Choosing Geothermal as an HVAC System
- By John D. Linsenbigler
- July 1st, 2002
The 109-year-old Johnson Bible College (JBC), located near the foothills of the Great Smoky Mountains National Park, in Knoxville, Tenn., has a growing student body, which led to a need to expand existing residence hall space. There also were aging mechanical systems in several older campus buildings that needed to be replaced. These systems consisted of steam boilers, closed two-pipe systems, DX systems, standard watersource heat pumps, through-the-wall heat pumps and window AC units.
As planning went into motion, we conducted a study on two existing residence halls to see what would be the best HVAC system, if the plan was to remodel and expand them. We also determined that both would need to be brought up to code. A feasibility study was done by West, Welch, Reed Engineers, Inc., on three types of HVAC systems -- geothermal heat pumps, four-pipe systems and standard water source heat pump systems (WSHP). These three types where chosen because we wanted to have individual heating and cooling controls for each room. After reviewing upfront costs, life cycle costs and payback, geothermal water source heat pumps were chosen. With a geothermal system, the mechanical room could be smaller and the individual units would be easier to maintain. Upon reviewing projected enrollment needs and the cost of building/life safety code improvements, we decided to raze the residence halls and build two new buildings.
What Type of Geothermal Design?
While our architect, Community Tectonics, Inc., and the JBC team were working on building design, we undertook a geothermal study. We contacted the Geothermal Heat Pump Consortium (GHPC), Tennessee Valley Authority (TVA) and our local utility distributor, Knoxville Utilities Board (KUB). GHPC had a lot of information; we used their Design Assistance Program to review our engineer’s plan and see where the latest technical information could be applied. They provided some cost-saving ideas.
Our main source of “hands-on” information was TVA. They took us to look at several geothermal systems and coordinated TVA’s assistance program in drilling two test wells. In addition, we participated in their public information and training programs, where we made several contacts to learn what worked and what didn’t. (Having TVA as our electricity supplier has a reliability benefit because the energy comes from several sources -- hydroelectric, nuclear, coal and natural gas.)
As their contribution to an all-electric system, KUB paid for the installation of underground wire and offered a three-year enhanced growth program, which is a rebated portion of the electric demand charge. We looked at open loops, closed loops, horizontal loops and deep well systems. We determined that a closed-loop geoexchange system with vertical wells was our best option.
Choosing the Contractors
GHPC provided a list of drillers and loop installers. Most loop installers hire the drillers and provide design cost analysis. We sent out specifications and prints to three installers. Upon review and checking references, we chose LoopMaster of Indianapolis, Ind. Steve McGowan with LoopMaster subcontracted the drilling and vertical loop installation to Bertram Well Drillers of Billings, Mont. JBC oversaw the geoexchange field installation into the mechanical room, where the interior mechanical contractor took over. LoopMaster replaced a costly concrete vault with a one-piece poly vault, which saved time and money. The two eight-in. headers from the mechanical room come into this vault into a built-in header system. It then goes to the individual vertical boreholes. Each residence hall has 72 vertical boreholes that are 300 ft. deep with one-in. piping loop inserted into each borehole, which is then backfilled with grout.
Choosing Interior Equipment
Each residence hall is 53,873 sq. ft., with a 144-ton geoexchange system. The field was made large enough to handle an additional future wing. Interior equipment comprises 96 console units for the rooms, and seven consoles, seven horizontal and seven vertical units for the common areas.
Once building design was in the closing document stages and contractors were being finalized, having input into equipment was imperative to optimize system payback. There are several good water-to-water heat pump manufacturers, but only a few heat pumps that are specifically designed for geo thermal systems. Since we service our own equipment, we had our local vendor demonstrate a couple of units from different manufacturers. We chose Water Furnace as our equipment manufacturer. In addition to the central HVAC units, Water Furnace also had a water-to-water heat pump system for our domestic hot water. The firm was also willing to keep our maintenance staff up-to-date with training and technical support. The equipment choice was given to our engineer in order to finish the design and specifications.
Cost and Payback
The comparison below is based on one new residence hall with the geoexchange system and a projected estimate of a standard WSHP system with domestic gas water heaters. In addition, the standard WSHP system requires a gas boiler to replace heat used by the individual heat pumps during the winter. The geoexchange system gets its heat and cooling capabilities from the ground.
It cost approximately $100,000 more to install our geoexchange system.
Annual estimated savings were $27,238 using a geoexchange system. Calculating a $100,000 difference to install our geoexchange system, there will be a 3.6-year payback. This does not include the three-year KUB enhanced growth rebate, which has averaged $3,600 a year. If you include this, the payback is 3.2 years. Initial payback projections prompted JBC to design a geoexchange system in the new Global Education Technology Center. This 31,000-sq.-ft. structure uses a 90-ton geoexchange system and has been online since August 2001.
In the End
With last year’s increase in the price of natural gas and the prospect of future price increases compared to an all-electric system, geoexchange has a large cost benefit. Most of the time, upfront costs seem high but, if you review current maintenance and utility costs and, if a five-year or better payback can be obtained, you are right to replace existing aging systems.
In campus planning, time needs to be allotted to look into replacing existing mechanical systems. You simply cannot wait to make a decision until a system goes down, as planning requires time to look at all options. If you wait for a system to fail before you begin replacement, you may not make the most cost-effective decision. As you go through the planning process, be sure to make contact with your local power supplier and distributor.
John D. Linsenbigler is the director of Plant Services at Johnson Bible College. He can be reached at . More information is available at the college’s Website .