most buildings will use steam heat exchangers located in each building to generate hot water that supplies the heat transfer media. Conversion of an existing campus district energy system to geothermal may include converting existing buildings to a new hot water temperature. After a building analysis is done to evaluate which heat transfer media are affected by different hot water supply temperatures, a higher hot water supply temperature may be selected because replacing a large amount of heat transfer media could be cost-prohibitive. Electrical consumption at the heat pump is the penalty for a higher hot water supply temperature. The amount of electricity needed to generate a 150 F hot water supply temperature is significantly greater than the electricity consumed to generate 140 F hot water supply temperatures.

• Equipment selection – It is important to determine the right equipment needed to meet the design criteria. Some of the types of heat pumps and their design parameters are as follows: Centrifugal chillers

•;600-2,500;tons
•;Up;to;155;F;hot;water;temperature
across all tonnage ranges
•;Up;to;170;F;hot;water;temperature
with machines between 1,500 and
2,000 tons

Screw chillers

•;50-600;tons;with;single;compressor •;Up;to;140;F;hot;water;temperature Scroll chillers

•;Up;to;150;tons
•;Up;to;130;F;hot;water;temperature
(but 120 F recommended)

• Space available for well fields – The space available on a campus for well fields is an important consideration for determining the geothermal distribution system type. Typically the spacing for boreholes for a well field will be between 15 ft on center to 25 ft on center. The spacing will be affected by whether the campus is cooling-dominant or heating-domi-nant and at what depth the bores are drilled.

• Where the well fields tie into the
distribution loop – Where the well
fields tie into the distribution loop is
an important consideration in select-
ing the type of geothermal distribu-
tion system that can be implemented.
For example, a single-pipe geother-
mal distribution loop is the least
expensive, but it is dependent on well
fields spread throughout the campus
and connected into the geothermal
distribution loop in various locations
to add or remove Btus being trans-
ferred to and from the buildings.

Campus Basis of Design

After decisions about the campus system have been determined and a direction for it has been agreed on, a campus utilities “basis of design” can be written. The basis of design will dictate all of the design parameters that need to be met to operate the district energy system and all of the parameters any new construction must meet to be part of the district energy system.

If your campus is a good candidate for geothermal, the importance of the basis of design is undeniable. It shapes the future operation of the campus system and acts as the starting point for any new building projects. The basis of design will standardize the building systems’ parameters during and after the geothermal conversion.

Paradigm Shift

A colleague once asked me if the development of campus geothermal systems has been ongoing and gradual or more of a recent trend. He was familiar with geothermal on a building system level but unaware of its application at universities and colleges, for example. The answer is that campus geothermal use reflects a paradigm shift within the engineering field and the district energy industry as well. We’re at the beginning of that paradigm shift and can expect to see increasing use of geothermal district energy on campuses in the years to come.

Michael Luster, PE, LEED AP, is enior mechanical engineer/project manager for MEP Associates LLC. With expertise in energy-efficient sustainable systems design, Luster currently manages the geothermal projects at Ball State University – the largest such project in the nation – as well as at Minot State University and Miami University. He is a registered professional mechanical engineer in Minnesota and South Dakota, and he earned a Bachelor of Science in mechanical engineering from Iowa State University. Luster may be reached at mikel@mepassociates.com.