Two Florida Schools to Reap Energy Savings
When a new high school and middle school complex was planned in Chipley, FL, the Washington County, Board of Education opted for geothermal heating and cooling despite higher initial cost than for conventional systems.
"The board invested additional money, about $500,000, for the long-term energy cost savings," said Bobby Creasp, vice president of TRA Architects of Tallahassee, FL, project architects. "The board put in a considerable amount of money up front to help save the taxpayers money forever on energy costs."
Creasp said preliminary studies showed possible long-term energy savings of up to 40% over the life of the geothermal system, whose use was initially proposed by some of the school board members.
Although geothermal traditionally is defined as 'of or relating to the earth's initial heat,' the geothermal source for the Chipley school project is groundwater. The system does not require a heat transfer from the hot strata of the earth.
The project architect said two types of geothermal systems initially were considered for the two-school complex, which is now nearing completion.
A piped well system, which would have involved installation of some 75 miles of pipes in the schools' athletic field, was considered until a test well hit water at a depth of about 60 feet and it was determined other wells for the piped system could not be drilled to the required depth at the site.
Plans then shifted to a supply and injection well system involving four eight-inch wells, each 240 feet deep and supplying 400 gpm, and three injection or disposal wells of the same diameter and drilled to the same depth This system also has lower initial cost than the other proposed system.
Creasp said the supply wells pump 73-degree water to a stainless steel plate heat exchanger and the water is discharged into the disposal wells at 88.3 degrees from the middle school and 88.1 degrees from the high school. The system allows the aquifer water to serve as a refrigerant condensing system and as a heat sink for water disposal. The wells are controlled by variable-speed pumps which also reduce energy costs for the geothermal system.
"The system also allowed us to use water source heat pumps with condenser loops and no chillers," Creasp said. "It's real inexpensive to operate and it's cost efficient, which means the owner saves money," He added the water source heat pumps also have a life expectancy about 50% longer than traditional split-source heat pumps, are smaller than traditional heat pumps, and do not require outdoor condenser units which could be damaged by students.
The geothermal system has a higher energy efficiency rating of 12.0 to 14.0 compared to 9.0 to 10.0 for an air-cooled system and it provides the capability of having the heating system turned on in some portions of the schools while the cooling system is running simultaneously in other parts of the facilities.
Creasp said temperatures in various parts of the school are thermostatically controlled just as they would be in a traditional climate control system.
"In the classroom you don't know the system is any different than other kinds of systems," he said.
Washington County school personnel are anxiously awaiting completion of the high school portion of the project so the full geothermal system can begin operating, said Mike Welch, deputy school superintendent. "We are anticipating considerable savings based on the cost of operating this system and a conventional heating and cooling system and we are certainly anticipating reaping the benefits of those savings for the school system," he said.
"We will achieve those savings over the life of the schools. If you consider the existing Chipley High School was built in 1930 and has been used for 70 years, and if the new geothermal system works like it's supposed to, we could save up to 40% on heating and cooling costs over the life of the new schools. That would amount to quite a lot of money saved during that time," he added.
Welch said the county school board didn't take the decision to utilize a geothermal system lightly. The board obtained information from Gulf Power Co., geothermal industry associations, and others before approving the system for the schools, which total 192,681 square feet and will serve some 1,200 students. "We were convinced by talking to everyone involved that a geothermal system would be the way to go," he said.
The deputy superintendent said the system selected for the two schools was chosen because it was the least costly of the geothermal systems the board considered. He said an important feature of the system is the ability to heat and cool different areas of the schools at the same time, rather than having to heat or cool the entire area at once.
"One of the first questions I asked was what if the sun was shining on one school and the other was shaded and they were different temperatures. Everybody assured me we could vary the heating and cooling as needed. With a boiler-based conventional system, you would have to wait until the water in the boiler cooled down before you could turn on the air conditioning."
Welch said school officials hope the geothermal system works as expected so others considering such systems can visit the schools to see how the heating and cooling functions.
"We want these schools to be a showplace. We are very proud of them and we want to be able to show them off," he said.
According to a report on the system prepared by Consulting Engineering Associates of Tampa, FL, mechanical engineers for the project, the well system for the project was drilled to 240 feet because the aquifer temperature at that depth is 73 degrees and higher-temperature water was not required for the project. Such well systems for geothermal projects have been used since 1940, the report states. The aquifer in the area flows to the North, allowing the water supply wells to be drilled upstream of the disposal well locations
Condensing water requirements obtained from the manufacturer of the heat pumps used in the schools indicated maximum condensing water required to provide greatest efficiency was 3 gpm per ton and the operating requirement was 2 gpm per ton. The system has capacity for future cooling loads of approximately 60 tons and the total installed capacity of the HVAC equipment is 1,125 tons.
Water from the supply wells is pumped to a stainless steel plate heat exchanger at each school at a rate of 736 gpm for the middle school and 864 gpm for the high school. The condenser water system is served by an 1,100 gpm condenser water pump for the middle school and a 1,456 gpm pump for the high school. Temperatures in the loop vary from 65 to 95 degrees.
On the cooling side, the closed loop condenser water enters the plate heat exchanger serving the middle school at 89.6 degrees and leaves at 80 degrees and enters the plate heat exchanger at the high school at 88.4 degrees and leaves at 80 degrees. The closed loop condenser loop has the capability of circulating up to 2,556 gpm.
The report cites advantages of a geothermal system include higher efficiency and ability to maintain stable heating and cooling capacity, better comfort and air quality in the school and simplicity of controls and equipment. Geothermal systems also have low maintenance cost because all heat pumps are indoors and not exposed to outdoor conditions and vandalism or other damage, no need for auxiliary heating, and that the systems are environmentally friendly.
According to the Environmental Protection Agency (EPA), such geothermal systems have the lowest carbon dioxide emissions of any heating system analyzed by the agency and use less energy because they are more efficient than other systems.
The report states that since 1992 geothermal technology has been singled out as the primary HVAC technology that can be employed to meet government and international guidelines for reduction of harmful chemical emissions by 2005.