the long thermopile

The Long Thermopile

Ed Yarmak, P.E.

Arctic Foundations, Inc.

Kotzebue – Maniilaq Health Center (1993) Fairbanks – FAA Flight Service Center (1987)

Program

• Introduction to the “Long Thermopile”

• Brief Bio of the Inventor

• The First Thermopiles

• Notable Early Projects using Thermopiles

• Aurora Tower – 1st Commercial Thermopiles (56 years and counting)

• Bethel OMS Building – Early At-Grade w/Passive Subgrade Cooling

• Thermopiles, Thermo Ring-Piles & Thermo Helix-Piles

• Thermoprobes; Straight, Sloping Evaporator and Flat-Loop Evaporator

• Thermopile Conversions

• Hybrid Thermosyphons

• Buried Condenser Thermosyphons

• Coupled Thermosyphons

• Wellhead Thermosyphons

• Projections

The Long Thermopile

Passive Two-Phase Freezing System

Two-phase thermosyphons are passive refrigeration devices that transfer heat

against gravity. Construction is typically a closed ended tubular vessel

charged with a two-phase working fluid. The vapor phase of the working

fluid fills the majority of interior of the vessel with the liquid phase filling the

minority of the volume. Typically, a thermosyphon is installed with a portion

of the vessel above ground and the remainder buried. When the above

ground portion is cooled below the saturation temperature of the vapor, the

vapor condenses on the interior of the cooled portion of the vessel and

releases its latent heat of vaporization. This slightly decreases the interior

pressure and initiates boiling and vaporization of the liquid whereby heat is

absorbed from the ground. The condensate in the upper portion of the vessel

flows via gravity to the lower portion of the vessel. Whenever the

condensate comes in contact with a warmer portion of the vessel, it

evaporates and causes that area of the vessel to cool. The cycle continues as

long as the above ground portion is colder than the below ground portion of

the thermosyphon

The Long Thermopile

Abbreviated Biography of the InventorErv Long was born to a farm family in Minnesota in 1920. He attended the University of Minnesota and earned a

bachelors degree in aeronautical engineering. His university time was interrupted by service in the US Army Air Corp

where he was a multi-engine pilot (B-17). While in school, he worked at for Strato Equipment Company specifically on

some of the early pressure suits and oxygen supply systems for high altitude pilots. Erv came to Alaska from Minnesota

in 1947 to sell an aircraft and ended up being a bush pilot for two years. Bush flying wasn’t paying the bills, so Erv

found a job as an engineering technician at the soils laboratory of the COE Alaska District. His work with the Corps

took him all over Alaska. He retired from the Corps in 1976 as the Chief of Foundations and Materials, Alaska District.

Erv started Arctic Foundations, Inc. in 1972 and lead the company until he passed away in June of 2012 at the age of

91.

The Long Thermopile

The Long Thermopile is a two-phase thermosyphon that moves heat

against gravity with no external power input. When the air is colder than

the soil, the system withdraws heat from the soil. When the air is warmer

than the soil, they system is dormant.

“The system is thermally self-regulating so that all heat travels upward

except for the normal thermal conduction of the soil materials” - ELL

Mr. Long granted the COE royalty-free use of his method while he was in

their employ. He proposed the method as a solution to problems at the

Bethel White Alice site in 1958, but was told that “it sounds too simple to

work”.

When a thawed aquifer was found at the 13 foot depth at the site of the

Aurora communications site in the Copper River Valley, the Corps opted

to try Long’s method because it was relatively inexpensive and could be

converted to a conventional mechanically refrigerated system if it didn’t

prove satisfactory. A test pile was installed to prove the refrigeration

system, and then, the first commercial thermopiles were installed in 1960.

Data from the instrumented test pile was reported by Erv Long at the

International Conference on Permafrost in 1963 at Purdue University.Aurora Test Pile (1960)

The First Commercial Long Thermopiles

Aurora Tower thermopile being installed and Aurora Com

building with installed thermopiles and steel framing (1960).

The First Commercial “Long Thermopiles”

Aurora Tower under Construction (1960)

The Aurora Tower

The Aurora Tower Thermopiles (1989)

The Aurora Tower

The Aurora Tower Thermopiles (2007)

Bethel National Guard OMS Building

Bethel National Guard OMS Building Constructed 1978-1979

Bethel National Guard OMS Building

Bethel National Guard OMS Building 1979

Thermopiles

Thermopiles are load bearing two-phase thermosyphons that are

generally used to found structures where permafrost soils exist.

Typical Thermopile applications follow:

Installation at sites with a frost susceptible active layer where heave

and pile jacking are problems. Thermo-cycling reduces frost heave

forces to negligible quantities.

Installation in marginal permafrost where pile creep rates are high.

Thermo-cycling reduces soil temperatures and subsequently

reduces creep rate.

