Geothermal Continued from page 54
lower manifold, insuring 25 psi at the furthest, fourth floor heat pump. “You take the furthest well and the most dis- tant heat pump, and that gives you the requirement for siz- ing the submersible pumps,” said Orio.
Pathogenic purity “Two key things come together when determining sys-
tem head pressure,” said Orio. “The design engineer deter- mines the TDH (total dynamic head) in the building, and the geothermal engineer determines the TDH from the
Four tips from Carl Orio for designing and installing a commercial standing column geother- mal system. • All the deep well drillers in the Northeast have a
second compressor on a trailer to back up the com- pressor on the drill rig. The truck-mounted compres- sor is sufficient to a depth of about 800 feet. Any deeper and one compressor just can’t keep pace with high-yield wells. • The handling of VFD systems can be tricky. Run
lines for VFDs separately. Even though you may have numerous VFD lines side-by-side, they all have to be in separate conduit piping. All VFD manufacturers require shielded wire, and some even require running the lines through steel conduit. Electronically speaking, VFDs create a very ‘dirty’ electronic signal. VFDs are actually capable of emit- ting signals in the AM radio range. You can drive through town with your car’s radio set on a weak AM frequency, and hear which house has an exercise bike or Stairmaster with a VFD. If the lines are run togeth- er, they can interfere with each other’s signal. • Over the years we’ve learned that when designing
a geothermal system over 10 stories high, it’s eco- nomically viable use a primary and secondary well loop with an intermediate heat exchanger, instead of pumping well water all the way to the top. Some effi- ciency is lost with the intermediate heat exchanger, but somewhere between eight and 12 floors, that effi- ciency loss is justified by the money saved in system water pumping. • The 10-8-6 standing column well is, for the most
part, a special purpose well. Because of the higher installation cost, industrial systems that incorporate standing column wells generally utilize 8-6-4 wells, and residential systems always do. The 10-8-6 shines when ground space is limited.
Various systems in New York City and several sys- tems in Connecticut have used this BTU monster. Using the larger well cuts down on the number of wells needed. At MCNH, it would have taken five additional wells if 8-6-4’s had been used. Not only would this have been too many wells to fit in the available green spaces of the parking lot, but would have also required a third manifold.
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well to the manifold.” Together, these provide the pressure drop to the highest heat pump in the building at peak flow. Suspended above drop-ceiling tiles are either three or
four-ton ClimateMaster TS units with copper-nickel heat exchangers. The majority of the units serve two bedroom areas. A big advantage in having many small units — as opposed to a large, central unit for each floor — is sanita- tion. With the smaller systems, air movement is limited to two rooms, greatly reducing the threat posed by airborne pathogens. “I was skeptical at first,” said Sid McDonald, director
of facilities at MCNH. “The bugs got worked out the first year the system was in, and ever since then, it’s has been phenomenal. I was really impressed with everyone involved and the technical solutions that were offered.”
BTU gusher; a “geo dream” According to Carl Orio, most standing column wells are
designed to bleed off 10 percent of the water used. In the case of MCNH, the wells were designed to bleed off only five percent of the geo-exchange water. This was done to prevent water from overfilling the property’s detention pond
So rich and steady is the supply of water-
borne BTUs that, for eight or nine months of the year, only 10 of the 16 wells are used. So, just to keep things equal in the wells, BTUs are tapped from different wells on a rotating basis year-round.
which would then put it on a downhill course and into Merrimack River, requiring another, higher level of environ- mental permitting. Yet aquifer flow under MCNH was much better than expected. The flow of water in the wells is so steady, eas- ily maintaining design temp despite the influence of sys- tem geo-exchange, that there’s no need even for a five per- cent bleed-off of water. But it gets better. So rich and steady is the supply of waterborne BTUs that, for eight or nine months of the year, only 10 of the 16 wells are used. So, just to keep things equal in the wells, BTUs are tapped from different wells on a rotating basis year-round. “It’s really amazing how well the system has worked
out, almost like a dream,” said Skillings. “By rotating wells, MCNH not only saves even more electric, but con- serves pump life and the aquifers as well.” The system is a great example of what can be achieved
when several outstanding companies come together for one project. n
March 2011
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