[Bldg-sim] calculating the mean monthly outdoor temp

[Joe Huang]

I was just responding to Chris' seemingly innocuous question on how to calculate the mean monthly outdoor temperature. How is that related to your program or any other loads or energy calculation method?  I haven't seen your program, but from your description, it sounds like a derivative of the ASHRAE TC47 bin method. When that first came out in the mid-70s, weren't there complaints then, too, that it was too complicated, compared to the previous degree-day method ?  I guess it's all a matter of your perspective. If I may generalize, a degree-day method reduces everything to a single calculation, a bin method calculates a few score of snapshot conditions, while an hourly simulation tracks the building hour-by-hour for 8760 hours.  Each has their limitations and applicability.

But back to what I had said about calculating the mean monthly outdoor temperature from hourly data, this has nothing to do with any calculation or simulation method. If the data are available, it can be done using a spreadsheet program in literally a few seconds, which is why I'm puzzled by your response.

Joe Huang
White Box Technologies, Inc.

----- Original Message ----- 
  From: billhclark at bar-x-soft.com 
  To: Joe Huang 
  Cc: bldg-sim at lists.onebuilding.org 
  Sent: Friday, November 28, 2008 6:46 AM
  Subject: RE: [Bldg-sim] calculating the mean monthly outdoor temp


  Where did you people get the idea the method used only max and min temperatures?  It uses total annual heating and cooling bin hours and langleys.  The DOE developed the method using nomographs - it works for them, and I don't see why it can't work equally as well now.  I do not claim it is as accurate as the full blown methods on the market that tabulate loads for every hour and every day.  (If you really want to get pedantic, that method is quite inaccurate, considering the extreme variability in weather.) My method is a very good approximation - it is quick enough that the program operates like a spreadsheet, and gives instantaneous data for every change made in the model.  You see the results on the same screen, and so can see exactly what the result of changing roof color (which is dramatic), adding double paned windows (which is effective only on south and west facing windows), changing outside wall color (which has a significant impact), and so forth.  What other program can claim that kind of immediate result?  You see the effect on annual load from every single building element, and can tweak them individually to find out what works best ~ all this one one screen, real time ~ no waiting for massive print outs with every iteration.

  Actually, there are just as many draw backs to the "standard" and "accepted" methods that do hourly calculations ~ the weather is so variable and undependable. All anybody can do is develop a method that gives dependable results, and that's what my program does ~ as good as any product out there.  Moreover, my software is quite simple ~ which actually makes it better because the user can actually understand what he's doing, see the results, and work forward accordingly.  

  How useful is a massive program that takes a Masters Degree for the operator to understand and use, a week to input all the data acceptably ~ versus a program that anybody can use in minutes, and obtain a result in an hour?  How many expert energy auditors are there who can do the number of energy audits needed to make any significant impact on energy usage for the U.S.?  The only way to make progress in reducing building energy use is to have a program like mine that gives decent results quickly and with zero experience required.  Having all the results appear instantly on the screen actualy makes the program fun to operate, and quite insightful and educational.  

  BC


    -------- Original Message --------
    Subject: Re: [Bldg-sim] calculating the mean monthly outdoor temp
    From: "Joe Huang" <joe at drawbdl.com>
    Date: Thu, November 27, 2008 10:07 pm
    To: "Chris Yates" <Chris at zed-uk.com>, "Building Simulation"
    <bldg-sim at lists.onebuilding.org>

    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" <Chris at zed-uk.com>
    To: "Building Simulation" <bldg-sim at lists.onebuilding.org>
    Sent: Thursday, November 27, 2008 1:58 PM
    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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