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

My first time looking at and measuring a DX evaporator coil was pretty intimidating. One of the first coils I encountered had four circuits (two intertwined and two face-split) with what seemed like a thousand capillary tubes, and it was installed at an angle. In reality, DX evaporator coils aren't more complicated than other types; they just have distributors that need to be considered during the measurement process. Still, I wasn’t sure how to price this properly.

There are several techniques to ensure accurate sizing and additional data from clients can help optimize performance. A coil schedule or any available performance data can be extremely helpful when dealing with space restrictions. These details also come in handy during the quoting process.

Although we usually visit a site only once per job for client convenience, there are times when we measure coils for budget pricing and plan to return later for more details. In these cases, especially when measuring multiple varying sizes of DX evaporator coils, there are certain variables that can always be counted on for quick and accurate pricing to the customer.

Before starting, get 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 face).

2. Next, measure the finned length, either at the top or bottom of the coil near the flanges (not the center). The tape should start and end 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. A critical factor in accurate pricing is the copper tube size (3/8”, 1/2”, 5/8”) and the number of rows.

Depending on the face area of a coil, over- or under-counting rows can make a big difference in the estimate. When I can access the end of the coil and see 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, where two u-bends might equal four rows. The number of circuits also affects pricing, which can be determined simply by counting the returns or distributors you see.

If you have access to all the above measurements, you’re ready to get an accurate cost without worrying about factors that could increase your costs and affect profits. Sometimes improvisation is needed, and that’s when it's crucial to know 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, and you can determine the CFM of the air handler (or assume around 350-400 CFM per ton), you can plug this data in to calculate the maximum number of ½" rows that can fit into a 5" casing depth. This will ideally bring back a capacity close to the 30-ton requirement, allowing you to proceed with the quote and consultation.

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