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<p class=MsoNormal><span style='font-size:11.0pt;color:#1F497D'>Based on the
fresh air volume in your example (108 l/s), the design air flow would have to
be at least equal to that amount and probably higher unless the primary air
handler is 100% fresh air. The design air flow based on 20F delta T should
always be trumped by the ventilation requirement, if ventilation requirement is
larger than it. <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:#1F497D'>In any case, I
would maintain a minimum of 0.4 cfm/sf as a minimum level of ventilation simply
as “good practice” to avoid stagnation. This may mean using
additional reheat energy or utilizing a fan-powered terminal unit to provide
additional recirculation air. <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:#1F497D'>However, if air
stagnation is not a concern, and design air flow is less than 0.4cfm/sf then I
would say that the minimum setpoint is at the discretion of the designer and any
value less than or equal to 0.4 cfm/sf would not violate the intent of the requirement.
In the same way, if the cooling design load required 1.0 cfm/sf but the heating
load for the space could be handled with less than 0.25 cfm/sf then I don’t
believe App G would require you to increase your minimum VAV setpoint to 0.4 since
that would be a silly waste of energy. The most extreme example of this
logic is an interior zone, which has zero heating load and zero fresh air load…Since
there is no reheat required, the 0.4 cfm/sf requirement does not apply and
therefore the VAV damper could be allowed to fully close when the space is
satisfied. Due to Standard 62 this occurrence is highly improbable, but
it helps to illustrate the point.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:#1F497D'>That’s my
two cents. <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:#1F497D'>Thanks,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></p>
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<p class=MsoNormal><span style='font-size:14.0pt;font-family:Cheltenham;
color:#A0002F'> </span><span style='font-size:18.0pt;font-family:Cheltenham;
color:#A0002F'>Dan Russell, EIT <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-family:Cheltenham;color:#A0002F'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-family:Cheltenham;color:#A0002F'><img
width=200 height=174 id="Picture_x0020_1"
src="cid:image001.jpg@01C944DC.7CE499A0"
alt="cid:image001.jpg@01C840A4.E711B250"></span><span style='font-size:11.0pt;
color:#1F497D'><o:p></o:p></span></p>
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<p class=MsoNormal><span style='font-size:11.0pt;color:#1F497D'><o:p> </o:p></span></p>
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<p class=MsoNormal><b><span style='font-family:"Tahoma","sans-serif";
color:windowtext'>From:</span></b><span style='font-family:"Tahoma","sans-serif";
color:windowtext'> bldg-sim-bounces@lists.onebuilding.org
[mailto:bldg-sim-bounces@lists.onebuilding.org] <b>On Behalf Of </b>Anis Ben
Ayed<br>
<b>Sent:</b> Wednesday, November 12, 2008 1:37 PM<br>
<b>To:</b> bldg-sim@lists.onebuilding.org<br>
<b>Subject:</b> [Bldg-sim] System 7 Min VAV setpoint<o:p></o:p></span></p>
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<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Dear all, <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The VAV minimum set point for system 7 in Appendix G is
calculated based on (0.4 cfm/ft2). For some spaces this number is bigger than
the calculated design airflow based on 20F delta T. What should the VAV set
points be in this case? <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Example:<o:p></o:p></p>
<p class=MsoNormal>Room: <o:p></o:p></p>
<p class=MsoNormal>VAVmin = 131 l/s<o:p></o:p></p>
<p class=MsoNormal>Design Air Flow = 84 l/s <o:p></o:p></p>
<p class=MsoNormal>Fresh Air = 108 l/s<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Thank you for your input,<span style='color:black'><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:12.0pt;font-family:"Arial","sans-serif";
color:black'><o:p> </o:p></span></p>
<p class=MsoNormal>Anis <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
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