That's a good question, as there are significant differences between Tier 1
and Tier 2 APS
in terms of both features and functionality. This article outlines and attempts to explain these differences.
A Tier 1 APS
works on a simple master/switched principle using current sensing technology. When the control device (a TV or PC) is on, the switched outlets (and hence the peripherals) are powered on. When the control device (a TV or PC) is switched off, the switched outlets and peripherals are powered off. Energy savings are derived from ensuring that peripherals are switched off when the TV is not in use. Higher energy savings occur when users leave peripheral devices in the on state something that is common with AV receivers and DVD players. A Tier 1 APS relies on user behavior to switch the TV on and off for generating energy savings. Tier 1 APS are simple to install, compatible with >99% of TVs, reliable, cost-effective, and form an important part of many energy savings programs in North America.
A Tier 2 APS
is an enhancement to a Tier 1 APS. In addition to master/switched functionality, the APS also controls the TV based on user engagement, or more specifically, the lack thereof. The principle is to generate extra energy savings from the TV when a user is no longer present by switching the TV off along with the peripherals (e.g. children have wandered off or someone has fallen asleep in front of the TV).
As a rough rule of thumb, a Tier 2 APS is roughly three times the cost of a Tier 1 APS due mainly to the additional sensor and more complex electronics. In addition, a Tier 2 APS is slightly more complex to install and so is best suited to Direct Install (DI) programs, which increases the overall measure cost vs. a Tier 1 APS (which can be self installed via a less costly retail or kit program delivery method).