Issue overview

When writing feature tests, new NodeData objects are often created in isolation. However, initializing piecemeal attributes of an air node can result in an unphysical psychrometric state at the node. Unit tests which only initialize NodeData's Temp, HumRat, and Enthalpy leave all other attributes, including Pressure, at default-initialized values. Pressure values should at least be reasonably physical (i.e. not zero).

(An impossible air state (relative humidity > 1) was discovered in a model's Outdoor Air Mixer, while adding an unrelated feature. Attempting to "correct" the state's dry-bulb temperature exposed unit tests which have been calculating node conditions in a vacuum!)