In this part of Full HVAC course, we will learn about Room Air distribution..

Room Air Distribution

This is the distribution of air throughout the room, and how the air is being pulled into different parts of the room.

Introduction

Air distribution systems (AD) are designed to move air throughout the environment to maintain comfort levels. AD systems use fans and ductwork to distribute conditioned or fresh air throughout a facility's interior spaces. In residential settings, these types of systems may be installed in rooms where people spend their time. A typical application would be in a bedroom or living room. Office environments often include a centralized AC system, which is then distributed among individual offices. Commercial buildings often have entire floors dedicated to HVAC cooling, including individual units that are connected to centralized chillers. Other commercial applications may include food and beverage processing facilities and warehouses.

Types of AD Systems

There are two basic types of air distribution systems: centralized and decentralized. A centralized system moves air through central equipment, whereas a decentralized system distributes air using a network of individual components. Centralized systems are generally more expensive than decentralized systems. However, centralized systems provide greater control over building-wide airflow conditions. Individual controls allow for precise temperature adjustments at each unit location. In addition, they are easier to monitor and operate. Decentralized systems are less expensive, but require more maintenance and monitoring.

Components

The following list includes some of the major components of an AD system.

• Air movement devices

• Ducting

• Heating, ventilating, and air conditioning (HVAC) filters

• HVAC systems

• Heat exchangers

• Humidifiers

• Heaters

• Fans

The most common method of air-distribution is called natural air-flow. In the case of natural air-flow, the ducts are in direct contact with the outside environment where the fresh air comes through the vents. As the fresh air enters the building, the warm stale air rises out of the building. There are many factors that influence how much air goes into each area of the room. These are:

• Room size

• Window size (if any)

• Vent size (if any)

There are two types of venting: forced and non-forced.

• Forced ventilation is similar to natural air flow except it forces the air though the duct system at high velocity. Since the air is being moved fast, the temperature of the air does not change greatly.

• Non-forced ventilation is done by using exhaust fans to pull the contaminated air out of the room and back to the outdoors.

In both cases, the air is moving around the room, but it is still going through the same path.

1. Room air distribution (RAD) refers to the method of distributing air throughout a space. In general, air should be distributed evenly across a room to ensure that everyone’s comfort level is met.

2. A fan or blower is used to blow the air around the room, distributing the air evenly.

3. Fans are generally placed high above the floor, while blowers are placed at lower levels to allow them to push air down below the ceiling.

4. There are two types of fans; centrifugal and axial fans. Centrifugal fans use blades mounted directly onto a motor shaft. Axial fans have blades attached to a stationary central hub. Both types of fan work similarly and they both pull air toward the center of the fan.

5. The speed of the fan determines how much air flow is delivered. Lower speeds produce less volume of air. Higher speeds create greater volume of air.

6. Radiator type units use hot water, steam, or electrical heating elements to distribute the warmed air throughout the room. These systems heat air before it enters the building.

7. Hot-air returns or return grills are designed to warm the air before re-circulation.

8. Cold-air returns or return vents are designed to cool the air before re-entry.

9. Central air conditioners are the most common way to circulate room air. These systems are connected to a single supply duct and exhaust through a drain pan located near the floor.

10. Warm air is drawn in through the return grill and then circulated through the occupied spaces. Cooler air blows out of the return vents.

11. Heat recovery ventilators (HRVs) are similar to central air conditioning in that they both work to remove stale air and bring fresh air into a space. HRVs are used extensively in residential applications. Their name comes from their ability to draw in stale air and expel warmer air back outside.

12. Humidifiers raise the relative humidity in a room to help prevent moisture problems.

13. Dehumidifiers reduce the amount of moist air in a space.

14. An evaporative cooler uses evaporation to take the place of air conditioning. Evaporative coolers rely on air movement over a cooling surface to transfer heat away from the system.

The air distribution system (ADS) is the set-up of the air handling units (AHU). An AHU is a device that moves fresh air into the building's interior spaces. It distributes conditioned air throughout the space. In terms of airflow, the ADS consists of two components, fans and ductwork. Fans move the air from the supply side of the AHU across an exhaust port and out into the room. Ductwork contains a plenum chamber where the fans mount; and then branches off into the rooms being supplied. These are the only two parts of the ADS that the average person would think about. When designing an ADS, some factors should be considered.

Airflow Volume

A major factor in determining how much air is moved through each branch of the ducting is the volume of airflow. A larger airflow volume equals a higher air transfer rate. This means the total number of cubic feet per minute (CFM) of air passing through each branch of the ADS. CFM is a unit of measurement that represents the mass of air flowing through each section of the duct over time.

Air Transfer Rate

The air transfer rate refers to the amount of air moving through each section of the air handler. The greater the air transfer rate, the faster the air is moving throughout the entire system. There are three types of air handlers, constant velocity, variable velocity, and centrifugal. Each type of air handler has its own unique method of distributing air.

