I am modelling some triple-glazed windows, by copying the default double-glazed units provided in the database and adding an extra air gap and pane (see below for details). But when I substitute low-e glass for plate glass, the U-value calculated automatically actually rises somewhat, when I would expect it to drop. Is there something I&#39;m missing here?<br>

<br><br>
<b>Normal glass</b><br>




<p><span>&nbsp;</span>Layer|Prim|Thick
|Conduc-|Density|Specif|IR<span>&nbsp; </span>|Solr|Diffu|
R<span>&nbsp;&nbsp;&nbsp; </span>|Descr<span>&nbsp; </span>|db<span>&nbsp; </span>|(mm)<span>&nbsp;
</span>|tivity |<span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span>|heat<span>&nbsp; </span>|emis|abs |resis|m^2K/W</p>


<p><span>&nbsp;</span>Ext<span>&nbsp;&nbsp; </span>242<span>&nbsp;&nbsp;&nbsp;
</span>6.0<span>&nbsp;&nbsp;&nbsp;&nbsp; </span>0.760<span>&nbsp; </span>2710.<span>&nbsp;&nbsp;
</span>837. 0.83 0.05 19200.<span>&nbsp; </span>0.01 plate
glass : Plate glass with placeholder s</p>


<p><span>&nbsp;&nbsp;&nbsp; </span>2<span>&nbsp;&nbsp;&nbsp; </span>0<span>&nbsp;&nbsp;&nbsp;&nbsp;
</span>12.0<span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span>0.000<span>&nbsp;&nbsp;&nbsp;&nbsp; </span>0.<span>&nbsp;&nbsp;&nbsp;&nbsp;
</span>0. 0.99 0.99<span>&nbsp;&nbsp;&nbsp;&nbsp; </span>1.<span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span>0.17 air<span>&nbsp;
</span>0.17 0.17 0.17</p>


<p><span>&nbsp;&nbsp;&nbsp; </span>3<span>&nbsp; </span>242<span>&nbsp;&nbsp;&nbsp;
</span>6.0<span>&nbsp;&nbsp;&nbsp;&nbsp; </span>0.760<span>&nbsp; </span>2710.<span>&nbsp;&nbsp;
</span>837. 0.83 0.05 19200.<span>&nbsp; </span>0.01 plate
glass : Plate glass with placeholder s</p>


<p><span>&nbsp;&nbsp;&nbsp; </span>4<span>&nbsp;&nbsp;&nbsp; </span>0<span>&nbsp; &nbsp;&nbsp;
</span>12.0<span>&nbsp;&nbsp;&nbsp;&nbsp; </span>0.000<span>&nbsp;&nbsp;&nbsp;&nbsp; </span>0.<span>&nbsp;&nbsp;&nbsp;&nbsp;
</span>0. 0.99 0.99<span>&nbsp;&nbsp;&nbsp;&nbsp; </span>1.<span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span>0.17 air<span>&nbsp;
</span>0.17 0.17 0.17</p>


<p><span>&nbsp;</span>Int<span>&nbsp;&nbsp; </span>242<span>&nbsp;&nbsp;&nbsp;
</span>6.0<span>&nbsp;&nbsp;&nbsp;&nbsp; </span>0.760<span>&nbsp; </span>2710.<span>&nbsp;&nbsp;
</span>837. 0.83 0.05 19200.<span>&nbsp; </span>0.01 plate
glass : Plate glass with placeholder s</p>


<p><span>&nbsp;</span>ISO 6946 U values
(horiz/upward/downward heat flow)=<span>&nbsp;
</span><b>1.874<span>&nbsp; </span>1.985<span>&nbsp; </span>1.743</b> (partition)<span>&nbsp; </span>1.603</p><br><br><b>Low-E glass</b><br>



<p><span>&nbsp;</span>Layer|Prim|Thick
|Conduc-|Density|Specif|IR<span>&nbsp; </span>|Solr|Diffu|
R<span>&nbsp;&nbsp;&nbsp; </span>|Descr<span> &nbsp; &nbsp; </span>|db<span>&nbsp; </span>|(mm)<span>&nbsp;
</span>|tivity |<span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span>|heat<span>&nbsp; </span>|emis|abs |resis|m^2K/W</p>

<p><span>&nbsp;</span>Ext<span>&nbsp;&nbsp; </span>246<span>&nbsp;&nbsp;&nbsp;
</span>6.0<span>&nbsp;&nbsp;&nbsp;&nbsp; </span>1.050<span>&nbsp; </span>2500.<span>&nbsp;&nbsp;
</span>750. 0.05 0.06 19200.<span>&nbsp; </span>0.01 low_e
glass : 6mm CF Low_e glass with placeh</p>

<p><span>&nbsp;&nbsp;&nbsp; </span>2<span>&nbsp;&nbsp;&nbsp; </span>0<span>&nbsp;&nbsp;&nbsp;&nbsp;
</span>12.0<span>&nbsp;&nbsp;&nbsp;&nbsp; </span>0.000<span>&nbsp;&nbsp;&nbsp;&nbsp; </span>0.<span>&nbsp;&nbsp;&nbsp;&nbsp;
</span>0. 0.99 0.99<span>&nbsp;&nbsp;&nbsp;&nbsp; </span>1.<span> &nbsp; &nbsp; &nbsp; &nbsp;&nbsp; </span>0.17 air<span>&nbsp;
</span>0.17 0.17 0.17</p>

<p><span>&nbsp;&nbsp;&nbsp; </span>3<span>&nbsp; </span>246<span>&nbsp;&nbsp;&nbsp;
</span>6.0<span>&nbsp;&nbsp;&nbsp;&nbsp; </span>1.050<span>&nbsp; </span>2500.<span>&nbsp;&nbsp;
</span>750. 0.05 0.06 19200.<span>&nbsp; </span>0.01 low_e
glass : 6mm CF Low_e glass with placeh</p>

<p><span>&nbsp;&nbsp;&nbsp; </span>4<span>&nbsp;&nbsp;&nbsp; </span>0<span>&nbsp;&nbsp;&nbsp;&nbsp;
</span>12.0<span>&nbsp;&nbsp;&nbsp;&nbsp; </span>0.000<span>&nbsp;&nbsp;&nbsp;&nbsp; </span>0.<span>&nbsp;&nbsp;&nbsp;&nbsp;
</span>0. 0.99 0.99<span>&nbsp;&nbsp;&nbsp;&nbsp; </span>1.<span>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </span>0.17 air<span>&nbsp;
</span>0.17 0.17 0.17</p>

<p><span>&nbsp;</span>Int<span>&nbsp;&nbsp; </span>246<span>&nbsp;&nbsp;&nbsp;
</span>6.0<span>&nbsp;&nbsp;&nbsp;&nbsp; </span>1.050<span>&nbsp; </span>2500.<span>&nbsp;&nbsp;
</span>750. 0.05 0.06 19200.<span>&nbsp; </span>0.01 low_e
glass : 6mm CF Low_e glass with placeh</p>

<p><span>&nbsp;</span>ISO 6946 U values
(horiz/upward/downward heat flow)=<span>&nbsp;
</span><b>1.897<span>&nbsp; </span>2.011<span>&nbsp; </span>1.763</b> (partition)<span>&nbsp; </span>1.620</p>

<br><p></p>

Thanks,<br clear="all">Evan Sterling<br>Mathematics &amp; Engineering<br>Queen&#39;s University<br>