Help in determining pen stock diameter

[rosiedog]

Hi Folks
Apologies for the rather weak question - how do I go about determining my penstock pipe diameter. I am hoping to put in a small turbine in Scotland. 
I have an average flow of 3.9lt/s and a head of either 45m or 85m (depending on which building I supply the power to, domestic or livestock).
The trench has been dug for the house water supply and I would like to take advantage of it and put in the penstock.

Also any suggestions of where I could buy a turbine to run of this potential supply would be very useful.

I have read a number of the posts on this site and sadly do not feel that I have the competence to make the most of this small supply by building a turbine my self.

Many thanks in advance.

[frepdx]

Penstock diameter is chosen by looking at the friction loss. Too small a diameter and you start to loose power to friction losses, too large a diameter and it's a waste of money. You need the total length in addition to the flow rate. Here's an on-line calculator; http://www.engineeringtoolbox.com/hazen-williams-water-d_797.html . Looks like you're somewhere around the ~2" pipe range, depending on how long the run is. With an 85 meter head that's over 100 psi static in your pipe.

Ask the people you buy the turbine from to help you size the parts. Hopefully they will do this for free.

I don't know about Scottish suppliers, but here's some links;

http://www.realgoods.com/category/wind-hydro-transportation/hydro.do
http://www.homepower.ca/dc_hydro.htm
http://www.aurorapower.net/products/list/1/categoryid/4/level/a.aspx
(looks like the aurorapower offers free world wide shipping)