PVC info needed -

[MooseToo]

i need to bury an air duct as deep as eight feet below grade - the air will be solar heated so i don't imagine the temp will exceed 160 degrees -

i'd like to use 4 inch schedule 40 PVC for the ducts -

how would i determine if my demands (heat, loading pressure) will exceed the characteristics of such ducts ? anyone have experience using PVC for something like this ?

thanks !

[randallhilton]

If you're moving air, I doubt you'll see much in the 160 degree range unless you have some sort of really efficient concentrator.

Standard PVC schedule 40 or SDR 35 pipe is typically rated for 140 degrees but that's a rating for pressurized water piping. If you're not going to have much pressure, I would guess that you have a bit more fudge factor.

NOTE: PVC expands and contracts with temperature fluctuations so if your duct is over 100 feet or so in length you'll need to allow for expansion some how. (I would use the SDR 35 with gasketed joints and perhaps some thrust blocks at each end just to help keep the pipe in place.

I would bed the pipe with gravel or sand, something that would allow a little movement. Big rocks will eventually eat through the pipe.

Lay the pipe on grade (sloping to one end) so that you can periodically drain condensation from the system.

I don't know what your plan is, of course, but with a little research you may find that a liquid will move heat better than air will.

[MooseToo]

the plan is to deliver heat to a buried gravel heat sink prior to constructing a pole barn - trying to bottle summer to use in the winter -

i'd seen PVC used as an exhaust stack on some propane water heaters and assumed they had a pretty decent hi-temp restriction figure -

[AlchemyAcres]

The manufacturer should have engineering literature or their engineering department should be able to help with questions on specific applications.

Around here most of the PVC comes from Charlotte Pipe.


~Martin

[randallhilton]

the plan is to deliver heat to a buried gravel heat sink prior to constructing a pole barn - trying to bottle summer to use in the winter -

I've seen a little info on that. I'd suggest some more research. I really don't think air is going to accomplish what you want. It just can't carry as many btu of energy as a liquid can. The higher the heat differential between your collector and your storage, the better off you're going to be and a liquid will handle that better.

Also... if you build it correctly, your collector can even gather some heat on sunny winter days.

Have you looked into insulating your heat sink pit? The surrounding earth will be relentless about soaking up your heat.

Here's one interesting link:
http://www.ces.purdue.edu/extmedia/ae/ae-89.html

i'd seen PVC used as an exhaust stack on some propane water heaters and assumed they had a pretty decent hi-temp restriction figure -

In 30 years of plumbing I've seen a lot of really bad installations like that too. :D Actually. . . a high efficiency "condensing" heater can, and should be vented with pvc but a plain ole water heater needs to have double wall metal flue pipe.

[machinemaker]

I remember Martin sharing a web site on passive annual heat storage. It looked like this is what they were doing and using pvc pipe. I think that a search on PAHS was where I saw this.
kent

[MooseToo]

I remember Martin sharing a web site on passive annual heat storage. It looked like this is what they were doing and using pvc pipe. I think that a search on PAHS was where I saw this.
kent
thank you !