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Re: [EnergyPlus_Support] Design coil load is zero
Filipe madureira wrote:
> Hi,
>
> I' m using the EnergyPlus 1.4.0.025 version. Could it be an issue related to
> this program version?
>
Not likely; but I wanted to look at the code and needed to be sure I was
looking at code that
corresponds to your problem.
For reheat coils, the coil load is calculated using the design heating
flow rate for the zone and
a design air delta T across the coil. The coil inlet temperature is the
"central heating design supply
air temperature" from the System Sizing input. This is 25 C in your
input. The outlet is the
"zone heating design supply air temperature" from your Zone Sizing
input. This is also 25
in your input, so your coil design delta T is zero and the design load
will be zero; which will
cause the design max hot water flow rate to be zero. If you set "central
heating design supply
air temperature" in System Sizing to 16, the same value as your "central
cooling design supply
air temperature" you should get a reasonable result. Unfortunately the
design calculation doesn't
know you don't have a central heatin coil - if it did, it could do
something more intelligent than
using "central heating design supply air temperature" as the coil inlet
temperature in the sizing
calculation.
Fred Buhl
> One more question related to this topic: If I define an Outside Air flow
> rate which will be supplied by the air loop, will it be accounted in zone
> sizing? I'm asking this because I didn't define a central heating coil.
>
No; the size of the reheat coil is set by the zone design heating load,
the zone design inlet air heating
temperature, and the system design supply air heating temperature, The
outside air will only
affect the size of the central coils, since it impacts the load they see.
Fred Buhl
> Thanks in advance
>
> Filipe Madureira
> Tel: +351 919 293 876 | E-mail: filipe.madureira@xxxxxxxxxxxxx
> __________________________________________________________________
> FluidInova, Engenharia de Fluidos, SA
> TECMAIA - Parque de Ciência e Tecnologia da Maia
> Rua Engº Frederico Ulrich, nº 2650 | 4470-605 Moreira da Maia | Portugal
>
> Tel: (351) 229 408 265 | Fax: (351) 229 408 266
> E-mail: geral@xxxxxxxxxxxxx | Web: http://www.fluidinova.pt/
>
>
> -----Original Message-----
> From: EnergyPlus_Support@xxxxxxxxxxxxxxx
> [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Fred Buhl
> Sent: 20 November 2007 20:49
> To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> Subject: Re: [EnergyPlus_Support] Design coil load is zero
>
> Filipe,
>
> What version of the program are you running?
>
> Fred Buhl
>
> Filipe madureira wrote:
>
>> Hi all,
>>
>>
>>
>> I'm trying to simulate a Constant Volume Air Handling Unit to control
>> temperature in a single zone. The AHU has a constant volume fan and a
>> cooling coil. Heating is provided by a terminal reheat coil.
>>
>> To control the exit cooling coil air temperature I've defined a
>> controller:simple and a Set - point manager: Warmest to reset the cooling
>> coil air temperature.
>>
>> To control zone temperature, I've defined a dual set-point with deadband
>> thermostat (heating set-point temperature 20ªC, cooling set-point
>> temperature 24ºC).
>>
>>
>>
>> The total air system and outside air volumetric flow rates are known.
>>
> For
>
>> this reason, in the zone sizing object I've defined the cooling and
>>
> heating
>
>> design air flow method to "flow/zone" and input the desired flow rates.
>>
> I've
>
>> defined also the outside air flow rate.
>>
>>
>>
>> ZONE SIZING,
>>
>> P1 - Sala_Cirurgia, !- Name of a zone
>>
>> 16, !- Zone cooling design supply air temperature
>> {C}
>>
>> 25, !- Zone heating design supply air temperature
>> {C}
>>
>> 0.008, !- Zone cooling design supply air humidity
>> ratio {kg-H2O/kg-air}
>>
>> 0.008, !- Zone heating design supply air humidity
>> ratio {kg-H2O/kg-air}
>>
>> flow/zone, !- outside air method
>>
>> 0, !- outside air flow per person {m3/s}
>>
>> 1.167, !- outside air flow per zone {m3/s}
>>
>> 1, !- zone sizing factor
>>
>> flow/zone, !- cooling design air flow method
>>
>> 5.139, !- cooling design air flow rate {m3/s}
>>
>> flow/zone, !- heating design air flow method
>>
>> 5.139; !- heating design air flow rate {m3/s}
>>
>>
>>
>> As I've read in the mailing list and in the EnergyPlus documentation, the
>> flow rates are sized on the sum of zone air flow rates. If I define
>> flow/zone method, design calculated flow rates are override. For this
>> reason, I didn't change the flow rate fields in the System Sizing to let
>> the program compute the flows I've entered in the zone sizing object.