Installation at sites with saline permafrost where allowable stresses

are reduced due to substantial quantities of unfrozen water in the

soil matrix. Thermo-cycling freezes water near piles and pushes

salts away. Also proven effective for moving glycol from a piling

face.

Installation at sites where development has increased the heat load

to the subgrade. Heat transfer rates of the Thermopiles need to be

sized to balance or exceed heat load.

Gakona HAARP (2003)

Top Left • Bethel, Alaska; Main Post Office

Bottom Left • Bethel, Alaska; Nexrad

Bottom Right • 12” Thermopiles

Thermopiles

Gakona Senior Center Thermo Ring-Piles

Thermopiles Loaded for Delivery in Erv Long’s Driveway (1979)

Thermo Helix-PilesThermo Helix-Piles are Thermopiles with helical shear rings

attached and can be used in all applications where Thermopiles

are appropriate. At one time, individual rings were used instead

of the helix. Most applications use a helix that has a strip width

of 2 inches (50mm). Typical Thermo Helix-Pile applications

follow:

Generally, Thermo Helix-Piles support greater loads than

adfreeze piles. Shear loading in lieu of adfreeze allows higher

unit stresses that equate to shorter embedment depths.

Thermo Helix-Piles are used when high transient loads are

expected. The flexibility of the helix allows a uniform load

distribution along the pile.

Thermo Helix-Piles are used to support critical structures where

consequences of foundation movement are high. Thermo Helix-

Piles offer high redundancy.

Thermo Helix-Piles are used when the installation must be

optimized for the lightest pile to carry the heaviest load.

Thermo Helix-Piles loaded for shipment to Kotzebue, Alaska

Thermo Helix-Piles supporting K-12 School at St. Michael, Alaska

Thermo Helix-Piles

RCMP Detachment, Inuvik, NWT, Canada – 2014

Thermo Helix-Piles

Kwigillingok – 18”Ø Thermo Helix-Piles for K-12 School Addition (2013)

Thermo Helix-Piles

Bethel – Yukon Kuskokwim Aquatic Health and Sefety Center (2013)

Thermoprobes

Thermoprobes are non-structural high-capacity two-phase

thermosyphons that are used to provide passive refrigeration to maintain

or create permafrost. Thermoprobes are used to allow heated structures

to be constructed at-grade on permafrost. Additionally, they are used to

passively refrigerate the soil around buried heat sources - i.e. pipelines,

wells, utilidors, etc. - to preclude thawing and subsequent settlement of

the permafrost. Thermoprobes are also used to create frozen barriers for

hazardous materials, to create impervious frozen dams for water control,and to provide frozen encapsulation of hazardous materials.

Thermoprobes loaded onto flatbed at plant for transport.

Thermoprobes for

tunnel portal

cooling in

Kyrgyz Republic

(2009)

Retrofit Existing Structure (2011)

Frozen Core Dams

Leslie Long Lake Dam, Ekati

Diamond Mine, NWT, Canada

Hybrid thermosyphons for dike cooling, Diavik

Diamond Mine, NWT, Canada

Arctic Bridge Pier Thermosyphons (2014)

Straight thermosyphons inside bridge piers, North Slope, Alaska (2014)

Sloping Evaporator Thermoprobes

Sloping evaporator Thermoprobes are found on the majority of existing

passive subgrade cooling system installations beneath slab on grade

structures. These units utilize a sloped evaporator to insure that the

condensate will flow from the condenser to the lowest portion of the

evaporator. Typically, evaporator slopes are between 10% and 3% with

the median being 5%.

Structures founded on grade over permafrost utilizing Thermoprobes for

subgrade cooling also have two other very important components of

design: subgrade insulation and NFS fill. The typical thermal design

methodology for this type foundation economically balances the three

major components. The insulation reduces the heat load on the subgrade

and limits the thawing of the underlying NFS fill during the summer

season when the Thermoprobes are dormant. The NFS fill contains the

seasonal thaw and provides a heat sink beneath the structure. The

Thermoprobes remove heat from beneath the structure primarily during

the freezing season and refreeze the NFS fill so that it is completely

frozen at the beginning of the thawing season.

Sloping evaporator Thermoprobe in typical subgrade

cooling installation beneath slab on grade structure.

Sloping Evaporator Thermosyphons

Thule, Greenland - Power Plant Subgrade Cooling System (1985)

Sloping Evaporator Thermosyphons

Evaporator Installation (2012) Condenser Installation (2013)

Thule, Greenland – New Tracking Station (Under Construction)

Flat-Loop Thermoprobes

Thermoprobes with flat-loop evaporators utilize

proprietary internal components within the riser to

force the working fluid to travel in one direction

within the evaporator. As the working fluid absorbs

heat, it vaporizes and expands. The expansion helps

to push the working fluid around the loop. The

working fluid moves around the loop in two-phase

flow, increasing in velocity as it proceeds around the

loop. This allows the loop to be placed on a

“relatively” flat plane. The term “relatively” means

that there can be some undulations in the vertical

profile of the loop. Typical designs allow for as

much as 150mm (6 inches) amplitude in the

undulations with no detrimental effects on the system.

