Open 24/7 July/August 2019

August 5th, 2021 by Nathan Hobbs

Proving Window Film

By Manny Hondroulis

For the past 11 years I’ve written this column, and I still see the need for customer education. We’ve all seen customers who think they know exactly what they want, but when they see different options they become overwhelmed.

One topic I find interesting is how to prove that window film works, specifically sun control or insulated window films. We often take for granted that a thin piece of coated polyester reduces heating and air-conditioning bills.

There are multiple tools at our disposal. It’s possible for each manufacturer to have a different approach, so before adopting any advice, check with your manufacturer.

Temperature Experiments

A reduction in temperature is something the average person will understand. There are two common temperature experiments with which I’m familiar:
• Take two windows, place them side-by-side, and install film on one. Then, wait for a sunny day to take a digital temperature gun and measure the temperature of the floor in front of both windows. You should see a difference. Note: you shouldn’t take the temperature of the glass because window film absorbs heat. The filmed window will have a higher temperature than the un-filmed window.

• Take two identically-sized offices that are side-by-side or top and bottom and install window film in the windows of one office. Wait for warm weather for the entire week. Then, set up temperature recording devices in each office. Turn off the air conditioning or close off the vents. Let the devices track the room’s temperature over the week. You’ll see a noticeable difference between the offices. If you’re unable to turn off the air conditioning or close off the vents, you can substitute temperature recording devices for BTU recording devices.

Additional Proof

Some clients want to know what the impact of window film will be on their bottom line. To answer this question, you’ll need access to energy modeling software such as eQuest, the most widely used modeling software by third parties such as ESCOs, consultants, and utility companies.

Modeling software estimates the energy consumption of a building without window film and compares it to the energy consumption of a building with window film. The difference in consumption multiplied by the appropriate utility rate is the estimated annual utility savings. The turnkey installation price divided by the estimated annual utility savings is the simple payback—how many years will it take for the client to earn back the initial investment (See illustration.)

To begin the energy modeling process, you’ll model the building as it exists today. You’ll need to gather information about the building from your client along with one year of utility bills that show monthly cost and consumption. After you plug in all of the inputs and run the model, you can determine the validity of the model by reconciling the simulated monthly consumption to the actual energy bills. A 10% variance generally is acceptable.

After you establish this, the rest is easy. Simply “copy” the base case and change the glazing to include the desired film. The software will estimate the consumption of the filmed case and then calculate estimated annual savings to determine a simple payback.

Don’t worry if this sounds too complicated. Most manufacturers perform building modeling for their dealers.

Not every building is a candidate for creating an energy model. But that’s a topic for a different day.

If you have any questions about any of this information, please feel free to email me at

Manny Hondroulis is the vice president of Energy Distribution Products in Baltimore.

To view the laid-in version of this article in our digital edition, CLICK HERE.

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