I want it cold but I don't want it ALL cold - Design Issues......................................... 1

[Kinemenematics]

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'
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M&E services area (i think around 29 degrees C)
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Ceiling panels
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ATC Room, Temp = {18,22} degrees C. dimensions: 10m x 7.5m x 3m.
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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.

 

[Kinemenematics]

The ideal is to operate it constant at 22C, a safe margin away from 24C which is when the equip starts to overheat and the condensation is worst in the morning. I just need to keep the temperature around 21- 23C. It does not have to be at 18C, so the supply air could be of higher temperatures. I will find out more about the heat load variation.


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

 

[MintJulep]

A dehumidifier is probably the worst of all possible solutions.

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.

 

[Kinemenematics]

ATC means Automatic Train Control

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?'

 

[DRWeig]

I'll let MintJulep discuss "correctly done control," but the most helpful thing for us to understand is the control sequence for this room. If it is possible, please post the sequence of control, flowchart, or other description of how the DCS makes its decisions. I, for one, am willing to look through it. Your problem is interesting.

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[Kinemenematics]

i can describe it to you or draw u a picture, but the control panel diagrams are protected property

Of course, i will try to get more info

thanks

 

[SAK9]

To add a new dimension to your problem

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.

 

[MintJulep]

Go pop up some ceiling panels and get us some pictures of what is above them please.

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?

 

[140Airpower]

Kinemenematics, It is strange to me that your equipment is overheating at a room air temperature of 24C. The cabinet interior temperatures must be very much higher than that. Equipment ventilation and spacing and placement with respect to air circulation, recirculation and the avoidance of one piece having it's intake air in the exhaust flow of another, etc should be looked at. Is there one unit that is most vulnerable to overheating? Note that more equipment cooling air flow will bring in-cabinet temperatures down and will not change the load on the AC system.
However, 24C is about the maximum you want for personnel as well.

 

[140Airpower]

Speaking of personnel, how many people are in this air space? Humans are a prodigious source of humidity. It's very hard to dry them out. They also tend to demand a high percentage of outside, "fresh", air, especially when they are crowded together.

 

[Kinemenematics]

at any time, zero. the equip is controlled and used and monitored via remote control.

 

[Drazen]

airpower is right, we probably did not pay enough attention to it being focused on initial questions (actually, in these tip-discussions usually it is more worthwhile to question initial question than to try to jump on problem which is possibly not problem at all): can you verify specifications for space temperature for your equipment?

that can possibly alarm for some misconception. 22 degrees is more customary in food processing rooms than in conjtrol rooms.

 

[Waramanga]

It looks like you have under ceiling units. These blow straight onto the ceiling so you will be getting a ceiling maybe 13 degrees. Any moisture entering the room will go straight there. Your pipe insulation must be the thinnest available and your roof is sitting at 90rh.