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A question on steam venting
I have been a loyal reader of Dan Holohan’s interesting engineering articles. One question was raised with reference to his column in Plumbing & Mechanical’s January 2012 issue (“Where there is air”). In steam design applications, doesn’t the end of a steam supply line terminate with a drip-and-trap assembly that connects to the condensate return line? Not an air vent. Venting of steam to the atmosphere only occurs from a discharge of a safety steam relief valve or a steam condensate collection tank, correct?
Tal Rabiah, P.E.
Fountain Hills, Ariz.
Dan’s response: Thanks for reading me, Tal. Many steam-heating systems have gravity returns and not condensate pumps. When these gravity returns are below the boiler’s waterline, there’s no need for a trap at the end of the main, but there is a need to vent air from the main, and that’s where the main vent comes in. If that doesn’t make sense, ask me more.
Measuring pH in the nick of time
Dan Holohan’s February 2012 column ( “The power of hydrogen”) was great timing. I picked up the service at a school which includes various systems, boilers, etc. We have a problem at the main school building. It has two natural gas steam boilers, low pressure, at a full firing rate of about 910,000 Btu each. We have been repairing the obvious leaks throughout this season, and have determined there are significant leaks in the condensate piping in the concrete floor/slab.
This line handles a good portion of the school. We are using high amounts of make-up water and the No. 1 boiler has developed a section leak right above the flame detection rod, lower left front.
The sight glasses are showing heavy signs of brown, muddy-looking debris, especially on the No. 1 boiler that is leaking. The leak is minimal and at times almost nonexistent while it is in operation. It usually appears during long shutdowns. I am sure the raw make-up water has caused this leak.
After reading this column, I am going to measure the pH and install a water meter on the make-up water line.
Michael J. Tucci
Ruane-Tucci Plumbing, Heating & Air Conditioning
More contractor envy of European coils
I am writing in response to an article written by John Siegenthaler regarding the small size of heat exchangers in American-manufactured indirect fired water heaters or domestic hot water tanks (“Coil envy,” December 2011).
I had always been unimpressed with the coils in the U.S.-produced DHW tanks. They typically have small diameters with ribbing on the wrong side of the heat exchanger. Calcium carbonate can deposit there and create a near-zero delta T across the supply and return lines to the coil. The coil is unfortunately placed near the bottom of the tank, requiring very hot boiler water to heat the volume of water above it.
We have used Buderus DHW tanks almost exclusively (and some Viessmann models) for about 16 years now with very little trouble. The ST/300 and ST/400 tanks are no longer available to us here in America as they have been replaced with SM tanks with dual coils — great for solar backup or geothermal.
I sincerely hope that some American manufacturer can produce a well-insulated (3-in. or more) tank with smooth, large-diameter single coils on smaller tanks and dual coils on the larger tanks, where the coils are spread throughout the tank for good heat transfer, as well as provide a “manhole” for cleaning. This DHW tank design is what we are accustomed to installing, and we have not had troublesome calls for insufficient DHW on our typically large home installations.
George’s Plumbing & Heating
Amen, John! It seems that we will always be behind the Europeans! We also seem to have to react to a situation instead of being proactive for future thinking. Keep up the great work and writing.
Joseph A. Lucchesi, P.E.
From socks to boilers
I just wanted to state a different view than what Dan Holohan wrote in his December 2011 column (“The work”). Many and maybe most economists would support a worldwide division of labor where everyone is doing what they are best at.
Dan pointed out in his column that people who used to make socks are now doing something else, such as making boilers. This does not “leave behind lots of Americans who can no longer afford to buy things such as socks.”