Gas in pulse tube connected to outlet via valve mechanism, releasing gas from pressure build-up.

Expansion of tube gas decreases temperature at cold end, handling refrigeration load.

Hot climates: hot-dry (e.g., Rajasthan: DBT $43-49^\circ C$, RH $5-20\%$) and hot-humid (e.g., Assam: DBT $37^\circ C$, RH $80\%$).
Human body is homeothermic, maintains relatively constant internal temperature.
Thermal machine with $20\%$ efficiency; $80\%$ of heat must be dissipated.
Heat dissipated via convection, radiation, and evaporation.
Comfort maintained if heat dissipated equals heat produced.

$H_m - W_e = H_e + H_c + H_r + H_s$

$H_m$: Metabolic heat produced in body.
$W_e$: Useful rate of working.
$H_m - W_e$: Heat to be dissipated to atmosphere.
$H_e$: Heat lost by evaporation.
$H_c$: Heat lost by convection.
$H_r$: Heat lost by radiation.
$H_s$: Heat stored in body (positive if temperature rises, negative if falls below $36.5^\circ C$).

$H_c = UA(T_b - T_a)$
- $U$: Heat transfer coefficient on body surface.
- $A$: Body surface area (e.g., $1.8 \text{ m}^2$ for normal man).
- $T_b$: Mean body surface temperature.
- $T_a$: Surrounding temperature.
If $T_a > T_b$, heat is gained. Increased $U$ (function of air velocity) increases heat gain.
Higher air velocity causes discomfort if $T_a > T_b$.

$H_r = \sigma (T_b^4 - T_a^4) \text{ W/m}^2$
- $\sigma$: Stefan-Boltzmann constant.
- $T_b$: Body temperature.
- $T_a$: Surrounding temperature.
If $T_a > T_b$, heat is gained; if $T_a < T_b$, heat is lost.
All bodies emit electromagnetic radiation; intensity and wavelength depend on temperature.
Hotter objects emit more radiation, shorter wavelength.
Most radiations (except sun) are long wave.

Short wave radiation effect differs from long wave.
Long wave radiation absorbed by skin regardless of color.
Absorption of color wave depends on skin/clothing color.
White clothing and fair skin reflect short wave radiation maximally.
Various shades of skin/clothing absorb radiation differently.
Indoor: skin/clothing color doesn't matter for long wave radiation.
Outdoors (direct sun): skin/clothing color is a determining factor for short wave radiation.

Interferes with air movement, reducing convective heat transfer and evaporation potential.
Decreases radiation heat transfer outdoors.
Decrease varies $20-50\%$ depending on clothing color.
White clot