Published in February 2008, the Defense Science Board (DSB) report More Fight – Less Fuel identified what has been acknowledged as a critical vulnerability to our national security: Military installations in the United States are reliant on local power grids for day-to-day operations. These grids have been described as brittle, and are extremely vulnerable to everything from natural events to sabotage. Therefore, DSB recommended “islanding” all military installations, or taking them off the local grid and using renewable power supplies to eliminate vulnerability. If protected by islanding, a military installation will no longer be a victim in need of assistance during an event, but can be part of the response.
When considering potential renewable energy sources, an installation must determine the proper solution relative to its location. Wind, solar, hydro, biomass, etc., are all viable in one location or another. However, low-temperature ground-source heat pumps (GSHP), which can reduce an installation’s power requirements to levels that make other renewable sources feasible by eliminating HVAC power loads, can be used virtually anywhere in the country.
GSHP technology is currently being demonstrated at a small reserve base in Londonderry, N.H. Responding to recent presidential executive orders, policy directives and U.S. Army energy conservation guidance, the Department of Public Works (DPW) Division of the 99th Regional Support Command (East) (RSC) recently completed an energy use survey of all operational facilities to determine the 99th RSC Area Maintenance Support Activity’s energy consumption profile. The energy budget per square foot conditions proved to be one of the top three energy consumers in the 99th RSC.
The key to a successful, cost-effective low-temperature GSHP system is the front-end protocol of testing and analysis that determines how many wells are actually needed and their energy budget, including where and how deep to drill. This regional protocol is called Pathfinder Low-Temperature GSHP and is intended to prevent unnecessary expense, time and resources, such as specifying too many or too few wells sited in suboptimal locations.
GSHP Viability Assessment
The 99th USAR DPW is embarking on an aggressive implementation of alternative renewable energy projects, including the application of low-temperature GSHP heating and cooling systems. Considering the current paucity of implementation guidance or standards, we offer the GSHP viability field protocol.
This protocol outlines the initial testing for GSHP viability. The exploratory test well reveals the actual heat/energy dynamic of the site’s geologic environs and is of paramount design importance. The following initial well development design concerns include:
- site identification;
- boring identification;
- soil composition and texture, using the Unified Soil Classification System;
- soil color, using Munsell soil color chart;
- lithology of cuttings;
- rock cutting color using, Munsell rock color chart;
- lithologic boundaries;
- loss of circulation, lack of cuttings returns, absence of cutting noise, bit drops and changes in circulation fluid color;
- increases in return of water or other fluids;
- relative hardness or indurations;
- degree of weathering;
- drill rig monitoring;
- changes in drilling fluid color, consistency and driller observations;
- daily post-drilling static water level (feet below grade);
- surveyed location and elevation (well pad and inner casing);
- volume of drilling fluids lost to the formation;
- volume of casing grout estimate and volume of grout used; and
- length of casing installed.
Following construction of the testing well, viability testing protocol requires that the architect/engineer:
- measure water levels, estimate volume and rate of fluids removed;
- remove sediment from the bottom of the well;
- remove stagnant water and other materials from within the open borehole;
- establish a good hydraulic connection with all transmissive parts of the formation; and
- estimate yield and pump capacity for follow-on draw-down test.
Due to the potentially large variability of the bedrock hydrogeology, the architect-engineer should have on hand a variety of equipment to accomplish the above goals. At least as much water as was introduced during drilling should be removed from the well, with the emphasis on removing rock flower from any transmissive fractures and the bottom reach of the well. Drawdown and field water quality parameters should be monitored until the estimated water lost during drilling has been removed, using the U.S. Geological Survey guidelines where practicable. Development should continue until pH, temperature, conductance and turbidity are stable. Stability of these parameters should be less than 0.2 change in pH units, ± 0.5°C change, less than 10 percent change for specific conductance, and turbidity within plus or minus 15 percent between two consecutive readings. Final development water quality data should be compared to drilling fluid values to verify removal of the drilling fluids and associated impacts from casing grout.
