Geo thermal thread got me thinking

[SolarAndWood]

Could you do a "geothermal" setup in a cistern in the basement? 12 x 12 x 5 gravity fed from a spring through an inch and a half pipe?

 

[btuser]

A water loop runs at a high GPM, and what you're really looking for is a differential between the loop and what you're heating. Once your cistern hits a temp you'd be out of luck and heat/cooling. I've seen stats as high as 20-40 gpm, which would eat up a very large cistern in very short order. Even an 10,000 cistern @70F would only hold the same heat as 250 gallons of heating oil before it froze solid. Maybe add some salt? No, probably not.

 

[semipro]

Could you do a "geothermal" setup in a cistern in the basement? 12 x 12 x 5 gravity fed from a spring through an inch and a half pipe?

Since this is spring-fed, is there an overflow from the cistern? If so, the heating/cooling capacity of a HP using the cistern as the source/sink would be dependent upon the flow rate through, and not the size of, the cistern. You'd basically be using the cistern as a heat exchanger.

 

[SolarAndWood]

It would seem I need to monitor water temps for a year and figure out what kind of flow I can maintain. It must be relatively warm as the line runs above ground in places through the woods and never freezes even though it can stay below zero for months at a time up there. This is for a camp, so even if a small system could keep the core of the building from freezing it would be huge. Then, when someone arrives, it will heat up a lot faster with the stove.

I would just have to pipe it in such a way that if the system did freeze the reservoir that the water could still flow for drinking water and keep the pipe from the spring from freezing.

 

[SolarAndWood]

Since this is spring-fed, is there an overflow from the cistern?

Yes, we maintain continuous flow through the pipe as there isn't a lot of drop from the spring box to the house and it gets cold up there. So, we are worried about sediment, air and freezing.

 

[Seasoned Oak]

Ground water is usually around 55Deg . After that spring exits the ground that may drop. Or are you picking up the water before it exits the ground?

 

[SolarAndWood]

The spring box is in the side of the hill and the pipe is a few feet below the surface. I've never seen it ice over but there is no way it is 55 degrees. It then travels a few hundred yards within a few feet of the surface until it ends up in the cistern which is about 8' below grade.

 

[Seasoned Oak]

The spring box is in the side of the hill and the pipe is a few few below the surface. I've never seen it ice over but there is no way it is 55 degrees. It then travels a few hundred yards within a few feet of the surface until it ends up in the cistern which is about 8' below grade.

The whole idea of Geo-THermal is to take the heat from 55 Degree water, return 45 deg water (approx) , it to the earth and let the earth rewarm it the start the cycle all over again,or in your case discard it and replace it with warmer water. Once you get too far below 55 or 50 there is not much heat in the water before it will freeze at 32 and you will use more electricity trying to extract it.If the spring water is closer to 32 Degrees it probably is not going to help you very much. Your better off with a well.

 

[SolarAndWood]

Once you get too far below 55 or 50

That is the big question and the only way to find out will be to do some data logging. The goal is to keep the core of the building from freezing, not to heat it. Wood is the way to do that.

 

[CALJREICH]

What Trump said about the temp. of the water you will use is true. You can't use water that is near freezing and have an effecient system. And that would be the even better reason to drill a well/wells.

 

[benjamin]

How much does a couple hundred yards of insulated 1 1/2" pex cost? OK never mind.

If you have enough flow, you can certainly get enough heat out of water at 40 degrees. The limiting factor is the lower working limit of the fluid (freezing) not the amount of heat available. Ground loops contain antifreeze because they routinely operate below freezing, as air to air heat pumps do.

That being said, if this is a camp and the spring is free flowing, why not pipe the water through some crude radiant tubing to keep the place from freezing? Insulating the pipe would go a long way towards keeping that water as warm as possible.

 

[SolarAndWood]

How much does a couple hundred yards of insulated 1 1/2" pex cost? OK never mind.

Probably not much as I am going to have to replace that line sometime soon anyway.

If you have enough flow, you can certainly get enough heat out of water at 40 degrees.

I have a ball valve on it where it enters the basement. When someone is there using water, we have it 3/16 of a turn open. When we leave, it is turned it down to 1/16. There is always water in the spring box no matter the time of year or how dry the season.

The limiting factor is the lower working limit of the fluid (freezing) not the amount of heat available. Ground loops contain antifreeze because they routinely operate below freezing, as air to air heat pumps do.

The uninsulated galvanized tank in the basement has never frozen. The temperature should only increase with a cistern with insulated walls and an uninsulated floor.

That being said, if this is a camp and the spring is free flowing, why not pipe the water through some crude radiant tubing to keep the place from freezing? Insulating the pipe would go a long way towards keeping that water as warm as possible.

If I had the rise to do that gravity fed, I would definitely consider it. As soon as I need electricity to pump it anyway, I think I might as well put a heat pump in the mix and have a closed loop system that won't freeze in the house.

Thanks for all the good ideas. I need to dig out and rebuild the spring box. Probably should do the line while I am at it. Then, figure out what kind of flow I can maintain and at what temperature.

 

[Seasoned Oak]

Even if you could maintain a 40 Deg floor temp, (by running spring water through pex in the floor) doubt that would change the air temp much IMO
Just what are you trying to prevent from freezing ? Toilets,sinks,ect?

 

[CALJREICH]

Just so I'm clear on this you are talking about a pump and dump or open loop system. The size of your cistern is way to small to contain a closed loop large enough to heat or cool your home. You can probably get a few free estimates from someone who installs the geothermal systems. Let us know what he thinks.

 

[SolarAndWood]

Not sure what a pump and dump system is. The water for the camp has come out of the side of the mountain and flowed through the house for about 80 years. The overflow exits on the downhill side of the house. My thought is to increase the size of the reservoir from the current 80 gallon galvanized tank to a cistern in the basement to serve as the heat exchanger. I guess the only question is can you move enough through the pipe to make it work. This could certainly be improved as Benjamin suggested by insulating the pipe and the cistern for that matter.

The heat pump would be relatively inexpensive to do. The cistern sits right underneath where the wood furnace will tie into the duct work. The real heat for the camp will come from wood as it does now.

 

[CALJREICH]

There are 2 kinds of loops you can have with a geothermal system CLOSED LOOP or OPEN LOOP (sometimes called pump and dump). The loops can go in the ground horizontally , vertical (wells). The loops can go in a lake or large body of water.
The closed loop circulates the water/solution over and over through the unit and back into the ground.
The open loop pump water from a source usually a well brings it to the unit and the the water is dispersed out of a pipe some where.

One of your earliest replies was from a man that alluded to the reality you may not have a big enough source of water to draw from and if you run out then your out of luck.

 

[benjamin]

You don't need a large tank for a heat exchanger, a water source heat pump has a coaxial heat exchanger inside it that the water flows through. You want about 2 gallons per minute PER ton (12,000btu/hr) or more if the water is cold, the higher the flow, the lower the temp drop.

You don't want the heat exchanger inside of the unit to ever freeze up, either from the power going off and the water stopping at the same time or not enough flow and the unit freezing itself.

There are old milk houses around here that have spring fed water supplies that keep from freezing throughout the winter just from that heat, and they're no models of superinsulation. You don't need the water to flow through the whole house by gravity, if it can flow through the basement and give up enough heat, then the air will circulate up on it's own.

 

[SolarAndWood]

One of your earliest replies was from a man that alluded to the reality you may not have a big enough source of water to draw from and if you run out then your out of luck.

Yep, I get that. Except that out of luck is not the end of the world and I guarantee you the source is big enough. What I need to figure out is how warm I can deliver it to the cistern and is it worth putting a big enough pipe in to get the flow I need to maintain 40 in the core of the house.

Either way, there is going to be a big stove as well as a big wood furnace in there to bring the building up to temperature as I have no intention of using the oil furnace again.

 

[CALJREICH]

One of your earliest replies was from a man that alluded to the reality you may not have a big enough source of water to draw from and if you run out then your out of luck.

Yep, I get that. Except that out of luck is not the end of the world and I guarantee you the source is big enough. What I need to figure out is how warm I can deliver it to the cistern and is it worth putting a big enough pipe in to get the flow I need to maintain 40 in the core of the house.

Either way, there is going to be a big stove as well as a big wood furnace in there to bring the building up to temperature as I have no intention of using the oil furnace again.

Is this for a geothermal system?

 

[SolarAndWood]

Is this for a geothermal system?

Of sorts. Use the energy from the water coming out of the side of the mountain as it is passing through the house. I suppose I could also insulate the spring house in addition to replacing the pipe with an insulated line.

It may be an entertaining project someday after I deal with more pressing things like keeping the building from falling in on itself.