Film-Tech Forum ARCHIVE: Humidity (RH%) in the projection booth

This is topic Humidity (RH%) in the projection booth in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Tom Bert (Member # 5719) on 05-24-2018, 02:08 AM:

Does anyone have data on what relative humidity (RH%) is typical/high/low inside a projection booth? Is it something that -advanced- NOC's monitor and collect?

Posted by Tanya Opilat (Member # 10129) on 05-27-2018, 03:42 AM:

Operating environment:
Temperature 10°C to 35°C (50°F to 95°F)
Humidity (non-condensing) 20% to 80%
Maximum ambient temperature 35°C
Non-operating environment:
Temperature -20°C to 60°C (-13°F to 149°F)
Humidity (non-condensing) 0% to 95%
That's from the User manual)

Posted by Marcel Birgelen (Member # 6801) on 05-27-2018, 12:38 PM:

I consider the modern booth to be more like a datacenter/computer equipment room than a traditional booth, essentially since most of them have become film-less and usually only see human beings if something goes wrong with the equipment. So, you should optimize the climate in such a room for your equipment and not so much for human beings.

So, a relative humidity between 40% and 60% should be your target. If you're hitting far below, you'll see a build-up of static electricity, which is bad for your equipment and anything on the high end can potentially cause condensation (especially on cold surfaces) and that's obviously also not good for the longevity of your equipment.

There are plenty of solutions out there that let you monitor room conditions using standard protocols like SNMP.

In my opinion, you should measure in the room itself, not so much inside an equipment rack. Even humidity sensors can get seriously out of whack if you place them near a hot air exhaust of some piece of equipment.

Posted by Tom Bert (Member # 5719) on 05-28-2018, 10:47 PM:

Looking beyond the user manuals and ideal situations, I am searching for realistic numbers/situations.

E.g. I've heard stories about HVAC being used in combination with exhaust, causing external -moist- air sneaking into be building via cracks and doors. Then you think you're aiming for dry air, but are actually running in a high RH%

Posted by Marcel Birgelen (Member # 6801) on 05-29-2018, 01:23 AM:

For rooms served by sufficiently sized HVAC systems, the 40-60% range should be pretty much attainable and it's indeed considered to be the optimum condition. It's still a pretty broad bandwidth and it's usually better to hit a bit above it than below.

If you're actively monitoring it, the 40-60% should be your "green zone", whereas 20-40% would be your "yellow zone" on the bottom side and 60-80% would be your "yellow zone" at the top. Anything outside that scope should raise an alarm, not just a warning.

It's pretty much a given fact that your electronics will usually last longer and will operate more reliable in an environment that has a RH > 40% and a RH below a sane level causing risk of condensation.

Condensation can also cause something like a feedback loop, increasing the RH even further. If you've got some cold ducts running through an otherwise warm room (which isn't unusual for booths) with high RH, you can easily spot the condensation building up alongside a cold water duct.

A constant high RH despite HVAC is a good indication of moisture creeping in somewhere. I've seen it happen with a small leak in a joint in some water duct above a false ceiling or due to leaks in the roof finding it's way in. Basements are notoriously hard to get right too, there is always some moisture finding its way in.
If the cause can't be remediated, separate dehumidification unit is a pretty good solution and they aren't really that expensive for smallish spaces. (Make sure you get professional units that dispose the water into a drain and not into a water tank!)

If your room is too dry, there are usually better solutions than to install humidifiers, unless you find yourself in a very dry climate: Some simple, automatically controlled direct ventilation will usually do the trick.

Posted by Randy Stankey (Member # 64) on 05-29-2018, 09:53 AM:

During storage and manufacture, electronic parts are supposed to be kept in an environment of LESS THAN 30% RH and 20ºC.

Humidity-sensitive chips are sealed in plastic bags with desiccant packs and humidity indicators. If the indicators show too much moisture, those parts must be baked @ 50ºC to 100ºC for 72 hours to get the moisture out.

If you don't get all the moisture out of those chips, they are likely to "popcorn" or burst as the moisture turns to steam in the reflow soldering ovens.

After the components are manufactured into completed circuit boards, they are, again, sealed inside plastic bags with desiccant before shipping to the customer.

Once the circuit boards are assembled into the finished product, the humidity ranges that Marcel and others have stated are the ones that apply.

Humidity, static and cleanliness are MUCH more important during manufacture than products in the field.

Posted by Tom Bert (Member # 5719) on 05-29-2018, 09:15 PM:

quote: Randy Stankey
Humidity, static and cleanliness are MUCH more important during manufacture than products in the field.

That is true for electronic components and their assembly onto modules.

The background of my question is more related to cooling and the temperatures you can/must bring components (cooling liquid, tubes, plates, heat exchangers,...) to. If you are below dewpoint, you get condensation. But where that dewpoint lies, depends on the ambient T° and RH%.

Posted by Marcel Birgelen (Member # 6801) on 05-30-2018, 01:12 AM:

The dew point even depends on barometric pressure to some extent. But if you want to calculate the dew point T(d) at a certain ambient temperature and RH percentage, you can use this on-line calculator. The guy also provides some formulas for Excel, so you can easily put in some numbers into your sheet and see where the T(d) is for your given circumstances (expected highs and lows on both ambient temperature and RH).

Posted by Adam Martin (Member # 641) on 05-30-2018, 09:47 AM:

Glancing through some Imax booth logs from 15 years ago when I was running 15/70 film, the readings for the projection room were typically 68-77 deg F and humidity was in the 45-65 percent range depending on the season in California.

This was a well-controlled environment with very particular film. These day's I can't imagine what the readings would be ... IF there was even any HVAC and IF it even worked.

Posted by Dave Macaulay (Member # 813) on 05-30-2018, 10:45 AM:

The multiplex booths I work in are generally "normal" indoor controlled temperature and humidity, some shut some of the HVAC off at night and the auditoria get stuffy but the booths seem to be still controlled.
The ones that had film projection mostly have humidifiers to help with static on the platters - the steam generator type. Either they've been turned off or the steam generator cells burnt out long ago, I have not seen one actually working in years. So RH gets quite low in winter, we have to be very careful with static sensitive stuff then.
Smaller cinemas with a few screens ... they get warmer and more humid in summer and cooler and drier in winter but not beyond habitable limits.