Entire Bulletin

VOL. 20, NO. 4
DECEMBER 1999
ISSN 0276-1084
INTERNATIONAL GEOTHERMAL DAYS
OREGON 1999
Vol. 20, No. 4
December 1999
GEO-HEAT CENTER QUARTERLY BULLETIN
ISSN 0276-1084
A Quarterly Progress and Development Report
on the Direct Utilization of Geothermal Resources
CONTENTS
PUBLISHED BY
Page
International Geothermal Days
John W. Lund
1
Small Power Plants: Recent
Developments in Geothermal
Power Generation in New
Zealand
Michael Dunstall
5
GEO-HEAT CENTER
Oregon Institute of Technology
3201 Campus Drive
Klamath Falls, OR 97601
Phone: 541-885-1750
Email: geoheat@oit.edu
All articles for the Bulletin are solicited. If you wish to
contribute a paper, please contact the editor at the above
address.
Geothermal Heat Pumps
Four Plus Decades of Experience
R. Gordon Bloomquist
13
Curing Blocks and Drying
Fruit in Guatemala
Luis Merida
19
Italian Geothermal District
Heating Systems
Roberto Carella
23
Stories from a Heated Earth
28
EDITOR
John W. Lund
Typesetting/Layout - Donna Gibson
Graphics - Tonya “Toni” Boyd
WEBSITE http://www.oit.edu/~geoheat
FUNDING
The Bulletin is provided compliments of the Geo-Heat
Center. This material was prepared with the support of
the U.S. Department of Energy (DOE Grant No. FG0199-EE35098). However, any opinions, findings,
conclusions, or recommendations expressed herein are
those of the author(s) and do not necessarily reflect the
view of USDOE.
SUBSCRIPTIONS
Cover: Conference field trips: (top) Wineagle
600 kW (net) binary power plant,
Litchfield, CA and (bottom) Group photo
at Medicine Lake (Glass Mtn.), CA.
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INTERNATIONAL GEOTHERMAL DAYS
OREGON 1999
John W. Lund
Geo-Heat Center
For the first time, the International Summer School on
Direct Application of Geothermal Energy (ISS), “International
Geothermal Days - Oregon 1999", was held outside of Europe.
A total of 114 participants from 30 countries attended the
conference on the Oregon Institute of Technology campus
from October 9 to 16, 1999, including a large delegation of city
mayors and provincial governors from Turkey.
The
conference, hosted by the Geo-Heat Center, was supported by
funds from the U.S. Department of Energy and donations from
Fuji Electric Corporation of America, Calpine Corporation,
Ormat International, Inc. and the Shaw Historical Library
Foundation.
The Conference was composed of the following
sessions:
•
•
•
•
•
International Workshop on Small-Scale Power
Projects
International Workshop on Geothermal Heat Pumps
International Course on Direct Utilization of
Geothermal Energy
Evening Seminar on Computer Software for
Geothermal Heat Pumps
Evening Seminar on HEATMAP© Computer
Software Utilization
Four field trips were also undertaken to nearby
geothermal projects and geologic sites:
•
•
•
•
Crater Lake National Park (for early arrivals)
Medicine Lake, CA to visit the potential sites of two
50-MWe geothermal power plants (Fourmile Hill by
Calpine Corporation and Telephone Flats by
CalEnergy Company geothermal projects). This field
trip also included a visit to Lava Beds National
Monument.
Direct-use projects in the Klamath Basin, including
the Oregon Institute of Technology mini-heating
district, the Klamath Falls district heating system, a
local residential heating system using a downhole
heat exchanger, and a combined greenhouse and
aquaculture heating project.
A final field trip from Klamath Falls to Reno, NV
visiting along the way two potential geothermal
projects at Canby, CA, and a hybrid plant (wood
waste and geothermal) and binary geothermal plant
(Wineagle) near Litchfield, CA.
This conference was also the 10th anniversary of the
International Summer School founded by Dr. Kiril Popovski
GHC BULLETIN, DECEMBER 1999
of St. Clement Ohridski University, Bitola, Macedonia , and the
25th anniversary of the International Geothermal Conference on
“Multipurpose Use of Geothermal Energy” held on the Oregon
Institute of Technology campus - and was the start of the then
Geo-Heat Utilization Center. The founders of the Center, Gene
Culver, Paul Lienau and John Lund all made presentations at
both conferences..
The first official function of the conference was the
Medicine Lake field trip lead by David McClain, a consultant
from Portland, OR.
His detailed knowledge of the
environmental work and local geologic setting for the two
power project provided interesting discussion for all,
especially during our stop for lunch at Medicine Lake under
beautiful fall weather. Subjects from the impact of noise from
the power plants and the visual impact of the power line, to
addressing local Indian and summer resident’s concerns were
presented and explained how they would be mitigated. We
ended the day by visiting several geologic structures in Lava
Beds National Monument, including a chance to cool off in
Skull Cave - a large collapsed lava tube. A reception was held
that evening on the OIT campus, hosted by the Shaw
Historical Library Foundation.
The conference was officially opened on Monday by
welcome talks from the President of Oregon Institute of
Technology, Dr. Martha Anne Dow, the Mayor of the City of
Klamath Falls, Todd Kellstom, and the chairman of the Klamath
County Commissioners, Steve West. Dr. Kiril Popovski,
representing the International Summer School and Dr. John W.
Lund, representing the Geo-Heat Center, also welcomed the
attendees and presented some of the background history on
the conference.
The one and a half day session on Small-Scale
Electric Power Generation was introduced with an excellent
summary paper by Ron DiPippo (see Vol. 20, No. 2). His paper
was followed by the topic of slim hole drilling presented by Jim
Combs and John Pritchett. Liz Battocletti presented material
on financing, and then Gordon Bloomquist and David
McClain discussed legal, institutional and environmental
issues. That evening, a dinner, complete with local Native
American, Wocus Bay Singers, dancers and drummers, was
hosted by Calpine Corporation. The audience participated in
one of the ring dances and drumming - to the delight of all.
For many, this was their first exposure to Indian culture and
traditions.
The next day, power plant case histories were
presented by Dan Schochet of Ormat, Ken Nichols of BarberNichols , Richard Campbell on the Mammoth, CA project
developed by Ben Holt Company, Gerardo Hiriart on CFE
projects in Mexico, Yuri Esaki on projects in Japan, Mike
1
Dunstall on New Zealand experience (inculed in this issue)
and Josefino Adajar on projects in the Philippines.
This was followed by a half-day session on
geothermal heat pumps. Kevin Rafferty of the Geo-Heat
Center started off by presenting US experiences with
commercial applications. This was followed by an overview
paper of European experience present by Ladsi Rybach of
Switzerland, Burkhard Sanner of Germany and Goran
Hellstrom of Sweden. Gordon Bloomquist presented material
on case studies of commercial/institutional installations in the
U.S. (included in this issue). Computer applications were then
presented by Gary Phetteplace of the U.S. and Burkhard
Sanner of Germany, followed by an evening workshop on
computer applications. There was lively discussion during all
of these presentations, as this was the first time the subject
had been presented at an International Summer School
conference.
To break up the indoor presentations, a local field trip
of direct-use sites in the Klamath Basin was held at midweek.
In additional to John Lund, Toni Boyd and Kevin Rafferty of
the Geo-Heat Center, the field trip was enhanced by
commentary from Gene Culver, retired from the Geo-Heat
Center, Brian Brown, a local consulting mechanical engineer,
Bruce Masl and Ray Gibson (retired) from the OIT Physical
Plant, and Manny Molina of the city of Klamath Falls. The
participants were divided into two groups and visited the OIT
wells and heating systems, an individual home downhole heat
exchanger system (Dick and Doris Pope), the city of Klamath
Falls district heating system, including the newly completed
Klamath County Courthouse, and downtown sidewalk snow
melt system. Lunch was arranged by the city at a local park,
and then we drove south of town to visit the Liskey Ranch
where geothermal water is used to heat a greenhouse complex
(Vicky Azcuenaga) and topical fish rasing ponds (Ron Barnes who can be reached at <gotfish@aol.com>). That evening a
dinner was hosted at the local country club by Fuji Electric
Company and Ormat International. Our English/Spanish
interpreter, Paul (Pablo) Lewis, provided the entertainment by
singing Mexican songs of his own composition.
The last two days of the formal part of the conference
were presentations on the direct utilization of geothermal
energy. The first set of presentations were on general aspects
of direct utilizations, including an overview of the technology
by John Lund, downhole heat exchangers experience by Gene
Culver, district heating design by Orhan Mertoglu, greenhouse
design by Kiril Popovski, aquaculture pond design and
refrigeration by Kevin Rafferty, industrial applications by Paul
Lienau, timber drying by John Lund, pavement snow melting
design by Brian Brown, an innovative concrete block and fruit
drying facility in Guatemala by Luis Merida (included in this
issue), and an introduction to HEATMAP© district heating
design program by Gordon Bloomquist. This was followed
by a computer workshop on the use of HEATMAP©
presented by Bob O’Brien of the Washington State University
Energy Program. That evening, the Mayor of the City of
Klamath Falls, Todd Kellstrom, hosted a reception at the Ross
Ragland Community Theater in downtown area - a building
that is also geothermally heated.
4
These general presentations were then followed by
specific examples of district heating design in Iceland (E.
Gunnlaugsson), USA (T. Boyd and B. Brown), France (C.
Boissavy), Romania (M. Rosca and C. Bendea), Slovakia (O.
Vana and O. Halas), Hungary (M. Arpasi), Lithuania (V.
Rasteniene and F. Zinevicius), Italy (R. Carella–included in this
issue), China (Zhu Jialing) and Japan (Y. Yusa). General and
greenhouse system potential and design were presented by
representatives from Albania (A. Frasheri), France (C.
Boissavy), Argentina (A. Pesce), Bulgaria (S. Fournadzieva
and K. Bojadzieva), Macedonia (S. Popovska), Portugal (A. M.
Rodrigues), India (D. Chandrasekharam), USA (B. Gordon) and
Italy (C. Campiotti).
The final evening, a western style dinner complete
with cowboy hats, bandanas and sheriff badges, was hosted
by OIT. Entertainment was provided by Belles and Beaus line
dancers, again with audience participation. Certificates were
presented to participants and lecturers.
