A Study of the Energy Savings that can Occur when Using INSULADD® Solar Reflective Paint on Irradiated Building Walls

For Tech Traders

By

H. F. Poppendiek, April 2003

GEOSCIENCE LTD

6260 Marindustry Drive, San Diego, California 92121

 

Photograph of the solar lamp array and INSULADD® painted wall panel.

Photograph of the millivolt recorder and solar lamp array

 INTRODUCTION

Geoscience was requested by Mr. David Page to perform several tasks relative to the energy savings that result when using INSULADD paint on the outside of the building envelope. One task dealt with comparative outer wall panel surface temperature and corresponding heat flux measurements for the solar irradiated panels painted with Insuladd paint as well as with ordinary paint. A second task involved determining the additional panel thermal resistances that would have to be added to insulated wall systems painted with ordinary paint to yield the low thermal heat fluxes through a building wall when using Insuladd paint on the outer surface. The last task that was requested involved defining a mathematical thermal wall model so that the equations can be used to calculate wall thermal performance characteristics when system parameter changes occur.

 MATHEMATICAL THERMAL WALL OR ROOF MODEL

 An elementary model has been used which gives the steady state wall or roof temperature and the required heat removal to maintain a given room temperature when the outside weather conditions are known. The heat balance for this system is,

 The equation used to determine the air conditioning load is,

 THE EXPERIMENTAL SYSTEM

 A wall panel having an R-value somewhat typical of a building wall, namely, R = 12 hr ft2 °F/Btu, was instrumented with surface thermo-couples, as well as a large, thin calibrated heat flux transducer. The vertical test panel front surface faced a battery of sun lamps that provided the simulated solar irradiation. The heat flux transducer was located in the middle of the vertical panel. Heat absorbed on the front surface of the panel was lost 1) by conduction through the panel into the air behind it and 2) by infrared radiation and natural air convection from the front surface of the panel.

 THE TEST PROCEDURE

 From the hot and cold panel surface temperatures, the front and back ambient air temperatures and the heat flow transducer heat flux measurements; the system R-values were determined. One set of measurements was made for the Insuladd-applied paint and the other set for ordinary house paint. From the two sets of data, one can obtain the energy savings and the additional thermal resistance that would have to be added to the panel with ordinary paint to get the reduced heat flux attained by the panel with INSULADD® added paint.

 TEST RESULTS

 The test results for the insulation panel with its outer surface painted with INSULADD® paint follow:

The test results for the insulation panel with its outer surface painted with ordinary (light green) latex house paint follow:

On the basis of these two sets of data, the energy savings obtained when using the INSULADD® paint instead of an ordinary paint is,

 

 It is also pointed out that if one added an additional thermal resistance of Radd. = 6.0 hr ft2 °F/Btu to the wall system having the ordinary house paint on its outer surface, the higher heat flux being conducted into the building, namely, 5.24 Btu/hr ft2 would be reduced to the lower heat flux value of 3.57 Btu/hr ft2 for the wall painted with INSULADD® paint. This additional resistance calculation is performed by a trial and error calculation using Equation (1) (by iterating Rr, t and q/A).

 CONCLUDING COMMENTS

 It is pointed out that the energy savings terms and add, values are not just functions of the solar reflectivities and IR emissivities, but also of the Rr and system temperature information. It is also to be noted that ordinary paints can have a range of solar reflectivities and IR emissivities, depending upon their chemical constituency.

 

 

 A STUDY OF THE ENERGY SAVINGS THAT CAN OCCUR WHEN USING INSULADD® SOLAR REFLECTIVE PAINT ON THE INSIDE OF BUILDING WALLS.

For Tech Traders

By

H. F. Poppendiek, April 2003

GEOSCIENCE LTD

6260 Marindustry Drive, San Diego, California 92121

 Introduction

If the emissivities in the infrared region of interior wall paints are lower than ordinary paints, then the radiant heat transfer from the outer walls of rooms can influence the energy savings and comfort of persons in the rooms. Under wintertime conditions, where furnace heating is normally required in residences and buildings, if the interior wall paints have lower emissivities than normal paints, ambient room temperature cooling would be less and the comfort level of persons in the rooms would be greater.

