No, they don't need to be put in a refrigerator at night but they do require proper High Land temps as Andreas indicated: cool days and cold nights. My own HL Nepenthes setup goes from 60-75*F days year round to 40-50*F nights year round and is set at 90% RH but actually hovers between 80-90%.
Now for my general commentary on High Land Nepenthes and Temps:
It seems to be a popular idea lately (and not a new one) that if people keep HL plants wet enough, bright enough or humid enough then proper HL temperature requirements can be ignored. While those aspects are also as important as temps you need a complete gestalt of ALL conditions being within proper ranges. If this were not the case who would bother with cooling setups? Certainly not I, when running my HL setup in summer doubles my electric bill.
Without proper temperatures for at least 9 months of the year HL Nepenthes will suffer a slow decline. This heat induced decline is typified by a reduction in growth point size and vigor - instead of increasing. At it's most simple the cold temps at night can be thought of as halting the HL plants growth. Without the trigger of the night time drop the plant will continue to metabolize and essentially "grow itself to death". As I mentioned, this is not good desirable growth, it's weak, twisted, rarely pitchers properly. The growing point gets smaller and smaller until it eventually disappears. This condition is entirely treatable however, by providing proper temps a plant not yet too-far-gone will bounce back, though it will take time.
There have been some people (who do not grow HL Nepenthes) propagating the idea that raising the daytime temps to very high ranges means that you won't have to drop the night time temps below ambient house temps because the plants are still getting a 20*F drop at night. This is also an erroneous assumption and will not work in the long term, this is simply too hot during the day and too warm at night. Although nothing is stopping anyone from trying - it's your money, feel free to burn it however you wish... Though if you do succeed at growing your HL Neps in LL conditions be sure and post the results at the 6 month, 1 and 2 year mark, I'd certainly be excited to see it.