The final field trip was from Klamath Falls to Reno, set
to arrive in time for the start of the Geothermal Resources
Council Annual meeting. The all-day bus tour with nine cars
following, toured a potential district heating project in Canby,
CA (Dale Merrick) and Kelly Hot Springs flowing at 400 gpm
(25 L/s) at 187oF (86oC) (Sal Pantano). A lunch stop was held
in Alturas, CA where several schools are heated with
geothermal energy. The park for lunch was reserved by the
Alturas Chamber of Commerce. After lunch and a 1.5-hour
drive, we toured the Operation Energy Corporation/Honey
Lake Power Company biomass/hybrid power plant near
Litchfield/Wendel, CA. This plant built in 1989, uses
geothermal water for the condensate preheater (1.5 MW) and
then wood chip waste as the main fuel to produce 35.5 MWe
of power. The massive plant was down for maintenance, but
we were still impressed with its unique type of operation.
Afterwards we toured the Wineagle Developers binary power
plant which uses 1,000 gpm (63 L/s) of 230oF (110oC)
geothermal water to produce a net output of 600 kWe. The
plant was design by Barber-Nichols Engineering Co.
From there, the nine trailing cars descended on the
lone gas station at Litchfield, and almost overwhelmed the
facility. All finally arrived in Reno safely and scattered to the
various motels. Some participants left the next day, and other
stayed for the GRC meeting.
Two volumes of the proceeding are available:
•
•
Small-Scale Electric Power Generation & Geothermal
Heat Pumps - 19 papers of 192 pages.
Direct Utilization of Geothermal Energy - 36 papers of
226 pages.
Each can be ordered from the Geo-Heat Center for
$15.00 or $25.00 for both plus postage. Copies of the three
field trip guides are also available free of charge. The four
papers in this issue of the Quarterly Bulletin, were presented
at the conference, but arrived too late to be included in the
Proceedings.
Many thanks to all the participants - a few
photographs are included for your enjoyment.
GHC BULLETIN, DECEMBER 1999
SMALL POWER PLANTS:
RECENT DEVELOPMENTS IN GEOTHERMAL
POWER GENERATION IN NEW ZEALAND
Michael Dunstall
Geothermal Institute, The University of Auckland,
Private Bag 92019, Auckland, New Zealand
WHAT IS SMALL SCALE?
None of the recent New Zealand power plant
developments truly qualify as “small” on a field wide basis.
The size of the individual units in these projects is however,
quite small. Over the last four years fourteen geothermal
generation units have been installed in New Zealand, eleven
of these having a capacity of less than 5MWe. Prior to the
recent period of activity three small units were installed at
Kawerau; each of these units were also less than 5MWe in
output.
All the recent construction has been undertaken by
individuals, local power companies, or by trustees of local
Maori tribes, often as joint venture projects. New Zealand's
first two geothermal power stations, Wairakei and Ohaaki,
were both large. They were built using NZ Government
money in 1958 and 1989 respectively.
RECENT NEW ZEALAND DEVELOPMENTS
Four new geothermal stations have been erected in
New Zealand since 1996.
One plant (Poihipi) uses
conventional steam turbine technology, while the three smaller
plants (Rotokawa, Ngawha and Mokai) use binary cycle
technology. Two older binary cycle plants also operate at
Kawerau.
Poihipi: Mercury-Geothermal (July 1996)
This 55-MW power station was imported to New
Zealand as a second hand unit, having been built for the
Geysers geothermal field but never run. The complete power
plant was reconfigured to generate at 50Hz (60Hz is used in
the USA) and has been erected in the western part of the
Wairakei geothermal field, tapping a shallow steam zone.
Electricity output is restricted by a resource consent that does
not allow the plant enough steam to run fully loaded 24 hours
per day. To get the maximum possible revenue it is run at
high load 14 hours per day, when electricity tariffs are high,
and runs at very low output (~3MW) during the night. It is
New Zealand’s only non-base load geothermal station.
Rotokawa: Transalta (September 1997)
The Rotokawa geothermal field is located in the
Taupo Volcanic Zone (TVZ) and contains wells with some of
the hottest downhole temperatures (>320EC) recorded in New
Zealand. Wellhead pressures at Rotokawa are also very high,
with some wells showing over 70 bar when shut in. The field
is bisected by the Waikato River and covers a wide area,
estimated at somewhere between 17 and 30 km2. The field is
GHC BULLETIN, DECEMBER 1999
thought to be one of the largest in New Zealand, containing an
estimated 2700PJ of useable heat (Hunt, 1998).
Fracture permeability is the main means of fluid
movement at Rotokawa as the andesitic reservoir rocks are
relatively impermeable. The wells are generally good
producers providing high temperature fluids with high
enthalpy. Because of the high enthalpy, the power station
installed at Rotokawa has an output double that of the Ngawha
plant, while processing about the same mass flow.
Silica content at Rotokawa is high so the fluid
separation pressure is maintained at 20-25 barg to prevent
scaling problems. The non-condensable gas contains a
considerable quantity of H2S, but due to the relatively small
size of the development this does not produce an odour
nuisance when the gas is vented to atmosphere.
The Rotokawa power station (Fig.1) utilises a 16MW
steam turbine which exhausts at just over 1 barg to two aircooled ORMAT binary cycle units. The hot brine from the
separator is used in a third ORMAT binary cycle unit. Total
output of the plant is 24MWe. The plant is supplied by two
production wells, about 1000m deep. After two-phase
transmission the steam and water are separated at the power
plant, passing separately through the units, and are then
recombined before reinjection. Three shallow reinjection
wells are used (~400m); a relatively impermeable layer exists
between the production and reinjection horizons preventing
cold fluid returns.
Figure 1. Rotokawa Power Station (24 MW) .
Several of the wells in use at Rotokawa were drilled
by the New Zealand Government during the early eighties and
have since been sold to the project. Some new wells have also
been drilled. Three other Government funded wells remain
unused at Rotokawa, because they are unsuitable for produc5
ton or reinjection, or because they are too far away from the
plant to be viable.
Rotokawa field also has three abandoned exploration
wells that were drilled by the Crown. These wells were
cemented after corrosion of the casing by acid fluids at
shallow level. This region of acid fluids has now been
delineated and covers only a small area of the field, near steam
heated surface features. This type of corrosion is not expected
to cause problems in the remaining wells.
Ngawha: Top Energy (July 1998)
The Ngawha geothermal field is the only high
temperature geothermal field in Northland New Zealand.
Compared to high temperature fields in the Taupo Volcanic
Zone (TVZ) the Ngawha field has a number of differences.
Reservoir pressures are somewhat higher due to a confining
layer near the surface. The reservoir is also mainly greywacke
rocks, which are often found as low permeability basement
rocks in the TVZ fields. At Ngawha these rocks are extensively fractured, providing very good permeability in wells
which intersect fractures and very poor permeability in others.
High boron, high non condensable gas and high
mercury levels characterize the fluids at Ngawha, which are
also at relatively low temperature (230EC) and enthalpy (~
970kJ/kg). The low enthalpy means that while the wells
produce high mass flow rates the electrical potential per well
is lower than is typical in the TVZ. Calcite scaling was
observed during early production tests at Ngawha and is
expected to be an ongoing concern during development of this
resource. The resource area is approximately 15km2, and the
stored heat has been quoted as 1400PJ (similar in size to
Ohaaki) (Hunt, 1998).
The current development at Ngawha consists of two
air-cooled ORMAT binary cycle units, with a combined output of just under 10 Mwe (Fig. 2). The units are supplied with
steam and hot water from two production wells, about 1000m
deep. Steam and water are separated at the wellpad before
transmission because of the steep terrain that must be
traversed. Separation pressure floats between 10 and 17 barg.
The steam and hot brine are passed through
separate heat exchangers in the power plant. Flows are then
recombined before being pumped to disposal in two
reinjection wells with depths of about 1300m. Noncondensable gases are vented to the atmosphere.
All the wells in use at Ngawha were drilled by the
New Zealand Government during the early 1980s. A further
ten unused wells drilled to depths up to 2300m and one abandoned well exist at Ngawha. This early drilling program reduced the economic risk of development considerably. However, the existing wells were drilled for exploration and are
quite widely spaced. This meant that approximately 7000 m
of steam-field piping was needed to connect the system
(Fig.3).
Figure 3.
Long pipelines were needed to connect the
widely spaced wells at Ngawha.
One of the wells used for fluid production at Ngawha
was completed in an unusual manner. Up until its recent
removal, NG9 (Fig.4) was New Zealand’s only “dual-
Figure 2. Ngawha Power Station (10 MW).
6
GHC BULLETIN, DECEMBER 1999
completion” well. The upper feed zone discharged through
the annulus between the 85/8” production casing and an inner
51/2” casing. The lower feed discharged through the 51/2”
casing. Although the two zones could feed to the surface
separately they were combined before phase separation when
the Ngawha development commenced. The dual-completion
has since been removed, increasing the well output.
Figure 4.
NG9 wellpad - a “dual completion.”
Mokai:
Tuaropaki Trust (October 1999)
The Mokai resource has many similarities to the
Rotokawa resource. The power development is also similar.
Figure 6.
GHC BULLETIN, DECEMBER 1999
Mokai was confirmed by drilling in the 1980’s after geophysical measurements suggested the presence of a large
geothermal reservoir. The wells drilled at that time were some
of New Zealand’s largest producers, with MK5 having
sufficient output for about 25MW of electric power. The
resource area is estimated to be 12-16km2, containing stored
heat of 2700PJ (the same figure attributed to Rotokawa)
(Hunt, 1998). The wells are high temperature (over 300EC),
have high wellhead pressure (>50bar), and produce high silica
fluids. Gas levels at Mokai are however quite low compared
to other fields in the Taupo Volcanic Zone.
The current development at Mokai uses four
production wells with depths between 1000 and 1500m.
Three shallower reinjection wells (<800m), drilled in the
outflow tongue of the reservoir, are used for fluid disposal.
Two further wells were drilled during the exploration of
Mokai in the 1980s, but these are not used in the current
project.
