Predicting RTU Mechanical Failures

Packaged rooftop units (RTUs) are essential to most commercial operations. They are vital to every cool ice cream shop on a hot day, warm coffee shop on a cold one, and now (more important than ever) the increased ventilation required for restarting business mid-pandemic. Because of RTUs’ key role in delivering a great customer (and staff) experience, problems with the unit need to be addressed as quickly as possible. A failed system could lead to an uncomfortable environment, resulting in missed sales, so noticing red flags and diagnosing problems with the unit are necessary steps to avoid crisis.


We want to help prevent as many of these failures as possible for our customers and friends in industry.  By analyzing data from a large sample of SiteSage installations, we were able to generate some insights about early warning signs of RTU failure that we hope you will find helpful.


The Data:

In this analysis, we pulled 90 days of RTU records from our data, spanning 18,000+ alerts for nearly 500 units. We focused on three of our main RTU alerts:

  • Delta T Below Threshold: Alert when the difference between an RTU supply and return temperature is below a specified threshold
  • Mechanical Problem: Alert when an RTU appears to have a mechanical problem
  • Target Temperature: Alert when the heating and cooling equipment is not reaching its target temperature set by the user


The Delta T alert is a warning sign for the machine, requiring minimal adjustments, while a Mechanical Problem alert is a sign of a larger problem that may require more extensive (read: expensive) repair.  The Target Temperature alert is the “lagging indicator” – an uncomfortable room as a result of an under-performing or failed RTU.


Daily Timing of Alerts

Below Return Threshold (BRT)

According to our data, the Delta T alert peaks at 10 a.m., and remains high for most of the morning. As employees arrive and stores begin to open in the mornings, RTUs kick into high gear. The BRT alert is the first sign something might be wrong with the unit because it triggers when the thermostat encounters insufficiently cooled supply air. Of the three alerts, this was also the most common.


Mechanical Problem

The Mechanical Problem alerts peaked at midday: 11 a.m. – 12 p.m. Any single event of daily operations might not be the sole reason for RTU mechanical failure. Instead, coolant leaks or clogged fans may be initially invisible as the store opens for the day, but unsustainable as the RTU draws more power throughout the day without cooling the air inside. Mechanical Problem alerts were less common than Delta T alerts and likely indicate a need for repairs.


Target Temperature Not Reached


The Target Temperature alert is more common much later in the day, with the peak times of 6-7 p.m. When the thermostat in the building is not reaching the comfort level set by the user, a number of causes are possible. Peak occupancy of a facility can truly expose under-performing or failed RTUs.  Under-powered or under-performing units might not be able to handle the increased heat that comes with more bodies, food to be cooked, opened doors, and other factors of peak occupancy.


While a lagging indicator, Target Temperature alerts point to conditions that are potentially the most damaging to retail or hospitality businesses, with an uncomfortable environment risking the loss of sales and unhappy customers.


Our data shows that these three key alerts follow a logical pattern:

  • Delta T alerts peak first (10am): there are symptoms of problems, but they have not yet resulted in mechanical failure or uncomfortable conditions
  • Mechanical Problem alerts peak next (12pm): those under-performing units may really be straining and ultimately failing at the job they’re designed to do
  • Target Temp alerts peak last (6pm): the result of under-performing or failed equipment. Of course, this alert peaks at the worst possible time – when your store or restaurant is busy and full of paying customers.


The moral of the story?  Pay attention to those early indicators!  If you are noticing that your RTU is racking up Delta T alerts in the morning, schedule a maintenance visit (typically for 1/3 the cost of a reactive repair).  This can save you many headaches. 


Contact us if you want to learn more about how you can better monitor your equipment with SiteSage, and follow our blog for more insights into our data.

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