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Hi Guys,
I have a small shop that and I'm looking into climate control. It's only 8'X16', looking at expanding to 8'X22'.
My question is, would a small AC unit be enough to control humidity? And if so, would you run it 24/7? I'm in Southern California, humidity is not extreme here most of the year.
Any suggestions in humidity control for a small space like this would be greatly appreciated! What do you have, likes, dislikes?
Thanks!

I have a corner of my shop closed in and it's 8x16'. A 5000 btu window unit with me in there will keep it at or near 50% during the day. At night I usually turn it off and let the the dehumidifier take over since I don't need it to be all that cool. I'm on the Texas Gulf coast, so it's plenty humid here.

My shop here in the mountains of North Carolina is a little bigger than yours, but still pretty small. We live in the middle of what is basically a rain forest, with generally cool temperatures and very high humidity. It's not usually warm enough up here to need an air conditioner (though that's been changing over the past few years), but when I do run a small window unit, it dehumidifies the shop fine.

In the summer, I run a small dehumidifier full time and it keeps the shop between 45 and 50% RH at about 70 degrees. In the winter, I have to run a small humidifier to keep RH in the same range.

Dave

How much dehumidification you need is entirely dependent on the building. A concrete slab puts more moisture in. Open windows or a leaky building put more moisture in. A humid climate puts more moisture in. Volume has nothing to do with it.

And you always want the smallest air conditioning unit that works because the dehumidification only happens when it is running. Too big a unit, it will short cycle on and off and not be on long enough to get the humidity starting to condense on the coils, and will turn off so any moisture on the coils will evaporate back into the building. You would like a unit to run 100% of the time on the hottest days of the year, that way you get maximum dehumidification out of it. And by the way, that is the lowest cost for purchase of the unit and operation too.

And Dave has the worst case for summer - lots of humidity and too cool to air condition.

Ed

You might want to look into a mini-split. Some of them help control humidity.

It also depends how much of the time you work in the shop and need precise RH control. If you are a professional builder and are doing RH critical operations like gluing bracing every day, then you need to invest in something robust. If, like me, you make 1 or 2 instruments a year and can delay a step for a few days until the weather is dry - then you need less airconditioning hardware. Maybe a small dehumidifier will meet your needs. Mine was less than $100 on E-bay and gets me by. But I would install a split system if my livelihood depended on it.

My RH room is about 10x12’. I have a London Drugs room humidifier with built in sensor to turn itself on and off. It sits on a Kenmore 30 pint dehumidifier. They battle each other and generally stalemate at 40%...

Anytime RH control comes up, it is worthwhile to mention that measuring it accurately is fundamental to controlling it, and measuring it accurately is not as easy as we would like. Many hygrometers are just not up to the task of measuring RH accurately in the range we care about. It is a good idea to make sure your hygrometers are giving you accurate readings before you do anything about controlling RH.

I live in a part of the country where RH control is pretty darn important, and somewhat demanding. It is insanely humid for over half the year, and super dry inside the heated home for about a fourth of the year. There is about a fourth of the year (some spring and some fall) where I could work on guitars without RH control. So Cal is very different from what I deal with, though.

The hourly humidity will vary greatly through out the day. I have read that Torres braced his guitars at night when the conditions were right. There may be some "golden hours" during the day that will allow the wood to acclimate and gluing to be done without supplemental humidity control.

Depends where in So Cal you live. I've lived in San Diego where there might be a moderate need for humidity control and have also lived in the high desert where the relative humidity rarely gets above 20%. First you need to understand how relative humidity varies in your area (maybe you do already) so you will know exactly how much control you need to implement. Then you can look for solutions.

_________________
Steve Smith
"Music is what feelings sound like"

This is all great info. Thanks guys!
I should have mentioned that my shop is a stand alone shed that has insulation and drywall. I'm about 12 miles from the coast, very close to San Diego weather. Not at all extreme.
Right now, building is purely a hobby. I build for myself. Some interest in my work has gotten me to think about taking the next small, very small step out of just building for myself. By no means, or even close to being a professional luthier, but build for friends and family.
I know that if I want to take that step, RH control is a must even though the weather in my area is acceptable a good part of the year.
Thanks again for everyone's input. Always great to learn from other's experience.
-Raúl

As Ruby50 said, it's' more about controlling the moisture that gets in than getting rid of it once it does. As with maintaining a 'good' weight, it's easier in some ways to eat less than to work it off afterward.

Concrete is transparent to humidity. A concrete slab on the ground will allow moisture in, and basement workshops can be impossible to keep dry. To be effective over the long run moisture barriers on cement/concrete have to go on the outside. If you're building new that's not too hard, but on existing construction it can be a nightmare. DAMHIKT.

Having had one bad experience with humidity control I was careful to make a tight vapor barrier when I set up my current shop. As a result I can keep things pretty well under control without to much effort. I've got about 800 sq ft of shop space, and keep the R.H. in the 40% range with just a room dehumidifier in the summer. The shop is a space within a larger barn,and the outer envelope helps moderate temperature changes, so the dehumidifier doesn't warm the shop up too much. I have more trouble keeping the humidity up in the winter, but a couple of small humidifiers and a kettle on the wood stove work out most of the time.

I got in a mini-split last year. It works great as a heater in the 'shoulder seasons', which was what I got it for. I have not needed it this summer as an A/C much. The dehumidfication setting works on the A/C mode, and tends to cool the shop, but in this case that's not the combination I want. The standard dehumidifier warms it up, and that's been fine most of the time, although I have run the A/C once or twice.

