Boston-based Shawmut Design and Construction installed several geothermal wells in Harvard University’s Radcliffe Yard to provide heating and cooling.
It has been well-established that the built environment has a profound impact on our natural environment, economy, health and productivity. That knowledge, combined with recent exposure in the media about environmental protection, has led to green design and energy efficiency becoming hot topics among builders, designers and clients. Under pressure from their students, faculty and donors, institutions across the country are increasingly implementing green building techniques in the construction of their facilities to foster more efficient energy use and help reduce the impact that their buildings have on the environment. While the technology behind geothermal heat pump systems, also known as ground source heat pumps, has been around for decades, institutions are only now beginning to seriously explore and embrace this renewable energy source as a way to not only limit their environmental impact but save money by cutting operational and maintenance costs associated with the heating and cooling of their buildings.
Locally, this trend has taken off – Shawmut Design and Construction has been involved in the installation of several area geothermal heat pumps, including the historically significant Trinity Church of Boston in the middle of Copley Square, and the rural Noble and Greenough School in Dedham. Recently, the Radcliffe Institute for Advanced Study at Harvard University commissioned a construction management team from Shawmut, engineers from Cosentini Assoc., and architects from Goody Clancy, to install five standing-column wells in Radcliffe Yard to provide heating and cooling for the renovated classroom building, Byerly Hall.
So, what are geothermal wells anyway? Although they have been gaining traction in the construction world, you may not have heard of a geothermal heat pump system. The geothermal heat pump system typically uses a standing column well design to tap into the relatively constant temperature of the earth which averages between 45-65 degrees Fahrenheit. The wells are typically drilled to a depth of 1,500 feet below the earth’s surface. At Byerly Hall, five standing columns have been drilled to that depth, each horizontally separated approximately 50 feet to 75 feet from an adjacent standing column.
A submersible pump installed in each standing column draws water from the bottom of the well and delivers it via a piping loop to the heat pump units within the building. The well water is then returned to the top of the well below the static ground water level. The water-to-air or water-to-water heat pumps convert the energy from the well water to meet the heating and cooling demands of the building.
Ground source heat pumps installed within the building are connected to the standing column wells with underground piping. The deep vertical standing columns act as a heat exchanger using the ground as a heat source in the winter and a heat sink in the summer. Building heat pumps have electric driven compressors that concentrate the energy absorbed from the ground and release it at a higher temperature in winter and a lower temperature in summer into the building.
The high efficiency of this system is due to the minimized temperature differential between the ground/earth source and the desired indoor temperature. This minimizes the load on the building’s heating and cooling system, especially during the temperature extremes of winter and summer. The system doesn’t have to work as hard and therefore uses less energy.
Another benefit of a geothermal heating and cooling plant is an aesthetic one – a manhole cover installed at grade level for each standing column is the only item seen outside the building. Therefore, outside HVAC equipment such as air cooled chillers or cooling towers are not required.
While the finished system is based on a refreshingly simple concept, these wells require careful planning and experienced construction managers and engineers. Part of project planning involves a long-term cost versus benefit analysis of the building systems. The drilling and installation of these wells does add initial cost to a project, however, energy savings due to system efficiency will typically pay back the investment within five to 10 years.
Drilling Wells
In July 2007, drilling and construction of five 1,500-foot deep, 6-inch diameter standing column wells began on the Harvard University campus in Radcliffe Yard, a busy urban site in Cambridge. Located in an academic and residential area, the site was challenged not only by sensitivity to the noise generated by the drilling process, but the fact that there were neighborhood ordinances in place which only allowed work between 7:00 a.m. and 7:00 p.m., which complicated the already tight schedule.
Because the space requirements for a large drilling operation are considerable, the small area made careful logistics planning a necessity – work had to be completed on the wells and drilling equipment moved out before work could begin on the renovation of the actual structure. Two large drill rigs were used during the drilling process in order to meet the project schedule.
The tight schedule was further impacted when higher groundwater volumes than anticipated were encountered. During drilling, the water is removed from the well using compressed air in order to optimize drill efficiency. The drilling contractors, DRAGIN Drilling of Wareham, included 100 GPM in their bid scope, with incremental costs over that water volume. When the wells yielded volumes in excess of 100 GPM, the project team was able to move forward quickly due to the already agreed upon pricing provisions for water management.
Wells associated with ground source heat pumps are typically regulated by the MassDEP under the ground discharge program and the underground injection control program. Because the water removed from the wells during drilling is filled with sediment and debris, permits had to be secured from the Massachusetts Water Resource Authority to ensure that the removed water is properly cleaned and filtered before it is returned to the site storm water drainage system. A filtration system was integrated into project planning and site logistics.
As the water and rock cuttings were expelled from the well during the drilling process, they were pumped through a series of holding tanks where the heavy sediment was able to settle out before entering a 3-step filtering process that removed any remaining sediment or contaminates, after which the water was returned to a nearby storm drain. This process ensured that the water was reclaimed and reintroduced into the environment without any negative impact to the local storm water system.
Harvard’s forward-looking planning will not only lessen the impact of their building on the environment but lessen their bottom line as well. Dramatic cost savings are possible with geothermal systems. Heat from the ground is free – and the only electricity needed is for moving that heat between the building and the ground. Although there is an initial cost to drill and install the system, that investment can be paid back in less than 10 years. Best of all, ground-source heat is a naturally renewable thermal source and friendly to the environment. With these benefits, we are sure to see more geothermal wells being installed not only at Harvard, but at institutions across the country.
