Other Programs for Ground-Coupled Heat Pump (GCHP) Design/Simulation Design/Simulation

Other programs that focus solely on GCHP system design, especially on Ground Heat Exchanger (GHX) design, have been developed. This study reviewed three GCHP

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simulation tools based on the finite line-source model and cylindrical source model: the Earth Energy Designer (EED) program, GLHEPRO, and GshpCalc. The EED program developed by BLOCON, Lund, Sweden (BLOCON, 2008), , and GLHEPRO developed by International Ground Source Heat Pump Association (IGSHPA), Stillwater,

Oklahoma (IGSHPA, 2012), use the finite line-source model, which is also referred as the Eskilson’s approach (Yang et al., 2010). On the other hand, the GshpCalc program developed by GeoKISS, Northport, AL (GeoKISS, 2013), uses a cylindrical source model.

The EED program originated from the Lund program, which was the PC-program for sizing vertical GHXs developed by Lund University, Sweden. It uses algorithms based on the Eskilson’s approach. The Lund program has a stored data file for pre-calculated g-function values which allow the Lund program to retrieve g-function values rapidly. However, the Lund program was difficult to use due to the number of inputs required and the complexity of input parameters (Yang et al., 2010). As a result, the EED program was developed to be a more user-friendly program version of the Lund program (Hellström and Sanner, 2001).

The GLHEPRO program (Spitler, 2000) was developed primarily to design vertical GHXs used in commercial or institutional buildings, based on the Eskilson’s approach. Yang et al. (2010) described that the GLHEPRO program was developed “…

in order to make the ‘Swedish’ methodology developed by Eskilson tractable for American users.”. Spitler claimed the Eskilson’s approach was the best currently available methodology (IGSHPA, 2012c).

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On the other hand, the GshpCalc program, for the design of vertical GCHP systems, implements the method developed by Kavanaugh (1984), which is based on the cylindrical model. The method uses cyclic load pulses (i.e., daily, monthly, and annual) for the heat extraction/addition to the ground. And, the method uses a steady-state heat solution to predict the required borehole length and effective thermal ground resistance corresponding to each pulse (Yang et al., 2010). Kavanaugh and Rafferty claimed the method has been used widely within the United States for design of GCHP systems (Kavanaugh and Rafferty, 1997).

In summary, whole-building energy simulation programs (the DOE-2.1e program, eQUEST, EnergyPlus, TRNSYS, and EnergyGauge) were reviewed in this section. The review determined that none of the five simulation programs satisfied the following features together: 1) detailed system description; 2) editable input files; 3) short simulation run time; and 4) accurate GCHP system simulation capability. A review of the GCHP analysis used in the most popular simulation programs showed that the DOE-2.1e program does not have the capability to simulate the GCHP system but other four simulation programs do. The g-function method is used in eQUEST and EnergyPlus, the DST model is used in TRNSYS, and EnergyGauge uses its own very simplified GCHP algorithm. In addition, three additional programs (EED, GLHEPRO, and GshpCalc) were reviewed that focused solely on GCHP system design based on the Eskilson’s approach (EED and GLHEPRO) and on program that used the cylindrical source model (GshpCalc).

54 2.8. Summary of the Literature Review

A number of energy codes and standards have been adopted to improve the energy performance of residential houses by offering guidance to users such as builders, building official, designers, and energy modelers. This study reviewed the IECC, the IRC, and ASHRAE Standard 90.2-2007 to identify the similarities and/or differences.

The IECC and IRC are the building energy codes that Texas has currently adopted as Texas Building Energy Performance Standards (TBEPS) for all residential buildings.

The prescriptive energy efficiency provisions of the 2009 IRC were adopted as the energy code in Texas for single-family residential construction (three stories or less) and the 2009 IECC is the current state energy code for all other residential that don’t meet the prescriptive requirements of the 2009 IRC, commercial, and industrial construction.

Several residential building certification software tools have been developed to simplify and clarify code compliance, and to estimate a building’s energy performance.

The five code-compliant software tools reviewed in this study were the OptiMiser program, REM/Rate, EnergyGauge, IC3, and REScheck. Only one tool, the IC3 software, can be used as a free, web-based tool that is RESNET-certified.

The IC3 software, developed by the ESL, is code-compliant software that allows users to check the code compliance of proposed single-family residences and multi-family residences according to the TBEPS. The simulation model in IC3 uses the DOE-2.1e simulation program. In order to account for building energy performance more properly, there have been on-going efforts to improve the DOE-2.1e simulation model, including the addition of a residential thermal distribution system (i.e., a duct model) and

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others. However, the current IC3 does not have the ability to simulate the GCHP system.

Therefore, there is a need to develop the ground-coupled heat pump (GCHP) system module in the IC3.

The use of the ground source heat pump (GSHP) system in high performance, energy-efficient buildings is becoming a popular option for building system designers.

Of the GSHP system models reviewed, the GCHP model with a vertical closed-loop ground heat exchanger (GHX) is the most widely used in residential systems (Lund et al., 2004).

Various GCHP models have been developed. All of the GCHP models focused on modeling the GHX loop to calculate GCHP system performance. The GHX models surveyed used either an analytical, numerical, or a hybrid modeling approach.

Regardless of the approach, the primary purpose of those GHX models is to accurately estimate the hourly return fluid temperature from the GHXs to the heat pump.

This study reviewed vertical closed-loop GHX models, including analytical (i.e., the line-source model and the cylindrical source model), numerical (i.e., the duct ground heat storage system model and others), and hybrid models (i.e., the Eskilson’s g-function model). In general, analytical solutions use simplified models whereas numerical

solutions use detailed calculations. These features can lead analytical solutions to be less accurate when compared to numerical solutions. However, analytical solutions provide faster computational time than numerical solutions. The hybrid solutions take advantages of both analytical and numerical solutions.

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Five whole-building simulation programs (i.e., the DOE-2.1e program, eQUEST, EnergyPlus, TRNSYS, and EnergyGauge) were reviewed in this study. Four of these programs have the capability to simulation GCHP systems; the exception is the DOE-2.1e program. However, none had well-documented GCHP models that could easily model complex building shapes with acceptable run times and modifiable input files.

Therefore, there is a need for a free, web-based, and RESNET-certified, code-compliant software, such as IC3, to have the capability to calculate the GCHP system performance together with the whole-building simulation program using a vertical closed-loop GHX.

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CHAPTER III