Solar path
On December 21st, Bostonians can expect the sun to rise at approximately 7:30 am at 120 degrees azimuth. This winter sun will reach its highest elevation of approximately 23 degrees in the southern skies at around 12pm. It will set at approximately 4:30pm at 240 degrees azimuth.
Conversely, on June 21st, Bostonians can expect the sun to rise at approximately 4:30am (I think that this should be adjusted to 5:30am for DST) at 60 degrees azimuth. The summer sun will reach its highest elevation of approximately 72 degrees (a mere 18 degrees shy of being straight up in the sky) at around 12pm. It will set at approximately 7:30pm (adjusted to 8:30pm for DST) at 300 degrees azimuth.
Annual temperature & relative humidity ranges
During the winter, the design temperature range is from 5 degrees F to 57 degrees F. In the summer, the design temperature range is from 57 degrees F to 92 degrees F. The average annual temperature range is from 44 degrees F to 58 degrees F. Boston has record high and low temperatures of 96 degrees F and 5 degrees F.
During the winter, the relative humidity ranges from 50% to 76%. In the summer the range is 52% to 82%. During June, July, and August the dry bulb temperature and humidity hover around the comfort zone, occasionally exceeding it. For the rest of the year, temperature and RH are below the comfort zone.
Annual wind speeds & directions
Average wind speeds annually range from 7mph to 21mph, with a mean of 13mph. The record high is 41mph.
In Jan, Feb, and Mar, winds are primarily cold and on the dry side and coming from North/North-westerly directions
In Apr, cool dry winds come from the west, while cool humid winds come in from the South and East.
In May, winds are cool and steady from all directions.
In Jun, cool dry winds come in from the Northwest, and warm/hot winds start to come in from the West/Southwest.
In Jul, warm/hot winds continue from the West/Southwest. Steady comfortable winds come in from all directions except for Northeast.
In Aug, warm comfortable winds come in from the West/Southwest.
In Sep, cool dry winds come in from the West/Southwest with some strong winds coming in from the Northeast.
In Oct and Nov, cool dry winds begin to come back in from the North/Northwest.
In Dec, the return of the cold winds returns from the North/Northwest, and Westerly directions.
Annual percent sunshine
The average amount of sunshine is approximately 42%.
In Jun, Jul, Aug, and some of Sep, shade is required for much of the day. The rest of the year is primarily cool/cold regardless of percent of sunshine.
Psychometric chart notes of interest
60% of the year, some form of conventional heating system is required.
Because of the cool dry air from the North, some type of Humidification is recommended for 44% of the year.
Protection from the wind is required for 34% of the year.
Conventional air conditioning is only required 2.2% of the year (provided natural ventilation and direct evaporative cooling methods are utilized).
Shading from the sun is required for approximately 9% of the year.
Summary
Boston is a cold weather city where exposure to the sun’s warmth is at a premium, and heating systems take precedence over cooling systems. Provisions should be made to maximize southern exposure to take advantage of the sun, to allow for cool southwesterly breezes during the warm summer months, and to protect from the cold north and northwestern winds throughout most of the year. Because of the predominately cool, dry air, some form of humidification may be desirable. During the summer months, shading from the sun and methods of natural ventilation should be provided.
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