1. IDA Indoor Climate and Energy On the effects of decoupling air flow and heat balance in building simulation models Per Sahlin EQUA Simulation AB Stockholm, Sweden www.equa.se IDA Simulation Environment IDA Indoor Climate and Energy IDA Room IDA Road Tunnel Ventilation

2. 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

3. Why DAE based building simulation? Traditional approach: –Flexibility –Reuse +Speed?

4. Why DAE based building simulation? GUI Equation Based Framework Symbolic Processor Language Parser Numerical Solver1 Numerical Solver2 Envelope&Zone HeatBalance Models Climate& Radiation Models Shading Models HVAC Models IndustryindependentIndustry specific Symbolic equation based approach: +Flexibility +Reuse +Secure model investment –Speed?

5. The experiment Full coupling: m 1-2 Enthal(T 1, H 1 ), m 1-2 > 0 q 1-2 = m 1-2 Enthal(T 2, H 2 ),m 1-2 < 0 “Ping-pong” decoupling: m 1-2,old Enthal(T 1, H 1 ), m 1-2,old > 0 q 1-2 = m 1-2,old Enthal(T 2, H 2 ),m 1-2,old < 0

6. Demo Link to demo

7. Test cases and results casedecoupled 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 

8. Alternative measures Apartment case: fanout=5simpl. zone kmax=2, n_jac=4, tol=0.2 no internal LVOs execution time √ - 46% √√ - 59% √√√ - 67% √√√√ - 79%

9. 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

10. Questions and discussion On the effects of decoupling air flow and heat balance in building simulation models Per Sahlin EQUA Simulation AB Stockholm, Sweden www.equa.se