RDH Building Science

Heating, ventilating and air-conditioning (HVAC) typically accounts for 30% to 50% of commercial building energy use. Small commercial buildings often use oversized and inefficient rooftop air handling units (RTUs) to provide both air conditioning and ventilation. A conversion strategy to reduce energy consumption is the installation of a very high efficiency dedicated outdoor air system (DOAS) to provide ventilation with a separate heat pump system to provide heating and cooling. Decoupling the heating and cooling from ventilation allows for improved energy efficiency and control of space conditions. Upgrades to mechanical systems can also improve the indoor air quality (IAQ) and comfort through control of carbon dioxide (CO2) concentrations, dry bulb temperature, and relative humidity (RH).

A pilot study of eight buildings was conducted to investigate the potential benefits of replacing existing RTUs with high efficiency heat recovery ventilators (HRVs) and air source heat pumps in the Pacific Northwest. This report contains results for a subset of seven buildings for which data is available. The building energy use before and after the conversion was determined using utility data, energy modeling and monitoring. Indoor environmental conditions were measured at hourly intervals for up to one year postconversion using CO2, temperature, and RH sensors. The data was analyzed to determine changes in energy use and IAQ before and after the conversion.

This paper presents the pilot building results pre- and post-conversion. While several factors need to be in place to ensure optimal performance and cost effectiveness, the pilot shows that replacing RTUs with DOAS systems in existing commercial buildings can both reduce energy use as well as improve indoor environmental conditions. This conversion type is viable for a wide variety of building types and scale-up of the retrofits has the potential to significantly improve a previously underserved segment of the building stock.

Presented at the 15th Canadian Conference on Building Science and Technology.

View slides here.

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