- Humidity must make a contribution here?
Humidity is THE question here. At every given temperature, air can hold only so much water before condensation occurs; generally, the colder the air, the less water vapor the air can hold. So the relative humidity, like you see on a weather app or broadcast, is the percentage of saturation of the current air temperature (and pressure). For example, right now where I live it's 21C (70F) and 34% humidity (quite low for us). So the air is holding about one third as much water vapor as it could, in the current conditions. Now, the dew point is the temperature at a given pressure and humidity level, where condensation will form. The dew point for my current conditions is 5C (42F), so if it suddenly plummeted to that temperature, there would be condensation. So to find out at what temperature condensation would form in a hive, you'd need to know the relative humidity and the temperature, and plug that into a dew point calculator. Td = T - ((100 - RH)/5), where Td is the dew point, T is the temperature in C, and RH is the relative humidity, will give you a reasonable estimate at humidities above 50%, but the real equation is too involved to do by hand unless you are some sort of genius.
- The jury seems to be out regarding ventilation or not?
This is why ventilation is so tricky. In conditions with high humidity, excessive ventilation increases the likelihood of condensation, because the humidity outside the hive is very high. But conversely under low humidity conditions and without much ventilation, the bees will be unable to vent the water vapor they are producing, creating condensation.