The hybrid power plant at Mokai (Figs. 5 and 6) is
similar in concept to the Rotokawa plant. Steam separated at
21 barg is used in a 29 MW steam turbine that exhausts at
about 1 barg to four ORMAT binary plants, where the steam
is condensed. A further two ORMAT binary plants make use
of hot brine from the separators, which are located on the
power plant site. The brine and condensate mix before being
pumped to the reinjection wells. The ORMAT units are aircooled and, as with other developments in New Zealand, the
non-condensable gas is vented to atmosphere.
Overview of Mokai Power Plant - 50 MW.
7
Figure 5.
Mokai Power Plant (50 MW).
Kawerau: BOP Electricity (1989, 19991)
The Kawerau geothermal field is the only geothermal
field still operated on a commercial basis by the New Zealand
Government, with day-to-day operation by Century Drilling
and Energy Services Ltd. The primary use of steam from the
Kawerau field is for direct use at the Tasman Pulp and Paper
Company mill. Geothermal steam is used in clean steam heat
exchangers to provide mill process steam. It is also used for
timber drying in high temperature kilns in the nearby Tasman
Lumber plant and a small quantity is used to heat a greenhouse
located in the steamfield (see Vol. 19, No. 3, 1998). An
8 MWe atmospheric back-pressure turbine at the mill is used
for load balancing to smooth out the mill steam demand,
allowing well output to be changed gradually (Hotson, 1994).
Development of the Kawerau field began in the early
1950’s with steam production for use in the mill predating
electricity generation at Wairakei. The resource area is
estimated to be 19-35km2, containing stored heat of 1300PJ
(about the same figure attributed to Wairakei). The field
poses no special difficulties for utilisation, having a
moderately high temperature of about 270E C. Some very
productive wells have been drilled at Kawerau and these have
generally had a long life. Today there are five production
wells operating, with an average depth of about 1000m. Some
wells tend to produce calcite scale but this is controlled by
injection of inhibitor chemicals or cleaned out in periodic
work overs (Bloomer, 1998). Non-condensable gas levels are
moderate, and variable venting of these gases provides a convenient method of control in the clean steam heat exchangers.
Up until the late 1980s, water from the separator
plants was flashed to atmospheric pressure and dumped in the
Tarawera River. Steam condensate from the mill heat
exchangers was also dumped to the river.
In 1989, two 1.3MWe ORMAT units were installed
to make use of the separated water supply from separator plant
21 on the east side of the river, and reinjection of some waste
brine was started. This first ORMAT plant was named TOI
(Tarawera ORMAT Installation) (Fig 7) and was capable of
cooling the brine from 180EC to 108EC. After some initial
teething problems these units proved reliable and the decision
was made to install another unit (TG2) on the western side of
the river, utilizing fluid from separation plant 35. TG2 is
larger than TO1, with 3.5 MWe output from a single unit.
This plant is also a newer design than the TO1 units and
includes a recuperator between the turbine and the condenser.
The outlet temperature of brine from TG2 is 95oC. All three
plants use air-cooled condensers and run unattended.
Figure 7. Tarawera ORMAT Installation 2.6 MW (Kawerau field - east side of Tarawera River).
8
GHC BULLETIN, DECEMBER 1999
Three reinjection wells are currently in use at
Kawerau, accepting about 25% of the water produced in the
field; the remainder flows to the river. All the condensate
from the mill heat exchangers is now collected and, after
stripping the non-condensable gases, is used as a source of
clean feed water for all of the mills boilers. The field has 23
unused wells of varying age and 12 abandoned wells.
New Zealand has quickly shifted from a position
where one Government owned company controlled power
generation and distribution, to a competitive system for
generation and retailing of electrical energy.
Some background to these regulatory changes is
needed to understand the circumstances that led to the recent
activity in geothermal power plant construction.
LOW EXPLORATION RISK FOR DEVELOPERS
The four recent power developments in New
Zealand, and the older Tarawera ORMAT plants, have all
presented a relatively low exploration risk for the developers.
In three cases, Ngawha, Rotokawa and Mokai, a
number of productive wells already existed and the New
Zealand Government had carried out a substantial amount of
scientific work from the early 1960s until the 1980s. Most of
the scientific information about these fields was in the public
domain and available free to the developers. The wells themselves were also sold to the developers at a reduced cost.
While this sounds simple enough the well ownership issue
was very complex and involved considerable legal wrangling.
In the case of the Poihipi development the plant was
built in the western area of the Wairakei steam field so quite
a lot was already known about this resource.
At Kawerau, the hot water resource used in the
ORMAT power plants had been pouring into the Tarawera
River for 35 years.
Despite the scientific and drilling work which had
already been done some developers chose to reduce
exploration risk even further by using “No steam - No reward”
contracts when drilling new wells.
NEW ZEALAND ELECTRICITY SYSTEM
New Zealand’s electricity network is highly
interconnected through a national grid of high voltage power
lines and an undersea DC cable linking the North and South
Islands. However, the grid has a limited capacity to carry
power north, where most of the demand exists. Over 50% of
New Zealand's population live north of an East-West line
through Lake Taupo (Fig. 9).
WHY THE RECENT SURGE IN DEVELOPMENT?
There have been many regulatory changes in the past
ten years in New Zealand which have had an impact on
geothermal development (Fig 8). Changes in resource
management and electricity industry regulations have had the
main impact.
Figure 9.
Figure 8.
Geothermal exploration
development 1950-1999.
and field
Through these rapid changes a number of new
interested parties have emerged.
GHC BULLETIN, DECEMBER 1999
Location of major power stations and
population (load center) in New Zealand).
The system has a high reliance on hydro stations
(which generate 60 -70% of the power), many of which lie on
the South Island, well away from load centres. Traditionally,
thermal generation has been used to meet peak loads and this
has been at high marginal cost. This situation is now changing
somewhat with the proliferation of high efficiency gas turbine
combine cycle and co-generation plants.
9
Figure 10.
High temperature geothermal fields.
New Zealand’s high temperature geothermal fields
are in a strategically good location, near load centres on the
North Island (Fig 10). Ngawha is the exception to this, lying
in Northland, but is relatively strategic to that area, which has
no major power stations following the closure of the Marsden
Point oil fired stations.
NEW ZEALAND ELECTRICITY MARKET
New Zealand’s electricity market has also undergone
a period of rapid change while continuing to show about 3%
annual demand growth. Electricity is now sold 1/2 hourly on
a wholesale market, where competitive retail and generation
sectors bid for the supply and purchase of electricity.
In theory, an electricity retailer can now make
electricity sales in any part of the country, but in practice
retailers have mainly stuck with their traditional local
customers. Distribution of electricity on a national level is
handled by TransPower, the grid operator, and at a local level
by smaller distribution (lines) companies.
10
RESOURCE MANAGEMENT AND ELECTRICITY
REFORM
Up until 1988, the Geothermal Energy Act 1953 was
the main legislation controlling the development of geothermal
resources for electricity. It was set up to allow development
at Wairakei and gave the Minister of Energy, through the
Ministry of Works and the New Zealand Electricity
Department, quite sweeping powers. The “Minister may
authorise search for geothermal energy and give power to
enter land”. The Public Works Act also gave the Government
power to take land needed for geothermal development,
although this was never used.
The Geothermal Energy Act was amended in 1988
when the Ministries were converted into State Owned
Enterprises (Government owned companies). The regulations
covering safe use of geothermal passed to the Health and
Safety in Employment Act 1992 and allocation of geothermal
resources for utilisation fell under the newly created Resource
Management Act 1991 (RMA). The purpose of the RMA was
GHC BULLETIN, DECEMBER 1999
“to promote the sustainable management of natural and
physical resources” and required resource managers to “have
regard to efficient use and development of natural and
physical resources” and to “have regard to any finite
characteristics of natural and physical resources” (Bloomer,
1994). Mineral resources were specifically excluded from the
RMA but geothermal was included.
Geothermal resources now have to be managed in a
sustainable and efficient way. This had never been a
requirement in New Zealand before.
Sustainable Management is defined as “...managing
the (use of) resources in a way, or at a rate, which enables …
social, economic, and cultural well being ... while; meeting the
reasonably foreseeable needs of future generations;
safeguarding the life-supporting capacity of air, water, soil and
ecosystems; and avoiding, remedying or mitigating any
adverse effects of activities on the environment.
Electricity Industry reform has also had a major
impact. In 1996 part of the Electricity Corporation of New
Zealand (ECNZ) was split off to form a competitor in the
generation market. The new company was called Contact
Energy. Rules were also put in place to ensure that the
dominant players could not shut independent power producers
out of the market. This year the Electricity Reforms Act
(April 1999) has had a major impact. The remaining ECNZ
assets were split into three competing state owned enterprises
(Meridian Energy, Genesis Power, Mighty River Power) and
Contact Energy was sold.
Local power companies were also forced to split into
energy companies (retailers) or distribution companies (lines
companies). It is no longer possible to own a substantial share
of a generating company and a lines company in New Zealand.
The national grid operator (TransPower) is at present
untouched and still owned by the New Zealand Government.
PREVIOUS INVESTMENT BY THE GOVERNMENT
The historical investment in geothermal exploration
made by the New Zealand Government during the 1950-1986
period is now coming to fruition. Excluding those wells
drilled at Wairakei and Ohaaki, 124 investigation wells were
drilled over this time. In many fields these wells proved the
resource. The scientific effort that was put into these fields
was also substantial and almost all of the information is in the
public domain. Of the 124 wells drilled between 1950 and
1986 82 remain, and the Crown has an ongoing commitment
to maintenance of these wells and abandonment where
necessary (Koorey, 1999).
Table 1.
A few of the exploration wells were drilled into fields
which are now classified as “protected” for their scientific,
cultural, heritage or tourism values (Luketina, 1999).
However, most of the effort was placed in fields recognised
early on as good candidates for development (see Table 1).
The existence of these wells has been a boon to developers.
Several of the highest producing wells ever drilled in New
Zealand have since been sold to developers at a low price.
Wells drilled by the Crown have been sold to developers at
Mokai, Ngawha, Tikitere, Tauhara, and Rotokawa.
