California Heat Study (video)

52% reduction in energy use

Hotel rooms make the perfect laboratory for measuring, monitoring and testing the effectiveness of this technological advance in window efficiency.

Two identical spaces, two identical, calibrated, Packaged Terminal Air Conditioning Units (PTAC), and two identical oversized windows with direct westward exposure for maximum solar heat gain.

This test was designed to determine the ability of the radiant barrier to control the behavior of both thermal and radiant heat gain during warmer months.

Thermal heat being the migration of the warm ambient air temperatures to a cooler space and radiant heat produced from the suns energy directly hitting and heating a surface.

Thermal heat movement generally happens at a 90º angle to the shade itself.
The material has a perforation rate of 38.6%, thus the reflective surface mass of 61.4% will offer close to the same percentage of thermal energy reflectance.

We see the results of this during our Canadian Winter study where the reflectance was measured by a 58% reduction in power use.

On a hot day, the barrier would reflect approximately the same percentage of thermal heat gained through the window but would also reflect an average of 65-80% of the radiant energy that is the result of solar exposure. The percentage of reflection will be determined by the angle of the radiant energy (solar) to the blind.

If the angle of the solar exposure is at 90 degrees, the reflective properties will be closer to the total mass of the barrier (61.4%). As the angle of the sun changes to be greater than 90 degrees to the surface of the radiant barrier, then the exposed area of the perforations is reduced as the round holes become oval in shape and reduce the exposed path of solar energy. Testing with BTU meters have indicated that the average reduction of solar energy through vertical windows is between 65-80%, depending on the time of day, arch path of the sun and various seasons.

It should be noted that radiant energy movement accounts for 80% of all heat movement whereas conductive heat is about 5-7% and  15% average for convection heat movement.

The hotel chosen for the California heat study was targeted because of it’s age and constant solar exposure presented by the westward facing wing of guest rooms.

Build in the mid-1980s, the windows are double paned glass with aluminum frames. As is typical of windows of that vintage and construction, any insulating gas between the two panes has most likely dissipated.

Although 54% reduction on energy use is impressive, the thermal heat reflectance could  be even higher with an increase in the exterior ambient temperature. During the test, outside temperatures ranged in the mid-eighties for the week. These temperatures were targeted because of the inability of the PTAC units to successfully balance and cool the rooms effectively when temperatures rose to triple digits. Another test with hotter daytime temperatures using capable cooling units could prove to have even greater results.

Creature comfort is something intangible yet verbalized by the unhappy guests who would enter a warm room to find that after an hour and a half of cooling, the rooms were still uncomfortably warm. The room with Solar Comfort was able to retain the cool air while keeping incoming heat at bay.

The radiant barrier material increased the rooms ability to reach the rooms cooling point 4.5 times faster than the one without.

The use of the infrared camera and thermography is an interesting and exact way to measure incoming heat. The radiant energy passing through the glass, on its way to heating objects in the room, is transferred and accurately recorded to a simple piece of construction paper. The camera instantly records the energy radiating from the paper.

As solar comfort radiant barrier is rolled down, the radiant and thermal heat is reflected, before it has a chance to enter the room. Incoming temperatures reaching 152 degrees  for extended periods were impairing the cooling units ability to cool effectively.

When we measure the incoming heat being blocked or reflected by the screen, there is a 32 degree reduction. Now the cooling unit is more easily able to comply with the thermostat request. The run and cycling time for the unit is reduced by 54%.

A 54% reduction in run time will directly correlate to similar reductions in power used and the drastic lowering of energy costs.

Increased longevity and lifespan for motors and compressors will also translate to even further savings when cycling times are reduced.

Room Size 13’ x 27’ – 351 square feet
Exterior Wall 88 square feet
Window/Screen Size 28.6 square feet in roller blind format
Product Solar Comfort Radiant Barrier (SC 300) 38.6% perforation/openness rate
PTAC Amana PTC 123A35AC
Cooling BTU/Hr 12000/11900 Amps 4.9/5.3
Data Loggers (2) HOBO U-12-012 placed in each room
Energy Logger Elite Pro – connected at electrical panel
Test run after calibration 54 hours

Special thanks to the Pacific Gas and Electric Companies’ Tool Lending Library for their equipment, support and knowledge.