MEP Tools - Basic of HVAC System

Basic of HVAC System

Mechanical systems in a building encompass all systems designed to control climate and maintain air quality. They are responsible for heating, cooling, and ventilating spaces, ensuring a comfortable and healthy environment for occupants.

Heating Systems:

These systems warm up a building. There are many ways to generate heat, such as using gas, electricity, or even recovering heat from other sources. They can be local (like a radiator in a room) or central (like a big boiler in the basement).

Heating Hot Water: The process begins with the boiler, where water is heated to a high temperature. This boiler uses a fuel source, such as gas or oil, to heat the water.

Pump: A circulating pump then moves the heated water from the boiler to various parts of the building.

Heat Exchanger/Coils: These pipes run through a heat exchanger, which in many systems is a coil located inside an Air Handling Unit (AHU) or a Fan Coil Unit (FCU). The heat exchanger or coil is where the hot water's heat is transferred to the air which is then distributed throughout the duct system.

Return Path: After releasing its heat to the air, the now cooler water returns back to the boiler through a separate set of pipes. The water is reheated, and the cycle begins again.

Thermostat: Throughout this process, a thermostat measures the temperature of the room's air. If the room's temperature drops below the set point on the thermostat, it sends a signal to the boiler and the pump to start heating and circulating water again.

Cooling Systems:

These systems remove heat to cool down a building. They use different methods like chilling water or evaporating it to cool down the air. They can be small units in each room or big ones that cool the whole building.

Chilled Water: At the heart of this system is a machine called the chiller. The chiller has a refrigeration cycle that cools down water. This process involves using a refrigerant, which changes from a gas to a liquid and back again. When the refrigerant turns from a liquid into a gas in the chiller's evaporator, it absorbs heat from the water. This process cools down the water drastically, usually to around 45 degrees Fahrenheit.

Pump: Once the water is chilled, a pump pushes the chilled water out of the chiller and towards the cooling coils located in air handlers or fan coil units throughout the building.

Cooling Coils: The chilled water flows through these coils. As room air is forced over these coils by a fan, the air absorbs the coolness from the chilled water. As a result, the air cools down and is then distributed throughout the building, thereby reducing the indoor temperature.

Return Path: After the water circulates through the system and transfers its cold energy to the air, it warms up. The now warmer water returns back to the chiller to start the process again.

Ventilation Systems:

Ventilation is all about controlling air movement. It gets rid of stuffy air, controls humidity, and provides fresh air. It can be as simple as opening a window or as complex as a system with fans, ducts, and filters.

Air Handlers: These are large metal units that condition and circulate air as part of the HVAC system. It's designed to be durable and to protect these elements from the elements and various environmental conditions. These elements include:

Fan: This is the heart of the system. It pushes air around, and its speed can be adjusted to control airflow.

Filters: These clean the air by trapping particles like dust and pollen. To keep the air fresh, filters need to be cleaned or replaced regularly.

Heating and Cooling Coils: These change the air temperature. Heating coils warm the air, and cooling coils cool it down.

Humidifier: This part adds moisture to the air, usually during dry months.

Dampers: These are like valves that control how much air goes to different parts of the building. In high-tech systems, they're usually adjusted automatically.

Mixing Box: This is where the system decides how much fresh outdoor air to mix with the air already inside the building.

Controls: This is where you make adjustments, like changing the temperature or fan speed.

Motor: This powers the fan that moves the air around.

• Belt and Sheave (pulley): The belt connects the motor to the fan, and the sheave controls the fan speed.
• Fan Coil Units (FCU) & Variable Air Volume (VAV) Boxes: These units heat or cool the air moving through a duct system.
• Exhaust Systems: These systems remove air from inside the building.

Building Management System (BMS):

The Building Management System (BMS) is the brain that controls these systems. It can adjust temperature, turn systems on or off, and even talk to other building systems.

Automated Control: The BMS uses Direct Digital Control (DDC) and Programmable Logic Controllers (PLC) to automate and manage the building's functions. This means it can turn systems on or off, adjust temperatures, or control lighting based on pre-set criteria or schedules.

Communication: The BMS is not an isolated system. It communicates with other systems in the building. For example, it might adjust the HVAC system based on information from a security system that tells it how many people are in the building.

Remote Management: One major advantage of a BMS is its ability to be controlled remotely. This means a facilities manager can adjust building systems from a computer, without having to manually adjust each system.