View Full Version : Humidity/Temp Control for two rooms

bob carnie
4-Aug-2009, 06:52
Hi Folks
The continuing darkroom saga continues for me, I have decided on the sound proofing and black out issues for my new darkroom and scanning room thanks to the wonderful advice on my last two threads. Now I am preparing for localizing humidity and temp.
As before your suggestions are really appreciated as it leads me to the right people in my area quickly.
I will have in the main space proper hvac system as well a 2500cfm*sp* exhaust unit on the roof that will be used to remove any fumes from the darkroom sink, as well service a dusty sawroom, and RA4processor.

The two rooms I want to concentrate on are the Darkroom and Scanning room.
As I plan to work in carbon and gum/platinum I need to be able to adjust temp and humidity with precision, as well the scanning room needs to be spotless.

The darkroom will be 800sqft with 14-16 ft ceiling.
The scan room will be 100sqft with 8ft ceiling.

I am hoping to keep my costs down , but need to do it right from the get go as we just signed a 5 year lease on our new space and I have no plans to retrofit after this year, but instead make prints.

I am looking for portable units first off that do both humidiy and temp control, off the bat I have heard of wine cellar units , which I know very little about.
I have in the past had a fuji system with controller in the room and compressor on the roof, and space is possible for this idea to happen again as the tubing can go through the roof inside the exhaust system ducting being installed by my landlord.*This option was very expensive the last time I did this*
It's been over 10 years since my last humidity temp controlled room was built and maybe the products for this are more numerous and cheaper
Any suggestions are very much appreciated.

I will do some before and after pics of the new lab to give those who responded to these threads and idea of the work in progress. I hope to be printing Sept 3 , and the darkroom is not built out yet.

4-Aug-2009, 07:47
I would contact a local HVAC contractor, and would not look at anything designed for darkrooms, wine cellars, or any other specialty use as they will be much more expensive.

Look at the heatpumps that Carrier and other companies make for Motel Rooms. These will cool in the summer and heat in the winter. Another option is just to make your rooms a seperate zone on your HVAC system but your system might not be able to do that without a major upgrade

4-Aug-2009, 08:06
I'd suggest a local HVAC contractor as well. I like the motel room heat pump idea.

I'd also add that the computer industry has small wheelable air conditioners for supplemental cooling in computer spaces. (big wiring closets) They have an exhaust duct which you could link up to your exhaust duct. Check Ebay for that sort of thing. What you need to control humidity is entirely dependent on your locale. Here on the coast of Maine, it never gets so dry that we have to humidify for instance, unless you use wood to heat. Simple air conditioning (or heat) will remove the right amount of moisture.

My own cooling needs are MUCH greater than a darkroom or small office. (small computer datacenter) We have dual split systems with fans on permanently, and I like that. We use 1-Wire sensors hooked to a computer to monitor and graph temp and humidity.

Bruce Watson
4-Aug-2009, 08:35
I would contact a local HVAC contractor, and would not look at anything designed for darkrooms, wine cellars, or any other specialty use as they will be much more expensive.

True. I'd look for a local HVAC guy who has commercial experience. Office buildings, museums, schools, hospitals, etc. Why? These guys will be used to larger heating/cooling loads, and active humidity control. The typical residence HVAC system has zero humidity control and most of the residential guys don't have the training to know how to size and install active humidity control. The resulting systems often seem like kludges, which isn't what you want. You want something functional, so go with someone who has experience making HVAC systems with active humidity control actually work well. Talk to the people using the systems to determine how well the guy (and it's nearly always a guy, sorry) knows his stuff. Experience is key IMHO.

