How Do Multi Zone Mini Splits Work?

Mini split air conditioning systems are a convenient and highly effective solution to control the

temperature and moisture levels in multiple areas of your home. They work year-round to keep the interior atmosphere pleasant, no matter the temperatures outside. Mini split AC systems effectively combine the advantages of a classic air conditioner and a heat pump.

Have you ever wondered how these devices function? Learn how multi zone mini splits work and differ from standard centralized air conditioning units.

How do multi zone mini splits work? On the surface, mini split air conditioning systems work according to the same basic principles as traditional ducted AC. Both systems employ an outdoor unit and multiple indoor outlets.

Depending on the outside temperature, the outdoor unit absorbs exterior air, either heating or cooling it to the desired target temperature. The outdoor unit then redirects the air through the house and into designated indoor outlets.

The primary difference between a standard ducted AC system and a multi zone mini split system is the delivery method employed to distribute cooled or heated air in the house.

In a house equipped with ducted air conditioning, the outdoor unit sends the air to a single, centralized air handling unit. The air handling unit possesses refrigerant lines and a powerful fan unit. This handling unit is, in turn, connected to an array of ducts, with air vents on the walls of each room or zone, allowing it to distribute heated or cooled air.

Although a centralized, ducted system can control air circulation and temperatures in the entire house with relative ease, it has several drawbacks:

• Ducted systems cannot function without ductwork. If the house is not equipped with ducts, you cannot use ducted air conditioning.
• Installing a ducted AC system can be prohibitively expensive, if not impossible, especially in smaller homes or apartments.
• The centralized nature of this system means that if the air handling unit or the ductwork are damaged or worn out, the system’s air circulation suffers from leakages, causing the heating/cooling efficiency to decrease overall.
• Worn or dirty ducts decrease air quality in the entire house.

Houses equipped with a ductless system rely on individual air handling units called mini splits. Each mini split is mounted on the wall of the room or area it serves, creating a designated zone.

Ductless mini split systems with a single indoor unit are single-zone, whereas systems equipped with two or more mini splits are called multi zone. There are names for each configuration, depending on the number of zones. Some of the most common examples include the following:

• 2-zone mini splits: Dual-zone
• 3-zone mini splits: Tri-zone
• 4-zone mini splits: Quad-zone
• 5-zone mini splits: Penta-zone

A typical household outdoor unit can support a maximum of eight indoor units (8-zone or octa-zone). However, systems with more than five zones are rare.

The primary advantage of a ductless mini split system is that there’s no need for a central air handling unit and a network of ducts. Instead, each mini split acts as its own air handling unit. This solution is ideal for houses without ductwork or homes that cannot support ducts.

They are also much less expensive than ducted systems while providing each zone with equivalent cooling and heating efficiency, making them highly cost-effective. Cleaning and maintenance are also easier and quicker, allowing for a higher overall indoor air quality.

The primary drawback of a ductless mini split AC is its reliance on a zone system. Mini splits do not technically control the atmosphere and temperature of the entire house; each indoor unit only covers a specific zone, the size of which depends on each unit’s capacity.

However, with enough zones and units of the correct capacity placed in suitable rooms, this drawback is unnoticeable. A correctly configured and installed multi zone mini split efficiently heats and cools the rooms you use the most without wasting energy on the least-visited parts of your home.

A typical multi zone mini split system features four groups of essential components:

• Refrigerant fluid
• Outdoor unit
• At least two indoor units
• Line set

Today’s mini split systems also come with an electronic remote control or wireless connectivity with a mobile application.

Most air conditioning systems, including mini splits, cannot function without refrigerant fluid. Refrigerant fluid, also called cooling fluid, is a chemical compound that can easily change between the liquid and gaseous states. Air conditioners exploit the refrigerant’s chemical properties to cool interiors. The basic principle of an air conditioning system is to circulate the refrigerant in a specific direction, causing the cool air to go inside and evacuating heat to the outside.

Under normal conditions, the refrigerant fluid is designed to last for the entire system’s lifetime (10 to 15 years on average). However, if your mini split system wears out, it may develop a refrigerant leak, reducing its overall effectiveness.

Your mini split system’s type of refrigerant fluid varies, depending on the age and manufacturer. Older systems used freon-based refrigerants such as R-12, banned in 1996 under the Montreal Protocol due to their severe impact on the ozone layer.

Current-production systems, such as the Mr. Slim Mitsubishi mini split product line, mainly use R-410A. This is a hydrofluorocarbon (HFC) refrigerant with a certified Ozone Depletion Potential rating of 0 and approximately 20% of the global warming potential of R-12.

However, this refrigerant is scheduled for phase-down and eventual elimination by 2023. The planned replacement is R-32, a refrigerant with approximately ⅓ of the global warming potential of R-410A (about 6% that of R-12).

The outdoor unit resembles a sizable box-shaped device equipped with a fan. As the name suggests, this element is designed to sit outside, interacting with the exterior air.

The outdoor unit consists of four major parts: the compressor, the expansion valve, the outdoor fan, and the condenser coils. The entire unit may sometimes be referred to as the compressor unit or the condenser unit. However, these only refer to individual elements of the outdoor unit, not the entire assembly.