Constant Velocity

The constant velocity air handler is one that uses a positive displacement pump to force air along a pipe at a predetermined speed. The advantage of a constant velocity air handler is that they have less noise than a centrifugal fan air handler and produce less vibration noise. However, they are not recommended for use in bathrooms because the air tends to circulate around the area instead of moving in a direct path. Also, they do not provide adequate coverage of the space, especially if the space is smaller than the size of the unit.

Centrifugal Fan

The centrifugal fan air handler is the most popular air handling unit among home owners. Centrifugal fans are extremely effective at transferring air throughout a small area of space due to their design. A centrifugal fan produces lower noise levels and less vibration than a constant velocity air handler. Because they rotate, they work well in spaces that require high air movement. Their drawback is that they tend to generate more noise than a constant velocity airhandler. Another downside to centrifugal fans is that they may need to be mounted close together, depending on the size of the space. If the space is small, it may be difficult to fit enough units.

Variable Speed

The variable speed air handler's speed can be adjusted based on the needs of the space. It provides the user with maximum flexibility in adapting to changing conditions. Its drawback is that it creates a lot of noise and its use in residential settings makes it illegal in many states.

Duct Size

Another factor in determining how much airflow is distributed through the ducts is the size of the ducts. Duct size is determined by the square footage of the space being heated plus any special requirements the owner might have. Larger duct sizes allow for a higher airflow rate.

Air distribution refers to how evenly air is distributed throughout a room or area. As we know, temperature is measured using degrees Fahrenheit. When it comes to air conditioners, the number of fans and their direction are two factors that affect air distribution. Fans force air at a certain velocity toward a specific point. There are three types of fan: ceiling-mounted, wall mounted, and under cabinet. Each type of fan has its own advantages and disadvantages. However, ceiling-mounted ones have the best air distribution, while under cabinet fans blow the least amount of air. Ceiling-mounted fans are not only the most effective way to distribute cooling down, they are also less expensive to install.

The room air distribution (RAD) system is the portion of the heating, ventilating, and air conditioning (HVAC) system responsible for delivering conditioned air throughout the space. In traditional systems, the RAD system consists of a series of ductwork located in the ceiling, floors, and walls designed to deliver conditioned air throughout the space in order to maintain a comfortable temperature. Depending on the size of the building, the number of occupants, and the amount of equipment that is being run simultaneously in the space, the HVAC system may comprise several different components including return grilles, fan diffusers, variable-speed blower motors, and dampers. As opposed to traditional systems, radiant cooling systems are distributed across the floor instead of being concentrated in one area. These systems use infrared technology to transfer heat away from the body. Unlike traditional systems, they do not use fans to distribute the air throughout the space; rather, they utilize high-powered lamps that emit infra-red radiation. Because these systems rely less on convection currents, they can reduce the noise level in an office environment.

The room air distribution system consists of a network of ductwork and diffusers that move conditioned air throughout a building. In residential applications, this is called home ventilation or HVAC (Heating Ventilation and Air Conditioning). A properly designed HVAC system moves air efficiently and effectively in order to keep rooms comfortable. If this system fails, then the temperature and humidity level inside the house may become uncomfortable and unhealthy.

In commercial buildings and school facilities, this is known as building automation systems (BAS) or facility management systems (FMS). BAS can monitor and control different aspects of facility operations including heating, cooling, lighting, security, fire alarms and sprinkler systems and many others.

There are two basic types of room air distribution systems: forced draft systems and whole house systems. Both have advantages and disadvantages. Let’s start with forced draft systems.

Description

A forced draft system blows fresh air into space via a fan. Sometimes these systems use only the power of the blower motor to push air through the ductwork. Other times, they require electricity plus fans or even special electric motors to supply additional power to help push air along. These systems use the same type of equipment that you would find in a central air conditioning unit.

Since forced draft systems depend exclusively on outside air flow, they do not work well in environments where the air is polluted. In fact, they might actually make conditions worse if pollutants are drawn into the room by the circulating air. When a building is located near heavy industry, it’s often advisable to avoid forced draft systems since their operation could exacerbate pollution levels in the surrounding area.

On the other hand, forced draft systems are great at delivering clean air into spaces where people are working or sleeping. Since they don’t rely on mechanical devices to suck dirty air out of the room, they provide a much higher degree of comfort than whole-house systems. They are also capable of supplying cool air in hot climates.

Advantages

Forced draft systems are generally less expensive than whole-house systems. Most forced draft systems cost $10-$15 per square foot to install. Because they draw in fresh air without using any electrical power, they operate silently. And thanks to the use of standard components, they can easily fit into existing ductwork designs.

As we mentioned earlier, forced draft systems depend solely on natural air movement. As a result, the temperature and volume of air moving through them cannot be adjusted. Many people like that aspect though since they want a steady stream of cool air and feel that variable settings in whole house systems are distracting.

