Criterion of energy equation convergence
 | (1) |
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where the residual error at the control volume (cv) is:
 | (2) |
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For the energy equation, the calculation of reference residual value is based on the use of approximation coefficients. The discrete operator:
 | (3) |
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approximates convection and diffusion terms of the equation at the control volume (“cv”). Here ωcv is a stencil of the operator L at the control volume (“cv”), c0 is a coefficient for H at the control volume under consideration and cj(j≠0) are coefficients for other control volumes from the stencil. Note, that the coefficients of the approximation are:
 | (4) |
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where un is the velocity component normal to the face and hcv is the characteristic size of the control volume.
The explicit member 
contains approximations of other terms
of the equation and the heat source at the control volume face equals q∙Vcv.
The reference residual value
(
) is introduces as:
 | (5) |
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In common case of 
, the first summand is the reference
value of the energy flux through the control volume (“cv”).
The second summand is the reference value of the energy flux in/out
of the control volume due to the heat source q∙Vcv.
In case of non-large Δt: 
.
Thus, 
is
treated as the reference value of the energy flux (jen,cv)
through the control volume. Finally, the convergence condition for
the energy equation is:
 | (6) |
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and the stopping criteria Equation 6 can be treated as:
 | (7) |
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