Working out heat loads in comms/server rooms.

[acnerd]

Let's ignore other heat loads such as solar gain, lighting, room size and people; let's concentrate on the sensible heat produced by the computer equipment:

a) The easy route is to ask IT if they have a power monitoring programme and tell us how many kW they are consuming.

b) We could take down the power supply ratings of each device in the room as a rough guide, add them all together, and produce a rough maximum kW value.

Or (c), I decided to be clever (used loosely :eek:) and measured the current draw from the local distribution board. Three phase supply, each phase had approximately 20A on it.

Calculation:
3 phases x 20A per phase = 60A current draw
P=VI (power = voltage x current draw)
P= 240v x 60A
P= 14 400W = 14.4kW

So the power consumption is 14.4kW; at which point it would be easy to assume you need more than 14.4kW of cooling ..... but am I right in the assumption that all of that electrical load is turned into heat?

PS: I am aware that all a/c is designed to deal with sensible and latent heat loads, but server rooms invariably have very low humidity!!

[Bartolo]

Hi ACNERD!

Your calculation seem to be good. As far as I know in case of serwer rooms You can take all of the power consumption as heat load. Electrical energy can be calculate as heat energy 1 to 1 if there is no mechanical parts. of course there are fans in serwers but it's energy is so low that you can just ignore it.
I'm always calculating heat load in server rooms as electrical power and it's ok.

[acnerd]

Thanks Bartolo. Sometimes when things look simple, I question it so that it doesn't bite me in the a$$ next time!! ;)

[dougheret0]

So the power consumption is 14.4kW; at which point it would be easy to assume you need more than 14.4kW of cooling ..... but am I right in the assumption that all of that electrical load is turned into heat?Yes, every watt. That doesn't necessarily mean it all becomes cooling load, especially if the equipment is powered down, or "sleeps" during off hours. Some of the heat may be conducted away to cooler adjacent spaces. However, since no outdoor air need be brought in to cover the load, a little oversizing hurts nothing.


PS: I am aware that all a/c is designed to deal with sensible and latent heat loads, but server rooms invariably have very low humidity!!

The ac must be sized to the sensible load. Equipment designed for server rooms typically has sensible heat capacity ratio of about .8, so a five ton unit, for example, could only handle 4 tons of sensible load. If the server heat load is 5 tons, then an unit with a total capacity of more than 6.25 tons would be needed.

[olddog]

If the server room is fully UPSed then a handy cross check is to find out what the UPS (s) are rated at

[acnerd]

The ac must be sized to the sensible load. Equipment designed for server rooms typically has sensible heat capacity ratio of about .8, so a five ton unit, for example, could only handle 4 tons of sensible load. If the server heat load is 5 tons, then an unit with a total capacity of more than 6.25 tons would be needed.

I think the crux here is "equipment designed for server rooms." So many small server rooms have a comfort cooling split thrown into it, and these are designed with higher latent heat loads in mind. Generally they are of the standard compressor variety, so all that happens is that the system starts to run too cold as it becomes too powerful for the room (with no moisture condensing on the coils), and we have suction pressures dropping below a 0'C evaporating pressure ..... resulting in iced up evaporators, suction lines, accumulators and compressors.

[acnerd]

If the server room is fully UPSed then a handy cross check is to find out what the UPS (s) are rated at

I've done that before, so good to hear I'm not the only one. :cool: