Pond Boss Forums INTRO Questions & Observations Heat pump for home and pond water source

Just had a light come on, in my head.

If I am looking at property on which to eventually build a new home and a pond, why not plan on putting in a heat pump system and discharging the water into the pond for a water source. Is there a downside to this?

Maybe many are doing this already but had not seen it yet in all my reading.

NG:

This has been discussed a fair number of times, although not for a few months. We have several members at least who heat and/or cool this way. Search for "geothermal" in the Questions & Observations and Help categories (and perhaps some others) and you will get about 20 threads to look over.

Yep, Theo has it covered.
WRT the downside of "pump and dump", the only potential issues that I recall were the well requiring a min output of about 12 gpm (?) and that the open loop systems (pump/dump) require a little cleaning maintenance because of mineral in the water medium.

The only downside I can think of is that the heat pump will create thin ice conditions around the discharge area in the winter time. Our heat pump discharges under our dock, we had a very old dog that drowned in that spot next to the dock Christmas morning many years ago. Typically the discharge area will leave a small area of open water, how far out dangerous ice conditions might occur would depend on the flow and current created under the ice by the HP.

OK, I'll do more searching.

12 GPM should not be any problem.

But did notice that geothermal sites now say the open systems are no longer very common.

NuttyGambler,

I have a geothermal unit that discharges into my front .62 acre pond. Like someone said, only downside is the open area it could create in the ice. Other than that I see no disadvantages. However when it's really cold you can get pretty close to the discharge. If the open area bothers you you could probably weight the hose down and have it discharge into deeper water? My household well is a 20 gpm well pump.

I wouldn't expect it to add a significant amount of water if that is what you are after. I've watched mine and it kind of runs in the pond in spurts like turning on a big garden hose sparadically. It runs more often when it has to work harder as in summer and winter. I remember measuring the discharge and it was about 20 gpms.

I thought of one other disadvatage, our heat pump discharge pipe is burried in the ground and discharges below the water line into the pond. During drought conditions when the pond is low the pipe is exposed, it gets cold enough for the pipe to freeze solid and we have to run on emergency heat. We have been in drought conditions for seven years now and every fall we have had to run the well pump to bring the water level up so the pipe is covered during the winter months.

I am building a system that does what you describe. Of course, here in Georgia we don't have the ice problems.

I am installing a "closed loop" that circulates a glycol mixture through 3000' of plastic pipe in the pond and back up to the geothermal unit in my basement. Using a closed loop is the only way to go, as it requires no maintenance, and you don't have to have a very big pump because you are not lifting the water. Even though my house is about 30' above the future pond level, the net lift is zero. The pump is only circulating water, not lifting it. The pump in a well system kills the efficiency.

My neighbor has a geothermal system also. He (and others too) have told me that the extra cost of a geothermal system (about double) will more than be made up every month by the savings in power.

I'll post some pictures when the guy starts puting in the pipe.

Jersey,

With an open loop you need to lift the well water but you other than that there is no lifting that I am aware of. Once the geothermal uses the water it just discharges to the pond.

For my location I feel the open system would be better. Well water at approximately 55 degrees is a real asset in the Summer. The winter would go along with this also as the water in the pond becomes cooler. I was thinking of installing 2 more large expansion tank so the well pump would run less often. Most of the articles I have read on using well water it has not created any problems. We loose enough water from evaporation to make the open system more desirable. The open system seems to be more efficient in heating and cooling. Very interesting topic.

Cecil,
You are correct, but lifting the well water uses a lot of energy ($$$). In my neck of the woods a well is 200-600 feet deep, so lifting 12gallons/min = 61,200 ft/lb/min = 1383 watts. Then you lose 30% efficiency in your pump motor, so it takes 1975 watts (about a 2HP pump) to lift the water, assuming a 600' well. A closed loop has no lifting load, only circulation, so we typically run a 1/15HP pump.

Also, how long can you pump 12g/min before your well gets low? Then what? Around here if you use a well for geothermal, you have to return the water into a seperate well.

