An introduction to heat transfer

The energy performance in buildings is influenced by many factors, such as ambient weather conditions, building structure and characteristics, the operation of sub-level components like lighting and HVAC systems, occupancy and their behavior. This complex situation makes it very difficult to accurately implement the prediction of building energy consumption. This paper reviews recently developed models for solving this problem, which include elaborate and simplified engineering methods, statistical methods and artificial intelligence methods. Previous research work concerning these models and relevant applications are introduced. Based on the analysis of previous work, further prospects are proposed for additional research reference.

A review on the prediction of building energy consumption

Introduction to heat transfer

Optimization Techniques with FORTRAN

Vertical-borehole ground-coupled heat pumps: A review of models and systems

The short-term behavior of ground-coupled heat pump systems is important for design of ground loop heat exchangers, energy analysis of ground source heat pump systems, and design of hybrid ground source systems. This paper describes the development of short time-step temperature response factors for vertical ground loop heat exchangers as used in ground-coupled heat pump systems. The short time-step response factors allow for a direct evaluation of system energy consumption and electrical demand in hourly or shorter time intervals. The development of the temperature response factors is based on an analytically validated, transient two-dimensional implicit finite volume model designed for the simulation of heat transfer over a vertical U-tube ground heat exchanger. The short time-step response factors are implemented as part of a component model for TRNSYS and an example application is provided based on an actual building.

A short time step response factor model for vertical ground loop heat exchangers

The ability to predict both the long-term and short-term behavior of ground loop heat exchangers is critical to the design and energy analysis of ground source heat pump systems. A numerical model for the simulation of transient heat transfer in vertical ground loop heat exchangers is presented. The model is based on a two-dimensional fully implicit finite volume formulation. Numerical grids have been generated for different pipe sizes, shank spacing and borehole sizes using an automated parametric grid generation algorithm. The numerical method and grid generation techniques have been validated against an analytical model. The model has been developed with two main purposes in mind. The first application is used in a parameter estimation technique used to find the borehole thermal properties from short time scale test data. The second application is the calculation of nondimensional temperature response factors for short time scales that can be used in annual energy simulation.

A transient two-dimensional finite volume model for the simulation of vertical U-tube ground heat exchangers

A preliminary study has been made of the effects of groundwater flow on the heat transfer characteristics of vertical closed-loop heat exchangers and the ability of current design and in-situ thermal conductivity measurement techniques to deal with these effects. It is shown that an initial assessment of the significance of groundwater flow can be made by examining the Peclet number of the flow. A finite-element numerical groundwater flow and heat transfer model has been used to simulate the effects of groundwater flow on a single closed-loop heat exchanger in various geologic materials. These simulations show that advection of heat by groundwater flow significantly enhances heat transfer in geologic materials with high hydraulic conductivity, such as sands, gravels, and rocks exhibiting fractures and solution channels. Simulation data were also used to derive effective thermal conductivities with an in-situ thermal conductivity estimation procedure. These data were used to design borehole fields of different depths for a small commercial building. The performance of these borehole field designs was investigated by simulating each borehole field using the pre-calculated building loads over a ten-year period. Results of these simulations, in terms of the minimum and peak loop temperatures, were used to examine the ability ofmore » current design methods to produce workable and efficient designs under a range of groundwater flow conditions.« less

A preliminary assessment of the effects of groundwater flow on closed-loop ground source heat pump systems

When designing ground heat exchangers used with ground source heat pump systems, a critical design property is the thermal conductivity of the ground. Thermal response tests are used to measure the site-specific thermal conductivity and are also used to measure the thermal resistance of a borehole heat exchanger as installed. Thermal response tests are commonly used today for design of multiple borehole ground heat exchangers, where knowledge of the ground thermal properties can help avoid undersizing of ground heat exchangers, leading to poor system performance, and oversizing of ground heat exchangers, leading to overly costly systems. This review covers the development of the mathematical and numerical analysis procedures, development of the hardware and test procedures, and validation of the results. We take a historical perspective, going as far back as Lord Kelvin's treatment of transient heat conduction problems in the 1880s, further development of which allowed analysis of conductivity measurements from transient needle probes by the 1950s. We focus on development of test rigs and test procedures in the 1980s and 1990s and validation of the measurements. More recent developments are covered throughout the review.

Jeffrey D. Spitler

Papers

A short time step response factor model for vertical ground loop heat exchangers

A transient two-dimensional finite volume model for the simulation of vertical U-tube ground heat exchangers

A preliminary assessment of the effects of groundwater flow on closed-loop ground source heat pump systems

Thermal response testing for ground source heat pump systems - An historical review

Reference data sets for vertical borehole ground heat exchanger models and thermal response test analysis