HVAC manufacturers keep making equipment smarter.

Contractor commissioning practices have not always kept up.

A new August 24 analysis in Contracting Business warns that inverter heat pumps are frequently being commissioned using procedures developed for traditional fixed-capacity equipment — and the result can be disappointing real-world performance. 

Inverters Behave Differently

A conventional single-stage system is relatively simple.

It turns on.

It runs at essentially full capacity.

It turns off.

An inverter system continuously adjusts compressor output and airflow according to load.

That makes the equipment more efficient — but also more sensitive to installation conditions.

Static Pressure Can Destroy the Efficiency Advantage

One of the biggest problems is duct resistance.

When external static pressure is too high, the blower has to work harder and the system can consume more electricity.

Contracting Business argues that every inverter installation should include documented measurements of return static, supply static and total external static pressure. 

Auxiliary Heat Can Cause Another Problem

Heat strips that stage too early can erase much of a heat pump's efficiency advantage.

Incorrect thermostat configuration, aggressive auxiliary-heat settings or a poorly calculated balance point can cause resistance heat to operate unnecessarily. 

The homeowner sees the utility bill.

The contractor gets the complaint.

Commissioning Cannot Be a Five-Minute Startup

The recommended process includes:

  • Static-pressure measurement
  • Airflow verification
  • Electrical testing under load
  • Auxiliary-heat configuration
  • Control verification
  • Observation of modulation

That requires time.

Which means contractors need to price commissioning into the installation.

The bigger message is important.

High-efficiency equipment does not automatically create a high-efficiency installation.

As inverter technology becomes mainstream, the contractor who can prove performance may have a much bigger advantage than the contractor simply offering the highest-rated box.