Dumping hot water!

[Aviatordave]

Hello folks,

I'm new to the forum and am building a 40x80 pole barn in lower Michigan. Trusses are up and steel starts going on tomorrow! I'm really excited!

I'm planning on heating the concrete floor with geothermal heat via loops of PEX in the concrete.

I've been researching different methods of dealing with the discharge water from the geothermal unit. (It's a single pass system being fed from the well.) I live on 10 acres of wooded land. What's the best way to deal with the discharge water? Just let it drain into a downhill run away from the barn somewhere away from the building? Dump it back into the aquifer with a second well a good distance from the source well? What has worked for you?

-Dave

 

[Alchymist]

What temperature is your discharge water at? Can you use it to preheat potable water prior to your water heater inlet via a heat exchange system?

 

[jonjon1]

Stay away from pump and dump, go closed loop, water furnace series 5... Also hard to leave the ac behind, geo ac is so efficient, why not cool too?

If you are set of p and d , then drill 2 wells, that water needs to be returned to the ground where it came out in pretty fast order, you dont want to drop it ground level and have it take 4 days to return and not to mention lose a ton to evap... Another way I seen it done is drill 500 ft, then pickup at 300 and dump at 500.... or vise versa....

good luck, I can not stress enough to go closed loop...

 

[Stuart in MN]

Check to see if an open loop system is legally allowed in Michigan before going too far with it.

edit: it appears they are allowed there, but there are some hoops to jump through. http://www.michigan.gov/documents/deq/deq-wd-gws-wcu-ghpsguidance_195216_7.pdf

 

[Bondo]

Ayuh,.... Ditto jonjon1,... Closed loop, Heat, DHW, 'n A/C all from the unit,....

 

[tomroblee]

There are advantages to both open and close loop geothermal systems. The efficiency of the system is very dependent on the temperature of the incoming water. Well water will likely be fairly consistent in temperature year round. With a closed loop system, the water temperature will likely drop in very cold weather when the system is running a large percentage of time. (The incoming water temperature will drop below 32 degrees at the closed vertical loop system in my house.) This is especially true when the system is a bit undersized. The main disadvantage of an open loop system is that more contaminants (lime, minerals, etc) are constantly being introduced and may build up in your system or create corrosion issues.

The cost of installing either type of system is very dependent on your land. If all of your land is heavily wooded and/or the soil is shallow or rocky it may be a problem to install a horizontal closed loop. Drilling multiple deep wells for a vertical closed loop system may be very expensive.

My wife's cousin has used an open loop system with good results for about 25 years. He lives on a farm in river bottom land. His source well is only about 30' deep, so it was very inexpensive to install. He discharges water into a drainage ditch----which contains water most of the year anyway.

Your title says "dumping hot water". I don't think that the water will be all that hot. The incoming well water will be in the 50 degree range, and the discharge water will be about ten degrees cooler after the heat has been extracted.

 

[jonjon1]

tomroblee
If your water is around still freeze temps, then your design is NOT correct, something was drastically undersized...

Pump and dumps around here use well pumps vs closed loops use circulators, these pumps run for 24 hours a day when they need to, that gets expensive. They used to say that the costs equal out, this is NOT the case, especially now with the variable speed, ecm, circulators available.. The up front cost is higher, but the future maintenance savings will more than make up for it... Geo air handlers and water to waters are $7K+ each, pumping all that sediment through them does a job on them. An open loop system will pump 500K to 1 million gallons a year!!!!

Yes the temps will be about 10% lower with closed loop, my home is over 4K sq ft with a lot of glass, high ceilings, and kids that leave doors open all the time. My average summer time tubing temp is 63 degrees in the summer and 44 in the winter, I have passive solar also, I heat cool and power my home for under $600 a year!!! Thats electricity too... To compare to homes of my size with similar occupants, with high efficiency natural gas, medium eff. cooling, and grid power they will spend around $9K a year!!! I have propane hydronic system also as well as a coal fired aux system, and a 16 seer air-heat pump system. Its what I do, lol...

I have been installing geo thermal for almost 20 years and with out a doubt, I would go closed loop every time, no contest...
buy once cry one..

 

[Aviatordave]

Thank you for all the input. Very helpful.

Stuart - Thank you very much for the link to the Michigan laws regarding this. It was very enlightening reading!

I don't know what the discharge temp of the water will be but you're correct in that it will be cooler than the inlet temp so my title is indeed misleading.

