Virtjoule

From the Blog

Feb

Thermostat – Friend Or Foe?

Posted by randy at 4:48 pm

Summary

It’s hard to imagine where control of our indoor environments would be without the lowly thermostat. Programmable thermostats have been a mainstay of both commercial and residential heating and cooling. But like the VCR “Blinking Twelve Problem”, the proliferation of thermostat interfaces has caused many to be completely misunderstood. Property owners and tenants ignore the thermostat to their own detriment.

This article discusses a client who was heating and cooling 24/7 on two of their Carrier HVAC units for a retail store in a small strip mall. The cause was mis-programmed Carrier Debonair thermostats. They had no idea. Without the HVAC monitoring capability of Virtjoule, this condition may have gone unnoticed for years.

Upon properly programming the thermostat, the units are now running just 12% of the time they were running before.

Carrier is a big and trusted name in HVAC, without a doubt. But that hasn’t solved the problem of complex programming interfaces for mere mortals. I have a 29+ year career working with computers and the interfaces on most thermostats can still be mind boggling. This store was using a Carrier Debonair thermostat. Within the Debonar lineup there are no less than 10 models to choose from. The model our client had was similar to this one:

Carrier Debonair thermostat

Since this client was very close to where I live, I took the opportunity to go check on it myself. First thing I did was to go on the Internet and find the owners manual for this model. I was able to find it here:

http://www.docs.hvacpartners.com/idc/groups/public/documents/techlit/33cs-7so.pdf

As is often the case, I was expecting that there would be some schedule problem or perhaps a misunderstanding about what happens when the fan mode is set to “On”. After all, we’ve seen that there is no predicting what the blower is actually doing when the heating and cooling mode is set to “Off” or even “Auto”. We’ve seen blowers continue to run when the thermostat mode is set to “Off” and it is thermostat dependent. Very counter intuitive, but who is going to go on the roof or hold a tissue in the air stream to notice if the blower is running after you shut down for the night?

What I found on this thermostat is that it has three different occupancy programming modes. The first and default mode, Occupancy 1, has the unique feature that the occupancy schedule can be overridden by a light sensor. That was a red flag to me as that means the thermostat was depending on yet another sensor which might or might not be working, rather than the building schedule that it also contains. It could also be getting confused by other inputs like street lights through windows and start times would change radically depending on what time of year it was. Why would you want that if the building hours are nearly identical throughout the year?

Without enough time or a good way to determine if the light sensor was working, it was clear to me that a retail establishment like this should not be depending on light to control its space.

Switching the thermostat to “Occupancy 2″ mode allowed it to be controlled by the occupancy schedule. On this thermostat each day has occupancy times and unoccupied times. Luckily there is a feature that allows you to copy one day to the next, but how you do that is completely inscrutable if all you had was your eyes on the thermostat. It took some careful reading of the owners manual to figure that out. By the way, where do you think the owners manual was on site? I don’t know either.

Besides the occupancy mode issue, both thermostats had their time and day set wrong. In the case of this seven day a week establishment, having the day set wrong was harmless. But here in February, both clocks were still set to daylight saving time.

Let’s take a look at the results. During this time the temperatures here in Colorado were temperate with daytime highs in the 40′s and 50′s and lows in the mid-20′s. The first image is a typical daily runtime graph of one of the units before the thermostat change. The blower was running 24/7 punctuated by cycles of heat. There was simply no schedule on this unit and it was always running.

Runtime before thermostat change

The “after” chart is one that is much easier on the eyes. You can see some periodic runtime during the night when the setback temperature of 58 was hit. But by late morning there was no runtime at all. So not only was the tenant saving night time and after hours runtime, the majority of their savings was actually achieved during business hours when outside air and activity in the building was working for them.

Runtime after thermostat change

Across the two units, I was able to compute that total runtime after the thermostat change was just 12% of what it was before. That’s what you call saving money. Without HVAC monitoring of these units, this money would have been wasted month after month.

[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]

Dec

Anatomy of a refrigeration condenser failure

Posted by randy at 10:53 am

Summary:

Refrigeration is a critical component of any restaurant for a variety of reasons, not the least is the health and safety of its customers. Keeping a close eye on how that refrigeration is working is key to avoiding health concerns and potentially the loss of all the contents of a walk-in cooler. In this article you will see how easy it is to notice that a walk-in refrigeration condenser unit is beginning to malfunction.

Key concepts:

Most any kind of fault will disrupt the observable common pattern of how the condenser unit operates.
Condenser faults may build up over time wasting energy and working equipment harder before a total failure occurs.
There can be adequate time to get a faulty unit fixed before it completely fails if the behavior change caused by the fault is detected.
Quick visual inspection of Virtjoule charts to compare patterns can easily identify changes in behavior that need to be investigated.

We recently notified a customer of a behavior change that we observed in the walk-in refrigerator for their restaurant. This is a critical unit for the restaurant as it’s the condensing unit for the only walk-in refrigerator that they have at this site. As you will see in this article, it’s not hard to figure out that something had radically changed in the operation of this unit despite the fact that the temperature in the cooler hadn’t risen. It was just a matter of time before this unit would have failed causing a big problem for the restaurant owner and the manager.

The walk-ins for this restaurant chain are made by Harford Duracool. Their labels don’t last in the sun and so I don’t have the exact model number for this condenser unit. The photo below is of the actual unit that failed.

Harford Duracool walk-in refrigerator condenser unit

What I want you to note in the following graphic is just how easy it is to determine that the unit has broken out of it normal pattern. This could be done visually or by using the Virtjoule cycle counter which would have shown a radical drop in the number of full cycles that occurred. The green and red highlights are mine.

You can see that just before 10:00 am on October 30, this unit stopped doing full cycles and ran continuously until about 4pm where it shut down for a few minutes and then started back up with an intense series of cycles only shutting down once every 5-6 hrs. Clearly this is much different than the cycles you see on the left hand side of the chart. The unit is working much more aggressively and constantly.

Harford Duracool Condenser breaking into failure pattern

The unit wasn’t fixed right away and luckily there was not a catastrophic failure that would have required moving or throwing away the food in the cooler. You can see this same failure pattern continued for quite some time.

Harford Duracool condenser in failure mode

Finally, about 9am on November 11th, the unit was shut down. It was thawed out, condenser cleaned, and then restarted just after 10:30 am. It ran continuously for a while in order to catch up on its cooling, but then settled back into its normal cycle rhythm about 6pm. It has been running normally ever since.

Harford Duracool condenser failure fix

In conclusion, you can see that it’s not at all difficult to notice that there was a problem developing and it was also quite easy to see when the problem was resolved. Virtjoule didn’t diagnose what the problem was, but it gave enough warning time for the unit to be looked at, fixed, and restarted before a catastrophic failure occurred. There was no other type of monitoring being done on this unit and it would have completely failed leaving the cooler to warm up at an inopportune time (night, food inspector dropping by, etc.). Compared to that inconvenience, a call to the Harford Duracool dealer and service was all it took to get things working well again.