Radiant Heat Windows

Reference data and engineering information about radiant heat windows for hvac systems applications.

radiantheatwindows

Overview

Engineering reference data for Radiant Heat Windows in HVAC systems.

Key Formulas

Sensible Heat

$Q = \dot{m} c_p \Delta T$

Heat causing temperature change.

Latent Heat

$Q = \dot{m} h_{fg} \Delta\omega$

Heat causing moisture change.

COP (Cooling)

$COP = Q_c / W$

Coefficient of performance.

Symbol	Description	Unit
$Q$	Heat transfer	W
$\dot{m}$	Mass flow rate	kg/s
$c_p$	Specific heat of air	J/(kg·K)
$\Delta T$	Temperature difference	K

Solar heat transmission and effective heat gain fraction for various window shading methods.
Type of Shading	Transmitted Solar Energy(%)	Reflected Solar Energy(%)	Absorbed Solar Energy(%)	Fraction of Gain (vs. Unshaded)
Unshaded Window	75 - 80	10 - 20	10 - 20	1
Inside roller shade - half-drawn				0.8
Inside roller shade - fully-drawn	< 25	15 - 80	20 - 65	0.62
Inside venetian blind	0	23	77	0.65
Canvas awning				0.3
Outside shading screen (solar altitude 20°)				0.38
Outside shading screen (solar altitude 30°)				0.25
Outside shading screen (solar altitude 40°)				0.18

Shading Performance Properties

The Fraction of Gain represents the ratio of solar heat gain through a shaded window to the gain through the same window without any shading. A value of 1.00 indicates no reduction, while lower values indicate greater shading effectiveness.

Key relationships from the data:

External shading (awnings, solar screens) is generally more effective than internal shading.
The effectiveness of external solar screens increases with solar altitude, meaning they perform better when the sun is higher in the sky.
Internal venetian blinds transmit nearly zero direct solar energy but still allow significant heat gain through absorption and re-radiation.

References

Original Source

Source: engineeringtoolbox.com