Geothermal for two buildings

[AllDodge]

Think I'm going with geothermal in the spring/summer. Currently have two heat pumps in the house, one main floor and one basement. Since I'm also wanting to condition my 30x48x16 shop off the back I wonder if it's feasible to use the same piping to run two or maybe even three separate geothermal heat pumps? While I'm at could hook it up to the water heater

Have a backhoe and space behind the house to dig trenches to lay in pipe. Found a site which says the average home can take between 1200 to 1800 sq ft. The space behind the hose is around 12000 sq ft (+/-). All the space is between the house and shop along with a gravel drive. Could drill but then the cost goes up.

 

[sms1974]

Geothermal is sized a bit differently than an air to air heat pump you will want a load calculation. After deciding on what size units you need you will then need to have a local contractor or distributor do a loop design, you geology has a lot of influence on what size and type of loop you need. I am not saying you can't install the loop or system on your own but there are a lot of ways you can go wrong without even trying...

To answer a few questions, yes you could run three systems on one ground loop. I have several commercial system I service that are set up in that fashion. For a residential system I would not recomed that, in my opinion each system should be independant.

As for ground loop sizes. Most of mine here in northern ohio are in a trench 5' deep 2' wide 140'-180' long, per ton. Meaning a 4 ton system would have 4 trenches that size. They are spaced 10' apart. If you don't have room for that then drilling is your best option.

 

[sseddon641]

I have geothermal in my house and like using it a lot. Even though I still heat with wood primarily. I see no reason why all 3 units couldn't be off the same loop. What I would recommend is piping a header inside where you can connect each individual run. The reason I say that is even though from what I've seen these systems don't typically leak but if you plan on living in the house 20 or 30 years it could happen. With that said I would run extra pipe and install ball valves where it goes into and out of the ground. That way if you
Have one run leak in the future you just valve it off and you are good to go. Otherwise you are trying to dig a trench without damaging other piping to repair the leak. What I have seen done with the piping is a trench is dug and you can run 3 pipes threw
Each thrench. One on each side and one down the middle so you can get away with less excavating to get the amount of pipe you need. The rule of thumb is you run 600 ft of pipe per 1 ton of heating/cooling. But that can vary with the type of soil. Since you already have a backhoe I would recommend digging a couple holes and see what type of soil you have and do a little research based on what you find to figure out if you need extra based on yer soil type.

 

[theoldwizard1]

...I wonder if it's feasible to use the same piping to run two or maybe even three separate geothermal heat pumps?

Not likely.

Calculating geothermal loads is not trivial. Hire a a good engineering firm to calculate what size you really need.

I would consider a mini-split with multiple (3 or 4?) air handlers for the shop.

 

[sseddon641]

It is definitely possible to run multiple heat pumps off of one common circuit. At Michigan state where I work we have a system that is 8 heat pumps side by side that each have (if I remember correctly) two ten ton compressors in them with probably around ten smaller heat pumps off that same loop that cool elevator rooms and server rooms and other things like that. The biggest thing is you have to size the loop to be able to handle the amount of heating/cooling you are going to be running of that loop. Also when that system was installed msu hired a fancy engineering firm and they butchered the job. We ended up with about 2/3 the loop we needed and ran the first winter on the very edge of all the heat pumps shutting down. For about two weeks we were running the loop at 30 degrees and if I dropped to 28 the whole system shut down.

 

[AllDodge]

Thanks, appreciate the input. Been looking into geo for a while now for the house and was going to discuss this spring about installing. With the cold I am unable to do much in the shop with it being uninsulated. so then I started thinking about doing both with one. Need to spray closed cell in the shop and see about a heat source, and if I can also get cooling that is even better.

 

[jkwilson]

One big negative of any kind of heat pump is that they don't do well at surge heating. Most include an electric or gas backup for extremes. Slow and steady is their strength. If you plan to keep the shop buttoned up and heated/cooled all the time, they will do well. If you want to turn them on and make the building comfortable before you go to work, you may not be happy.

 

[AllDodge]

Good point forgot about that one, thanks. Currently use regular heat pump in the house and never touch the thermostat due to the toasters (heating elements, all elect) that would turn on if I let it go down. Guess one could remove the toaster elements in the shop for just such an issue.