I'm going to try to finish one place in front of Big Dawg on possibly almost worthless info. My hay shed is 64' x 120' x 20'. So I installed 4 louvered fans above the rafters on the east end (my shed is orientated east to west). These fans are on timers, so I run them generally 9-10 am until 5-6 pm ONLY for about 3 weeks after new hay is placed in storage. The total air movement capacity of these 4 fans (in theory) will displace all the air in the hay shed every 19-20 minutes. Notice that they are on east side and louvered to minimize allowing light infiltration. North side would have been better, but where I built shed wasn't conductive of that orientation.
If you look closely at these pictures you will notice fans that I have placed in the rafters. Of each set of two, one blowing horizontally, one on a 45 degree angle down. These fans are place at 40' and 80' from east end wall. There is 6 fans in each of two rows (just cheap 20" box fans). Spaced roughly at 16', 32' & 48' from side wall, aimed towards east end of shed. These fans I run 24/7, for 3 weeks after new hay is placed in storage. I have no fans on the west wall, but I don't use that 40' for much hay storage (concrete floor verses asphalt floor on the east 80').
Now, I have a 20'x16' door on the west side, a 12'x16' and two 16'x16' doors on the north side, and a 16'x16' door on the east side of the shed. Only one window on the north side (west end) that is not covered (has a screen so I do open in the summer). All these overhead doors have electric door openers also, so they are only open generally when necessary.
I seem to be able to retain a fair amount of color with my methods (not saying there isn't room for improvement ). Here's a pic of 255 bales heading to a happy customer, just yesterday. I grow alfalfa or alfalfa/grass hay BTW.
Now, what I would consider doing, to your shed IF you are losing color via light (not air as Big Dawg mentions) and you want to help maintain it.
- Block the light coming in from windows (window shades, cardboard, to paint)
- Keep doors closed as much as possible
- Created some sort of artificial air movement (to help disperse moisture during hay sweat).
- Cover the concrete with 1 1/2" - 2" of asphalt (to reduce moisture migration up from floor).
But I'm spending YOUR money.
Lastly, it's generally only cosmetic on hay color, but in MY situation of selling hay for a premium price to horse folks. They buy by color. So I work to give them what they WANT.