Attic Radiant Barrier Research Articles

Hybrid and Reflective Insulation Assemblies for Buildings

Materials with a low thermal emittance surface have been used for many years to create reflective insulations that reduce the rate of heat flow across building envelopes. Reflective insulation technology is now being combined with other energy conserving technologies to optimize overall thermal performance. The basis for the performance of reflective insulations and radiant barriers will be discussed along with the combination of these materials with cellular plastic or mineral fiber insulations to form hybrid insulation assemblies. Calculations of thermal resistance for enclosed reflective air spaces and current field data from Southeast Asia will be presented. These data show that reductions in heat transfer across the building enclosure can be effectively reduced by the use of enclosed reflective air spaces and attic radiant barriers. Reflective technology increases the overall thermal resistance of the building enclosure when used to insulate poured concrete structures.

Evaluation of the thermal performance of a roof-mounted radiant barrier in residential buildings: Experimental study

The objective of this study is to examine the reduction in heating and cooling loads that may be attributed to the use of attic radiant barrier and to identify environmental parameters that influence this reduction. To this end, an experimental study was conducted in Zachary, Louisiana for 8 months on two houses built in the same manner and instrumented with thermocouples to measure the temperature in each hour and each layer of the roof. Results showed that an attic radiant barrier can reduce energy loads from 8% to 25% depending on the climatic conditions. Among the evaluated climatic parameters, ambient air temperature had the greatest effect on the ceiling heat flux.

Development and validation of a simple estimating tool to predict heating and cooling energy demand for attics of residential buildings

The application of attic radiant barriers as a residential building energy conservation tool has received considerable attention in recent years. Quantifying the benefits of radiant barrier is complicated because the energy savings provided by this system depend on various factors including local climate, geometry, and other building parameters. Therefore, the objective of this study is to develop a simple estimating tool that may be used by homeowners and designers to assess the effectiveness and economic benefits of radiant barrier under different climatic conditions in the US. The developed tool is based on transient three-dimensional finite element models that were validated based on the results of an experimental field study. The results of the finite element models were used to develop a set of regression equations to predict the thermal performances of radiant barriers under a wide range of operating conditions. Although the theoretical basis behind this tool is robust and accurate, the developed tool is simple, flexible, and user-friendly to encourage its use among practitioners and homeowners with minimal background about this system and heat transfer mechanisms. It is anticipated that the developed tool will facilitate the integration of energy efficiency in residential design and construction.

Performance evaluation of an attic radiant barrier system using three-dimensional transient finite element method

A three-dimensional transient finite element model was developed to evaluate the thermal performance of an attic radiant barrier system as an energy-efficient insulation technology. The finite element model simulates different heat transfer modes including convection, radiation, and conduction. Hourly experimental data collected in a housing complex in Zachary, LA, were used to validate the finite element analysis. Upon validation, the design variables and their influence on the performance of the radiant barrier insulation system were investigated. Among the different design variables, the presence of an air gap on both sides of the radiant barrier had a significant effect on the performance of the insulation system.

Evaluating the Sensitivity of Attic Radiant Barrier Performance to Climate Parameters

By employing a calibrated and tested computer model, simulations of ceiling heat transfer in typical residential attics located in 12 locations across the United States were obtained to study the sensitivity of attic radiant barrier performance to local climate parameters. For each location, the net ceiling heat flux over the summer cooling season was computed for an attic with and for an attic without an installed radiant barrier. The net reduction of heat flux induced by the radiant barrier was computed and then related to climate variables. Among the local environmental parameters, the local ambient air temperature, local ambient humidity, and latitude had significant effects on the performance of radiant barriers. It was concluded that the installation of radiant barriers would be most beneficial in regions with high outdoor air temperatures and high relative humidity.