Ed Richards
4-Aug-2009, 12:40
What is your climate?

bob carnie
4-Aug-2009, 13:34
Wet and Warm in the April till Oct
Cold and Dry Nov till March

Drew Wiley
4-Aug-2009, 16:25
Creating a cleanroom is straightforward. Enamel paint walls or fiberglass panels (everything washable and antistatic), real electronic air cleaner, microfiltered and deionized air lines, dacron cleanroom smocks, etc. Precise humidity control, on the
other hand, can be an expensive problem to engineer. No big deal conceptually, but
dehumidification and cooling simultaneously is going to cost you. I agree with the above posts - call pros in your area, and keep searching until you find someone who
understands just what you have in mind.

4-Aug-2009, 17:02

I'll just offer a re-quote of my recent Darkroom Portraits post over at APUG, assuming humidity control means only being able to remove moisture from the air:

"I ended up with the smallest available "split system" heat pump which serves only the DR. There is no air communication to the outside (no light leaks), as it recycles room air (I have separate outside fresh air by negative pressure exhaust). It is very efficient and effective for both heating and cooling as well as dehumidifying (really, cooling). I cannot recommend these systems highly enough. They are used widely throughout the world and are beginning to replace forced air systems in the U.S. The unit cost for small units sufficient for small rooms is not much more than a stand alone cooling or window-type unit (actually the same as better units, ~$200-$400). The extra cost (either judged to be worth it or necessary) is in the installation, where it pays to obtain someone with experience in split systems."

Although advised by the installer that rust might be a problem in the unit within my tight, sometimes humid space, I have seen no evidence of such and it has performed flawlessly for over 6 years. I have no financial interest in Soleus, Hitachi or actually ANYTHING anymore.

Ductless Split Type Room AC w/Heat Pump, which may be like your old Fuji:



Herb Cunningham
5-Aug-2009, 07:40
Ditto ROL-I have a Fuji "mini split", which is the wall mounted unit with the outside compressor. Very quiet. I got a couple of baffles from Calument that are light tight, and use an exhaust fan to pull air from the room where the unit is to the darkroom.

Humidity control to a few percentage points is really expensive. i did that work as an engineer many moons ago, but I think if you have enough cooling the moisture level will not be a problem. Ask Sandy King what kind of system his lab has.

If you can control outside air inflow and interior temperature, the humidity will be pretty low. I would suggest a cheap vaporizer if you need to add moisture, and a hygrometer will tell you what is going on.

Drew Wiley
5-Aug-2009, 09:11
You might want to check with carbon printers to see just how much humidity control
is essential. If you're thinking of working in color carbon, heaven help you! I looked at
the cost of all the heat pumps etc and what it would do to my utility bill and wisely
backed off. I also have a lot of procedures which require relatively stable humidity.
I get steady low humidity only in the Fall months, but that's also when I most like to travel! The rest of the time it's quite foggy here on the coast.

Donald Miller
5-Aug-2009, 10:01
Bob, I agree with what others have said. If your budget permits a HVAC contractor would help but since you mentioned portable units, I don't know that they would be particularly helpful past an advisory capacity.

Part of my business career was operating my business in which I dealt with commercial heating, cooling, and air quality conditioning albeit as a minor aspect of my business.

The first thing that you need to determine is what someone else has already mentioned...what humidity and temperature are you targeting for you process. The second thing is to determine somewhat accurately what the maximum departure of both temperature and humidity of your ambient conditions from your targeted values.

I agree that a heat pump would best serve your needs. Remember, however, that when you lower temperature that you are also dehumidifying the air and additionally the heat that is removed from the space must be released somewhere. Where do you foresee this being deposited. The moisture removed in the condensing effect must go somewhere and plans need to include means for this disposal. In designing for dehumidification not only must the ambient air be considered but also the moisture that you are adding via your darkroom process. Additionally, when determining the heat load of the space you wish to cool you need to consider not only the ambient air temperature but also any additional load of human bodies, and any equipment such as plate burners etc. As I recall your new space is actually enclosed within surrounding inhabited space so do you want to release this heat to this space or would it be best to release it to the outside surroundings? If the latter than utilizing a portable appliance becomes problematic since ductwork would be involved. The opposite effect occurs when you intend to heat the space because you are bringing heat from somewhere outside your room to inside the room. This would tend to reduce the air temp in the surrounding space and increase the load on your heating system for that space.

