Q for HVAC guys re: server room cooling

[BokCh0y]

We have a server room with servers that output 19,000 BTU's. The company cheaped out, and instead of buying a wall mounted unit they opted for 2 x portable AC units with each unit outputting 12,000 btu's. From an HVAC perspective, do those 2 12,000 btu AC's equate to 24,000 btu output air? Those AC's are really struggling to even cool the server room in general - as in they're doing fuck all.

I've never used portable AC's to cool a server room before with the exception of emergency situations like primary AC shits the bed. And even then, I noticed the portable AC units clearly don't cool a server room efficiently.

So my question is:

1. Can you combine the BTU's to make an air output of 24,000 btu's?

I'm pretty sure our HVAC contractor is on crack. He's fighting with me that we have our BTU calcs incorrect and that his 2 x 12,000 btu portable AC units should be more than sufficient for cooling...but my background isn't HVAC.

I understand the volume of the room needs to be taken into consideration. That 2 x 12,000 btu AC's do in fact use more power. A room thermostat is required to regulate the overall room temperate rather than using the built in thermostat on those portable AC units.

Thanks in advance.

[firebane]

Portable AC units if they have the twin hoses need to exhaust the air outside and if they aren't your just recycling hot air around and around.

What type of portable units are they?

[BokCh0y]

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Portable AC units if they have the twin hoses need to exhaust the air outside and if they aren't your just recycling hot air around and around.

What type of portable units are they?

Yeah the AC units are being vented properly into the ceiling utilizing the proper venting hoses, so that isn't an issue. It's the ability for those units to cool the server room with or without load.

[ExtraSlow]

Where is the hot air exhaust of these portable units directed?

[BokCh0y]

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Where is the hot air exhaust of these portable units directed?

The ceiling. It's vented into the ceiling.

[ExtraSlow]

I hate to hammer on this point and I'm not an HVAC professional, but what do you mean the ceiling? Do you mean out the roof of the building to the exterior? Or into an attic space that is well separated and insulated from the server room? Or just into the space above the ceiling tiles?

- - - Updated - - -

If you think of the portable air conditioner as two machines. Really it's a very efficient heater and a much less efficient cooler. You need to pay close attention to where you are putting all that heat.

[Thaco]

Also the hoses job is to evacuate the hot air, so the hose its self gets very warm and will definitely transfer that heat back in to the room, so you need to make sure the hose is a short as possible or well insulated so it doesn't just heat the room back up like a radiant heater.

I dont know a lot about hvac, but there are a few things that could be done to make it slightly more efficient.

[JRSC00LUDE]

If they fry all their shit, they won't cheap out next time.....

[firebane]

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The ceiling. It's vented into the ceiling.

Into proper evacuation hvac? Or just into a void?

[BokCh0y]

Just into the void.

Can you guys just answer the q on whether the combined output of 2 x 12,000 Btu ac's is equal to 24,000 Btu? I understand the variables, trust me. And those are discussions I'm having with our wonderful office services group.

I'm just not confident with the hvac vendor we have right now, and I don't understand how in the fuck they'd recommend two portable stand alone ac units over a dedicated wall mounted unit

The ac vent tube does got hot, but it doesn't create enough heat to increase the temperature of a room to 100+ degrees farenheit.

To add, before this gets derailed and focused on something else, I also understand that the two portable units are less efficient power wise than one unit. As in I know it uses double the electricity. I also know the two portable units will die sooner than the dedicated wall mounted unit. I also understand venting the units to the ceiling is not suitable, hence my discussion with office services.

[roopi]

I know nothing about HVAC but if you think multiple servers combine to output 19,000 BTU's why wouldn't multiple A/C units combine to output 24,000 BTU?

Like everyone said maybe vent the units you have properly before doing anything else.

[BokCh0y]

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I know nothing about HVAC but if you think multiple servers combine to output 19,000 BTU's why wouldn't multiple A/C units combine to output 24,000 BTU?

Like everyone said maybe vent the units you have properly before doing anything else.

Good point and yet: facepalm:about venting.

HVAC guys please. Just need that one question answered.

[HiTempguy1]

The answer is "yes", followed by a "but".

The "but" being unless they are installed properly, which they are not, it won't matter.

