Geothermal heat pumps at Fort Polk: Early results

At Fort Polk, LA an entire city (4,003 military family housing units) is being converted to geothermal heat pumps (GHP) under a performance contract. At the same time other efficiency measures such as compact fluorescent lights (CFLs), low-flow water outlets, and attic insulation are being installed. If these contracts and this technology are to be used widely in US Department of Defense (DoD) facilities and other public buildings, better data from actual projects is the key. Being the first GHP project of this type and size, Fort Polk proved to be very challenging for all concerned. To get from RFP to start of construction took several years. This hard work by others created a once-in-a-lifetime opportunity to address many of the due diligence issues that delayed the Fort Polk project. So that future projects can move faster, an evaluation has been undertaken to address the following barriers: absence of a documented large-scale demonstration of GHP energy, demand, and maintenance savings (a barrier to acceptance by federal customers, performance contractors, and investors); newness of large-scale facility capital renewal procurements at federal facilities under energy savings performance contracts (ESPCs) or traditional appropriations (lack of case studies); and variability in current GHP design tools (increases risks and costs for federal customers, performance contractors, investors and designers). This paper presents early energy and demand savings results based on data collection through January 1996

The evaluation of a 4000-home geothermal heat pump retrofit at Fort Polk, Louisiana: Final Report

This report documents an independent evaluation of an energy retrofit of 4,003 family housing units at Fort Polk, Louisiana, under an energy savings performance contract (ESPC). Replacement of the heating, cooling, and water heating systems in these housing units with geothermal heat pumps (GHPs) anchored the retrofit; low-flow shower heads and compact fluorescent lighting were also installed, as well as attic insulation where needed. Statistically valid findings indicate that the project will save 25.8 million kWh, or 32.5% of the pre-retrofit whole-community electrical consumption, and 100% of the whole-community natural gas previously used for space conditioning and water heating (260,000 therms) in a typical meteorological year. At the end-use level, the GHPs were found to save about 42% of the pre-retrofit electrical consumption for heating, cooling, and water heating in housing units that were all-electric in the pre-retrofit period. This report also demonstrates an improved method of predicting energy savings. Using an engineering model calibrated to pre-retrofit energy use data collected in the field, the method predicted actual energy savings on one of the electric feeders at Fort Polk with a very high degree of accuracy. The accuracy of this model was in turn dependent on data-calibrated models of the geothermal heat pump and ground heat exchanger that are described in this report. In addition this report documents the status of vertical borehole ground heat exchanger (BHEx) design methods at the time this project was designed, and demonstrates methods of using data collected from operating GHP systems to benchmark BHEx design methods against a detailed engineering model calibrated to date. The authors also discuss the ESPC`s structure and implementation and how the experience gained here can contribute to the success of future ESPCs

Low-risk and cost-effective prior savings estimates for large-scale energy conservation projects in housing: Learning from the Fort Polk GHP project

Many opportunities exist for large-scale energy conservation projects in housing. Energy savings performance contracting (ESPC) is now receiving greater attention, as a means to implement such projects. This paper proposes an improved method for prior (to construction) savings estimates for these projects. The proposed approach to prior estimates is verified against data from Fort Polk, LA. In the course of evaluating the ESPC at Fort Polk, the authors have collected energy use data which allowed them to develop calibrated engineering models which accurately predict pre-retrofit energy consumption. They believe that such calibrated models could be used to provide much more accurate estimates of energy savings in retrofit projects. The improved savings estimating approach described here is based on an engineering model calibrated to field-collected data from the pre-retrofit period. A dynamic model of pre-retrofit energy use was developed for all housing and non-housing loads on a complete electrical feeder at Fort Polk. The model included the heat transfer characteristics of the buildings, the pre-retrofit air source heat pump, a hot water consumption model and a profile for electrical use by lights and other appliances. Energy consumption for all 200 apartments was totaled, and by adjusting thermostat setpoints and outdoor air infiltration parameters, the models were matched to field-collected energy consumption data for the entire feeder. The energy conservation measures were then implemented in the calibrated model: the air source heat pumps were replaced by geothermal heat pumps with desuperheaters; hot water loads were reduced to account for the low-flow shower heads; and lighting loads were reduced to account for fixture delamping and replacement with compact fluorescent lights. The analysis of pre- and post-retrofit data indicates that the retrofits have saved 30.3% of pre-retrofit electrical energy consumption on the feeder modeled in this paper

