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Boiler Operator's Handbook
Published in Carl Bozzuto, Boiler Operator's Handbook, 2021
A VAV box can be a simple device, consisting of nothing more than an enclosure with a damper controlled by a modulating motor to open or close the damper depending on the temperature in the space served by the air passing through the VAV box. One VAV box can serve several offices along one exposure of one floor of an office building. Because of multiple exposures (sunlight being the major load in most air conditioning systems), corner offices typically require an independent VAV box. That is not always the case. When the box serves all offices along one building wall and, the executive gets the corner office, the thermostat will be in the corner office. When space utilization, or heating or cooling load, varies, such as interior versus exterior exposures, office space versus conference room, or operating room in a hospital compared to a patient’s room, separate VAV boxes are normally provided. Changes in use of a space, installation of partitions, and the like can make space temperature control impossible. Thus, despite the advantages of VAV boxes, satisfying everyone is not always possible. The variable speed drive of the fan is controlled to maintain a constant pressure at one or more points in the distribution system. Cooling and fan motor horsepower are saved by these systems, while simultaneously providing more precise cooling and heating in the conditioned spaces.
Web Based Wireless Controls for Commercial Building Energy Management
Published in Barney L. Capehart, Timothy Middelkoop, Paul J. Allen, David C. Green, Handbook of Web Based Energy Information and Control Systems, 2020
VAV systems have variable-speed fans and terminal dampers that are controlled so that the amount of simultaneous heating and cooling or re-heating is significantly reduced. There are two common kinds of VAV systems: single-duct and dual-duct. Single-duct VAV systems supply cooled air to each zone terminal unit, where it is metered with a control damper when cooling is required or re-heated when heating is required. When heating, the amount of cooled air is reduced to a low level by the terminal controls, so there is much less wasted re-heat energy than a single-duct CAV system. Dual-duct systems deliver heated air and cooled air all the way to each zone terminal unit with separate air ducts. Dual-duct VAV terminal units have independent dampers that modulate the hot airflow rate to heat a zone and modulate the cold airflow rate to cool a zone. Unlike the dual-duct CAV system, the dual-duct VAV system does very little mixing. Most of the time it supplies a variable amount of hot air when heating and a variable amount of cooled air when cooling. It only mixes air when the zone load is small so that adequate ventilation air is provided.
Web Based Wireless Controls for Commercial Building Energy Management
Published in Barney L. Capehart, Lynne C. Capehart, Paul Allen, David Green, Web Based Enterprise Energy and Building Automation Systems, 2020
VAV systems have variable-speed fans and terminal dampers that are controlled so that the amount of simultaneous heating and cooling or re-heating is significantly reduced. There are two common kinds of VAV systems: single-duct and dual-duct. Single-duct VAV systems supply cooled air to each zone terminal unit, where it is metered with a control damper when cooling is required or re-heated when heating is required. When heating, the amount of cooled air is reduced to a low level by the terminal controls, so there is much less wasted re-heat energy than a single-duct CAV system. Dual-duct systems deliver heated air and cooled air all the way to each zone terminal unit with separate air ducts. Dual-duct VAV terminal units have independent dampers that modulate the hot airflow rate to heat a zone and modulate the cold airflow rate to cool a zone. Unlike the dual-duct CAV system, the dual-duct VAV system does very little mixing. Most of the time it supplies a variable amount of hot air when heating and a variable amount of cooled air when cooling. It only mixes air when the zone load is small so that adequate ventilation air is provided.
Demand response potential of district heating and ventilation in an educational office building
Published in Science and Technology for the Built Environment, 2020
Behrang Vand, Kristian Martin, Juha Jokisalo, Risto Kosonen, Aira Hast
Figure 8 shows the effect of demand-response control and ventilation airflow control mode (CAV/VAV), on the indoor air temperature of the coldest room (office room 8 shown in Figure 3) with 40% occupancy ratio. Results of the reference cases show that for more than 55% of the occupied hours (1560 h) the indoor air temperature with the VAV ventilation system is higher than the CAV one, and for the rest hours (1275 h) the differences between these systems are insignificant. The VAV ventilation system provides a wider range of the indoor air temperature than the CAV ventilation system and then requires lower fan speeds, because it uses less energy.
Co-simulation of fuzzy control in buildings and the HVAC system using BCVTB
Published in Advances in Building Energy Research, 2018
Christina Anastasiadi, Anastasios I. Dounis
This section discusses the HVAC system where each control strategy is applied. A Single Zone Variable Air Volume (VAV) system is chosen to condition the building. A VAV system maintains the zone’s desired conditions by varying the air flow supplied to the zone according to the control signal. However, the supplied air properties are kept constant. Towards the HVAC system design a rather simplified approach was followed. The VAV system modelled is a 100% fresh air plant which includes the sub-models of a heater and a cooler.
A multi-occupants’ comfort-driven and energy-efficient control strategy of VAV system based on learned thermal comfort profiles
Published in Science and Technology for the Built Environment, 2018
Yuli Xu, Sheng Chen, Muhammad Javed, Ning Li, Zhongxue Gan
There are two main energy sources for HVAC system operations (Pérez-Lombard et al. 2008), electricity and gas, and they are generally measured at the building level since precise measurement of energy for each zone demands submetering of electricity and gas. This is usually tough and expensive work. Variable air volume (VAV) systems work based on the principle of changing air volume to meet the heating/cooling load of each zone and maintaining a constant static pressure in the ductworks. The supply air temperature is controlled by the water cycle of the chiller, which remains almost constant. Thus, fan electricity energy consumption in VAV systems is directly associated with airflow rates (Ke and Mumma 1997). What’s more, the experimental result in Ghahramani et al. (2014) shows that the required energy of VAV systems is proportional to the rate of airflow entering the thermal zones and the airflow model is even a function of the zone temperature set-point. Thus, based on the operational mechanism, we searched for a function that bridges the gap between zone-level HVAC energy consumption and the temperature set-point, as shown: where is the airflow rate of the VAV system, is the real-time indoor heating/cooling load, represents the air density, represents the air specific heat at constant pressure, is the temperature set-point, and is the supply air temperature of fan. Though this function does not include all the energy consumption components of HVAC system, it is adequate to be applied to indicate the energy efficiency variation of a VAV system controlled by a different strategy (i.e., the traditional fixed set-point strategy and the human learning method proposed in this article).