looking for humidistat control

hi everyone, I'm new in the business (just got my EPA type I and II licenses) and have a request from a customer for a manuscript storage area with a need for a humidistat control. temperature does not matter as it's year-round cool due to a high altitude but the area gets rain 5 days out of 7 and humidity control is difficult
as the documents are stored in an area with irregular electric service, we've already created a generator and solar (with inverters and battery banks) backup system which is instantly activated if there is a power loss.
I have a couple very promising mini-splits on hand which have the ability to run blower at very low speeds and the systems would be started in series (relays already installed) with a 5 min delay to minimize instant on power surge
the humidistat control I'm looking for would have to be a fairly simple piece of 24v controller, it can have the usual 5% accuracy but would have to have at least some of these capabilities
maximum 52% relative humidity with ability to turn off at a lower value or range no reheat system ability to set minimum and max for relative humidity
all the controls I've looked at so far have a range of 6 or 8% and don't have any adjustment capability when the new visionpro iaq became available I was hoping it would allow me a way to program only based on humidity range but it's also limited in this
the ideal control would monitor indoor humidity (not temperature) and turn on first system when 53% is detected but have the ability to shut down when humidity is dropped to 49-50%.
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There are systems that can control Relative Humidity's with in 3 or 4% with out any problems however you are looking at big bucks I work on systems that control temperature plus and minus 1/2 Deg. F. and like wise Relative Humidity's plus and minus 1%. for example 70 Deg. F. and 36% RH. Once you start to control RH the cost of instrumentation goes up quickly. I would suggest that you have talk to you customer If he want that type control let me know I will point you in right direction. Good luck from Dido www.cas-environ.com

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AKS wrote:

just checking to be sure you and I are writing about the same thing. I am *not* concerned over the accuracy of the RH measurement. what I *am* interested in is finding a control that will operate within a very narrow range. all of the plus $100 humidistats on the market have the ability to set value for RH within +/-1%. that *is not* what I am writing about.
when a humidistat opens 24v due to a humidity rise, it typically does not do it in a range of 1% despite the setpoint value. thus, the control may be programmed to 40% and it will not activate at 41% but will likely do so at 44% or 45%.
similarly it will not close the 24v at 39% but will likely do so at 36% to 37%
if you have a control in mind that can do better than this, please post a link
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Yes we are talking about same thing control I am talking about will turn on and off with in 1% and even with in less then that Proportional controllers will turn on and off in some cases with in plus and minus 1/10 of % but system is not cheap Dido

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