Ummm, what does base unit 'BTU' is not is registered with the QuantityConverter mean?
irb(main):037:0> OpenStudio.convert(10000, "m^2", "ft^2").get
=> 107639.10416709722
irb(main):038:0> OpenStudio.convert(10000, "GJ", "kBTU").get
[openstudio.units.QuantityConverter] <1> Cannot convert to a target Unit containing base unit 'BTU', because it is not registered with the QuantityConverter.
RuntimeError: Optional not initialized
from (irb):38:in `get'
from (irb):38
from /usr/bin/irb:12:in `<main>'
