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A Trane Tracker controlled office and warehouse building had a rogue schedule, resulting in a HVAC bill that was 20 percent higher than necessary for the tenant.  The building had 10 roof-top units (RTU’s), including one CRAC (Computer Room Air Conditioning) unit and nine package units.  In addition to running during normal operating hours, all nine RTU’s were showing runtime on Saturdays — when the building was unoccupied.  Neither the owner nor tenant were aware of the issue.  Simply put, these machines were operating 20 percent longer than needed which not only led to higher HVAC expense for the tenant but, ultimately, would have shortened the lifetime of the equipment, reducing the property owner’s ROI.

Although BAS (Building Automation Systems) can streamline and help control a big facility, mistakes in BAS programming are often compounded — or missed altogether — without monitoring tools.    As buildings with BAS get passed from tenant to tenant and HVAC service to HVAC service, valuable knowledge is often lost as to how the BAS and subsequent schedules were set up.  It can be tedious and expensive to recommission the building and do a full audit of schedules within the BAS.  Until there is a complaint, these sort of problem situations can drag on for months or years,  wasting energy and money.

Key Concepts

  1. Mistakes in BAS programming can be magnified across a building system, resulting in higher than necessary expenses, and still not be readily apparent.
  2. Programming of BAS, if properly done, has benefits for both the property owner and the tenant(s).
  3. Many BAS, if not most, lack the kind of internal monitoring controls that can uncover these money-wasting mistakes.
  4. BAS systems are complicated and system knowledge is often lost when new tenants move in or when HVAC services are switched.

The facility we were working on is a typical high tech office building with an attached warehouse area.  It has a total of 10 units, one Trane Voyager used as a CRAC unit and 9 other Trane Voyagers of various vintages.  All the units that we were monitoring were on the roof of the building.

BAS controlled building running after hours

Two story office, one story warehouse space

Soon after Virtjoule’s HVAC monitoring sensors were installed on the Trane Voyagers, it became apparent that there was a scheduling problem with the building.  All the units would start up on Saturday mornings at, but not exactly on, their normal weekday hour.  The slightly different start time was the first clue that an extra schedule was in the system.  Shutdowns were often at the same time as the weekday schedule for each unit.

This is a professional building with product developers and executives and featuring some manufacturing and warehouse space.  Although employees can come in on the weekend, there is no need for the building to be completely heated or cooled for just a few people.  Employees do have access to thermostats to regulate heating or cooling if they wish.

The building engineer was alerted and initially puzzled by the situation since he thought the building should be in “unoccupied mode”.  He proceeded to work carefully through the BAS system and located the rogue schedule.

Because the rogue Saturday schedules were so similar to the weekday schedule, it’s easy to see that the owners of this facility have now reduced the wear and tear on the equipment they own by one day a week — or 52 days a year!  The tenant is saving over 16 percent on their HVAC expenses (having paid 20% more than they should have) and presumably, over a longer period of time, will save on maintenance as the number of calls should decrease.

[Randy Cox - CEO and co-founder of Virtjoule - He is the software designer and analytics engineering for Virtjoule Sense sensors. He studied Chemical Engineering and Petroleum Refining at the Colorado School of Mines. You may contact Randy at: randy at virtjoule dot com]


If you have a BAS (Building Automation System) you can’t assume that everything is always well.  Our experience has shown there can be numerous control problems with BAS systems even when staffed by full time employees (earlier blog article).  

In this article we’ll discuss problems with a Trane Tracker BAS used on a small 12,500 ft2 office and retail building in Niwot, CO.  

Without the knowledge of the building owner and operator or their HVAC service company, three out of the four Trane Voyager units were running 24 hrs a day multiple days a week, including weekends, when the building was not occupied.  The BAS programming interface was obtuse enough that even an experienced HVAC control technician failed to correct the problem on the first trip.  The problem was fixed on all four units on the second trip and our monitoring showed that the building owner would save over 5,600 hours of runtime over the course of a year.

This building is managed like many others where the building owner hires an HVAC service provider to provide varying levels of service, primarily to handle complaints and do some routine maintenance a few times a year.  The building is not large enough to justify a full time facility manager or maintenance person.

