Reflective Insulation Research Articles

Thermal Resistance of Air Ducts with Bubblepack Reflective Insulation

A series of measurements to determine overall heat-transfer coeffi cients for air-handling ducts was used to obtain the R-value added to the ducts by bubblepack reflective insulation Heat fluxes determined from steady-state energy balances were combined with temperature measurements to determine U-values and R-values. The five configurations tested were no insulation, reflective insulation ap plied directly to the inside or outside wall of the duct, and exterior reflective insula tion installed with two types of spacers to form 0.75 inch air gaps. The R-values added to the initial value of 1.56 ft2·h·°F/Btu varied from 0.82 to 4.09 ft2·h·°F/Btu for the configurations tested.

Effect of Environmental Contaminants from Agricultural Buildings on Emittance of Reflective Surface Insulations

Three reflective aluminum-faced insulations were exposed to four agricultural building environments for 14 months in both wall and ceiling configura tions. The insulations were foil-faced bubble pack (FFBP), uncoated foil-faced poly isocyanurate (PIR), and white coated foil-faced PIR. The buildings were designed for swine finishing, poultry layers, feed processing, and machine storage. Samples of FFBP were also exposed in sample stud wall cavities for 11 months. Surface emit tances were measured over time and most of the exposed reflective surface insulations had a sigmficantly higher emittance after 14 months. Wall cavity exposed FFBP did not experience a significant increase in emittance.

Two-Dimensional Heat Transfer Effects on Vacuum and Reflective Insulations

Heat transfer in directions normal to the imposed temperature gradi ent can have an important influence on the overall performance of insulation systems. An analysis of two-dimensional heat transfer in vacuum insulations and reflective in sulations is presented.

Thermal Performance of Agricultural Building Sections with Reflective Surface Insulation

Thermal resistance values (R-values) were estimated for typical agricultural building sections with reflective surface insulations. The estimates were based on ASHRAE calculation methods (ASHRAE, 1989) and recently published information on reflective surface insulations. These estimates also include the reduction in R-value due to dust collection on the reflective surfaces of the insulation.

Effective thermal conductivity of reflective multiplate thermal insulation

The roof slab of the sodium-cooled fast breeder reactor must be thermally insulated to reduce the heat flux reaching it from the hot sodium pool of the reactor. The environment, consisting of argon gas laden with sodium vapor and aerosols, does not permit the use of conventional thermal insulation for the roof slab, which comes into contact with the reactor cover gas. This necessitates the development of special types of thermal insulation that can serve inside the reactor cover gas atmosphere. The reflective multiplate thermal insulation concept has been chosen for detailed study. This paper describes initially a theoretical model and its prediction of effective thermal conductivity as a function of various parameters and then gives detailed description of the experimental setup to determine the effective thermal conductivity of multiplate thermal insulation. Some experimental results of the determination of the effective thermal conductivity as a function of temperature and number of plates of insulation are presented.

Heat Transfer Analysis of Fiberglass Insulations With and Without Foil Radiant Barriers

This work compares analytical results with experimental data for the total heat transfer through typical fiberglass insulations subjected to a time-varying incident radiative heat flux and with time-varying temperature boundaries. The insulation configurations and thermal environments analyzed are consistent with conditions that exist in residential attics during the summer months. A heat transfer analysis was performed, which treats the problem as one of coupled transient conduction and radiative heat transfer in a fully participating medium (absorbing, emitting, and scattering). Computations were performed for both isotropic and anisotropic phase functions and for both gray and nongray radiative transport. Temperature data recorded for summer-time conditions in FL and MS were used to describe the boundary conditions for the heat transfer analysis. The effect of foil radiant barriers on the overall heat transfer through the insulation also was studied. Calculations are presented that compare the foil radiant barrier and no-foil cases; the foil barrier is shown to reduce the total heat transfer by about 42%. All computations used the discrete ordinates solution method to solve the radiative transport equation and a control-volume based finite difference technique to solve the energy equation.

Thermal Resistance of Wall Cavities Containing Reflective Insulation

The numerically computed heat transfer coefficients are less than the measured values and do not reduce the disagreement between predicted and measured R-values for reflective assemblies. The Nu calculated in this project were 9 to 27 percent less than those published previously for aspect ratios from 4 to 100, and include aspect ratios greater than previously considered. The introduction of a vertical temperature gradient on the cavity reduces the difference between predicted and measured heat transfer coefficients. The calculated Nu increased when a temperature gradient is specified for the vertical boundaries and this results in a decrease in the calculated R-value.

Effect of Condensation on Emittance of Reflective Insulation

This paper reports a measured relationship between the surface density of droplet condensation on a reflective aluminum surface and the emittance to infra-red radiation. The data can be used to predict the effect of condensation on the thermal resistance of foil lined building cavities. The effect is quite strong with 1 g/m2 of condensate increasing the emittance of bright aluminium from .06 to 0.25. This would reduce the thermal resistance of a 100 mm deep reflec tive cavity with downward heat flow from 1.4 to 0.6 m2 K/W.

FIELD TEST OF REFLECTIVE INSULATION

Summary A field test has demonstrated that reflective foil insulation in the roof of a house having cavity brick walls can significantly reduce inside temperatures. A Strathfield (Sydney) home was tested during the summers of 1968 and 1969. with temperature readings being taken at various locations. Reflective foil insulation was installed for the second summer. From the large number of readings taken over an extended period, two almost identical hot days were selected. and inside temperatures, temperature increases, etc., were compared. The tests showed that if blue coated reflective foil insulation is used as sarking between rafters and tile battens. inside temperatures on a day of century heat can be expected to be 15°F cooler than outside. The house with insulation was also nearly five degrees cooler than could be expected it' no insulation were used.