Managing temperature and humidity in my tropical sunroom/greenhouse

[cso]

Hey all, new to this forum and excited to get some insights and help! Thanks for your time I've recently moved home to the Bay Area in California and am bringing my tropical fruit obsession with me.

My home has a previously unused south-facing sunroom on the second floor that I am in the process of turning into a greenhouse. I have a bunch of plants on the way (finger lime, abiu, soursop, achachairu, moringa, bilimbi, vanilla, dragonfruit) but so far just have a few passionfruit cuttings, rescue orchids and seeds germinating in there. It's a small space, a bit over 100 sf, with electricity. I have a humidifier and small fan that are up to the task of keeping humidity and airflow at appropriate levels for tropicals. However, it gets HOT in there in the afternoon. It hit 107˚F in there yesterday before I opened the window, which brought the temperature back down to 85˚F, but the humidity then plunged to around 30%. This time of year the sun is low enough in the sky that the room gets flooded with direct sunlight basically all day, but summers are mild here (80˚F max) and only the plants right up against the windows will get direct light so I'm (potentially incorrectly!) less worried about the heat in there during the summer.

I'd love to hear what you think my best options are for managing the hottest & sunniest parts of the day without losing all that good humidity. I would like to use as little electricity and water as possible so would prefer physical options like curtains or a thermal mass (and don't have a good window for an A/C unit) but am open to any and all suggestions. Thanks so much!

[SaltwaterTx]

I’m considering setting up a small swimming pool in the greenhouse and cycling the water like you would an aquarium. You could use any container and any amount of water. Maybe add some type of small hardy fish + crawfish/crabs/etc, and adjust water pH to majority of your plants likings. Once cycled, can put on auto fill from rainwater catchment system or let city water sit a few days then add to big tank. It will keep humidity up and you would have a never ending stream of good water. Can get a cheap heat pump (small spa heater etc.) and it would assuredly keep the greenhouse temps up in winter. Would plumb just like a large swimming pool, drain lines to pump to filter/heater to return lines. Have to make sure drain intake is clean. Maybe a pre filter like guys use in ponds. Can also have all types of cool water plants and put drip irrigation or flood beds on timers or hand water as needed. Been wanting to implement this for years, going to do it this year.

[Lovetoplant]

SaltwaterTx I am struggling to control the RH inside my greenhouse too.  The RH is in low 20%s early afternoon when tempt are in the 90s-100°. At night fall RH will be in the 80s%. 
I set thermostat to turn on the exhaust fan when tempt inside the greenhouse reaches 90° , but the RH hardly change.  Any recommendation?  I did put a fountain inside the greenhouse along with overhead misting system (Arizona Mist) too

[K-Rimes]

SaltwaterTx I am struggling to control the RH inside my greenhouse too.  The RH is in low 20%s early afternoon when tempt are in the 90s-100°. At night fall RH will be in the 80s%. 
I set thermostat to turn on the exhaust fan when tempt inside the greenhouse reaches 90° , but the RH hardly change.  Any recommendation?

Just like me up the pass on the 154, identical conditions. I don't bother with humidity values that much anymore, I used to try all kinds of things to keep RH up and had little success, even soaking every single plant and the floor doesn't do much.

[Lovetoplant]

Does the inside of your GH reach 100* now too?

[K-Rimes]

Does the inside of your GH reach 100* now too?

It hits and holds 90f or whatever I set the fans too. The fans are so strong it sucks the walls in and I am sure is replenishing the air with ambient rapidly. I put 50% shade cloth over top once it starts hitting 90f ambient, so around April or May.