Sheet metal & Air Conditioning Contractors’ National Association

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Improper installation leads to poor HVAC performance, wasted energy, says study

Faulty installation of an HVAC system can result in a 30 percent increase in electricity consumption, according to a recent research study by the National Institute of Standards and Technology (NIST).

The NIST study, “Sensitivity Analysis of Installation Faults on Heat Pump Performance,” found that duct leakage, refrigerant undercharge, oversized heat pump with nominal ductwork, low indoor airflow due to undersized ductwork, and refrigerant overcharge have the most potential for causing significant performance problems and increased annual energy consumption.

A significant increase in annual energy use can be caused by lowering the thermostat in the cooling mode to improve indoor comfort in cases of excessive indoor humidity levels due to installation faults.

Extensive simulations of house/heat pump systems in five climate zones led to these conclusions:

  • Effect of different installation faults on annual energy use is similar for a slab-on-grade house (ducts located in the unconditioned attic) and a basement house (ducts located in the semi-conditioned basement), except the duct leakage fault.
  • Effect of installation faults is similar in different climates except for:
    • Duct leakage: significant increase in the indoor RH for an installation in a hot and humid climate
    • Heat pump oversizing with undersized air ducts: in heating-dominated climates, heat pump oversizing reduces the use of backup heat, which compensates for the increased indoor fan energy use associated with overcoming the higher external static pressure.
  • Undersized cooling mode TXV: little effect in heating-dominated climates, while a significant increase of energy use is possible in cooling-dominated climates.

 This free study can be downloaded on the publications portal of the NIST website.