GSHP: Ground Source Heat Pump
I have yet to find a way to afford to create the unique Solar Pond GSHP combo at my eco - adventure, my old house.   The GSHP will save energy, save money, and reduce carbon (Click Here for more).  The simple payback is less than 15 yrs.  I just don't have the capital, nor a good enough job to get a loan.  Below are links to my rough design concept, building energy calculations, GSHP calculations, energy savings, energy and ground source heat pump costs, etc..
GSHP Design Click Here
DIY GSHP Calcs  Click Here
Solar Assisted Ground Source Heat Pump Click Here
First Attempts: GSHP Feasibility and Payback Click Here

The Good News: 

I've come up with the ULTIMATE GUIDE TO Ground Source Heat Pumps
Here's what will make you the ideal GSHP candidate: Click Here


GSHP: Ground Source Heat Pump - Design


Indirect Pond Loop

The slide show above seques through the conversion of the pond to the thermal sink for an indirect pond loop GSHP. 

This a tiny pond by all the rules of thumb.
-- There is a large water flow from 2 springs 
-- It ices over only when temps drop into the teens and quickly re-melts.  
Using spring water directly with a heat exchanger creates a maintainence task, and a limited life for the heat exchanger as it reacts to oxygen, minerals and chemicals in spring water - and the solutions needed to keep it "clean". 
Using the pond and indirect loop as a huge heat exchanger is:
--  Maintainence free
--  Chemical free
--  Uses fewer resources - as it won't need replacement
--  Would be applicable to use in true "dirty" water environments
Though too small for stratification I've seen evidence it does at times. 
Why does this matter?  
Efficent GSHP tubing / coil placement.
We all know hot water rises, but, cold water rises too, surprise!  From about 40 to freezing cold water rises. 
If I can encourage this in winter, then putting the loop near the the bottom will increase efficency summer and winter!  The Physics of Cold Water - Surprise
Backup Plan:  The indirect gshp loop in the pond will tranfer the greatest part of the BTU load, but, there is potential in the grounds to "finish it off".  If the pond and spring flow does not work, I can easily drop a double run of 1 1/2 inch tube at the bottom of a 6 foot deep trench, and get over 600 feet of tubing, enough for 1/5 the load plus, which can also be thought of as 1/5 of the typical 10 degree delta T on the ground loop, or, 2 degrees.  GSHP Site Work - Practice and Theory 
Energy Savings and Carbon Reduction
Ground source heat pumps do:
-- save energy - SOURCE energy!
-- reduce carbon use!
-- use renewable energy - geothermal energy and solar energy!
Consider the entire Life Cycle Analysis, as LEED v4 is moving to embrace.