(By: Dana Weeder, AIA LEED AP and Mike Fields)
I really like geothermal energy.
Before I am redressed by scientist friends, I should clarify that there is not much in the way of usable geothermal energy in the Northeast United States.
Direct Geothermal Energy harvesting is probably best known in places like Iceland, where more than half of the nation’s energy needs are met by capturing heat that escapes between the Earth’s tectonic plates. While this has a low environmental impact, there are a limited number of places on the planet which are close enough to tectonic heat sources to make effective use of it. If you are close enough, you run the risk of seeing more of the inner workings of the planet than one might like.
However, the growing geothermal industry in New England is based on what is called Ground Source Heating and Cooling (and I like that too). This type of system exploits the Earth’s ability to insulate, store and dissipate heat, allowing the ground to act as a sort of thermal flywheel.
So, what is a Ground Source Heat Pump (GSHP) system?
While our atmosphere is dynamic, with huge temperature extremes, temperatures several feet below surface of the earth are a relatively stable +/-55 degrees throughout the year. We can use the difference between the ground and the air to control building temperature with heat pumps which amplify the temperature differential through a change of state, similar to what happens in an air conditioner or refrigerator.
No, seriously, what is it?
Basically, you stick a plastic tube into the ground and pump a solution of water and glycol through the tube. The solution is then pumped into a heat pump which will either remove ‘heat’ from the solution (heating cycle) or add ‘heat’ to the solution (cooling cycle). In the summer, the heat pump returns the solution to the ground in a warmer state and is consequently cooled by the earth. In the winter, the heat pump returns the solution to the ground in a cooler state and is consequently warmed by the earth. So it’s a bit counter intuitive, but in a heating cycle, a heat pump can actually pull ‘heat’ out of a 55 degree solution and return the solution to the ground at 35 degrees. That 20 degree differential is borrowed out of the ground and put into the building. And the exact opposite occurs during the cooling cycle.
Why is this so great?
A Ground Source Heat Pump system differs from conventional systems by its ability to transfer heat rather than produce heat. A GSHP system does not heat from fuel, it simply moves existing heat from one place to another. This greatly reduces the building’s carbon footprint and lowers operational costs. So, the idea of borrowing heating/cooling is what makes it great.
Is that it?
No, since the only energy going into the system is electricity, the real promise of GSHP is as a component of on site power generation or more sustainable infrastructure. As electrical power inevitably becomes more efficiently generated and distributed, the savings from the economic and environmental savings will increase with them instead of becoming obsolete. There is no large roof top cooling tower that needs to be replaced every 20 years and no boiler taking up internal space.
But unfortunately, a lack of familiarity with these systems has been keeping clients and contractors wary and costs up. Many will require backup heat, oversize the systems, or avoid them altogether. There is great potential to plug our buildings into the Earth and architects and engineers need to build confidence by collecting and dispersing data on carefully designed systems.
Winter Street Architects recently completed the Needham Public Services Administration Building which has a series of (16) five-hundred foot deep wells located under the parking lot. Heat pumps are distributed throughout the 22,000 sf building which collects available heat to circulate through the building in the winter and discharge heat back into the ground in the summer. The system went on-line this past November and has been running without incident or backup heat through this most recent winter. The building was also designed to be ‘solar-ready’ with a large south facing sloped roof.
Is it right for all buildings?
Not yet. There are many variables in play; from the size of the building to its life expectancy to the thermal conductivity of the ground on which it is built. While the initial costs can still be steep and the return on investment still a bit long, it has to be a balance of economics, sustainable commitment and optimism. We think it will get there.
And we dig it.