Hi I'm just a layman and a newbie at HVAC. I am looking for second or
third opinions on the advice that we're getting from a local HVAC
We have a computer room that needs more cooling capacity. Currently
there are 2 cooling units, about 5 tons each. This has been adequate,
until one of them fails. Also we are adding a lot of computer and
network equipment and expect to add a lot more. We expect to need 25 -
30 tons at the end of 5 years from now.
The computer room has a raised floor with only cabling underneath and
no room for anything else. There is a drop ceiling, which contains the
supply and return ducts. The air cooling is done in a room in the
floor above. Apparently there is no more room above the drop ceiling
for more ducting. The approach we've been using so far is the cold
aisle/hot aisle method, where you dump cold air in the aisle between
two rows of computer racks, suck the cold air through the computer
equipment and dump the warm air in the aisles behind the racks, where
the return ducting sucks up the warm air. Seems to work fine.
We've hired a local HVAC consulting engineer but I'm not sure he's had
much computer room experience. We don't want to put additional cooling
units inside the computer room itself. His advice was to add a
mechanical room to our building right next to the computer room (ground
level), put the cooling units in the mechanical room, and punch holes
through the computer room's outside concrete wall for the ducting.
There would be 2 Lieberts of 25 tons each. The supply ducting would be
two semi-circular rings that run just under the drop ceiling and right
against the walls. There would be no return ducting, just two big
return vents built right into the outside wall back to the cooling
So it looks to me like he's just going to let the new cooling units
cool the room air as a whole, instead of dumping the cold air in the
cold aisles. He seems to know what he's doing but I don't know if this
approach is OK. I guess he's depending on the air to just mix around
but is that good enough? I know he's really overloaded with work so
I'm just a little nervous that he may not be putting enough thought
into this, but I don't know enough to question his approach.
Any thoughts or advice?