How can I dry lumber outdoors for furniture?

I did some more research and thought I'd share some of my findings.

One thing is that relative humidity and moisture content both use percentages but they are describing the idea of "water saturation" in a much different way. It seems obvious but having humidity of 80% would not mean your wood would try to reach 80% moisture. Equilibrium would be achieved much much lower. There is actually some charts that show what kind of equilibrium moisture content would be at for a given RH.

https://www.woodworkerssource.com/wood-moisture-content.html

So looking at the chart above, we can see what kind of equilibrium moisture content we will achieve given a constant temperature and relative humidity. In my specific area, we've been seeing temps at this time of year (mid autumn) around 70F. Today, we had a RH of 80%. If left alone in this exact condition for a long period of time, EMC would reach around 16%. In other words, it would not be possible to achieve my goal of 6-8% moisture (amended after further research, not 8-10% as I initially thought).

I've created a drying room today that I just checked on and has a RH of 45% in there. Not bad but it's still getting started since I just added the dehumidifier into the room and those boards I'm sure are still releasing moisture, as I have about 150-200 board feet of wood in perhaps a 588 ft^3 space--quite a small space (12L x 7W x 7H). In a real world scenario, I am expecting the maximum RH in this space to drop as the moisture within the wood also drops, as my dehumidifier is constantly condensing water in the air and eventually, there will simply be less water to pull out. In other words, very wet wood will release a lot of moisture quickly, dry wood will release a little moisture slowly. This effect is why furniture might take months or years after being put into a real home before it warps. So ideally, I think this room can achieve 30% RH (I suppose this will be a good test of the insulation in that room, since outdoor RH is usually 50-90% here). With those numbers, I can achieve EMC of about 6%.

One thing to note is that cold air does not hold as much moisture as warm air. So at colder temperatures, EMC is reached at a much higher moisture content than warmer temperatures, given a constant RH. So attempting to dry wood in the winter outdoors would be even more difficult than in the summer time, on average.

Another thing to note is that RH is much more of a factor in a lower EMC than temperature. If you can adequately control RH to about 30%, then your lumber should adequately dry for furniture anywhere from 30F to 130F. A bonus would be controlling temperature as well but you should be careful with increasing temperature if you do not control RH. While higher temperatures means lower EMC, if you do not control RH, then you have a chance for fungal growth, which can happen anywhere after 50% RH.

So to summarize, your best bet is to control humidity in some fashion. If you can reach 30% humidity or lower, you should be able to adequately reach a moisture content adequate for furniture. To help speed things up, increasing temperature also helps but you should not try to dry wood by only controlling temperature, unless using high heat like in the case of kiln-drying.