WHERE TO FROM HERE?
Geothermal energy in New Zealand continues to face
stiff competition from natural gas, which has been chosen as
the fuel source in a number of new power plants. The low
price of natural gas in New Zealand is expected to continue
for some years to come, as it results from historical “take or
pay” contracts inherited by Contact Energy during its
formation.
The impact of targeted CO2 reductions, which New
Zealand has committed to in the international Kyoto protocol
agreement, may yet have an effect on the price of competing
fuels. Although all New Zealand geothermal stations emit
CO2 they do so at a much lower rate than natural gas stations,
which are their main competition. This issue remains open,
since the mechanism by which New Zealand will set out to
achieve CO2 emission reductions has not yet been decided.
Although the New Zealand Government no longer
provides money for new geothermal exploration programs the
benefits of the earlier work will continue to flow for some
time. Several as yet undeveloped fields have proven potential.
As electricity demand rises new geothermal power
plants will be built in New Zealand. In the short-to-medium
term, the most likely scenario is small incremental developments and expansions in the recently developed fields. Efficiency improvements planned for long established fields like
Wairakei are also expected to result in some new construction.
ACKNOWLEDGEMENT
Thanks to Kevin Brown, Andy Cass, K.C. Lee and
Arnold Watson for providing information and photographs of
the power plants described.
Government funded wells drilled into systems now classified as “Development Systems.”
Field
Production
Horohoro
Kawerau
5
Mokai
4
2
Ngawha
1
Rotokawa
Tauhara
Source: Koorey (1999)
GHC BULLETIN, DECEMBER 1999
Injection
3
1
2
1
-
Shut-in
5
23
10
3
14
Abandoned
12
1
1
3
1
11
REFERENCES
Bloomer, A., 1994. Rotokawa Geothermal Power Station:
Resource and RMA issues . Proc. 16th New Zealand
Geothermal Workshop, pp. 51-56
Bloomer, A., 1998. Kawerau Geothermal Development: A
case study. Geo Heat Center Quarterly Bulletin, Vol.19 No.3,
pp. 15-18.
Hotson, G. W., 1994. The long term use of geothermal
resources at the Tasman Pulp and Paper Co. Ltd mill,
Kawerau, New Zealand. Proc. 16th New Zealand Geothermal
Workshop, pp. 261-268.
12
Hunt, T. M., 1998. Geothermal resources in New Zealand. An
overview. Geo Heat Center Quarterly Bulletin, Vol.19 No.3,
pp. 5-9.
Koorey, K., 1999. Investigation drilling: History and Issues.
Proc. NZGA Seminar - Geothermal Energy: Adding Value,
24-25 June 1999, Taupo New Zealand. 4pp.
Luketina, K., 1999. The Waikato Regional Plan: How it
affects small-scale users of geothermal resources. . Proc.
NZGA Seminar - Geothermal Energy: Adding Value, 24-25
June 1999, Taupo New Zealand. 4pp.
GHC BULLETIN, DECEMBER 1999
GEOTHERMAL HEAT PUMPS
FOUR PLUS DECADES OF EXPERIENCE
R. Gordon Bloomquist, Ph.D.
Washington State University Energy Program
P.O. Box 43165
Olympia, WA 98504-3165
INTRODUCTION
Despite the fact that commercial geothermal heat
pump (often called ground-source heat pump or geoexchange) systems first gained moderate popularity as early as
the late 1940s and early 1950s, widespread acceptance of the
technology by architectural and engineering firms, mechanical
design teams, developers, and building owner/operators has
been extremely slow. And although there was a momentary
increase in the installation of geothermal heat pump systems
following the oil crises of the 1970s, it has not been until the
past few years that interest in commercial geothermal heat
pump systems has once again been on the rise. However,
uncertainty over first cost, life cycle cost, operation and
maintenance questions, and system long-term reliability have
continued to plague the industry and prevent greater adoption
of the technology.
In order to meet this need, a number of studies have
been completed to document maintenance and operation
histories, equipment replacement requirements, actual cost of
service, and long-term system reliability. The number of such
studies has, however, been fairly limited and good data has not
always been readily available as few building owners maintain
good records and often ownership has changed, some times
several times, since the system was first installed. In order to
improve and strengthen the operation and maintenance data
base Washington State University (WSU) has completed a
series of case studies of commercial geothermal heat pump
systems.
The United States, and especially the state of
Washington, has long been a leader in geothermal heat pump
installation and use following the first successful
demonstration of the technology at the Commonwealth
Building in Portland, Oregon, in 1946. Most of these early
systems are still providing a high level of service to building
owners, and include systems in Tacoma (Tacoma City Light
Building, 1954), Vancouver (Clark County PUD, 1956) Walla
Walla (Whitman College 1964), Ephrata (Grant County PUD,
1955).
Data obtained through the course of the current study
indicates that geothermal heat pump technology is energy
efficient with total building electrical energy use for those
buildings where data was available ranging from 9.40 to 24.7
kWh/sq.ft./year while HVAC-related energy use ranged from
8.43 to 10.14 kWh/sq.ft./year. Maintenance costs were also
found to be very attractive and averaged $0.17/sq.ft./year
(Table 1). The most interesting findings of this work,
however, were the high level of reliability that most systems
GHC BULLETIN, DECEMBER 1999
had provided over periods exceeding 25 to 30 years if routine
maintenance procedures were followed and the very high level
of owner satisfaction that was witnessed during the course of
the interviews that were conducted.
PRESENT STUDY
The present study was conducted in two phases. The
first began with a look at a number of installations in
Washington State with an emphasis on obtaining information
on building size and use, type and size of geothermal heat
pump system, reasons for selecting geothermal heat pump
technology, and owner/operator satisfaction with the system.
The second phase of the study expanded the geographic area
to include systems in several additional parts of the country
and the scope to include much more concentration on
operational, maintenance, and reliability issues.
Systems were first identified through conversations
with equipment sales representatives, architectural and
engineering firms, well drillers, ground loop installers, HVAC
contractors, and utilities. Once a substantial number of
systems had been identified, the owner/operator of each
system was contacted by phone and an interview conducted to
determine whether or not the system should or could be
further considered. The prime criteria for selection was
willingness on the part of the owner/operator to participate in
the study, availability of data, and age of the system. Every
effort was made to include as many systems as possible with
20+ years of operating history, and as few as possible with
five years or less of operating history.
Once the systems had been selected, detailed
interviews were conducted with the owner/operator,
maintenance staff, and, when possible, the system designer.
The interviews were conducted by phone and often required
discussions with several individuals. Once the interviews
were completed, all of the systems were visited, additional
interviews conducted, and each system gone through in as
much detail as possible. Table 1 summarizes the important
building and ground source heat pump (GSHP) system
characteristics of the 22 buildings that serve as the basis for
this paper.
As a baseline for a comparison of the results of this
study, ASHRAE operation and maintenance estimates were
reviewed. The ASHRAE Handbook (ASHRAE, 1995)
provides a standard method for calculating maintenance cost
for commercial-size HVAC systems. Based on calculations
using the ASHRAE method, geothermal heat pump system
maintenance can cost from $0.11 to $0.22/m2/year in 1996
13
Office &
Commercial
Complex
Vancouver, WA
1957(a)- New
Farmington, CT
1971 - New
Clark
County PUD
Admin.
Exchange
Building
Eugene, OR
1981 - Retrofit
Salt Lake City,
UT
1972 - New
North Bonneville,
WA
1995 - Retrofit
Winchester, MA
1965 - New
Lane
Community
College
LDS Office
Tower
North
Bonneville
City Hall
Parkview
Apartments
Downtown
Comm.College Converted
Montgomery
Ward Store
Offices & Public
Rooms - 30-story
tower plus 2
Wings
City Hall
Administration
and Offices
Condominium
Complex
318 apts.
