I want it cold but I don't want it ALL cold - Design Issues.........................................
I want it cold but I don't want it ALL cold - Design Issues.........................................
(OP)
hi, i'm starting this thread because I'm in a design dilemma and also for others who face similar design issues.
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Just let me get excerpts from my report up here:
REPORT BRIEF
The site visit was incepted to conduct an inspection following a reported fault in an air-conditioning system. The operation of three air-conditioners (2 x 50% duty) has resulted in water condensate forming on the ceiling surfaces, which if not resolved will result in damage of equipment....
Main Air-conditioning Issue
The operation of three air-conditioners (2 x 50% duty) has resulted in water condensate forming below and above the ceilings for each of the two rooms. The severity of the condensation issue was greater in the ATC Room.
To date, equipments in the ATC Room are operating at a required controlled temperature of 22°C. the Contractor has reported that when the room’s temperature reading was 24°C, the ATC equipment began to overheat.
Certain attempts have been made by the Contractor's staff to manage and mitigate the prevailing condensation issue:
a) Thickness of condensate pipe insulation was increased, which did little to improve the situation. Drops of condensate water still formed on the insulation’s outer surface.
b) Turning off of one duty air-conditioner, which resulted in equipment overheat.
c) Placing ply-wood planks above the “roof-less” electronic equipment to prevent drips of condensate water from entering the equipment, as a temporary solution.
Other Information:
1. The ceiling panels (possibly asbestos) rested on metal (possibly galvanized iron) frames. Condensation occurred on the surfaces of these frames. Subsequently, the edges of the ceiling panels were damaged and more importantly, water condensate on these surfaces dripped onto the ATC equipment. The lower-roof directly above the M&E Services and ceiling panels were made from a ‘special’ fire-fighting composite described by the fire dept which consists of ply-wood and polymeric material:
2. The compressor units for all 6 units were isolated in a well ventilated room on the lower roofs, and it is assumed that the source of water dripping was indeed condensation and not leakage due to equipment defect.
3. Even the bolts which held the ceiling-exposed air-con units to the ceiling had condensate forming on them.
4. Layout of ATC Room:
'Special fire-fighting material'
---------------------------------------------
M&E services area (i think around 29 degrees C)
---------------------------------------------
Ceiling panels
---------------------------------------------
ATC Room, Temp = {18,22} degrees C. dimensions: 10m x 7.5m x 3m.
---------------------------------------------
5. Equip Spec:
ATC Room: 3 ceiling exposed units (2 duty 1 standby) of ACSON A5CM 62C, capacity 55,000 btu/hr (6.41kW)
Central Control Room: 3 ceiling exposed units (2 duty 1 standby) of ACSON A5CM 50D, capacity 43,000 btu/hr (4.70kW)
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Question:
As i described the scenario above,
The room MUST be kept cold (22 degrees and below) but if it's too cold, condensation forms on the ceilings and end up damaging the equipment anyway. That's the dilemma.
What would be a feasible solution which is still relatively economical? Localising the cooling area? Setting up an exhaust fan in the M&E Services space to convect air in/out?
Thanks.
____________________________________________________________________________________________________________________________
Just let me get excerpts from my report up here:
REPORT BRIEF
The site visit was incepted to conduct an inspection following a reported fault in an air-conditioning system. The operation of three air-conditioners (2 x 50% duty) has resulted in water condensate forming on the ceiling surfaces, which if not resolved will result in damage of equipment....
Main Air-conditioning Issue
The operation of three air-conditioners (2 x 50% duty) has resulted in water condensate forming below and above the ceilings for each of the two rooms. The severity of the condensation issue was greater in the ATC Room.
To date, equipments in the ATC Room are operating at a required controlled temperature of 22°C. the Contractor has reported that when the room’s temperature reading was 24°C, the ATC equipment began to overheat.
Certain attempts have been made by the Contractor's staff to manage and mitigate the prevailing condensation issue:
a) Thickness of condensate pipe insulation was increased, which did little to improve the situation. Drops of condensate water still formed on the insulation’s outer surface.
b) Turning off of one duty air-conditioner, which resulted in equipment overheat.
c) Placing ply-wood planks above the “roof-less” electronic equipment to prevent drips of condensate water from entering the equipment, as a temporary solution.
Other Information:
1. The ceiling panels (possibly asbestos) rested on metal (possibly galvanized iron) frames. Condensation occurred on the surfaces of these frames. Subsequently, the edges of the ceiling panels were damaged and more importantly, water condensate on these surfaces dripped onto the ATC equipment. The lower-roof directly above the M&E Services and ceiling panels were made from a ‘special’ fire-fighting composite described by the fire dept which consists of ply-wood and polymeric material:
2. The compressor units for all 6 units were isolated in a well ventilated room on the lower roofs, and it is assumed that the source of water dripping was indeed condensation and not leakage due to equipment defect.
