evaporative coolers in equest

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Hello all
I am modeling a building in Bridgeport, CA which has evaporative coolers.
I dont see any benefits if I replace existing clear glass with low-e in
cooling energy consumption.
Did anyone model evaporative coolers/swamp coolers before?
I want to know whether there is a way to show cooling benefit with such HVAC
system.
Thanks
Regards
Deepika

DEEPIKA KHOWAL
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are you trying to show the cooling benefit of the windows? or just
comparing the evap cooler to a baseline packaged unit?

i've done this with fire stations, and been successful, but it is often
more in the ventilation savings from not running a compressor in the
evap system than the building envelopes themselves. at least in my
experience. there is also the trade off in the simulation though that
the evap cooler will have probably have a larger fan power (in reality)
than the baseline packaged unit.

and if a leed project don't forget the baseline outside air is the
minimum required, which will probably be lower than your evap even if it
is not a 100% outdoor air system.

Patrick J. O'Leary, Jr.'s picture
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Hi Deepika,

I'm not certain any increase/decrease in cooling loads (such as solar
loads affected by changing glazing) should have any effect on the
reported "space cooling energy" when you're using evaporative coolers.
Direct evaporative (swamp) coolers of the simplest sort have only fan
and pump energies to consider - no refrigerant! I would advise looking
up the Detailed Simulation Reports Summary page 158/160 to review end
use categories and what they cover.

I am unfamiliar with Bridgeport's climate, but as a general rule if I
observed a significant amount of glazing in a space served by a direct
evaporative cooler... I'd be extra cautious to ensure the HVAC designer
is carefully considering condensation and potential for other
humidity-driven issues along the way. I'm most used to seeing them
applied to well-ventilated and/or open-air spaces such as garages and
gyms/hangars.

~Nick

NICK CATON, P.E.

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This is an existing building with evaporative coolers.
the proposed design to upgrade the windows and check the relative benefits.
I dont see much benefits in energy because evaporative coolers are sized
based on Cfm and not btus, the savings will be in cfms.
correct me if I am wrong.
is there any other way I can show the benefit in the proposed case if not
HVAC benefits?
Thanks

DEEPIKA KHOWAL
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I hope we're at a simple vocabulary disconnect here...

* Upgrading the windows will reduce your solar cooling loads.

* Reducing your solar cooling loads will reduce the amount of
heat to be removed from the building.

* Reducing the amount of heat to remove will reduce the required
hours of operation of your HVAC system (in this case, evaporative
coolers) to maintain comfort.

* Reducing the runtime of your evaporative coolers will result
in reduced energy consumption. Fan energies primarily, in the case of
evaporative coolers.

* In the event the existing system is not of sufficient capacity
to begin with, you may also/instead observe a reduction in unmet cooling
hours.

The reduction of solar loads with a glazing upgrade could be negligible
for a variety of possible reasons, but it's unlikely the net effect is
absolutely zero.

~Nick

NICK CATON, P.E.

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i would agree with nick on this except for part #3. if you're using
ashrae 62, or the 2000/2003/2006 imc (at least the way it is enforced in
southern arizona), the evaporative cooler fan is required to run while
the building is occupied so despite glazing upgrades you shouldn't be
seeing any savings from the hvac system during occupied hours. you
would probably see some during night setback if the building there's
some thermostat setting that will operate the evap coolers to remove air
(and the associated heat build up) but i would not think it to be that
significant of a savings compared to heat gain during occupied hours.

i would think, as nick mentions in point 5, that the ummet cooling hours
might be a better measure of what you are looking for. improved glazing
should help reduce the rate of heat gain so the evap coolers should be
able to meet whatever setpoint you are using with less unmet cooling
hours. in reality i would think it would be more obvious by an occupant
working proximity to the windows - if they're currently affected by the
solar heat gain. i don't know your climate but in southern arizona you
don't really want to be seated right next to a window with a direct sun
exposure and insufficient airflow (evap) or mechanical cooling and poor
windows.

Patrick J. O'Leary, Jr.'s picture
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the building has windows only on south facade.
I thk changing the glass type will have impact on unmet hrs.
however, I agree that since its diff to have a thermostat control for
evaporative coolers during day, the savings are hard to quantify.
Thanks for help.

DEEPIKA KHOWAL
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This is the wrong way to look at evap cooling performance. In fact, the whole logic of
sizing using design conditions falls apart when it comes to evap coolers. Evaporative
cooling works by taking advantage of the wet-bulb depression to trade off latent for
sensible heat.
When the wet-bulb depression (DBT - WBT) is low or when the WBT is high, evap cooling
will provide little cooling. A better way to size evap cooling is to either minimize the
unmet
cooling hours, or if there is an AC backup, maximize the energy reductions.

If you're working with a fixed evap cooling size, then you should look at the number of
unmet cooling hours to see the benefits of a window upgrade, as well as the reduction (if
any) of electricity use.

Joe

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Patrick, thanks for the heads up!

My experience applying evap. coolers has been on a limited basis
explicitly for space comfort, operated staged & cycled off via
thermostat, so my brainstorming for Deepika was tailored to my past
experience. In those cases (auto garages), a mechanical ventilation
system was provided as an entirely separate system, so the 62.1/IMC
requirements for ventilation during occupancy were addressed elsewhere.

If one is in fact using a swamp cooler functionally to supply required
ventilation air, then I would agree it makes complete sense to operate
continuously during occupied hours.

I recall evap. coolers being a breath of fresh air (har har) to design
around as they do make you rethink how you use your psych charts =).
I'll defer any specific swamp cooler application queries to the Arizona
engineer below me though - we don't use them quite so often locally,
outside of the desert ;).

~Nick

NICK CATON, P.E.

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Thanks Patrick
I read the following link which talks abt sizing evaporative coolers
http://www.consumerenergycenter.org/home/heating_cooling/evaporative.html

DEEPIKA KHOWAL
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