What is HVAC & how it works?
Welcome to our easy guide on HVAC basics! Whether you're planning a new project or just curious about how heating, ventilation, and air conditioning systems work, this page is for you. Our goal is to help you understand the essentials of HVAC systems, so you can make informed decisions about your home or business needs. This page will guide you step by step from the very beginning.
What is HVAC?
HVAC stands for Heating, Ventilation, and Air Conditioning. It's a system used in both residential and commercial buildings to regulate indoor temperature and air quality. The heating element keeps you warm in winter, the ventilation part ensures fresh air circulation, and air conditioning cools your space during warmer months.
Did you know that the concept of air conditioning is not a modern invention? It dates back to ancient Egypt, where inhabitants used to hang wet reeds in windows to cool the air blowing through! This process, known as evaporative cooling, is still used in some modern air conditioning systems. This ancient technique laid the groundwork for the sophisticated HVAC systems we rely on today to keep our homes and workplaces comfortable.
Types of Systems
Heating
Furnaces:
Use fuel like gas, oil, or electricity to heat air. This warm air is then blown through ductwork to distribute heat.
Boilers:
Heat water and provide either hot water or steam for heating. Steam is distributed via pipes to steam radiators, while hot water can be used in radiators or underfloor heating systems.
Heat Pumps:
Work by extracting heat from the outside air or ground and transferring it inside.
Ventilation
Natural Ventilation:
Utilizes doors, windows, vents, and other openings to allow air to flow naturally into and out of a building.
Mechanical Ventilation:
Uses fans and duct systems to remove stale air and bring in fresh, filtered air from outside.
Air Conditioning
Central Air Conditioners:
Designed to cool the entire building using a system of ducts.
Ductless Mini-Split Systems:
Provide targeted cooling to specific areas without the need for ductwork.
Window Units:
Compact units installed in windows, ideal for cooling single rooms. We are not going to go over these units as they have the same function as any other AC system. Also we do not provide window installation, repair or maintenance.
Let's Go Over Each System & It's Components
Central Air Conditioning
Types of Systems:
Central air conditioners are generally of two types: split systems and packaged units.
Split Systems:
Common in residential settings, split systems have an outdoor unit (housing the condenser and compressor) and an indoor unit (containing the evaporator and often a furnace or air handler). This setup is economical if your home already has a furnace but no air conditioner.
Packaged Units:
These are single units housing the evaporator, condenser, and compressor, typically located outdoors on a roof or near the building's foundation. They often include heating elements as well, making a separate indoor furnace unnecessary.
Air Handling Units (AHU):
AHUs are classified based on their structure (horizontal or vertical), location (internal or fresh air units), and fan placement (blow-through or draw-through). These classifications impact the system's capacity and placement within a building.
Heat Pump
Air-Source Heat Pumps:
The most common type, air-source heat pumps, transfer heat between your house and the outside air. They are efficient in moderate climates and have seen technological advancements allowing them to function effectively even in colder regions. These can be ducted, connecting to a home’s existing ductwork, or ductless, known as mini-split heat pumps, suitable for homes without ducts or for zoning specific areas.
Geothermal (Ground-Source or Water-Source) Heat Pumps:
These pumps transfer heat between your house and the ground or a nearby water source. They are more efficient than air-source heat pumps, especially in extreme climates, due to the more consistent temperatures underground or underwater. However, they have higher installation costs but lower operating costs due to their utilization of relatively constant ground or water temperatures.
Absorption Heat Pumps:
A less common type for residential systems, absorption heat pumps (AHP) are driven by heat or thermal energy sources such as natural gas, steam solar-heated water, or geothermally-heated water. They are larger and more complex than electric-driven heat pumps but have a lower electricity demand.
Hybrid Heat Pumps:
These systems combine the technology of air-source heat pumps with a gas furnace, offering flexibility and efficiency. They are particularly useful in regions with colder climates, as the system can automatically switch between the electric heat pump and the gas furnace based on temperature conditions.
Ductless Mini-Split Heat Pumps:
These are suitable for older homes, buildings with limited access, or those with historic value. They offer high efficiencies, small electrical requirements, and the ability to condition specific areas or zones within a home.
Water Source Heat Pumps: These use a nearby body of water as a heat source/sink instead of the outside air, common in lakeside or seaside homes. They are efficient in transferring heat but require proximity to a suitable water source.
Furnace
Natural Gas Furnaces:
These are the most economical and popular in the U.S., especially in regions where natural gas is readily available. Modern gas furnaces are highly efficient, with some models reaching up to 98% efficiency. However, they are more expensive upfront compared to oil furnaces and have a slightly shorter lifespan (up to 25 years).
Oil Furnaces:
Common in the northeastern U.S., oil furnaces are a viable option where natural gas isn't available. They have a lower upfront cost but are less efficient than gas furnaces (80-90% efficiency) and require a storage tank for the oil. Oil furnaces can last up to 30 years and are known for producing more heat, which can be beneficial in very cold areas.
Electric Furnaces:
These are budget-friendly in terms of initial cost and installation. Electric furnaces are suitable for areas without natural gas access and have a longer lifespan (up to 10 years more than gas furnaces). However, they are less efficient in terms of operational costs due to the higher cost of electricity.
Propane Furnaces:
Used in about 10% of U.S. households, propane furnaces are an option in areas without access to natural gas. They are known for being clean and safe, with a lower risk of fires and no toxic emissions. Propane furnaces produce a higher heat temperature compared to electric furnaces and are about a third cheaper to operate than electric furnaces.
