What are the different models of the GeoCube?
The GeoCube is offered in three standard configurations that vary based on the depth that the unit can serve. The depth capacity (400 feet, 500feet, 700 feet) is determined by the pump, other hardware, heating elements and electrical system design that are associated with each model. The heating capacity is determined by the amount of power that needs to be injected per foot, per ASHRAE guidelines. The GeoCube is able to inject 15-25 watts/foot of borehole for the model that is selected and the user can select the appropriate power to deliver the heat injection for their specific test borehole.
Can the GeoCube perform T.C. tests in all times of
the year?
The time of year does not have a direct relationship to the T.C. test. The GeoCube is internally insulated so that the circulating liquid is not heated or cooled by changes in ambient temperature. The loopfield lines always should be insulated to prevent the loopfield lines from directly exchanging heat with the air. The GeoCube also may be blanketed if desired although the GeoCube does not require additional insulation.. The data analysis takes into account the heat energy from the heating elements and the circulating pump to determine the thermal conductivity results. In other words, the thermal conductivity data will accurately reflect the borehole and surrounding soil characteristics regardless of the time of year. In colder climates, an appropriate antifreeze solution may be necessary to prevent freezing of the liquids when the test is being setup or when the test is being taken down.
What test standards are used by the GeoCube to
determine T.C. Data?
In North America, ASHRAE guidelines are the accepted standard for determining the thermal conductivity of a borehole. The data analysis that is used by the included software G is based on the line-source analysis methodology described in
ASHRAE 111-8TRP and specified in the ASHRAE 2007 HVAC Applications Handbook - Chapter 32.12-32.13 The software produces a report that provides working definitions and explanations of how the data are analyzed and used. The standard test accurately (and optionally) will estimate the undisturbed loopfield temperature and will calculate the soil thermal conductivity of the loopfield. Tests typically are a minimum of 40 hours in duration., During the initial 12 or so hours of the test, heat from the GeoCube fully saturates the borehole. During the remainder of the test, heat radiates out from the borehole and provides data for thermal conductivity determination using the previously mentioned standard line-source method. Precision Geothermal has published a paper titled,
"What to Look for in Thermal Response / Conductivity
Test Services". This document describes procedures,
standards and recommendations for performing Thermal
Conductivity (TC) testing.
Do I have to
use special grout in the test borehole to get
good T.C. data?
An experienced driller understands the importance of grouting boreholes and it is a requirement of IGSPHA and NGWA. This answer is intended to respond to the need for a "special" grout when doing T.C. testing.
The borehole may be any size that is appropriate to drill and the borehole should be grouted with material that is suitable for the project. A typical TC test will try to simulate exactly what will be used for the future loopfield so that the test boring can be incorporated into the production system. The thermal conductivity testing results are not affected by the borehole, since the T.C. result is a measure of the thermal characteristics of the earth surrounding the loopfield and not the borehole itself. The testing analysis will disregard the first 12 hours of data as the borehole and loop piping heats up and thermally saturates. For the purpose of the testing, a borehole does need some kind of grout because air gaps between the pipe and borehole will effectively insulate the pipe from the borehole, which will likely devastate loopfield performance. The T.C. test does not test the borehole, the loop pipe, the grout or the type of fluid that is used. A T.C. test is testing the thermal characteristics of the earth that surrounds the borehole. The type of grout does however effect the "borehole thermal resistance" which also is calculated from the test and should be representative of the production loopfield design for the project that is being planned. Good commercial loopfield design software can utilize both the Thermal Conductivity data AND the Borehole Thermal Resistance data from a test loopfield.
What is a data logger??
A data logger is an electronic instrument that records measurements such as temperature, voltage, pressure and events over time. A Typically a data logger is a small, battery-powered device that is equipped with a microprocessor, data storage capacity and sensors. Most data loggers utilize purpose specific software on a PC to start the logger and view the collected data. Data loggers are used in remote areas or anywhere you need to record measurements using a compact, convenient, self contained and battery powered unit.. They are ideal for field studies, monitoring, testing and general research. The data logger in the GeoCube eliminates the need for a full PC system to be dedicated to the test site and allows data to be shuttled between the test and the user's computer by means of a physical shuttle or through GSM telemetry to an internet data site.
The GeoCube data logger records data for entering and return fluid temperatures, voltage, current, flow rate, date and time. The GeoCube comes with a custom software module from GAIA Geothermal that can be loaded on any PC. This module can read the data logger data and present a time analyzed output which documents the test conditions and outputs with test conclusions for use in geothermal loopfield designs. This data also can be analyzed using a text or spreadsheet program if so desired.
I want
to use shore power instead of renting a generator. Why is
that not recommended?
