28
2 Review of Literature: Motorcycle helmet
than cooling the torso (at a temperature of 26–50 °C and a relative humidity of 45%)
[118]. The effects of forced air [119] and water [120, 121] to cool helmets have been
investigated, and it was found that both are effective in reducing thermal stress in hot
conditions (40–50 °C under both humid and dry conditions 15–80 mm Hg). However,
these systems are heavy and large and thus not convenient for use in environments
such as forest harvesting.
Heat transfer from the head to the helmet microclimate, in the case of helmets with
passive ventilation, seems to be more than for helmets without vents of similar design
and shape [76, 111, 115, 122]. Holland et al. [123] investigated forest harvesting
helmets and found that the exchange of air between the helmet microclimate and the
ambient environment was fastest in the helmets with top vents.
Guan et al. [124] designed a test rig to evaluate the thermal/moisture mapping
of industrial safety helmets with and without ventilation openings, which measured
both temperature and relative humidity in various locations inside the helmet. They
indicated that the ventilation openings were essential for thermal comfort inside
the helmet. The psychophysical tests conducted by Davis et al. [125] showed that
ventilation contributes to a greater extent to safety helmets’ comfort. In addition, the
weight and fit are important factors in helmet design.
Liu and Holmér [112] studied the evaporative heat transfer characteristics of
helmets and concluded that wind simulation considerably increased heat loss in all
helmets under various environmental conditions. In addition, they indicated that the
cradle design and construction were important for successful heat loss from the head.
Industrial helmets have been modified to provide increased ventilation to the head
and also to reduce the weight so that they are widely accepted by users in a hot climate.
This improved ventilation increased the convection that assists heat dissipation from
the helmet shell and also provided better insulation against radiant heat. Hsu et al.
[104] studied the thermal discomfort of industrial safety helmets and redesigned
them to improve their thermal properties. The new helmet designed by Hsu et al.
[104] was proven both subjectively and objectively to be superior to commercially
available safety helmets.
2.12 Thermal Energy Storage Systems
Thermal energy storage (TES) systems work as a tool for energy management by
storing thermal energy at periods when it is abundantly available and then using
it when and where it is required. The primary function of the TES system is to
fill the gap between energy supply and energy demand that is caused by higher
energy consumption or primary energy source variation or both, such as the periodic
variations of solar radiation energy. There are three types of TES systems, namely
sensible, chemical and latent [126]. Sensible heat storage is based on increasing the
temperature of any substance without its phase change. In chemical systems, the
thermal energy storage is based on the thermo-physics of the reactions. In latent TES
systems, heat is absorbed or released when the substance changes from solid to liquid
2 Review of Literature: Motorcycle helmet
than cooling the torso (at a temperature of 26–50 °C and a relative humidity of 45%)
[118]. The effects of forced air [119] and water [120, 121] to cool helmets have been
investigated, and it was found that both are effective in reducing thermal stress in hot
conditions (40–50 °C under both humid and dry conditions 15–80 mm Hg). However,
these systems are heavy and large and thus not convenient for use in environments
such as forest harvesting.
Heat transfer from the head to the helmet microclimate, in the case of helmets with
passive ventilation, seems to be more than for helmets without vents of similar design
and shape [76, 111, 115, 122]. Holland et al. [123] investigated forest harvesting
helmets and found that the exchange of air between the helmet microclimate and the
ambient environment was fastest in the helmets with top vents.
Guan et al. [124] designed a test rig to evaluate the thermal/moisture mapping
of industrial safety helmets with and without ventilation openings, which measured
both temperature and relative humidity in various locations inside the helmet. They
indicated that the ventilation openings were essential for thermal comfort inside
the helmet. The psychophysical tests conducted by Davis et al. [125] showed that
ventilation contributes to a greater extent to safety helmets’ comfort. In addition, the
weight and fit are important factors in helmet design.
Liu and Holmér [112] studied the evaporative heat transfer characteristics of
helmets and concluded that wind simulation considerably increased heat loss in all
helmets under various environmental conditions. In addition, they indicated that the
cradle design and construction were important for successful heat loss from the head.
Industrial helmets have been modified to provide increased ventilation to the head
and also to reduce the weight so that they are widely accepted by users in a hot climate.
This improved ventilation increased the convection that assists heat dissipation from
the helmet shell and also provided better insulation against radiant heat. Hsu et al.
[104] studied the thermal discomfort of industrial safety helmets and redesigned
them to improve their thermal properties. The new helmet designed by Hsu et al.
[104] was proven both subjectively and objectively to be superior to commercially
available safety helmets.
2.12 Thermal Energy Storage Systems
Thermal energy storage (TES) systems work as a tool for energy management by
storing thermal energy at periods when it is abundantly available and then using
it when and where it is required. The primary function of the TES system is to
fill the gap between energy supply and energy demand that is caused by higher
energy consumption or primary energy source variation or both, such as the periodic
variations of solar radiation energy. There are three types of TES systems, namely
sensible, chemical and latent [126]. Sensible heat storage is based on increasing the
temperature of any substance without its phase change. In chemical systems, the
thermal energy storage is based on the thermo-physics of the reactions. In latent TES
systems, heat is absorbed or released when the substance changes from solid to liquid