Comprehensive Study Sheds Light On The Efficiency Impacts of HVAC System Faults

The results of an extensive three-year study undertaken by the National Institute of Standards and Technology (NIST) have just been released in a report titled "Sensitivity Analysis of Installation Faults on Heat Pump Performance."  NIST is a division of the U.S. Department of Commerce.  The goal of the study was to assess the impacts that HVAC system installation faults had on equipment electricity consumption.

A full copy of the NIST report  can be downloaded by clicking here

The report's Abstract is located below.


"Sensitivity Analysis of Installation Faults on Heat Pump Performance"
by Piotr A. Domanski, Hugh I. Henderson, W. Vance Payne

Numerous studies and surveys indicate that typically-installed HVAC equipment operate inefficiently and waste considerable energy due to different installation errors (faults) such as improper refrigerant charge, incorrect airflow, oversized equipment, leaky ducts. This study seeks to develop an understanding of the impact of different faults on heat pump performance installed in a single-family residential house. It combines building effects, equipment effects, and climate effects in a comprehensive evaluation of the impact of installation faults on a heat pump’s seasonal energy consumption through simulations of the house/heat pump system.

The study 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 degradation and increased annual energy consumption. The effect of simultaneous faults was found to be additive (e.g., duct leakage and non-condensable gases), little changed relative to the single fault condition (e.g., low indoor airflow and refrigerant undercharge), or well-beyond additive (duct leakage and refrigerant undercharge). 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 ndoor humidity levels due to installation faults.

The goal of this study was to assess the impacts that HVAC system installation faults had on equipment electricity consumption. The effect of the installation faults on occupant comfort was not the main focus of the study, and this research did not seek to quantify any impacts on indoor air quality or noise generation (e.g., airflow noise from air moving through restricted ducts). Additionally, the study does not address the effects that installation faults have on equipment reliability/robustness (number of starts/stops, etc.), maintainability (e.g., access issues), or costs of initial installation and ongoing maintenance.
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