[Bldg-sim] Unable to satisfy heating coil load

[Alan Jackson]

Hello             

 

I have been working on a GSHP model in a northeast climate that is sized
for cooling and has an auxiliary boiler system to handle remaining
heating load for the building. The main air system is VAV Fan Powered
Boxes, but the errors are occurring only on the systems that happen to
be constant volume. For whatever reason I am getting a bunch of warnings
about the heating coils not having sufficient capacity, or rather the
system does not have sufficient capacity to handle the heating loads. I
have left everything auto-sized and used the appropriate equipment
controls to have the boiler pick up the remaining load but there must be
an error in my methods. I am getting capacity out of the boiler in the
hourly reports so it makes me think that my problems are related to the
air side system sizing or controls, but to be honest I am not sure here
is the Warning:

 

             PREHEAT/HEATING-CAPACITY in SYSTEM Process AHU Lower


             is too low to provide the requested supply temperature for

             the calculated mixed air temperature using total ZONE loads

             (on LS-A/B) and SYSTEM design parameters, plus outside air

             conditions (on LS-C), and specified capacities & air flows.

             Requested temperature is  55.00 calculated is   3.24

             Check HEATING-CAPACITY, HEAT-SET-T, PRE-HEAT-T,
MAX-SUPPLY-T,

             DESIGN-HEAT-T, and ZONE loads for consistency.

 

 

 

This is a snippet of the INP file.

 

"Heating Hot Water Loop" = CIRCULATION-LOOP

   TYPE             = HW

   LOOP-DESIGN-DT   = 10

   DESIGN-HEAT-T    = 130

   LOOP-PUMP        = "DEFAULT-HW-PUMP"

   HEAT-EQUIP-CTRL  = "Heat Pump HW Control"

 

"Aux Boiler" = BOILER          

   TYPE             = HW-CONDENSING

   CAPACITY-RATIO   = 1.2

   HW-LOOP          = "Heating Hot Water Loop"

   HW-PUMP          = "Boiler Pump"

   HW-FLOW-CTRL     = VARIABLE-FLOW

 

"Process AHU Lower" = SYSTEM          

   TYPE             = VAVS

   HEAT-SOURCE      = HOT-WATER

   BASEBOARD-SOURCE = HOT-WATER

   MAX-SUPPLY-T     = 70

   MIN-OA-METHOD    = DCV-RETURN-SENSOR

   MIN-OUTSIDE-AIR  = 0.1

   RECOVER-EXHAUST  = YES

   FAN-CONTROL      = CONSTANT-VOLUME

   NIGHT-CYCLE-CTRL = CYCLE-ON-ANY

   REHEAT-DELTA-T   = 15

   HW-LOOP          = "Heating Hot Water Loop"

   CHW-LOOP         = "Chilled Water Loop"

   ERV-RECOVER-TYPE = ENTHALPY-WHEEL

 

"EL2 West Perim Zn (G.W1)" = ZONE            

   TYPE             = CONDITIONED

   FLOW/AREA        = 1

   HEAT-TEMP-SCH    = "Process Heat Sch"

   DESIGN-COOL-T    = 85

   COOL-TEMP-SCH    = "Process Cool Sch"

   SIZING-OPTION    = ADJUST-LOADS

   SPACE            = "EL2 West Perim Spc (G.W1)"

   OA-FLOW/AREA     = 1

 

"Heat Pump CHW Control" = EQUIP-CTRL      

   TYPE             = COOLING

   CIRCULATION-LOOP = "Chilled Water Loop"

   CHILLERS-1       = ( "GSHP-1", "GSHP-2", "GSHP-3" )

   CHILLERS-SEQ-1   = ( 1, 2, 3 )

   ..

"Heat Pump HW Control" = EQUIP-CTRL      

   TYPE             = HEATING

   CIRCULATION-LOOP = "Heating Hot Water Loop"

   LOADS-THRU-1     = 999

   BOILERS-1        = ( "Aux Boiler" )

   CHLR/HTRS-1      = ( "GSHP-1", "GSHP-2", "GSHP-3" )

   CHLR/HTRS-SEQ-1  = ( 1, 2, 3 )

 

Thanks in advance for any help.

 

Alan Jackson, LEED(r) A.P. 

Senior Mechanical Engineer

Buro Happold Consulting Engineers, PC

100 Broadway 

New York, NY 10005

USA

 

Tel: (+1) 212 334 2025

Direct: (+1) 212 616 0267

Fax: (+1) 212 334 5528

Email: alan.jackson at burohappold.com
www.burohappold.com <http://www.burohappold.com/> 

 

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