buildings Article Improving Building Energy Performance Using Dual VAV Configuration Integrated with Dedicated Outdoor Air System Nabil Nassif * and Iffat Ridwana   Citation: Nassif, N.; Ridwana, I. Improving Building Energy Performance Using Dual VAV Configuration Integrated with Dedicated Outdoor Air System. Buildings 2021, 11, 466. https:// doi.org/10.3390/buildings11100466 Academic Editor: Fabrizio Ascione Received: 31 August 2021 Accepted: 4 October 2021 Published: 12 October 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Department of Civil and Architectural Engineering and Construction Management, University of Cincinnati, Cincinnati, OH 45221, USA; ridwanit@mail.uc.edu * Correspondence: nassifnl@ucmail.uc.edu Abstract: As building systems account for almost half of the total energy consumed by the building sector to provide space heating, cooling, and ventilation, efficiently designing these systems can be the key to energy conservation in buildings. Dual VAV systems with an effective control strategy can substantially reduce the energy consumption in buildings, providing a significant scope of further research on this system configuration. This paper proposes to utilize the warm air duct of the dual VAV system as a dedicated outdoor air (DOA) unit when no heating is required, which allows the cooling load to be effectively distributed between two ducts. A specific control sequence is proposed with different supply air temperature reset strategies to estimate the heating, cooling loads, and fan power energy consumption of the proposed system. A simple two-zone office building is taken as a preliminary case study to simulate the airflow rates and fan power of a single duct VAV and proposed dual VAV systems to illustrate the concept. Finally, a larger multi-zone office building is simulated to measure the annual heating, cooling loads, and fan power energy and compare the energy savings among the systems. The results show significant fan power reduction ranging from 1.7 to 9% and notable heating energy reduction up to 76.5% with a small amount of cooling load reduction varying from 0.76 to 2.56% depending on the different locations for the proposed dual VAV systems. Further energy savings from different supply air temperature reset strategies demonstrate the opportunity of employing them according to climates and case studies. The proposed dual VAV system proves to have the potential to be adapted in buildings for the purpose of sustainability and energy savings. Keywords: building energy efficiency; dual VAV system; dedicated outdoor air; optimization; HVAC system control; building energy performance 1. Introduction Buildings in the residential and commercial sectors have accounted for 40% of the total energy consumption in the USA in 2020 [1]. According to the building energy data book of the US Department of Energy, about 50% of the energy consumed by the building sector is directly associated with space heating, cooling, and ventilation [2]. As such, it is crucial to design these systems in a safe and efficient manner while minimizing energy consumption. In the last decade, a significant amount of research has been carried out to achieve better performance and improve the efficiency of such systems [3]. Previously, heating, ventilation, and air conditioning (HVAC) systems were designed to control the temperature with constant air volume (CAV) which did not satisfy the requirements of every zone in a building. Variable air volume (VAV) was later introduced to the systems as a novel solution to control the temperatures in multiple zones [3]. Consequently, Variable air volume (VAV) air conditioning systems have proven to be more economical than other alternatives due to their ability to adjust in response to load variations. Thus, they are being widely adopted in buildings in the USA [4]. As a result, any modification in the design and operation of the VAV systems to reduce building energy consumption will contribute largely to total energy savings in the building sector. Buildings 2021, 11, 466. https://doi.org/10.3390/buildings11100466 https://www.mdpi.com/journal/buildings