We have 25 fixed single pane windows that are roughly 3 feet wide by 6 and a half feet tall in our house in Houston, TX. Some of the windows face east, some face west and some face south. We had film put on them, but there is still a lot of heat transferred through them. What can be done to improve their energy efficiency without replacing the entire window? We need to improve their energy efficiency due to all of the air conditioning cooling we have in Texas.