After taking last week off for the author to recover from the ASHRAE conference, we're back with week 7 of PBA's blog series on the coming updates to the Michigan Energy Code! We're covering essential updates in the new Michigan Commercial Energy Code (based on ASHRAE 90.1-2019) before the adoption date on April 22, 2025. Click here if you've missed our previous posts!
Every new revision of ASHRAE Standard 90.1 seeks to reduce energy usage compared to the previous version. Improvements are pursued across many realms, but there's one energy user we can't directly affect: receptacles. Historically, it was reasonable to assume that roughly 25% of a building's energy usage would be from things plugged in by occupants. However, as envelopes, HVAC, and lighting have improved while plug loads have remained the same, that percentage has increased. Refer to the graph below - for a recent project, the expected energy usage of plug loads was roughly the same as the building's entire heating energy.
The problem with plugs is that we can't control what gets plugged into them. HVAC temperatures can automatically adjust up or down to a more efficient level, but it's all moot if someone has plugged in an always-on space heater. Lighting can dim when ample daylight permeates a space, but it's all moot if someone has plugged in an always-on lamp. All of these energy improvements are negated as soon as someone decides to use their landlord's electricity to mine Bitcoin.
As long as receptacles must accommodate any appliance, what can we do? Enter: Automatic Receptacle Control. A percentage of the plugs in certain types of buildings must turn themselves off at certain times. That way, even if someone has left a parasitic load plugged in, energy usage is minimized. This isn't actually a new requirement of ASHRAE 90.1, but the State of Michigan exempted this section when adopting the 2015 energy code. That exception is removed for the 2021 code.
For the new 2021 energy code, receptacle control covers at least 50% of plugs in the following spaces:
In order to make sure you don't accidentally plug something important into a controlled receptacle (eg: the freezer in the break room probably wants to be powered 24/7), the controlled receptacles must be permanently marked. Generally, this means a receptacle with specific markings from the factory. Markings are available for an entire duplex receptacle, or for a split option (eg: one plug on a duplex is controlled, the other is constantly on).
Photo credit: Legrand
These plugs must turn themselves off either based on a time of day schedule (eg: after the close of office hours) or based on an occupancy sensor (eg: turn off after people are sensed to leave). Exactly what equipment is used for this switching can vary. Receptacles are available where the switching occurs in the receptacle itself. Control modules are available to intercept a wire going to a bank of receptacles. Controlled breakers can turn off an entire branch circuit. The best solution will vary project-to-project, and a successful project may include multiple types of switching equipment. This all adds project complexity, but luckily it shouldn't add a new control system: controlled receptacles can generally be managed by the lighting controls system required by most new commercial projects.
As a final note of reprieve, there are some key exceptions for receptacles not requiring control.
Next week, we'll continue in electrical and discuss granular electrical metering.
