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Re: [EnergyPlus_Support] RE: Loop Temperature Control With Heat Exchangers



Hi Ned,
In testing various PlantLoop applications (ChW, HW, CW for WSHPs), I've also observed unexpected pumping behavior when the min flow on the pump is set to a non-zero number.  Basically, the pump runs continuously, regardless of load and even if operation is set to Intermittent. I believe this bug was reported to the E+ dev team through various avenues, and is addressed in E+ v8.2.  Not sure if this was exactly your issue, but based on your second post, it sounds it is related.

David
--

David Reddy

360 Analytics
Building Energy Analysis Consultants
mail:     9750 3rd Ave NE, Suite 405, Seattle, WA 98115
office:  206.557.4732 x 201
cell:      206.406.9856
web:    www.360-Analytics.com

On 2/11/2015 6:01 AM, 'Edward G. Lyon' eglyon@xxxxxxx [EnergyPlus_Support] wrote:
 

…to partially answer my own question, E+ apparently has a problem controlling loop temperature when the loop flow is greater than it needs (why bypass doesn’t seem to help I don’t know).  Once I let my main loop pump slow to zero flow (I initially slowed to about 20% flow for typical VFD control) and autosize it instead of using the flows from the ME, loop temperature control improved…

 

I am uncertain if the control properly cascades through the heat exchanger isolations I am using.

 

Ned Lyon, P.E. (MA, WV)
Staff Consultant

SIMPSON GUMPERTZ & HEGER
781.907.9000 main
781.907.9350 direct 
617.285.2162 mobile 
781.907.9009 fax
www.sgh.com

 

From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
Sent: Tuesday, February 10, 2015 11:22 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Loop Temperature Control With Heat Exchangers

 

 

I am modeling a proposed design for a mixed loop water to air HVAC system.  The cooling tower and boilers are connected to the mixed loop by heat exchangers.  I’m having trouble controlling the mixed loop temperature and plant operation.  For instance for the cooling tower, the mixed loop is pumping 300 gpm (minimum pump flow from a 1800 gpm variable speed pump) while the cooling tower side of the heat exchanger ramps all the way up to 1800 gpm full capacity (headered pump).  The cooling tower is temperature controlled off the supply branch outlet and the mixed loop is temperature controlled off the mixed loop mixer for cooling and heating heat exchangers.  The mixed loop also does not drop to the low temperature set point even though there is heating call to the boiler.

 

We also seem to have some issues with zone multipliers.  We have plenty of mixed loop pumping capacity, but we have lots of unmet hours with the equipment we were given.  When we autosize the zone equipment, we get 2-3 times equipment sizes, but still at minimum pump flow.

 

Any insight could be helpful.    

 

Ned Lyon, P.E. (MA, WV)
Staff Consultant

SIMPSON GUMPERTZ & HEGER 
     | Engineering of Structures and Building Enclosures

41 Seyon Street, Bldg. 1, Suite 500
Waltham, MA 02453


781.907.9000 main
781.907.9350 direct 
617.285.2162 mobile 
781.907.9009 fax
www.sgh.com




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Posted by: David Reddy <david@xxxxxxxxxxxxxxxxx>


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