3. Even the bolts which held the ceiling-exposed air-con units to the ceiling had condensate forming on them.
4. Layout of ATC Room:
'Special fire-fighting material'
---------------------------------------------
M&E services area (i think around 29 degrees C)
---------------------------------------------
Ceiling panels
---------------------------------------------
ATC Room, Temp = {18,22} degrees C. dimensions: 10m x 7.5m x 3m.
---------------------------------------------
5. Equip Spec:
ATC Room: 3 ceiling exposed units (2 duty 1 standby) of ACSON A5CM 62C, capacity 55,000 btu/hr (6.41kW)
Central Control Room: 3 ceiling exposed units (2 duty 1 standby) of ACSON A5CM 50D, capacity 43,000 btu/hr (4.70kW)
____________________________________________________________________________________________________________________________
Question:
As i described the scenario above,
The room MUST be kept cold (22 degrees and below) but if it's too cold, condensation forms on the ceilings and end up damaging the equipment anyway. That's the dilemma.
What would be a feasible solution which is still relatively economical? Localising the cooling area? Setting up an exhaust fan in the M&E Services space to convect air in/out?
Thanks.





RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
You've told us nothing about the air dew-point or the temperature of the surfaces that condensate forms on.
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
however, was the scenario a clearly painted one? Would using a dehumidifier help if say, the relative humidity was already 100% (i mean condensation is already happening, yes?)
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
It is possible that cold supply air flow from the units are directed towards metal structures taking it down below the dewpoint.
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
Sak9's guess is a good guess, but considering the lack of information it's only a guess. Same guess that I would make.
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
http://www.eng-tips.com/viewthread.cfm?qid=334316
Best to you,
Goober Dave
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RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
if it originates on upper surface, ventilation of ceiling space might be solution. it is not impossible that ceiling area reaches over 90% RH.
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
The jobs were in Singapore and Hawaii. Infiltration happens.
Best to you,
Goober Dave
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RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
you should seemingly know more about vapor diffusion. "basic engineering logic" is to not make statements, at least not firm statements, if you are not informed enough.
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
Normally, air coming out of the evaporator is dehumidified and will not condense water out onto anything, but if it is mixed with outside air that is hot and humid, then it may be circulating already close to its dew point.
It is also curious that metal parts associated with the evaporator units are dripping. It means those parts are not insulated well enough from the evaporators and are cold by conduction. Note that the bottom panels on a unit may have thermal insulation inside that is wet. What can help is to replace it with insulation sealed in plastic film (bags might do).
Other than these questions, a solution can be simply much better thermal insulation of everything connected with the evaporators.
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
the problem lays in practical fact that vapor seals always have some cracks, somewhere, and, on the other hand vapor pressure mechanisms always create negative pressure differentials in such places, and the outcome is that vapor is gradually entering through cracks, raising humidity indefinitely.
when air flow is allowed, such scheme is prevented as air is allowed to come in and go out. such a space should not be ventilated to the outside directly, but linked via openings with rooms at appropriate places, like restrooms or similar.
that way the problem will at least be "spread" over the whole space, and if too high dew point temperature is overall problem, it needs to be handled via AHU or space dehumidifiers.
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
or deal with the space above the tiles as an attic and ventilate it as they ventilate attic in houses or use HRV if possible.
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
what information i can provide now however:
1. yes the entire room is situated in a humid environment. DRWeig, it's located in Malaysia, neighbour to Singapore and the climate is the same. It could be that infiltration happens, will keep an eye out for that. The ATC room is sealed off from the outside humid air (except for space under entrances).
2. 140Airpower - kinemenematics, you do not state clearly if the 22C room air is condensing or if ceiling space air is condensing. It logically seems the latter. Is the ceiling space vented to the outside? If so that is a big problem. It is an endless source of moist air. If it is room air that is condensing, is the room air re-humidified or is AC air mixed with outside air?
Both the 22C room air and ceiling space air is condensing. In the 22C room (realistically around 18C), the AC units have condensate forming on its surface, and is as well causing the metal ceiling frames to become cold. In the ceiling space, i do not know if air is condensing on the upper surface of the metal frames, but it definitely is condensing on the copper pipe insulation (even after its thickness has been increased). I will double-check if that ceiling space is exposed to outside air. It didn't seem so.
3. SAK9 - the cold air has been directed away from the ceilings (albeit the AC unit themselves touching the suspended ceilings) and onto the area that requires cooling. This local area which requires cooling contains metal surfaces and equipment all over, but no condensate seems to forming on them (i think cause the equipment consistently generates heat) My guess is that the the metal ceiling frames are also losing heat through conduction.
Thank you all for trying to address the issue, with the lack of pertinent information i provide.
Cheers
ATTACHMENTS:
1. the 'area' that requires cooling. http://files.engineering.com/getfile.aspx?folder=7...
2. copper pipe insulation in ceiling space http://files.engineering.com/getfile.aspx?folder=7...
