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Re: [EnergyPlus_Support] Return Air Setpoint Control Strategy

To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Return Air Setpoint Control Strategy
From: Jose Coutinho <coutinho@xxxxxxxxx>
Date: Thu, 12 Apr 2007 08:37:00 +0100
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right. Thank you both for your help and clarifications. I guess that I
manage with the setpoint manager warmest solution. perhaps this problem
will be useful for future improvments.
all the best.
jose'


Fred Buhl wrote:
> 
> 
> Jose,
> 
> Sorry - I should have answered this in the first place. The simple
> controllers in EnergyPlus
> operate by iterating the air loop side of the air loop / zone equipment
> combination. Furthermore, zone
> temperatures are not updated until the full HVAC (system, plant)
> solution is complete. Another way of
> saying this is that the zone temperatures are held fixed while the HVAC
> system is simulated. This
> has some good features; a bad feature is that the return temperature
> will not vary significantly
> during an HVAC simulation. Thus the simple controller, by varying the
> water flow rate through the coil,
> will not influence the return temperature. So you are right, you can not
> control off of the return temperature
> and the return temperature setpoint.
> 
> The only way forward would be to use a Setpoint Manager; one could write
> a setpoint manager that
> would look at the return temperature and adjust the setpoint at the coil
> outlet to try to maintain a given
> return temperature. Getting this to work well would be somewhat
> difficult. Otherwise you are left
> with what Mike suggests - using zone temperatures as surrogates for the
> return temperature and using
> one of the exisiting set point managers.
> 
> Fred Buhl
> 
> Jose Coutinho wrote:
>> Thanks a lot Mike,
>>
>> However, from the I/O manual, It looks that CONTROL objects that actuate
>> on Air Loop coils can not sense setpoints at nodes that are located
>> downstream after the Zone Equipment subloop. Is this correct? If it is
>> so, solutions 1-3 are not possible to implement. Actually, your first
>> suggestion is exactly what I tried to model on the first hand.
>>
>> Anyway, thanks again for your suggestions. After all, it is always
>> important to realize that we are thinking the right way.
>>
>> Cheers.
>> Jose'
>>
>>
>>
>> Michael J. Witte wrote:
>>
>>> This is not a supported control strategy in EnergyPlus, but I will add
>>> it to
>>> the suggested enhancement list.
>>>
>>> Here are some approaches you could try, but I do not know if they
> will work.
>>>
>>> 1. Use SET POINT MANAGER:SCHEDULED to place the desired return air
> control
>>> temperature as a setpoint on the Air Loop Inlet Node. In the
>>> CONTROLLER:SIMPLE
>>> object for the cooling coil, set the Control_Node to be the Air Loop
> Inlet
>>> Node.
>>>
>>> 2. Same as 1, but use the ZoneEquipGroup Outlet Node instead of the Air
>>> Loop
>>> Inlet Node. These nodes both represent the same physical point in the
>>> system,
>>> but they are updated at different times in the iteration sequence, so
>>> you might
>>> find one to behave better than the other.
>>>
>>> 3. Use SET POINT MANAGER:WARMEST to place a setpoint on the cooling coil
>>> air
>>> outlet node, and set the controller control node to that node. If
> this is a
>>> draw-thru system, then place this setopint at the fan outlet and use
> a SET
>>> POINT MANAGER:MIXED AIR to place an adjusted setpoint at the cooling
>>> coil air
>>> outlet node.
>>>
>>> 4. Choose the dominant zone on the system and use it to control the
>>> supply air
>>> temperature with SET POINT MANAGER:SINGLE ZONE COOLING.
>>>
>>> Note - whatever approach you use, be sure to set the cooling priority
>>> (in the
>>> ZONE EQUIPMENT LIST) for the DIRECT AIR units to be 1, and the unit
>>> vents to be
>>> cooling priority 2.
>>>
>>> Mike
>>>
>>> On 7 Apr 2007 at 11:31, coutinho301272 wrote:
>>>
>>>
>>>> Dear All,
>>>> I have several zones served by a single constant volume AHU (cooling
>>>> only) plus individual cooling unitvents on each zone. The air system
>>>> has cooling prioriry over the UnitVents and provides fresh air.
>>>> UnitVents will complement cooling needs on each zone.
>>>>
>>>> I wonder how can I control water flow rate in the central cooling coil
>>>> based on return air temperature, ie, by setting a target temperature at
>>>> the Air Loop Inlet Node.
>>>>
>>>> Thanks a lot in advance,
>>>> Jose'
>>>>
>>>>
>>>>
>>>>
>>>> The primary EnergyPlus web site is found at:
>>>> http://www.energyplus.gov <http://www.energyplus.gov>
> <http://www.energyplus.gov <http://www.energyplus.gov>>
>>>>
>>>> The group web site is:
>>>> http://groups.yahoo.com/group/EnergyPlus_Support/
> <http://groups.yahoo.com/group/EnergyPlus_Support/>
>>>>
>>> <http://groups.yahoo.com/group/EnergyPlus_Support/
> <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
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>> ========================================================
>>> Michael J. Witte, GARD Analytics, Inc.
>>> EnergyPlus Testing and Support
>>> EnergyPlus-Support@xxxxxxxx <mailto:EnergyPlus-Support%40gard.com>
> <mailto:EnergyPlus-Support%40gard.com>
>>>
>>>
>>>
>>
>>
>> The primary EnergyPlus web site is found at:
>> http://www.energyplus.gov <http://www.energyplus.gov>
>>
>> The group web site is:
>> http://groups.yahoo.com/group/EnergyPlus_Support/
> <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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References:
- Re: [EnergyPlus_Support] Return Air Setpoint Control Strategy
  - From: Michael J. Witte
- Re: [EnergyPlus_Support] Return Air Setpoint Control Strategy
  - From: Jose Coutinho
- Re: [EnergyPlus_Support] Return Air Setpoint Control Strategy
  - From: Fred Buhl

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