Geosource Heating

[tbedford]

Hello all;

I have before me an interesting problem.

We are sinking a PVC frame approx 10 feet Wide by 30 Length x 4 feet High. No problem to place it floating in the ocean. The frame will fill with saltwater once there. The frame will hold 9 coils of 2" HDPE approx 200 feet per coil. Eventually the coils will be filled with a glycol solution serving as a heat exchange medium for a bank of compressors.
The frame will rest on a sandy, gentle slope at approx 40 feet below the surface.

Question is ...what is the best way to control a slow, accurate descent for this large frame?



Thanks, TAB

 

[VinceNY]

Speaking from a SCUBA divers stand point, if I had to raise something without a mechanical hoist, I would use air bags. So if I had to lower it, I quess I would do the opposite. Start with inflated and deflat the lift bag. 40' isn't very deep, how accurate do you have to be with your location? If not pinpoint, can't the divers guide it and nudge it into place when it's close to the bottom using by bouncy control.

 

[ActiveSolar05]

Hi;

FIRST> You DO NOT want to use HDPE. It develops cracks when coiled like this. You want PEX-A, engel method. This is a cross linked polyethylene made with a hydrogen peroxide process yielding more cross linking than PEX-B, or PEX-C.
See

http://www.REHAU.com

Second> Use a vertical tube at each corner with a second tube inside. The outside tube has some relatively large holes in the side wall at the bottom end, and the holes get smaller as you go up the tube. ... Now we have a gradually increasing resistance as the unit finds bottom.... The free descent rate is controlled by an air bag on each corner with an air valve that is remotely controlled.

Have Fun ( OTEC MAN )

 

[marcoh]

Talk to some local commercial divers, technically should not be an issue to lower it and position it whereever you would like it to rest, just need the right equipment (lift bags etc).

Hope you have thought about how to anchor it all to the bottom, sand migration, tidal movement etc. Any decent storm will create sufficient surge at 40ft to wreck any PVC frame!

 

[atlas06]

Consider some serious shock absorbers, may be the whole thing should rest on large inner tubes just in case you lose control of the thing as it goes down. The inner tubes should help saving your structure.

Let us know how this thing went, will you?

 

[Jason9999]

If you are hiring profesional divers to place this you shouldn't have a problem. If not a few of the statements alluded to using lift bags to drop this. You need to add air as you decend not reduce. As your depth increases the air takes up less space decreasing the displacement of your lift bags. This could lead to a runnaway decent. Something to consider if you attempt to place from the surface. The opposite can also be a problem. If you have nearly neutral buoyancy and wave action causes a surge and pushes your contraption up enough you could experience positive bouyancy that would lead to a quick decrease in depth and a corrosponding increase in displacement of you air ballast. This could lead to a runnaway ascent. It's not usualy a problem until it hits the surface and dumps all the air and then sinks.

Just something to consider. Good Luck

Jason

 

[MarauderX]

For this system, I would place structural supports for the frame to be connected to. You don't want it to just rest there, as it will drift away. Slopes can be deceiving, and I wouldn't trust one just because it is underwater.

To drop it down slowly I would use a crane. Provide connections at multiple points, if not surrounding it, so that it can level out automatically whether lowered or lifted. A crane operator has a lot of experience with moving things slowly into place, and (s)he can stop when connection points are reached to hold it in place while it is lashed down and doesn't slip during placement.

http://www.eypmcf.com

 

[south4scuba]

Just returned from a dive trip. The surge at about 50 feet was sweeping me 4 to 5 feet back and forth. You don't give the geographic location that I read so I don't know your local conditions, but beware of the powerful forces of the ocean. A recent hurricane rolled a 500+ foot shipwreck over in Key Largo, FL.

Sinking this frame could be done similar to the way oil rigs are sunk for installation. Put a couple of valves on the PVC pipes and slowly open them to flood the pipes and it should sink.

Just my humble opinions.

 

[tbedford]

Thanks for all the return posts.

The coil fields are located in the small protected Depature Bay adjacent to BC Ferry terminal, Nanaimo, BC, Canada There is no surge although small waves (2 feet) can be expected. The substrate is sand ( we did squish one starfish but they can wriggle out and grow more arms) and I expect our field will sink about 6 inches over time.
We used a small crane on a barge to lower the coil fields. Each field was filled with freshwater slowly from the local fire hydrant. It sank slowly and perfectly level... about an hour from start of fill to bottom placement. We sank five fields over four days as we couldn't have a diver in the water when a ferry boat was in. The diver basically watched but was ready to halt the drop if things went tilt-y.

Start-up is in about two months.

Thanks, Tom