# Looking for help calculating heat transfer for PEX ground loop project

• Misc.
Gold Member
You don't really know that. It's obvious to me that the OP likely has more experience in knowing how much energy it takes to keep HIS tank from freezing in HIS environment based on HIS experience. What he lacks is understanding how much heat he can pull out of the ground with this method. Which in my opinion is not much.
Well, if its 1500W, and he is making his own coil out of PEX that size he is going to be in for a surprise before he even gets to extracting the heat from the ground. I do know that.

Parameters:

Relevant Heat Transfer Equation:

This is the point about trying to compute the losses from the tank. If it's not 1500 W perhaps it could require significantly less tube...to get the heat into the tank (at least).

Overall I suspect its not going to be feasible, but hey...that's what we are trying to figure out for them. Perhaps there are configurations that could be considered so that it could work. I don't know yet...because we haven't tried to compute the actual losses from the tank ( 100 gal - which is not huge as far as tanks go).

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Lnewqban
Gold Member
Another thing I should consider is how big a fool I am trying to fine tune design something for free that someone else could sell with no financial obligations. This is the story of my life...everyone is making money but me! I'll always be a schmuck...

Gold Member
...because we haven't tried to compute the actual losses from the tank ( 100 gal - which is not huge as far as tanks go).
The loss from the tank will be much larger than the heat loss from one of the units in the link I provided due to ground contact. An automatic waterer is designed to avoid contact with anything that can draw heat away from the bowl Also, the more animals that drink from an automatic waterer, the less trouble they will give. Their thermostats can be set so that incoming water is warmer than the setpoint. So the more water that is drank, the less the bowl heater needs to run.
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So, while this post gives no help in determining the heat loss, I thought it was worth pointing out the differences. It's a no brainier to me. I'd use one of these before attempting what the OP wants to do.

Lnewqban and erobz
Gold Member
The loss from the tank will be much larger than the heat loss from one of the units in the link I provided due to ground contact. An automatic waterer is designed to avoid contact with anything that can draw heat away from the bowl Also, the more animals that drink from an automatic waterer, the less trouble they will give. Their thermostats can be set so that incoming water is warmer than the setpoint. So the more water that is drank, the less the bowl heater needs to run.
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So, while this post gives no help in determining the heat loss, I thought it was worth pointing out the differences. It's a no brainier to me. I'd use one of these before attempting what the OP wants to do.

View attachment 321573
Yeah, see post #7. I was skeptical immediately. I've made Teflon pipe heat exchanger in the past to control the heat of formation in mixing water and concentrated sulfuric acid. Plastic tube is not good material for transferring heat radially through its walls.

Dullard
I don't know how large the trough is - 300' of pex will coil nicely in a 6' circle. I've seen it done with a PVC frame.

The other significant concern is: a 1500W electric heater works (or can work) 24 Hours/day. This ain't that.

erobz
Gold Member
I don't know how large the trough is - 300' of pex will coil nicely in a 6' circle. I've seen it done with a PVC frame.
Admittedly shocked, but the math does support that.
The other significant concern is: a 1500W electric heater works (or can work) 24 Hours/day. This ain't that.
Yeah, it can stay cold (and cloudy) for 24 hr/day for long periods of time (at least where I live). Unless there is a barn full of batteries or you are in a climate that doesn't experience prolonged cold spells, there might be some issues.

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