Condominium,
Hotel Complex,
Convention
Center, Spa, and
Pools
Middle School
Bend, OR
1992 - Retrofit
Kittitas, WA
1992 - New
College Library
Library
Haverhill, MA
1994 - Retrofit
Wapato, WA
1991 - New
Courthouse &
Courthouse Annex
Ephrata, WA
1982 - Retrofit
Kittitas
Middle
School
Heritage
College
Library
Inn of the
Seventh
Mountain
Grant
County
Courthouse
Haverhill
Public
Library
Administration
Offices
Smithfield, RI
1996 - Retrofit
Bryant
College
2 College
Dormitories
Location
Issaquah, WA
1994 - New
Site
Beaver Lake
Middle
School
Building
Type
Middle School
Open loop – 2 wells
11 to 15 ºC
95 L/s total flow
207,400
4,600
Open loop – 4 wells - total
flow 513 L/s. two wells at 119
meters deep. two wells at 192
meters deep, 19-24ºC
Ground loop – horizontal
1,829 linear meters
Open loop – 3 wells – 16 ºC
Total flow 16 L/s
Ground loop – vertical bores
70 bores, 61 meters deep
Total 8,534 meters
Open loop – 1 well 73 L/s
Open loop – connected to 31
ºC municipal water supply
system
Open loop – four wells standing column – 14 ºC
4-5 L/s per well isolated with
heat exchanger
Open loop 10+ºC isolated with
plate and frame heat exchanger
System Type
Ground loop - loop under
athletic field - 45,062 meters
in loop - 840 kW e electric
boiler
Ground loop – 36 @ 138
meters deep vertical bores 9,963 meters total
Open loop – heat exchanger
well - 116 meters deep – 12
ºC, 19 L/s possible
Open loop – four wells - 84
meters deep – 13 ºC total flow
32 L/s
680,000
58,000
39,000
280,000+
350 units and
convention
center
44,000
including
27,000 1994
addition
18,000
52,000
275,000
32,000
38,000
Square
Footage
109,000
2 Compressor/
units
2
3
30
(18 H2O-to-air)
(12 H2O -toH2O)
1
3 compressors
2
13
19
1x2
495
4
16
Number
of HP
Units
52
TABLE 1. BUILDING AND GSHP DESCRIPTIONS
1,407
35
7,913
317
295
1,759
169
378
3,848 kW t
plus an 879
kW t chiller
to provide
heat to loop
1,055
352
281
Heat Pump
Capacity,
kWt
879
15.35 (F)
9.40
(a)
19.97
(a)
24.47 (e)
(a)
16.13
(a)
17.18
(a)
(a)
kWh
Square
Foot/Year
11.00
1.43 (f)
0.87
(a)
1.86
(a)
2.27 (e)
(a)
1.50
(a)
1.60
(a)
(a)
kWh/Square
Meter/Year
1.02
0.12 - 0.15
0.05
0.12 (h)
0.13 - 0.15
0.20
0.16
0.64 (g)
0.09 - 0.14
0.11
0.16
0.50
0.01
Maintenance Cost
$0.00US/Square
Foot/Year
0.23 - 0.35
Yakima, WA
1980 - Retrofit
Walla Walla, WA
1995 - New
Walla Walla, WA
1995 - New
Tower
Building
Walla Walla
Community
College
Walla Walla
Corps of
Engineers
Whitman
College
Science
Building
Administration
Building
Correction
Facility
Walla Walla, WA
1989 - Retrofit
Yakima, WA
1983 - New
Administration
office, classrooms,
student lounge,
and cafeteria
Administration
Office and
Printing Shop
Science Building
Offices with first
floor Commercial
Administration &
Office Building
Drug & Alcohol
Rehab Complex
120,000
(1983)
60,000
(1991)
Total
180,000
30,000
88,000
91,432
100,000
133,000
61,800
20,650
39,736
7,500
130,000
Square
Footage
15,000 sqm
bld. – 9,000
sqm snow
melt
Open loop – 274 meters well
21ºC connection via heat
exchanger
Open loop – pumped well
23ºF with intermediate heat
exchanger - 47 L/s
Open loop – 2 wells - 14ºC–
27 meters deep – 50 L/s
12ºC – 65 meters deep – 79
L/s - shallow well winter; deep
well summer - separated by
heat exchanger
Open loop – connected to two
wells via heat exchanger
37 meters and 74 meters deep
16-18ºC
Open loop – one production
well - 11-12ºC, - 366 meters. –
63 L/s - water rejected to city
water system prior to treatment
Open loop – connected to
municipal water system via
heat exchanger - 4-16ºC
Open loop – pumped well
23ºC with intermediate heat
exchanger
47 L/s
Open loop – 2 wells -61
meters deep - total flow 35 L/s
10+ºC
System Type
Closed loop – horizontal
ground loop - 2,880 meters
2
39
120
2
152
139
50
89
19
2
Number
of HP
Units
4
(a) Not separately metered.
(b) Originally 2 centrifugal chillers were used; however, in 1988 one was replaced with a twin screen Dunham Bush chiller.
(c) Sized to provide conditioning to Law and Justice Center but never connected.
(d) Average daily winter HCAC system usage, facility not occupied or used year round.
(e) 1.43 kWh/m2/yr. equals total consumption. HVAC consumption equals 0.78 kWh/m2/yr.
(f) 2.27 kWh/m2/yr equals total consumption; however, HVAC consumption equals 0.94 kWh/m2/yr.
(g) Maintenance contract.
(h) Includes $0.0023/square meter/year for chemical treatment.
Whitman
College
Administration
Building
Yakima
County
Correctional
Facility
Walla Walla, WA
1955 - New
Yakima, WA
1985 - New
1990 - New
1992 - New
1995 - New
Tacoma, WA
1954(b)- New
Sundown M
Ranch
Tacoma
City Light
Location
Squaw Valley, CA
1993 - New
Site
Squaw
Valley Day
Care
Building
Type
Day Care Center
with Snow Melt
1,055
352
422
943
2,110
1,055
(528 kW t )
(703 kW t )
700
197
524
102
1,231
Heat Pump
Capacity,
kW
141
19.81
(a)
(a)
21.50
(a)
(a)
??????
37.15
31.27
43.27
44.65
24
kWh
Square
Foot/Year
0.013 (d)
1.84
(a)
(a)
2.00
(a)
(a)
2.23
1.92
0.001 (d)
kWh/Square
Meter/Year
0.006- 0.007
0.06 - 0.08
>0.10
0.57 (a)
0.10 - 0.15
0.11
0.51
0.12 - 0.15
total square footage
Maintenance Cost
$0.00US/Square
Foot/Year
0.02 - 0.03
dollars U.S. compared to $0.38 (medium) to $0.05/sq.ft./ year
(mean) for an average conventional HVAC system. As a
comparison, the Fort Polk,
Louisiana, (Pratsch, 1999) project is budgeted at
$0.018/sq.ft./year while the 4,000 kW t Galt House East Hotel
in Louisville, Kentucky, has a cost of $0.12/sq.ft./year.
(Geothermal Heat Pump Consortium, 1996).
GEOTHERMAL HEAT PUMP INSTALLATIONS
Selection Criteria
A number of the GSHP systems that date back to the
1950s were installed as a result of the building owners’ wish
to adopt a unique, quality design that would create a positive
impression in the community. This was also at a time when
air conditioning was becoming more and more of an issue, and
a driving force in selection of many of the geothermal systems.
In the mid to late 1970s and early 1980s, a number of systems
were built as a direct result of the oil crises of the early 1970s.
Many of those interviewed who had responsibility for the
construction of these systems indicated that the availability of
a secure, locally available, indigenous resource was extremely
important in the decision-making process, especially in a time
of rapidly escalating energy costs and concerns over fossil fuel
availability. Many owners of the more recently-developed
systems contributed their decisions to go with geothermal heat
pumps to past experience with such systems, very high quality
of the installation, energy efficiency, and cost savings. Other
reasons given included:
•
•
•
•
•
•
•
environmental considerations
compatibility with building design or retrofit requirements
utility incentives
reputation of engineering design firm
need for individual temperature control
reduced space for mechanical equipment
life cycle cost savings.
In truth, the publicity that many of the early systems
received played a major role in replication of the technology
in nearby areas. This can be clearly seen with the success of
the Commonwealth Building in Portland, and the press that is
was afforded. To a large extent, many of the systems that
were built in that era were a desire on the part of building
developers to capitalize on the positive publicity that the
Commonwealth Building generated.
DEVELOPMENT TRENDS
Development trends can be divided into several
distinct designs, including pumped wells with central or
distributed heat pumps and loop systems, horizontal or
vertical, relying primarily on a distributed heat pump system
layout. Fortunately for the industry, all of the above seem to
offer unique solutions to meet building design or retrofit
requirements. Unfortunately, the industry has not yet matured
to the point where all engineering design teams feel
comfortable with all available technical alternatives, and thus
design is often as much a factor of prior experience as it is a
conscious decision to select the most appropriate technology
for a given application.
16
Most early systems were based on pumped wells with
either injection or disposal to nearby surface water. Other
systems used surface water sources such as lakes, but were of
essentially the same design. The heat pumps were water-towater and two- or four-pipe systems were used to circulate
water to fan coil units situated throughout the building. By the
early 1970s, pumped systems were still dominating the
geothermal heat pump scene, but distributed systems were
becoming a major player.
With the availability of
polybutelene pipe in the late 1979s, the trend seems to be
moving more and more toward horizontal or vertical closed
loop systems, although for many large commercial
applications, the open loop water source system does seem to
provide some economic advantage and continues to capture a
significant market share where constraints on ground or
surface water use have not been adopted.
On the building side, decentralized or distributed heat
pump systems seem to increasingly dominate the field
primarily because of the ease of operation and localized
temperature control that they provide. This seems to be an
extremely attractive configuration in schools where the
individual needs of each classroom can be easily met, and
each teacher has total control over the system. Large,
centralized systems, however, continue to play a major role
and are ideally suited to many retrofit situations, especially
where, because of the historical nature of buildings, major
changes are very difficult or impossible. Centralized systems
are also an extremely attractive choice for office parks or
where low-temperature hydronic heating can be provided.
Because of the wide range of water sources and
ground loop configurations that can now be used and the
number of in-building systems that are possible, geothermal
heat pump systems can now be tailored to fit almost any
possible need. The only challenge for the design engineer is
to determine the best combination of water or ground source
and in-building configuration to best serve the client’s needs
in the most efficient, reliable, and cost-effective manner
possible.
BUILDING AND GSHP SYSTEM CHARACTERISTICS
Table 1 presents information on in-building system
design and energy performance. Unfortunately, because of the
age of many of the installations, no actual capital cost data
was available for most systems and, therefore, no attempt has
been made to cover capital cost information in any detail. For
the 22 systems that are covered in this paper, the installed heat
pump capacity varies from a low of 1.36 tons/sq.ft. per 1,000
square feet to a high of 6.00 tons/sq.ft. (the system was
designed to meet future growth at the college) per 1,000
square feet. For the water source systems, flows range from
1.30 gpm per ton of installed capacity with an average of 3.43
gpm per ton. Required flow is, of course, very dependent
upon water temperature and heating and cooling requirements.
For closed loop systems, the heat exchanger circuit pipe length
ranged from 236 feet per ton to 600 feet per ton, with an
average of 454 feet per ton. Of those with vertical bores, the
range is 166 feet of bore per ton to 204 feet.
GHC BULLETIN, DECEMBER 1999
Building electrical energy use ranges from 9.40 kWh
per square foot per year to 24.47 kWh per square foot per
year, with an average of 18.7 kWh per square foot per year.
For those systems where it was possible to determine electrical
load for the mechanical system, the range was 8.43 kWh per
square foot per year to 10.14 kWh per square foot per year.
Electrical rates and demand charges are so utility-specific that
no meaningful trend could be discerned from an analysis of
available data.
EQUIPMENT AND DESIGN PROBLEMS
Due to the fairly unique differences between open
and closed geothermal heat pump systems, the equipment and
design problems will be treated separately as will maintenance
issues and costs.
Open-Loop System
As was mentioned earlier, open systems dominated
the geothermal heat pump market from 1946 until
approximately 1980 when horizontal and vertical closed loop
systems became readily available. A majority of open loop
systems rely on one or more wells.
Water is withdrawn from the well or other source and
disposed of through the use of injection wells, through surface
discharge, or, in the case of standing column wells, the water
is returned to the outer annulus of the production well.
