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2. Comments on How Exterior Paints and Interior Paints Can Play Roles in Conserving Energy
A Study of the Energy Savings that can Occur when Using Thermilate/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 Thermilate/Insuladd painted wall panel.
Photograph of the millivolt recorder and solar lamp array
I. INTRODUCTION
Geoscience was requested by Mr. David Page to perform several tasks relative to the energy savings that result when using Thermilate/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 Thermilate/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 Thermilate/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.
II. 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,
where
The equation used to determine the air conditioning load is,
where
III. 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.
IV. 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 Thermilate/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 Thermilate/Insuladd added paint.
V. TEST RESULTS
The test results for the insulation panel with its outer surface painted with Thermilate/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 Thermilate/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 Thermilate/Insuladd paint. This additional resistance calculation is performed by a trial and error calculation using Equation (1) (by iterating Rr, t and q/A).
VI. 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.
VII. SYNOPSIS (From Tech Traders)
The following table shows the effective “R” values for
common wall types.
As you can see from the test report by Geoscience Labs, the use of Thermilate® can dramatically increase the effective “R”value
of these common wall types by over 50%!
| No. | System Description |
Whole Wall R-Value (Rww) |
| 1. | 12-in two-core insulating units concrete 120lb/ft3, EPS inserts 1 7/8-in thick, grout fillings 24 in o.c. | 3.6 |
| 2. | 12-in two-core insulating units wood concrete 40lb/ft3, EPS inserts 1 7/8-in thick, grout fillings 24 in o.c. | 8.6 |
| 3. | 12-in cut-web insulating units concrete 120lb/ft3, EPS inserts 2 1/2 in thick, grout fillings 16 in o.c. | 4.1 |
| 4. | 12-in cut-web insulating units wood concrete 40lb/ft3, EPS inserts 2 1/2 in thick, grout fillings 16 in o.c. | 9.2 |
| 5. | 12-in multicore insulating units polystyrene beads concrete 30lb/ft3, EPS inserts in all cores | 14.7 |
| 6. | EPS block forms poured in place with concrete, block walls 1 7/8 in thick | 15.7 |
| 7. | 2 x 4 wood stud wall 16 in o.c., R-11 batts, 1/2-in plywood exterior, 1/2-in gypsum board interior | 9.6 |
| 8. | 2 x 4 wood stud wall 24 in o.c., R-11 batts, 1/2-in plywood exterior, 1/2-in gypsum board interior | 9.9 |
| 9. | 2 x 6 wood stud wall 24 in o.c., R-19 batts, 1/2-in plywood exterior, 1/2-in gypsum board interior | 13.7 |
| 10. | Larsen truss walls 2 x 4 wood stud wall 16 in o.c., R-11 batts + 8-in-thick Larsen trusses insulated by 8-in-thick batts, 1/2-in plywood exterior, 1/2-in gypsum board interior | 38.5 |
| 11. | Stressed-skin panel wall, 6-in-thick foam core + 1/2-in oriented strand board (OSB) boards, 1/2-in plywood exterior, 1/2-in gypsum board interior | 21.6 |
| 12. | 4-in metal stud wall 24 in o.c., R-11 batts, 1/2-in plywood exterior + 1-in EPS sheathing + 1/2-in wood siding, 1/2-in gypsum board interior. NAHB Energy Conservation House Details. | 10.9 |
| 13. | 3 1/2-in metal stud wall 16 in o.c., R-11 batts, 1/2-in plywood exterior + 1/2-in wood siding, 1/2-in gypsum board interior | 6.1 |
| 14. | 3 1/2-in metal stud wall 16 in o.c., R-11 batts, 1/2-in plywood exterior + 1/2-in EPS sheathing + 1/2-in wood siding, 1/2-in gypsum board interior. AISI Manual details | 8.0 |
| 15. | 3 1/2-in metal stud wall 16 in o.c., R-11 batts, 1/2-in plywood exterior + 1-in EPS sheathing + 1/2-in wood siding, 1/2-in gypsum board interior. AISI Manual details | 9.5 |
| 16. | 3 1/2-in metal stud wall 24 in o.c., R-11 batts, 1/2-in plywood exterior + 1/2-in wood siding, 1/2-in gypsum board interior. AISI Manual details | 7.1 |
| 17. | 3 1/2-in metal stud wall 24 in o.c., R-11 batts, 1/2-in plywood exterior + 1/2-in EPS sheathing + 1/2-in wood siding, 1/2-in gypsum board interior. AISI Manual details | 8.9 |
| 18. | 3 1/2-in metal stud wall 24 in o.c., R-11 batts, 1/2-in plywood exterior + 1-in EPS sheathing + 1/2-in wood siding, 1/2-in gypsum board interior. AISI Manual details | 10.2 |
Comments on How Exterior Paints and Interior Paints Can Play Roles in Conserving Energy For: Tech Traders
By: H. F. Poppendiek
GEOSCIENCE LTD
6260 Marindustry Drive
San Diego, California 92121
I. ENERGY SAVINGS PRINCIPLES
There are two types of paint that can assist in saving energy in residential and industrial buildings. One relates to the reduction of the solar load to roofs and to exterior walls. The second one relates to interior room wall paints. These features are discussed below.