Specifically, the radiation heat loss to cold, interior outer walls would be less, and the ambient air temperature reduction would be less. Thus, energy can be conserved if low emissivity interior wall paints are utilized.

David Page, of Tech Traders, Inc., asked Geoscience to investigate this thermal system.

MATHEMATICAL THERMAL ROOM MODEL THAT DEFINES ENERGY SAVINGS VIA LOW IR EMISSIVITY PAINTS

This thermal room model describes heat transfer processes that are operative in the wintertime. Specifically, convection from warm room air and radiation from warm inside walls to the inside surface of the outer room wall surface are conducted through the outer room wall and finally lost by convection and radiation to the ambient, cold outside air and the cold outside surroundings. The equations that define the heat transfer follow:

1)*

 

2)

3)

* In this thermal model, it is postulated that the air and mean radiant temperatures are equal, in the building room as well as in the outside environment, respectively.

Upon rearranging Equations (1), (2) and (3) and taking note that the three heat fluxes in the three equations are all equal at steady state, one adds the three equations and obtains,

The denominator in this Equation is the total thermal resistance of this thermal heat flow circuit.

THE EXPERIMENTAL SYSTEM

A wall test panel having an R-value of 2.75 hr ft2 °F/Btu was chosen to perform this test work. It is pointed out that a typical building wall R value is about 11 hr ft2 °F/Btu and the R value for a window system with a ½” air space between two glass panes is about 0.6 hr ft2 °F/Btu. Thus, it was thought to be appropriate to use a panel having an intermediate R value for the subject test effort* (specifically, a R value of 2.75 hr ft2 °F/Btu). The surfaces of the panel were instrumented with surface thermocouples and a thin, calibrated heat flux transducer was located on the cold side of the wall panel. A cardboard box with an open side was placed over the hot side of the test panel; this box then simulated a building room. A large plate electric heater was located opposite the panel to heat the simulated building room. Hot and cold air thermocouples, as well as a hot wall room thermocouple were also added to the system. The various heat transfer processes that occur in the test system were previously defined in section II above.

Test Procedure

The hot and cold panel surface temperatures, the hot and cold air temperatures and the hot wall temperatures and steady state heat fluxes were measured. One set of data was obtained for the case where the room walls and the test panel interior surface were painted with ordinary house paint; another set of data was obtained for the case where INSULADD paint was used. From the two sets of data, the energy savings that accrue when using Insuladd is determined.

*In future testing, it would be better to perform two separate tests, one where only a wall is used and another test where only a window is used.

Test Results

The test results for the two paint types follow:

                                                                          Test System                                 Test System      

ORDINARY PAINT       INSULADD PAINT

Heater power, watts                                          42.5                                   37.9

Wall panel heat flux, Btu/hr ft2                  2.38                           1.97

Hot wall surface temperature, °F                       100.2                                  99.0

Hot side temperature of wall panel, °F                 90.8                                   91.8

Hot air temperature, °F                                       92.1                                   91.2

Cold air temperature, °F                                     78.8                                   79.5

Total thermal resistance

(air to air) hr ft2 °F/Btu                                       5.59                                   5.94

 

CONCLUDING COMMENTS BY TECH TRADERS INC.

The results outlined in the previous section clearly demonstrate energy Savings as a result of using INSULADD®; specifically the total thermal resistance of the model has increased with a corresponding drop in the Heat Flux. Real life Energy Surveys find that the energy savings realized from the inclusion of INSULADD® into interior house paint ranges from 10% to 22% depending on the type of construction, location, and exposure of the home. An energy savings increase of only 10% in actual heat flux (heat loss) can equate to a much greater increase in actual energy savings due to the increased amount of time that Insuladd helps a homes interior remain in the “human comfort zone”. The human comfort zone is that small range of temperature where humans (and animals) feel most comfortable. This zone is quite narrow and tends to be between 70 degrees F. to 78 degrees F. When indoor temperatures stray outside of the “human comfort zone” we use heating or air-conditioning to bring the temperature back within the zone.