Disadvantages

Forced air systems do nothing to remove moisture from the air. That means they can create problems for those who suffer from allergies or asthma. Moisture is critical to the health of everyone, especially infants.

To get around this problem, some forced air systems are equipped with an activated carbon filter. Activated carbon filters remove unpleasant odors and particles from the air before it enters the space. However, these filters are not 100% effective and they still allow some contaminants to pass through.

In order to understand room air distribution, we need to start with some basic building science. A room is basically a box of space where people live, work, exercise, sleep, and much more. A room has two sides; the inside side (where stuff happens) and the outside side (the place where people go). There's a difference between them. Let's take a look at it.

You may have heard terms like WET-AIR AND DRY-AIR before, but what does it actually mean? Wet air refers to high moisture content in the air inside the house. Dry air means low moisture content in the air. You want the dry air to get to your lungs and not the wet air. How do you make sure the right kind of air gets to your lungs? That's what I'm going to show you today.

Let's say you're sitting in your home watching TV. Your house has three rooms. Room 1 is the living room and Room 2 is the kitchen. In between these two rooms is an open hallway called the Lobby. Let's say you're sitting comfortably in your lounge chair, enjoying some Netflix while looking out the window at the beautiful view. Now let's say you turn off the television, close the curtains and walk down the hall to the kitchen.

Before you got to the kitchen if you walked into the lobby first, would you be feeling comfortable walking around? If you said yes, then you've experienced the benefit of having good airflow throughout your house. But, how did you feel about your comfort level once you were in the kitchen? Did you walk around feeling warm and cozy? Most likely not! Not only was your environment uncomfortable to stand still in, but you also didn't even realize it until now. Why? Because you weren't exposed to the dry air. When you pass from one area of your house to another, the quality of air changes.

The same applies to the way our bodies function. Our body processes food differently depending on the temperature or humidity of the air we’re breathing. If we’re in a hot, humid environment, we sweat more than usual and therefore lose more water from our body.

When you breathe, your body absorbs oxygen and releases carbon dioxide. However, the amount of CO2 absorbed is based on the CO2 concentration in the surrounding air. If the air is saturated with CO2, less CO2 will enter our bodies. So, if you stay in a stuffy house all day long, you won’t get enough fresh air into your lungs. This makes you tired and sluggish. On the contrary, if you spend time in cold, dry air, your body will overheat due to sweating. Sweating causes increased blood flow and causes your entire body temperature to increase. As a result, your brain starts working harder to cool down your body which causes headaches.

A study conducted in 2015 reported that children who spent more time indoors had higher levels of asthma symptoms compared to those who spent less time indoors. Asthma is caused by allergies and inflammation of the lung. People who suffer from asthma tend to have chronic respiratory illnesses.

So, keeping your house clean, airtight, and ventilated will help keep your body healthy. There are several ways to measure air quality in your home. Different devices are used to determine different factors. Here are some examples of the types of instruments you'll find:

Breathing Rate Oximeters

These tools use infrared light to measure respiration rate. These machines come in various shapes and sizes; their accuracy varies.

Humidity Humidifiers

These units use sensors to detect moisture in the air. They range from small portable handheld models to larger floor standing units. They may have a fan built into the unit and often feature a display screen to indicate the current humidity level.

Room air distribution is simply the type of forced air distribution system that you would use inside of a house. This type of ventilation is designed to move air throughout the home. There are two types of room air distributions systems: central supply units (CSU) and whole-house fans (WHF). CSUs distribute conditioned air throughout a specific area of the building while WHFs distribute cooled and heated air throughout the entire house at once. A CSU uses either ductwork or piping to deliver conditioned air to each location. In comparison, WHFs use electric motors or blowers to blow air through duct work. While they both have many similar features, CSUs are generally used for smaller spaces like offices and smaller rooms, whereas WHFs are ideal for larger spaces like bathrooms and kitchens.

Ventilation rates

Ventilation rate is the amount of fresh air delivered per minute. Most people think about airflow rate in terms of cubic feet per minute (CFM), but CFM is only useful when comparing different ventilations systems. To determine how much air a fan delivers, multiply the number of hours, minutes, and seconds it runs by the number of square feet it covers. For example, if the fan is set to run continuously for 24 hours and covers 10,000 square feet, then its flow rate would be 10,000 x 24 2,400,000 CFM. The bigger the fan, the higher the flow rate; however, the higher the flow, the greater noise level and power consumption.

Venting mode

The purpose of venting mode is to control where conditioned air exits from your HVAC system. There are three main modes: return, exhaust, and mixed. Return mode creates positive pressure and pulls stale air back into the system. Exhaust mode creates negative pressure and pushes stale air out of the home. The mixed mode combines these features together to create balanced pressure. Different types of houses require different levels of venting mode. You should consult an expert before making any changes.

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