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The challenge behind perimeter heating using linear diffusers

Nowadays, commercial office buildings typically require cooling all year to satisfy the comfort of occupants. This is due to the amount of internal gains generated by the occupants themselves as well as equipment such as lighting, computers, printers and other types of equipment.

It is typical to divide space floor into two zones: the main zone and the perimeter zone. As seen in the figure below, the main space of the building is shown in red and the perimeter zone in yellow.


Core perimeter

Generally, the perimeter of an office floor represents a zone delimited by the building’s facade and ends approximately 10ft away from that wall. During the winter season, heating is required in the perimeter zone of a building while the main zone requires cooling. On the other hand, cooling is required in both zones during summer. When a ceiling diffuser is installed, the challenge is to properly direct the air in both zones according to the season especially in new modern architectural buildings with glass facades. Let us consider different air projection scenarios and the consequences during both seasons.


Diffuser projects air towards the main zone of the building all year Diffuser projects air towards the window in the perimeter zone all year
Cold air is projected properly and away from the window for comfort of occupants.
Cold air is projected towards the window in the perimeter zone and a draft of cold air is generated. Occupants are therefore uncomfortable.
Hot air is projected away from the window allowing condensation. The warm air mixes with the cold air used to cool the main zone and increases its temperature wasting energy in both cooling and heating.
Hot air is projected towards the window preventing condensation. Occupants in the perimeter zone are comfortable and no energy is wasted.


The solution commonly used in the industry is to allow the diffuser to project the air in both directions at all times. This is called the 50/50 compromise because 50% of the air is always projected in the wrong direction.

Fortunately, Titus-HVAC offers an Auto-Changeover linear diffuser allowing a bi-directional air pattern. As seen in the figures below, the EOS perimeter diffuser is equipped with an actuator arm that switches position as it detects the supply air temperature and consequently redirects the air pattern. The standard set point temperature for the actuator arm is 71°F in cooling and 78°F in heating. Thus, the diffuser will project the air towards the main zone of the building when supply temperature is below the cooling set point. The arm will reposition itself to discharge the air towards the window when the supply temperature is above the heating set point temperature.



Other advantages of the EOS Auto-Changeover diffuser include

  • Adjustable set point temperature of 2°F above or below the standard set point temperature
  • Solar powered actuator arm. There are solar cells mounted on the face of the diffuser which also store energy allowing the diffuser to stay functional even in the dark.
  • Energy savings that may contribute to a LEED certification

The EOS Auto-Changeover allows for a more suitable solution than the 50/50 compromise which is the current industry standard.

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