[Equest-users] VAV minimum flow

[Nick Caton]

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.

PROJECT ENGINEER

Smith & Boucher Engineers

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

www.smithboucher.com 

 

From: xiaoyang shi [mailto:xs2144 at gmail.com] 
Sent: Monday, March 14, 2011 11:17 AM
To: Nick Caton; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] VAV minimum flow

 

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



On Fri, Mar 11, 2011 at 5:18 PM, Nick Caton <ncaton at smithboucher.com>
wrote:

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...

Error! Filename not specified.

... 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):

Error! Filename not specified.

 

 

~Nick

Error! Filename not specified.

 

NICK CATON, E.I.T.

PROJECT ENGINEER

Smith & Boucher Engineers

25501 west valley parkway

olathe ks 66061

direct 913 344.0036 <tel:913%20344.0036> 

fax 913 345.0617 <tel:913%20345.0617> 

www.smithboucher.com <http://www.smithboucher.com>  

 

From: equest-users-bounces at lists.onebuilding.org [mailto:
equest-users-bounces at lists.onebuilding.org] On Behalf Of xiaoyang shi
Sent: Friday, March 11, 2011 2:35 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] VAV minimum flow

 

Hi folks,

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?

Thank you.





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