Question

The importance of distinguishing clock time from solar time is emphasized in environmental

system design. If this distinction is not considered, what impact might that have on building

design? Would such impacts show up primarily in lighting design, thermal design, or something

else? Explain and discuss.

Answer 1

THE DIFFERENCE BETWEEN ‘SUN TIME’ AND ‘CLOCK TIME’

Solar time is a calculation of the passage of time based on the position of the Sun in the sky. The fundamental unit of solar time is the day. Two types of solar time are apparent solar time (sundial time) and mean solar time (clock time).

When the clocks go back to Greenwich Mean Time, it’s no longer necessary to add that British Summer Time hour to our sundials, but we still have to be aware of another difference between ‘sun time’ and ‘clock time’. At certain times of year, the time shown on all but the most sophisticated dials can vary by about 15 minutes from the time on clocks and watches.

CAUSES TO CONSIDER THE VARIATIONS:

That’s because the Earth’s orbit around the Sun is not perfectly circular and the tilt of the Earth’s axis is not perfectly perpendicular to its orbit, which means that the length of time between noon (when the sun is at its highest point in the sky) from one day to the next is not always exactly 24 hours. The small time-variations build up to produce larger differences as the year progresses.

The sundial, the oldest of all time-measuring devices, tells the time as it really is, based on the position of the sun in the sky. So in spring, when we change the clocks to British Summer Time, sundials fall out of step with ‘clock time’.

THEORIES TO OVERCOME:

There's a concept of Mean Solar Time that evens out this discrepancy, but it doesn't help with the difference in time between various locations. This became a big problem with the advent of railways nearly 200 years ago: each station had a different local time. That was the rationale for the introduction of Time zone ,areas where the local time was set to be the same.

Time zone

• When they did need to have a different time, because of significantly different longitude, it was done in uniform steps, usually an hour, sometimes half an hour, or in some cases even a quarter of an hour.
• Because, if you want to talk accurate solar time, then you have to calculate it for every change in longitude.That is the whole purpose of time zones.
• Time zones are made for human continence. It gives us shared standards of time that are based off of the mean solar time across a region, while decoupling us from the rigorous calibration demands if we wanted to use actual solar time.

Daylight Saving Time (DST)

The issue of Daylight Saving Time (DST) is an indirect consequence of dividing the surface of Earth into time zones. After decades of measurements, this action was taken at a conference in Washington DC in 1884 to facilitate communication and travel between places with different sun times

• There are good sides to DST, such as coming home “earlier” (by the sun clock but not by the social clock) from school or work and therefore having more hours of daylight during the free time after work. These positive effects may go beyond subjective feelings. A study has shown for example that activity increases with longer evening daylight

IMPACTS ON CONSTRUCTION:

• Impacts on construction is that the inconvenience in lighting and the labor cycle.
• Results show that the labor cycle is equally distributed through seasons if measured in local time.
• It is an everyday experience which is a major outcome of DST. The sleep/wake cycle displays disturbances punctuated by solar events: sunrise, sunset and noon. In week-ends, under free preferences, sleep onset delays in summer, opposing to the regulation and following the delay in sunset time, while sleep offset advances, despite clock time already advanced in the spring transition. This advance still follows the advance in sunrise times.
• The best explanation for these findings is that human cycles are not misaligned by the size and direction of DST regulations, which explains the success of that practice. The sleep/wake cycle in Great Britain and France exhibit fewer statistically significant excursions than the sleep/wake cycle in Spain, Italy and United States, despite light and dark seasonal deviations are larger. That could be indicating that the preference for a seasonal regulation of time decreases with increasing latitude above 47°.
• The preferences for a seasonal regulation of clocks and for the choice of permanent summer time or permanent winter time are sketched from a previous report on human activity.

CLOSING THOUGHTS:

Either way, the seasonal regulation of human activity in industrialized, urban societies synced to clocks meets the biannual transitions that characterizes DST.

• The sleep/wake cycle is more prone to seasonal deviations, specially at lower latitudes. Nonetheless these deviations are still linked to solar activity —the advance of sunrise and the delay of sunset, and the changes in the efficiency of the insolation at noon— which reveals that human activity is not misaligned by DST regulations.