Re: [EnergyPlus_Support] Re: VAV Boxes

[fred buhl <wfbuhl@xxxxxxx>]

 From the cases I have seen, the average temperature is close to (but 
below) the zone heating
setpoint. It depends on how much cooling the system provides in the min 
cooling
state compared to the zone loads, zone heat capacity etc etc. In the 
cases I have
looked at, the effect on annual energy consumption is minor. I think the 
1.3.0 treatment
of reheat is better than previous versions, but still needs (and is 
being) improved.

Fred Buhl

enerdata wrote:

>Mike,
>
>Do you think this 'oscillation' with each timestep will produce an 
>average heating energy input to the zone over, say, a one hour period 
>sufficient to  maintain the space at close to the heating setpoint?  
>Is the effect therefore similar to a thermostat with slow reactions?
>
>I think the version 1.3.0 modelling is probably still more realistic 
>than earlier versions in terms of reheat assessment but would be 
>interested in your views.
>
>Jeff
>
>--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Michael J. Witte" 
><mjwitte@...> wrote:
>  
>
>>After some digging, we have verified that there is a problem with 
>>    
>>
>the behavior 
>  
>
>>of the reheat controls in version 1.3.0 under certain conditions.  
>>    
>>
>Without 
>  
>
>>getting into too much detail, if the zone thermostat predicts that 
>>    
>>
>the zone 
>  
>
>>would be in the deadband (between the heating and cooling setpoint) 
>>    
>>
>with no 
>  
>
>>HVAC operation, it sets a "deadband" flag.  When the deadband flag 
>>    
>>
>is active, 
>  
>
>>the reheat coil will not operate.  If the min flow of cold air from 
>>    
>>
>the VAV 
>  
>
>>terminal unit cools the zone below the heating setpoint, the reheat 
>>    
>>
>coil will 
>  
>
>>not come on until the next time step.  The solution is oscillating 
>>    
>>
>between 
>  
>
>>these states.  I do not know of a workaround to get this to behave 
>>    
>>
>any better 
>  
>
>>in 1.3.0.018.
>>
>>Mike
>>
>>
>>On 15 Jun 2006 at 11:33, Peter G Loutzenhiser wrote:
>>
>>    
>>
>>>>Hello All,
>>>>        
>>>>
>>>I have just started using the 1.3 version of 
>>>EnergyPlus with a VAV reheat system and a dual 
>>>heating/cooling setpoint temperature.  I have 
>>>13.6°C air entering the coil and I have a heating 
>>>setpoint of 22°C.  I have given the reheat coils 
>>>plenty of capacity and yet I still get zone 
>>>temperature below the heating setpoint (in the range of 21.7°C).  
>>>      
>>>
>Why is
>  
>
>>>this?
>>>
>>>Peter
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>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.idf 
>>>      
>>>
>and press the
>  
>
>>>"search" button.
>>> 
>>>Yahoo! Groups Links
>>>
>>>
>>>
>>> 
>>>
>>>
>>>
>>>
>>>
>>>      
>>>
>>========================================================
>>Michael J. Witte, GARD Analytics, Inc.
>>EnergyPlus Testing and Support      
>>EnergyPlus-Support@...
>>
>>    
>>
>
>
>
>
>
>
>
>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.idf and press the "search" button.
> 
>Yahoo! Groups Links
>
>
>
> 
>
>
>  
>


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