Overheating Chaos: The Deadly Sin of Gluttony

The Sweltering Summer Mystery

In August 2017, apartment residents faced a heatwave inside and out. Their heating and cooling system, a high-tech Ground Source Heat Pump (GSHP) system, was supposed to keep them comfortable. But it was struggling. The reason? The fluid temperature in the system had climbed to an unbearable 125°F—far beyond what the heat pumps could handle.

This wasn’t a sudden failure. It was years in the making, caused by one critical sin: gluttony. Let’s uncover how overloading the system led to its downfall—and the lessons learned to avoid it happening again.

The Problem: A System Overloaded

The GSHP system was designed to heat and cool the apartments, while domestic hot water (DHW) and fresh air were heated using natural gas boilers. Here were the main issues with the system:

1. Heating and Cooling Loads:
   • The building needed 300 tons of peak heating and cooling capacity.
   • 900 tons of heat pump capacity was installed —three times what was required.
2. Pump Mismanagement:
   • A 100-hp circulation pump ran constantly, circulating fluid through the heat pumps at 2,700 gallons per minute (gpm)—three times the flow needed on the hottest day of summer.
   • A 50-hp circulation pump did the same for the underground ground heat exchanger (GHX). Friction of the fluid circulating through both the building and the GHX added heat to the earth around the GHX piping.
3. Energy Imbalance:
   • The efficient building envelope required more cooling than heating, adding more heat to the GHX. Electricity powering the heat pump compressors added even more heat to the GHX, creating a large energy imbalance.
   • The GHX was buried in shale. Groundwater does not flow through shale, and heat rejected to the shale builds up over time, causing the GHX to overheat.
      

By the summer of 2017, the temperature of the GHX increased to 125°F, beyond where the heat pumps could operate. The system couldn’t cool the building. Residents suffered, and the once-promising system was on the brink of collapse.

The Fix: Restoring Balance

To save the system, engineers had to address years of mismanagement. Here’s how they brought the GSHP back from the brink:

1. Right-Sizing the Pumps:
   • The 100-hp building side pump was replaced with a smaller, more efficient 10–15 hp pump. A variable speed pump control reduced flow rates to match the actual heating and cooling loads of the building, reducing electricity use and friction through the piping system. Motorized valves were installed on the heat pumps to stop circulation through them when they weren’t operating. 
   • A variable speed drive was added to the GHX pump to further reduce electricity consumption and friction through the GHX.
2. Balancing Energy Loads:
   • Heat pumps were added to pre-heat domestic hot water to divert heat from the GHX.
   • Heat pumps were installed to preheat fresh air for the building, further reducing the amount of heat injected into the ground. 
3. Monitoring for the Future:
   • A monitoring system was installed to track GHX temperatures and predict future issues before they could cause major problems.
      

The Lesson: Balance Is Key

This case is a textbook example of the sin of gluttony in system design and operation. Oversizing equipment and ignoring energy imbalances led to inefficiency, rising costs, and eventual failure. The fix? Designing systems to match actual needs, using smart controls, and continuously monitoring performance.

Don’t let gluttony ruin your GSHP system. Balance is the key to efficiency, longevity, and comfort. Learn from this story—and stay tuned for more tales of the “Seven Deadly Sins: Lessons from the Field” series, where we’ll explore how other sins, like pride and sloth, can wreak havoc on system performance.