There is little doubt that well problems dominate
when it comes to open loop systems. The two most often
encountered problems are inadequate flow in the production
well and plugging that causes pressure build-up in the
injection well. Production problems are most often a result of
excessive draw down of the acquifer due to over use or severe
drought. It can also be a result of sedimentation in the bottom
of the well. In many cases, the wells are simply not drilled
deep enough or completed correctly. Many such problems can
be corrected by deepening the production well or by
reworking. In those cases where sedimentation is a problem,
correct screening can provide a relative straightforward
solution. However, the vast majority of problems associated
with open loop systems are caused by the injection well. The
principal cause appears to be iron bacteria and, where a
mature colony is established, extremely difficult to eliminate.
The problem can, however, be minimized by regular
maintenance including chlorination (once every 3-6 months)
and back pumping of the well. In some cases, the pressure
build up problem is caused by scaling (often calcium
carbonate, CaCO3). Again, the problem can be minimized
through the use of chemical treatment, although in some
severe cases, some reworking of the well on a regular basis
may be required. Of course, excessive injection pressure may
also be the result of poor well completion or an inadequate
injection horizon.
The next most common problem associated with open
loop systems is pump failure. Both open shaft, vertical downhole pumps; and submersible pumps are regularly employed
and, at least for those cases where high volume is desired, the
GHC BULLETIN, DECEMBER 1999
down-hole shaft system appears to dominate. Principal
problems seem to be with bearings and seals, often resulting
in the need for major maintenance and, in a worse case
scenario, resulting in a broken shaft. Major pump problems
seem to be avoided through proper sand screening and by
ensuring adequate lubrication.
Finally, the lack of a heat exchanger (shell and tube
or plate and frame) to isolate the production flow from the inbuilding equipment can result in major system problems
including excessive corrosion in the heat pump tube bundle.
Most systems are now moving from shell and tube to plate and
frame exchangers due to the closer approach temperature, the
ease of maintenance and the flexibility they offer in terms of
ease of expansion.
Closed-Loop System
Closed-loop systems began to challenge the
dominance of the open-loop systems in the late 1970s/early
1980s. However, unlike open-loop systems where required
flow can easily be determined based on load, source
temperature, and equipment performance, loop length is much
more difficult to calculate and is highly dependent upon soil
characteristics including temperature, moisture content,
particle size and shape, and heat transfer coefficients. Correct
sizing of the ground loop continues to be a cause for
continued design problems and special attention should be
placed on minimizing inference between loops, whether they
be horizontal or vertical.
Other problems associated with loop design and
installation include improper header design, inadequate system
purging, leaks associated with corrosion of fittings, or poor
workmanship. All of the above problems can be minimized
through proper system analysis and design, and the use of
well-trained and experienced installation personnel. One of
the most often encountered problems is related to the
circulated heat transfer fluid. Methanol and Environol seem
to be the least problematic and best heat transfer fluid choices.
Central vs Distributed Heat Pump Systems
There seems to be very few problems associated with
either the choice to employ a centralized or decentralized heat
pump arrangement. Both afford the capability to provide
supplemental heating or cooling through the use of boilers or
cooling towers. The only major design problems that seem to
be somewhat common in many centralized heat pump systems
is the use of a two-pipe system to circulate hot or chilled
water. Because the two-pipe system does not allow for the
simultaneous supply of both heating and cooling, the building
owner/system operator must choose which service will be
provided at any given time. Because most such systems are
difficult to reverse once the decision is made to go from, for
example, heating to cooling, the system can not readily be
changed back should a late spring cold spell come
unexpectedly. Because the provision of heating is almost
always more critical than cooling, operators most often
chooses to error on the side of having heat available.
17
OPERATION AND MAINTENANCE
Open-Loop System
Most maintenance problems associated with openloop systems are well related. The problems include problems
with pumps, including bearings and seals. Other maintenance
issues include the need to clean or even rework production
and injection wells and the need for chemical treatment of
injected water to control scaling or bacterial growth that plugs
the injection wells. Another potentially major maintenance
issue is removal of sand from the heat exchanger(s) if
adequate filters and/or sand traps are not used.
Closed-Loop System
Maintenance of closed-loop systems appears to be
extremely minimal and restricted to circulating pumps unless
the heat transfer fluid results in corrosion of fittings and other
system components.
Central and Decentralized Heat Pump Systems
Central heat pump systems seem to require very
limited maintenance, and because all major pieces of
equipment are located in a central location, most maintenance
chores can be carried out easily. Decentralized systems, on
the other hand, do require considerably more routine
maintenance including changing filters every three to six
months. For example, when the Tower Building in Yakima,
Washington, was purchased by the present owner,
approximately one compressor per week required replacement;
however, once a routine preventative maintenance program
was put into place, only one compressor failure occurred over
the entire following year. Care should be taken when
installing a decentralized system to ensure that maintenance
personnel have adequate access to each unit for routine
maintenance and also for repairs when they become necessary.
Despite the maintenance issues mentioned,
maintenance costs are relatively low in all but a few cases,
averaging $0.016 per square meter per year (see Table 1). In
only three of the cases evaluated was maintenance considered
a major concern. In one of these, the equipment was in
definite need of replacement after nearly 35 years of service,
18
and with the others, problems with the heat transfer fluid had
resulted in serious corrosion problem and leaks as well as
control problems due to the leaks. Anonymously high
maintenance costs were a result of, in one case, a poorly
structured maintenance contract; in another, lack of local
maintenance providers; and in two cases, to relatively high inhouse personnel costs assigned to the HVAC system.
CONCLUSION
Geothermal heat pump systems are an increasingly
attractive option for commercial buildings. Based on over 50
years of operating experience, it is safe to say that earlier
concerns over long-term reliability, operation, and
maintenance costs were, to a large extent, unfounded.
Although some systems have had to be replaced due to
problems related to production and/or injection well problems,
a majority of the systems have proven to be extremely reliable,
with many having been in service over 25 years, and
maintenance problems and costs have been acceptably low.
Advancements in equipment, installation techniques,
and control systems as well as knowledge of heat transfer
continues to reduce equipment and design problems.
Increasing knowledge and use of a wide variety of water
sources as well as ground loop designs and configurations,
together with the number of in-building systems that are now
possible allow that geothermal heat pump technology can be
tailored to fit almost any possible building need.
REFERENCES
ASHRAE, 1995. Handbook: HVAC, American Society of
Heating, Refrigeration and Air-Conditioning Engineers,
Inc., Atlanta, GA.
Geothermal Heat Pump Consortium, 1996. Earth Comfort
Update--The Geothermal Change, National Information
Resource Center Newsletter, Washington, DC.
Pratsch, Lew, 1999. Personal communication, U.S.
Department of Energy, Washington, DC.
GHC BULLETIN, DECEMBER 1999
CURING BLOCKS AND DRYING FRUIT
IN GUATEMALA
Luis Merida, Designer and Manager
Eco-Fruit and Bloteca
Guatemala
INTRODUCTION
In Guatemala, there are six geothermal fields
recognized as potential sources of exploitation and only two
have already been utilized. The first two successful uses of
geothermal energy in Guatemala have been direct-use
applications at the Amatitlan Geothermal site.
Figure 1. Geothermal areas of Guatemala.
The first one is Bloteca, a construction block factory
established about 20 years ago and that recently started using
geothermal steam in the curing process of concrete products.
The other one is Agroindustrias La Laguna, a fruit dehydration
plant, that was setup as an experimental and demonstration
project. While developing this second project the owners
decided to bring a product, Eco-Fruit, to the local market
using the plant. The product was so successful that it has been
in all supermarket chains for the past two and a half years.
BLOTECA
In the 1976 Guatemala earthquake, poor construction
materials caused most of the destruction. Most of the houses
where built with adobe bricks, and casualties where not really
from falling objects, but from collapse and suffocation. From
this experience the goverment implemented new building
regulations mainly for house construction.
Because of these regulations, a group of investors decided to setup a construction block factory since few existed
in the market. Since Amatitlan was just 30 km away from the
city it offered a good spot, not only because it reduced
transportation costs, but due to the fact that it was located in
a volcanic zone where suitable materials are located close by.
The materials used are pumice, gravel, limestone, etc., which
are very abundant in a volcanic zone; however, it never
occurred to use geothermal steam to supply the factory for the
curing process of the plant.
Figure 3. Bloteca loading area.
Figure 2. Detailed map of the Amatitlau region.
GHC BULLETIN, DECEMBER 1999
By 1993, the demand on the products from Bloteca
was so high that the production could not keep up with the
demand and new factories started to come into the market.
The need to set up a new production line was obvious. Since
the steam supply was one of the biggest problems and having
to buy a new boiler, the project was put on hold for some time.
19
Figure 4.
Well and supply line.
The answer came up while drilling a well to obtain a
water supply. The drilling had to stop because the water was
too hot. The well actually started flowing steam and water and
the geothermal resource was discovered. A few geophysical
studies where conducted, like electrical resistivity and electric
potential. This showed the most favorable site to drill a
production well.
In May 1994, a second well, B-2, was drilled to a
depth of 700 feet (213 m) and with a downhole temperature of
185 C. This wells produces enough steam to supply the needs
of the plant.
The system consists of two different lines that control
the flow of the well, one that goes into a silencer and then into
a weir to measure the water before injection, and the other line
that goes into a cyclone separator. Since the steam is not
needed all the time, it is controlled by regulating the flow that
goes into the cyclone separator and then to the distribution
lines.
how much steam they do not have to produce by burning fuel.
A plant with this capacity needs to consume around 16,000 gal
(57 tonnes) of diesel fuel a month. The price on Guatemala of
diesel fuel in Guatemala is about US$ 1.50/gal ($0.40/liter);
so, this come up to a savings of US$ 24,000 a month.
All of the installation including the drilling of the
well, cyclone separator and distribution lines came up to
around US$ 200,000. So the investment was paid of in less
than one year and if we multiply the next three years of
operation, we come up to a benefit of US$ 864,000. This is a
benefit not just economically for the plant but for Guatemala
not having to depend on the import of fuel. It also qualifies
Bloteca as a plant with a environmental friendly process.
Figure 6. Bloteca process line 2.
