Control Strategies in Multi-Zone Air Conditioning Systems
3. Control Strategies in VAV Systems
- Occupied zone set-point temperatures and night set back
- VAV box minimum flow (typically 30%)
- Optimum start
- Supply air temperature reset
- Economiser and minimum outdoor air intake
3.1. Duct Static Pressure-Based Control Strategies
- The air flow at the dampers has not changed and the set point is kept—No action required.
- The total air flow increases but the current pressure setpoint is still enough—No action required
- A wide-open damper triggers a request for air from the beginning. The total flow rate is fixed by increasing the pressure set point until the request is fulfilled.
- A partially open damper turns into a wide-open damper and then send a request for air. The total flow rate is fixed by increasing the pressure set point until the request is fulfilled.
3.2. CO2-Based Control Strategies
- Increase the air flow rate of a terminal unit in the critical zone—do not increase the outdoor air flow rate.
- If ventilation CO2 concentration is low, use recirculated air —do not increase the outdoor air flow rate.
- If above actions are not possible, increase the outdoor air flow rate.
3.3. Fault Tolerant Control Strategies
3.4. Room Pressure-Based Control Strategies
- Climate controls:
- First climate controller: controls each zone’s input throttle flaps opening cross section to ensure the desired zone climate.
- Second climate controller: adjust the input fan requirements to ensure enough pressure is available to provide the necessary airflow in all zones.
- Pressure controls:
- First a fine differential pressure sensor (with pressure piping to indoor & outdoor) and controller: controls each zone’s exhaust throttle flaps opening cross section to ensure the desired zone pressure.
- Second pressure controller: adjust the exhaust fan power required to maintain the desired pressure in all the zones.
- Third pressure controller: controls each zone’s input throttle flaps opening cross section to ensure the desired zone pressure.
- Fourth pressure controller: controls the inlet AHU fan power in case that the exhaust fan power is not enough to maintain the zone pressure and climate levels in all the zones.
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|VAV Box||Koulani et al. ||2014||Denmark||Static Pressure Reset (SPR)||Simulation Experiment||Energy consumption reduced by 14% compared to CSP.|
Control is integrated with BMS.
No IAQ parameters involved in the control strategy.
|Walaszczyk and Cichón ||2017||Poland||Static Pressure Reset (SPR)||Simulation||Trim & Respond method has a better performance than the PID control|
No IAQ parameters involved in the control strategy.
|Rahnama et al. ||2017||Denmark||Static Pressure Reset (SPR)||Simulation/Experiment||Control based on duct pressure instead of damper opening.|
No IAQ parameters involved in the control strategy but planned for future work.
Energy consumption reduced in at least 21%.
|Lin and Lau ||2014||USA||CO2 reset||Simulation||CO2 levels involved in the control strategy for the outdoor air flow.|
Still requires design parameters for defining occupancy levels.
Reduction of outdoor air flow of 14.6%.
Monetary savings are estimated between 0.3% and 11%.
|Liu and Lau ||2015||USA||CO2 reset||Simulation||CO2 levels involved in the control strategy for the outdoor air flow and the zone airflow supply.|
System efficiency involved in the control strategy.
Reduction of outdoor airflow of approximately 45%.
Monetary savings are estimated between 25% and 45% approximately.
|Kim et al. ||2017||Korea||CO2 reset||Simulation||Control both recirculation air flow and outdoor airflow depending on zone CO2 level.|
Thermal comfort and IAQ levels achieved.
Energy consumption reduction of 20% compared to fixed air flow systems.
|Motor Flaps||Robert Bosch GMBH ||2015||Germany||Zone pressure-based||Patent||Zone pressure and climate parameters (i.e., Temperature and CO2) controls supply and exhaust fans and flaps.|
An overpressure or under pressure could be set for each zone.
|Zucker et al. ||2017||Austria||CO2 and Static Pressure reset based||Simulation||A pressure model is used to estimate the supply airflow of each zone and adjust the fan power.|
A CO2 model is used to estimate zone requirement of air flow.
Models developed are too complicated and different for each scenario so that this solution is not practical.
Investment cost savings are estimated in 55%.
Improvement in the energy efficiency of 5%.
|Jing et al. ||2019||China & Singapore||Improved SPR||Experimental||A model-based, improved SPR strategy is used to well-balance the ventilation system.|
A damper position control method and an optimal static pressure set-point selection method guarantee the system is energy efficient and, at the same time, the required airflows are achieved.
This strategy achieves energy savings of 21% relative to traditional SPR.
This methodology is complex so that for large-scale, ducted networks, the model of the systems needs to be simplified.
|Smart VAV-T with motor Flaps||Saxby and Tuck ||2016||UK||Gas Law algorithm||Patent Pending||System & Controls solution; based on gas law equations with kinetic energy transfer.|
SMART system with IoT and real-time monitoring, analysis, control, reaction, reporting, and alarming. The Atomic Air algorithm calculates in real-time the required energy demand, fresh/re-circ air mixing, supply-return fan (independently in 1% increments) based on (individual) in zone molecular expansion ratios, heat loads and air quality. Resulting in near zero stratification (via stochastic molecular motion).
Investment cost savings are typically 30–60%
Improvement in energy savings 40–70%
Controlling the CO2 level 100%
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Rismanchi, B.; Zambrano, J.M.; Saxby, B.; Tuck, R.; Stenning, M. Control Strategies in Multi-Zone Air Conditioning Systems. Energies 2019, 12, 347. https://doi.org/10.3390/en12030347
Rismanchi B, Zambrano JM, Saxby B, Tuck R, Stenning M. Control Strategies in Multi-Zone Air Conditioning Systems. Energies. 2019; 12(3):347. https://doi.org/10.3390/en12030347Chicago/Turabian Style
Rismanchi, Behzad, Juan Mahecha Zambrano, Bryan Saxby, Ross Tuck, and Mark Stenning. 2019. "Control Strategies in Multi-Zone Air Conditioning Systems" Energies 12, no. 3: 347. https://doi.org/10.3390/en12030347