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Geothermal Open Loop vs. Closed Loop

Posted by Taylor Hendricksen on Jan 16, 2012 in Ground Loops | 0 comments

This is a topic that is too large to cover in depth in one article. This will be just a few of the basic points to consider.

Closed loop system circulate fluid, open loop systems get feed water and then discharge it. They both have their ideal applications and I will not attempt to say which one is better.

Geothermal Open loop systems

Geothermal Open loop systems require abundant groundwater to operate and this is not available in all areas. The water is pumped from the aquifer through the heat pump and then is discharged. Most often the water is discharged directly back into the aquifer that it came from resulting in no consumptive use of the water. Different local areas will have their own rules and regulations with regard to ground water and will need to be followed. Open loop systems are generally less expensive than closed loop because you do not need to design and build a closed loop heat exchanger into the earth. You simply access the ground water and pump as much of as you need to the heat pump and then discharge it. For this same reason open loop systems will operate with higher average efficiencies than closed loop. The entering water is always the same temperature and will not lower during the heating season as will happen with closed loop.

Geothermal Closed loop systems

Geothermal Closed loops can be build in several different configurations but they are all simply acting as a heat exchanger with the earth. Many considerations are part of a closed loop design including: site characteristics, soil and rock conductivity, static water levels, system loads, and geographic location. The basic closed loop types are: horizontal, horizontal slinky, vertical, and pond. We have specific articles on each of those types. A heat transfer fluid is used to circulate through the earth loop and is usually water/methanol or glycol/water to provide adequate freeze suppression. A closed loop system requires a flow center or pump pack. Flow centers are a non pressurized tank and circulator that will be non pressurized. Pump packs are used when the earth loop will be pressurized. In both pressurized and non pressurized systems the circulators need to be sized to be able to move the fluid through the earth loop pipe err 3 feet per second. This speed will provide a turbid flow and will most effectively use all the surfaces of the pipe for heat transfer.