Hi, In closed vertical loop, how to decide the minimum design temperature of loop fluid, by coldest temperature ? HP only has a minimum EWT. Thanks.
Min EWT is a parameter which the system designer will specify after weighing costs/benefits of first cost vs. system efficiency/operating cost. A good starting point for minimum EWT in design is about 20-25F below the deep earth temp in your project location. E.G. - If the deep earth temp in your area is 50F, a good starting point for minimum EWT would be around 30F.
If you push 3 gpm/ton through the loopfield, which is the nominal flow rate you want to shoot for in a closed-loop GHEX, the fluid will return back to the field 4-6F colder. If the minimum EWT coming into the unit reaches 30F, it will return to the field at 24-26F. That will be the coldest fluid temp you should see throughout the year.
