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Temperature Setting of Panel Air Conditioners

10/02/2016 1:51 PM

Dear Friends

In our Corrugator plant, the temperature rises up to 45C in summer season. We have installed panel ACs with all field panels of machines having PLCs and drives. As per your experience, what should be the set point temperature of ACs to avoid any problem with equipments and ACs byself. Some one tell set below 30C, some one 35C and some one at 40C.

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#1

Re: Temperature setting of panel Air Conditioners

10/02/2016 2:03 PM

Your machines should have a maximum operating temperature from the supplier/manufacturer...another concern is humidity, for glues and other humidity sensitive operations, then there is an ideal temperature for workers...which will correlate with the physical activity levels....For workers it can be between 72°-77°F for humidity 35 to 60% rh....

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#2

Re: Temperature setting of panel Air Conditioners

10/02/2016 4:00 PM

It depends on what temperatures the wire sizes were selected for. If this is not known, you may need to do some reverse engineering of your panels.

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#4
In reply to #2

Re: Temperature setting of panel Air Conditioners

10/02/2016 9:27 PM

Whoever voted this as OT is desperately incompetent.

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#6
In reply to #4

Re: Temperature setting of panel Air Conditioners

10/02/2016 11:42 PM

Even though it's Lyn, I fixed it.

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#7
In reply to #6

Re: Temperature setting of panel Air Conditioners

10/03/2016 12:13 AM

Thanks!

The NEC uses 30ºC (86ºF) as a baseline value for many calculations. This ambient temperature is often exceeded, and almost as often is not accounted for. A "Code God" could do well to bump that up to 40ºC (104ºF).

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#3

Re: Temperature setting of panel Air Conditioners

10/02/2016 5:04 PM

The thermostat should be set at whatever setting will yield the desired air temperature in the building. Picking an arbitrary setting lacks any resemblance to a common sense approach.

Since operator health and safety are not a consideration, the operating environment for most commercial equipment is 0-70°C.

45°C is well within the operating limit of the equipment, but seems to be an inhuman working condition for employees, depending on indoor humidity levels, and whether or not that matters.

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#5

Re: Temperature Setting of Panel Air Conditioners

10/02/2016 10:35 PM

Most electronics are going to be rated for 40C max, circuit breakers are calibrated for 35C ambient. Circuit breakers will not fail at higher temperatures, but they may nuisance trip. However I would not be comfortable letting anything electronic be exposed to even 40C for any length of time. I generally set enclosure AC units for 30C, that helps avoid having eddies and swirls in air flow inside cause individual components to overheat.

I recently saw some VFDs crammed into an enclosure fail. The AC was set for 70F (21C), but there were areas inside where the temperature still exceeded 110F because of eddies behind barriers. Capacitors over heated and swelled, causing a power supply board failure.

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#9
In reply to #5

Re: Temperature Setting of Panel Air Conditioners

10/03/2016 2:40 AM

I agree, JRaef. I also prefer to keep electronic component's temperatures low to ensure long life. It is clear the the OP is referring to panel aircons as per your answer, not room aircons as others may have thought. And the effect of local ventilation "dead spots" has been brought home to me - expensively, I may add!

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#8

Re: Temperature Setting of Panel Air Conditioners

10/03/2016 2:15 AM

The addition of an air conditioner to a room full of electronics is no guarantee that there will be adequate cooling for the equipment unless there is some form of thermal analysis to determine how and where to direct air flow around and through the enclosure.

A simple thermostat will only provide the average temperature of the return/supply air without any regard for the actual temperature/heat-load of any particular piece of equipment. It is quite possible overheat a subassembly located in a stagnant air pocket while cooling the supply air to some arbitrary setpoint.

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#10
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Re: Temperature Setting of Panel Air Conditioners

10/03/2016 6:23 AM

There's a can of worms.

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#11

Re: Temperature Setting of Panel Air Conditioners

10/03/2016 12:19 PM

Check the wiring junctions inside every panel and adjust the thermostats until the desired temperatures are reached.

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#12

Re: Temperature Setting of Panel Air Conditioners

10/03/2016 12:21 PM

Air conditioning is for comfort control, so the best thing to do is ask the people who are working there.