Solar Load Reduction Paints
When the sun shines on exterior surfaces of commercial and residential buildings, the solar load can be high enough in the summertime to require the use of excessive air conditioning in interior rooms in order to have comfortable conditions. If the exterior paints or coatings have reasonably good solar reflectivities, however, then the solar load being absorbed by the building would be reduced and the air conditioning required would also be less, thereby conserving energy.
Interior Room Heat Transfer Reduction Paints
If the emissivities in the infrared region of interior
wall coatings or paints are lower than ordinary paints, then the
radiant hat transfer from the warmer outer walls of rooms would
be less in the summertime, thus giving greater comfort to persons
in the rooms because the radiant heat fluxes would be less, and
there would be less warming of ambient room temperatures. Under
these conditions, energy would be conserved because less air conditioning
would be required.
Under wintertime conditions, where furnace heating is normally required
in residences and buildings, if the interior outer wall paints have
lower emissivities than normal paints have, ambient room temperature
cooling would be less and the comfort level of persons in the rooms
would be greater because the radiation heat loss to cold, interior
outer walls would be less, and the ambient air temperature reduction
would be less. Thus, again, as in the summertime case, energy can
be conserved if low emissivity interior wall paints are utilized.
II. ENERGY SAVINGS RESULTS WHEN USING Thermilate®
In the case of solar load reduction, the energy savings accrued by using Thermilate® additive paint rather than ordinary house paint would be,
(0.81 - 0.70) ÷ (1 -0.70) X 100 = 37%
The radiant heat flux gain from a warm interior surface of an outer wall of a residence or building in the summertime is reduced if the infrared emissivity is reduced by a paint additive like Thermilate®. Specifically, the percent energy savings in this flux term would be,
(0.85 – 0.75) ÷ (0.85) X 100 = 11.8%
The radiant heat flux loss to a cold interior surface of an outer wall of a residence or building in the wintertime is reduced if the infrared emissivity is reduced by a paint additive like Thermilate®. Again, the energy savings in this flux term would be about 11.8%.
PROPERTY CERTIFICATION
| Infrared Emissivity Test Results | ||
| MATERIAL INVESTIGATED: | MEASUREMENT METHOD: | RESULTS:* |
| Dry wall painted with two coats of latex house paint | ASTM E-408 85% | (0.85) |
| Dry wall painted with two coats of latex house paint with Insuladd (32 fluid oz. per gallon of paint) | ASTM E-408 | 75% (0.75) |
| Solar Reflectivity Test Results | ||
| MATERIAL INVESTIGATED: | MEASUREMENT METHOD: | RESULTS:* |
| Dry wall painted with two coats of latex house paint | ASTM E-1918† | 75% (0.75)‡ |
| Dry wall painted with two coats of latex house paint with Insuladd (32 fluid oz. per gallon of paint) | ASTM E-1918† | 81% (0.81)‡ |
*Details of the investigation are not included in this Property Certification; the results presented here apply only to the samples tested.
†incident and reflected solar radiations are measured using 3' X 3' coated test samples. The procedures of ASTM E-1918 are similar to those of the CEC shading coefficient test method under Title 25 (Chapter 1, Subchapter 1, Article 5). A number of measurements are made over the period 11:00 A.M. to 3:00 P.M. under clear sky conditions.
‡ Please note that the incident solar radiant fluxes measured by the radiometer are in good agreement with ASHRAE solar radiation values for our latitude, the time of the year and time of the day.
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