Do you know how to set the "VAV minimum flow" (percentage) at the "HVAC
zones: temperatures and Air Flows" panel? eQUEST default number is 40%. Is
there any standard?
VAV min flows can be set both in wizards and in detailed edit modes.
See following screenshots.
The "standard" depends on the HVAC design, and specifically how
ventilation air is being distributed. There's a range of CFM's that the
factory will set as a minimum terminal unit at depending on the size,
but it may well be zero if you are distributing ventilation air via DOAS
in certain ways. I'd suggest asking your HVAC designer directly what
the minimum is for each unit (it's probably scheduled), and use that
info to either come up with an average for each zone or to set the
minimum for each zone separately.
Here's the wizard...
... and in detailed, double click on a space served by a VAV system,
under the Airside HVAC tab, to find the following window. In this case,
the minimum flow is set to 30% (0.30):
How do you think this standard from ASHRAE 90.1 G3.1.3.13 VAV Minimum Flow
Setpoints (Systems 5 and 7). Minimum volume setpoints for VAV reheat boxes
shall be 0.4 cfm/ft2 of floor area served or the minimum ventilation rate,
whichever is larger.
In my opinion, it means, if we set "Minimum Design Flow is 0.5 cfm/ft2", the
VAV minimum flow should be set 80% (we assume the minimum ventilation rate
is smaller than VAV minimum flow.), Or I am wrong?
0.4 cfm/ft2 can be entered in the same detailed edit window I copied you
on earlier.
If you set the minimum flow to 0.5 cfm/ft2, that implies a proposed
system design decision. Note that the referenced section is
specifically for Baseline HVAC systems, not your proposed model.
You can avoid making an assumption of which is greater, simply enter
both the ventilation requirements and the minimum cfm/ft2. eQuest will
work out both for each hour, and provide cfm to meet hourly ventilation
needs in excess of the minimum ratio as necessary - this meets the
requirement of the referenced section.
Hi there Xiaoyang,
VAV min flows can be set both in wizards and in detailed edit modes.
See following screenshots.
The "standard" depends on the HVAC design, and specifically how
ventilation air is being distributed. There's a range of CFM's that the
factory will set as a minimum terminal unit at depending on the size,
but it may well be zero if you are distributing ventilation air via DOAS
in certain ways. I'd suggest asking your HVAC designer directly what
the minimum is for each unit (it's probably scheduled), and use that
info to either come up with an average for each zone or to set the
minimum for each zone separately.
Here's the wizard...
... and in detailed, double click on a space served by a VAV system,
under the Airside HVAC tab, to find the following window. In this case,
the minimum flow is set to 30% (0.30):
~Nick
NICK CATON, E.I.T.
Hi Nick,
How do you think this standard from ASHRAE 90.1 G3.1.3.13 VAV Minimum Flow
Setpoints (Systems 5 and 7). Minimum volume setpoints for VAV reheat boxes
shall be 0.4 cfm/ft2 of floor area served or the minimum ventilation rate,
whichever is larger.
In my opinion, it means, if we set "Minimum Design Flow is 0.5 cfm/ft2", the
VAV minimum flow should be set 80% (we assume the minimum ventilation rate
is smaller than VAV minimum flow.), Or I am wrong?
Thank you very much.
Best,
Xiaoyang
Hi Xiaoyang,
0.4 cfm/ft2 can be entered in the same detailed edit window I copied you
on earlier.
If you set the minimum flow to 0.5 cfm/ft2, that implies a proposed
system design decision. Note that the referenced section is
specifically for Baseline HVAC systems, not your proposed model.
You can avoid making an assumption of which is greater, simply enter
both the ventilation requirements and the minimum cfm/ft2. eQuest will
work out both for each hour, and provide cfm to meet hourly ventilation
needs in excess of the minimum ratio as necessary - this meets the
requirement of the referenced section.
~Nick
NICK CATON, E.I.T.