Honestly I find the more I remove myself from the care of my plants the better they do. I've tried so many things like humidifiers, heaters, grow lights, I even bought a misting system for amphibians and built a glass case for some plants. It all got to time consuming and costly to keep up so finally just went with the room at its normal light, temperature and humidity. I devote one morning a week which is Sunday from 6AM to 9AM to watering, if I have time I water a few plants again on Wednesday. I use a pump sprayer to water so I can control the water flow. I like to spray a small amount of water over a longer period of time instead of dumping water into the pot and having it spill right out the bottom. I feel this gives more time to let the roots soak up water. For plants in standard pots I will even put my finger over the drainage hole for a minute to be sure everything is saturated. MOunted plants and plants in baskets I will soak in a bucket of water for 5 minutes or so. You have to change the water between plants to prevent spreading bugs or disease. I use the waste water for my dirt plants. For plants that don't like to be dry I use semi hydroponic pots with hydroton as a media, I also have switched some plants to hydroton as the media in regular pots. Sometimes its hard to find good potting bark, I find a lot of places store their potting media outside where it gets wet and breaks down so if the bag isn't clear I don't buy it. As for suggestions on fragrant plants I like Zygopetalums are great, the scent can fill the room. I like the BLC Tangs and LC love knot are good because the bloom a few times a year. Brassavola Nodosa and Angracums are nice because they are fragrant at night. Check out the Oakhill gardens site. They have a list of fragrant plants , I also see they have a Angracum Sesquipedale in seedling size. Good luck

I have three thermostats and the have been in place for about 5 years. Two are the inaccurate springy type and the third is a very generic programmable that came with the Southern Burner heater. While the springy thermostats may not be accurate, they are consistent. Once set, they trigger at the same temperature every time. Besides the thermostats, I have 5 thermometers scattered around, one of which reads remotely inside the house. I set them side by side initially to be sure that they were all on the same page. In the greenhouse they read quite a range of temperatures. I have pretty good air movement and still have many micro-climates which is good for me given the range of plants I have. I have them sheltered from light and water but otherwise open to the air. The only one that is "accurate" is the remote one, and it is only accurate for the spot it is mounted in, not the greenhouse as a whole. If your battery is running down, there may be a problem with the way it is hooked up. I would expect a year or two minimum for those batteries.

Hmmm. I'm with the others who know that spider mites can thrive in very humid conditions. Misting (why mist in a humid greenhouse?) simply moves them around. Insecticidal soaps can be helpful, and I do like cold-pressed Neem oil. It is not a broad spectrum killer, and is not even likely to kill the mites outright, but works as an anti-feedant and acts as a growth regulator as well. Thus, the mite (or whitefly) feeding will decrease even though the pests are still visible. Over time, you will see the population die down. If you are interested in trying the neem oil, but sure to purchase a product that clearly states that it is cold-pressed. Some manufacturing processes can remove or greatly reduce the active ingredient in Neem, Azadirachtin. Read the labels of any product that you use to make sure that greenhouse applications are appropriate.

Without power you'll need to admit more solar radiation in order to raise the temperature. That means a conversion of the roof or south side to something that transmits solar radiation. You might want to consider double or triple wall polycarbonate or similar. There are other possiblities like a compost pile inside but not a good plan in most cases. You need light along with the heat.