HVAC Monitoring Without a Building Management System

Yes, you can monitor commercial HVAC equipment without a building management system (BMS). Most small commercial buildings don't have one. Equipment monitoring puts sensors directly on each AC unit, reads how it's running, and sends an alert when something starts to go wrong. It doesn't connect to the building's controls, so it works the same way whether a BMS is there or not.

What a building management system does

A building management system, also called a building automation system (BAS), is a central control system for a building's equipment. The U.S. Energy Information Administration describes it as a system that uses remote sensors and control software to monitor changes in temperature and operating systems, and to manage energy use for heating, cooling, ventilation and lighting.

Its main job is scheduling. A Pacific Northwest National Laboratory (PNNL) report on these systems calls the ability to schedule major equipment, such as packaged air conditioners and heat pumps, "the single most important function." The other basics in that report include thermostat control, setpoints and alarms. A typical alarm is a room temperature moving outside its acceptable range.

So a BMS runs the building on a schedule and tells you when a space is too hot or too cold. Most of what it reads is about the rooms and the schedule.

Most small buildings don't have one

In the federal government's 2018 Commercial Buildings Energy Consumption Survey, about 11% of U.S. commercial buildings under 10,000 square feet had a building energy management and control system. For buildings between 10,000 and 50,000 square feet it was about 26%. For buildings over 100,000 square feet it was about 70%. Those figures come from an ACEEE summary of the survey data.

A typical restaurant, shop or storefront is in the first group. The AC is usually one or more rooftop units, each run by its own thermostat. PNNL researchers describe how these small buildings usually run: programmable thermostats that mostly aren't networked, and no remote diagnostics, alarms or trending. They also note that in many small buildings without a dedicated operator, the HVAC equipment "tends to be serviced only when occupants complain or when the equipment completely fails."

The reasons PNNL gives for skipping a BMS include cost and the fact that the building owner is sometimes not the tenant, so nobody has a reason to pay for one. For a single restaurant, a BMS is a lot to take on just to keep an eye on a few AC units and a walk-in.

What a BMS usually can't see, even when there is one

Having a BMS doesn't mean every piece of equipment is connected to it. It also doesn't mean the BMS can tell when a machine is wearing out.

The refrigerant side of rooftop AC units

A BMS can schedule a rooftop unit and watch the temperature in the room it serves. What it usually doesn't have is the refrigerant side: the line temperatures that show a low charge, a dirty condenser or a restriction. A PNNL field project on rooftop unit diagnostics found that most units "do not install all the sensors necessary for diagnostics, especially to do a refrigerant-side diagnostics." Adding them meant extra sensors and a controller upgrade, and the sensors had to be placed carefully to give accurate readings.

Walk-in coolers and freezers

A walk-in has its own controls. A thermostat or a refrigeration controller turns the cooling on and off, and a timer or the controller runs the defrost cycles. Whether a BMS sees the walk-in at all depends on whether someone connected those controls to it.

How hard the equipment is working

A room temperature alarm goes off once the room is already outside its range. It doesn't tell you the unit has been working harder than normal for the past few weeks. Power draw is one way to see that. PNNL has tested a low-cost approach that uses only a unit's power and the outdoor temperature, and found it can detect a unit's performance getting worse over time, though it is limited in saying why.

What sensors on the equipment add

SmartHVAC puts the sensors on the equipment itself. On an AC unit, an install places nine sensors: seven temperature probes and two current sensors. Five probes clip onto the refrigerant lines, two sit in the supply and return air, and the two current sensors clamp around the wires to the compressor and the fan. The refrigerant circuit is never opened, and nothing connects to the building's network or controls. Sensors are fitted during a normal service visit, about an hour per unit. Our post on non-invasive monitoring explains why we don't open the system.

The first weeks are the software learning each unit's normal: how long it runs to hold its setpoint, what it draws, and how fast it recovers. After that it watches for specific faults, including refrigerant undercharge and overcharge, condenser fouling, liquid line restriction and compressor valve leakage. When something changes, the alert goes to you, your service company, or both. It says in plain language what was detected and what to tell the technician.

The aim is to find the problem early enough that the repair can be booked ahead. Our guide to what HVAC monitoring is covers the basics, and the post on a walk-in that won't hold temperature shows what that looks like for refrigeration.

With a BMS or without one

Because equipment monitoring doesn't depend on a BMS, it fits both cases.

No BMS. This is most small restaurants and shops. The sensors give you the equipment readings and alerts you don't have today, without a controls project.

A BMS is already there. The BMS keeps doing what it does: schedules, setpoints and room temperatures. Equipment monitoring adds the readings it usually doesn't have, like refrigerant line temperatures and compressor current. It doesn't control anything, so it doesn't change how the BMS runs the building. Fault detection software built for large buildings usually assumes a BAS is in place, which our post on FDD and predictive maintenance explains.

Running several sites

If you manage a handful of restaurants or stores, most of them probably have no BMS. Equipment monitoring gives you one view of every unit at every site, so you can compare them. An AC unit that runs twice as hard as the same model at your other locations is a repair you can schedule. More on that on our facility management page.

Common questions

Do I need a building management system to monitor my HVAC?

No. Equipment monitoring uses its own sensors and a cloud dashboard. Nothing connects to your building's controls.

Can I add equipment monitoring if I already have a BMS?

Yes. It runs alongside the BMS and doesn't control anything. The BMS keeps handling schedules and comfort, and the monitoring adds equipment-level readings.

Does it replace a BMS?

No. A BMS controls equipment. Equipment monitoring only watches it and tells you when something needs attention.

Does it connect to our network?

No. Nothing connects to your building's network or controls.

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