# Ideal earth temperatures when air temp is hot, and when cold?

Discussion in 'General Discussions' started by Rich76, Feb 8, 2019.

1. ### Rich76New Member

I was wondering what would be the ideal temperature of the earth in a geothermal horizontal closed loop system when the air temperature is really hot outside (100 °F), and also what ideal temperature of the earth when it's cold outside (20 °F) based on energy efficiency with thermostat set at 72 °F?

I understand I cannot pick my earth's temperature, but if I could, what would the temperatures be in the two scenarios?

2. ### docjenserWell-Known MemberIndustry ProfessionalForum Leader

This is not how this works. You reject heat to the ground over the season during A/C season, and you will heat it up. The more heats up the ground, the more inefficient (relatively speaking) the geo gets. Then you start heating, and the whole process reverses. It does not matter what the outside temperature is, since the whole system is ground coupled, which means the ground temp matters, not the outside temp.

3. ### Rich76New Member

Maybe I'm confused but I am referring to the ground (earth) temperature, and not the air temperature. I'm asking about what's the ideal earth temperature when you want to heat your house, and the earth temperature when you want to cool your house.

Less then 90*F in summer, more then 25*F in winter.

We are really talking about EWT, entering water temp, not ground temp.

Sure you could put miles of pipe in the ground to get the EWT closer to average ground temp, upfront cost would be very expensive.

Last edited: Feb 9, 2019
Rich76 likes this.

Not an expert but here's what I think I know (the experts might say I'm wrong, and if they do...I am!!)

The higher the EWT in the winter, the higher efficiency of geothermal, the lower the EWT in summer, the higher the efficiency of the geothermal (to a point...we rarely use our air conditioning in the summer in MN, so our normal ground temp of around 50 degrees is more than sufficient and I don't think higher temps would increase efficiency).

But the question doesn't make a lot of sense, because once you start extracting heat in the winter or rejecting heat in the summer, the ground temp surrounding the geo loops is affected.

Why are you asking? Maybe knowing that would help the experts give you better answers.

Rich76 likes this.
6. ### docjenserWell-Known MemberIndustry ProfessionalForum Leader

The warmer the ground is for heating, the better. The colder the ground is for cooling the better.

I don't want to sound like an smarta**, but this is what it comes down to.

Rich76 likes this.
7. ### Rich76New Member

This is exactly what I was wondering. Thanks.

Thanks to everyone for helping me understand.