Chillers, AHU, RTU How they work

How Chillers, AHU's and RTU's work

How Chillers AHU and RTU work

In this article, we'll look at how chillers, AHUs, and RTUs work together, the difference between them, and the basic operating principles behind each. Chillers, air handlers, and rooftop units are widely used in HVAC systems for commercial properties.

You can watch the video in this article by scrolling down!

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chillers

Air and Water Cooled Chillers

Chillers are used to generate chilled or chilled water that is pumped around the building to provide air conditioning by collecting unwanted heat.

There are two main types of chillers, Air cooled and water-cooled. The term "air" or "water" chilled simply tells the engineer how the chiller's condenser rejects heat from the building.

Water Cooled Chillers

water cooled chiller

Water coolers are usually located in the basement or the lowest floor of a building. This type of chiller requires a cooling tower to reject heat from the building. The chiller produces chilled water and pushes it through the building to Air Handling Units (AHUs) and Fan Coil Units (FCUs), etc. These units circulate the air in the local space as well as in the building. The air is forced through heat exchangers, which contain the cold water, which removes unwanted heat before the air is distributed throughout the building.

Unwanted heat, which is extracted from the air, accumulates in the cold water circuit. This loop returns to the chiller and once it reaches the evaporator, the unwanted heat is transferred to the chiller's condenser via a refrigerant loop.

The condenser absorbs this heat and then discharges it into the "condenser water" loop that connects the chiller condenser and the cooling tower. The cooling tower will force ambient air through the condenser water to remove unwanted heat. The cooling tower fan blows this heat out of the system and out of the building and out into the atmosphere. In this case, the chiller's condenser has been cooled with water, so it is a water-cooled chiller.

Cooling towers in large commercial buildings

Water cooled chillers are typically used in large commercial properties with high cooling loads, you can tell if a building has a water cooled chiller as you will need cooling towers which are usually on the roof. Typically there will be more than one chiller and cooling tower, it is not uncommon to have at least 2 or 3 or even more just for redundancy as well as variations in cooling demand.

Air Cooled Chillers

air cooled chiller

Air-cooled chillers are usually located on the roof of the building or outside, e.g. in the parking lot. Air coolers also generate chilled water that is pumped throughout the building to air handling units as well as other appliances such as fan coils etc. This is to cool the building by capturing unwanted heat.

Air Cooled Chiller Animation

Air is forced to circulate around the building and local space, and will pass through the heat exchangers in the AHU and FCU. This unwanted heat is transferred back to the chiller condenser from the evaporator. It is transferred through a refrigerant that circulates permanently between the evaporator and the condenser and is forced by the compressor. The difference with this type of cooler is that a fan blows air over the condenser, which removes the heat. So in this case the chiller condenser was air cooled, so it is an air cooled chiller.

Rooftop Air Cooled Chiller

Air-cooled chillers are typically located outdoors because they need access to a large amount of ambient air to reject heat. This type of cooler can usually be found in medium to large commercial properties.

Air handling units and roof units

CTA and RTU

These two systems serve a very similar purpose and can look quite similar. Both are used to distribute air around the building and will contain fans to achieve this. Both draw fresh air from the room and clean it through a filter before heating or cooling the air to meet building requirements. The main difference between the two is how the air is heated or cooled and we will look at each one to learn the basics of how it works.

Air handling units (AHU)

AHU in the building

Air Handling Units are also called AHUs for short. AHUs are usually located inside the building, although they can also be found in technical rooms on the roof and it is increasingly common to find rugged and waterproof AHUs outdoors on the roof, to free up valuable space within the building. Its purpose is to distribute the air around defined areas within the building.

Sometimes one AHU powers the entire building, but it is common in newer buildings to have several smaller AHUs powering different parts to provide a better indoor environment and energy savings. AHUs usually do not have their own built-in cooling system, instead they will be connected to a central water- or air-cooled chiller, sometimes using some sort of separate air conditioning unit, and you can also find them connected to district cooling networks.