Chapter 5.1.7 - Radiant Design Programs Include Thermal Comfort

Early energy design and simulation programs did not incorporate mean radiant temperature
(MRT) and human thermal comfort design factors into their governing
algorithms. The result is the design assumption that average unheated surface temperatures
(AUSTs) are equal to the air temperature. There are many architectural
features, building materials, and operating conditions that result in circumstances in
which this assumption is invalid. The programs were not able to model dynamic
occupancy-oriented use of radiant systems.

Computer programs that incorporate these factors recognize the performance
characteristics that are unique to radiant heating panels in terms of design load,
human thermal comfort, and energy consumption. For design purposes, radiant panels
were treated as though their heat transfer process was identical to that of con-

vection heating systems.A Btu was considered to be a Btu, regardless of its use, heat
transfer mode, or actual quantity requirement for the particular design purpose and
heating system. The heating Btu requirement using each system was accepted as
being the same.

Efforts to increase the efficiency of heating treating processes and travel into outer
space necessitated accurate calculation of all three forms of heat transfer. The expo-
nential increase in computer and programming capability make it practical to address
the built environment with the same precision. Dynamic computer programs closely
link lifestyle, building use, weather conditions, internal load contribution, indoor air
quality requirements, and human thermal comfort in order to provide engineers with
better information for heating system selection and design optimization.