Generic vs specific backup equipment #15

[urwahah]

per #15 & #8, for backup heating/cooling equipment (chiller, boiler, electric heater) calculations:

• differentiate between generic and specific equipment
  • generic equipment has no capacity, refrigerant, and eventually space, electric load, etc. data
  • defaults are set to specific equipment
• if using specific equipment, calculate the number of units
  • the number of units has no effect on the calculations except total chiller refrigerant weight

additionally, revised the wrapper creating the list of options when selecting equipment to show nominal capacity (& efficiency for backup heating). i did not include unit conversions at the moment