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<TITLE>RE: [bldg-sim] VAV control of underfloor air</TITLE>
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<P><FONT SIZE=2>Although I have always been interested in designing such a system I have yet to do so. However, that doesn't seem to stop me from adding in some anecdotal information from friends who have designed such systems. First off (not from friends, this is my own observation), a VFD for an air handler tends to be nearly the same cost as a starter, except for the additional control point-that being the differential pressure sensor. Additionally, to keep costs down, I would let the VFD control the situation, not the EMCS. Just have the VFD update the EMCS, and allow the EMCS to reset the differential pressure sensor. Go ahead and monitor all the points you want, and at least do start / stop, status, and DP sensor reset. Like Robert says, the VFD is a cost wise investment, even if you end up later on setting it up to be a constant speed system, the cost risk is low.</FONT></P>
<P><FONT SIZE=2>Now I would like some additional information. The IRR of 30% to 50%; is that just for the mechanical investment or everything? Since this type of system uses a raised floor system, all the utilities end up running under the floor. Code will dictate the use of plenum rated cable (even when run inside conduit), the floor system itself tends to be proprietary-or at best limited in number of suppliers--hence supply and demand comes into play driving the cost of the floor up and that is beyond the fact that it is already more expensive since it needs to be structurally capable of carrying the loads (including areas for very large filing systems), there are a limited number of suppliers of underfloor vav systems (and the quality varies), as a positive there is a greatly reduced amount of sheet metal used for ductwork, there usually is not a realistic coordination between cubical / office layout and diffuser placement (in large jobs, the eventual leasee is unknown hence their layout needs are unknown) causing problems by a maintenance staff that is unfamiliar with the system (despite training), and another maintenance problem are users who do not understand nor properly utilize the system hence they will block the diffusers (more often then the overhead type). Plumbing may also be run in the floor space as well as other utilities causing a need for additional wall furrings then may be in a more traditional layout. Was there any account of these items in the IRR, or was it a theoretical value based only on the mechanical components?</FONT></P>
<P><FONT SIZE=2>I do not mean to discourage anyone from using this system, I actually am very interested and excited to implement this type of system, and believe (instinctually) that it is an energy efficient alternative to the traditional diffusion method of airside systems. The points listed above are things you should be aware of, and are questions to ask so as to minimize their impact.</FONT></P>
<P><FONT SIZE=2>As Rob says Good Luck, and have some fun!</FONT>
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<P><FONT SIZE=2>Eric Kirchhoff, PE</FONT>
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<P><FONT SIZE=2>-----Original Message-----</FONT>
<BR><FONT SIZE=2>From: Robert Lord [<A HREF="mailto:rgl.lsbris@lincolne.com.au">mailto:rgl.lsbris@lincolne.com.au</A>]</FONT>
<BR><FONT SIZE=2>Sent: Sunday, November 03, 2002 2:55 PM</FONT>
<BR><FONT SIZE=2>To: bldg-sim@gard.com</FONT>
<BR><FONT SIZE=2>Subject: [bldg-sim] VAV control of underfloor air</FONT>
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<P><FONT SIZE=2>A typical design is to zone the floor compartment according to aspect and allow the individuals to adjust the swirls.</FONT>
<BR><FONT SIZE=2>There are only a handful of large VAVs and the fan speed is varied according to duct static pressure (not plenum pressure).</FONT></P>
<P><FONT SIZE=2>In most instances, I have found that the internal rate of return is between 30% & 50% and hence is a good investment. I am sure VSD pricing and energy pricing varies but a point to note is that the RH control is improved.</FONT></P>
<P><FONT SIZE=2>Good luck!</FONT>
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<P><FONT SIZE=2>Rob Lord</FONT>
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<P><FONT SIZE=2>-----Original Message-----</FONT>
<BR><FONT SIZE=2>From: Molinini, Louis [<A HREF="mailto:lmolinini@syska.com">mailto:lmolinini@syska.com</A>]</FONT>
<BR><FONT SIZE=2>Sent: Saturday, 2 November 2002 8:37 AM</FONT>
<BR><FONT SIZE=2>To: bldg-sim@gard.com</FONT>
<BR><FONT SIZE=2>Subject: [bldg-sim] VAV control of underfloor air</FONT>
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<P><FONT SIZE=2>Do any of you out there have any experience designing an underfloor air</FONT>
<BR><FONT SIZE=2>system with VAV control. The particular system I am looking at is a plenum</FONT>
<BR><FONT SIZE=2>based system with manually adjustable swirl diffusers (Titus/Krantz). I am</FONT>
<BR><FONT SIZE=2>curious if it ends up operating like a constant volume system or is it worth</FONT>
<BR><FONT SIZE=2>the expense of installing the freq drive and the Static pressure sensor or</FONT>
<BR><FONT SIZE=2>differential pressure sensor. Any help is greatly appreciated.</FONT>
<BR><FONT SIZE=2>Thanks,</FONT>
<BR><FONT SIZE=2>Louis</FONT>
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