[Bldg-sim] calculating the mean monthly outdoor temp

[Peter Simmonds]

Chris, perhaps I can shed some light on this apparition for you. I was a
member of the ASHRAE 55 committee when the adaptive comfort method was
introduced. From data sets with unknown origins a group came up with
statistical evaluation of the results, the mean outdoor temperature. I
see some of the top weather statisticians have already replied and
wonder above wonder when you take the mean temperature, it is somewhat
lower than the design temperature most of us old fogey's are used to
working with. So mysteriously a 32C design temp gets slimmed down to a
26C mean temp and it fits the graph.

When we have to 'cook' the books in this manner we simply take the
monthly outdoor dry bulb temperature and divide this by the number of
hours. Now the next question that isn't explained in 55 is whether or
not the weather data should be taken for only the occupied period or the
whole month ?  The plot thickens. A simple explanation on how to use
this methodology is whether or not the user is liable for the
calculations and designs. Imagine a litigation case, when asking the
engineer 'How did you calculates this?" well I took the mean of the
outdoor temperature and I...................... Case closed.

 

Peter Simmonds Ph.D.

Senior Associate, Advanced Technology Group

 

IBE Consulting Engineers

14130 Riverside Drive Suite 201

Sherman Oaks, CA 91423

p:   (818) 377-8220 ext. 246

f:    (818) 377-8230

m:  (818) 219-1284

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-----Original Message-----
From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Chris Yates
Sent: Thursday, November 27, 2008 1:59 PM
To: Building Simulation
Subject: [Bldg-sim] calculating the mean monthly outdoor temp

 

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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