Humidifier

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I have an Equipment Rack Room (ERR) that has a chilled water/hot water
single zone system, with de-humidification and humidification. When i try
to model this, i enter in the appropriate inputs into the system and zone
levels, and then for humidification i enter in my design parameters, 60% and
35% with electric cansister humidifier type.

My problems begin now, when i run the model the humidifier is never turning
on throughout the year, and dehumidification seems to work just fine. Also
the program is currently sizing my cooling coil to a size much larger than
previously determined by hand.

More notes: the Rack load is 90kW with minimal other loads (lights and
people). 99% sensible heat ratio. Using this i need about 30 tons of
cooling, which translates to a coil that should be slightly larger than
that, due to de/humidification. my thermastat is set to 72deg and design
temperature is also 72 deg.

This has been alluding me for about 2 hours, so any help is appreciated.

--
Rob Hudson

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After more putzing around, i have notices that if you set the OA to 0 then
you cannot humidify, so i set it to 1 cfm, and now it works...

Cooling coil is still bothering me though.

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Hrmmm... No straight answers, but few questions have I!

Humidifier isn't running? With no outside air and little/no exhaust ...
seems to me the moisture present at the beginning of the simulation
isn't ever leaving the space - so why supply more moisture? The
dehumidifier is probably only removing the moisture from the people
also, so I expect it's not major. You might get different results if
you specify "OA from system" with a corresponding minimum quantity, if
in the real world new, moisture-ridden/barren air is introduced from
other spaces.

Coil size off? If the simulated design loads do check out (check
reports), keep an eye on the specified/calculated CFM as well. Note
project altitude may mess with you in this regard if you're specifying.
Also: 90kW*3413/12,000 = about 35.8 tons, so 36 is probably the floor
for what to expect. Also: 90kW is an important number, but equally
important is the schedule... is that running @ 100% 24/7 or for a single
hour at a time? You'd end up with different coil sizes I bet.

And just for fun... I just found a Yoda-speak translation tool
:

Coil size off, hmm? If check out (check reports), the simulated design
loads do, as well keep an eye on the specified/calculated cfm.
Specifying, note project altitude may mess with you in this regard if
you are. Also: 90kw*3413/12,000 = about 35.8 tons, so probably the
floor for what to expect, 36 is. Also: An important number, 90kw is,
but the schedule, equally important is... For a single hour at a time
is that running at 100% 24/7 or, hmm? End up with different coil sizes
I bet, you would.

~Nick

NICK CATON, E.I.T.

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Good questions, and even better translation tool! i enjoy how almost every
engineer out there is a nerd in some way shape or form.

The unit started humidifying when i entered 1 cfm of OA into the system.
Not sure why, but this is good enough for now.

The coils is over sizing, and altitude is 1.02, and my CFM is set at 18,000,
which should be enough for the space. I'm expecting to see coil size of 360
to about 425 kBtu/h, but am ending up with 520 kBtu/h.

The space has 90 kW all year long at 100% during the day and 60% at night.

Thanks and may the force be with you

Rob

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