View Full Version : Humidity

06-10-2002, 04:09 PM
We were called out by one of our customers last week to look at an ongoing problem with low humidity levels within one of the rooms within the factory area.

The customer makes kitchen cabinets among other things and applies some type of pvc film to the cupboard doors.
Anyway, the problem is that the room, (within the factory) has an average humidity level of 38%RH and as the "film" is drawn off the roll ready for the machine to bond it onto the product or door in this case, static electricity is causing all sorts of dust particles to be attracted to the film and a high rate of failures/waste is being produced.

The room is supplied with 4.25m3/s of air via an AHU (bag filter, panel filter and fan section) discharged into the room via a ceiling mounted discharge plenun and final filters. Extract is discharged directly to atmosphere. The room is held at 10% positive pressure to eliminate factory contamination.

During the summer months the air input is taken from outside and during colder months the air is taken from the factory area. All this is achieved by manual switching and motorised dampers.

The factory operates 16 hours a day and at present there is no means of controlling temperature or humidity.

As static is eliminated above about 45%RH and human comfort is around 50%RH has anyone got any ideas how to solve this problem before I tell you what sort of scheme we have put forward (and won the job!).
Come on, get those brain cells working!


P.S. Bear in mind the energy input costs!

07-10-2002, 04:27 AM
Are you saying there is no heating or A/C system? Just bringing in makeup air? If that is the case, then we must assume that the outdoor air averages 38% RH (or less).

07-10-2002, 05:11 AM
Does the ahu serve other rooms?

In clean room application, many systems have secondary air return. Increase primary air return, decrease secondary. and maintain room temperature, would help for raising RH.

07-10-2002, 05:45 PM
That's right Gary - no heating or A/C on the AHU, just panel filters, bag filter and fan section.

The low humidity is being caused mainly by the product in the factory which is MDF board.


07-10-2002, 05:46 PM
Hi Lin
No the AHU only serves the Press area which is an enclosed room within the factory


07-10-2002, 06:06 PM
You could try going to 24 hour operation in hopes that the product would be less thirsty during the day (having absorbed some moisture during the night) and the room would be precooled (which raises humidity).

You could also increase the airflow, since presumably the outdoor air is more humid than the indoor air.

However, during the winter, you may still have problems, because the outdoor dewpoint will be lower.

07-10-2002, 11:29 PM
I worked in a bindery which had a similar problem. We installed a centrifugal diisk humudifier and achieved good results. I would think a humidifier of some sort would be the cheapest way to go.

But I suppose that is too straightforward a solution.:)

08-10-2002, 08:18 AM
Hi, Frank:)
what about an electrode boiler. In label rooms(paper labels) that I have worked on in the past have been fitted with IMI Calder units, these units are a complete split system with a cooling coil(never comes on) a heater battery and a electrode boiler.
These seem to work well, dependant on the solids in the water, with the boiler cube requiring changing once a year aprox.

Hope this helps.
Regards. Andy.

09-10-2002, 06:56 PM
Thats a good choice Andy but to generate the amount of moisture we need for this room the energy input to the boiler (electrical) works out in excess of 90kw!

You are on the right track - the only way to cure the low humidity in the room is to introduce moisture. Any thoughts on how else it can be achieved?


09-10-2002, 07:21 PM
Hi, Frank:)
now that's what I can an electrode bolier. I take it that you must be using something like a number of those atomiser type spray water humidifiers I see advertised in the trade magazines, carel makes some I think.
Regards. Andy.

10-10-2002, 03:58 AM
Hi, Frank, Marc O'Brien wrote me a hello on a private message and besides telling me hello, wondered if you opted for an evaporitive cooler, which seems like a good idea that would address both comfort and humidity in favorable fashion.

I give up. Not enough information for me.

I still think that direct humidification would be the best way to go, but somehow I think you went another way for reasons I don't feel privy to.:)

10-10-2002, 06:11 PM
I would say you want a cool humidifier such as swamp cooler plus a steam generator. that would cover heating and cooling needs. You could run both at the same time too.
That is simalar to what we did in a cotton lab. Dust was a big factor there as well. The swamp cooler had outside or inside air option.

12-10-2002, 11:12 AM
Yes Dan, Mark is right (as usual):D

From the pshycrometric chart we could see that a large amount of moisture was required to raise the humidity level up above 50%. The customer requested that we achieve 60% so here's what we have designed.

As there isn't any heating or cooling on the system at present we have addressed this as well.

First, we are installing a 3 stage DX coil into the air handler together with an 18kw electric heater battery to give us flexibility. The air cooled condensing units will work as heat pumps to raise the air within the air handler up to 34deg C. This will be delivered onto an adiabatic humidifier which will raise the RH to 50% but lower the air temperature down to 21deg C. This method of providing the base load is more energy efficient than direct fired steam due to the C.O.P. of the heat pumps.

To achieve the 60%RH target we are then using a small steam humidifier to inject into the air stream just before the air is delivered into the room.

To control it all our controls guy has written some software for a Trend digital controller which will modulate the fresh air/ factory air dampers, the dx circuits, electric heater (thyristor controlled for use when a full stage of dx isn't required) the base load humidifier and the top up humidifier.

The adiabatic humidifier is rated at 146kg/hr and the steam humidifier is rated at 35kg/hr. We have a total of 75kw of dx cooling which will give nearer 90kw of heating. We are also looking at diverting the rejected air from the condensing units (evaporators) into the factory area during the summer months giving 75kw of "free" cooling.

The adiabatic humidifier can operate between 15% to 100% output via a 0-10v dc input.

I'll let you know how the job turns out - we should be ready for commissioning in about 5 weeks from now.


14-10-2002, 01:24 PM
That area really interests me as well Mark but when I see him making all those notes after asking how I want the system controlled and all those flow charts and decision boxes - well - it sure looks complicated!


31-10-2002, 03:53 AM
Here we would use a natural gas fired Nortec or Drysteem Humidifer to save energy and maintain production humidity levels.

29-11-2002, 09:01 PM
Well guys we are due on site on Tuesday for the installation so I will keep you posted with the odd picture as well

06-12-2002, 08:35 PM
As promised here are a couple of pictures showing the existing ductwork being modified. Look for the size of the fitter standing next to the unit - he is really dwarfed!

More to follow next week


Sorry = 1 of the photo's was too big to upload

08-12-2002, 03:21 PM
Here's the other photo - reduced in size

Frank :)

30-12-2002, 04:59 PM
I have been having trouble attaching photo's to the thread because of the file sizes, so I have just uploaded some more onto this address - hope it works!

Frank :eek:

30-12-2002, 07:53 PM
Hi, Frank:)
give us the members name/ password and we'll all have a nosey
Regards. Andy

30-12-2002, 08:06 PM
Sorry Andy - it works from my end :D

Try this http://www.picturetrail.com/frank17