Overnight Demand Spikes: What Actually Causes Them

This is Charles, also known as Chuck, Tralka. I’m an electrical engineer and the founder of ZeroQuest, where I focus on energy optimization for grocery stores and cold storage facilities. 

In the previous video, we looked at how demand charges work and why refrigerated facilities are especially vulnerable to them. We saw that a single 15-minute spike—often occurring overnight—can quietly set the demand charge for an entire month. 

In this video, I want to answer the next obvious question: what actually causes those overnight spikes? 

When operators see a demand peak at two or three in the morning, the first instinct is often to assume something is broken. A failed component, a fault, or some unusual one-time event.  But in most grocery stores and cold storage facilities, that’s not the case. 

In reality, these demand spikes are usually caused by normal equipment doing normal things, just not in a coordinated way. 

Let’s start with the biggest contributor: defrost cycles. 

Refrigeration systems need to periodically defrost evaporator coils to maintain efficiency and airflow. That typically involves electric heaters, which are very power-intensive. In many facilities, defrost schedules were set years ago—often during commissioning—and never revisited. 

Over time, equipment gets added, operating hours change, and loads increase. But the defrost schedules stay the same.  If multiple refrigeration systems defrost at the same time, even briefly, the result can be a large, sudden increase in electrical demand. 

Next, consider compressor staging and sequencing. 

Compressors don’t run continuously at full output. They stage on and off in response to temperature and pressure. Under certain conditions—such as recovery after defrost or a load shift—multiple compressors can start within the same 15-minute window. 

Each individual start may be reasonable. But when several occur together, demand spikes sharply.  A similar effect happens with condenser fan ramp-ups. 

As head pressure control responds to ambient conditions or load changes, fans may ramp up simultaneously. Again, nothing is malfunctioning. The system is behaving as designed. But the timing matters. 

Now layer in operational contributors. 

Most facilities have multiple systems operating independently: refrigeration, HVAC, lighting, and sometimes process or kitchen loads. 

There is often no coordination between these systems from a demand standpoint. Each system is optimized locally, not globally. 

So while refrigeration is defrosting and compressors are staging, HVAC units may also be cycling, or lighting blocks may still be on overnight schedules that no longer reflect actual occupancy. 

Another key issue is lack of visibility.  Most operators never see 15-minute demand data. Utility bills summarize the outcome, not the event. There’s no timestamp, no equipment context, and no clear explanation of what caused the peak. 

Without interval data, these spikes remain invisible. 

From an operational perspective, everything appears normal. The facility is quiet. No alarms are triggered. Nothing feels wrong. 

But electrically, that short window becomes the most expensive moment of the entire month.  This is why demand charges are so difficult to manage in refrigerated facilities. 

They’re not driven by average behavior. They’re driven by short-duration overlaps—often overnight—between systems that were never designed to work together from a demand standpoint. 

The important takeaway is this: most overnight demand spikes are operational in nature, not equipment failures. 

And that distinction matters because operational issues can often be addressed without major capital upgrades—once you know where to look and what to measure. 

In the next video, I’ll talk about which of these demand-spike drivers can typically be mitigated through operational changes, controls adjustments, and better scheduling—and which ones truly require capital investment. 

This has been Charles Tralka, known to my friends as Chuck, for ZeroQuest Energy.