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Wheel and air streams
The matrix stores heat in the exhaust half and gives it to the fresh air in the other half. Time speed is a multiplier on real time because the matrix needs minutes to warm up.
Model checks
The science
What is modelled
The wheel is 72 independent thermal masses. Each passes through the exhaust stream and then the fresh-air stream. In each stream a sector exchanges heat with the inlet air through a conductance that is the series combination of the matrix conductance and the air-side flow capacity. The air outlet temperatures follow from the total heat taken or given.
Equations
- Sector:
Cs dT/dt = g (Tair - T) - h (T - Troom)withg = U Ca/(U + Ca)per sector. - Fast-rotation limit: matrix at one temperature, so
Q = n gh gc/(gh + gc) (Thot - Tcold). - Effectiveness:
ε = Qc / (Cmin |Thot - Tcold|).
Checks run in the page
- Fast-rotation limit against the series-conductance formula.
- A stopped sector warming exponentially with time constant C/g.
- The energy balance of stored heat against heat flows.
- Rotation-speed independence above a few rpm.
Honest simplifications
Each sector has a single temperature node and sees the inlet air temperature, so the air does not cool along its path. This makes the effectiveness about half of the classical counterflow epsilon-NTU value, and the model is a teaching tool, not a certified HVAC sizing calculation. No moisture transfer, no pressure-drop curve beyond a simple fan law and no frost model.
What to try
- Press Slow wheel: the matrix temperatures swing widely and the effectiveness drops.
- Press Fouled matrix and compare the recovered power.
- Raise the speed above 10 rpm: the effectiveness stops improving, as the check says.