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IDA Indoor Climate and Energy
On the effects of decoupling air flow and heat balance in building simulation models
Per SahlinEQUA Simulation ABStockholm, Swedenwww.equa.se
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IDA Room
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Problem and Outline
• Why air-flow coupled thermal simulation by symbolic equations and general-purpose, variable-timestep DAE solvers?
• A decent GUI will be used
• Coupled models may be mathematically sticky:non-linearities + stiffness = short steps
• Will “ping-pong” decoupling help?simpler structure – stability problems > 0 ?
• Brief demo
• Test cases and results
• Alternative measures
• Summary and conclusions
Why DAE based building simulation?
Traditional approach:
– Flexibility
– Reuse
+ Speed?
Why DAE based building simulation?
GUI
Equation Based Framework
SymbolicProcessor
LanguageParser
NumericalSolver 1
NumericalSolver 2
Envelope & Zone Heat Balance
Models
Climate & Radiation
Models
Shading
Models
HVAC
Models
Industry independent Industry specific
Symbolic equation based approach:
+ Flexibility
+ Reuse
+ Secure model investment
– Speed?
The experiment
Full coupling:
m1-2Enthal(T1, H1), m1-2 > 0
q1-2 =
m1-2Enthal(T2, H2), m1-2 < 0
“Ping-pong” decoupling:
m1-2,oldEnthal(T1, H1), m1-2,old > 0
q1-2 =
m1-2,oldEnthal(T2, H2), m1-2,old < 0
Demo
Link to demo
Test cases and results
case decoupled execution time
family apartment two-zone constant air volume (CAV) office with open door -
13%temperature controlled variable air volume (VAV) ditto +
74%single-zone office with natural ventilation + 59%single family, naturally ventilated house
Bedroom 1Living room
Entrance
Bedroom 1Kitchen
Bathroom
0,90m
Alternative measures
Apartment case:
fanout=5 simpl.
zone
kmax=2,
n_jac=4, tol=0.2
no internal LVOs
execution time
√
- 46%
√ √
- 59%
√ √ √
- 67%
√ √ √ √ - 79%
Summary and conclusions
•“Ping-pong” decoupling provided minor improvements for some cases.
•It also gave rise to fatal instabilities, making the approach unattractive
•A combination of other means proved effective in dealing with the problematic Apartment case
•Packaging and automating the application of such means seems to be a viable alternative
Questions and discussion
On the effects of decoupling air flow and heat balance in building simulation models
Per SahlinEQUA Simulation ABStockholm, Swedenwww.equa.se