RE: [EnergyPlus_Support] Re: winter design day

The fixed outdoor temperature for the 24 hour period does not mean that the heating load change of the building is also zero. There are other variables in the simulation.

I use the DesignDay simulation all the time, because I am the only person in this group still using a slow Pentium I, WindowsME PC.

In addition to the heating and cooling load sizing, I also use it to verify the correct expansion of the schedules and the use of temperature setpoints, and to verify the People, lights on weekdays, holidays, etc. are correctly calculated. It is so simple to get the 24 outdoor temperature numbers by changing only two numbers (Max. and range.) Of course, you can enter zero for SummerDesignDay as well. It will happen on a rainy day.

For places like Malaysia, Singapore and HongKong, there is no snow cover nor severe Winter. My WinterDesignDay is a rainy cloudy day. It is very flexible and convenient to change and use.

So feel free to change the field values, and observe the effects and make the most of it.

Of course, if you are submitting an energy Green Star report, for example, you need to follow the ASHRAE standard.

Jerry,

ASHRAE Technical Committee (TC) 4.2 Climatic Information developed the design day concept, working with TC 4.1 Load Calculations as a way to calculate the peak heating and cooling load conditions. (Sorry if I'm repeating subsequent discussion... just catching up here.)

The 0.4%, 99.6% represent the number of hours in a year that you could reasonably expect a particular temperature to be exceeded. This is calculated from the most recent 20-30 years of weather for that location. The ASHRAE Fundamentals Handbook--which is our primary source of data--also have the most extreme conditions.

These design conditions are simply used to size the heating and cooling equipment. The hourly weather data is what is used by EnergyPlus to calculate the operating energy performance of the building.

Hope I haven't confused the issue more.

Dru Crawley

DOE

From: EnergyPlus_Support@yahoogroups.com [mailto:EnergyPlus_Support@yahoogroups.com] On Behalf Of Jerry McManus
Sent: Wednesday, June 24, 2009 5:36 PM
To: EnergyPlus_Support@yahoogroups.com
Subject: Re: [EnergyPlus_Support] Re: winter design day

Thanks for the quick reply, but to be honest I'm still not convinced. If a
design day is intended to be worst case scenario (as opposed to realistic
weather simulation) then why wouldn't summer design days also have a 0 daily
temperature range?

You seem to be saying that there is an unspoken assumption in HVAC that heat
is always on in the winter, but cooling is only when you actually need it in
the summer. Is it the experience of building designers that once you get
below a certain outside temperature then a few degrees either way makes no
difference in heating loads?

----- Original Message -----
From: "JV Dirkes II" <jvd2pe@xxxxxxx>
To: <EnergyPlus_Support@yahoogroups.com>
Sent: Wednesday, June 24, 2009 10:44 AM
Subject: [EnergyPlus_Support] Re: winter design day

> Jerry,
>
> Without checking E+ docs, but using my experience......
> A "design day" is a "worst case" condition. For winter, that means a
> sustained cold period with no sun and no internal heat (e.g., lights or
> PCs). Using a zero degree daily range is a fairly normal approach to
> those criteria.
> A practical example in Michigan, where I'm from, would be an extended
> weekend (say, Christmas) when the temps drop very low and stay there for
> hours on end. The sun, as is usual in MI, doesn't shine. (Of course it
> could also be night time. We're why light therapy got popular.
> In that instance, the heating system is all you've got; it better be big
> enough!
>
> --- In EnergyPlus_Support@yahoogroups.com, "Jerry McManus" <jerrymcm@...>
> wrote:
>>
>> Hi Folks,
>>
>> I'm new to EnergyPlus, and a total noob when it comes to HVAC, so please
>> be gentle! Here's my first newbie question:
>>
>> While learning about design days I was confused by the fact that all of
>> the winter design days in the example weather data have a 0 daily
>> temperature range modifier. Searching the input\output reference yielded
>> this note:
>>
>> "Note that usual Winter design conditions are for very cloudy days
>> (clearness = 0), and low temperatures (temperature range=0)."
>>
>> Unfortunately no explanation is given why low temperatures should have 0
>> for the daily temperature range...? This is one of those things that is
>> probably obvious to an HVAC pro, but it's not at all clear to me why a
>> winter design day should not bother with highs and lows in the
>> temperature range.
>>
>> Any help will be greatly appreciated. Thanks!
>>
>
>
>
>
> -----------------------

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