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Formula for environment-friendly grout revives heat pump industry

DOE/Brookhaven National Laboratory : 17 July, 2003  (Technical Article)
Scientists at the U.S. Department of Energy's Brookhaven National Laboratory have received an award for a three-year research program credited with reviving the geothermal heat pump industry in northern New Jersey.
The award, from the Eastern Heating and Cooling Council, recognizes Brookhaven's success in developing a grout that meets New Jersey's strict environmental standards while increasing the efficiency of this technology.

The main advantage of geothermal heat pumps is that they heat and cool buildings without burning fossil fuels. Instead, water-filled pipes draw heat from or dump heat into the ground 200 to 300 feet below the surface. If the grout surrounding the heat-exchange pipes cracks or shrinks, however, the boreholes housing the pipes can channel surface runoff contaminants directly into groundwater.

'The whole industry came to a grinding halt,' says Brookhaven materials engineer Marita Berndt, who was contacted by the New Jersey Heat Pump Council for help. Brookhaven was already working on grouts with increased thermal conductivity. These grouts also had advantages in terms of sealing capability, reduced shrinkage and improved crack resistance. Brookhaven performed additional tests to ensure that their formulation would meet the NJDEP requirements.

'This is a great example of scientists working together with industry and environmental regulators to solve a real world problem,' Berndt says. The new grout, called Mix 111, is composed of cement, water, silica sand and small amounts of superplasticizer and bentonite. Brookhaven does not manufacture the substance, but rather, has made the formula available to the industry.

'The whole objective was to come up with something people in the geothermal heat pump industry could use. They can buy the ingredients themselves and mix it themselves to keep the cost down,' Berndt says.

Experimental tests have shown that Mix 111 is less likely to be infiltrated by water, bonds more firmly to pipes, and is much more resistant to shrinkage and failure than conventional grouts. Numerical analysis was performed by A.J. Philippacopoulos to examine heat transfer characteristics and thermal stresses developed in the grout under operational conditions. Furthermore, when tested in two different climates and geological areas, Mix 111 was 29 to 35 percent more efficient at heat transfer than traditional grout.

Mix 111 is now approved for use in New Jersey. It has already been used in several residential and commercial projects throughout the U.S., and has proven to be cost-effective.
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