During the project development phase, there are several fundamental systems that you need to work with professionals to figure out the system's capacity and location.
Mechanical systems are the first and foremost system to consider. That is especially true when the project is still figuring out the program and area. During that phase, you and the architect/engineer will estimate the space needed for the mechanical equipment. How air or water will be distributed throughout the building must be considered.
What is a mechanical system?
When space needs a machine to function, that is often indicated by the mechanical system. Often, we categorize that as HVAC: Heating, Ventilation, and Air Conditioning. The most crucial factor when considering the HVAC system capacity is the building's total heat gain and loss during extreme conditions. Sometimes, the cooling equipment will be slightly undermined to keep the initial cost low. The building's passive heating or cooling system also needs to be considered because that will reduce the size of active equipment.
Typically, you can choose from three kinds of systems: air-water, all-air, and all-water. (*)
What to consider when choosing a HVAC system?
We could make decisions based on the following variables when determining the required area.
Scope: Local, centralized, or district. A local system is usually for small buildings. A centralized system usually serves several zones from one location. A single-plant-served-district system offers heating and cooling for several buildings.
Types: all-air, all-water, electric, and direct expansion system
Building Size: Size affects the volume of heating and cooling.
Building Type: The building type affects how complex the system is needed.
Passive system: Solar heating may be used during spring and fall.
What to consider during the preliminary sizing?
In a medium to large building, the mechanical room should have an area equal to 3% to 10% of the total used square feet when using an air-based system. The served area includes space for the boiler, chiller, fans, fuel pumps, and pipes. An all-water system needs a mechanical room of about 1% to 3% of the total area. Buildings such as apartments or hotels require less mechanical space; hospitals or laboratories with more complex mechanical services require more mechanical room.
There are also other factors we can consider when sizing the ductwork.
Building geometry and orientation: How much solar radiation reaches any spot depends on the angle of the sun rays to the building surface. Building forms also determine how much heat will gain through the building envelope. A skin-load-dominate building is thermally controlled by the condition outside. It also provides more opportunities for passive cooling and heating. Structures like a small shed are considered a skin-load dominate. Conversely, an internal-load-dominate building tends to be a larger mass with a lower skin-to-volume ratio containing programs that gain significant internal heat from people, lighting, or equipment. Facilities such as hospitals or offices are considered this type and are not as tied to the weather outside.
Heating Degree Days (HDD) and Cooling Degree Days(CDD): HDD is calculated by subtracting the average daily temperatures for each day through the heating season from a base of 65°F. Then we aggregate the difference on each day to establish a single-number rating to gauge the severity of the winter. CDD, on the other hand, is calculated in the same way; only the 65°F is subtracted from the average daily temperature throughout the cooling season. We get these metrics to gauge the severity of the summer.
Window treatment: Window covering can affect a building's heating and cooling load. Fore example, a space of at least 2 inches between the glass and window covering to avoid heat buildup.
How is the ductwork distributed?
Ductwork takes up a lot of space in a building, and people often use "trees" as a metaphor for distributing heating and cooling. The "root" is the source of producing heat and chill. The "trunk" is the main duct from the source equipment, and the "branches" are the many smaller ducts that lead to zones and individual spaces.
There are two types of ducts: round and rectangular. The round duct is more efficient and maintains better pressure. However, rectangular ducts are often used because they are suitable above the ceiling and vertical chase. Because air distribution trees are bulky and likely to have a major visual impact, designers tend to conceal them above the ceiling, below floors, or within chases.
What to expect during the coordination?
The architect coordinates the location of supply-and-return air diffusers with other ceiling items, such as lights, sprinkler heads, smoke detectors, and speakers. They are also responsible for verifying these locations and ensuring the elements do not cause conflict with the other systems. For example, the air supply register should be near windows, while the return grille should be placed away from the supply point to provide good circulation around the space.
Mechanical vocabulary good to know:
Duct, pipe & mixing box: In most commercial construction, horizontal ducts run in the plenum, and vertical pipes run in the chase. The mixing box controls the air that flows into a space from the main air supply.
Plenums: plenums are spaces between a suspended ceiling and the structure floor.
Air diffusers: Many kinds are based on their function and adjacent structure. From a sectional perspective, there are three types of diffusers.
Lay-in-air diffuser: it usually fits into the suspended ceiling grid.
Residential diffuser: it has a trim flange and fits into the residential ceiling.
Slot air diffuser: it also has flange trim and is usually installed in the office building's plenum space.
People also call out different names to these diffusers based on their appearance, such as standard square, architectural square, round, linear slot, nozzle, etc.
Boiler room: A boiler room is a room that contains a boiler for central heating. A height of 12-18 feet is generally needed. There are usually at least two boilers if the other fails the operation. Chillers are often located in the same room as the boiler. A chimney in the mechanical room will be about 4 square feet for a small building and 36 square feet for a large building.
Fan room: A fan room has many air-handling units that drive forced draft ventilation throughout the entire building. It is often on an exterior wall. It includes fans, filters, humidifiers, preheat coils, dampers, etc. These types of equipment are heavy, noisy, and produce a lot of vibrations.
What's Next
Acquiring a viable HVAC system involves thorough actions and decisions. Solving all HVAC conditions by one attempt in the early design phase would be unlikely. Because the system types are numerous, and the expected system outcome can vary widely. This article is only an introduction to basic concepts. It would be helpful to facilitate your project during the initial engagement.