At present, Bloteca produces 1.5 million units a
month and it offers 24 types of blocks and 4 grades of fire
resistance blocks.
Figure 5. Cyclone separator.
Although in Bloteca they are concerned on how much
steam this well can produce, they are concerned more on
20
ECO-FRUIT
Agroindustrias La Laguna was originally just a
experimental and demostration project on which it was
intended to prove in Guatemala that geothermal energy could
be applied in a agroindustrial project. In this case, dehydration was the process selected. The pilot plant was setup
and proven and while the investors decided to find a way to
make it economically attractive they decided to dry fruit.
GHC BULLETIN, DECEMBER 1999
Fruit is abundant in Guatemala and a lot of the
harvest does not go into export since it does not comply with
international standards of shape, color and form. All of the
reject fruit stays in the country and goes to waste, which is
available in the market at a very low price. The intention of
the project was to give the exporters a service on which they
could give an added value to the fruit they do not export and
make it attractive to the export market.
This project was undertaken in order to start making
some profit by extending the market of a local product and
selling it in small stores as a natural product with a environmental friendly process. The product was so successful that
it has been in all the supermarket chains for more than two
years. The products produced are: pineapple, mango, banana,
apple and pears.
Figure 8. Setting up the DHE.
Figure 7. Samples of the dried fruit.
The project started with the idea to use a downhole
heat exchanger to extract the heat. A well was drilled with a
12" diameter all the way down. A downhole heat exchanger
was installed and tested. The performance decreased after a
few hours of operation so some tests where conducted. A
temperature profile was taken and it did not give very good
result. (see Fig. 10 - no enhancer).
To increase the performance of the downhole heat
exchanger an enhancer tube was used. This is a 4-in. diameter
pipe with perforation at the two bottom tube segment, solid in
the middle and perforated again at two tube lengths at almost
the top of the pipe. This creates a convention cell that causes
the temperature profile to be almost linear all the way down
(see Fig. 10 - enhancer installed).
After setting up the enhancer, the performance of the
downhole heat exchanger increased more than enough to
supply the heat load of the dehydration plant.
The concept of the system is very simple. The
resource is only used as a heat source and does not supply the
system with any amount of fluid. Water is pumped from a
process water tank through the heat exchanger where it gains
temperature. This water is then pumped through a finned tube
heat exchanger (radiator coil, three step) where the airstream,
that dries the fruit, is heated. The air dries the fruit that is set
GHC BULLETIN, DECEMBER 1999
Figure 9. Setting up the enhancer.
up in trays and tray-trucks inside a tunnel drier. The fruit
stays inside the tunnel drier until its water content is reduced
to 4%.
21
Figure 10.
Temperature profile of well L-2.
At the moment, the capacity of the plant varies
depending on the fruit it handles and the way the fruit is set
up. Either slices or cubes yield a different capacity for the
plant, the average is:
Fruit
Banana
Mango
Pineapple
Pear
Apple
Capacity
Pounds (kg)
Drying Time
(hours)
1800 (816)
1600 (726)
1800 (816)
1500 (680)
1500 (680)
22
16
18
12
12
CONCLUSIONS
I believe that, although direct-use projects are
generally smaller in scale that power generation, they have a
greater economical benefit in countries like Guatemala. You
have to build something around the use of the geothermal
energy use. You keep more people involved at all times so in
the long run they will create a larger development in a country
like Guatemala.
REFERENCES
Lienau, P., 1999. “Industrial Applications,” Geothermal
Direct-Use Engineering and Design Guidebook. Geo-Heat
Center, Klamath Falls, OR.
Merida, L., 1994. Fruit Dehydration Thesis. Geothermal
Institute, University of Auckland, New Zealand.
Popovski, K., 1994. “Direct Application in Agriculture.”
Geothermal Institute, University of Auckland, New Zealand.
Rafferty, K. and G. Culver, 1991. “Heat Exchangers,”
Geothermal Direct-Use Engineering and Design Guidebook.
Geo-Heat Center, Klamath Falls, OR.
22
A. Weighing the fruit.
B. Slicing.
C. Setting up in trays.
D. Tray trucks.
Figure 11. Steps in processing the fruit.
GHC BULLETIN, DECEMBER 1999
ITALIAN GEOTHERMAL
DISTRICT HEATING SYSTEMS
Roberto Carella
Milano, Italy
SUMMARY
Italy has large geothermal resources, both high and
low temperature. It is the most important producer of
geothermal electricity in Europe, but it also uses its lower
enthalpy fluids in spas, agriculture, industry and district
heating. The main plants for this last application are briefly
described.
Figure 1.
GHC BULLETIN, DECEMBER 1999
ITALY’S GEOTHERMAL SETTING AND DIRECT
USE STATISTICS
The Italian territory is characterized geologically by
two mountain ranges: the Alps and the Apennines. The latter
constitutes the backbone of the peninsula and separates an
outer foredeep to the east, with basins which can be defined as
“cold” if compared with the average temperature of the earth,
from an inner “hot” Tyrrhenian belt, with back-arc basins.
The Alps limit to the north, the “cold” Po basin (Fig. 1).
Italy geothermal scheme and space heating plants.
23
The “hot” Tyrrhenian belt is associated with young
mainly intrusive magmatism in Tuscany and volcanism in
Latium and Campania. Geothermal gradient may reach 520oC/100 m; maximum temperature in some wells exceed
400oC. Geothermal targets in the area are mainly highenthalpy resources used for electricity production, but lowenthalpy prospects are also important at the edge of the main
thermal anomalies or as cascaded use from geo-power plants.
The outer “cold” foredeep induces a number of sedimentary
basins from the most important Po basin in the north to the
Adriatic coastal belt and to central Sicily. These basins are
filled with a thick sedimentary sequence consisting of
Quaternary and Tertiary clastics overlying a Mesozoic
carbonate section. Geothermal gradients (2-3oC/100 m) are
typical of subsident basins and commercial prospects are lowand medium-enthalpy fluid applications. Concerning Italian
direct uses, projects for the equivalent of 240,000 TOE/y are
operational, of which 125,000 are for therapeutically-related
uses in spas; 60,000 for greenhouses and fish farming; 40,000
for residential heating, and about 15,000 for industrial
purposes.
A large portion of civil space heating uses is
concentrated in the Abano spa resort area, in northeast Italy.
As regards district heating, the most important plants are those
of Ferrara and Vicenza in the eastern Po Valley which started
operation in 1990. Smaller DH systems are installed in the
Tuscany geothermal steam fields area and in the lesser spa
towns of Bagno di Romagna (northeast Apennines) and Acqui
Terme (Piedmont).
The main plants are briefly described below
(locations in Fig. 1).
Figure 2.
24
ABANO AREA (Po Valley, Veneto)
This area concentrates the largest consumption of
geothermal energy for building heating, and is the most
important example of integrated use of this energy for health,
recreation and residential heating purposes in Europe. The
spa area for Abano, extending for about 23 km2, is located on
the Euganea volcanic district, mostly at its eastern edge;
several small towns with many hotels and resorts dedicated to
the health and relax business are concentrated in the area,
famous since ancient times for its hot springs.
Most hotels in Abano and Montegrotto have their
own wells (2 or 3) and are equipped with spa facilities (Fig.
2). Some 230 wells produce by pumping 3,600 m3/h of 65 to
87oC low salinity water during the five months of the main
tourist season (yearly average yearly production 2,500 m3/h).
Average well depth is 300-400 m, with some reaching 700 m.
Completion is open-hole in fractured Upper Mesozoic
limestone.
Geothermal water is used for curative treatments, in
swimming pools and to heat buildings and provide domestic
hot water. Heat for these last two purposes is transferred
through plate or shell-and-tube heat exchangers to a fresh
water network. Back-up conventional boilers are seldom
installed and emergency needs are generally taken care of by
connecting to nearby wells. To regulate the flow, hot and cold
water storage tanks are commonly set up. The exhaust water,
at a temperature of about 40-45oC, is discharged at surface. In
total about 120 hotels in the Abano area are fitted with
geothermal spa facilities. Total heated volume is around 2.5
million m3, equivalent to 12,500 standard flats, in addition to
200 swimming pools.
Wells in the Abano Terme area.
GHC BULLETIN, DECEMBER 1999
Substituted energy is estimated about 25,000 TOE/y
for building heating and sanitary water, and 90,000 TOE/y for
therapeutical and recreational uses.
FERRARA (Po Valley, Emilia)
The Ferrara geothermal field was discovered in 1956,
as a result of oil and gas exploration by AGIP, the then national oil company. Well Casaglia 1 drilled to the depth of
3,379 m without finding hydrocarbons evidenced the presence
of 100oC salt (65 g/l) water starting at about 1,100 m in fractured Mesozoic carbonates within a vary large structural high.
In 1981, after reentering and testing successfully the well, it
was completed for geothermal production under a joint venture with the national utility ENEL. In the same year, a new
well (Casaglia 2, about 1 km from Casaglia 1, and 1,960 m
deep) was drilled and tested up to 400 m3/h of fluid on pump.
After signing a preliminary heat sale contract in 1983
with the Ferrara Municipality, which undertook to gradually
build the downstream heating plant and DH network, the first
geothermal heat delivery took place in 1990. The initial
production facilities consisted of Casaglia 2 used as producer
(at the rate of 200 m3/h on pump) and well Casaglia 1 acting
as reinjector, both with open-hole completion. In 1995, a
second producer (Casaglia 3) was drilled, parallel and few
meters from Casaglia 2 to 2,000 m, doubling the field’s flow
rate. The surface equipment works in a closed circuit at 18
bar pressure. Anti-corrosion additives are injected in the
producing wells; while, bactericides are mixed with the
reinjected fluid. After a filtering unit, a set of titanium plate
heat exchangers pass the available heat to a freshwater circuit
belonging to the municipality feeding the DH system.
A pre-insulated steel double line, 2 km long, conveys
the heated 95oC freshwater to the municipal heat plant, halfway between the production wells and the town, then carries
the fluid back, cooled to an average of 60oC to the AGIPENEL heat exchangers. The heat plant (Fig. 3) is composed
of the geo-system terminal, peak-load and back-up gas boilers,
hot and cold water regulating storage tanks, a 150-ton/day
solid waste incinerator and an inter-connecting pump station.
