[time-nuts] Practical considerations making a lab standard with an LTE lite

Poul-Henning Kamp phk at phk.freebsd.dk
Sun Nov 23 12:49:46 EST 2014

In message <CANX10hB0KdrnaAYzGvM1gkDUJ7gkLth0AcdxCZG894hxbUScFQ at mail.gmail.com>
, "Dr. David Kirkby (Kirkby Microwave Ltd)" writes:

>He installs  ground source
>heat pumps for the geothermal energy.  He says that they actually work
>quite poorly in many cases.

There is a BIG difference between geothermal and ground heating.

Geothermal means you drill at least 50m (Iceland) or more likely
half a kilometer down, in order to harvest water at near boiling
point from the Earths geological heat-sources (mostly uranium decay).

Extracting more energy than available just means the temperature
drops temporarily.  It will increase again once you reduce the
pump rate.

Horizontal ground heat means that you are harvesting sunshine
accumulated in the top one meter of the soil.  Much of the energy
is harvested from freezing the water around the pipe thus pulling
out the relatively high melting energy of water.

If you extract more energy than you deposit sunshine, you end
up freezing a larger and larger volume of water/soil around
the pipe and your compressor will eat a lot of electricity.

In practice it looks like this:


(The two pictures show the same pipe, with and without frozen ground.)

Finally there is vertial ground heat where you drill down only about
40-80 meter, tapping heat mostly from ground water resources.    Most
places the ground water doesn't move fast enough to deliver the amounts
of energy extracted, and over time the source returns unusably low
temperature and must be abandonned.  Typically after 25-30 years.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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