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Field Performance of Reduced-Scale Structures Coated with a Polymer-Based Thermal Coating

By:  J. Larralde, Ph.D.
​College of Engineering

California State University, Fresno

Fresno, CA

November 15,2007



Introduction


Delta Plastics Co. of Terra Bella, CA has developed a new application fro a pre-existing formulation (herein referred to as Delcoat®) that can be applied on the exterior and interior surface of buildings to improve their thermal efficiency.  This report presents the results of a series of experiments conducted on two structures.  The experiments were conducted to determine the thermal enhancing characteristics of the Delcoat®.  This report describes the experimental procedure and specimens, test results and analysis and conclusions.


Experimental procedure


Two identical, reduced-scale structures, 3 ft by 3 ft by 3 ft, were tested to determine the thermal enhancing characteristics of Delcoat®.  The structures were fabricated with galvanized steel in advance at the Delta Plastics Co. plant.  One was coated with Delcoat® and the other was painted with a latex-based paint.  Both structures were sealed at all joints to prevent heat and air leaks.  Each structure was also fitted with an air conditioning unit of 6000 BTU to study the performance of the coated and uncoated structures with air conditioning.


The two units were wired with the sensors and tested for continuity in teh laboratory.  Each structure was instrumented with four sensors:  (1) outside air temperature (at approximately 2 inches from the surface), (2) inside air temperature (at approximately 2 inches from the inside surface), (3) outside surface temperature (touching the outside surface) and (4) inside surface temperature (touching the inside surface).  The A/C units were installed very carefully in the structures and all cracks and gaps were filled with expanding foam.  The structures were placed on the roof of the laboratory and all sensors and connections were checked an calibrated.  The two structures were oriented with the axis of symmetry in the N-S direction to ensure that both would receive the same amount of sun radiation and at the same angle.



 











                                FIG. 1  Photograph of the coated and plain structures set-up at the roof of the Laboratory.


Temperature data was collected for eight hours, starting each run in the morning at 9:00 AM, taking one set of readings every one minute.  A total of four runs were conducted in four days; two runs with the A/C units in the off position and two with the A/C units in the on position, and set to the maximum cooling setting.


Test Results


The temperature readings from all thermistors for both structures are shown in the following figures.
































                      FIG 2.  Temperature readings from all thermistors in both coated and uncoated structures


The temperature differentials between inside and outside temperatures were calculated as the inside temperature (hotter) minus the outside temperature (cooler) for both the coated and coated structures and the following graphs are generated:






















                                                                 

                                       FIG 3.  Temperature differentials of the inside with respect to the outside at the                                                                                                     surface and at 2 inches from the surface (ambient) 


As can be seen in the previous figures, the temperature differential in the air inside with respect to the air outside was much higher in the uncoated structure than the coated one.  Also, since the structures have spent the whole night prior tot he start of each test run in the morning, the air in the inside remained cooler in the coated structure than in the uncoated one.  In both cases the coated structure exhibited higher insulating characteristics.  Notice also that the temperatures at the surface of the structures inside and outside are very similar with higher dissimilarity in the coated structure.  If the temperature differentials are normalized for both the coated and uncoated structures to represent them at the same initial reference of zero degree differential, the following graphs are obtained:
























                                 FIG 4.  Temperature differentials of the inside with respect to the outside ambient temperatures and                                                                                  normalized to zero initial condition.


The previous graphs exhibit very conspicuously the increase in temperature in the interior of the structures as the sun moves above the horizon and the air temperature increases.  The heating effect on the inside of the structures is much less pronounced in the coated structure than in the uncoated structure.  In the uncoated structure the temperature differential reached a maximum of approximately 22°F after 5 hours, while the coated structure exhibited a maximum differential of only approximately 10°F after approximately the same amount of time.


The same effect was observed when the experiments were run with the A/C units in the ON position and set at the maximum cooling capacity.  The results are shown in the following graphs:






















                                            FIG 5.  Temperature differentials of the inside with respect to the outside

                                ambient temperatures and normalized to zero initial condition.  Air conditioning units ON.


As can be seen in the last graphs the temperature increase on the inside of the structures was much smaller when the A/C units were ON.  The units effectively kept the air temperature inside cooler than when the A/C was not running.  Also, the structure that was coated with Delcoat® remained at a much cooler temperature than the uncoated one.


It would be expected that the A/C unit in the coated structure was then running less frequently than in the uncoated one.  This effect can be seen when the inside air temperatures are examined carefully in both structures as shown in the following graph:













                                                 FIG 6.  Inside air temperatures with Air conditioning units ON.


In the previous figures it can clearly be observed that the structure with the Delcoat® coating was kept at a lower temperature than the uncoated one.  Also, by counting the peaks and valleys in the graphs it is possible to determine the number of times the A/C units cycled.  In the uncoated structure the A/C units came on/off an average of 14 times in the period of 8 hours.  In contrast, in the coated structure the unit came on/off an average of 11 times.  Also the air was kept cooler in the coated structure.  This represents a reduction in energy consumption for cooling of approximately 20%.


Conclusions


The air and surface temperatures were measured accurately in two small identical structures, one coated with a specially formulated polymer with insulating characteristics.


The structures were exposed to natural sun radiation by placing them on the roof of the laboratory.  The structures were oriented with the axis of symmetry in the N-S direction to ensure that both will receive the same amount of radiation and at the same angle.


Temperature readings were collected automatically from the inside and outside of the structures at the structure's surface and at 2 inches from the surface.


Temperature readings clearly indicate a different thermal performance of the structure coated with Delcoat® as compared with the uncoated one.  The uncoated structure reached a maximum temperature differential on the inside with respect to the outside of 22°F, while the coated structure approached only 10°F.


When the A/C units were turned on, the inside temperature was again higher in the uncoated structure as compared with the coated one; 12°F in the uncoated vs. 5°F in the coated structure.


As a result, the A/C unit in the coated structure worked less and maintained a lower temperature than the A/C unit in the uncoated structure.  The energy savings required for cooling would be approximately 20%.