A review of available technologies for seasonal thermal energy storage

Review of analytical models for heat transfer by vertical ground heat exchangers (GHEs): A perspective of time and space scales

A computationally efficient numerical model for heat transfer simulation of deep borehole heat exchangers

In this paper, a compact overview of the state-of-the-art in modeling of ground-coupled heat pump (GCHP) systems and an in-depth review of their optimal control along with the associated research challenges are given. The main focus is on optimal control but since design of an optimal controller may require a model, a relatively short literature review of modeling approaches is also discussed. Adopting the adage “a picture is worth a thousand words”, we tried to include a minimal number of representative schematics and result figures for some of the reviewed studies for clarity and a better understanding of the presented material. In addition to the literature review, we included our comments, points of view, alternative solutions and some potential future directions. This review paper is useful both for engineers and researchers involved in modeling and optimal control of GCHP systems. The second part of the paper, “Ground-Coupled Heat Pumps: Part 2 – Literature Review and Research Challenges in Optimal Design”, focuses on the literature review on optimal design and the associated design challenges for GCHP systems.

Ground-coupled heat pumps: Part 1 – Literature review and research challenges in modeling and optimal control

Simulation of thermal performance of horizontal slinky-loop heat exchangers for ground source heat pumps

This work presents a validation of two common methods for designing vertical ground heat exchangers. Both a simulation-based design tool and the ASHRAE handbook design equation are used to find design lengths for four different real systems, using actual experimental data, including building loads as well as physical parameters as inputs. The measured minimum and maximum ground heat exchanger exiting fluid temperatures were used as the design constraint. The simulation-based design tool predicted the borehole length to within 6% in all cases, while the ASHRAE handbook design equation yielded systems with errors from –21% to 167%. Most of this error can be explained by the way loads are represented in the ASHRAE handbook equation, with differences in the borehole thermal resistance also playing a smaller part. The ASHRAE handbook equation relies on a very simple load representation; although this allows it to be used as a simple hand calculation, it also precludes it achieving acceptable accuracy. It does ...

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Validation of vertical ground heat exchanger design methodologies

A computationally efficient hybrid time step methodology for simulation of ground heat exchangers

A new type of ground heat exchanger that utilizes the excavation often made for basements or foundations has been proposed as an alternative to conventional ground heat exchangers. This article describes a numerical model that can be used to size these foundation heat exchanger (FHX) systems. The numerical model is a two-dimensional finite-volume model that considers a wide variety of factors, such as soil freezing and evapotranspiration. The FHX numerical model is validated with one year of experimental data collected at an experimental house located near Oak Ridge, Tennessee. The model shows good agreement with the experimental data—heat pump entering fluid temperatures typically within 1°C (1.8°F)—with minor discrepancies due to approximations, such as constant moisture content throughout the year, uniform evapotranspiration over the seasons, and lack of ground shading in the model.

Foundation heat exchangers for residential ground source heat pump systems—Numerical modeling and experimental validation

1. ABSTRACT Due to their higher efficiency, ground source heat pump (GSHP) systems offer an attractive alternative to conventional systems for residential and commercial heating and cooling applications. However, the higher first cost of GSHP systems has been a significant constraint for wider application of the technology. One way to reduce the first cost is to reduce the imbalance in the ground thermal loads by incorporating a supplemental heat source or sink into the system, which creates a hybrid ground-source heat pump (HGSHP) system. This work presents a new, computationally efficient method for sizing HGSHP systems based on a hybrid time step simulation. This design method utilizes an optimization routine to configure the ground heat exchanger (GHE) length and the size of the supplemental device so that the system meets both the desired maximum and minimum heat pump entering fluid temperature limits as closely as possible. This method is compared to existing methods for a cooling-constrained HGSHP system serving a three-story office building in four U.S locations. The proposed method produces the closest life-cycle cost to a cost-optimized design method in three of four cases, while requiring substantially less computation time. The other methods occasionally, but inconsistently, provide close cost matches.

https://www.hvac.okstate.edu/sites/default/files/pubs/papers/2010/01-Spitler%2C%20J.D.%2C%20and%20Cullin%2C%20J.%202010_WEB.pdf

James R. Cullin

Papers

Validation of vertical ground heat exchanger design methodologies

A computationally efficient hybrid time step methodology for simulation of ground heat exchangers

Foundation heat exchangers for residential ground source heat pump systems—Numerical modeling and experimental validation

Comparison of Simulation-based Design Procedures for Hybrid Ground Source Heat Pump Systems

Improvements in design procedures for ground source and hybrid ground source heat pump systems