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RE: [EnergyPlus_Support] similar to Purchased Air
Thanks for very good explanation.
Najad Tuffaha, PE, CEM
Pepco Energy Services
703 253-1774
202 309-0553
-----Original Message-----
From: Richard J. Liesen [mailto:r-liesen@xxxxxxxx]
Sent: Wednesday, January 22, 2003 4:55 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx;
EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: RE: [EnergyPlus_Support] similar to Purchased Air
Hello,
You ask a very good question. Until the autosize option was implemented
there was no way that you could simulate the building to obtain the
loads
necessary to size the system and plant so you could do the
simulation. There was the classic which came first the chicken or the
egg
problem; in this case the building or the loads. Therefore there had to
be
a way to specify a system that had no capacity limits to determine the
loads so that an air system could be properly sized and simulated. That
is
why the temperature is specified and the volume flow is calculated. In
actuality the autosize runs this same type of calculation to determine
this
information and then those results are propagated to the correct fields
in
the system components. If you look at the Zone Sizing Object you will
see
several inputs that replicate the Purchased Air inputs.
Some people still like to do this in a multi step process for greater
understanding of the loads and sizing of there components, instead of
turning on some parameters and letting the program take off into the
great
unknown. Others like the idea of using the autosize option to alleviate
the tedium of model building and checking. But there is another group
that
may be doing a study on the envelope and want to avoid the time and
complexity investment of adding an air system for their study. This
seems
to be the greatest utility of Purchased Air at this point! But that is
also why Purchased Air does not do all of the things that have been
asked
about lately.
Thanks
Dr. Richard Liesen
Associate Director, Building Systems Laboratory
Department of Mechanical and Industrial Engineering
University of Illinois at Urbana-Champaign
At 01:15 PM 1/22/2003, Najad Tuffaha wrote:
>It appears that "Purchased Air" option does not represent any actual
type of
>airside HVAC system. What is the purpose of simulating such an option,
>rather than simulating real airside systems?
>
>Najad Tuffaha, PE, CEM
>PEPCO ENERGY SERVICES
>Office 703 253-1774
>Mobile 202 309-0553
>Fax 703 253-1799
>
>-----Original Message-----
>From: Richard J. Liesen [mailto:r-liesen@xxxxxxxx]
>Sent: Wednesday, January 22, 2003 12:39 PM
>To: EnergyPlus_Support@xxxxxxxxxxxxxxx;
EnergyPlus_Support@xxxxxxxxxxxxxxx
>Subject: Re: [EnergyPlus_Support] similar to Purchased Air
>
>Hello,
>Purchased Air can not do this. However all of the Constant Volume
systems
>do provide this, ie. Single Duct Terminal Reheat, Fan Coils, etc..
>
>Thanks
>Richard Liesen
>
>
>At 09:31 AM 1/22/2003, li zhang wrote:
> >Hello, Everyone,
> >In purchased air, the air temperature is given, and
> >the flow rate can be calculated and provided based on
> >the load. Is there a way in which the supply air
> >flow rate is given, however the air temperature can be
> >calculated and provided?
> >
> >Thank you!
> >
> >Li Zhang
> >Department of Mechanical Engineering
> >Iowa State University
> >Ames, IA 50011
> >
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