HFO-1234ze is trans-1,3,3,3- tetrafluoroprop-1-ene to which ASHRAE Standard 34 has assigned the nomenclature of R-1234ze(E). The suffix (E) indicates that it is an isomer. The other isomer (suffix (Z)) is cis-1,3,3,3- tetrafluoroprop-1-ene. The physical properties of the (E) and (Z) isomers are different: both are ultra low GWP molecules with GWPP<1,   but R-1234ze(Z) has a high boiling point (49.6°F) associated with a higher critical temperature (308.66ºF) and a volumetric capacity roughly 50% lower than R-1234ze(E), which means it is not a good candidate to replace R-134a. Even if the properties of R-1234ze(Z) could be utilised in specific applications like high temperature heat pumps, R-1234ze(E) will show operating conditions and applied costs much more in line with R-134a according to system and compressor sizes.