why there are two adaptive thermal comfort model equations?
I found two different adaptive thermal comfort model equations from de Dear et al's two papers.
1) Comfort operative temperature = 18.9 + 0.255*[mean outdoor daily effective temperature]
... from the paper
de Dear, R., & Brager, G. S. (1998). Developing an adaptive model of thermal comfort and preference. ASHRAE Transactions, 104(1), 145-167.
2) Tcomf = 0.31*[Ta,out] + 17.8
... where Tcomf means indoor comfortable temperature, and Ta,out means mean outdoor air temperature,
... from the paper
de Dear, R., & Brager, G. S. (2002). Thermal comfort in naturally ventilated buildings: revisions to ASHRAE Standard 55. Energy and Buildings, 34, 549-561.
I don't have access to the latest ASHRAE Standard 55-2013 now, so I don't know which one is actually adopted by ASHRAE.
So, can anybody know about adaptive thermal comfort model kindly advise?
Thank you!