Wrong initial motor efficiency for zone exhaust fans.

[KaiyuSun]

This original motor efficiency assumption of existing_motor_eff = 0.7 does not apply to zone exhaust fans 90.1-2010 and older, which should be 0.29 instead. Motor efficiency assumptions came from this G-sheet. The consequence is the zone exhaust fans of these older vintages get an extremely low total efficiency of 0.066. Should this original motor efficiency assumption be differentiated based on vintage? Is there other considerations that I ignored?

openstudio-standards/lib/openstudio-standards/standards/Standards.Fan.rb

Lines 158 to 164 in 9fd0542

	# Calculate the existing impeller efficiency
	existing_motor_eff = 0.7
	if fan.to_FanZoneExhaust.empty?
	existing_motor_eff = fan.motorEfficiency
	end
	existing_total_eff = fan.fanEfficiency
	existing_impeller_eff = existing_total_eff / existing_motor_eff