geothermal using collector in a stream

We are due to build a new house shortly, we plan to build using T8 poroton blocks, and to install underfloor heating both in ground and first floor. We plan to install a solid first floor.
We will be using solar panels, and are still unsure whether we should use either geothermal or a pellet boiler. The house will be 5,100sq feet.
We have an everlasting stream running around the full site. We have heard you can use a stream as a geothermal collector. We know nothing about this type of system, and what are the requirements. Does anybody know anything about this type of system, or have used this type of system themselves? We are concerned we need permission from the County Council to install this system in a stream.
Our Builder is suggesting using a dual system of both geothermal and oil due to the size of the house? Would prefer not to go in this direction.
Any opinions?

No suggestions, but I'm jealous 5000 sq ft is practically a hotel!!

Wexfordman

It's a special build for reasons of disability, a main house and an annexe.

Assuming the T8 performs as its sold (different thread for this one) I would expect geothermal and ufh to be more than capable of heating your house. I am working on the assumption that you will be building airtight with HRV, high spec windows etc.

A wall u-value of 0.18 is very good. Get your plans out to a few companies and see what they say.

Your builder potentially is basing his opinion on his experience with the regular build type common in this country i.e. why would you want to put in more insulation than the building regs. Mixing oil and geothermal sounds like a terrible idea.

I got a heatload done for 3700 sq ft house based on T8, windows with u-value of 0.89, door 1.2, floor 0.1 and roof 0.13 and the peak load was going to be 11kw (8.5 for heating and the excess for hotwater). These meant quite a small heatpump.

Anyway, good luck with the build.