Multinode Water Heater Model

[jmaguire1]

Current model is only 1 node. We'll eventually want to allow n nodes (probably 12 in most cases). Things we'll have to update:

• Different UA values for the top/bottom and middle nodes
• 2 elements, located dynamically based on number of nodes, with master/slave control
• Change tank temperature code to solve for all n node temperatures
• Calculate mixing between nodes (might require iteration)

[jmaguire1]

We're going to push this down the priority list and try to get a single node HPWH into the code, if we can fake the control logic ok we'll run with that until we're sure enough of the funding to implement a multinode model.