surface area would cut the heater on time dramatically.

Gary

[wdyasq]

Do a bit of research on 'heat pipe'. I believe a heat pipe will do what you want without additional power input.

Ron

[Dan M]

about 44 degrees N Latitude in MI.

Not 6 hours of daylight...

but by the time you take into account the insane amount of time with snow in the air  (both blowing and lake effect)and overcast, and the worthless first and last hour or so of daylight (as far as passive solar is concerned), it doesn't seem there are more than 6 hours or so each day (maximum) available to heat a fixed passive solar array.

[wooferhound]

If you do Geothermal, then in the Summer you could run the system to Cool the water.

[BigBreaker]

A heat pipe is a phase changing thermosyphon.  A closed pipe has a fluid in it that is liquid at the cold side to be heated (34F+) and vapor at the hot side (50F ground temperature).  The phase changing is what transfers heat, not the delta T, so that the heat pipe approaches isothermal between the "hot" and "cold" side.  It's like a heat superconductor compared to simple heat sink materials.  This is especially true if the hot side is above the cold side.

But you don't want a heat pipe here.  Why?  They sound great but the problems come if you want to tap the heat in soil.  Soil has very low thermal conductivity.  You need to have a lot surface area to heat at much heat.  Heat pipes are a pressure vessel and are expensive per unit of surface area.  Unpressurized, circulating fluid is cheap per unit of surface area, so that's what I think would work best.

[Bruce S]

Dan M;

 I lived at 41N (Baroda, MI) for a short while;I know the snow you're talking about!!

We boarded horses for locals who had hundreds more grape acreage than we did.

We had a 8 stall barn.

Our neighbor always ran his 48 inches minimum. I remember this because he got caught using one of his wife's quilt rods and got hell for it :-().

Your depth of 66 inches will be lower than frost line but to keep the output water from flash freezing when the wind blows and hits coffee freeze levels, you'll need to be able to hold enough water in the lines the 1/2 fill the trough, plus a better solution would be pipe in pipe, this will help stabilize the temps. will add one more level of protection and insulation. Also if you have access to a tractor coolant line heater and add this at the output will keep the flash freeze problem down.

They generally run 300 - 600 watts , get the smaller set, put it at a mid-point where the water just comes out of ground and the end into trough with some type of windshield and you should be golden.

If you're going to have an open trench, then it would be good to run at least one loop good and deep more loops means more warmth, this will keep the cold from migrating too far in, plus the looped warmth will allow a better freeze protection.

I know physics says that cold doesn't go towards heat, that heat travels to cold, but I'm thinking these people haven't been on Lakeshore dr and watched their coffee go from boiling to cold in seconds when the winds blows or they haven't seen snow flakes the size of pancakes and covers a '68 Chevy Impala 1/2 covered in the time it takes to jump start someones snowmobile :-).

Stay Warm!!

Bruce S

 

[hayfarmer]

try a mirafont type geothermal horse water system you dig a hole 5 feet down and cut bottom out of old 5 gallon buckets and place in hole to vent up the 55 degree heat in ground and place the mirafont on top.it has 2 balls horses push down to drink that keep the air from freezing water.I had this at a farm in virginia working 10 years no problem.

[sbotsford]

I'd use black PE pipe.  ABS = drain pipe -- rigid.  Not commonly available below 1.25"

PE = flexible, available in long rolls.

Consdier the following methods:

1.  Side your tank with minimum of 4" of styrofoam. This reduces heat loss on the sides.

   
   

2.  Sink it into the ground so that the waterline is a few inches above ground level.
   
   
   

This further reduces heat loss.

3.  Cover the ground for 3 feet in every direction with styrofoam -- 4" thick

This helps the ground around the tank from losing heat to the air.

4.  Put a layer of planking and a layer of dirt on top of the styrofoam to protect it.

   
   

5.  Arrange fencing so that the water point is available only to 1 horse at a time, and only from one place.  This keeps most of the snow on the ground untrampled, so there is yet more insulation

   
   

6.  Arrange an overflow point from the trough so that excess water can run away without soaking in around the trough.

   
   

7.  Cover most of the trough with an insulator both to keep the wind off it, and to prevent heat loss.  May have to sneak up on this gradually, as horses seem to be suspicious of change.

   
   
   

Doing this much may mean that the heater doesn't run nearly as much.

 Now:  It may be cheaper to run extra water through the system rather than heat it.

E.g. My groundwater temp is 50 F. 1500 watts = 1500 Joules/sec = 1.42 BTU/sec

Since each pound of water supplies 18 btu (50-32) you would need 1.4/18 pounds of water per second.  Call it 1/10 of a pound a second = 6 lbs a minute = 3 quarts a minute.

Yikes!  Is my math screwed?

Does that water heater run ALL the time?

So if you super insulate the trough, you may cut your heat loss by a factor of 10.

Keeping the water just liquid would give you another factor of 2.  So now you might be able to keep it molten with a 50-100 watt heater or a few gallons an hour of flow.