I am trying to optimise exterior shading design for an office building. To make a head start with building and climate, I have chosen large office building from the ASHRAE's 90.1-2013 Commercial Building Prototype Models, to be simulated with Chicago climate. Further, in order to speed up simulations as I'd like to employ genetic algorithm in optimisation, I have decided to delete all HVAC related details from the model and replace them with IdealLoadsAirSystem for each zone, such as:
ZoneHVAC:IdealLoadsAirSystem,
Basement Purchased Air, !- Name
, !- Availability Schedule Name
Basement Inlet Nodes, !- Zone Supply Air Node Name
, !- Zone Exhaust Air Node Name
50, !- Maximum Heating Supply Air Temperature {C}
13, !- Minimum Cooling Supply Air Temperature {C}
0.015, !- Maximum Heating Supply Air Humidity Ratio {kgWater/kgDryAir}
0.01, !- Minimum Cooling Supply Air Humidity Ratio {kgWater/kgDryAir}
NoLimit, !- Heating Limit
, !- Maximum Heating Air Flow Rate {m3/s}
, !- Maximum Sensible Heating Capacity {W}
NoLimit, !- Cooling Limit
, !- Maximum Cooling Air Flow Rate {m3/s}
, !- Maximum Total Cooling Capacity {W}
, !- Heating Availability Schedule Name
, !- Cooling Availability Schedule Name
ConstantSupplyHumidityRatio, !- Dehumidification Control Type
, !- Cooling Sensible Heat Ratio {dimensionless}
ConstantSupplyHumidityRatio, !- Humidification Control Type
, !- Design Specification Outdoor Air Object Name
, !- Outdoor Air Inlet Node Name
, !- Demand Controlled Ventilation Type
, !- Outdoor Air Economizer Type
, !- Heat Recovery Type
, !- Sensible Heat Recovery Effectiveness {dimensionless}
; !- Latent Heat Recovery Effectiveness {dimensionless}
The problem now is that there is a large discrepancy between results obtained for heating and cooling loads. The initial ASHRAE model requires 10.8 GJ of electricity and 5325.81 GJ of natural gas for heating, and 2748.36 GJ of electricity for cooling. However, the IdealLoadsAirSystem version reports only 550.65 GJ for district heating and 21417.95 GJ for district cooling. Hence almost 10 times less energy for heating and almost 8 times more energy for cooling?! What am I doing wrong here? Convincing demystifications are welcome! What has to be done to keep IdealLoads (and shorter simulation times), yet to obtain more realistic ratio of heating/cooling loads?
If you're interested, you can see the modified IdealLoads version of the model at https://www.dropbox.com/s/3xcsr4ighrgr9u7/ASHRAE90.1_OfficeLarge_STD2013_Chicago_NO_HVAC.idf?dl=0
Thanks in advance, Sanya Stevanovic