All four package units were the same Trane YCD120B3HCEB, a 10 ton package unit, installed in a small quad on the roof of this building.

After the first few weeks of monitoring, a clear picture emerged that suggested that all the units were running on flawed schedules.  Here’s a summary of what we found:

Unit 1:
Sunday through Tuesday – Unit ran 24 hrs each day
Wednesday – Saturday – 5:00 am – 11:00 pm

Unit 2:
Monday – Midnight to 7:30 pm
Tuesday – Friday – 4:30 am – 7:30 pm
Sat – on demand
Sun – 24 hrs midnight to midnight

Unit 3:
Monday – Midnight to 10:00 pm
Tuesday – Friday – Starts ranged from 3:00 am to 5:00 am with stops at 10:00 pm
Saturday – 6:00 am – 7:00 pm
Sunday – 24 hrs midnight to midnight

Unit 4:
Monday – Friday – 4:30 am – 6:30 pm
Saturday – Sunday – 3:00 am – 5:00 am and then on demand

To summarize that list, there were several units running 24 hrs per day for several days, several units with startup and shutdown times well before and after the building was occupied, and unexpected weekend runtime.

Keep in mind that this was a professional building that had some empty suites and the rest were 9-5 offices and a doctor’s office.  There was rarely any activity outside of normal business hours.

The byzantine BAS interface

This particular vintage of Trane Tracker BAS had a serial interface to the system.  The HVAC technician to had to “jack” into it with his laptop computer and was presented with a command line interface.  The building is divided into zones and groups and any particular suite would belong to both a zone and a group.

The HVAC service company for the building had only been in charge for about a year and was never asked to fully commission the building.  They had only been at the building a few times and never to fully explore the current BAS programming.  This particular BAS was old enough that their experience with it was out of date.

Everything is not as it seems

The technician discovered that there were several zones assigned to multiple groups, almost certainly caused by tenants moving in and out followed by layer upon layer of changes being made to the system.  Some of those groups had the obsolete schedules and somewhere along the line a programmer didn’t reconcile what was going on with all the zones and all the groups.  Who knows, perhaps someone did notice something amiss, but left it alone assuming the last person knew what they were doing and the problems kept stacking on.

Once we found this nest of issues we were sure that the problem would be fixed.  In the command line interface, the technician changed the schedules from things like 03:00 to –:– which was his latest understanding of how to zero out a schedule entry.

With much tedium through this interface, day by day, zone by zone, group by group, the technician dutifully found and “zeroed” out all the offending schedules by putting in –:–.  We wrapped up quite sure all was going to be well again.  It turned out it wasn’t.  Virtjoule was still detecting bad schedules, but this time it was a different set of bad schedules and all four units had the same bad schedule.  That was a disappointment, but also a clue.

The technician returned a few days later after conferring with a colleague who used to work at Trane and was an expert in these systems.  It was suggested that putting –:– to zero out a schedule entry left the Trane Tracker system assuming that it should continue whatever the last state was.  If the last state was that the building was occupied then it would go through the next schedule with the same state.  The new schedules were leaving the building in an “occupied” state at the wrong times.

The fix

Since it was not possible to tell this version of the Trane Tracker that a specific day was unoccupied, the technician had to set up very short run times on Saturday and Sunday such that the units would come on, but they would not stay on for very long.  Correcting all of the weekday schedules and double checking that the same zone did not belong to multiple groups cleaned up the other issues.  It became obvious that the new schedules were in place and correct.

Wrap up

Without the Virtjoule monitoring system, the schedule flaws programmed into this BAS would have gone unnoticed for years.  No one really knows how long it had been like that.  Left unchecked this could take years off the life of the equipment not to mention the extra utility expenses most often passed on to the tenants.

Even after a trained technician made changes, things were still not right.  Without the monitoring capability to actually know the machine was running, there would have been little resolve or patience to notice that the service call didn’t actually fix the problem.  Virtjoule not only found the problem, but it was able to verify that the problem hadn’t been fixed initially and was fixed on the second trip.

