Superior Performance for Mission Critical

Continued from page “37” connecting the boiler to the nine-station manifold, we can apply Holdorf’s trick. The trick involves converting the longest pipe length into a developed length and then converting it to head loss. While Holdorf likely didn’t originate this method, he taught it to me.

For our example, the 20 ft. of copper pipe is multiplied by 1.5, resulting in a calculated length of 30. The 1.5 accounts for a worstcase scenario considering the fittings in the system. Multiplying this by 0.04, which represents four-ft. of head loss per 100 feet of properly sized pipe, gives us a final head loss of 1.2 ft. for properly sized pipe. If you were to calculate the actual head loss for 5.4 GPM flowing through a three-quarter-inch copper pipe, you would get 0.7 ft. of head, but this doesn’t include all the fittings yet.

This straightforward rule of multiplying the total pipe length by 1.5 to obtain an equivalent length with fittings, and then

But since we assumed there was no specific design in our case, let’s apply the method again. We mentioned that our longest radiant boiler, three-quarter-inch header piping, and 2,660 ft. of half-inch PEX tubing. Additionally, we need to deliver 5.4 GPM at a head loss of 12 ft, which requires a pump capable of meeting these specifications.

The key takeaway here is not to completely ignore CAD and proper design, but rather to be open to applying effective rules of thumb to quickly assemble a material quote and estimate for a radiant floor system. These rules of thumb also come in handy when troubleshooting a system. : multiplying it by 0.04 to calculate the equivalent head, is an effective method for estimating head loss. If you perform a proper calculation of the head loss, you will find this method to be accurate. floor circuit is 300 ft. long. Since we don’t have any fittings to account for (as it is impractical to use 10-foot lengths of PEX cut-offs for a floor), we can multiply the length by 0.04 and obtain 12 feet of head. For the purposes of this article, I actually designed the radiant loop using CAD software, and after all calculations, I determined that the total load was 54,375 btu/h, with a flow rate of 5.46 GPM and a total head loss of 10.1 ft., including the header piping and the radiant floor tubing.

However, there is a slight flaw in the above calculation. The math we just performed is for the pipe leading to the manifold, and I did this intentionally for demonstration purposes. Usually, when we have a radiant design, we only need to calculate the piping head loss to the manifold, not the total head loss in the floor.

We now know that we need a 54,000 btu/h

Michael Ridler is a technical services manager at Eden Energy Equipment. He started out working for a Ont-based HVAC company and now focuses on providing field support and technical training to contractors, engineers, and builders on heat pumps, boilers, and all things hydronics. He can be reached at edenenergymike@gmail.com

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