Benchmark for Performance: Geothermal Applications in Lincoln Public Schools

Vertical-bore, geothermal heat pumps (GHPs) have been providing heating and cooling to four new elementary schools located in Lincoln, Nebraska since 1995. According to representatives of the local utility and school district, the systems are providing a comfortable, complaint-free environment with utility costs that are nearly half of that of other schools in the district. Performance data collected from on-site energy management systems and district billing and utility records for all fifty schools in the Lincoln district indicate that only five consume less energy than the best performing GHP school; however these five cool less than 10% of their total floor area, while the GHP schools cool 100% of their floor area. When compared to other new schools (with similar ventilation loads), the GHP schools used approximately 26% less source energy per square foot of floor area. Variations in annual energy performance are evident among the four GHP schools, however, together they still consume less source energy than 70% of all schools in the district. These variations are most likely due to operational differences rather than installed equipment, building orientation, or environmental (bore field) conditions

Methodology for the evaluation of a 4000-home geothermal heat pump retrofit at Fort Polk, Louisiana

The US Army and a private energy service company are developing a comprehensive energy efficiency project to upgrade the family housing at Fort Polk, Louisiana. The project includes converting the space conditioning systems of more than 4,000 housing units to geothermal (or ground-source) heat pumps (GHPs). This interim report describes the methodology of the evaluation associated with this project, including the field monitoring that has been conducted at the base

The Thermal Behaviour of Three Different Auger Pressure Grouted Piles Used as Heat Exchangers

Three auger pressure grouted (APG) test piles were constructed at a site in Richmond, Texas. The piles were each equipped with two U-loops of heat transfer pipes so that they could function as pile heat exchangers. The piles were of two different diameters and used two different grouts, a standard APG grout and a thermally enhanced grout. Thermal response tests, where fluid heated at a constant rate is circulated through the pipe loops, were carried out on the three piles, utilising either single or double loops. The resulting test data can be used to determine the surrounding soil thermal conductivity and the pile thermal resistance, both essential design parameters for ground source heat pump systems using pile heat exchangers. This paper uses parameter estimation techniques to fit empirical temperature response curves to the thermal response test data and compares the results with standard line source interpretation techniques. As expected, the thermal response tests with double loops result in smaller thermal resistances than the same pile when the test was run with a single loop. Back analysis of the pile thermal resistance also allows calculation of the grout thermal properties. The thermally enhanced grout is shown to have inferior thermal properties than the standard APG grout. Together these analyses demonstrate the importance of pile size, grout thermal properties and pipe positions in controlling the thermal behaviour of heat exchanger piles

Seeing Savings from an ESPC Project in Fort Polk's Utility Bills

Federal agencies have implemented many energy efficiency projects over the years with direct funding or alternative financing vehicles such as energy savings performance contracts (ESPCs). While it is generally accepted that these projects save energy and costs, the savings are usually not obvious in the utility bills. This is true for many valid technical reasons, even when savings are verified in other ways to the highest degree of certainty. However, any perceived deficiency in the evidence for savings is problematic when auditors or other observers evaluate the outcome of energy projects and the achievements of energy management programs. This report discusses under what circumstances energy savings should or should not be evident in utility bills. In the special case of a large ESPC project at the Army's Fort Polk, the analysis of utility bills carried out by the authors does unequivocally confirm and quantify savings. The data requirements and methods for arriving at definitive answers through utility bill analysis are demonstrated in our discussion of the Fort Polk project. The following paragraphs address why the government generally should not expect to see savings from ESPC projects in their utility bills. We also review lessons learned and best practices for measurement and verification (M&V) that can assure best value for the government and are more practical, straightforward, and cost-effective than utility bill analysis

A New Method to Determine the Thermal Properties of Soil Formations from In Situ Field Tests

