Mixing Metaphors: BAC! Who left this MES?

I have been learning a bit about building management systems (BMS) and realized that, abstracted the right way, the manufacturing execution systems (MES) of semiconductor fabs are pretty similar in overall concept and components. That parallel made it much easier for me to frame my learning. 

The brains of the system: BMS vs MES.

These s/w systems take schedules, control targets and feedback to make the building "work" (literally).

The communication protocols: BACnet vs SECS/GEM.

Granted, building equipment use many more protocols than just BACnet, some of which are proprietary to the equipment vendor.

 The building equipment which is actually being controlled for the purpose of making the building useful for its owners. 
An office building could be thought of a making an environment conducive to worker productivity with maximum efficiency.
A fab could be thought of as controlling the flow of materials between equipment to maximize output of wafers/chips at minimum cost.

 The sensor systems which allow the control system to make smart choices about controlling the building equipment.
For an office building this might mean feedback control for HVAC (don't over cool) and switching off unused lights or dimming lights for daylight harvesting.
For a fab this might mean monitoring the voltage and flow rates for a particular piece of process equipment and adjusting the process recipe for the next lot or wafer to ensure uniform film properties from lot to lot.

Micro generation meets micro consumption - Energy Scavenging Wireless Networks

 In a previous post I wrote a bit about wireless mesh networks as a means to cost effectively retrofit sensors into a building to allow feedback control and continuous monitoring of environmental conditions to reduce energy usage.

One problem with wireless: batteries.
While they may last for years, they do need to be replaced eventually. If you have truly adopted a full building installation of sensors, that would be hundreds of nodes and batteries tucked into all kinds of hard to access locations where the HVAC, power distribution, and other systems are located or routed.
Replacing all those batteries in all those places: not trivial.

Energy scavenging to the rescue!
Using versions of the technology that power your kinetic watch (mechanical micro-generators) or that can be stuffed into a shoe (piezoelectric), enough power can be generated from ambient vibrations to power the sensors. It's not a lot of energy, but it's probably enough for low power network devices:

• MCU + Transceiver for ZigBee (IEEE 802.15.4) draws somewhere between ~20mA and <200mA (say 50mA) (at ~3.3V) when transmitting with <1 uA in sleep mode
• Transmissions last a few tens of milliseconds (~15ms - 48ms) and sensors may transmit ~1/min.
• Energy required is, therefore ~7.9 mJ per minute (for 48ms transmissions).
• Micro-mechanical energy generators produce on the order of a few (1-5-ish... say 2) mW of power. This could yield up to ~120 mJ of energy per minute (depending on the consistency of vibrations).

So, even with a smaller or less efficient generator than I found in a few minutes of searching, with a small battery or capacitor to store the micro-generator's energy you're in business without battery changes.

image credit: inhabitat

LEEDing to Better Building Control and Efficiency via Wireless Mesh Networks

LEED v3 has expanded the emphasis on measurement and verification (M&V) in order to offset concerns that green buildings don't maintain designed performance over time.

The rating system where this is most evident is in the LEED 2009 Existing Buildings: Operations & Maintenance (EB:O&M) If you dig through the credits with an eye towards the ones that:

• Require or could benefit from some sort of real time or on-going monitoring
• Could use a portable monitoring system comprised of sensors and small data network.
• Address the toxicity and recycle-ability of the sensor & networking systems

You find that something on the order of half of the credits (around 46 of 92 when I last checked) could be affected by having a good sensor system available.

Sensors, of course, need a communication network to feed their data back to a building automation system, (BAS) or building management system (BMS). If you are forward thinking and lucky enough to be engaged in new construction, then you can build many of these networks into the plan. Then when you meet the USGBC requirement for ongoing performance monitoring by following the EB:O&M certification route, you will be ready. For new construction, this is probably a good way to go.

However, if you're in the position of having an already complete building and you want to obtain EB:O&M, getting such a network in place could cost a considerable sum due to the wire routing involved. In such cases, using a low power wireless network would be preferable. Given the large area to be covered by a wireless sensor network and the large number of discrete sensors needed, this kind of application lends itself to a wireless mesh network (ala IEEE 802.15). Basically a network that uses the nodes to communicate with each other rather than requiring all units to communicate with a central access point. The more nodes (sensors) in place, the better the network becomes... and it's low power enough to run on batteries for months at a time... important if you need to pay someone to replace all those batteries.

UC Berkeley has pioneered work on this topic, coining the phrase "smart dust," and spun off at least one company (Archrock) that aims to address this kind of market space.