A co-generation unit was added in 1999.
The DH network covers an extensive area along the
central axis of Ferrara town, starting from its northwest
outskirts. A 30-km grid of double preinsulated steel pipes
connects 270 large users for a total of 2.7 million m3 of heated
space. Optimization of the return temperature is being
investigated and the network is being expanded.
Geothermal energy currently provides 5,000 TOE/y
of the energy needed, corresponding to almost 60% of the
total, as compared to about 20% each originating from the
incinerator and the gas boilers.
Figure 4.
Ferrara hot reservoir with solid waste
incinerator in the background.
Figure 5.
Ferrara pumping plant.
VICENZA (Po Valley, Veneto)
Hot freshwater in Mesozoic limestones was
discovered by AGIP in 1977 in an oil and gas well (Villaverla
1) located 14 km north of the town of Vicenza. A detailed
technical evaluation indicated that the resource should extend
to Vicenza and, after signing a preliminary sale agreement
with the local municipal company, AIM, AGIP and ENEL in
a joint-venture drilled a well in 1983 located within the town
limits. Vicenza 1 was successfully completed open-holed in
Mesozoic limestone at 2,150 m, producing by pumping up to
125 m3/h of 67oC freshwater with a limited amount of H2S.
Figure 3.
Ferrara heat plant.
GHC BULLETIN, DECEMBER 1999
25
After the granting of an exploitation lease and
signing in 1985 a contract for the purchase of the hot water,
AIM built the heat plant and the DH network between 1988
and 1991. Geothermal heating began in winter 1990. The
heat plant is quite complex and included, after plate heat
exchangers to isolate the geothermal fluid, dual-power (gas or
electricity) heat pumps with heat recovery components,
cooling towers, peak and back-up gas boilers, and a pumping
system. The DH network consists in a 7.4 km double
preinsulated steel pipeline and a parallel one-way sanitary hotwater line fed by 20 m3/h of geothermal fluid. Inlet-outlet DH
temperatures are 90-60oC.
The geothermal fluid was discharged in the town
drain works at 20-25oC. The DH system services 74 main
users, heating 1.33 million m3 of space. Geothermal energy
use with gas heat pumps amounts to about 2,700 TOE/y.
Because of technical problems with the heat pumps
and a dispute over the geothermal water sale price, use of the
geo-heat is suspended after a few years and the DH system
operates with co-generating units installed in 1996. Solution
of the controversy is imminent and could lead to resumption
of the geothermal operations.
Figure 6.
Figure 7.
26
Overview of the city of Vicenza.
Vicenza heat pumps.
BAGNO DI ROMAGNA (Northeastern Apennine, EmiliaRomagna)
The municipality of this small spa town with 45oC
springs, which has exclusive rights on the use of the resource,
decided in the 80s to develop a geothermal DH system. The
availability of sufficient amount of resources was verified by
drilling some very shallow wells which evidenced a potential
of over 200 m3 /h of 30-40oC nearly freshwater in fractured
sandstones of Miocene age. Well No. 3, 50 m deep, completed with slotted liner for a production by pumping of 90 m3/h
of 37oC water, was selected to feed the DH system. The well
is located only 400 m from the main spring; however, no
interference occurs. The heat plant consists of gas-electric
heat pumps with heat recuperator, co-generation units, and
gas-gasoil back-up boilers. A network of 9-km two-way
preinsulated steel pipelines connects several hotels and houses
with about 190 substations for a heated space of 220,000 m3.
HE inlet temperature is 80o C and return 60oC. Spent
geothermal water is rejected at 20oC in a nearby river. The
system was built in 1983-86 and went on stream in 1987.
Geothermal energy output is about 500 TOE/y.
Ongoing expansion of the grid will double the
connected heated space by the end of 1999.
ACQUI TERME (Northwest Italy, Piedmont)
Acqui is a spa town with a quite hot spring (La
Bollente) with a temperature of 70oC and a free-flow rate of
33 m3/h. A private operator uses the resource for therapeutical
purposes. During 1986-87, the municipality developed a DH
plant and grid to utilize the Bollente spring water in periods
when the spa facilities are closed (spring, autumn and part of
winter). The heat station consists of a steel plate heat exchanger, gas-fed heat pumps with heat recuperator and gas-fueled
boilers for peaking and backup. The DH network is a 2.2 km
two-way preinsulated steel line, with input temperature of the
water 80oC and outlet 60oC. It connects public buildings with
11 substations for a total of 130,000 m3of heat space. Design
temperature of the spent geothermal fluid is 35oC with an
expected energy output of around 300 TOE/y. Heat delivery
started in 1988, but because authorization for the energy use
of the spring water has not yet been granted, the DH network
is fed provisionally by conventional boilers.
TUSCANY
In several west Tuscany towns, ENEL utilizes part of
the steam available from power generation or, more often,
steam unsuitable for electricity production because of low
pressure or temperature, for direct uses (mainly space
heating). Geothermal energy supplied to several centralized
and district heating plants in the ENEL area amounts to about
7,000 TOE/year.
The largest share (70%) is utilized in the Pomarance
Municipality where DH systems are installed in four suburbs
(Larderello, Montecerboli, Serrazzano and Lustignano). In
Larderello, offices and living quarters of ENEL are served
directly; while, the other heat systems are owned and operated
GHC BULLETIN, DECEMBER 1999
by the municipality. The main fluid used is power-plant grade
steam at 160-200oC tapped from the steam lines; while, in
Lustignano, 170oC steam from a dedicated well is employed.
Heat is transferred to the DH water circuits via shell-and-tube
heat exchangers. Return temperature is 70 to 95oC.
A small DH system serves the town of Monterotondo
Marittimo using 95oC steam with a return temperature of
70oC.
Other small geothermal DH networks are developed
in the Castelnuovo V.C. Municipality, downtown and in the
Sasso Pisano suburb.
The downtown heat plant was completed in 1987,
being fed with high-grade steam tapped from the pipeline to
the Castelnuovo power station.
The plant was recently refitted to use low-pressure
105oC steam from shallow wells and a separate distribution
line for domestic hot water was laid down. Steam from the
power station network will be used for peaking.. The Sasso
heat plant owned by ENEL (while the DH network belongs to
the municipality) was completed in 1994-95. It serves 150
dwellings for a total of 50,000 m3. Low pressure 105oC steam
from refitted shallow wells is fed into a shell-and-tube heat
exchanger to cover base load needs of the DH system. Peak
demand is met by steam tapped from the Sasso Pisano power
station feeder line, through as second shell-and-tube heat
exchanger. The plant has a gas disposal unit and the spent
geothermal fluid is reinjected at 70oC (Fig. 8).
Figure 8.
GROUND-SOURCE HEAT PUMPS
Contrary to several central and northern European
countries (including Switzerland), Italy has very few systems
of this type.
POSSIBLE NEW DEVELOPMENTS
Most of the action is concentrated in Tuscany, where
installation of geothermal DH units in the town center of
Pomarance and in the S. Dalmazio suburb started in 1999.
ENEL will also provide geothermal heat for the Santa Fiora
Municipality DH system (for a total of 2,400 TOE/y) and has
proposed a similar arrangement for the town of
Piancastagnaio. Use would be made of hot water effluents
from power plants and of steam not suited for electricity
production.
Outside Tuscany, the Grado Municipality, on the
Veneto coast (northeast Italy) is interested in a DH project
involving also some spa use. The system would be fed by 5060oC water from a well to be drilled to the depth of 1,000 m,
in the town center, tapping a Mesozoic limestone reservoir.
Sasso heat plant scheme: 1) to/from DH grid, 2) power steam line, 3) heat meter, 4) heat exchanger, 5)
shallow production wells, 6) gas disposal, 7) pond and 8) to reinjection wells.
GHC BULLETIN, DECEMBER 1999
27
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GRC Publications
soils for farming, and rock for buildings and
tools. A drawing from a neolithic village in
Turkey dated at 6200 B.C. shows multistory rectangular homes flanking an erupting volcano—lava, tuff and volcanic bombs
flying from the crater. But time and again
people returned to the looming slopes, as
they do today, for the good offered by the
Earth’s fire overwhelms the bad.
Does soaking in thermal water cure illness? Through time immemorial, people
around the world have thought so. With little
more to guide them than curiosity and their
own experiences, people from Asia and
Africa to Europe and the Americas have
bathed in hot springs to alleviate arthritis,
rheumatism, psoriasis and leprosy. Many
North American Indian Tribes—including
those at The Geysers in northern California—retained health-giving hot springs as
neutral ground, open to the use of all.
Thermo-mineral muds collected for
skin care through the millennia from the
edges of hot springs and other geothermal
features now sell for high prices at beauty
counters in exclusive stores for the same
purposes. Pumice, always used for though
cleansing, is still sold commercially as a skin
abrasive and a key ingredient in
“extra-strength” soaps.
At Chaudes-Aigues in the heart of
France, the world’s first geothermal district
heating system started up in the 14th century
and is still going strong. Stories from a
Heated Earth highlights old tax records, pipe
making and distribution methods, legal disputes, and the great success of this project
started so long ago. The Icelandic chapter
laments that early Nordic settlers on the island did not use geothermal resources in the
same way, suffering unnecessarily for centuries in cold, unheated houses.
With these and other highlights, Stories from a Heated Earth is an historical
guide to our geothermal world. Turning
from an exquisite painting on the cover of
a small boy gazing at Japan’s Mount Fiji,
the book embarks on its journey of our geothermal globe with an essay on Easter Island, then spans the world, ending in the
final chapter among the peaks of the Andes
in South America. Coming full-circle, the
book’s inside back cover brings the reader
once again to Easter Island, the most isolated inhabited island on Earth—and one
with a rich geothermal heritage.
Stories from a Heated Earth offers a
fascinating journey through time, focused
on the cultural influences of geothermal
phenomena on the peoples of the world. As
you open the book for the first time, its authors and editors hope you will enjoy the
trip.
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Stories from a Heated Earth — Our Geothermal Heritage
Edited by Raffaele Cataldi, Susan Hodgson and John Lund
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Geothermal Resources Council
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