Light on the North!
Can the north facade be overlooked?
Does the sun reach the north facade of a building
It is often presumed that glazing on the northern façade is not much of a concern as compared to other orientations. It is believed that these windows receive only indirect diffuse light and are predominantly in the shade without the need for any glare control. Northern exposure is considered advantageous and maximum glazing is prioritized on the orientation assuming least exposure to solar rays.
However, the reality is quite different. The sun travels via the north in the summer months. Thus, bringing in peak heat gain of the hot summer days into the space through the north facing glazing. Also, it is difficult to generalize the sun path for an entire country/region.The latitude of a place heavily determines the movement of the sun.
Discomfort caused by glare
A comprehensive study of the sun path along various critical latitudes of India, ranging from north to south and east to west has been conducted to assess this assumption. Considering weather stations from Ladakh, a region along one of the northern most latitudes in India at 340 N, through the central city of Nagpur, very close to the Tropic of cancer at 210 N, to the southernmost latitude of 80 N along which the city of Trivandrum is located. Mumbai represents the western edge of the peninsula at 720 E and Agartala marks the eastern edge at 920 E longitude. From the tabulated results below, it is evident that there is solar ingress from the north oriented glazing in all latitudes. However, the number of hours of ingress is lesser in the northern latitudes of India.
Sun Path for different location in India
Solar Heat Gain
Analysis of the solar heat gain through the north facing glazing has been performed. The results clearly show that the northern latitudes where the sun minimally moves via north, have lesser solar heat gain as compared to the cities in the southern part of the Indian peninsula. The southern latitudes where the sun path moves towards north during summers, have high solar heat gain from northern glazing when there is no shading. Thus, shading is recommended for north facing windows for two scenarios. Firstly, to cut the overhead high angle sun during mid-day. Horizontal overhangs will help eliminate solar ingress during these hours. Secondly to cut the low angle morning and evening sun, vertical fins would be useful. On implementation of shading devices on the north façade there is a clear reduction in the solar heat gain in all latitudes. Their level of impact varies depending on the latitude under consideration.
Conclusion:
To conclude, the north light is not always indirect. There is direct sun entry during many hours of the year which need addressal. Detailed analysis of the sun path and sun entry into spaces based on geographical location, orientation and façade design are important before deciding on the requirement of shading and recommending shading deign proposals.