At the conclusion of well development, the architect-engineer should then collect a development water sample for field and laboratory analysis. Results should be compared to those measured in the drilling fluid to verify removal of the drilling fluids. Results should also be tabulated and discussed in field viability report.
Drawdown Test. The architect-engineer should evaluate the hydraulic performance of the pathfinder test well while monitoring changes in water chemistry. Hydraulic testing should consist of step drawdown and constant rate discharge tests, using drilling and well-development data to size pump capacity with the appropriate aquifer gallons-per-minute performance curve.
Step-Drawdown Testing. A step-drawdown test must be performed to assess specific capacity. The architect-engineer should determine pumping rates, pump capacity and pump placement based on drilling observation and optional borehole geophysics data. The test is to be run with a high flow rate first to remove water in well bore storage quickly, and therefore shorten the overall duration of the test.
The results will be used in the field to establish target pumping rates for constant rate discharge tests, assess potentially significant well loss and grossly estimate hydraulic parameters such as transmissivity and storage. The step-drawdown test is not expected to stress the aquifer over a long enough period to estimate hydraulic parameters such as transmissivity.
Constant-Rate Discharge Test. The constant-rate discharge test, optimized based upon the step-drawdown test field results, will stress the aquifer over a 24-hour time period. The 24-hour constant-rate discharge test provides more accurate gross estimates of hydraulic parameters than the step test.
Hydraulic Testing Procedures. A transducer should be placed in the well to monitor ambient water levels for at least 48 hours before testing commences. A submersible pump with a capacity based on the well development data will be used. Water levels during pumping should be monitored using the well’s transducer, backed up by manual measurements. Flow discharge should be monitored using an electronic (induction, ultrasonic, or in line impeller) flow meter and data logger. Field water quality also should be monitored and logged using a flow-through cell. Recovery should be monitored and considered complete when the water level recovers to 95 percent of its original pre-test level.
At the start, middle and end of the steady-state testing, water samples should be collected for field and fixed laboratory analyses. One sample suite should be submitted for the new drinking water supply well tests required by the state, or Federal Housing Authority where state guidance is not available. This will establish the potential for potable water supply, as warranted. Field water quality data should be plotted with drawdown data to assess general chemistry changes with time.
Thermal Property Assessment and Evaluation
The architect-engineer should execute a bedrock formation thermal conductivity testing program to generate necessary input parameters for determining feasibility and to collect design information for implementing GSHPs. The architect-engineer should use site data and applicable bedrock methods and equipment outlined in American Society of Heating, Refrigeration, and Air Conditioning Engineers 90376 and 1118-TRP. Recent advances in equipment, procedures and modeling in bedrock should be evaluated and incorporated based upon site conditions and data collected during drilling, drawdown testing and geophysical logging. Estimate thermal diffusivity and discuss the limits of this estimate. Evaluate borehole thermal resistance.
The architect-engineer should install the necessary electrical and plumbing equipment to support a multi-day thermal property evaluation using International Ground Source Heat Pump Association-accredited installer, your state of licensed pump installer and plumber and other disciplines as needed. The installed equipment should support a full-scale application should the test data and evaluation support going forward.
A successful test program is expected to provide a design basis for a low-temperature GSHP that will lead to a dramatic reduction in operational costs and significant environmental benefits. While there have already been a number of successful Department of Defense GSHP projects, this pathfinder protocol effort for the Army Reserve can serve as a model for future garrisons’ GSHP viability.
GSHP systems are a proven technology that provide a highly cost-effective and efficient renewable energy resource; for every unit of energy used to recover heat from the ground, approximately four units of recovered energy is made available to heat or cool. Through its geothermal well test program, the 99th RSC (East) expects to show that boilers, chillers and smoke stacks are no longer a cost-effective or desirable method of energy production, and no longer provide an assured energy posture for the Army Reserve.