Re: UGF Heating Alternative

> > I was thinking about UGF and came up with the following: What about =
> > putting a spaced coil of hard PVC tubing(say 1/8 inch diam) under =
> > the substrate and pumping warm( or hot) water through it in a closed =
> > loop system? Any thoughts on this??
> 1. PVC is a relatively good insulator.  You would not get very
> effective heat transfer from the tubing to the substrate.

I agree, but ...

> 2. The gravel near the "hot" end of the coil would get more heat than
> the gravel towards the outlet end of the coil as heat is slowly
> dissipated.  Depending on how it was set up, you might be heating only
> the first foot or so.

A couple of things:

a. Since the PVC IS a good insulator, little heat would be lost during it's 
   travel.  Therefore, the water in the tube could be maintained at a 
   relatively constant temperature.

b. If the PVC is not a great insulator, the heat transferred out of the
   tube, would be proportional to the temperature difference.  If the 
   first foot were hot for some reason, less heat would be transferred,
   saving the heat for the next foot.  This transient behavior
   will eventually even out, again keeping the temperature in the tube
   relatively constant.

> 3. How hot does the water need to be to warm the gravel enough?  The
> Dupla coils get to about 90 F.  If the PVC acts as insulation, how
> much hotter does the water need to be?  And how will you get it that
> hot?

I think the question should be, How fast is the heat sinked away?
Wires have the advantage of having nearly instant heat transfer,
while the water and insulating pvc would tend to have a slow transfer.
Luckily in this case the environment is fairly moderate.  I do not
really know the exact impacts.

Recently, I was reading an article (unfortunately I cannot find
the reference) where the author did this setup.  In his case he used 
a parallel grid of 1/2 inch plumbing pvc.  On the ends of the grid
he used 3/4 inch piping.  He plumbed this to an outside box with a 
small powerhead and submersible heater.  His results were positive, 
I have not had the opportunity to experiment.  This setup offers
relative simplicity using commerically proven products, and relatively
inexpensive.  My concern with this setup is that I am not sure the 
flow, and temperature, would be the same in all legs.

Mark and/or Paula Bailey                  Time Flies Like an Arrow,
mbailey at crosslink_net                     Fruit Flies Like a Banana.