None of this would work out well if it were not for the tight vapor barrier though.

My solution has been to line a closet with plastic sheeting and put a foam seal around the door and use a portable dehumidifier to dry the air within that small space. It allows me to condition the parts and cure the glue in humidity controlled conditions. It reduces energy costs over trying to control a "leaky" shop environment.

I’ve posted about my RH-controlled wood storage and assembly room before. An 11x14 room shared by the home’s mechanical stuff. It has a floor drain, which is handy for a dehumidifier. I have a simple dehum as well as an evaporative humidifier connected to a joint electronic controller I fabricated using an industrial humidity/temperature controller. The unit is programmable and can be calibrated. Only one piece of gear can operate at a given time (so they don’t fight each other). They key is to have humidifier and dehum without any controls and the ability to simply resume operation full blast when powered up. With the controller, the equipment operation is optimised. If the room is between 42 and 44%, nothing is running.


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The weather here on the west coast is sure different from the eastern US and Canada. From Mediterranean climate here in CA to the rain forests in WA & BC.
I get 10% to 40% outside RH from May to October here in the Sierra foothills and it can be 70% to 100% in the winter and electric charges are high for the tools to control it.
For the amateur builder RH control can be high. So with evaporative coolers in the summer and wood stove in the winter it can be an interesting dance.
So far nothing has cracked or broken.
Oh, except from a guitar I got from Vietnam, neck way backbowed and B&S cracked several places. I guess it was a lot drier here.

WOW That's a great setup!
Is it easy to make? Do you sell the electronic controller? I'm very interested in something like this for my shop.

Mine was built 10 years ago, when I lived in NZ. A kiwi HVAC engineer was somewhat bored and helped to identify an appropriate 1/8 DIN format PID controller and remote humidity sensor. I wired the controller into a project box with a transformer stepping down to 12v, and fed in cables for power, humidifier, dehumidifier and sensor. The controller has contacts with a high enough rating to manage the switching load without relays. The programming instructions were a bit obscure — and I’m screwed if I ever lose them — especially for the calibration adjustment. The only modification made since was the change to 120VAC when I returned to Canada (changed transformer).
No, I don’t offer to make them. I don’t think my PID controller (by LAE of Italy) is made anymore (one reason I got it cheap), but I’m sure companies like Auber or Honeywell got help identify suitable parts.

A split photo shows the innards (and controller spec) and the external display.



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Found photos of my controller and wall-mounted humidity sensor in service. The HT2W sensor is still sold, but LAE has a newer line of controllers. Don’t think you’ll find LAE products in North America, but showing this to Auber Instruments or Honeywell would communicate what you want to build.




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That’s awesome! In my part of the world, though, it would not be needed, because we don’t have wild swings in RH from super wet to super dry. I have the dehumidifier running half the year, with its own controls, and the humidifier running a fourth of the year, with its own controls. The few weeks in the fall and spring when I need little of either one tend toward one or the other. They are manageable as separate systems. But your setup is very cool. If it were easily obtained, I might want to look into it, just to reduce my own monitoring time.

The first thing I did when converting a 2 car garage to my shop was to acid-clean the concrete floor and coat it with an epoxy paint. I am sure that it is not as effective as a real vapor barrier, but it definitely helps.

During certain times of the year (what Al calls the "shoulder seasons") I regulate the humidity level of the closet using a heater - just as heating the house in the winter lowers the R.H. , heating the closet in the shop can also lower the humidity. To do this I bought a humidistat from Honeywell off of ebay. When the humidity is too high it turns on the portable oil filled heater to lower it. Internally I found some leads that could also be used to turn on a humidifier when the humidity went too low, but I've never tried hooking up both at the same time. During times when I need heat in the closet constantly (winter temperatures too cold for glue to cure properly) I would only need the humidifier to run, so I swapped the leads to make that happen. Buying two humidistats and rewiring one to turn on a humidifier might allow you to regulate the humidity with either heat or humidification and be less trouble than swapping leads as I have done.
Still in some areas it is possible to keep a "weather eye" and only do critical glueups when conditions are right. If you happen to live in El Cajon, California area the humidity is predicted to be in a good range from 10am to 7pm today, and from 10 am to 7pm tomorrow.
https://forecast.weather.gov/MapClick.p ... =graphical
On the other hand in San Diego the humidity levels are not as low either day:
https://forecast.weather.gov/MapClick.p ... =graphical
Again, these are predictions, so they don't take the place of the hygrometer in your shop, but they do allow you to have an idea when you may be able to work without humidity modification. (I wonder if the links will update as time goes by?)For your own weather predictions and hourly humidity charts this site is useful:
https://www.weather.gov/

I started down the humidity control path in New Zealand, where humidification was never needed. I tried using controls on household dehumidifiers to set 42-44% for gluing braces, etc., but the best I could do was between 35 and 50%. That seemed rather a broad range (although probably ideal for wood seasoning). Plugging the unit into a home humidistat from a big box store was no better. That’s why I sat down with my bored HVAC engineer friend and presented my problem.

When I came back to Canada, I needed to consider humidification as well, often in the same week. My controller has a second output, so that was easy. Control is 24/7 without any monitoring by me, and RH during brace glue up is always 42-44%.


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