It's very important the fact that they are venting into the void. That is essentially heating the room. An A/C unit is nothing more than a glorified heat exchanger, the heat is removed from the room air and put into that void. If it is typical drop down commercial ceilings, there is approximately between 0 and fuck all sealing that void from the room.

So basically, those AC units are doing nothing but wasting a ton of electricity and pumping air around.

[BokCh0y]

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The answer is "yes", followed by a "but".

The "but" being unless they are installed properly, which they are not, it won't matter.

It's very important the fact that they are venting into the void. That is essentially heating the room. An A/C unit is nothing more than a glorified heat exchanger, the heat is removed from the room air and put into that void. If it is typical drop down commercial ceilings, there is approximately between 0 and fuck all sealing that void from the room.

So basically, those AC units are doing nothing but wasting a ton of electricity and pumping air around.

Understood, thank you for this. Helps me with pushing for a proper unit rather than this mickey mouse setup.

[realazy]

Basically the laws of thermodynamics apply here. If you do not vent the waste heat out of the system (the room including the ceiling void in this case), you will just end up generating more heat from the ac unit running because you are bringing energy in (in the form of electricity and turning it into heat and work, but the work is not doing anything because the waste heat is just in the void).

It's like trying to cool your house by leaving the fridge open, it doesn't work.

[ExtraSlow]

Wait, venting matters?

[HiTempguy1]

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It's like trying to cool your house by leaving the fridge open, it doesn't work.

Now that I think about it, it is actually adding heat to the system. 2000+W of additional energy I reckon at those BTU levels. I heat my 24x24 garage to 15*C with 2400w of electric heat.

The only reason I can fathom them doing this, is because there is some sort of air exchanger in the void. Plausible, just not probable.

[Maxt]

All portable and condensed versions of a/c are low on airflow. The golden rule for air conditioning is 400 cfm/ton, you'll find those portables only put out 225-275 cfm. Also, they sit on the floor so the air distribution is poor. The heat leakage from the ceiling space venting isn't helping anything.
What size is the UPS on the rack? that or doing an amp draw on the room panel is the best way to size a server room, or you can call every manufacturer of everything in the rack and ask for heat rejection rating, and add in a little for lights and people.
I would guess you are getting about 8000 real btu/hr out of those machines, so you have 16,000 with really bad air distribution... A real machine to handle that load runs about 11-12k installed...

[BokCh0y]

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All portable and condensed versions of a/c are low on airflow. The golden rule for air conditioning is 400 cfm/ton, you'll find those portables only put out 225-275 cfm. Also, they sit on the floor so the air distribution is poor. The heat leakage from the ceiling space venting isn't helping anything.
What size is the UPS on the rack? that or doing an amp draw on the room panel is the best way to size a server room, or you can call every manufacturer of everything in the rack and ask for heat rejection rating, and add in a little for lights and people.
I would guess you are getting about 8000 real btu/hr out of those machines, so you have 16,000 with really bad air distribution... A real machine to handle that load runs about 11-12k installed...

Thanks for this info, really appreciated.

My firm's office services group took this on rather than leaving it to the IT group. We had requested a wall unit, basically a ductless split air air conditioning unit you find in most server rooms, but they had their own HVAC company come in and unbeknownst to us, they went with the portable AC unit route. Definitely didn't make sense to us, and when we questioned the HVAC company, they were insistent that this solution was not only economical, but would be MORE than suitable. Lots of doubt for us...and sure as fuck when the servers were moved into that new server room, shit went south and fast.

I've done a bunch of research on the proper solution, similar to what we have in all our other server rooms but since I'm not familiar with HVAC, was looking for some info on the two 12,000 btu units, basically something that I can throw in the office services and HVAC companies face. Have pretty much was I need from other research and examples as well what all is required for venting to build a case to bring up with our SVP to push for the correct equipment. The biggest factor here is cost savings proposed by office services....and in the end it'll end up costing more with their half ass setup.

Thanks Maxt.

[Maxt]

The mistake always made in sizing for things like server rooms, is not breaking down the "split" rating of an air conditioners over all rating. The split is the amount of percentage of the rating which is sensible load and latent load. The lower the CFM per ton, the greater the amount of the split is towards latent load, but things like server rooms are all sensible loads.