This proposal is to introduce a standard method that can provide a base-line for R-value determination of window coverings. The use of Computational Fluid Dynamics (CFD) can then be used to add correction factors for the many variable factors that occur with windows coverings.

It should be noted that this process will NOT generally be useful for curtains, which can easily have negative R-values depending on their installation.

The role of boundary layers and convection currents are unique with window shades.  For most construction materials the R-value must exclude these effects because they disappear as soon as they are brought in contact with another material.  With window coverings these boundary layer effects are a major part of their effectiveness.

For most materials a “guarded hot-box” is used to measure the R-value, and it effectively eliminates the boundary layer effects.  The cold walls of the window frame on the cold side of the test unit are the major source of heat inflow that causes problems.  This region is about 2.5 inches wide (depending on installation of the test piece).  A “guarded hot-box” (actually a guarded cold-box) around this area is needed to get accurate R-values with high R-values test samples.

With high R-values (>8 or so) the amount of heat flow through the test unit is small. The cold side walls of the test unit are then very cold so the delta T to the outside is high, and it takes only a little outside heat to affect the calculated R-value.  So, the guarded-cold-box around the cold area of the window frame is needed.  The problem can be reduced somewhat by making a bigger “window” area (area versus circumference), but a bigger test unit is more awkward and expensive to build and test.

The business model for this testing effort is to perform testing for window covering manufacturers and perhaps for other researchers.  A frame would be sent to the customer by UPS, who would install their covers to their own specifications and return it for testing. This frame would be  2’ x 2’ x 2.” with 1/8” plywood face covering 5/8″ foam, and would fit smoothly into the test unit.  When tests were complete the frames (with the customers covering) would be returned to the customer, who could return them with a new cover for additional testing or retain them.

The design and mathematical analysis would all be open-source and be available on our web-site, along with results that were performed by us privately and any that customers allowed to be published

The standard test unit would simulate a typical window frame that is 2ft x 2ft x 5.5” deep.

The test unit would consist of a cold section containing a cold face (the “window”) maintained at about 32F with ice water, and an electrically heated warm face (the “room”) at about 68F.  The heat to the hot face would be provided by an electric heater. The power required would be a check on the R-value determined by the temperatures.

An instrument system would record the important variables over the time of the test.  This would include verification of the 32F window temperature, the history of the warm face temperature, and the ambient conditions.  Although the unit would be insulated with at least 3” of foam insulation on all sides, corrections for heat inflow from the ambient room will likely be needed. The calculated R-Value would be calculated in real-time and when the conditions were stable the program would alert the operator that the test was complete.  The operator could then load the next panel, and check that the ice container was sufficiently full, the melted water container not too full, and then start the next run.

To promote the service a number of standard materials would be tested and the results published on a web site and in a white-paper.