CFD Online Discussion Forums - Negative energy loss in cardiovascular flow simulation

Hello all.
I am trying to simulate flow in an idealized model of Total Cavopulmonary Connection(TCPC).Simulations are run in FLUENT.
As boundary conditions,two sinusoidal time varying flows are imposed as velocity-inlet, and outflow is applied at outlets.
For calculation of energy loss,the simplified control volume approach is used.

Energy loss= $\Sigma_{inlet}\Bigg(\Big(P_{static}+\frac{1}{2}*\rho* (\frac{Q}{A})^{2} \Big)*Q \Bigg) - \Sigma_{outlet}\Bigg(\Big(P_{static}+\frac{1}{2}*\rho* (\frac{Q}{A})^{2} \Big)*Q \Bigg)$

Now part of the cycle shows negative energy loss .Does this indicate that there are some errors in the setup, or the absolute value of the quantity is to be considered.The average energy loss is positive though.

Thanks in advance.