>>
>>
>>
>> SYSTEM SIZING,
>>
>> UTA_BO 2, !- name of an AIR PRIMARY LOOP object
>>
>> sensible, !- type of load to size on
>>
>> autosize, !- Design (minimum) outside air volumetric
>>
> flow
>
>> rate {m3/s}
>>
>> 1, !- minimum system air flow ratio
>>
>> 7, !- Preheat design set temperature {C}
>>
>> 16, !- Central cooling design supply air
>> temperature {C}
>>
>> 25, !- Central heating design supply air
>> temperature {C}
>>
>> noncoincident, !- Sizing Option
>>
>> no, !- Cooling 100% Outside Air
>>
>> no, !- Heating 100% Outside Air
>>
>> 0.008, !- Central cooling design supply air humidity
>> ratio {kg-H2O/kg-air}
>>
>> 0.008, !- Central heating design supply air humidity
>> ratio {kg-H2O/kg-air}
>>
>> design day, !- cooling design air flow method
>>
>> , !- cooling design air flow rate {m3/s}
>>
>> design day, !- heating design air flow method
>>
>> ; !- heating design air flow rate {m3/s}
>>
>>
>>
>> In the components (coils, fan...) I left the fields with the autosize
>>
> option.
>
>>
>>
>> To simulate a worst case scenario, I defined the day type as
>>
> WinterDesignDay
>
>> and defined the internal gains schedule to off for this day.
>>
>>
>>
>> I ran the sizing objects and the design day simulation and I' get the
>> following warning:
>>
>>
>>
>>
>>
>> ** Warning ** The design coil load is zero for COIL:Water:SimpleHeating P1
>>
> -
>
>> SALA_CIRURGIA REHEAT COIL
>>
>> ** ~~~ ** The autosize value for max water flow rate is zero
>>
>> ** ~~~ ** To change this, input a value for UA, change the heating
>> design day, or lower
>>
>> ** ~~~ ** the system heating design supply air temperature
>>
>>
>>
>> To debug the problem I' ve asked the following report variables:
>>
>> Zone/Sys Sensible Load Predicted
>>
>> Zone/Sys Thermostat Heating Setpoint
>>
>>
>>
>> I don't understand why I get this warning because zone temperature is
>>
> lower
>
>> than the set-point, a heating load is predicted and the thermostat heating
>> set point is 20ºC. I also checked the component connections, flow rates
>>
> and
>
>> availability schedules and everything seems to be alright.
>>
>>
>>
>> I'm missing something? Could anyone help me?
>>
>>
>>
>> Thanks in advance for your help
>>
>>
>>
>> Best regards
>>
>>
>>
>>
>>
>> Filipe Madureira
>>
>> Tel: +351 919 293 876 | E-mail: filipe.madureira@xxxxxxxxxxxxx
>>
>> __________________________________________________________________
>>
>> FluidInova, Engenharia de Fluidos, SA
>>
>> TECMAIA - Parque de Ciência e Tecnologia da Maia
>>
>> Rua Engº Frederico Ulrich, nº 2650 | 4470-605 Moreira da Maia | Portugal
>>
>>
>> Tel: (351) 229 408 265 | Fax: (351) 229 408 266
>>
>> E-mail: <mailto:geral@xxxxxxxxxxxxx> geral@xxxxxxxxxxxxx | Web:
>> <http://www.fluidinova.pt/> http://www.fluidinova.pt/
>>
>>
>>
>>
>>
>> [Non-text portions of this message have been removed]
>>
>>
>>
>> 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
>>
> folder in the Files area of the Support Web Site.
>
>> EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the
>>
> Documentation link and press the "search" button.
>
>>
>> Yahoo! Groups Links
>>
>>
>>
>>
>>
>
>
> 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
> folder in the Files area of the Support Web Site.
>
> EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the
> Documentation link and press the "search" button.
>
> Yahoo! Groups Links
>
>
>
>
>
>
> 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 folder in the Files area of the Support Web Site.
>
> EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
>
> Yahoo! Groups Links
>
>
>
>
[Non-text portions of this message have been removed]
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