I know a good bit about geothermal systems and how they work in warmer climates. Lakes around here will always be (relatively) cool on the bottom in summer and warm in winter. I suspect this is the same up north. If your pond is deep enough to not freeze solid.

Engineering would be fun if it weren't for all the technical stuff.

A 600' deep well.

One of ours is 125', the other is just 75'.

how about that shorty? we have two wells, one 550' the other 220'. the 550 footer only makes ~1.5 gpm, the 220 footer ~10 gpm. this is why i need to save $$ to install a third to support the pond if i am even lucky enough to get decent production....assuming i hit good water (i have a good spot picked out) then i struggle w/ either expensive solar or costly elec. to git the wet stuff out. i've recently heard of solar set ups for ~$3-4k that produce 25,000 gallons a day (~17 gpm).....when i get more info i'll make a post about it.

i am surprised you need those depths in GA....jersey....are you in the mountains or what?

it all depends on the depth and production capability of aquifer and the specs of the installed pump.

the aquifer in which my good well was installed makes ~10 gpm, and static water level is about 20 feet. the (3/4 hp) pump i installed at 210 feet initially produces about 16 gpm, as the water level drops the pump performance decreases to less than 10 gpm, then the water level begins to rise again, and under constant running, pump performance maintain about 10 gpm and can never pump the well dry. a lot of people oversize their pumps for the aquifer conditions.

D.I.E.D, the 75 ft well is our pond support well. The previous owner who built the pond said it is tapped into an underground river and would be impossible to pump dry. :rolleyes: Our pond also has a spring above it that feeds it as well.

springs...underground rivers....awlright shorty, quit braggin...

i wish i could hit a underground river....you're probably tapping into an old subsurface glacial feature.

http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=20;t=002145;p=1 is a good thread that I will not try to repeat info. If you plan to aerate your pond I would seriously consider a pump and dump system or burried loop over a pond loop. I am happy with my pond loop but according to the manufacturer of my unit I should not aerate or otherwise mix the water column. My all electric house monthly bill has averaged less than $100 per month for over two years now. My Dad's house next door is 1/3 smaller than mine with an older traditional heat pump, electric furnace, and even using his wood burning stove his electric bill is more than double mine.

My neighbor has a 6 ton and 3 ton geothermal systems. His loop are buried 6' in the ground under his yard. His house is 7000 sq ft. He says his worst bill in the 2 years he has lived there was $200.

My dealer told me the pond loop is by far the most efficient, and it makes sense, that it's easier to transfer heat from water-to-water than water-to-dirt.

Waterfurnace.com has a lot of info and if you'd rather watch the movie, go HERE

I will be putting in a 6 ton WaterFurnace. The guy says that the pond loop will be about 40' x50'. He says he has seen his loops years later where the pond had been drained and you can't even tell where the loops are because they bury themselves in the bottom.

There is a product called a "Slim Jim" that is just a nice copper radiator that can be set on the bottom or mounted under a dock. They are rated in "tons". I was going to get one until I found that it would cost $2000 more than the pipe loops. They also create more resistance, requiring a larger pump.

What am I missing in regard to running one with a pond closed loop.

Up here, the water below the ice is basicly 39 degrees, much colder then the ground at 6'

In the summer surface water temp would be 80 in a small pond and about 10 degrees cooler below one thermocline. Which would be much warmer then the ground.

Now I do realize water is much better at heat transfer, but aren't the differences in these temps more then enough to make them less eff?

"Pump and dump" systems are a lot less to install. The issues are water quantity and water quality. There would be a problem if you used pump and dump and had times where there was insufficient water quantity in gpm. The qualtity of the water will determine maintenance cost - pumps and stuff get dirty/coated with rust, etc. Can lead to lots of filter changing, breakdowns, etc.

Closed loops are quite a bit more to put in, but eliminate quality and quantity issues. Where we are in NE Ohio all we install at my company are closed loops. But we potentially have quantity and quality issues.

