They are wasting so much heat at this opened slider, that the IR image actually looks like flames are pouring out the window opening. This is only one of many windows that are always left opened by the occupants, because it gets too hot in the uncontrolled baseboard heated units on the upper floors (according to Owner).
This is common in the older steam heat rental units here in Chicago.
They usually place the senors in the coldest unit.
This is why so many landlords have switched to HVAC units as a precurser to selling.
Let the tenants pay for it.
Interesting to see how a metal screen intercepts/reduces radiant energy emission from the closed right operable window!! Looks quite a bit cooler than the center fixed pane!! This a life size, not microscopic, version of the “Low E” coatings on glass.
Then again…Always a chance that a curtain may be blocking heat movement to that window. It is a pretty distinct sharp edge deliniation though!!
Window glass, naturally, is a reflector of IR radiation. IR is, mostly, reflected by glass. There are special glasses (pyrex, which is a boron-silica product) that are better than regular glass.
Remember, Low E means low emissivity. The energy is absorbed and re-emitted.
Glass will transmit (allow to pass through) UV light, but it will refract the light into the lower IR frequency. That is how greenhouses work.
Low E glass depends upon the placement of the treated surface and is, usually, only effective in triple paned windows.
BTW: The Krypton-Argon gas between the windows has little effect on the transmittance / emissivity of the system. It is just an inert gas mixture that keeps out moisture if the seals are not broken. If the seal does break, the r value of the window is not significantly affected (only about .3 R per square foot).