Modeling DOAS-II Reply and Unexplained Fan Energy Increase

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Modeling DOAS-II Reply

Thanks for addressing the issue with the thermal error for the Dummy
Zones. My recommendation to avoid the issue with an oversized DOAS fan
is increase the "INFILTRATION ACH" instead of the "SUPPLY AIR ACH".
Equest then sizes the DOAS fan based on the Outside Air demand of the
attached AHUs downstream. And of course still increase the Zone
Cooling/Heating Setpoint Temperature to something ridiculous like 150 F
/ 0 F so no fictitious load occur.

Unfortunately I have yet to enter ERV or ECO into the DOAS or AHU so can
not say whether it provides spurious results. Yet, from digging into
the Air Flow Rates of the DOAS and AHUs, the process of a DOAS works.
Additionally, the DOAS systems show a pretreatment of the Outdoor Air
before entering the AHUs. For example, my DOAS units with DX Cooling
accounts for ~25% of the total school's cooling energy with the rest
handled by the Chilled Water Coils in the AHU.

Unexplained Fan Energy Increase

Inevitably a warning in the .SIM file will state that the Air Flow Rate
of the DOAS system has been resized to meet the demand of the AHU
ventilation rates. The warning then states that it is strongly
recommended that you enter this Flow Rate into your DOAS system.

I have checked the DOAS and AHU flow rates without and with entering in
the DOAS Flow Rate. Although the amount of Air Flow does not change AT
ALL, the fan energy increases. This makes no sense.

If anyone could explain the reason for the reduced fan energy, I would
be very appreciative.


Date: Fri, 12 Sep 2008 19:19:10 +0200

Doebber, Ian's picture
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