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<DIV><FONT size=2 face=Arial>Mean monthly outdoor temperature was
incorporated in the ASHRAE Standard 55-2004, because this parameter can be found
easily from readily available climatic data, such as published by <A
title="http://www.ncdc.noaa.gov CTRL + Click to follow link"
href="http://www.ncdc.noaa.gov">www.ncdc.noaa.gov</A> </FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>In the ASHRAE RP-884 project, which
formed the basis of the adaptive thermal comfort in ASHRAE Standard 55, the
outdoor temperature index used was the mean effective temperature
(ET*). ET* combines temperature and humidity into a single index and
for RP-884 was calculated based on measured data. It should be noted that RP-884
involved nearly 21,000 sets of raw data compiled from 160 different office
buildings located over a broad spectrum of climate zones spread across 4
continents. For more information regarding the relationship between thermal
comfort and the environmental index- ET*, please refer to the Thermal Comfort
chapter in ASHRAE Handbook of fundamentals. </FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>As mentioned earlier, the mean monthly outdoor
temperature was introduced in the ASHRAE Standard 55, because it is easy to
use and can be estimated quickly. The</FONT><FONT size=2 face=Arial>
regressions (between the indoor operative temperature and the
outdoor temperature index) that were finally incorporated in Figure
5.3 in the ASHRAE Standard 55 were recalculated based on mean monthly outdoor
temperature (original index being ET*). </FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>It is not necessary, that everyone agrees with
the adaptive thermal comfort envelope yielded by using the mean monthly
outdoor temperature and figure 5.3 of ASHRAE Standard 55-2004. According to
one of the voting members of ASHRAE Standard 55 committee, the method was
incorporated in the Standard because the majority of the members voted in favor
of this method. And as you are all familiar with the public comment
procedure of ASHRAE Standards, please do voice your opinions.</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>To answer the original question by Chris-
</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV><FONT size=2 face=Arial>
<DIV><BR>One may purchase the last years weather data for a small fee at
NOAA website which provides the mean monthly outdoor temperature or
may use a TMY3 weather file to extract the hourly data for the month in
question. Calculate the daily max and daily min and then calculate the
average of daily max and average of daily min and then calculate the average of
these two averages. One may use only the summer months and/or shoulder
seasons (depending on the climate) for estimating the adaptive thermal
comfort envelope, because that’s when one would use natural ventilation for
cooling. Once you have the adaptive comfort envelope for the month in question,
use the internal operative temperatures during the occupied
hours to determine if 80% of those hours are within the upper and
the lower limit of allowable indoor operative temperature.</DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV>Furthermore, some researchers believe that adaptive thermal comfort is a
much complex phenomenon and hence the adaptive comfort envelope be estimated
using the running average of the past 30 days to calculate the thermal
comfort envelope for a particular day in a month and some
simplify that to only past one day. Please refer to the work by McCartney
& Nicol (2002), Nicol & Raja (1997) and Humphreys and Nicol (1998).
</DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV></FONT> </DIV>
<DIV><FONT size=2 face=Arial>Thanks.</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial>Gaurav Mehta</FONT></DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV><FONT size=2 face=Arial></FONT> </DIV>
<DIV style="FONT: 10pt Tahoma">
<DIV><FONT face=Arial></FONT><BR></DIV>
<DIV style="BACKGROUND: #f5f5f5">
<DIV style="font-color: black"><B>From:</B> <A
title="mailto:energy.wwind@cox.net CTRL + Click to follow link"
href="mailto:energy.wwind@cox.net">JRR</A> </DIV>
<DIV><B>Sent:</B> Monday, December 01, 2008 10:02</DIV>
<DIV><B>To:</B> <A
title="mailto:nathanm@rushingco.com CTRL + Click to follow link"
href="mailto:nathanm@rushingco.com">Nathan Miller</A> ; <A
title="mailto:bldg-sim@lists.onebuilding.org CTRL + Click to follow link"
href="mailto:bldg-sim@lists.onebuilding.org">bldg-sim@lists.onebuilding.org</A>
</DIV>
<DIV><B>Subject:</B> Re: [Bldg-sim] calculating the mean monthly outdoor
temp</DIV></DIV></DIV>
<DIV><BR></DIV>John Ross wrote;<BR><BR>Using a mean monthly temperature ties the
hands of innovative engineers in opportune climates.<BR>In Northern Virginia I
use an opening roof skylight to dump excessive solar gain in the late
afternoon.<BR>This operational variation is only practiced the last week of
September to the second week of October<BR>depending depending on the
particular year's weather<BR><BR>It would be appropriate to use mean monthly
temperature for calculating long term Geothermal field<BR>effects on the
other hand.......<BR><BR><BR>Nathan Miller wrote:
<BLOCKQUOTE cite=mid:008301c953d7$f42c7c80$dc857580$@com type="cite"><PRE wrap="">I'm no statistician, but I've always been dubious about that calculation.
