Motor Control Center (MCC) refrigeration

[lucaspenalva]

Hello,

So we have a Motor Control Center with big VFD's.

Those equipments altogether create more than 250.000 BTU/h of dissipated power.

Currently we have 4x 60.000 BTU/h split air conditioners to cool the MCC down. The panels have built-in exaust system and we've built a collecting duct that throws the hot exaust air outdoors.

However, it's not working properly and temperatures are getting high.

We are considering chaging the convencional split AC system to an Air Handling Unit system, re-calculate the thermal load (as equipments were selected before with no prior calculation) and place supply duct outlets as close as possible to the panel's exhaust grilles (at the same level), so we'll have cooler getting air sucked by the panel's exhaust system.

I would be very thankful to hear comments and suggestions from you.

PS.: I attached an image of the location.

 

[DrRTU]

We have built and maintain a few of these. We have utilized both DX & CW split systems and RTUs. The simplest is a 30 ton RTU placed on top of the MCC enclosure inside the plant. A few points:
1. Your 4x60K will only be about 70% sensible, thus you only have 168K of cooling. Compare the actual machine performance to published OEM data tables.
2. How are you making up for the exhaust? Plant or outside air may be increasing your load.
3. How was the total load calculated? It is very difficult to calculate the heat production based on eff % of the drive and total load serviced. Load density may be higher.
4. Most of these are protected via a FM200. Ensure isolation dampers are fully functioning.
5. Raceways or cable tunnels connected to a plant which is negative will pull conditioned air from the MCC. This is below the metal floor or under the drives.
6. Most equipment can handle up to 95F. Operations or maintenance get concerned if the room is GT 74F.
7. Hot isle design. Move the highest cfm AHU can run with.
8. It looks like you have a 60K DFS in the picture. Most are not 5 ton. Be cautious of the condensate on high wall DFS. Drain pans are very poor and water in the drive cabinets is bad.

 

[GroovyGuy]

Howdy Lucus,
I encounter the same situation several times a year (ie very large air-cooled dives in a small e-House). I have used both mechanical cooling and air handler units (AHU) to such the heat out of the bldg. The AHUs that I have routinely used are rated 30,000cfm each, usually installed in pairs. The differential temperature rise is usually set to be no more than 8C. With a max outside temperature of 30C, this limits the max inside air temperature to 38C. These AHUs cost approx. $125k US each, with installation extra. I have priced the ASD OEM AHU options for large drives, and they cost almost as much as the drive itself.

It may be less expensive for you to simply install a couple more 5T AC units (at this point in time).

GG

ps BTW do the existing AC units have economizers in them? What is your min/max outside air temperatures?

"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)

 

[lilliput1]

You also need to improve airflow to avoid short circuiting. Supply air down or low. Pickup return above the MCC hot air outlets.

 

[quark]

and place supply duct outlets as close as possible to the panel's exhaust grilles (at the same level), so we'll have cooler getting air sucked by the panel's exhaust system.

Did you mean panel inlet grill? If the panels are venting in to the exhaust duct, without any external fan, you do find some problems.

Split ACs create their own hazards. Your idea of a central AHU is good. Atleast, it should be ductable split.