Operative temperature is the uniform temperature of a radiantly black enclosure in
which the occupant would exchange the same amount of heat by radiation plus convection
as in the actual nonuniform environment, thereby experiencing thermal
comfort, or thermal neutrality. This condition is represented by the term operative
temperature (OT).Within the temperature range common to the built environment,
OT is the simple average of dry-bulb air temperature and MRT. It is that simple.

The trailblazing work of P.O. Fanger resulted in the development of a methodology
called predicted mean vote (PMV), which provided for the evaluation of thermal
comfort based on clothing and activity levels under a given set of thermal conditions
(Fig. 4.2). The entire subject of thermal comfort is covered in detail in Sec. 3 of this
Handbook.

The attractive feature of the Comfort-Check Meter described earlier in this chapter
is that all three figures are shown digitally almost instantly.The MRT represents
120° solid-angle view, and the air temperature is sensed in the housing.A micropro-

cessor calculates the OT every 6 s. The MRT impact may be quickly demonstrated
by using a glass of ice water or a hot coffee cup.The tool demonstrates the ease with
which the concept may be implemented, as well as the significance of its impact. It
also demonstrates the downside of blindly controlling to OT.

Consider, for example, a second home that is kept operating, but used occasionally.
There is poor insulation and a lot of glass. If a thermostat, which is sensitive to
MRT, replaces a convection bimetal thermostat, you will naturally find that a higher
air temperature is called for as defined by OT.Yet, if this is a vacant vacation house,
where setback is designed to lower energy costs, the exact opposite will occur—bills
will go up! Under such conditions, the OT set point can be lowered to reflect the
MRT that is considered acceptable.This was the net effect of the bimetal thermostat
that only sensed air temperature and was kept at 50°F, which was the minimum setting
considered to keep pipes from freezing.

The use of OT may also open up the field of task heating. Many believe task heating
holds as much promise for energy savings as task lighting, which swept the country
with support from the EPA, DOE, and the nation’s electric utilities. A recent
study by the authors and ASHRAE Student Member Jamie Howell, entitled Radiant
Panel Surface Temperature over a Range of Ambient Temperature, develops
guidelines for placing and sizing radiant heaters in large occupied spaces where the
indoor temperature is below occupant thermal comfort levels to provide localized
thermal comfort.The project was performed by using the methodology described in
detail in Sec. 8 of this Handbook.

There are many obvious benefits to using OT. The purpose of a heating or cooling
system, aside from shielding the building and its contents from damaging temperatures,
is to make people comfortable. The shift in focus from heating space to
heating people demands recognition of MRT.The recognition of MRT makes it possible
to harness the benefits of radiant, as opposed to or in combination with convective,
heat transfer. One of the key benefits is energy conservation resulting from
heating people before or instead of space.

Operative temperature is the uniform temperature of a radiantly black enclosure in
which the occupant would exchange the same amount of heat by radiation plus convection
as in the actual nonuniform environment, thereby experiencing thermal
comfort, or thermal neutrality. This condition is represented by the term operative
temperature (OT).Within the temperature range common to the built environment,
OT is the simple average of dry-bulb air temperature and MRT. It is that simple.

The trailblazing work of P.O. Fanger resulted in the development of a methodology
called predicted mean vote (PMV), which provided for the evaluation of thermal
comfort based on clothing and activity levels under a given set of thermal conditions
(Fig. 4.2). The entire subject of thermal comfort is covered in detail in Sec. 3 of this
Handbook.

The attractive feature of the Comfort-Check Meter described earlier in this chapter
is that all three figures are shown digitally almost instantly.The MRT represents
120° solid-angle view, and the air temperature is sensed in the housing.A micropro-

cessor calculates the OT every 6...