<html>
<body>
I do not think this problem should be ignored. It is often
difficult to get everyone on the same page as to the exact definitions of
data items, but it is very important or we'll soon be feeding unknown
data into unknown algorithms ...<br><br>
ASHRAE algorithms are based on the thermodynamic wet bulb temperature, t*
= the temperature of adiabatic saturation. t* is a unique property
of moist air (not dependent on velocity etc.) and is the input data
required by most simulation programs. It can be approximately
measured with a psychrometer with a sufficient air flow rate or
calculated from the dew point. From your description, it sounds
like the Met service is publishing a wet bulb defined differently than
this (?).<br><br>
It may be possible to derive t* if you have the details of the Met
service instrumentation and/or algorithm. Alternatively, if the Met
service data includes dew point, you should be able to work from that
using ASHRAE algorithms.<br><br>
Regarding your comment that velocities inside buildings are usually low
... if a given simulation includes velocity-related algorithms (for
comfort modeling, perhaps), those would need the true absolute humidity
(or some variant) as input. The models would provide velocity
adjustments as required. For HVAC calculations (coil models,
evaporative cooling, etc.), t* or a suitable alternative is needed.
I am not aware of any situation where a "partial saturation
temperature" is useful as primary data.<br><br>
In am curious how the Met service data relates to WMO standards. I
am not familiar in detail with these, but I am sure the wet bulb and its
measurement are rigorously defined. I am surprised that a national
service would choose an alternative procedure (if in fact they
have). If you get more info, I would be interested in hearing about
it.<br><br>
Chip Barnaby<br>
Chair, ASHRAE TC 4.2 (Climatic Information)<br><br>
<br>
At 10:09 AM 07-06-05, Samuel Hassid wrote:<br>
<blockquote type=cite class=cite cite=""><font face="arial" size=2>
I was wondering if anybody has encountered a similar problem - and how it
was solved<br>
</font> <br>
<font face="arial" size=2> In Israel the metorological years
contain both the Wet Bulb Temperature and the the relatrive humidity.
These, however, are not consistent with the ASHRAE algorithm - which is
used in most simulation programs. The Meteorological service stands
behind its algorithm for calculating the Relative Humidity from the Wet
and Dry Bulb temperatures, on the grounds that the wet bulb temperature
recorded is under natural ventilation, and therefore the incresed value
of the hygrometric constant is relevant.<br>
What should one do<br>
a. Calculate from the Relative Humidity Readings a new wet bulb
temperature, consistent with teh ASHRAE algorithm (or with the high
velocity wet bulb temperature algorithm) ?<br>
b. Not bother - on teh grounds that anyway the wet bulb temperature
inside buildings is usually based on relative low velocity - as in the
measured wet bulb temperature ?<br>
</font> <br>
<font face="arial" size=2> A quick check shows that the difference
may be of the order of several percentage points for the relative
humidity, or of the order of 1 oC for Wet Bulb Temperature.<br>
</font> <br>
<font face="arial" size=2>
Thanks
S. Hassid<br>
</font><br>
<pre>
You received this e-mail because you are subscribed
to the BLDG-SIM@GARD.COM mailing list. To unsubscribe
from this mailing list send a blank message to
BLDG-SIM-UNSUBSCRIBE@GARD.COM
</pre><font face="Courier New, Courier"></blockquote>
<x-sigsep><p></x-sigsep>
---------------------------------------------------------<br>
Chip
Barnaby
cbarnaby@wrightsoft.com<br>
Vice President of Research<br>
Wrightsoft
Corp.
781-862-8719 x118 voice<br>
394 Lowell St, Suite 12
781-861-2058 fax<br>
Lexington, MA
02420
<a href="http://www.wrightsoft.com/" eudora="autourl">www.wrightsoft.com<br>
</a>---------------------------------------------------------</font><PRE>
======================================================
You received this e-mail because you are subscribed
to the BLDG-SIM@GARD.COM mailing list. To unsubscribe
from this mailing list send a blank message to
BLDG-SIM-UNSUBSCRIBE@GARD.COM
</PRE></body>
</html>