Issues with the Panasonic Air Conditioners
Panasonic Air Condition unit HZ35XKE
This AC unit has serious issues with its temperatur regulator, which fails to maintain the set-point.
Each time I've contacted Panasonic support about this software bug, they've insisted on sending out an HVAC technician. Please ... Well, except for that one time when they sent me a reply clearly generated by ChatGPT (hello "Susanne"). This page is a last, desperate attempt to get them to understand and escalate the issue within Panasonic. So far, I've never seen an HVAC technician rewrite firmware code ...
The picture below illustrates how the unit fails to down-regulate power, even as the measured temperature rises way beyond the set-point, until I manually lowered the set-point.
[legend: "Ställ in" = set-point, "Inomhus" = indoor (temp), "Utomhus" = outdoor (temp), x-axis hours]
Please note that these are the AC unit's own measurements. There are no airflow issues or other external factors at play here. The problem lies entirely within the unit itself. The system measures temperature only at the air inlet and does not rely on remote sensing in the room. Therefore, this issue has nothing to do with room obstructions or similar external factors. Of course, room temperature fluctuations will be even larger.
The PID controller
A PID controller is the standard method for handling this kind of regulation. A well-tuned PID controller performs exceptionally well! You simply can't outperform such a system manually! It not only accounts for the current deviation (the P or "proportional" factor) but also considers historical data (the I or "integrative" factor) and predicts future trends (the D or "derivative" factor).
In the Panasonic air conditioning unit, however, you’re forced to adjust the set-point (the desired temperature) manually from time to time to achieve your desired temperature. This behavior is a clear indication that the PID controller is not doing its jobs. Instead of maintaining the displayed set-point temperature, the unit delivers a few degrees above to a few degrees below what the display of the remote control shows, as the graph above illustrates.
A properly tuned PID controller also overshoots and undershoots the target about equally often. This balance indicates that the parameters (the coefficients for P, I, and D) are optimized as good as it gets. Panasonic's controller? Not so much. It consistently lags behind, barely reacting to measured temperature changes - a clear indication it is out of touch with reality.
I have no idea whether Panasonic's temperature controller was tuned using a pair of dice or if it’s simply broken.
Panasonic Quality Assurance?
I can’t understand how Panasonic could have overlooked such a glaring issue. I’m quite certain this is a problem with the model itself, not just my specific unit.
So why and how did I notice this issue?
- I replaced an old but functional SANYO AC unit and noticed how much worse the Panasonic performed in maintaining temperature.
- This heat pump is the primary heating source in my house, so there are no other heating systems to compensate for its errors.
- Living in Sweden, where outdoor temperatures can fluctuate significantly throughout the daily cycle - particularly during the fall and spring - any flaws in a poorly tuned controller become especially apparent.
- As a system developer experienced in embedded systems and control engineering, I may know a bit more than the average Joe about where to look.
Costs
This isn’t just about staying comfortable - it can completely undermine the whole point of getting the heat pump in the first place. A heat pump is supposed to save you money, but if you have to raise the indoor temperature to compensate for its poor performance, those savings might as well fly straight out the window.
According to the UK Department of Energy and Climate Change, lowering your thermostat by just 1°C can reduce heating energy usage by approximately 10%, resulting in substantial savings on energy bills. With the Panasonic controller being off by several degrees, the potential energy waste is significant.
Food for thought.
About
Questions? Criticism? Praise? Other feedback? Send me a mail!
I'd really love to hear from Panasonic Aircon! ❤️
/By Mikael Q