Posted By engineer on 29 Apr 2010 02:33 AM
I wonder if the Slim Jim requirement of 2' feet of unfrozen water above assumes static water (lake or pond).

If a Slim Jim were immersed in water with any significant flow I doubt it would need any depth above itself to transfer design heat.

Whatever heat exchanger is installed would have to deal with floods, debris and other effects of moving water, but if the water is truly always moving the heat exchanger could be much much smaller than that typically required in a pond / lake.

Agreed, but a slim jim panel partially immersed during dry season is not so good. Description of this intermittant stream has a picture in my minds eye that suggests depth may be better measured in inches during the dry season. Further the slim jim design is compact owing to the vertical installation (much like recipe cards in a file box). if you had to install them horizontally to keep them underwater, the design may stretch longer than the property line and expose a terrific amount of loop to impact damage.

OP,
I think your plan is more the product of available technologies and material than end benefit. You know where to get and how to handle PVC there fore you'd rather use it. If it is exposed in a stream, you could repair it.
If that is the case, let's consider meeting in the middile with pecs. Long runs can be buried with confidence, tools and pipe are readily available and joints can be made by tools from big box store.
Fittings and manifolds concealed by lawn irrigation box or sump well can be reached if repair is needed in future. Isolation valves in the same place permit flushing with a garden hose.
j

I think your plan is more the product of available technologies and material than end benefit. You know where to get and how to handle PVC there fore you'd rather use it. If it is exposed in a stream, you could repair it.

You got me. Nailed it. That is exactly right. When I build stuff, I usually use materials and technologies that I know and adapt as needed, though I am open to new stuff.

Pex eh? Ive heard about it and have done some research. Im a little foggy about when its proper to use oxygen barrier or aluminum core or neither. I thought pex did not tolerate sun exposure. As for HDPE, I have no problem renting a fusion machine and learning how to use it.

What would be a good price and place to buy the amount of pipe that I need?

Price is impacted by many things....size yet to be agreed upon among them. All plastics are degraded by sunshine, which is why we suggest buried loops.
J

Posted By evil_admin on 29 Apr 2010 01:09 PM
What would be a good price and place to buy the amount of pipe that I need?

As I recall, my local plumbing supply warehouses sell the 100psi 1.25" PE in 300' rolls for about $350,  but the price per foot is less if you buy in 1000' rolls. That's a bit cheaper than the nearest Home Depot, but not by much.

Well, I think ill go with PE like it has been suggested. I leaning to 1.25" but is 1.5" is not much more, Ill go with that instead. I do not think that 1" is a good idea due to the run length.

Posted By evil_admin on 04 May 2010 12:11 PM
Well, I think ill go with PE like it has been suggested. I leaning to 1.25" but is 1.5" is not much more, Ill go with that instead. I do not think that 1" is a good idea due to the run length.

Our M.O. is 1.25" headers to loop field, then individual loops in 3/4" which is much easier to work with.
j

Thank you guys for all your help. I have decided to make a few changes because of what has been suggested here. First and foremost, I will be using black poly pipe for my long runs out to the creek. Secondly, the creek exchanger is a 100 foot by 2 inch piece of 316 stainless steel. Inside the pipe is stainless steel logging chain and a few baffles welded in for turbulence. I just finished welding it up and have installed it. In testing it had excellent delta T, and could likely provide 5 tons. (20 GPM, Tin 90deg, Tout 60, creek 65)

Anyway, I have a new question. Im about to rent a ditch witch and am wondering what (if any) trench prep I should do to protect the pipes. Should I add a thermal grout over the pipes? My plan was to run 2 separate trenches, one for supply and return, so that the hot water from the house does not warm the cool water from the creek. If grout was not used, I was considering a sand bed.

A side question, how does a ditch witch respond to tree roots? Never hit any in the past so I do not know.

Small roots do not slow down a Ditch Witch that much.  Larger roots will take more time to cut through them.  Now rocks, that a different story.  Avoid rocks - can damage the teeth.  Talk to the rental company.  They will be the best to advise you on what to rent and what to watch out for in your area.  Some of my projects had to use a Back Hoe or Track Hoe (traveling excavator) instead of a Ditch Witch because the ground was so hard and rocky.  I actually prefer the use of a small Track Hoe with a small bucket over a Back Hoe.  Much faster not having to put down feet every time you move.  I think Track Hoes are a lot safer to operate than a Back Hoe.  A Back Hoe reminds me of how an elephant would look and act on roller skates.

RE trench prep, sharp things and rocks are a lousy back fill so get 'em out. These are header pipes so most of your heat transfer should take place in the creek. Doesn't hurt to make sure compaction is good to move what heat you can, but I definately wouldn't truck in other fillers.
RE roots, it'll go through small ones. stay out of the "drip edge" of trees if you can and it will be a non issue. Getting too close to a tree can impact it as well.