Smart Meters Can Provide ExtraHVAC Troubleshooting Challenge

Issues related to power line use are difficult to predict and equally difficult to diagnose.

As power companies seek to improve the efficiency of the electric grid by better matching demand with supply, they are relying with increasing frequency on smart meters. Smart meters record electricity and gas usage in real time in homes and businesses and relay that information back to the utility company. Once applied primarily to commercial and industrial customers, the practice of automatic meter reading (AMR) through the use of smart meters is finding its way into the residential market and putting HVAC contractors to the test.

The advantages of AMR for utilities include the ability to monitor electric usage without paying someone to read individual meters once a month. AMR also provides more detailed information about electricity usage, enabling utilities to better manage the electric grid. In some instances, power companies are able to use this information to charge homeowners different rates at different times of day, depending on the demand on the grid.

For the most part, the impact of AMR and smart meters on the homeowners goes unnoticed. Homeowners may not have to sign up for the installation of a smart meter, and many are unaware their homes have a smart meter, much less understand what it does. Meanwhile, the meters are delivering information to the utility in one of three ways: short range RF transmission (ERT), long range RF transmission and power line carrier (PLC). It is the PLC that sometimes brings the presence of a smart meter to the homeowner’s attention, and usually not in a positive way.

The PLC method uses the existing power line infrastructure as a method of transmitting and receiving digital signals. The power company embeds a signal onto the 60Hz power signal that requests information from the meter. The smart meter then includes a return signal on the 60Hz power signal to communicate back to the power company. Although simple in theory, the system is complicated by a variety of transmission levels, transformers and substations that the power company uses for power distribution.

When the power company adds a signal to the power line, many consumer devices see the signal as noise, or a deviation from or distortion of the regularly curved sine wave. Like many household devices, heating, ventilation and air-conditioning (HVAC) controls use the 60Hz as a timing mechanism. Noise can trick the control into thinking that fewer or greater cycles than expected have occurred, which can cause different issues depending on how the control reads the signal. For example, in controls that use incoming voltage to verify the power has been wired in phase, noise can fool the control into thinking that there is a voltage potential when there should not be. The reaction of a furnace or air handler to noise varies by manufacturer, by control supplier to the equipment manufacturer, by the age of the control and by the circuit board design.

Unfortunately, issues related to power line use are difficult to predict and equally difficult to diagnose. The transmission grid itself is a very large, very complicated entity with all sorts of absorption, reflection and amplification in progress. Additionally, each individual home is a random assortment of inductive or capacitive loads and wire lengths that can snub, reflect or amplify noise. Often these loads can even add noise and waveform distortion. For example, fluorescent lights that are on the same circuit as a furnace can cause different issues with the furnace, ranging from invalid fault codes to furnace shutdown.

Fault codes and equipment shutdowns bring the contractor to the homeowner’s home, and the search begins for the source of the problem. In the case of problems triggered by noise on the power line, a contractor cannot expect to visit the home, take a measurement (using a standard voltmeter, for example) and use those measurements to detect the cause of the fault code.

So what’s a contractor to do? First, don’t assume you have a smart meter problem. Begin by ensuring the equipment is installed and operating properly. Check the basics. In the case of a gas furnace, this means looking at both the fuel supply, checking the duct system and air supply, and the electrical supply, including wiring. Incorrect wiring at the unit may be the culprit. Bad wiring throughout the home may also interfere with any filtration provided by the power company. In reality, noise on power lines is quite common and can come from loose grounding wires at pole transformers or radio signals leaking into transmission lines.

Next, change the load on the circuit that contains the malfunctioning unit. This can be accomplished by adding an RF filter choke, which may result in a small enough change in load and enough filtration to correct the problem. It may be necessary to re-wire certain devices or outlets to change the load to individual circuits, but check with an electrician before making any such changes. A contractor can also use a copper coil placed on the incoming power line to help dampen any noise coming to a furnace or air handler. And, when a smart meter is installed and sending signals on one of the two legs of power coming into a house, it may help to move the equipment to the other leg of power.

If the indoor equipment has been in operation for 10 years without experiencing problems and suddenly is generating fault codes of undetermined origin, it is a good idea to consider what has changed.

Absent other causes, avoid the temptation to blame the control board. Contractors do not have a way to troubleshoot what is going on inside the board, so they may opt to replace it. And the immediate result may be a furnace or air handler that performs correctly. However, the problem may present itself again, in which case it’s time to take a big picture approach to problem solving.

If the indoor equipment has been in operation for 10 years without experiencing problems and suddenly is generating fault codes of undetermined origin, it is a good idea to consider what has changed. Maybe the homeowner has installed LED light bulbs in the house. These bulbs have a tendency to distort the sine wave, especially when placed in close proximity to the furnace. Cell phones, too, can disrupt equipment operation. Or maybe smart meters have been or are being installed.

Step back and look at the entire neighborhood for a clue. Are patterns evident? Are problems occurring at the same time at different homes? Discuss this problem with other contractors and/or members of professional organizations like the Refrigeration Service Engineers Society (RSES) to learn whether they are encountering similar problems or experiences.

Finally, and just as importantly, talk with the local power company. Develop a relationship with them that encourages a regular exchange of information. Most power companies employ an individual whose job it is to ensure that the outgoing power to the grid is clean, so feedback regarding noise on the line is important to them. And because the power company knows when smart meters communicate, the utility should be able to help determine if these regularly scheduled times match fault codes associated with residential furnaces.

Additionally, federal law requires utilities to attempt to remedy a situation in which they are interfering with the operation of devices in the home. If the smart meter is likely to blame, the power company has the ability to change parameters within the smart meter, which might solve the interference problem. Replacing the meter may also remedy the situation, as the electronics in smart meters can vary, with some being more sensitive than others.

Problems that smart meters can introduce are illusive and often difficult to identify. But they are also very real and require the intervention of contractors who are confident and competent in their basic troubleshooting skills and at the same time, willing to step back and develop relationships that will help them see the big picture. The problem may extend beyond the furnace and the house to the smart meter and the grid. Proving that requires the skill of a well-trained contractor with the ability to think beyond what has always been done and solve customers’ problems in a professional manner.

Bryan Rocky is director of residential product management for Johnson Controls.

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