Low-e windows are not just for sunny climes - it's arguably the dominant benefit of modern windows. Interestingly, when you put low emissivity layers on each pane, it doesn't matter whether it's pointing towards the inside or the outside. When pointing outwards, it reduces the propensity to radiate outwards, when on the inside it reduces the propensity to be heated by radiation. More layers are good because that increases the number of low-e layers you have - with double glazing, you only have two on the insides; with triple glazing you have 4.