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Unreasonable results for water heating desuperheater

asked 2019-06-11 13:19:34 -0500

updated 2019-06-13 07:19:29 -0500

Previously, I modeled a water system with desuperheater in Model 1 which gave happy results (about half water heating energy saving). Now I need to integrate this technology into another model( Model2) with exactly the same approach. However, the Model 2 results showed about 10X more water heating energy usage than its baseline, which is unreasonable. I am using E+ v9.1.0.

The approach I used to model desuperheater is quite straightforward, I'd like to elaborate:

  • I created a constant temperature schedule of 55C (setpoint is 52.6667C) as desuperheater setpoint, which requires a little bit higher than water heater setpoint to be activated.


  desuperheaterStp,        !- Name
  Temperature,             !- Schedule Type Limits Name
  55;                      !- Hourly Value
  • I used Coil:WaterHeating:Desuperheater object, the snippet was like


   Desuperheater,             !- Name
   ,                          !- Availability Schedule Name
   desuperheaterStp,          !- Setpoint Temperature Schedule Name
   2,                         !- Dead Band Temperature Difference {deltaC}
   0.25,                      !- Rated Heat Reclaim Recovery Efficiency
   50,                        !- Rated Inlet Water Temperature {C}
   35,                        !- Rated Outdoor Air Temperature {C}
   60,                        !- Maximum Inlet Water Temperature for Heat Reclaim {C}
   ,                          !- Heat Reclaim Efficiency Function of Temperature Curve Name
   DesuperheaterIn,           !- Water Inlet Node Name
   DesuperheaterOut,          !- Water Outlet Node Name
   WaterHeater:Mixed,         !- Tank Object Type
   water heater,              !- Tank Name
   Coil:Cooling:DX:SingleSpeed,  !- Heating Source Object Type
   central ac clg coil,       !- Heating Source Name
   0.001,                     !- Water Flow Rate {m3/s}
   ,                          !- Water Pump Power {W}
   0.2;                       !- Fraction of Pump Heat to Water
  • And finally I got these two water nodes connected with WaterHeater:Mixed


res wh,                  !- Name
0.136274824222915,       !- Tank Volume {m3}
WH Setpoint Temp,        !- Setpoint Temperature Schedule Name
2,                       !- Deadband Temperature Difference {deltaC}
99,                      !- Maximum Temperature Limit {C}
Cycle,                   !- Heater Control Type
5500.06477392209,        !- Heater Maximum Capacity {W}
0,                       !- Heater Minimum Capacity {W}
0,                       !- Heater Ignition Minimum Flow Rate {m3/s}
0,                       !- Heater Ignition Delay {s}
Electricity,             !- Heater Fuel Type
0.8,                     !- Heater Thermal Efficiency
,                        !- Part Load Factor Curve Name
0,                       !- Off Cycle Parasitic Fuel Consumption Rate {W}
Electricity,             !- Off Cycle Parasitic Fuel Type
0,                       !- Off Cycle Parasitic Heat Fraction to Tank
0,                       !- On Cycle Parasitic Fuel Consumption Rate {W}
Electricity,             !- On Cycle Parasitic Fuel Type
0,                       !- On Cycle Parasitic Heat Fraction to Tank
Outdoors,                !- Ambient Temperature Indicator
,                        !- Ambient Temperature Schedule Name
,                        !- Ambient Temperature Zone Name
Model Outdoor Air Node,  !- Ambient Temperature Outdoor Air Node Name
0.704227539803499,       !- Off Cycle Loss Coefficient to Ambient Temperature {W/K}
1,                       !- Off Cycle Loss Fraction to Zone
0.704227539803499,       !- On Cycle Loss Coefficient to Ambient Temperature {W/K}
1,                       !- On Cycle Loss Fraction to Zone
,                        !- Peak Use Flow Rate {m3/s}
,                        !- Use Flow Rate Fraction Schedule Name
,                        !- Cold Water Supply Temperature Schedule Name
Node 13,                 !- Use Side Inlet Node Name
Node 14,                 !- Use Side Outlet Node Name
1,                       !- Use Side Effectiveness
DesuperheaterOut,        !- Source Side Inlet Node Name
DesuperheaterIn,         !- Source Side Outlet Node Name
1,                       !- Source Side Effectiveness
Autosize,                !- Use Side Design Flow Rate {m3/s}
Autosize,                !- Source Side Design Flow Rate {m3/s}
1.5,                     !- Indirect Water Heating Recovery Time {hr}
IndirectHeatPrimarySetpoint,  !- Source Side Flow Control ...
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answered 2019-06-13 11:03:47 -0500

updated 2019-06-13 11:04:44 -0500

E+ pull request created to address this issue. Thank @rraustad for guidance!

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Asked: 2019-06-11 13:19:34 -0500

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Last updated: Jun 13 '19