Ideally one would place the condensing unit (compressor/condensor/fan) outside any inhabited space. When this is done an air handling unit is placed in the space that you wish to heat/cool. However in your winters, I would imagine that your ambient falls below 35 degrees and for many heat pump systems this is a point at which they become marginally effective at removing heat from the ambient outside air...even though everything has heat down to absolute zero. This deficiency of being to able to extract heat from low ambient outside air temperature is usually compensated for by strip (resistive) heating installed in the air handler itself.

The dual approach heating/cooling--humidification/dehumidification complicates things because of the impingement of affect of the former on the latter.

The links below are a couple of sources for portable devices:



I realize that I have not given you any clear cut direction but I think that these are all things that must be considered.

Best regards,
Donald Miller

Nathan Potter
5-Aug-2009, 11:46
I would reiterate what Donald has said above. Temperature and humidity control can be quite complex. Not mentioned above, I think, is the need for particulate control. You should consider keeping the spaces relatively dust free. Electrostatic dust precipitators can do a good job and HEPA filters and even better job. Such units are placed in the incoming conditioned air stream. There are specs for particulate levels. My darkroom is designed for class 100 and it is fine for critical work. Maybe class 1000 would be OK for you. Maybe even class 10,000 but I think you'd be disappointed.

A driving principle should be to keep a positive pressure in your spaces to keep out outside air infiltration. Thus you ought to supply enough conditioned air to more than compensate for the air that is exhausted. Donald has mentioned a critical issue and that is the exposed wet baths in the space. They will dump humidity into the rooms and that will be a variable. Pretty complex stuff indeed! But ultimately such facilities are a series of compromises.

Nate Potter, Washington DC.

5-Aug-2009, 12:06
I've been a stringed instrument maker for over 30 years, this subject is very close to my wallet. One warning, if you use mist humidification, the water you use better be distilled or you will be breathing all the solids contained in the water you DO use. If your water is hard, you'll be hurt'n.... old fashioned fan driven wicked units are safe. I've found air cond to be less efficient in removing water from air beyond just cooling the air so it will hold less H20. Standard, and better yet, special highly efficient dehumidifiers have worked for me, my needs are year round 45 to 55%. Vapor barrier your space if you can.... Dehumidifying is very expen$ive, if you find a more "green" alternative please let me in on it.... Bill

bob carnie
5-Aug-2009, 13:18
Once again I really appreciate the help. I will be bringing in a couple of **experts** and I will print out all your posts and highlight concerns and observations.

Going tommorow at 9am to meet with the construction crew putting this all together. Once the walls are in I will bring in the air guy.

thanks again


bob carnie
5-Aug-2009, 13:21
I had a workshop with Mark Nelson and Sandy King a couple of years back and the need for humidity control was obvious.
As I do plan on working in carbon and gum , meeting specific humidity needs within a couple of hours and staying at this point is critical.

Bruce Watson
5-Aug-2009, 14:31
A driving principle should be to keep a positive pressure in your spaces to keep out outside air infiltration.

Just a thought here. If you want the place to *stay* clean, you'll want to maintain the positive pressure 24x7. You won't be able to turn it off over the weekend because you'll get leakage into the clean space. Creeping dirt.

I'm thinking about this because of scanning. I just took the top cover off my scanner today (first maintenance it's needed in five years) and when I went to replace the cover I found that the inside was dirty. And this dirt was hanging just a couple of cm above the drum while it was spinning. So... I cleaned it. Can't hurt, right? An hour later I was making some of the cleanest scans I've ever made with it. Just be a coincidence? Maybe not.

Just sayin' that dirt is an insidious and pervasive problem, especially for scanning. And at least scanning rooms are generally dry!