Airside Economizer HVAC


Economizers play an important role in determining the energy efficiency of your building. This makes them an integral part of the HVAC system. In areas with a temperate climate like California, economizers can reduce AC energy consumption.

Regardless of their importance in HVAC systems, economizers are still misunderstood. Also, in most buildings, they’re either misapplied or operating poorly. In this guide, we’ll share with you everything you need to know about Airside economizers.

First, let’s describe what an airside economizer is!

What’s an airside economizer?

As the name suggests, an economizer is a mechanical unit that saves energy. ASHRAE defines economizers as devices that initiate control actions to conserve energy. Note, ASHRAE stands for the American Society of Heating, Refrigerating & Air-Conditioning Engineers. For these definitions, it’s clear that the primary goal of an airside economizer is to save energy. To accomplish this, an economizer utilizes a damper fitted with a motorized actuator. Also, it has a controller that includes temperature sensors.

Types of economizers in HVAC units

There are 2 types of economizers in the Heating, Ventilation & Air Conditioning industry. They include; water-side and airside economizers.

HVAC units of all uses use airside economizers. On the contrary, large commercial HVAC systems use water-side economizers. In this guide, we’ll focus on airside economizers since they’re the most common.

Note, in the HVAC industry, an economizer refers to sensors, controls, and dampers. But technically, an economizer only refers to the HVAC components and the controller. In this article, we’ll refer to the former. That said, let’s look at how an economizer works!

How an airside economizer operates

To understand how an airside works, you need to know the basics of the HVAC system design. Most buildings with 10,000 to 100,000 sq. ft. are cooled by RTUs (Rooftop Units). There is a good chance your building uses this type of system, especially if it’s below 50,000 sq. ft. This information is essential since some HVAC systems cannot apply economizers.

Generally, HVAC systems utile the refrigeration cycle. This involves recirculating air through the building to remove heat. The main component of the refrigeration cycle is the compressor. This device requires some energy to cool the air. Instead of cooling air with compressors, it brings in outdoor air that’s already cool.

The Basics of Air Movement

It’s important to understand how air moves through rooftop units. One reason for this is that, with economizers, the air is dynamic. In this case, air movement refers to the amount of air leaving and entering the rooftop unit. That said, there are certain terms you’ll come across in air movement. They include’ exhaust air, mixed air, return air, outside air, and supply air.

Airside Economizer Components

An airside economizer consists of various components. These components work together, ensuring the economizer operates effectively. They include;

1. Mixed Air & Outside Air Temperature Sensor

This sensor determines the decision of the controller. It measures the temperature of the rooftop unit’s mixed air and outside air.

2. Controller

It reads the temperature and tells the actuators to close and open. For that, it’s considered the brains of the entire operation.

3. Actuators

A motorized actuator is an electromechanical device. It obtains a signal from the unit’s controller. The actuator then commands the damper to close or open. Usually, an RTU has 2 motorized actuators. One is for the return air, while the other one is for outside air. However, small economizers have 1 motorized actuator.

4. Damper Assembly

This is a set of sheet metal blades that close and open. It’s the component responsible for changing the amount of airflow.

Airside Economizer Airflow

Advantages of installing an economizer in your HVAC system design

As we stated earlier, the main benefit of economizers is to save energy. Ideally, the outside air damper prevents the compressor from working as hard when it opens up. This leads to significant energy savings. Better still, you can quantify the financial savings linked with these energy savings. Besides, this plus the total project cost makes it easy to calculate the ROI (Return on Investment).

Moreover, airside economizers improve the building’s indoor air quality. These devices dilute contaminants like VOCs and viruses with fresh air. This makes them one of the best ways for enhancing indoor air quality.

Drawbacks of Economizers

Even though economizers offer various benefits, they’ve their drawbacks as well. For instance, they’re susceptible to breaking. Another issue is that the damper assembly may get stuck. Moreover, the controller may experience incorrect programming. On top of that, the rooftop unit may be affected by compromising conditions. All these factors cause the unit’s energy consumption to skyrocket.

Thankfully, you can mitigate these downsides. To accomplish this, you can adopt a technology known as Fault Detection & Diagnostics. This is a system that alerts the property manager when the device is malfunctioning. Alternatively, you can contact an HVAC contractor to resolve the issue for you.

Code Compliance

In California, Title 24 requirements apply to all economizers with more than 4.5 tons. If your house has more than 10,000 sq. ft., there is a good chance you’ve RFUs exceeding this threshold. Units below the 4.5-ton threshold are known as ’residential units. In most cases, such units cannot economize.

This compliance only applies when you’re replacing HVAC units /renovating the building. So, if your building doesn’t have economizers at the moment, you aren’t out of compliance. However, if you decide to replace the HVAC units, you need to submit the permits. Otherwise, your facility will be non-compliant.

Luckily, no authority comes around to check if your facility meets the energy code. Nonetheless, it’s good to ensure your building complies with the necessary measures. This includes things like installing economizers. Doing so will cut your utility bills. Also, it will enhance indoor air quality and the equipment’s performance.

Final Word

Most building owners overlook the implementation and selection of airside conditioners. Yet they can help them to lower energy costs. Also, economizers can enhance indoor air quality. Even better, they add tremendous value to the building and extend the equipment’s lifetime.

Before you install an economizer, determine if your HVAC system design can implement it. Or contact Innodez Design and Engineering. Our HVAC experts will help you choose the fit airside economizers for your facility.

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