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.