You are taking the mean of two means, which seems to be getting farther
and farther from actual data.
It also seems to punish some of the climates that are best suited for
natural ventilation, since having cool nights significantly drops the
acceptability limits. I assume they are pushing you to take advantage of
night pre-cooling and thermal mass, but I find it curious that there are
no allowable hours outside of the range. All of the pre-cooling in the
world isn't going to help you keep the temperatures down during that one
string of 90 degree days in the tmy2 file...
Nathan Miller
Senior Energy Engineer/Mechanical Engineer
direct: 206.788.4577
fax: 206.285.7111
-----Original Message-----
From: <A class=moz-txt-link-abbreviated href="mailto:bldg-sim-bounces@lists.onebuilding.org">bldg-sim-bounces@lists.onebuilding.org</A>
[<A class=moz-txt-link-freetext title="mailto:bldg-sim-bounces@lists.onebuilding.org CTRL + Click to follow link" href="mailto:bldg-sim-bounces@lists.onebuilding.org">mailto:bldg-sim-bounces@lists.onebuilding.org</A>] On Behalf Of Chris Yates
Sent: Friday, November 28, 2008 2:30 AM
To: Building Simulation
Subject: Re: [Bldg-sim] calculating the mean monthly outdoor temp
There is a small difference between the arithmetic mean of the monthly
mean max and min and the overall arithmetic mean of 720 hours of weather
data. Like you say, it's probably a legacy from the old pen and paper
days.
I've heard that some would use occupied period only to calculate the
mean. However, I can not find any reference in the text of A55 to
justify this. Being able to average the warmer occupied hours would make
things a whole lot easier - even the 80% acceptability temperature can
regularly be lower than the summertime peaks. It's a tough call for
natural ventilation.
Many thanks
Chris
Joe Huang wrote:
</PRE>
<BLOCKQUOTE type="cite"><PRE wrap="">The cited method sounds like a carry-over from when stations reported
only max/min temperatures.
If hourly data is available, why wouldn't you just calculate the mean
of all the temperatures ?
Joe Huang
White Box Technologies
----- Original Message ----- From: "Chris Yates" <A class=moz-txt-link-rfc2396E title="mailto:Chris@zed-uk.com CTRL + Click to follow link" href="mailto:Chris@zed-uk.com"><Chris@zed-uk.com></A>
To: "Building Simulation" <A class=moz-txt-link-rfc2396E href="mailto:bldg-sim@lists.onebuilding.org"><bldg-sim@lists.onebuilding.org></A>
Sent: Thursday, November 27, 2008 1:58 PM
Subject: [Bldg-sim] calculating the mean monthly outdoor temp
</PRE>
<BLOCKQUOTE type="cite"><PRE wrap="">For the purpose of acceptability limits, can anybody cite any
guidance on calculating the mean monthly outdoor temperature? I've
read ASHRAE 55 and it states: "mean monthly outdoor temperature is
the arithmetic average of the mean daily minimum and the mean daily
maximum outdoor (dry bulb) temperature for the month in question."
Thanks
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