A Fan Retrofit Requires Planning And Measurements To Make The Best Selection

When considering a Q-PAC Fan for a fan retrofit, there are a few things that need to be determined before the selection process starts. The type of air handler, the existing fan technology, the operating envelope, and the control system in place are critical to understand before a Q-PAC Fan can be configured. To best evaluate the sizing and configuration of the fan, follow these steps:

1. Determine the type of air handler

2. Evaluate the current fan and operating space available

3. Measure performance point

4. Use the Q-PAC Configurator to build your fan based on the measurements

Assess Your Air Handler

Determining the type of air handler is important as it will determine how much space you have to install the fan and will give you insight on the available external control options. When replacing a fan in a traditional packaged or unitary AHU, the fan section usually has distinct maximum dimensions. The Q-PAC Fan is designed to fill the entire aspect ratio of that fan section. This means that once you have measured the internal wall-to-wall dimensions, those same dimensions will be used for the fan measurements.. When the AHU is a Built-Up air handler - meaning the AHU is an entire room or part of the building - there may be no clear fan section. You may have more freedom to expand the dimensions of the Q-PAC Fan to fit the space you have.

Evaluate the Operating Space of the Fan

The Q-PAC Fan is designed to eliminate the need for a custom bulkhead wall. It’s Fan Frame takes up the entire cross sectional area of the airstream, so no custom sheet metal work is required in most cases. The Q-PAC Fan can mount into a cutout of a bulkhead wall if needed, but was designed to eliminate that need. If the fan being replaced did have a bulkhead wall (like a centrifugal blower), it is recommended to remove existing bulkhead and size the Q-PAC Fan to the internal walls of the AHU. When taking the measurements, the wall-to-wall dimensions are used for sizing the Q-PAC as there is a tolerance built into the product to account for minor deviations or imperfections in the mounting surface.

A common oversight is that the Q-PAC Fan sizing on QUIPS includes a 0.5” tolerance baked in! You do not need to account for any clearances when taking measurements. Another oversight is the Q-PAC Fan’s internal controller can be on the left or the right of the fan frame to make the conduit run shorter depending on where the incoming power is on your unit. Double check that your handing is correct when selecting the controller location. Left and Right would be determined with air hitting you in the face, not the back of your head!

Measure the Fan Performance Point

For determining the performance point you need, its best to use the design point that would live on the AHU’s submittal. If that original design point isn't available, it is possible to estimate the operating point based on the existing fans information, assuming that the fan was able to meet the required duty before replacement. Below are the equations that can be used to get the estimated CFM and TSP.

CFM = (W × H ÷ 144) × 500

TSP = (Existing Motor HP× 6356 × 0.65) ÷ CFM

Selecting Your Fan

Now that you have the dimensions and the operating point, you can use our online selection tool to input your requirements and instantly get the correctly sized fan. The only other requirement is the voltage which should be on the existing motor’s nameplate or listed on the AHU. If you are unsure of what configuration to pick, you can contact our team and we can provide a Q-PAC recommended option. That option will be the fan with the lowest upfront-and-operating cost over 5 years, while also meeting a minimum resiliency value. Resiliency is the percentage of airflow that can still be maintained with a single motor failure.

Once you have a fan selected, you need to select which control option is best for you. If your air handler already has a control panel with a 3 phase power supply output and a 0-10V analog speed signal output, you may not need any additional hardware from Q-PAC. If you require BACnet connectivity or other features like local speed control, Hand-Off-Auto functionality, you would need to also get the external control panel that Q-PAC offers. The details on those can be accessed from the resources section on q-pac.com.

With a fan selected, you will have access to the specific drawings with dimensions, the submittal and quote, as well as the user manual for the product.