A successful T.C. test requires reliable, consistent power in
order to maintain data validity. "Shore Power" or
commercial power can have variations of up to 20% in normal
operations. Utilities deal with wide ranges of load
conditions and it is not uncommon to see brownouts in the system
or power surges that will invalidate the data for your entire
test. Below find a report dialog from using an "unstable"
power source that has exceeded the +/- 10% threshold that was
set for the test: The graph clearly shows the instability
and the resulting "wobbles" in the temperature.
Results like this are clearly unacceptable. We recommend
using a diesel powered generator that is 2X the load for most
optimal results.
Based on the standards from ASHRAE and IGSHPA, a proper test must maintain a maximum +/- 1.5% power input standard deviation from the average power level. Peak variations must be kept at less than 10% of the average power level.
Does it make any difference if I use plain
water instead of an anti-freeze solution?
The GeoCube can use plain water or an antifreeze solution. The T.C. test results will not be affected if the environment calls for a solution that involves propylene glycol or ethanol (for example). The GeoCube will maintain adequate flows with antifreeze solutions and the mathematics used to determine the TC value are not affected by whether the test is run with water or antifreeze. If the testing is being conducted in cold climate conditions, steps should be taken to insure that freezing does not occur in the exposed loopfield piping or the GeoCube. Normal ground temperatures will protect the standing liquid below the surface. Exposed portions of the pipe should be protected with antifreeze or kept dry before and after the testing is completed. The GeoCube should be drained completely between uses.
Why do I have to run
tests for 40 hours? Can't I perform shorter tests that are
just as accurate?
 Standards for thermal analysis of the earth surrounding a borehole have been developed over the years by studies which have been used by organizations like ASRAE and IGSPHA. These empirical tests have been established to provide a meaningful and consistent test that does not attempt to extrapolate data beyond the norms that have been established.
A typical borehole and surrounding formation takes 12-20 hours
to saturate at the rate of heat injection that is used.
The TC value is based on finding a "steady state" slope of the
temperature curve once saturation is achieved. Testing equipment such as the GeoCube and testing organizations that provide T.C. tests as a third party service are not creating the science but are following the accepted standards. While shorter tests will provide data, the results may not be acceptable by an engineering firm that must use the data to do a project design In addition to the duration of the test, the test also must be continuous and may not be stopped and restarted without waiting for a minimum of (5) days for the earth to rreturn to its native, undisturbed state. Test operators are well advised to take precautions to make sure that generators have sufficient fuel to last the entire duration of the test since any interruption likely will require the test be completely re-run.
It gets very cold at night and hot during the
day. Don't I have to keep the GeoCube in an insulated trailer?
The GeoCube is internally insulated with a minimum of 2" of Formular® 250 insulation to shield the sensors and piping from outside temperature swings. The exposed loopfield piping is a larger source of temperature variation than the GeoCube. Exposed pipes should be fully insulated and only the necessary amount of pipe to make the connections should be used. The photos below show GeoCubes in operation with insulation applied. If available, thermal blankets may be used to cover the pipes for maximum protection. Insulation of the connecting pipes in ALL climates and seasons is the correct way to run conductivity/response tests. Although not required, some users prefer to protect the unit from direct solar radiation during the test.
Can I see examples of different versions of the GeoCube
The GeoCube is offered in three standard configurations that vary based on the depth that unit can serve. The depth capacity (400 feet, 500feet, 700 feet) is determined by the pump and heating elements that are associated with the model. These units appear the same from the outside. The heating capacity is determined by the amount of power that needs to be injected per foot, per ASHRAE guidelines. The GeoCube is able to inject 15-25 watts/foot of borehole for the model that is selected and the user can select the appropriate power to deliver the heat injection for their specific test borehole. The pumps, electrical system and thermal elements are sized appropriately for the 400 foot, 500 foot, 700 foot GeoCubes. A high capacity GeoCube may be used for shallower boreholes without any problem by selecting the appropriate power levels with the standard controls available in the unit.
While all three units have the same external configuration, customization options, including multiple finishes, connections and multiple data logging options, are available. All units share the same reliability levels for the basic functionality. Units with the Advanced Data logger feature offer extra protection for the electronic logging unit due to the waterproof internal housing for the electronics. Units that have the anodized chassis will retain their "new" appearance for a greater percentage of their lifetime and can stand up to everyday wear and tear to a greater extent than the polished finish of the standard unit. While the anodized chassis adds extra production to the unit, the performance is 100% the same as the standard finish. The anodized unit (below right) also shows the optional "H" valve assembly, which facilitates reliable start up and tear down by allowing the loops to be fully purged and filled. By reliably eliminating air from the test loop, you protect the integrity of the test and prevent accidental damage to heating elements which could be prematurely damaged by dry operation.
