# Thermal exchange calculations between water/glycol

1. May 28, 2012

### mwcon

I am trying to determine the expected heat exchange between flowing ground water in gravel/clay soil (that runs on top of blue clay) and glycol fluid in plastic pipe (1 1/4"). For my current interest, estimated ground water temperature of 60 degrees seems best. I am trying to determine the efficacy of a horizontal geo heat pump system for a residence. Outside ambient temperature would be 45 degrees.

Michael

2. May 29, 2012

### haruspex

These are the other relevant factors:
The thickness of the pipe wall (is 1.25 the i.d. or the o.d.?)
The conductivity of the plastic
The conductivity of glycol
The flow rate
Whether the flow will be turbulent
The pipe length
The initial temperature of the glycol
The lateral flow rate of the water

Why do you mention the ambient temperature? Is that the initial glycol temperature?

My instant reaction is that the pipe is rather fat. You need a long narrow pipe with a thin wall. The choice of material could be significant.
If there's limited room in the watercourse, it's best to have the glycol flowing in the opposite direction to the water. I.e. the glycol starts at the end where the water may have been cooled somewhat by earlier glycol.

3. May 29, 2012

### mwcon

Thanks for responding. I realized after posting that it was a pretty complicated question. I am trying to determine if a horizontal ground loop geo heat pump system can work for heating a house that I am planning on building. The pipe size is the standard tubing that is used in these applications if copper isn't used. The reason for listing ambient temperature is I thought that this was the best approximation for the incoming glycol tempurature. The BTUs per foot will determine the length of the piping but I am anticipating about 1800 lineal feet of double tubing. I don't know the lateral flow of the ground water. When I have excavated a discovery trench, it ran like a small stream over the blue clay. My hope in asking this question is that I would be able to identify 'range' data for the various categories to determine what range (pipe sizing, flow rate and heat exchange) I would have to fit into to make the project work financially.

My reason for phrasing the question as I did was that the heat exchange data would help me determine the pump sizing and the cost for running the pump to the exchanger in the basement. Thanks again. Michael