Development and Evaluation of a Multi-Zone VAV HVAC System with Demand-Controlled Ventilation for Energy-Efficient Homes

This study develops and evaluates a multi-zone Variable Air Volume (VAV) HVAC system with demand-controlled ventilation (DCV) for efficient climate control in residential buildings. Traditional systems often fail to maintain optimal conditions in highly insulated homes. The novel system uses heat valves, VAV dampers, and sensors to adjust airflow and temperature based on each room's specific needs. In laboratory tests, the system-maintained temperature set points with minimal deviation (±0.3°C), adapted to heating demand changes, and reduced energy consumption by up to 30% compared to conventional systems. Future research will focus on field testing and humidity control integration.

Keywords: Variable Air Volume (VAV) system; Demand-controlled ventilation (DCV); HVAC system; Energy efficiency; Residential buildings; Climate control; Multi-zone

HVAC systems are essential for maintaining indoor climate control and ensuring thermal comfort and air quality across residential, commercial, and industrial buildings. These systems have evolved to meet the increasing energy-efficiency demands driven by stricter building codes and sustainability goals. In well-insulated residential buildings, where energy requirements for heating and cooling are minimized, traditional HVAC systems often struggle to provide optimal climate control across all rooms, leading to inefficiencies and discomfort (Georges et al., 2014; Berge & Mathisen, 2015).

HVAC systems are generally classified into all-air, all-water, and air-water categories. All-air systems, commonly used in residential buildings, offer a cost-effective solution for low thermal demand settings by providing heating and cooling via conditioned air. However, systems using Constant Air Volume (CAV) often rely on a single temperature reference zone, resulting in unsatisfactory climate control in other rooms like bedrooms and kitchens with differing thermal preferences (Seyam, 2018; Berge et al., 2016).

The demand for independent temperature control across different zones in homes has risen with the development of high-performance, insulated buildings. Traditional CAV systems are inadequate for such zoning because they cannot independently adjust airflow and temperature for each room, leading to inefficient energy use (Berge et al., 2017). Variable Air Volume (VAV) systems, which allow individual control of airflow and temperature in each room, provide a more energy-efficient alternative for residential HVAC systems. VAV systems adjust airflow according to the heating or cooling needs of specific zones, offering flexibility and improved energy efficiency (Rismanchi et al., 2019). Although traditionally used in commercial buildings, VAV systems are becoming more feasible in residential applications due to advances in affordable control technology like Internet of Things (IoT) devices (Lee et al., 2020).

A key innovation in residential HVAC systems has been the integration of demand-controlled ventilation (DCV) with VAV strategies. These systems use sensors to monitor occupancy and environmental conditions such as temperature and CO₂ levels, adjusting heating or cooling accordingly. This approach improves energy efficiency while maintaining comfort, making it ideal for residential buildings with low heating or cooling loads (Anand et al., 2019; Vindel et al., 2021).

A limitation of earlier VAV systems is their focus on single-zone control without addressing the need for room-specific temperature regulation. Polak et al. (2020) addressed this gap by introducing the Heat Valve Ventilation (HVV) system, which controls room-level temperature without energy-intensive local reheating. The HVV system adjusts both airflow and temperature based on the specific heating or cooling demand in each room, ensuring comfort while minimizing energy use.

The present study develops control logic for a novel multi-zone VAV HVAC system for residential buildings. The system integrates DCV and room-based temperature and airflow regulation, ensuring efficient operation and individualized comfort across all zones.

Study Objectives:

1.    Develop control logic for room-based temperature and airflow regulation in a multi-zone VAV system.

2.    Evaluate the system’s performance in maintaining thermal comfort and air quality in a laboratory environment.

3.    Assess the energy-saving potential of the proposed system compared to conventional HVAC systems.

The following sections describe the methodology used for testing the control logic, present the experimental results, and discuss the system's performance in terms of comfort and energy efficiency.

Methodology

This study focuses on developing, implementing, and evaluating a novel multi-zone VAV HVAC system with demand-controlled ventilation (DCV) to provide independent room-level climate control in residential buildings. The following summarizes the system design, experimental setup, and evaluation framework.

System Design

The system is based on the Heat Valve Ventilation (HVV) system developed by Polak et al. (2020), integrating heating and ventilation through an air-handling unit (AHU). It uses heat valves (HVs) to regulate air temperature and VAV dampers to control airflow to individual rooms, improving energy efficiency by eliminating the need for local reheat coils.

Key components include:

·         AHU: Supplies conditioned air for heating and ventilation.

·         Heat Valves (HVs): Adjust the air temperature by controlling the bypass around the heating coil.

·         VAV Dampers: Control airflow to rooms based on real-time heating or cooling needs.

·         Temperature and CO₂ Sensors: Monitor and adjust air quality and temperature in real-time (Anand et al., 2019).

The system uses a DCV algorithm to adjust airflow and temperature based on room occupancy and thermal needs, prioritizing energy efficiency while maintaining thermal comfort (Rismanchi et al., 2019).

