Chapter 5.4.6 - Thermal Comfort

Although material and safety limits define relevant radiant panel temperature
boundaries, comfort requirements are the defining design determinant within the
physical temperature limits. Selection of occupant thermal comfort parameters

defines the range of mean radiant temperatures (MRTs) within which the radiant
panel design must operate. Radiant temperature asymmetry is a design determinant.
Radiant temperature asymmetry is defined as the plane radiant temperature difference
between the surface temperature of the two defined parallel planes.

The methodology for determining the planar human thermal comfort limits is
detailed in ASHRAE Standard 55-92, Thermal Environmental Conditions for
Human Occupancy. Additional information on the relationship between the MRT,
thermal comfort, and radiant heat transfer is available in the final report for
ASHRAE Research Project 657 by Jones and Chapman (1994). Section 3 of this
Handbook covers the entire subject of thermal comfort in detail, reviewing the thermal
comfort models,MRT, and operative temperature (OT).

Thermal comfort delivery from a radiant hydronic system may be provided using
controls that sense fluid, panel surface, dry-bulb air, mean radiant, operative, or
some combination of these temperatures. Control algorithms may be employed, or
the occupant, in relation to whichever temperature reading it is capable of developing,
may simply adjust the control. Control may be automatic, electronic, or occupantactivated
automatically or manually.

The system may be zoned by means of local valves—an array of circuit, injection,
flow, or mixing valves—zone controls functioning directly through the central system
or operating on a discrete zone basis with finite, independent heat generation
capability. Zone control may be designed for the purpose of providing individual
room or area comfort control, for energy conservation, or for other reasons.

Control of radiant hydronic systems, though sometimes complex, is almost always
successful in providing occupant comfort because a key factor of human thermal com-

fort,MRT, is satisfied. Forced-hot-air convection systems, normally controlled solely to
dry-bulb air temperature, correct MRT deficiencies by elevating dry-bulb air temperatures
to produce the OT required for human thermal comfort.The temperature profile
for residential buildings graphically shows the comparative floor-to-ceiling
dry-bulb air temperatures. (See Fig. 4.8.Also, see Sec. 8 for additional information.)

Although material and safety limits define relevant radiant panel temperature
boundaries, comfort requirements are the defining design determinant within the
physical temperature limits. Selection of occupant thermal comfort parameters

defines the range of mean radiant temperatures (MRTs) within which the radiant
panel design must operate. Radiant temperature asymmetry is a design determinant.
Radiant temperature asymmetry is defined as the plane radiant temperature difference
between the surface temperature of the two defined parallel planes.

The methodology for determining the planar human thermal comfort limits is
detailed in ASHRAE Standard 55-92, Thermal Environmental Conditions for
Human Occupancy. Additional information on the relationship between the MRT,
thermal comfort, and radiant heat transfer is available in the final report for
ASHRAE Research Project 657 by Jones and Chapman (1994). Section 3 of this
Handbook covers the entire subject of thermal comfort in detail, reviewing the thermal
comfort models,MRT, and operative temperature (OT).

Thermal comfort delivery from a radiant hydronic system may be provided using
controls that sense fluid, panel surface, dry-bulb air, mean radiant, operative,...