The geothermal or ground-source heat pump (GHP) has been shown to be a very efficient method of providing heating and cooling for buildings. GHPs exchange (reject or extract) heat with the earth by way of circulating water, rather than by use of circulating outdoor air, as with an air-source heat pump. The temperature of water entering a GHP is generally cooler than that of outdoor air when space cooling is required, and warmer than that of outdoor air when space heating is required. Consequently, the temperature lift across a GHP is less than the lift across an air-source heat pump. The lower temperature lift leads to greater efficiency, higher capacity at extreme outdoor air temperatures, and better indoor humidity control. These benefits are achieved, however, at the cost of installing a ground heat exchanger. In general, this cost is proportional to length of the heat exchanger, and for this reason there is an incentive to install the minimum possible length such that design criteria are met. The design of a ground heat exchanger for a GHP system requires, at a minimum, the operating characteristics of the heat pumps, estimates of annual and peak block loads for the building, and information about the properties of the heat exchanger: the size of the U-tubes, the grouting material, etc. The design also requires some knowledge of the thermal properties of the soil, namely thermal conductivity, thermal diffusivity, and undisturbed soil temperature. In the case of a vertical borehole heat exchanger (BHEx) these properties generally vary with depth; therefore, in the design, effective or average thermal properties over the length of the borehole are usually sought. When the cost of doing so can be justified, these properties are measured in an in situ experiment: a test well is drilled to a depth on the same order as the expected depth of the heat pump heat exchangers; a U-tube heat exchanger is inserted and the borehole is grouted according to applicable state and local regulations; water is heated and pumped through the U-tube (using a field generator to power the equipment, or line voltage where available); and the inlet and outlet water temperatures are measured as a function of time. Data on inlet and outlet temperature, power input to the heater and pump, and water flow rate are collected at regular intervals--typically 1 to 15 min--for the duration of the experiment, which may be as long as 60 h. Two common methods for determining soil thermal properties from such measurements are the line source method and the cylinder source method. Both are based on long-term approximate solutions to the classical heat conduction problem of an infinitely long heat source in an infinite homogeneous medium. Although there are some differences in the way the two methods are implemented, the only difference between the two models is whether the heat source is considered to be a line or a cylinder. In both methods, power input to the water loop is assumed to be constant. The simplicity of these methods makes them attractive, but they also have some disadvantages. First of all, because the line source and cylinder source approximations are inaccurate for early time behavior, some of the initial data from the field test must be discarded. The amount of data discarded can affect the property measurement. Also, both methods assume that the heat transfer to the ground loop is constant. In practice, heat input to the loop may vary significantly over the course of a field test due to rough operation of the generator or short-term sags and swells in power line voltage. Presumably, this variation affects the accuracy of the thermal property measurement, but error analysis is rarely performed. This report presents a new method for determining thermal properties from short-term in situ tests using a parameter estimation technique. Because it is based on numerical solutions to the heat conduction equation, the new method is not affected by short-term variations in heat input. Also, since the model is accurate even for short times, there is no need to discard initial data. The parameter estimation technique used to determine the properties is based on statistical principles that provide quantitative estimates of measurement accuracy. The parameter estimation method has now been tested with a laboratory test rig at Oklahoma State University and in field tests at two elementary schools in Lincoln, Nebraska. Using our estimation algorithms, and building on the validation achieved during testing, we have developed a computer program, the Geothermal Properties Measurement (GPM) model, that allows users to determine thermal properties from short-term in situ field tests. This program is currently available free of charge

