Measuring DX Evaporator Coils For Pricing: In the field with Chris Wright

My first time measuring a DX evaporator coil was a bit overwhelming. The first one I encountered had four circuits—two intertwined and two face-split—and it looked like there were a thousand capillary tubes. Plus, the coil was installed at an angle. In reality, DX coils aren't any more complex than other types of coils; they just have distributors that need to be accounted for in the measurement process. Still, I wasn't sure how to price it competitively.

There are several techniques you can use to ensure accurate coil sizing, as well as additional data from clients that can help optimize performance. Having a coil schedule—a chart showing estimated performance and capacities based on input specifications—or any available performance data can also be useful when dealing with space constraints. This data is especially helpful during the quoting process.

Although we usually only visit a site once per job for the client's convenience, there are many situations where we're measuring coils for budget pricing and know we'll return later for more details. For these cases, especially when measuring a large number of varying DX evaporator coil sizes, there are certain variables you can rely on to quickly and accurately provide pricing to the customer.

Before you start, download a free blank coil worksheet to record your measurements.

1. Measure the finned height, from the top to the bottom of the fins on one end of the coil (not in the middle of the coil face).

2. Next, measure the finned length on the face, either at the top or bottom of the coil near the flanges (not in the middle). Ensure the tape measure starts and ends inside the end flanges.

While on the face, take the fins per inch. You can do this by counting the number of fins between 2” and 3” on the tape from left to right.

3. Moving on, a key factor in accurate coil pricing is the copper tube size (3/8”, 1/2”, 5/8”) and the number of rows.

The number of rows can significantly impact the cost estimate. When I have access to the end of the coil that exposes the U-bends, I count the rows by determining how many tubes come out of the end plate from left to right. This can sometimes be confused with the number of U-bends, as two U-bends could equal four rows. The number of circuits also affects pricing, which can be determined simply by counting the returns or distributors you see.

When all the above measurements are accessible, you’re ready to get an accurate cost without worrying about factors that might increase your costs and affect profits. Sometimes improvisation is needed, and that’s when it becomes crucial to learn what additional performance information the building can provide. For example, if the U-bends on an evaporator coil aren’t visible from either end, you can use the casing depth and condensing unit capacity to estimate the number of rows. If the casing depth is 5” and the condensing unit is 30 tons, you can calculate the maximum number of ½” rows that fit in 5”. Using this data helps you determine a capacity close to the 30 tons required, allowing you to proceed with the quote and consult with the customer.

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