<table cellspacing="0" cellpadding="0" border="0" ><tr><td valign="top" style="font: inherit;"><p>Hi,</p><p> I am simulating type 1b solar thermal collector using type 15-2 weather files.I want to calculate the useful energy of the collector for london environment.but the useful energy is in negative,why is that it should be positive.take a look of the simulation result below:I have highlighted it with the red color. waiting for the reply</p><p>              Time                                                   QColl                                           <br>  +0.0000000000000000E+00                      +0.0000000000000000E+00           <br>  +1.0000000000000000E+00           
              +0.0000000000000000E+00           <br>  +2.0000000000000000E+00                         +0.0000000000000000E+00           <br>  +3.0000000000000000E+00                         +0.0000000000000000E+00           <br>  +4.0000000000000000E+00                         +0.0000000000000000E+00           <br>  +5.0000000000000000E+00                         +0.0000000000000000E+00           <br>  +6.0000000000000000E+00                         +0.0000000000000000E+00          <br>  +7.0000000000000000E+00                  +0.0000000000000000E+00           <br>  +8.0000000000000000E+00                         +0.0000000000000000E+00           <br> 
 +9.0000000000000000E+00          <font color="#ff0000">               -2.4173684203587297E+02</font>    <br>  +1.0000000000000000E+01         <font color="#ff0000">               -2.5441648977456410E+02</font>    <br>  +1.1000000000000000E+01                         +4.8138101649880042E+01          <br>  +1.2000000000000000E+01                          +1.6144304197108370E+03          <br>  +1.3000000000000000E+01                          +3.4669850296828163E+03         <br>   </p></td></tr></table>