Maintaining the air quality inside the buildings is extremely important for property managers, and owners alike. Office buildings, hotels, hospitals, malls are some of the places wherein a large number of people either work, or stay, or visit. And exposing these large numbers of people to bad air can result in severe health issues. The air can become bad with high concentration of carbon dioxide CO2, or carbon monoxide CO, or with some dangerous particles in the air. All of these unwanted gasses and particles can lead to bad air quality and subsequently when a large number of people inhale this bad air for longer periods of time then there is a high possibility of falling sick. To avoid such a situation, building owners, property/facility managers are always on guard to maintain the air quality inside the buildings. How is this achieved? How is the air quality maintained inside the buildings? This is also an extremely crucial consideration when implementing the HVAC system in any given building. The air quality is maintained by installing sensors, controllers, actuators, dampers, and filters at various places ideally in close proximity to wherever the Air Handling Units (AHUs) are functioning in the building. This is how the system of air enhancement works.
Air Handling Unit and Fresh Air Unit
An air handling unit (AHU) conditions the air and distributes this conditioned air to different parts of the building. The AHU has a supply line and a return line. In any given building there may be several AHUs on any given floor. Sometimes all of the AHUs are located in a single AHU room on each floor, while in some buildings, there may be 2-3 AHU rooms on each floor. Besides the AHU, there is also a fresh air unit shaft that is connected to the AHU. The function of the fresh air unit (FAU) is to supply fresh air to the AHU. Therefore, an AHU and an FAU work in tandem. This FAU unit is ideally located on the rooftop and a ductline passes through all the floors and through this FAU ductline, the shafts are carved out for each and every floor. These shafts carrying fresh air are then connected to the AHUs on each and every floor. Now, what is the determinant factor to increase or decrease the supply of fresh air to the AHU? What is the mechanism of mixing the fresh air with the return air in the AHU?
As highlighted above, the return line in the AHU sucks the air from a given floor and supplies it to the AHU. The AHU conditions this return air and again supplies this conditioned air to different parts of the floor. This is a closed cycle wherein the same air circulates. However, external factors such as increased number of people, external gasses, smoke, etc. can increase the concentration of carbon dioxide CO2, carbon monoxide CO, and other particles in the return air. And if the AHU continues to supply this unclean air to different parts of the floor, then there is a strong likelihood of people falling sick.
To avoid this situation, a CO2 sensor or a corresponding multi-detector sensor is installed in the return line of the AHU. This sensor captures the quality of the return air and accordingly sends a signal to the controller. The controller is situated between the return duct of the AHU and the shaft carrying the fresh air. A motorized volume control damper is placed in the shaft carrying the fresh air. The actuator is mounted on this volume control damper. This actuator takes a signal from the controller. Now, based on the input signal that the controller receives from the sensor, the output signal generated by the controller triggers the actuator to open/close the volume control damper in the shaft.
For example, if all of a sudden, the numbers of people in the mall, or hospital, or office building, or hotel, or any other building, increase, then in that scenario, the CO2 concentration will increase as well. The sensor placed in the return line of the AHU will sense that and send a signal to the controller. The controller in turn will send a signal to the actuator to open the volume control damper fully. This will allow increased volume of fresh air into the AHU. This fresh air will mix with the return air and will eventually bring down the concentration of the CO2 in the building. The volume control damper will remain fully open until a point when the sensor placed in the return line sends a normal signal to the controller. At that time, the controller will correspondingly send the signal to the actuator to remain partially open thereby limiting the volume of fresh air into the AHU.
While designing the controller, the engineers can program for 2, 3, or 4 output signals to the actuator. Based on the output signal received from the controller, the actuator can fully open the damper, or partially open the damper, or fully close the damper. It is to be noted, there must be at least 2 output signals such as either fully opened or fully closed. This controller must also send a signal to the variable frequency drive (VFD) panel placed inside the fresh air unit. If the dampers on all floors are fully open, then, the VFD instructs the fresh air unit to work at the highest frequency. If the dampers on all floors are fully closed, then, the VFD instructs the FAU to stop down. However, if some of the dampers are open and some are closed, then, the VFD instructs the FAU to operate at an intermediate level. This sending of signals from the controllers to the VFD is all part of the programming that engineers perform before implementing the system.
This way the whole system of maintaining the quality of air inside a building is fully automated.
Installing of such a system is not an easy task. If, for example, there are 50 AHUs in any given building, then, 50 units of sensors, 50 units of controllers, 50 units of actuators, 50 units of volume control dampers would have to be installed. Additionally, suppose a single FAU was supplying fresh air to 5 AHUs, then, 10 VFD panels would need to be installed in 10 fresh air units that are located on the rooftop. Wiring work would run in thousands of meters. Besides, a massive amount of civil work would need to be carried out. Civil work such as enlarging the wall for placement of volume control dampers in various shafts, brickwork to facilitate the wiring work, cutting of false ceiling to connect sensor and controller, etc. The whole process takes a massive number of manhours. Even before installing such a system, a great number of man hours are spent in the planning and design. However, if planning and design stages have been carried out meticulously, then, installation stage will be relatively easy. The equipment such as sensors, controllers, actuators, dampers, drives should ideally be tested properly before installing them. The objective is to minimize the rework. High grades of electrical wire should be chosen for such a project. A lot depends on the quality of wiring work in such a project. After the installation stage, testing should be performed rigorously before handing over the system to the client. BMS compatibility also needs to be maintained.
In recent times, in addition to maintaining the fresh air in a given building, the HVAC industry is also focusing on reducing or eliminating the viruses, bacteria, and unwanted odors from the building. This is achieved by installing in-duct purifying systems. In other words, these purifying systems are installed either in the supply line or in the return line. Some of these systems such as UV treatment or filtration treat the air in the return line, whereas some of these systems such as ionizers send ionized oxidizers along with the supply air to the different parts of the building.
The concept of UV treatment is very straightforward. The return air passes through the UV treatment process in the return duct. The viruses, unwanted odor, bacteria are eliminated in this UV treatment of the return air. In other words, the viruses, bacteria would have to be sucked out by the HVAC system before they can be eliminated.
On the other hand, ionizers are placed in the supply line. These ionizers are supplied into the building along with the conditioned air. The ionizers send different kinds of friendly ionized oxidizers that destroy the viruses, bacteria, and unwanted odor at the source.These ionizers are easily integrated either in the plenum or in the supply side of an AHU.
TheSmartHVAC works with its clients across India to maintain the air quality in the buildings.
Sensors, controllers, actuators, dampers, drives, UV treatment processes, and ionizers are some of the tools and instruments used to achieve the desired air quality in buildings across India. The team of engineers at TheSmartHVAC analyzes the requirements in detail before proposing the design to the client. Thereafter, installation is carried out.