The original design work on Geothermal heat pumps, and most of the performance data has been developed in Tulsa Oklahoma. The conditions are will suited, winter thermal loads and summer cooling loads are fairly equal, and well balanced. The sub-surface is sandy loam soil with good moisture conditions (ie. good heat transfer).

As far south as Dallas the conditions are fairly good, however the summers are hotter. Because of this somewhat asymmetrical load the loops tend to build heat very slowly from season to season. A good running system matched with a very efficient house will run summer loop temperatures of 85-88 deg. All is good.

GeoSmart Supply heat pump for pool geothermalFurther south things start to change, the differential in winter/summer load is much more pronounced, and asymmetrical with a much larger cooling load (putting heat in the earth loop) vs. winter load when heat energy is removed from the ground loop.

Other factors in areas west of the uplift, Austin, Waco, San Antonio (West of I-35) is that the subsurface is mostly dry limestone. In this area seasoned ground loops commonly in operation two years or more run summer temperatures of 95 deg. and higher depending on the load and the age of the ground loop.

The physics at play are simple, the earth is a good insulator, and without moisture to help move the heat energy it simply stays and accumulates, unless it is removed by other means.

So what is the effect of higher ground loop temperatures on the performance of a Geothermal Heat pump?

Geothermal heat pumps have performance numbers published under three standards each with different entering water temperatures. Advertisements by the manufacturers can post performance numbers derived from the most favorable testing temperatures, regardless of the actual temperatures that can be realized in areas of asymmetrical loads and or Sunbelt heat conditions.

The performance data below is from a two speed 3 ton Geothermal heat pump, you see the three ratings, Water loop at about 85 deg. water, Ground Water at about 58 deg. and Ground loop at standard test std. 77 deg. entering water.

In the low speed mode the numbers jump up to 27 EER for the ground water number. Naturally that temperature does not exist in the south. If you look at the 80 and 100 deg. numbers the EER for 95 deg will be about a 11.5 EER.

All the sales guys will talk about is the number printed on the brochure 27 EER, and not the nominal real time performance based on actual entering water temperatures in the South.

Pool Geothermal heat pumpSince the virgin sub-soil temperature is 68/70, a newly geo system will have loop temperatures about starting out about 10 above sub-surface temperature, and will increase over a few years to 25 deg. above sub-surface temperature. In areas east of I-35 where there is more moist sub-surface soil the loops will run around 85 to 90 deg. If a house has lots of glass, and is a larger heat load, longer run times, the loops will warm up a little faster.

There are several solutions that can be employed when the system is new or after the fact and the loops are overheated. Hybrid Geothermal is a concept that uses an evaporative heat rejection device a Thermalflow Cooler, in addition to the ground loop. The devices are used in several ways, one application is to use the loop cooler to offset the need for some ground loops thus saving on first cost. The Thermalflow unit will reject a huge amount of heat and offset the need for a number of expensive ground loops.

Another Hybrid application is called “Enhanced Geothermal” where the cooler is used to enhance the performance of the Geothermal system by reducing the loop temperature. It can be used in the summer to reject the high grade heat before it gets to the earth loop thus lowering the return water temperature. The more active and effective application is to use the Thermalflow system in the winter to take advantage of the free cooling, and actually pull heat energy from the earth around the well bores. The earth can then ab

Pool geothermal with cooling tower

sorb much more heat during the summer and provide dramatically lower loop temperatures thus enhancing operating efficiency. The Thermalflow system has one more very interesting application in which a swimming pool can take the place of a ground loop. The pool provides a good deal of earth interface with the added advantage of having a huge heat sink in the thermal mass of the water itself. The Thermalflow system keeps the pool at the desired temperature in the summer. The Geothermal heat pumps units get a constant 85 deg. water, and the customer gets free pool heating in the spring and fall to extend the swimming season. The “PoolTherm” system installs as about half the cost of a ground loop system.

pool geothermal heat exchangers install heat pump

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