I have a proposition to explain Dark Energy from purely thermodynamic principles, though it requires a paradigm shift: absolute zero is no longer the minimum temperature of the universe. Negative temperature (c.f. Dark Temperature) exists. I'll go through each of the laws, and explain how Dark Temperature fits in this framework.

>The Zeroth Law of Thermodynamics:
>If two systems are both in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.
This statement remains unchanged. If a system is purely Dark Temperature, then it's in thermal equilibrium if and only if there is a uniform Dark Temperature everywhere. If there are disparate Dark Temperatures, they are not in thermal equilibrium. If there is a system with Dark Temperature, and a system with ordinary temperature, the two systems are not in thermal equilibrium.

>The First Law of Thermodynamics:
>In a closed system, the change in internal energy of the system $\Delta U$ is equal to the difference between the heat supplied to the system (Q) and the work (W) done by the system on its surroundings: $\Delta U = Q - W$
Here we get our first modification. Dark Temperature does not supply heat to a system; Dark Temperature extracts heat from a system by doing work on its surroundings. As such, with Dark Temperature, the first law reads $\Delta U = -Q - W$. This has some interesting consequences. Typically, energy is transferred to an object via heating it up. Dark Temperature works different in that an object gains energy via losing temperature (gaining Dark Temperature).