Showing papers by "Jeffrey D. Spitler published in 1999"

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

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

Abstract: 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.

On The Relationship between the Radiant Time Series and Transfer Function Methods for Design Cooling Load Calculations

Abstract: In practice, design cooling load calculations are based on steady periodic inputs, but historically cooling load procedures have not taken advantage of this fact. The generalized response factors, conduction transfer functions and room transfer functions currently used in cooling load methods impose an unnecessary computational burden on the procedure. This paper discusses the steady periodic nature of the cooling load calculation and develops the steady periodic conduction and thermal zone response factors used in the new Radiant Time Series Method (RTSM) that was introduced by Spitler et al. (1997). The periodic response factors used in the RTSM are compared to the aperiodic response factors used in the Transfer Function Method (TFM) described by McQuiston and Spitler (1992). Periodic response factors simplify the computational procedure and provide a means of comparing zone and surface types.

Development of periodic response factors for use with the radiant time series method

Abstract: Harris and McQuiston (1988) developed conduction transfer function (CTF) coefficients corresponding to 41 representative wall assemblies and 42 representative roof assemblies for use with the transfer function method (TFM). They also developed a grouping procedure that allows design engineers to determine the correct representative wall or roof assembly that most closely matches a specific wall or roof assembly. The CTF coefficients and the grouping procedure have been summarized in the ASHRAE Handbook —Fundamentals (1989, 1993, 1997) and the ASHRAE Cooling and Heating Load Calculation Manual, second edition (McQuiston and Spitler 1992). More recently, a new, simplified design cooling load calculation procedure, the radiant time series method (RTSM), has been developed (Spitler et al. 1997). The RTSM uses periodic response factors to model transient conductive heat transfer. While not a true manual load calculation procedure, it is quite feasible to implement the RTSM in a spreadsheet. To be useful in such an environment, it would be desirable to have a pre-calculated set of periodic response factors. Accordingly, a set of periodic response factors has been calculated and is presented in this paper.

Proposals for a Building Loads Diagnostic Test Procedure

Abstract: Design cooling load calculation methods are, by the nature of the processes they seek to model, complex, and they require detailed input data involving many parameters. Diagnosing deficiencies in the calculation method or its computer implementation can be correspondingly difficult. A set of tests are proposed that are designed to exercise the principal features of any implementation of a design cooling load calculation method. Diagnosis of weaknesses of the method, or faults in its implementation, are made by making calculations with test data sets that induce a single type of heat gain or heat transfer by a particular path and comparison with a set of reference results for each test. In the tests proposed here, the ASHRAE heat balance method is used as a reference model. Details of the test input data specification are given along with the heat balance method results so that others can use the same tests. Some examples of how the tests were used in the project “Comparison of Cooling Load Calculation Methods (942-RP)” are also given.