Based on the Thermal Conductivity Test, Geothermal Innovations has designed a geothermal field for our three building “district” that will have 10, 400ft bores. Since only one of the three buildings is currently being upgraded to an Energy Star Model, the engineers were required to take into account the fact that two of the buildings will require much higher heating and cooling loads since they will not be as well insulated or have Energy Star windows. Once the remainder of Yale Acres is upgraded to Energy Star, the current geothermal field will be able to service four, four-unit buildings. Even though a bore could have been eliminated from the system design through use of a propylene glycol instead of pure water, it was determined that the trade-off in equipment selection restrictions outweighed the cost benefits of a reduced field.
All ten of the bores have been drilled at this point and the vertical installations of GI.4TM heat exchanger should be completed by the end of the week. Next week the vertical bores will be connected via vertical trenches and then will be connected to the basements of the units.
Installation of the GI.4TM heat exchanger differs from the typical u-bend pipe installation. Unlike u-bend which comes in large roles, GI.4TM comes in 20-ft sections that have to be butt fused together as it is installed. During butt fusion, the squared ends of two pipes are heated by holding them against a heated plate. The plate is removed when the proper melt is obtained and the ends are promptly brought together and the joint is allowed to cool while force is applied. This welding technique creates and extremely durable bond that does not run the risk of separating like mechanical joints can sometimes do. However, since the heat exchanger comes in 20 ft sections and must be welded, installation time per bore is typically longer than u-bend. For a 300-400 ft bore, a team of two requires 3-4 hours for installation and about half that time with the assistance of an excavator or crane, which allows for installation of longer sections. However, both time and money are saved in the overall drilling and installation process with GI.4TM due to the significantly reduced field size.
Once the heat exchanger is installed, it is grouted in place with a thermally enhanced bentonite grout from the bottom of the hole up. Grouting is usually quicker for the Gi.4TM product as it has a grout tube slot in the center of the pipe to make for easy insertion. It also requires roughly 25% less grout volume in each well than with u-bend. The system is later pressure tested at pressures above the system design to ensure that there are no leaks.