A perspective on the effect of climate and local environmental variables on the performance of attic radiant barriers in the United States

This paper offers a perspective on how climate and local environmental variables affect the performance of attic radiant barriers across the United States. Transient heat and mass transfer simulations were performed on a vented triangular attic with insulation level of 3.5 m 2 K / W (R-19) and the results were based on integrated hourly ceiling heat fluxes over 3-month periods during the cooling season. The ceiling heat transfer percent reductions ranged from 36.8% in the Tropical Savanna climate to 2.3% in the Mediterranean climate. Peak-hour percent reductions in ceiling heat flux ranged from almost 100% in the Marine West Coast climate to 23% in the Desert climate. The results suggested that local ambient air temperature, humidity, cloud cover index, and altitude had first-order effects. The amount of local solar radiation had no effect on the performance of the systems.

Numerical Heat Transfer Attic Model Using a Radiant Barrier System

A two-dimensional, steady-state finite-element model was developed to simulate the thermal effects of the application of an attic radiant barrier system (ARBS) inside a ventilated residential attic. The attic is ventilated using the exhaust air from an evaporative cooler. The study uses a k-ε turbulent model to describe the velocity and temperature distributions in the attic. The ambient temperature and solar isolation densities on the outside inclined attic surfaces are used as driving functions for the model. The model also included the appropriate heat exchange modes of convection and radiation on these outside surfaces. Several recirculation zones were visually observed in the attic flow pattern. Also, the use of the ARBS seems to lower the heat transfer through the ceiling by 25–30%, but this effect decreases significantly as the outside ventilation rates are increased through the attic space. The 2D model revealed some interesting temperature distributions along the attic surfaces that could not have been predicted by the one-dimensional models. The lower emissivity ARBS seems to raise the temperature of the inclined attic surfaces as well as the temperature of the exhausted ventilation air.

Effect of a Radiant Barrier on the Cooling Load of a Residential Application in a Hot and Arid Region: Attic Duct Effect

A computer simulation showed that an attic radiant barrier system (RBS) (a commercial product laminated to the underside of the roof sheathing) significantly reduces cooling load requirements in hot desert climates. This reduction was due to both a reduction in sensible heat transfer through the ceiling and an even greater reduction in losses (heat pickup) by the HVAC ducting system in the attic. These reductions were around 16% in runtime over the daytime hours and an overall 9% reduction over a five-day period. This latter effect indicates the need to improve current duct-loss calculation methods.

Attic radiant barrier systems: A sensitivity analysis of performance parameters

During the past seven years, the Florida Solar Energy Center (FSEC) has conducted extensive experimental research on radiant barrier systems (RBS). This paper presents recent research on the development of mathematical attic models and results from a sensitivity analysis of RBS performance parameters. Two levels of modelling capability have been developed. A very simplified model based on ASHRAE procedures is used to study the sensitivity of RBS performance parameters, and a very detailed finite-element model is used to study highly complex phenomena, including moisture adsorption and desorption in attics. The speed of the simple model allows a large range of attic parameters to be studied quickly, and the finite-element model provides a detailed understanding of combined heat and moisture transport in attics. This paper concentrates on the sensitivity analysis of attic RBS performance parameters using the simplified model. The development of the model is described, and results of the analyses are presented and discussed. Results from the finite-element model are also presented and compared with measurements from a test attic to illustrate the effects of moisture adsorption and desorption in common attics. The simplified steady-state model shows excellent agreement with measured steady-state data when thermal stratification of the attic air is modelled. Results of the sensitivity analysis using this model show that the radiant barrier surface emittance and the attic ventilation inlet air temperature are the most sensitive performance parameters for attic radiant barrier systems. The detailed, finite-element model shows that moisture sorption phenomena can have significant effects in attics. The daily temperature extremes in attics are significant, and they induce a moisture flux at the surfaces of the materials bounding the air zone(s). If this moisture flux is not accounted for in detail (i.e. with fully coupled heat and moisture transport equations) inaccurate surface temperature predictions are likely to occur.