Laboratory Setup

A full-scale prototype was tested in a controlled laboratory simulating six residential zones: two bedrooms, an office, a living room, a kitchen, and a large bedroom. Heating loads varied, with the largest load of 505 W in the living room and the smallest at 187 W in Bedroom 1. The setup included independent cooling loads and simulated real-life occupancy and humidity conditions to test the system's response (Polak et al., 2020; Executive Order on Building Regulations, 2018), see Figure 1.

Control Logic Development

The system's control logic focused on energy efficiency while maintaining room-specific set-points and air quality. Key features include:

1.    Temperature Control: HVs adjust air temperature, and if necessary, VAV dampers increase airflow (Rismanchi et al., 2019).

2.    Airflow Control: VAV dampers respond to temperature or CO₂ concentration exceeding set thresholds (Anand et al., 2019).

3.    Critical Zone Reset: Fan speed is adjusted based on the most demanding zone to reduce energy use (Rahnama et al., 2017).

4.    Humidity Control: While not tested, provisions are included for high-humidity zones like bathrooms (Berge et al., 2017).

Data Collection and Performance Metrics

The system's performance was measured using several key metrics:

·         Temperature Stability: Sensors tracked how well-set points (±0.3°C) were maintained.

·         Airflow Rates: The airflow in each zone was monitored to ensure indoor air quality per Danish regulations (Executive Order on Building Regulations, 2018).

·         Energy Consumption: Recorded to compare the novel VAV system’s efficiency against traditional CAV systems (Berge & Mathisen, 2015).

·         System Stability: Monitored to ensure no overshoot or instability in temperature or airflow (Rahnama et al., 2017).

Experimental Procedure

The 36-hour experiment tested the system's response to varying temperature set points and heating demands across the six zones. Adjustments in set points were made to simulate real-world changes, such as increasing the living room set point from 21°C to 24°C during the experiment. Data were collected regularly to evaluate the system's ability to maintain comfort, efficiency, and air quality (Polak et al., 2020).

Figure 1. Novel-designed air heating and ventilation system, so-called HVV system: Overall design (left) and the manifold side view (right).

Results and Discussion

The system successfully maintained temperature set points across all six zones, with minimal deviations (±0.3°C). For example, Bedroom 1 remained between 20.8°C and 21.2°C with a set-point of 21°C, while the living room (46 m²) maintained a 24°C set-point with a deviation of 0.2°C (Polak et al., 2020). The system adapted well to heating demand fluctuations, adjusting airflow and temperature dynamically. In high-demand zones like the kitchen and living room, it managed significant temperature variations caused by activities such as cooking. The dual strategy of adjusting both airflow and temperature helped maintain comfort without excessive energy use.

When set points were adjusted mid-experiment, such as raising the living room from 21°C to 24°C and lowering the kitchen from 23°C to 21°C, the system responded quickly and accurately. The living room reached its new set point within 15 minutes without overshoot, while the kitchen stabilized within 10 minutes (Rismanchi et al., 2019). This fast and stable response highlights the system's ability to adapt to frequent changes in set points, a common issue in conventional CAV systems.

Airflow rates were dynamically adjusted based on occupancy and heating demands, keeping airflow as low as possible while meeting ventilation requirements per Danish building codes (BR18). For example, Bedroom 1 maintained the minimum airflow rate of 4.5 ℓ/s, while the living room fluctuated between 12.4 ℓ/s and 18.6 ℓ/s depending on the heating load. The system’s prioritization of temperature control over unnecessary airflow adjustments reduced energy consumption and prevented discomfort from excessive airflow (Berge & Mathisen, 2015).

The VAV system demonstrated significant energy savings, reducing fan energy use by up to 30% compared to conventional CAV systems. By modulating fan speed based on demand and adjusting airflow only, when necessary, the system operated at reduced speeds during low-demand periods, further lowering energy consumption (Anand et al., 2019; Polak et al., 2020).

The system maintained stable temperature and airflow, responding smoothly to fluctuations in heating demand and set-point changes without overshooting or instability. It managed simultaneous temperature adjustments across multiple zones, a significant improvement over conventional systems that struggle with complex multi-zone environments (Polak et al., 2020).

However, the controlled lab setting limits real-world applicability. Future research should focus on field testing in occupied homes to assess performance under varying occupancy and daily activities. Additionally, the system's humidity control, untested in the lab, should be evaluated in real environments, particularly in high-humidity zones like kitchens and bathrooms, see Figure 2.

Figure 2. HVV prototype — Supply zones temperature together with the temperature set-point, the minimum, and the maximum temperature limits.

Conclusion

The experimental results confirm the effectiveness of the novel VAV HVAC system in maintaining individualized thermal comfort, improving indoor air quality, and reducing energy consumption in residential buildings. The system’s ability to regulate both temperature and airflow at the room level, combined with its demand-controlled ventilation strategy, ensures that energy use is minimized without sacrificing comfort. While further field testing is needed, the findings from this study suggest that the system offers a promising solution for modern, energy-efficient residential buildings.

For detailed information:https://www.sciencedirect.com/science/article/pii/S2352710222017727?via%3Dihub

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