Not going to worry about using the geothermal for A/C. The geo unit will serve as a water to water heat exchanger to heat a closed loop of zones and circuits of PEX in the 4" concrete slab. (Will have vapor barrier and foam insulation under it.) Running cold water through the slab would just produce condensation on the floor. There's not going to be any ductwork in the barn for moving cold air. I'll have plenty of overhead doors and windows to open for warm days. Worst case I'll install a window A/C unit.
(I do have a geothermal unit currently for my house and love the combined heat/A/C aspect of it.)

I've decided to go with a modified open circuit dump. The geothermal discharge will wind up in a gravel filled subterranean basin. Drain line will be below the frost line. The basin will basically be about 1200 cu/ft of gravel beneath 4 feet of dirt. This should allow plenty of drainage space and eliminate evaporation. The ground around here perks very well and the location of the pit will be at the lowest point on the property, which just happens to be downhill from the barn. I have a well currently feeding the house geothermal. I'm going to tap into that line to feed the barn geothermal. The heavily wooded aspect of the property makes a closed circuit geo system very cost prohibitive. A horizontal field would require the removal of lots of trees and lots of $$ A vertical one would also be lots of $$. My heating costs are quite decent for a 4000 sqft home and I'm going to use spray foam to insulate the barn so it should be pretty thermally efficient.

Thoughts?

 

[Radix2]

Where does the house geothermal discharge now?

Have you calculated how many gpm will be required to generate the heat you need for the barn ? How does that compare to 1200ft3?

 

[tomroblee]

It sounds like you have a plan!!

My only concerns would be that everything needs to be sized correctly. As jonjon1 says, you are going to flow a lot of water through your system(s). Make sure that your well and/or pump have the capacity to supply the additional water that you will need and that the basin will be large enough to dispose of the water.

 

[jvitez]

We have an open loop geothermal system installed 9 years ago, 4 zone fan coil system with 2 water to water heat pumps. We have two wells, one for potable water and geothermal input and one for geothermal discharge. We were going to go with closed loop and a cistern for potable water as people said the ground water is very hard here, but I really didn't want a cistern. In discussion with the HVAC contractor we decided to go with well to well open loop. He said our winter ground water is 43°F and summer is 53°, and that closed loops do freeze if we get a couple of weeks of -30°C which does occur every few years here.

In hindsight, closed loop and cistern would have been better. I've had to replace one heat exchanger because of mineral buildup, and have to regularly flush the heat pumps with CLR or muriatic acid then bleach (not at the same time! ). We have a large water softener which leaves salt stains on fixtures and counters if water isn't wiped up.

With the cost of NG now and our rising cost of electricity, even our POCO says a SCOP of 2 geothermal system is more expensive to run than high efficiency NG. But we do save in cooling vs regular AC.

If I knew then what I knew now, I'd be prescient..... but I would have been better off going with a high efficiency NG boiler with in-floor radiant heat and regular AC.

 

[LS6 Tommy]

Check to see if an open loop system is legally allowed in Michigan before going too far with it.

Can't do it in New Jersey. I don't know why anybody in their right mind on well water would want to anyway.

I've never heard of a closed loop freezing. The system is supposed to be WAY below the frostline and where the lines go into the ground isn't supposed to be outside...


Tommy

 

[dutchgray]

Plus a closed loop can have antifreeze to stop it freezing.

 

[Aviatordave]

I have done some research and calculations. I talked to the guy who installed and maintains our well. He was adamant that I didn't need a second well. (Ours is a 5" well with a 1hp motor rated at 28gpm. It sits at 80 feet deep in a 110 foot deep well with the water level at 43 feet.) The barn geo unit will demand 6-7 gpm. The well guy explained that the 28gpm capacity of the pump is based on 80' of static head pressure. Since my pump is only at about 40 feet deep the actual gpm capability is more around 32-34 gpm. There's an 80 gallon holding tank in the system. Plenty of capacity from the well. If need be I'll add another holding tank to the system in the barn.

If the geo unit consumes 6-7 gpm (this I got from my HVAC installer who's ordering the unit) then the discharge should be the same. If the unit ran nonstop for 24 hours (which it may in the beginning to heat up the slab but won't as a normal course of maintaining the heat.) then it would dump a shade over 10,000 gallons in 24 hours. There's 7.5 gallons in a cubic foot of space. That equates to 1,333 cubic feet of discharge in a day. I decided that 1200 cubic feet of gravel would be sufficient to handle a full day's discharge. The basic size of the basin will be 20'x10'x10' deep. 6' of this will be gravel with 4 feet of dirt on top to bring the system back to ground level. The ground perks quite well around here. I don't anticipate the gravel in the basin being overloaded.

