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Re: [EnergyPlus_Support] Economizer/Heat recovery operation

1. Currently, if the economizer is available, the heat exchanger will be 
bypassed, even if the economizer set point modulation results in minimum 
outside air flow.  I will post a suggestion to allow this option, but that does 
not help you now.  I cannot think of any way to activate the heat exchanger 
except to use upper and lower temperature and enthalpy limits.

2.  There are two problems with the temperature controls.  

2a.  Both SET POINT MANAGER:SINGLE ZONE COOLING and SET POINT MANAGER:SINGLE 
ZONE HEATING are placing setpoints on the same 3 nodes.  There is a single 
temperature setpoint on each node.  Only one of these setpoint managers is 
active, the other one is being overwritten.  

2b.  The second problem is that the fan heat is added after the coils.  The set 
point managers are setting supply air temperatures at the coils, and the fan 
will always raise the temperature.  To avoid this a SET POINT MANAGER:MIXED AIR 
must be used to subtract the fan delta temperature from the setpoint.  In your 
system, you must do this twice, one for the heating coil setpoint and once for 
the cooling coil setpoint.  This also means you need a place to store the base 
suppy air setpoints before adjusting them for fan heat.

Example:
SET POINT MANAGER:SINGLE ZONE COOLING, Set point node = AHU_FC_P1 Air Loop 
Outlet
SET POINT MANAGER:MIXED AIR (for cooling), reference set point node name = 
AHU_FC_P1 Air Loop Outlet
Set point Nodes = AHU_FC_P1 Cooling Coil Outlet and AHU_FC_P1 Mixed Air Outlet

SET POINT MANAGER:SINGLE ZONE HEATING, Set point node = AHU_FC_P1 Zone Equip 
Inlet
SET POINT MANAGER:MIXED AIR (for cooling), reference set point node name = 
AHU_FC_P1 Zone Equip Inlet
Set point Node = AHU_FC_P1 Heating Coil Outlet

Mike


On 11 May 2006 at 19:15, alexandrevarela2000 wrote:

> Dear all,
> 
> I'm trying to simulate a constant flow system with generic heat
> exchanger and an air side economizer. As I get it from "Input-Output
> reference" pg. 1023 (PDF pg. 1060), when all other user definable
> limits are satisfied, the economizer has the following control:
> 
> Cond.1)"Outside Air (OA) Temperature" >= "Mixed Air (MA) temp. set
> point" --> Maximum outside air flow
> 
> Cond.2)"OA Temperature" < "MA temp. set point" --> Modulated outside
> air flow in order to meet "MA temp. set point".
> 
> Regarding heat recovery/economizer operation. If I choose ECONOMIZER
> or BYPASS in CONTROLLER:OUTSIDE AIR without any other limit, heat
> recovery will always be bypassed.
> 
> My system. After satisfying all the other limits, I need my economizer
> to always modulate OA flow, from minimum to maximum, in order to meet
> "MA temp. set point". That is, independently of OA Temp./MA Temp.
> relationship. The economizer should "know" that it was OFF, once the
> OA flow was set to a minimum, allowing heat recovery to operate.
> 
> Is there any way of doing this? Has I see it, we can play around with
> "all the other limits" but not with Cond.1 and Cond.2 . Is this right?
> 
> I know I could try to work with the weather file, and try controlling
> this operation with TEMPERATURE LIMIT and TEMPERATURE LOWER LIMIT.
> That could be an option, but it would be great have E+ controlling
> this automatically, and on the other hand this model is to be used in
> very different climates.
> 
> By the way, this model is always in cooling mode (very high internal
> loads) and I'm controlling zone temperature in deadband. Deadband
> control is also behaving a bit strange. My system insists on keeping
> the zone's cooling set point temperature when it could be just keeping
> the zone inside the deadband range. This means that, at times, MA
> temp. is suitable to keep the zone in the deadband range and is also
> in the acceptable supply air temperature range, but the system insists
> on heating the air a bit to keep the zone's cooling set point
> temperature. To make it a bit clearer:
> 
> Zone deadband thermostat: 19-23ºC
> Mixed air temperature: 19.9ºC
> Supply air temperature range:16-28ºC
> Heating Coil Outlet temperature: 22.6ºC
> Resulting zone temperature: 23ºC (when it could be kept at around
> without the additional heating 21ºC)
> 
> Sorry for the long and maybe not so clear problem explanation. Thank
> you very much for all your help. Best regards,
> Alexandre
> 
> 
> 
> 
> 
> 
> 
> 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@xxxxxxxx





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