HYDRONICS e Continued from p 44
heat pump, and that gives you the requirement for sizing the submersible pumps,” said Orio.
Pathogenic purity “Two key things come together when
determining system head pressure,” said Orio. “The design engineer determines the TDH (total dynamic head) in the building, and the geothermal engineer determines the TDH from the 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 sanitation. 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,
46
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 which would then put it on a downhill course and into Merrimack River, requiring another, higher level of environmental permitting. Yet aquifer flow under MCNH was much better than expected. The flow of water in the wells is so steady, easily maintaining design temp despite the influence of system geo-exchange, that there’s no need even for a five percent 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 conserves pump life and the aquifers as well.” The system is a great
e Circle 31 on reader reply card
example of what can be achieved when several outstanding companies come together for one project. ;
phc march 2011
www.phcnews.com
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