The typical interior layout of an outdoor unit comprises two parts: a large section containing the outdoor fan and the condenser coils and a smaller section containing the compressor and valve. Each part works as follows:

• Compressor: Pressurizes the refrigerant as it exits the condenser coils, helping it transition from hot gas to cold liquid, and then pumps the refrigerant back to the indoor units.
• Condenser coils: Receives hot refrigerant gases from the indoor unit and makes it circulate several times around the outdoor fan to cool it down.
• Outdoor fan: Pulls in outside air and blows it over the condenser coils to help cool the refrigerant down.
• Expansion valve: Allow the liquid refrigerant to expand as the compressor pressurizes it, helping it cool down further.

Each indoor unit covers a specific zone inside your home. Common examples include the master bedroom, guest bedrooms, bathrooms, the kitchen, and the living room.

Although mini split indoor units can take on many shapes, all possess the same components: an array of evaporator coils, a circular blower, and an air filtering unit. Here is the purpose of each part:

• Evaporator coils: Receives the cold refrigerant from the outdoor unit, making it circulate long enough for the blower to push cold air into the room. As it does, the coils also absorb heat, causing the refrigerant to transition from cold liquid to hot gas and return to the outdoor unit.
• Circular blower: Draws hot air from the room and blows cold air from the coils back into the room.
• Air filtering unit: As the circular blower sends cold air back into the room, it passes through an air filtering unit, catching dust, allergens, spores, and other contaminants. It is the element of a mini split that helps improve air quality.

The most common indoor unit type is the wall mount like those featured on LG ductless mini split systems. Wall-mounted indoor units are typically rectangular devices designed to be installed high on one of your walls, near the ceiling. Wall-mounted units are the least expensive, the easiest to install, and one of the most efficient.

Alternative indoor units include the following:

• Ceiling cassette: A square-shaped unit mounted directly into your room’s ceiling. Although more challenging to install, this unit type allows your walls to remain free of obstructions.
• Floor-mounted: A floor-mounted mini split sits on the floor instead of one of your walls. This solution may be preferable for ease of access (e.g., if the home’s occupants cannot safely reach a wall- or ceiling-mounted unit for cleaning); however, they take a significant amount of space that furniture could have occupied.

The line set is a collection of cables and pipes connecting the outdoor unit to each indoor unit. The line set of most home mini split systems can fit in a 3" wide conduit, making it significantly smaller and easier to install compared to traditional ducts.

The line set comprises four types of tubes and cables: the refrigerant lines, the drain lines, the power cables, and the electronic control cables. Here is the purpose of each part:

• Refrigerant line: Insulated copper tubes designed to carry the refrigerant through the system. The diameter of the refrigerant tubing changes depending on the refrigerant’s state: smaller when liquid, wider when gaseous.
• Drain lines: Captures water condensation generated during the evaporation process, redirecting it outside.
• Power cables: Provides power to the indoor units. The power cables are directly wired to your home’s electrical system, eliminating the need to plug the indoor units into outlets.
• Electronic control cables: Allow the outdoor unit, indoor units, and either your remote control or mobile device to communicate with each other, ensuring the system only runs at the correct times.

The refrigerant continuously circulates between the outdoor and indoor unit, forming a cooling cycle. All the indoor and outdoor elements interact to regulate your interior home temperature.

The cooling cycle begins with the outdoor unit’s compressor. Cold, liquid-state refrigerant travels from the compressor to the indoor units through the refrigerant lines. Once in the indoor unit, the refrigerant circulates through the evaporator coils.

The rotating blower absorbs the room’s indoor heat from top-mounted vents and delivers cool air back to the room, decreasing the ambient temperature. The cool air passes through a filter, making it cleaner and healthier.

Simultaneously, the cold refrigerant fluid in the coils absorbs the heat and progressively evaporates, changing it to a gaseous state. The process also generates water condensation, which the indoor units capture and redirect outside via the drain lines to prevent water from leaking inside your home.

The now hot and gaseous refrigerant fluid travels through the refrigerant lines back to the outdoor unit, circulating through the array of condenser coils surrounding the outdoor fan. As the outdoor fan spins, it attracts outside air, cooling the condenser coils and allowing the refrigerant to return to a cold, liquid state.

The cycle begins anew, continuing until reaching the target temperature. The mini split enters a power-saving mode, ceasing the cooling process but keeping the sensors powered. The mini split only restarts when the interior temperature is no longer at or near the target, keeping the energy bills low.

There are two types of outdoor units: standard units and heat pumps. Standard mini split outdoor units are designed exclusively for cooling. In contrast, a heat pump possesses additional parts to reverse the temperature flow, allowing it to either cool or heat.

Heat pumps are an excellent solution if you live in a climate with cold winter months and warm or hot summer months. They can keep your interior home temperature comfortable year-round.

The essential component exclusive to heat pumps is an additional valve inside the outdoor unit, the reversing valve. The purpose of this valve is to reverse the direction of the refrigerant circuit.

When enabled, the cooling cycle reverses, sending hot, gaseous refrigerant to the indoor units and cold, liquid refrigerant to the indoor unit.

Consequently, the indoor unit’s evaporator coils turn into condenser coils (they discharge heat instead of absorbing it). The outdoor unit’s condenser coils become evaporator coils (they absorb heat from the outdoor air instead of releasing it).

Mini split air conditioning systems are lightweight and cost-efficient and have fewer requirements than traditional ducted systems.

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