1What is HVAC? – HVAC Definition
What is the actual HVAC definition or HVAC full meaning?
Heating, ventilation and air conditioning, or HVAC, is the technology of vehicular and indoor environmental comfort. Its objective is to control the temperature of the air in a designated “air conditioned” space. Besides that, it also controls the level of moisture, filtration of air, the movement of air or draught, the presence of air borne particles, as well as the supply of outside fresh air for regulating the carbon dioxide and oxygen levels in the air conditioned space. There have been many advances in the world of air conditioning – this technology has evolved from just cooling a space, to an effective control of the previously mentioned parameters.
The following are the processes by which an effective control of the parameters in an air conditioned place is maintained.
- Heating – the process of adding thermal energy to a space in order to increase the temperature
- Cooling – the process of removing thermal energy from a space in order to decrease the temperature
- Ventilating – the process of adding external air for maintaining gas ratio and freshening up the air
- Humidifying – the process of adding steam or water vapor in order to increase the relative humidity of a space
- Dehumidifying – the process of removing the humidity of a space
- Cleaning – the process of removing dust, pollens, smoke and contaminants from the air in a space
- Air movement – the process of controlling the movement of the supplied air so that the inhabitants of the air-conditioned space feel comfortable
2History of HVAC
The beginnings of HVAC are in 1902, when the 25 year old engineer from New York, Willis Carrier invented the first modern air-conditioning system. This mechanical unit sent air through water-cooled coil, however, it was not aimed at human comfort, but it was rather designed to control the levels of humidity in the printing plant where he worked. A couple of years later, in 1922, he invented the centrifugal chiller, which added a central compressor in order to reduce the size of the unit. It was first introduced to the public in 1925 on Memorial Day weekend, at the Rivoli Theater in Times Square. 1851 when Dr. John Gorrie was granted a US patent for a refrigerating machine.
This innovation shaped the 20th century America. It spread to department stores, rail cars and offices, which significantly increased productivity in the 1930s. Until this invention, the only relief for the hot weather were wide-open windows and central courtyards.
3The Importance of the HVAC Design
When planning to install a HVAC system in either your office or home, it is of utmost importance to choose an air conditioner that has the proper tonnage and specifications for your space. Professional HVAC designers have a heat load calculation chart which will help you ensure that you will choose the proper system for your space’s conditions. Therefore, make sure to consult one before making any rash decisions. Here are the sources of heat that affect the heat load calculations and the design of a HVAC system.
- Heat gained by the walls – It is a well known fact that the walls of the room gain heat from the sun, therefore, the amount of heat that a wall will absorb will depend on the material the wall is constructed from, as well as its alignment with respect to the sun. If the wall of the room is exposed to the west direction, the maximum heat that it will gain will be mostly during 2-5 pm.
The southern wall will gain most heat between 12-2 pm, while the wall facing North will usually absorb the least heat. The heat that the walls gain during daytime is stored and released into the rooms at night, which may cause excessive heating in the room.
However, if the walls of the room are well insulated, this will help to significantly reduce the heat absorption.
- Heat gained by the roof – if the roof is directly exposed to the sun, it will absorb the maximum heat possible. If there are other rooms above the air-conditioned room, the amount of heat gained from the roof will be significantly reduced.
- Heat gained by the windows – the heat from the sun enters the room by radiation, so just as in the case of walls, the heat that the windows will absorb will mainly depend on their alignment. The type of window glass also affects the amount of heat gained through the windows.
4What is a HVAC System & The Parts of a HVAC System
A HVAC system installed in a commercial or an office space differs a lot than a a HVAC system installed in a house.
In a house, the heating system is set up in a way so it delivers warm air during winter time and cool air in summer. This is done with the use of a furnace, an air-conditioner and a common set of ductwork. When the thermostat detects that the home is getting too cold, it sends signals to the furnace which starts delivering warm air every part of the home at the same time. Bear in mind that it is typical to have only one thermostat which is placed in one room and it does not account for the temperature variations in the other parts of the house.
Meaning, it will start working based on the temperature in the room that it is set in. Similarly, in summertime, the thermostat will detect when the temperature inside the home is so high that it makes staying in it uncomfortable, so it will signal the air-conditioning system to deliver cool air to all parts of the house at the same time. Again, note that the thermostat is measuring the temperature in only one room.