[Randy Cox - CEO and co-founder of Virtjoule - He is the software designer and analytics engineering for Virtjoule Sense sensors. He studied Chemical Engineering and Petroleum Refining at the Colorado School of Mines. You may contact Randy at: randy at virtjoule dot com]


Is your package unit or split system cycling too much?  How do you know?  The correct answer is that it depends on the unit and the manufacturer.  However, common sense can play a huge role in figuring out if your machines are excessively cycling.  Finding out how often your machine is cycling and how long the cycle times are can tell you a lot about how healthy your machine is or whether you need to change your control regime. 

In this article we’ll look at a case study of a 90 ton chiller from Carrier and how we helped a customer cut over 14,000 cycles per year in normal operation even when the chiller was operated on a building automation system (BAS) with a dedicated maintenance staff.

Key concepts: Excessive cycling and compressor short cycling can be controlled.  Avoid excessive wear and tear on HVAC equipment.  Stop excessive HVAC energy consumption and expense.

Let’s set the scene.  This 90 ton Carrier chiller has normal operating hours of 6 am to 6 pm.  We could tell that its start up and shut down times were programmed correctly because it’s obvious from the Virtjoule beat chart below that the unit is running all the time between those hours.  The building was not occupied outside of 6 am to 6 pm and the owners of the building did not expect to see any unit operations in the off hours.  However, you can see from the graph below that even though there was a noticeable shutdown, the unit continued to cycle on and off throughout the night and early morning hours.

The extra cycles were typically 3-4 minutes in duration and numbered 40 or more per day and many more than that on weekends adding up to over 14,000 cycles per year of extraneous cycling and run time.  That’s 14,000+ cycles and over 700 hours of extra run time not to mention that electric motors can take up to three times the amount of electricity to start them than it takes to run them.  At common electricity rates all of this could add up to around $5,000 per year not to mention the wear and tear on a very expensive asset.

Here’s a snapshot of the run time graph for a typical day with out-of-hours cycling.  You can see out-of-hours cycling through the early morning hours up to 6:00 am and then solid operation between the hours of 6 am and 6 pm.  Out-of-hours cycling begins again at 6 pm and continues through midnight on this chart.  The excessive cycling continues until 6 am the following day.

Excessive cycles

Excessive cycles and out of hours operation on a 90 ton Carrier chiller

The following graph is how the machine operated on Saturdays and Sundays.  Two out of the seven days of the week had close to 90 extraneous short cycles.

Extra cycles and runtime on weekends when there should be none

Extra cycles and runtime on weekends when there should be none

Keep in mind that this was the main cooling unit and was operated on a building automation system.   Soon after this run time behavior was noted the building engineers were able to make control adjustments that completely eliminated the extra cycles.  Now you can see a very clean start up and shutdown of this chiller each day.  No extra cycles.  No wasted energy.  No unnecessary wear and tear.

Control problem fixed for out-of-hours operations and excessive cycles

Control problem fixed for out-of-hours operations and excessive cycles

If you’ve operated BAS before you are probably aware of how much work it can be to extract and analyze the data points that are available.  We often hear that the BAS should catch these kinds of problems, but case after case has shown us that it isn’t happening.  BAS has proven many times that it’s better at control than monitoring.  Even when it’s used for monitoring it can cost hundreds of dollars per data point to extract and then someone has to interpret and monitor the results regularly.  Maintenance organizations often have more urgent needs to attend to in their building and this sort of problem doesn’t usually cause immediate comfort problems in the building.

The steady burning of electricity and asset wear should make for a foul smell of burning money to someone in the building and so this should be a comfort problem under someone’s seat eventually.  The top maintenance organizations that we see deal with the issues of comfort, maintenance, energy conservation, and cost every day in their operations.  They like things to run well and to cost the least amount possible.  Fortunately those things usually go hand in hand.  With Virtjoule, after a 1 hr installation and setup, a few days later we had enough information to show that a change was needed.  The owners of the building were able to get their maintenance organization to make the changes and make an immediate difference on the healthy operation of this unit.

[Randy Cox - CTO and VP of Software Engineering, Virtjoule - is the software designer and analytics engineering for Virtjoule Sense sensors.  You may contact Randy at:  randy at virtjoule dot com]

Virtjoule installation on Carrier 90 ton chiller

Virtjoule installation on Carrier 90 ton chiller