Conduction Transfer Function Research Articles

On the reliability of ASHRAE conduction transfer function coefficients of walls

The transfer function method recommended by the ASHRAE can be considered the most modern tool currently available for the thermal analysis of a building. It is particularly well suited for use with a computer as it makes it possible to describe with great accuracy the internal heat gain of walls using a small set of coefficients. The present paper shows how to calculate sets of coefficients diverse from that proposed by Mitalas who first developed the method and on the basis of an unequivocal criterion, to prove the advantages in using them. The authors also investigated some of the paramount mathematical and physical aspects which affect the approximation degree of the ASHRAE method and, with reference to the optimal number of poles and coefficients, they tried to offer some certainties for a more conscious use of it.

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

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.

Multidimensional Transient Conduction Analysis by Generalized Transfer Functions Tables

This work provides a general tool for accurate multidimensional transient analysis by means of polynomial heat conduction transfer functions (CTF) which are valid for the whole class of objects having the same geometric shape. With this aim the governing conduction equations were turned into dimensionless variables, such as the well known Biot number (Bi) and Fourier modulus (Fo), and thereafter handled through a finite-element technique to create the CTF with respect to any arbitrary point of the conductive field. In addition, by selecting the nondimensional time interval (ΔFo) according to the sampling theorem, i.e., as a function of Bi, the CTF were scheduled in the form of one-entry tables. The Bi incremental values were furthermore assessed to provide, for any input function, temperature histories within equal percent deviations, say 10 percent. Since for many purposes a five percent tolerance will usually suffice, the CTF tables can be used without the necessity of interpolating. As an example, generalized CTF tables are presented for the central and one of the corner points of a cube.

Experimental and numerical determination of a new wall-heat-gain function

A new «wall-heat-gain function» is developed, which provides the heat entering a space through a wall under period outdoor conditions and constant indoor air temperature. The proposed function, which is much simpler than the well-known conduction transfer function, contains three coefficients U, w 1 and w 2 characterizing the wall and three parameters T M , T C and T S characterizing the outdoor conditions (temperature and solar radiation). The wall coefficients U, w 1 and w 2 may be determined numerically by the use of the finite difference method or experimentally in the case of existing (built) walls of unknown properties. A related experimental set up has been developed. Ready to use values of the wall coefficients are provided for 15 typical wall constructions. The climatic parameters T M , T C and T S either are available for some locations or may be easily calculated by least-squares fitting to local climatological data. In a modified form of the proposed function the three climatic parameters are reduced to two, which are available from ASHRAE for about 1000 stations around the world. The accuracy of the proposed wall heat gain function is very good for practical applications as proved by comparisons with corresponding finite difference solutions

A Comparison of Two Test Methods for Determining Transfer Function Coefficients for a Wall Using a Calibrated Hot Box

This paper experimentally verifies and compares two dynamic test methods for a calibrated hot box to characterize the transient thermal performance of complex walls. In these methods, a wall specimen is sandwiched between the two conditioning chambers of a calibrated hot box. The exterior surface of the wall specimen is subjected to a time-varying excitation function in air temperature. At the interior surface, the air temperature is maintained steady, and the heat transfer response is measured. Conduction transfer function coefficients that relate the measured heat transfer response to the excitation function are derived. The two dynamic test methods were applied to an insulated hollow concrete block wall that contained significant thermal bridges and lateral heat flows. Empirical transfer function coefficients derived by the test methods predicted with good agreement the heat transfer response of this wall specimen when its exterior surface was subjected to excitation functions that differed markedly from those used to derive the coefficients.

Conduction transfer functions for predicting heat fluxes into various soils

ABSTRACT CONDUCTION transfer functions for predicting heat fluxes into a variety of soils and one greenhouse floor heating system are presented. These functions can be used to simulate surface soil heat fluxes in computer models of greenhouses and other structures. The soil heat flux is computed from a sum of products of past su-face temperatures and the conduction transfer functions, which are based on the governing differential equation for heat conduction. No numerical solution of differential equations is required at simulation time, so large savings in computer time can be attained. Comparison with an analytical solution for homogeneous soil showed that a diurnal heat wave with an amplitude of 325 W/m2 could be predicted with a standard deviation of 5 W/m2.

Nerve-bundle conduction velocity distribution measurement and transfer function analysis

Human peripheral nerves are composed of thousands of individual nerve fibers whose signal conduction velocities vary from 0.2 to 100 m/s. Though good correlation exist between fiber velocity and the physiological function subserved by these fibers, considerable variation is found for specific end organs (20 to 40 m/s for a single muscle). Though clinical neurophysiologists have routinely measured the maximum conduction velocity of peripheral motor nerves for 30 years, it has not been possible to determine the velocity distributions. This report details a model and noninvasive methodology for motor axon conduction latency distribution mesurement. This distribution, proportional to velocity dispersion, possesses a low-pass filter characteristic which agrees with theoretical predictions and may be significant in some sensory and motor functions.