Terry Fields wrote:

Very approximately, the number of grams of water per cubic metre in
saturated air is the numerical equivalent of the temperatu at 15
degC the air can hold 15g of water per cubic metre.

Let's say your shed has small swings in temperature, from say 6 degC
overnight to 10 degC during the day. If the humidity remained constant
at 50 percent, then even if the machinery remained at 6 degC because
it warmed up slowly, there would be no condensation as then the dew
point at 10 degC and 50 percent (relative) humidity is 5 degC:

The air is 50 percent saturated (50 percent RH at 10 degC); and 50
percent of 10 grams (saturated air at 10 degC) is 5 grams. but 5 grams
is enough to saturate air at 5 degC, and so 5 degC is the dew-point.

If, however, the temperature swing was from 6 degC overnight to 13
degC all at 50 percent RH, then the dewpoint would be 6.5 degC and
condensation would take place.

How do you justify your assumptions?

Suppose your shed begins its day at 6 degC and is full of 50% RH air
(and therefore contains about 3g of water per m3), and suppose further
that by the early afternoon it warms up to 13 degC. This warming
up is going to reduce the RH of the shed air (to about 23%), and then
by the time it cools down to 6 degC again, the RH will have gone back
up to 50% (and hence still be non-condensing).

The only way to increase the 13 degC RH to 50% would be to add water
to the shed air. Where is this going to come from?

OK, so there could have been a change in the weather, increasing
the outside RH, and if the shed has been in use, with doors/windows
wide open, then the shed air would become well enough mixed with
outside air to be indistinguishable from it. But if the shed has
remained closed, and its structure and windows/doors are reasonably
well sealed, the absolute (not relative) humidity is going to remain
constant at 3g/m3.