Pond loops will operate more efficiently if they don't get buried in the mud. Heat transfer is maximized by contact between the surface area of the pipe (polyethylene) and the water. The water being a fluid will convect (cooler water is denser and falls, etc.) increasing heat transfer as compared to contact between the pipe and the mud.

When we install pond loops we put spacers between the pipe coils so they don't touch and allow water to convect more efficiently. 1/2" spacers holding 3/4" coils of pipe apart. And we use concrete blocks to weigh them down and to hold them up off the bottom. Great structure!

The pond systems seem to perform very similar to the ground loop systems we bury horizontally at 5' depth, and the vertical systems (150' deep). The "efficiency" of the heat transfer has a lot to do with the amount of pipe vs. the size of the machine. If the installing contractor puts too little pipe in the ground for the size of the machine (in tons of capacity) it will hurt efficiency.

We have seen pond closed loop systems not work properly due to no spacers. The contractor just took 500' loops of 3/4 polyethelyne pipe, headerred them together and put them in the pond. No convection. Very poor performance. Contact with the mud would be a lot better than having the pipes contacting themselves.

As to the pond temps yes it makes a difference but not as much as you think. Ground loops acutually get warmer all summer as the ground is used as a dumping ground for heat - peaking at about 70 or 80 degrees in Sept. here in NE Ohio. Conversely they ground loops build up ice - as much as 6" - as heat is extracted and peak at coldest in February or March. The ice thaws as the machine "hits the loop" less - the heat migrating from the ground to warm the loop is a slow gradual process. The ice is probably still there in May when cooling season begins (very efficient at that point). So the loop changes "incoming" temperatures over the year, yet the system is still giving you 4 times the energy consumed - a very efficient way to heat and cool. Point being the efficiency does not change that much when the source changes temperature over the year.

A bigger concern would be the size of the pond. If you add or take away heat from a smaller pond the temperature change would be significant and a big problem for both the pond and the performance of the system. We usually start with requiring 1/2 acre pond with at least 12' of depth. There are variables of course but this just to give you an idea.

WaterFurnace has a new unit now that has a COP (efficiency rating) of 5. This translates into 5 units of energy for the home for each unit (kW) consumed. Awesome.

I have researched on this forum for geothermal and would be interested in up dating to find out what has been installed in the past two years. Brand and type along with problems. I plan on installing two more pressure tanks on the well and I am 75 feet deep with enough water. I filled my pond with my a 3 hp pumpand the pond is about 3 acres . I ran the pump wide open until the pond was full , it is approximately 10 foot deep or more in certain areas. Since I am almost complete with the hurricane damage I will be able to give this more thought. thanks

deaner,
With the pond you have, why would you want the monthly expense and maintenance of pumping water from 75 feet down? Why not just put in a closed pond loop? Just curious.

Well water is approximately 55 degrees more or less. My pond water in southern Mississippi becomes much warmer in the summer so air conditioning would be more difficult. I felt that most would still have the open system and this is what I desire to know. This would cost you more to pump the water but the run time of the compressor would be less. With the more effecient units now it would influence a person to make the move.

Deaner,
I really like my open loop waterfurnace. It is 13 years old and I have had no maintenance issues other than changing the air filter. I have very hard water, but I only soften the water that feeds my water heater. I do not believe that it is practical, or necessary to soften water used by the water furnace. When it is running, it uses 6 gpm to heat/ cool a 2000 sqft home. The water dumps into my pond, but in the summertime I loose more water to evaporation than the waterfurnace provides.
If you already have your own water well and pump, the open loop geothermal should not cost much more than a standard air cooled heat pump. (I paid an $800 premium to get the waterfurnance and installed the water lines myself). It paid off the first year.
These openloop geothermal units are so simple they should cost less than a standard heatpump system because there is no outside condensor system.

Thanks Gainesjs for your answer on geothermal. I appreciate your input as it gives me more details to assist me in my decision. thanks