GHM Delta OHM HD32.3TCA, Руководство по эксплуатации

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HD32.3TC
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V1.1
3.3 M
EAN RADIANT TEMPERATURE
The medium radiant temperature T
r
is defined as the uniform temperature of a fictitious black
cavity in which an individual would exchange the same amount of radiant thermal energy that it
exchanges in the real non-uniform environment.
To evaluate the mean radiant temperature, we must detect: the globe thermometer tempera-
ture, the air temperature and the air speed measured close to the globe thermometer.
The formula for calculating the mean radiant temperature is the following:
•
In case of
natural convection
:
( ) ( )
273
10 25 . 0
273
4 / 1
4 / 1
8
4
−










− ×








−
ε
×
+ + =
a g
a g
g
g r
T T
D
T T
T T
•
In case of forced convection :
( ) ( )
273
10 1 . 1
273
4 / 1
4 . 0
6 . 0 8
4
−








−
× ε
× ×
+ + =
a g
g
a
g r
T T
D
V
T T
where:
D = globe thermometer diameter
ε
g
= 0.95 globe thermometer presumed emissivity
T
g
= globe thermometer temperature
T
a
= air temperature
V
a
= air speed
The mean radiant temperature does not coincide with the air temperature: if within a room there
are areas which have a temperature much higher than that of the air (think, for example, of the
flame of a fireplace), the mean radiant temperature is an average significantly affected by the
presence of this very hot area.
The mean radiant temperature is detected with the globe thermometer, which is a temperature
probe consisting of a copper sphere painted with matt black, with emissivity
ε
g
equal to 0.95 (as
required by ISO 7726), with a Pt100 sensor inside.
The temperature of globe thermometer may be significantly higher than the air temperature, as
in the case of a mountain hut, where the air is 0 °C, but where the presence of a fireplace
produces a medium radiant temperature of 40 °C, ensuring a comfort situation.
Under normal conditions, maintaining a mean radiant temperature significantly higher than the
air temperature is an advantage in terms of environmental quality. In homes, where fireplaces
or stoves no longer exist, usually the mean radiant temperature coincides with the air tempera-
ture, or it is even lower. These situations (the main case is represented by buildings with large
glazed surfaces) are not particularly healthy as the warm and wet air facilitates the development
of pathogens. From this point of view, the heating with lamps or radiant panels is much healthier.
It is more hygienic to ensure the comfort conditions with a mean radiant temperature greater
than the air temperature. The legislation erroneously establishes the air temperature rather than
the mean radiant temperature as the evaluation parameter for heating systems.
To calculate the mean radiant temperature, the following probes must be connected:
•
TP3276.2 or TP3275 globe thermometer probe.
•
HP3217.2R or HP3217R combined relative humidity and temperature probe.
•
AP3203.2 or AP3203 hot wire air speed probe.
To calculate the mean radiant temperature, reference is made to the
ISO 7726
standard.