Henry answered the point well. I can add that I was Superintendent of Building and Grounds after new construction of a large building. The new auditorium floor was a beautiful parquet. When the summer came, the floor waved and buckled terribly. The installers had to come back to redo.
If I turned the air conditioning off to save electricity, the walls sweated water and the floor changed. We had to maintain a range of about 20% relative humidity between 35 and 55 to keep stability - and it is much more comfortable.
I suggest you abandon the inexpense of the swamp cooler and use air conditioning to control the humidity. Going from a 30% winter relative humidity to a 100% summer relative summer humidity is a lot of work for wood floors and the wood furniture as well.