Window coverings provide an opportunity to largely block big heat-loss holes in otherwise tight building envelopes.  No standard tests exist for measuring the R-value of window coverings, probably due to the large number of variables, many of which would change with a particular installation.  It would be useful to have a standard testing procedure that would allow quick testing to provide comparison R-values, and provide a baseline for corrections for the many operational and installation variables.

Two studies of real windows on the internet use a few air temperature measurements on real windows in a real house.  My own testing used a simulated window with a wall of ice-water bottles behind a plastic sheet to simulate the cold window.  All the methods use the known R-value of one component to allow calculation of the R-value for the window covering.  The first two studies used the R-values of the windows, while my tests used a foam insulation plate of known R-value on the “room side” of the unit. My system used room temperature to provide the heat across the foam plate, while the two real world studies used the room temperature directly.  These different methodologies provide some guidance on creating a standard methodology for evaluating the R-value of window coverings.

Use of actual windows as a test platform has the disadvantage of being dependent on cold and varying ambient temperatures, so quick testing of many different materials is impossible.  My testing, while standardized, had several shortcomings.  Since I had no heat source except the room, the warm side temperature facing the test piece was below room temperature.   In addition, the heat inflow to the window frame sides was not originally accounted for, and contributed to significant errors at higher R-values.

The use of air temperatures in the first two studies is another problem.  These temperatures are always subject to convection currents, and the proper location for an average temperature between the window and the shade changes with circumstances.  One of the internet studies showed the significant effect of sensor location.  My tests used surface temperatures for most sensors. Each sensor was attached to a small aluminum plate to minimize the effect of the wires, and to partially average the temperature. These sensors were attached to the plastic cover of the “window” and on both sides of the hot face foam panel.