So in a nutshell, dig a hole with an excavator, dump some gravel into it, flop the drain line into it and cover it back up. The whole system will be well below the frost line.

I don't know where my current home geothermal discharges to. The pipe disappears into a hole in the wall. I asked the previous owner when we bought the place and he didn't know the answer either, unfortunately.

We don't have NG available to us as we're out in the country. LP would be crazy expensive and I'm not going to chop wood on a daily basis to feed a wood boiler.

You'd have to see the layout of the barn relative to the house and the positions of everything on the property to appreciate it but the only direction I could put a horizontal closed loop system is a rolling hill/ravine area that's loaded with trees. I'm just not going to do it.

Thoughts on my calculations?

 

[pepi]

Without knowing one thing about this type of heating, I can see from here that a closed loop would be the direction to take... It just shouts more efficient.

 

[Radix2]

I have done some research and calculations. I talked to the guy who installed and maintains our well. He was adamant that I didn't need a second well. (Ours is a 5" well with a 1hp motor rated at 28gpm. It sits at 80 feet deep in a 110 foot deep well with the water level at 43 feet.) The barn geo unit will demand 6-7 gpm. The well guy explained that the 28gpm capacity of the pump is based on 80' of static head pressure. Since my pump is only at about 40 feet deep the actual gpm capability is more around 32-34 gpm. There's an 80 gallon holding tank in the system. Plenty of capacity from the well. If need be I'll add another holding tank to the system in the barn.

If the geo unit consumes 6-7 gpm (this I got from my HVAC installer who's ordering the unit) then the discharge should be the same. If the unit ran nonstop for 24 hours (which it may in the beginning to heat up the slab but won't as a normal course of maintaining the heat.) then it would dump a shade over 10,000 gallons in 24 hours. There's 7.5 gallons in a cubic foot of space. That equates to 1,333 cubic feet of discharge in a day. I decided that 1200 cubic feet of gravel would be sufficient to handle a full day's discharge. The basic size of the basin will be 20'x10'x10' deep. 6' of this will be gravel with 4 feet of dirt on top to bring the system back to ground level. The ground perks quite well around here. I don't anticipate the gravel in the basin being overloaded.

So in a nutshell, dig a hole with an excavator, dump some gravel into it, flop the drain line into it and cover it back up. The whole system will be well below the frost line.

I don't know where my current home geothermal discharges to. The pipe disappears into a hole in the wall. I asked the previous owner when we bought the place and he didn't know the answer either, unfortunately.

We don't have NG available to us as we're out in the country. LP would be crazy expensive and I'm not going to chop wood on a daily basis to feed a wood boiler.

You'd have to see the layout of the barn relative to the house and the positions of everything on the property to appreciate it but the only direction I could put a horizontal closed loop system is a rolling hill/ravine area that's loaded with trees. I'm just not going to do it.

Thoughts on my calculations?

It seems a mighty big question to be doubling your local discharge without knowing precisely what is happening with your current discharge.

The well guy knows all these fact and figures about the well and pump but has no idea what is happening with the current possible 10,000 gallons a day ?

does this same well/source supply your drinking/potable water as well?

With such permeable ground, and these high flows I would be concerned with flushing contaminants like fertilizers, sewage, etc. down through the soil and polluting your ground water.

More simply stated, I would want to have a clear picture of where your drinking water well, septic system, Geo discharge points, etc. are so that you can make sure of what is happening.

I don't see anything in your calculation that justifies a drain field equal to one days discharge as being sufficient (not saying it isn't, but it sure looks like a complete SWAG) - a volume of gravel will only hold a fraction of it's volume of water - so your assumption is that your ground will absorb faster than you can pump over an area of 200 sq ft - 50 g/ft2/day - maybe, but have you dug down and tried 'percing at that rate for a long period of time ?

If your house system is working, and I assume is able to dispose of a similar flow - seems like a good example to understand IMO.

 

[Radix2]

Another observation - you say this pump will need 6-7GPM to heat a 40x80 pole barn in MI...

I would think the design delta T you could pull from that water would be about 10 degrees - say 40-50 in and 30-40 discharge ?

So... the most you can get from the ground water under those condition is about 32K BTUs - I doubt that that is enough to heat a 40x80 - How many BTUs are you expecting to need to heat your building ?