Determining Price Reasonableness in Federal ESPCs

This document reports the findings and implementation recommendations of the Price Reasonableness Working Group to the Federal ESPC Steering Committee. The working group was formed to address concerns of agencies and oversight organizations related to pricing and fair and reasonable price determination in federal energy savings performance contracts (ESPCs). This report comprises the working group's recommendations and is the proposed draft of a training curriculum on fair and reasonable price determination for users of federal ESPCs. The report includes: (1) A review of federal regulations applicable to determining price reasonableness of federal ESPCs (section 2), (2) Brief descriptions of the techniques described in Federal Acquisition Regulations (FAR) 15.404-1 and their applicability to ESPCs (section 3), and (3) Recommended strategies and procedures for cost-effectively completing price reasonableness determinations (sections 4). Agencies have struggled with fair and reasonable price determinations in their ESPCs primarily because this alternative financing vehicle is relatively new and relatively rare in the federal sector. The methods of determining price reasonableness most familiar to federal contracting officers (price competition based on the government's design and specifications, in particular) are generally not applicable to ESPCs. The regulatory requirements for determining price reasonableness in federal ESPCs have also been misunderstood, as federal procurement professionals who are inexperienced with ESPCs are further confused by multiple directives, including Executive Order 13123, which stresses life-cycle cost-effectiveness. Uncertainty about applicable regulations and inconsistent practice and documentation among agencies have fueled claims that price reasonableness determinations have not been sufficiently rigorous in federal ESPCs or that the prices paid in ESPCs are generally higher than the prices paid for similar goods and services obtained through conventional procurements. While claims of excessive prices are largely unsubstantiated and based on anecdotal evidence, the perception that there is a problem is shared by many in the ESPC community and has been noted by auditors and oversight organizations. The Price Reasonableness Working Group determined that a more formal emphasis on FAR 15.404-1 in the ESPC process could remove much of the doubt about price reasonableness determinations. The working group's recommended consensus policy on price reasonableness stresses the price analysis techniques described in the FAR that are applicable to ESPCs and includes guidance for agencies use of these techniques in determining price reasonableness for their ESPC delivery orders. The recommended policy and guidance, if communicated to federal ESPC stakeholders, can ensure that agencies will comply with the FAR in awarding ESPCs, obtain fair and reasonable prices and best value for the government, and follow procedures that provide auditable documentation of due diligence in price reasonableness determinations

Geothermal Heat Pumps in K-12 Schools -- A Case Study of the Lincoln, Nebraska, Schools

Geothermal heat pumps (GHPs) have been shown to have a number of benefits over other technologies used to heat and cool buildings and provide hot water, combining high levels of occupant comfort with low operating and maintenance costs. Public facilities represent an increasingly important market for GHPs, and schools are a particularly good application, given the large land area that normally surrounds them. Nevertheless, some barriers remain to the increased use of GHPs in institutional and commercial applications. First, because GHPs are perceived as having higher installation costs than other space conditioning technologies, they are sometimes not considered as an option in feasibility studies. When they are considered, it can be difficult to compile the information required to compare them with other technologies. For example, a life cycle cost analysis requires estimates of installation costs and annually recurring energy and maintenance costs. But most cost estimators are unfamiliar with GHP technology, and no published GHP construction cost estimating guide is available. For this reason, estimates of installed costs tend to be very conservative, furthering the perception that GHPs are more costly than other technologies. Because GHP systems are not widely represented in the various softwares used by engineers to predict building energy use, it is also difficult to estimate the annual energy use of a building having GHP systems. Very little published data is available on expected maintenance costs either. Because of this lack of information, developing an accurate estimate of the life cycle cost of a GHP system requires experience and expertise that are not available in all institutions or in all areas of the country. In 1998, Oak Ridge National Laboratory (ORNL) entered into an agreement with the Lincoln, Nebraska, Public School District and Lincoln Electric Service, the local electric utility in the Lincoln area, to study four new, identical elementary schools built in the district that are served by GHPs. ORNL was provided with complete as-built construction plans for the schools and associated equipment, access to original design calculations and cost estimates, extensive equipment operating data [both from the buildings' energy management systems (EMSs) and from utility meters], and access to the school district's complete maintenance record database, not only for the four GHP schools, but for the other schools in the district using conventional space conditioning equipment. Using this information, we were able to reproduce the process used by the Lincoln school district and the consulting engineering firm to select GHPs over other options to provide space conditioning for the four schools. The objective was to determine whether this decision was the correct one, or whether some other technology would have been more cost-effective. An additional objective was to identify all of the factors that make it difficult for building owners and their engineers to consider GHPs in their projects so that ongoing programs can remove these impediments over time