On the other hand, the conditions in an office or a commercial space are quite different. The higher concentration of equipment and people consequently generate more heat, which makes the air conditioning or re-circulation of air far more important than providing heat. However, although the air-handling equipment is centralized, naturally, different regions and rooms in the building have different needs for heating and cooling. These needs are called “loads” because they put a demand or a load on the HVAC system.
Loads are mainly determined by the equipment, the weather, the amount of people working in that building and many other factors. In the simplest case, this is managed by providing a constant supply of cool air which is afterwards handled by the HVAC distribution system. The air conditioner uses heat exchangers and circulated fluid or gas to cool the air that has passed through it.
The air handler is a blower or a fan that moves air throughout the building’s ductwork. Axial or centrifugal fan types may be found in the air handler. Based on the design and the configuration of the fan, different strengths and speeds can be derived.
Depending on the activities that are performed in the building as well as on the requirements of the occupants, different grades of air filters can be used in the HVAC system. General-purpose air filters are included in the air handle, while the more modern filters, such as HEPA filters, can be used in the downstream ductwork. These can filtrate and purify the air from contaminants, dust, as well as other matters described in the specifications of the requirements for the system.
Ductwork and Dampers
Square, round or rectangular ductwork provides the pass for the conditioned air from the air-handling unit to the environment. A damper comprises of one or more blades which can be used to control the amount of airflow that passes through the duct. Manual dampers are used to make sure that there is a proportional ventilation in different parts of the building based on the demand and the area. Automated dampers may be installed at firewalls because they close in case of a fire. A terminal unit is a device which uses an automated damper in order to control the amount of air that is being delivered to a region or a room. Typically, the damper is controlled by a pneumatic, electric, or a digital actuator which is regulated by a thermostat.
Heating and Cooling Zones
A set of adjacent regions or rooms in a building that have identical air-conditioning and heating needs, are called zones. Typically, at least one terminal unit and a corresponding thermostat is assigned to each zone. Heating coils may be installed after a terminal unit in order to provide heat on a zone by zone basis. As we have already mentioned, buildings that have a great number of occupants may not require extensive heating even during the coldest months of the year.
These coils are a pretty efficient way to provide heat for those couple of areas that need it and are controlled by the same thermostat system as the terminal unit. In order to dampen the noise within a duct, there are various kinds of linings available. An attenuator is a short length of lined ductwork which is frequently installed following the terminal unit in order to dampen discharge noise.
Ultimately, the test of a good HVAC system lies in its ability to deliver conditioned air to the occupants of the residential or commercial space. The air from the ductwork enters the space through registers, grills, or diffusers and all these are often called GRD’s.
- The term grill is usually applied to any air outlet or intake that has a square or rectangular face and neck and whose facial appearance consists of a louvers which can be used to deflect the air.
- A register is a grill that has one or more than one adjustable blades or dampers which are used for controlling the amount of air that passes through them.
- A diffuser is an air outlet which incorporates structures such as louvers, veins, perforations as well as other features for the sole purpose of distributing and directing air. The job of the diffuser is to direct the air flow throughout the occupied space in the most efficient manner possible.
Where does the air that enters the space go? Air circulates through the return inlets and returns to the air-handling unit. This return does not require any advanced veins, unlike the air outlet. Nevertheless, the relative location of the air inlets and outlets can be critical for the system’s efficiency. After returning to the air handler, a certain portion of the returned air is exhausted and replaced with a fresh exterior air. In an average office building, or a commercial space, approximately 10-20% is replaced.
5HVAC System Types
Generally, there are four basic types of heating and cooling: split systems, hybrid heat split systems, duct-free split systems and packaged systems.
- Split Systems are the traditional and most typical heating and air-conditioning system type. They have parts that reside both inside as well as on the outside of your home.
- Hybrid Heat Split Systems are a more energy-efficient variation of the traditional type. They have a heat pump which enables electricity-fueled heating and air-conditioning beside the gas furnace heat.
- Duct Free Split Systems can be installed in places where the conventional ducted systems cannot be. These act as the ideal complement to a ducted system.
- Packaged Heating and Air Conditioning Systems – from one-room units, to entire home systems in one package, there are several packaged solutions that can be found. No worries if your home does not have enough space for all the multiple separate products that are typically found in a split system, the market abounds with efficient solutions.