3. could the condensers have anything to do with it? Installation clearance, clog, etc. http://files.engineering.com/getfile.aspx?folder=c...
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
1.Infiltration:There is no ventilation air whcih means the space is not pressurised.This leaves the door open for infiltration of humid outside air at 80% RH levels.If the equipment room is located in the core area of the building surrounded by conditioned spaces,this may not be an issue.If not there will be infiltration due to stack effect as well as temperature difference. Since the internal temperature is around 18C,the infiltration can be higher than normal.Sealing of doors and windows is definitely required.There will be infiltration through the lay in ceiling tiles as well which will not be easy to stop.It is not clear if the ceiling is insulated.Ideally the space needs to be pressurised with dehumidified air as perfect sealing is difficult to achieve
2.Equipment load variation:If the internal temepraure is set to 18C,the supply air temperature is likely to be around 10C.If the equipment load is variable,there may not be enough sensible load in the room at times and this could result in high humidity and condensation build up.Compensating heaters is one easy solution.
A data log of temperature and RH with in the space and outside for a few days as well as power draw of equipment will give a better understanding of the issues.If the equipment can be made to function at higher temperatures,that would be the cheapest and easiest solution.
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
1.
Infiltration would likely be the case. Two rooms have this condensation issue; the room with a greater exposed surface area to the external environment is experiencing more severe condensation. A dehumidifier would still be ideal yes? I need to recommend an economical solution too.
2.
by a variable heat load, you mean a constantly changing heat output from the equipment that needs to be cooled? Could you describe what a compensating heater is? I'm on Google but i can't get much info.
If the equipment can be made to function at higher temperatures, that would be the cheapest and easiest solution.
- Would the equip not overheat? The whole idea of AC in the first place was to cool the equipment in the room.
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
So my view is that the need for such a low temperature for equipment room needs to be questioned before doing any modifications.If you were to operate it say 25C,there would not be any condensation.Most equipment rooms such as data centres,telecom exchanges etc operate in a high temperature band of 25~28C.
Equipment heat rejection may not remain constant in many cases.If it varies a lot, it is not uncommon to provde electric reheaters that will come on during periods of low load to keep the room within an acceptable humidity range.
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
1. I've yet to be informed if the AC is currently taking in fresh air from the outside. If that's the case, the AC can be set to re-circulate. Can any work be done at the condenser area to improve the situation?
2. Anyway, I'm thinking of recommending a dehumidifer + reheater as a practical solution. At this point the owners are parsimonious and the AC themselves are inverter-types. As such i think they would agree to that rather than doing major renovation works. Besides the equipment needs to work 24-7. What do you think?
Do correct me if i'm wrong,
Thanks Sak9, and everyone
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
Firstly, if you already have cooling equipment in the space then you already have the ability to dehumidify.
Secondly, adding a dehumidifier and reheat increases the owners operating and maintenance costs forever. An irresponsible solution.
The first step to solving any problem is the understand the problem, and you don't understand what the problem is yet.
So far we all appear to be assuming that this is a room full of electronic equipment. To me "ATC" means "Automatic Train Control", but it could also mean "Air Traffic Control", "All Terrain Cycle" or any of a hundred other things.
If it is an electronic equipment room then it really doesn't need much outside air does it? So if the system is bringing in outside air, why? If you have a leaky building, seal the leaks.
How is the cooling being controlled? Having inverters allows good load matching, but doesn't mean that the controls were done correctly in the first place.
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
Temperature is sensed via thermometers on a wall, not via thermocouples on the equipment itself, processed in a DCS, and actuated by three ACs. So what do you mena by a 'correctly done control?'
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
Best to you,
Goober Dave
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RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
Of course, i will try to get more info
thanks
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
It appears from the photograph that the "Automatic Train Control Electronics" is residing in a metal cabinet with ventilation slots at the top end of the cabinet.If sufficient quantity of cold air is not entering the steel cabinet, the components inside can heat up. There should be ventilation slots at the bottom for the cold air to get in and the hot air should be leaving through the slots at the top.The temperature inside the cabinet is the critical parameter and therefore the thermostat should be located close to the vents at the top.Air flow through the slots will depend on the buoyany created by the equipment heat.If the equipment load is high,the airlfow may need to be fan assisted as in computer racks.Try and get an understanding of the extent of the equipment load and it will help you determine whether the airflow patterns are correctly set up.
I worked on a few signalling equipment rooms last year and they were pretty much like computer racks generating about 2 kw per rack.They were arranged in the cold aisle/hot aisle configuration with air conditioning units supplying air at low level in the cold aisles.
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
What is the temperature in the space where the condensers are located?
There is no coordinated control? Each air conditioning is working by its own controller?
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
However, 24C is about the maximum you want for personnel as well.
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................
that can possibly alarm for some misconception. 22 degrees is more customary in food processing rooms than in conjtrol rooms.
RE: I want it cold but I don't want it ALL cold - Design Issues.........................................