What do all these photo’s represent?

multishot shoulder seasons


If you travel you’ve probably heard the term “shoulder season”.  It’s the time between high (peak) and low (off-peak) season.  A building also experiences shoulder seasons, except we’re talking about energy use instead of tourists.  In Canada we have two peak energy seasons, during the hot summer and the cold winter.  The times between these two peaks are considered the shoulder seasons, which would be spring and fall — hence the photos above.
Shoulder seasons are important for a building.  It’s starts right from the design.  A building needs to be designed for the ‘worst’ case, or near worst.  Engineers have design day criteria for this.  In Toronto the criteria is -20°C for the winter and +29°C in the summer (ref: ASHRAE 90.1-2010 which is part of the OBC).  These numbers are chosen because they are rarely exceeded (only ~1% of the time).  Yes this ensures the building has enough heating and cooling capacity, but how does the building operate on more moderate days?  If we don’t look beyond these design days then for 99% of the year we’ll have a poorly operating building. Would you design a car to go one speed?
Engineers don’t design buildings this way either. However the options and technology available to them has dramatically improved.  We’re talking about pumps, fans, chillers, boilers, valves, burners, humidifiers, dehumidifiers, compressors, and that sort of thing.


Older “Constant” Technology:
Often referred to as “robust”, a lot of older equipment was actually quite finicky.  It wouldn’t break, but it only ran at a constant speed or load, and even then was sorely inefficient, much worse still at part loads (e.g. 25%, 50%, etc).  To compensate the design had to keep things moving ‘constantly’ to minimize impact on the equipment.  These systems are like driving your car with the pedal to the floor and regulating the speed with your brake.  Obviously not the most efficient.  If a building is designed like this we have a building that operates poorly 99% of the year.
Modern “Variable” Technology:
Today, designers seek to improve efficiency using systems with highly variable control. This includes variable frequency drives for motors, modulating and condensing boilers, two-way valves, variable compressors, a wide variety of setpoint resets, free cooling, pressure and flow sensors, and much more. Variable control allows us to ramp systems up or down depending on the need. Using the same analogy, a variable system is like using the gas petal to regulate your speed. — Don’t need to go as fast? Just step off the gas!


At UHN we have a number of older buildings, which makes it a challenge implementing variable control.  The good news is that when we do, it will save energy, improve control, and increase comfort throughout the year.

It’s a big task to improve shoulder season control, but a few things we’re working on include:

  • Variable pumps on chilled water systems
  • Variable flow for fans on air handling system
  • Software that optimizes building systems to run them as efficiently as possible
  • Resets on condenser and chilled water temperatures
  • Resets on heating water temperatures


So what can you do at home to improve efficiency during shoulder seasons?

  • Adjust your thermostat (or better yet program it) for a wider range of acceptable temperatures. You don’t want the heating coming on in the morning when the A/C will turn on an hour later to cool it back down
  • Try turning off heating and/or cooling in shoulder seasons (If you do need it, you can always turn it back on)
  • Use fans instead of A/C, ceiling fans are great for this
  • Open windows to cool the house when it’s temperate outside
  • If you have your windows open, make sure your heating or A/C system is not
  • Program an outdoor temperature reset on radiator heating
  • Use your blinds and drapes. Closing blinds during the day and opening them at night will keep out the heat. Keep them open if it’s cold out.

Have a great long weekend and enjoy the season!