Types of AC Units

Types of AC Units: What’s the Difference and What’s Right for You?

If your air conditioning system is getting older and performing poorly, it’s a great idea to plan for proactive system replacement in advance instead of waiting for a breakdown to force your hand. That way, you won’t have to deal with the inconvenience of going without AC while the replacement is in the works. For businesses, or even for homeowners who rely on AC for health reasons, living without AC for weeks or longer can cost you much more than that.

As you begin to shop for a new system, educate yourself by learning a little bit about the types of AC units. This article will help you do that in 10 minutes or less!

Chances are, it’s been a while since you had to think about buying an air conditioner, and there are modern air conditioning options that you may not know about. Also, be aware that some air conditioning installation vendors won’t bother to tell you about the newer types of AC systems. Unfortunately, many are in the habit of just recommending a newer version of what you already have. If you don’t know any better, you could miss out on the chance to get something that will work better for your needs.

Here’s an overview (intended to help the consumer who is not an HVAC expert!) of the types of AC units that are suitable for residences and businesses in the NYC area.

 6 types of AC units and their uses (an overview)

1. Variable Refrigerant Flow (VRF) systems

VRF systems are the HVAC system of choice in Europe, Japan, China and other parts of the world, and the technology is becoming popular in the US over the past 10 years.

Like older types of AC units found in suburban homes, VRF systems use refrigerant to cool the air via outdoor condenser units and indoor fan coil units. But the similarity stops there. These systems have variable-speed compressors that run only at the capacity needed for the current conditions. VRF systems can be designed with individually-controlled zones to provide customized comfort throughout the space. And, VRF technology is capable of providing not only cooling, but also heat, and even both simultaneously to different areas within the space.

The benefits include:

·         Consistent cooling and superior, customized comfort, even for very large spaces

·         Extremely quiet operation

·         Reduced energy consumption

·         Smaller units and small pipes allow for higher ceilings in living and working space

·         Longer life span due to more efficient design that reduces wear on parts

COMMON USES OF VRF SYSTEMS: Manhattan’s brownstone townhouses, apartment buildings where possible, restaurants, retail stores.

2. Variable Air Volume (VAV) distribution systems

Some large buildings, typically 30+ story high-rises, have water cooled base HVAC systems that serve the entire building. Water-cooled systems, as the name implies, use chilled water rather than refrigerant to remove heat from the air in your space. Chilled water is pumped from a large chiller unit that serves the whole building (probably located in the basement or a mechanical room) through pipes to a central fan coil units for each apartment or commercial space in the building.

If your building has a water-cooled base system, you’ll need to install equipment in your space that ties into the building’s base system and circulates the air throughout your space. VAV distribution systems are often installed for this purpose.

VAV distribution units direct varying volumes of air from the central fan coil unit (as needed) to different rooms in your space, using a series of ducts. Using VAV technology is a way to create customized, zoned air conditioning using a water-cooled system. 

The advantages of VAV systems over constant-volume systems include:

·         more precise temperature control

·         reduced compressor wear

·         lower energy consumption by system fans

·         less fan noise

·         additional passive dehumidification

COMMON USES OF VAV DISTRIBUTION SYSTEMS: residential apartments and offices located in high-rise buildings with a water-cooled base system

3. Rooftop packaged units (RTU)

An HVAC rooftop unit also (known as an RTU or packaged unit) provides the heating, cooling and most of the ventilation for large, single-story light commercial spaces. As the name implies, it’s typically installed on the roof. An RTU is a single assembled unit that includes a condenser and an evaporator coil for cooling, a heat source and a fan for forced air heating, and an opening for the intake of outside air.

While they often can’t be used in high rises, RTUs are often easier (read: less expensive) to install and maintain than other types of AC units, since all the equipment is self-contained in one box. However, it’s important for your installer to conduct an evaluation of your space and its usage to determine the duct work design and plan for where the supply and return grills are located.

COMMON USES FOR ROOFTOP UNITS: big-box stores, shopping centers, warehouses, and sometimes for restaurant kitchens.

4. Ducted split systems

Split systems get their name because they have two major components: the compressor and condensing unit (often called the outdoor unit) and the evaporator coil and air handling unit (often called the indoor unit). In a ducted system, air ducts are used to distribute cooled air from a central air handler to the various areas within the space. A ducted split systems can cool a space up to 10,000 square feet.

The indoor unit can be installed in the ceiling if there is adequate clearance, or in a closet space. Sometimes the indoor unit is also connected to a furnace or heat pump that supplies heat to the space. The outdoor unit, which releases the heat absorbed from the air, is typically installed under a window on the outside of the building, or in a mechanical room if available.

Depending on the size of the unit and where it is installed, ducted split systems are quieter than some types of AC units including PTACs (described below) but can be louder than ductless systems. However, they tend to be better at removing humidity than ductless systems.

As little as 5 years ago, these systems accounted for 75% of new residential air conditioning installations in the city. Today, their popularity is down to about 25% due to the development of VRF technology.

COMMON USES FOR DUCTED SPLIT SYSTEMS: suburban homes, apartments or smaller commercial spaces with access to outdoor space or a mechanical room.

5. Ductless mini splits

Ductless systems (often called “mini splits”) are often smaller, supplemental systems intended to cool a specific, contained area such as a room addition. In buildings where duct work cannot be installed, they can sometimes be used as the primary cooling system. However, they are not a practical choice for a large space.

In a ductless split system, the outdoor and indoor units are connected by a small conduit with refrigerant and electrical lines. The outdoor unit is typically installed under a window on the outside of the building, or in a mechanical room if available. Indoor units are needed in each area to be cooled, and can be wall mounted, or installed in the ceiling if there is adequate clearance.

Since they don’t require ducts, mini splits are often quick and easy to install. Ductless split systems are quieter than PTACs, since the condenser is outside, but indoor units can have noisy fans. However, some brands have packages available to muffle sound.

COMMON USES FOR DUCTLESS MINI SPLIT SYSTEMS: Supplemental cooling for room additions, storage areas, or computer rooms, or for smaller spaces without existing duct work.

6. Packaged Terminal Air Conditioner (PTAC)

PTAC units look like window air conditioners, but are installed through the wall of the building. Some units can provide heat as well as air conditioning (you often see these in hotels).

PTACs are older technology with many drawbacks:

·         They can only cool a single room (and sometimes require more than one unit even for a large room).

·         They cycle on and off frequently, so comfort levels are inconsistent.

·         Units can be quite noisy.

·         Access to an outside wall is required.

However, in an apartment situation where you are not allowed to make new penetrations in exterior walls, you may have little choice but to replace older PTACs with new ones that fit into the existing holes.

COMMON USES FOR A PTAC SYSTEM: Older hotels and historic landmark buildings in Manhattan (where occupants are not allowed to make new modifications to the structure).