The Beginner’s Guide to Integrating Battery Storage with Existing Building Management Systems

If you have been managing any commercial building for a while, you are already familiar with how to manage HVAC, lighting, and access controls through a Building Management System. Bringing battery storage in requires less of a reinvention and more of an extension, a new asset in the same ecosystem you have been running for years.

Protocol Translation: The First Real Hurdle

Many building management systems use BACnet or LonWorks protocols. These have been the standard for building automation systems for years. For instance, your HVAC and lighting systems likely communicate using either of these protocols. However, when it comes to commercial battery inverters, battery management systems communicate using Modbus TCP/IP.

These two protocols are incompatible. Hence, to successfully integrate your battery with your building’s operations, you’ll need an additional piece of hardware, a gateway device. This device converts signals back and forth between BACnet or LonWorks and Modbus TCP/IP.

Design this step into your system planning. Not all gateway devices will work with all inverters, so you’ll want to ensure you know in advance which inverters you’ll be using and which gateways they’re compatible with. Most inverter manufacturers provide preferred gateway options, and gateway devices themselves are a mature product line. Implementing them after installation is where costs begin accelerating, so plan ahead.

Programming Peak Shaving Automation

Demand charges can make up 30% to 70% of a commercial customer’s total electric bill (National Renewable Energy Laboratory). That’s the business case for combining battery storage with your building automation system in hard numbers.

And peak shaving captures the majority of that value. The battery automatically begins to discharge when the BMS senses real-time power consumption at the utility meter approaching a pre-determined threshold. The battery stops discharging once the peak threat has passed, then remains idle or else begins a trickle charge during lower-rate times.

This will take a few billing cycles to perfect. You’re looking to capture a true demand peak without asking the battery to respond to inconsequential ebbs and flows. Most veteran facility managers will program their system to respond about 5-10% below the inflection point of their largest expected demand peak. This gives the battery time to ramp up before the meter registers the need, so that you don’t inadvertently limit your peak savings.

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What to Read Versus What to Write

When your BMS is connected to your battery system, there’s a temptation to want to give it write access to everything immediately. Resist that urge.

Data the BMS should read is pretty much everything: SOC, voltages, currents, cell temperatures, system health flags, and fault alerts. Data the BMS should write should be as small as possible: start and stop charging or discharging. That’s about it. You’ve already correctly designed the maximum charge and discharge power limits into the battery when you requested a quote from the manufacturer, so there’s no need for the BMS to futz with that. The battery will handle it. In an emergency, the BMS can always throw a direct digital I/O that disconnects the battery with a contactor, but that’s a “break glass in case of emergency” option, not a day-to-day operating strategy.

Your battery has already been designed by a competent engineer with deep knowledge and understanding of electrochemistry to gracefully degrade if abused. Embrace that design and let the BMS just passively monitor what’s going on. It will make both the customer and the BMS manufacturer’s support lifetimes easier.

Coordinating HVAC and Battery Thermal Loads

Battery systems produce heat both during charging and discharging processes. Although commercial lithium-ion and LFP systems are equipped with integrated thermal management, this management system uses some amount of power and leads to the generation of additional heat that must be dissipated.

Your BMS should take this aspect into account. If the battery room shares the cooling system with the rest of your building, the peak cooling load of the building and the peak cooling load of the batteries may happen at the same time. An uncoordinated system may cause batteries to overheat, overload the cooling system, or even both.

The solution is to provide the battery’s thermal management status to the BMS as a monitored point and design interlocking logic that can modify the building’s cooling capacity when the battery is under high load. This does not need to be very complex. A basic interlock that increases the cooling airflow for the battery room when an active discharge cycle is detected can already make a big difference.

Designing a Fail-Safe Communication Loop

In any system that relies on networked communication, there will be occasional hiccups, where one packet or command doesn’t get through. A lost BACnet packet on a lighting system likely means a light stuck on. A lost command in a battery integration likely means the inverter continues charging or discharging based on the previous reading from the BMS.

In absence of anything better, this often results in the inverter falling gracefully back to whatever charging or discharging mode it was at prior to the failed command, and the system twiddles its thumbs until updated by the BMS.

That’s often not ideal. A few extra minutes of skewed charge / discharge state won’t hurt most systems, but maybe there was a reason the battery was asked to stop charging. Instead, you can enforce a failsafe behavior, where the inverter never charges or discharges without being explicitly told to by the BMS, until communication is lost for a pre-defined length of time.

Setting Operational Boundaries That Protect Battery Lifespan

How often the system cycles, how deeply it discharges, and how aggressively it charges are the primary drivers of battery degradation. Your BMS can really help or hurt with all three of those.

If you’re using your BMS to software limit any of those three factors, the daily cycling limit is your number one priority. Many batteries are unlikely to cycle more than once daily, if the manufacturer advises they will be fine with up to one cycle per day, configure the BMS to refuse to do more.

Cycling is also where you can most directly adjust the batteries’ potential lifetime in years. Since the benchmarked lifespan might’ve initially been set from a power, not an energy application, cutting your daily cycles in half is typically a conservative yet informed estimate. This might stretch your payback timeline, but don’t overly prioritize faster ROI when the space is already programmed to be empty.

Bottom line: Set it and Forget it is a bad strategy – but only because you really should check your user manual every 12 months to make slight adjustments to these otherwise static figures based on real-world performance. The more you cycle, the more conservative you want to be with your maximums.