Redundant data sensors are available for every configuration and provide peace of mind during the critical hours of test operation. All redundant measurement channels operate independently and provide a failsafe for malfunction of any individual data logger channel or unit sensor. This is an internal feature of the GeoCube and is not visible from the outside of the unit but is evident in the additional data points that are collected during the testing.
The Advanced Data Logger option with GSM telemetry requires no external antenna and is fully protected inside of the locked housing. This option provides for real-time remote reading of data from your GeoCube during any test conducted in a location with cellular coverage. All loggers collect and store the full data set even if the coverage of the GSM is weak or spotty at the project site.
GeoCube - Standard Finish |
GeoCube - Anodized Finish |
Why are there different types of data loggers for the GeoCube?
The loggers in all GeoCubes collect digital data that are stored in flash memory inside of the logger. The standard data logger can store multiple tests and can stay in the unit for extended periods of time for later retrieval. Since a T.C. test involves routine handling in outside environments and with exposure to liquids, some customers prefer to minimize accidental exposures to moisture. The Advanced Data Logger offers a waterproof housing internal to the GeoCube as well as the ability to provide optional telemetry for projects that require real-time readouts of data points. The GSM option for the Advanced Data Logger provides for communication via commercial cellular coverage and data are received by an FTP site for viewing over the web. There are no exposed antennas visible on the GeoCube, which protects the logger unit and eliminates unnecessary attention when the unit is unattended in the field. The subscription service that comes with the GSM logger option provides for secure, backed up data storage that can be read from anywhere in the world.
Advanced Datalogger -
Waterproof Internal Housing |
Standard Datalogger
(removeable) |
What is the Accuracy of the GeoCube?
The GeoCube utilizes a data logger system with sensors that have been tested and approved for the particular logger included with the GeoCube. Depending on the model of the sensor, there will be several types of sensors that are applied in different locations within the unit. Units that employ redundant temperature sensor sets will have multiple sensors that measure loop temperature in multiple locations within the GeoCube. Our sensors exceed the requirements of ASHRAE and IGSHPA standards.
-
Voltage: Accuracy ±1%
from 10% to 130% of rated voltage (AC Potential transformer)
-
Current Sensing:
Linearity accuracy ± 1% from 10% to 130% of rated current
(AC Current Transformer)
-
Flow Meter: Accuracy -
AWWA spec, 97 - 103% (Pulse Output Flow meter)
-
Temperature Sensor: <
+/-0.2 deg C in 0 to 50 deg C operating range - 12 bit smart
sensor
Note: The primary and
redundant sensors will NOT read the exact same temperatures due
to their mounting locations and initial calibration from the
factory. They will exactly track temperature variations to
provide a fallback in the event of sensor failure or momentary
bubble in the fluid path.
What can go wrong with a GeoCube?
Quite simply, the most likely thing to go wrong with the GeoCube itself is damage
caused by improper operation. The internal components have been selected for accuracy,
reliability and rugged use in the field. The mechanical parts most vulnerable to
user-induced damage are the pump and the heating elements.
Introducing mud and
gravel into a loop will kill most pumps. GeoCubes shipped after November 1, 2011 contain
a stainless mesh filter in the standpipe assembly to catch the unknown sediment or gravel
that have inadvertantly found their way into the loop pipe. Units with the 4" standpipe
that were purchased prior to November 2011 can use the new filter, which is available as
a replacement accessory.
Accidently restricting flows to the
heaters inside the GeoCube will cause the high-temp cutout circuits to trip or
worse, cause the heating elements to burn themselves out. One of the most common
mistakes is to burn out a heating element by not purging the loopfield and cube
properly prior to turning on the heating elements. Precision Geothermal offers
an optional "H" valve assembly for making it easy to properly purge a system prior
to starting the test but even this requires that the operator take proper steps to
eliminate air from the system.
Just like running an engine without oil - running the GeoCube heaters without properly
proper purging is a near certain guarantee of damage or shortened life. Your GeoCube
is an investment worthy of proper care and operator training. With proper operation,
your GeoCube will provide years of reliable service.
The driller introduced mud and sand into the test loop.
How can I protect the GeoCube?
 Precision
Geothermal has repaired a number of units that were returned
after failure due to gravel and sand clogging the pump and
causing damage to the pump and the heaters. The current
product design now incorporates a built in, cleanable, stainless
steel filter assembly. This filter will catch sand and
gravel before it can get into
the GeoCube and will help prevent damage from sediment that was
introduced by the driller or through vandalism. Older
units will also accept the new filter system and may be field
upgraded by ordering a replacement filter assembly. Our
filter is rated nominal 140 micron and will stop particulates .0055" and larger while allowing
for full rated pump flows.
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