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Direct Use of Geothermal Resources 217

moisture contents for the product (~6% to ~14%, depending on species and product specifications).
Drying is accomplished by placing cut, dimensioned lumber in spaced stacks in a building-sized kiln
and allowing warm air to circulate around it. The air is heated by hot-water finned heat exchangers
around which air is circulated by a ventilation system.
Although the thermodynamic efficiencies of geothermal drying systems are relatively low
because of the low temperatures and low ∆T of the process, they are economically and environmen-
tally advantageous because they eliminate the need for a fuel cycle, have zero emissions associated
with the heating process, allow easy scheduling for indefinite durations, and have a predictable and
constant cost.
The heat losses and energy demands associated with drying are relatively simple to compute,
compared to the aquaculture case discussed above. The primary parameters that must be dealt with
and that are usually well established for any given industry, are the initial moisture content of the
material, the target moisture content, and the drying rate for a given humidity and temperature. The
exchange efficiencies of commercially available heat exchangers are well known and therefore do not
need to be computed. The principle process of interest is convective heat transfer and the associated
energy and temperature change associated with removing water from the commodity of interest. In
most cases, empirical relationships and experience form the basis for the design and operation of
such facilities.
An important consideration for efficient and environmentally sound management of direct use
systems is the possibility of constructing cascaded systems. A cascaded application is one in which
the outflow of warm water from one process is used as the source of heat for a process that can
function at that temperature. In Canby, California, such a cascaded system has been employed to
meet multiple needs of a community.

case sTUdy: canby cascaded sysTem

Cascaded systems allow multiple applications to be linked to a single geothermal fluid source. The
basic design takes advantage of the broad temperature range that different applications require. By
staging applications in a sequence in which successive applications require lower temperatures, it
is possible to cascade a series of applications into a single system. A few examples of such systems
that are either installed or underway include:

• Klamath Falls, Oregon: District heating, greenhouses, brewery, and snow melting
• Cotton City, New Mexico: Power generation cascaded to a greenhouse complex
• Geinberg, Austria: Power generation cascaded to district heating, spas, swimming, and
greenhouses
• Hungary: Power generation cascaded to greenhouses
• Podhale, Poland: Power cascaded to timber drying, greenhouses, fish farming, and space
and hot water heating
• Lendova, Slovenia: Power cascaded to district heating and cooling, aquaculture, green-
houses, and spas

The case study presented here represents a low cost effort that efficiently utilizes a small
resource. The experiences from this development provide insight regarding how to deal with poten-
tially adverse chemical characteristics of geothermal waters, and the types of applications limited
resources can support.
Many locations have the potential to develop cascaded geothermal applications. In 2008, the
GeoHeat Center of the Oregon Institute of Technology published a survey of the western United
States to determine the number of communities located within a few kilometers of geothermal
resources. The result documented that 404 communities have the potential to utilize geothermal
resources (Boyd 2008; Figure 11.9). The resources available to these communities are sufficient