Phillip W Childs

Thermal behavior of mixtures of perlite and phase change material in a simulated climate

Carefully controlled and well documented experiments have been done for two candidate configurations to control the heat load on a conditioned space. The 2:1 PCM/perlite mixture and the 6:1 PCM/perlite mixture, both on a weight basis, accomplished thermal control. The 2:1 system seemed to have enough PCM to be effective and involve a much larger fraction of its PCM in diurnal freezing and melting than the 6:1 system. It is a good starting point for engineering design of an optimum thermal control system. The results from the 2:1 system were reproduced with the computer program HEATING to prove that we know the relevant mechanisms and thermophysical properties of the PCM used in the system. Even without a model for the supersaturation and hysteresis that this material exhibited, HEATING reproduced the heat fluxes to the conditioned space in the experiments accurately enough to mirror the good thermal control performance of the system. The modified sensible heat capacity that was used in HEATING is a handy way to account for phase change effects and could be used in a subroutine to compute hourly phase change effects for whole building models like DOE-2. The experiments were done with PCM/perlite mixtures sealed in small methylmethacrylate boxes and covered top and bottom by XPS. The boxes allowed precise placement of the instrumentation used to follow the phase change effects. The XPS gave high R-value per unit thickness. A more practical prototype configuration such as PCM/perlite hermetically sealed in plastic pouches between layers of batts or blown-in insulation should be tested over a larger cross section. A good candidate is the whole attic cavity of the manufactured home test section used in the present work. Use of a PCM that does not exhibit supersaturation and hysteresis would make interpretation of the results easier. If the results of the larger scale test areas are as encouraging as the test cell results, a whole house model with a phase change algorithm should be constructed to optimize the configuration for the climate in which it will perform.

Field Testing of Low-Cost Bio-Based Phase Change Material

A test wall built with phase change material (PCM)-enhanced loose-fill cavity insulation was monitored for a period of about a year in the warm-humid climate of Charleston, South Carolina. The test wall was divided into various sections, one of which contained only loose-fill insulation and served as a control for comparing and evaluating the wall sections with the PCM-enhanced insulation. This report summarizes the findings of the field test.

An Experimental and Analytical Evaluation of Wall And Window Retrofit Configurations: Supporting the Residential Retrofit Best Practices Guide

A Retrofit Best Practices Guide was developed to encourage homeowners to consider energy conservation issues whenever they modify their siding or windows. In support of this guide, an experimental program was implemented to measure the performance of a number of possible wall siding and window retrofit configurations. Both thermal and air-leakage measurements were made for a 2.4 x 2.4 m (8 x 8 ft) wall section with and without a 0.9 x 1.2 m (3 x 4 ft) window. The windows tested were previously well-characterized at a dedicated window test facility. A computer model was also used to provide information for the Best Practices Guide. The experimental data for walls and windows were used in conjunction with this model to estimate the total annual energy savings for several typical houses in a number of different locations.

A comparison of two techniques for monitoring the field thermal performance of roof systems

Two independent techniques, one intrusive and one non-intrusive, for monitoring the thermal performance of in-situ roof systems (roofing materials) are compared. The intrusive technique requires thermocouples on inside and outside surfaces of the roof system and a heat flux transducer (HFT) embedded in the system. The non-intrusive procedure has the same thermocouple placement and a series of HFTs on the inside surface of the deck. The crucial difference in the methods is in the HFT placement and the technique for HFT calibration. Results of a one-year field study using both methods on the same roof assembly are described. The roof assembly is a built-up roof with molded expanded polystyrene (EPS) insulation above a metal deck. 13 refs., 10 figs., 1 tab.

An Apparatus for Thermal Performance Measurements of Insulated Roof Systems

The US Department of Energy conducted thermal performance measurements on low-slope roofs with a recently developed field test apparatus at Oak Ridge National Laboratory (ORNL). The apparatus accommodates four 4 ft x 8 ft test specimens and includes the measurement capabilities for specimen temperatures, temperature gradients, heat flows and moisture content. A weather station characterizes outdoor weather conditions. Tests underway include (1) validation of a roof surface temperature model developed to study the effects of wet insulation; (2) measurement of temperature distributions and heat transfer in high R-value roofs; and (3) validation of an analysis of the effectiveness of high reflectance surfaces. Preliminary experimental results are presented and correlations between experiment and modeling are discussed.