Re: [EnergyPlus_Support] autosizing components in hybrid DV/radiant heating system

["Josh K" <jeemang@xxxxxxxxx>]

Hi Fred;

Thanks in advance for taking a look at it. I uploaded the .idf to the
Problem_Submittals folder. It's called "DV_test."

Thanks,

Josh


On Nov 20, 2007 3:56 PM, Fred Buhl <wfbuhl@xxxxxxx> wrote:
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>  josh_miarch wrote:
>  > I'm attempting to model a cold climate system in which heating is
>  > provided by a combination of centrally conditioned air (delivered via
>  > displacement ventilation) and a radiant panel. The zone in question
>  > has a constant setpoint of 21 C. Air is delivered from the central AHU
>  > at 19 C, with the balance of the heating load being made up by the
>  > radiant panel.
>  >
>  > I've modeled this with a DIRECT AIR object given heating priority 1
>  > and a LOW TEMP RADIANT SYSTEM:HYDRONIC object (heating control
>  > temperature = 18 C, throttling range = 3 C) given heating priority 2.
>  >
>  > The problem I'm having is that the autosizable fields of several
>  > objects are being filled incorrectly. For example, the maximum hot
>  > water flow of the radiant panel is being autosized to 0. Strangely, I
>  > noticed that when I increase the "zone heating design supply air
>  > temperature" field in the ZONE SIZING object from its original value
>  > of 19 C, at a certain point the maximum hot water flow of the radiant
>  > panel starts getting autosized to numbers greater than 0.
>  >
>  > Investigating this further, I noticed that the "DesLoad" outputted in
>  > the "Zone Sizing Information" section of the .eio output file changed
>  > when I changed the zone heating design supply air temperature in the
>  > ZONE SIZING object. For example, when the design supply air temp was
>  > set to 19 C, the "DesLoad" was 0.20703 W, and when it was set to 80 C,
>  > the "DesLoad" was 13194 W.
>  >
>  > I'm guessing that this is the source of my problems. It seems strange
>  > to me that the design load would change based on the supply air
>  > temperature -- shouldn't these variables be independent of one another?
>  >
>  Yes; in theory anyway. But other design constraints might be affecting
>  the initially calculated, pure
>  design load. Why don't you upload your input and we will take a look.
>
>  Fred Buhl
>
>  > I know that EnergyPlus can sometimes struggle with hybrid systems like
>  > this; I'm wondering if there is an error on my part, or if this an
>  > example of EnergyPlus' limitations in this area. Any advice that
>  > anyone could give me that would get me closer to an accurate
>  > simulation would be greatly appreciated.
>  >
>  > Thanks,
>  >
>  > Josh
>  >
>  > --
>  > Josh Kjenner, EIT, LEED AP
>  > Manasc Isaac Architects Ltd.
>  > 10225 100 Avenue :: Edmonton, AB T5J 0A1
>  > 780.429.3977
>  >
>  >
>  >
>  >
>  >
>  > The primary EnergyPlus web site is found at:
>  > http://www.energyplus.gov
>  >
>  > The group web site is:
>  > http://groups.yahoo.com/group/EnergyPlus_Support/
>  >
>  > Attachments are not allowed -- please post any files to the appropriate
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>  >
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> Documentation link and press the "search" button.
>  >
>  > Yahoo! Groups Links
>  >
>  >
>  >
>  >
>  



-- 
Josh Kjenner, EIT, LEED AP
Manasc Isaac Architects Ltd.
10225 100 Avenue :: Edmonton, AB T5J 0A1
780.429.3977


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