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#13
In reply to #12

Re: Temperature Setting of Panel Air Conditioners

10/03/2016 5:46 PM

From the OP: "We have installed panel ACs with all field panels of machines having PLCs and drives."

This isn't for the comfort of people, it's to keep silicon from going "PFFT (that is the sound the magic smoke makes as it escapes)"!

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#14
In reply to #13

Re: Temperature Setting of Panel Air Conditioners

10/03/2016 6:30 PM

My way of telling people to think about this, especially for anything electronic, is a simple formula:

Heat2 x Time = Failure.

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#15
In reply to #14

Re: Temperature Setting of Panel Air Conditioners

10/03/2016 7:01 PM

Yep. Even if you don't exceed the temperature spec, it will shorten the life.

Besides, most VFDs and PLCs have some type of LCD screen for an operator interface, and the temperature spec on those is usually considerably lower.

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#16

Re: Temperature Setting of Panel Air Conditioners

10/05/2016 3:40 PM

Why aren't you talking to the panel manufacturers, then?

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#17
In reply to #16

Re: Temperature Setting of Panel Air Conditioners

10/08/2016 11:09 PM

As we have recently installed new BOBST Martin flexo graphic printing machine on which the set point temperature of all cabinet ACs is 40C, I have talked with OEM and according to them, temperature must not set below 40C because the electronic items can be work up to 55C. This is strange for me because there are Lenze servo drives, Siemens PLC field I/O cards and other electronic items are in the panels and according to the discussion made in this thread, cabinet temperature should be maintain within 30C.

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#18
In reply to #17

Re: Temperature Setting of Panel Air Conditioners

10/10/2016 6:27 PM

Printing....

I seem to remember about Benjamin Franklin thinking printing was a good job because they had to heat the works in winter else the ink would not flow. Which is to say that printing gear may like a high temperature.

But why cook the electronics because another part of the system has high temperature requirements? I endorse the replies pointing out that electronics failure rate is increased at 40'C vs 30'C -double the failure rate is a "rule of thumb".

It may be that the A/C cuts in/out alternately letting the equipment heat up with natural circulation, then blasting it with fan driven cold air.

Temperature cycling is worse for equipment than a steady or slowly changing high temperature - maybe the supplier has found it is best only to use the A/C when it gets really hot.

This suggests to me a sub-optimum A/C system - would it not be better to have variable speed compressor and fans to achieve a stable equipment temperature rather than a bang-bang control?

I would quiz the OEM closely on why he recommends such a high setting.

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#19
In reply to #18

Re: Temperature Setting of Panel Air Conditioners

10/15/2016 10:23 PM

At BOBST machine, we have all RETAL brand ACs with 40C set point temperature pre-set by OEM.

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#20
In reply to #19

Re: Temperature Setting of Panel Air Conditioners

10/16/2016 2:32 PM

That's RITTAL!

I would suppose the 40'C is the delivery temperature into the enclosure (at bottom) from these "front panel" coolers. The temperature of the highest mounted electronics in the cabinet may be well over 40'C.

As has been mentioned, just blowing air around may actually create a "dead spot" which gets little inflow of cooling air to some equipment - may be worse than natural convection.

RITTAL have fan thermostats - electromechanical on/off control like a room thermostat and optional temperature dependent variable speed fan control. What do you have??

Cooling units have a capacity that depends on temperature differential, say you have Δt = 45 - 40 = 5'C that requires smaller capacity than Δt = 45 - 30 = 15'C.

But equipment is even more sensitive to humidity, usually 90% max, the term non-condensing is probably in specs of equipment inside your panel. If you cool 45'C, 80% relative humidity [R.H.] air to 40'C you have 100% R.H. and condensation! (I took a New Delhi climate as example). It may be this which dictates the high 40'C setting.

If your panels are well sealed, entry of external air should be slow. A good A/C unit has part of the cold matrix well below mean exit temperature - this will condense out the humidity in a closed volume and drain it out so the internal humidity at 40'C is reduced. From 100% RH to 80% RH at 40'C requires removing about 10g water per kg of air - that requires the air to be cooled to 35'C to condense it.

So if you wish to check the ambient of a vital equipment within the enclosure, you need to check its temperature (preferably on a critical heatsink or component) as well as local humidity where cold air goes from A/C into the panel.

I hope this helps.

67model

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