The subgrade can just be graded to a near flat

condition and the loops then placed directly on the

graded material. Typically the level of the loops is

approximately 0.5m to 1.0m (1.5 feet to 3 feet) below

the base of the subgrade insulation. Loop lengths of

220m (720 feet) are not uncommon.

Deadhorse – Baker Hughes Facility

(2008/2009)

86m x 102.2m At-Grade Structure Over Insulated Subgrade on Permafrost.

Basic Details:

150mm insulation beneath slab

Thermosyphon evaporators on 1.2m spacing

1.07m NFS fill beneath insulation over tundra

Interior Design Temperature is 21°C

Deadhorse – Baker Hughes Facility

(2008/2009)

Air and Evaporator Temperatures

Deadhorse – NSB Service Area 10 WWWTP

Flat-Loop Evaporator Thermosyphon System for 252’ x 252’ (77m x 77m) At-Grade Building

October 12, 2013

Deadhorse – NSB Service Area 10 WWWTP

Completed Building

Prudhoe Bay – Thermopile Conversions (1981)

Central Compressor Plant – 474 Standard Piles were converted to Thermopiles

Hybrid Thermosyphons

Hybrid thermosyphons are designed so that they can

be cooled actively as well as passively. Active

cooling means some external energy must be

expended to promote cooling and mechanical

refrigeration is typically used. Most any of the

thermosyphons manufactured by AFI can be built as

hybrid units with the addition of an internal heat

exchanger. A hybrid unit does not have to be

actively cooled. The hybrid portion of the design

might be to provide a higher redundancy factor over

the life of the project. A typical application for

hybrid thermosyphons is to accelerate construction

on a project by active freezing. In 1984, hybrid

thermosyphons were first used to actively freeze

Thermopile foundation for a communications site in

Galena, Alaska. Prior to that time, blowing chilled

air across the condensers was the method used for

actively cooling thermosyphons. Thermosyphon

evaporators had also been used as evaporators for

active refrigeration, however, the working fluid had

to be evacuated for refrigeration to occur and then

replaced afterward.

Hybrid Heat Exchanger

Galena – First Hybrid Thermosyphons (1984)

Thermo Helix-Piles were fitted with internal heat exchangers and refrigerated to allow full load 2 weeks after installation


Hybrid flat-loop evaporator type Thermoprobes being refrigerated during building construction to accelerate construction of

a service building for the new Denali Canyon Lodge located just outside the entrance to Denali National Park (2005).


Hybrid Thermo HelixPiles for Wind Tower Foundation, Deering, Alaska (2015)

Oak Ridge National Laboratory – HRE PondHybrid Thermosyphons for Containment (1997)

Created Permafrost to Contain Sr90 and Cs137 for 7 ½ Years

Fairbanks (UAF) – Thompson Drive (2003)Buried Hairpin Thermosyphons

This infrared image shows heat from the condensers of

totally buried Thermoprobes radiating to the cold

ambient air at Thompson Drive in Fairbanks, Alaska.

(Photo courtesy of Doug Goering, UAF)

Thermoprobes with buried condensers are designed to release

the heat picked up from the subgrade through the near surface

soils or embankment. A typical application for these units is in

roadway or airfield sections where heat is released just under

the pavement. The condensers can be coupled to either vertical

or sloping evaporators. The system is designed to provide a net

cooling below the embankment section to preserve the

permafrost. Because the condensers release heat through the

surface, insulation can be used in the design without the icing

effects that are typical of insulated sections. In cold climates,

this system is generally not designed to thaw ice and snow on

the pavement, however, it will cause sublimation that will

loosen the bond between the pavement and the ice. The closer

the condensers are to the surface, the better this system will

work. The standard finned condenser will out-perform a buried

condenser in most cases, however, the standard condensers are

prone to damage and can be inundated in snow, rendering them

inoperative.

Coupled Thermosyphons (2011)

Wellhead Thermosyphons (2014)

“Alpine-Style” thermosyphons with condensers offset 100’ for well bore cooling, North Slope, Alaska (2014)

Projections

Crystal Ball (2015)

• There are new extraction,

transportation and infrastructure

projects in cold regions. To adapt to

climate change, more passive freezing

technology will be used in places it’s not

been used before.

• Likewise, hybrid (passive/active)

freezing systems will be used for

facilities.

• Foundation retrofits to stabilize existing

infrastructure so that it can last another

30 or 40 years.

Thank You!

Thermopile Fence Posts – Gakona HAARP Project (2004)

the long thermopile

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