triple
"Low E-glazing" and "k-glazing" are trademarks for one and the same type of glazing ,others are "Pilkington-glazing" and " Vistatherm-glazing".The correct term would be "metalized glazing" (or something like it) meaning "covered with a thin layer of metal ".
Permanent aerating -leaving a window open-would dilute any insulation effect,windows or otherwise.The correct way of aerating is to open the windows fully and for a short time to exchange the air volume once,if necessary several times a day.To keep the small window permanently open would also mean to have the heating/radiator turned off permanently.Having both "working" at the same time is wasteful/ illogical.For the motorist:You don't push down the accelerator whilst breaking .
Retrofitting of old double glazing with better ones is no problem,as long as the frame is good enough to take them.
Asthma is not caused by windows.But asthma attacks could be caused by dust from carpets,ash from the open fire etc.,dirt in the air.Ask your doctor or contact the asthma association.