Heat Pumps:
These are not traditional furnaces but are worth mentioning as they provide both heating and cooling. Heat pumps are energy-efficient and suitable for climates that don't experience extreme cold.
Other Types:
There are also specialized furnaces like waste oil furnaces (eco-friendly, using recycled oil), wood burning furnaces (use firewood, require manual feeding), dual fuel furnaces (combine gas furnace with an electric heat pump), modulating furnaces (provide precise temperature control), and others for specific needs and applications.
Boiler
Firetube Boilers:
These boilers have tubes carrying hot gases through a water-filled chamber. They are efficient and reliable, found commonly in older buildings and ideal for constant, heavy-load applications.
Watertube Boilers:
In contrast to firetube boilers, watertube boilers have water-filled tubes that circulate through a furnace. They are used in power generation plants and large industrial facilities due to their faster steam production, higher efficiency, and ability to handle high pressure and temperature.
Electric Boilers:
Utilizing electricity as the primary heat source, electric boilers are compact, quiet, and emission-free. They are increasingly popular in residential buildings, hospitals, and small commercial spaces for their high energy efficiency and reduced operating costs.
Condensing Boilers:
These boilers extract additional heat from flue gases, significantly increasing efficiency. They are suitable for both residential and commercial heating applications and are known for their remarkable energy efficiency and lower greenhouse gas emissions.
Combi Boilers:
A combination of a water heater and central heating boiler, combi boilers are compact and efficient, ideal for small homes and apartments. They provide hot water and heating on demand, eliminating the need for separate water heaters or tanks.
System Boilers:
Suited for larger households with multiple bathrooms, system boilers can provide hot water to multiple outlets simultaneously. They require a cylinder to store hot water but are generally more efficient than regular boilers.
Regular/Conventional Boilers:
These are older units, best suited for larger households with multiple bathrooms. They require both a hot water tank and a cold water tank (usually in the attic) and provide a large amount of hot water.
Solid Fuel Boilers: These boilers use solid fuels like coal, peat, wood, or biomass. They are ideal for areas without access to gas supply or where electricity prices are high. They require regular cleaning and maintenance for safe and efficient operation.
Mechanical Ventilation
Exhaust Ventilation Systems:
These systems pull air out of the building to lower the air pressure inside. Fresh air then enters through passive vents and other openings. However, they can contribute to higher heating and cooling costs because they don’t temper or remove moisture from the incoming air.
Supply Ventilation Systems:
These systems work by pressurizing the building, forcing outside air into the building while air leaks out through holes in the building shell and other vents. They offer better control of the air entering the building and can minimize outdoor pollutants. However, like exhaust systems, they may also lead to higher heating and cooling costs.
Balanced Ventilation Systems:
These systems neither pressurize nor depressurize the structure but introduce and exhaust approximately equal quantities of fresh outside air and polluted inside air. They are suitable for all climates and can include filters for dust and pollen. However, they are typically more expensive to install and operate than other systems.
Energy Recovery Ventilation Systems:
These systems provide a controlled way of ventilating while minimizing energy loss. They transfer heat from warm inside exhaust air to fresh outside supply air in winter, and vice versa in summer. Energy Recovery Ventilators (ERVs) and Heat Recovery Ventilators (HRVs) are two types of these systems, with ERVs being particularly useful for humidity control.
Other Solutions:
This includes roof ventilators, ducts for underfloor or displacement ventilation, ventilated façade systems, and mixed-mode ventilation, which combines mechanical and natural ventilation. Mechanical ventilation can filter out pollutants, reduce noise pollution, and increase security by allowing buildings to be more sealed.
Natural Ventilation
Basic Principles:
Natural ventilation relies on wind and the "chimney effect" to circulate air. Wind-driven ventilation occurs when air enters or leaves through open windows, depending on their orientation to the wind. The chimney effect, on the other hand, is based on convection and happens when cool air enters a building at a lower level, absorbs heat, rises, and exits through higher-level windows. This is especially effective in designs with open-air spaces and high windows.
Design Considerations:
Effective natural ventilation requires careful design. Each room should ideally have two separate supply and exhaust openings to maximize the stack effect. Windows across the room should be oriented and offset from each other to facilitate air mixing. Features like ridge vents, clerestories, or vented skylights can help by providing an outlet for stale air and acting as solar chimneys to augment airflow. Additionally, interior doors should allow for internal airflow, and in cases where privacy is required, ventilation can be facilitated through high louvers or transoms.
Types of Ventilation Strategies:
Cross ventilation is suitable for buildings up to approximately 12 to 15m in depth, beyond which internal courtyards or atriums might be necessary. Stack ventilation's effectiveness is influenced by the area of openings, the height of the stack, temperature differences, and external pressure differences. Advanced natural ventilation strategies can involve specific architectural features to promote ventilation through stack effect, wind-driven ventilation, or a combination of both.
Advanced Natural Ventilation Approaches:
Designing natural ventilation can become complex due to the interaction between cross ventilation and the stack effect, complex building geometries, and distribution of openings. This can require computational fluid dynamics for analysis. Automation of natural ventilation systems or training for occupants can ensure these systems operate as intended.
Appropriate Climate and Building Type:
Natural ventilation is most effective in climates where the outdoor conditions remain comfortable for most of the year. However, it may not always maintain indoor conditions within the comfort zone, especially during extreme weather. Therefore, it's most appropriate for buildings where space conditioning is not a strict requirement.
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