A Second Look at Cycle-rate Controls

THE PHONE CALL: A regular customer of our supply house was on the line. I talk to him or one of his two brothers at least once a day, as they put in many commercial boilers every year. Recently, he added a cycle-rate control to a steam system at a large apartment building owned by two brothers. When we met these brothers two weeks before, it wasnt hard to see that they were as different as night and

THE PHONE CALL: A regular customer of our supply house was on the line. I talk to him or one of his two brothers at least once a day, as they put in many commercial boilers every year.

Recently, he added a cycle-rate control to a steam system at a large apartment building owned by two brothers. When we met these brothers two weeks before, it wasn’t hard to see that they were as different as night and day.

One (Silk Suit) wore a blue silk suit and kept his hands clean, while the other (Work Shirt) wore a blue work shirt and kept his hands busy. One wanted a new boiler control installed, while the other thought the existing control was just fine.

My customer had wanted me to see the original control system that Work Shirt had jerry-rigged. It was a jigsaw puzzle of toggle switches and radio dials with a handwritten chart to indicate the position of each for every possible winter temperature.

This was quite a piece of work. However, Silk Suit wanted it replaced with an electronic control that didn’t require near constant manual adjustment, which is quite a lot of work.

I recommended a cycle-rate control based on the size of the boiler. I feel that any steam system more than 500,000 Btuh will operate more efficiently with that type of control.

Silk Suit had my contractor customer install the control over the protest of Work Shirt. Now my customer is telling me the new control isn’t working properly and some tenants are complaining of cold radiators.

Work Shirt is pointing out that his controls had always worked fine before. Silk Suit is pointing out that the new control isn’t working as advertised. Since I sold the control, I was now in the doghouse. We arranged a second site visit.

The troubleshoot

Cycle-rate steam controls are designed to provide both comfort and efficiency. They automatically adjust the run time of the boiler in relation to the outdoor temperature. As it gets colder outside, the run time increases. They can be fine-tuned to the building’s heat loss characteristics, geographic location and the owner’s willingness to pay the utility bill. The point sometimes overlooked is that the system has to first work properly.

The 1920s-era, horseshoe-shaped building surrounds a wide courtyard. The boiler, which originally was coal-fired, is tucked into one corner. This makes the length of the supply mains quite different. The cold apartments were as far away from the boiler as possible, on the top floor off the longest steam main.

The obvious suspect with one-pipe systems is venting. Many experts before me have stressed the importance of steam main air removal, especially after a coal-shoveled to automatic-fired conversion. Coal fires were slow to make steam. The air had more time to get out of the mains, so steam distribution was more even.

Automatic-fired boilers make steam much faster, quickly forcing air to the end of the main. Somehow Work Shirt was able to simulate a slow coal fire with his positioning of the switches and dials. Heck, he had years and years of hands-on experience to find the right combinations. The cycle-rate control appeared to be working fine, so I suspected the venting wasn’t up to the task.

We walked from the boiler room to the end of the longest steam main. I wanted to see how much venting was installed. We found just one small vent at the end of 200 ft. of 6-in. pipe. The customer and I calculated that it could take as long as 10 minutes to get the volume of air in the main through the port of the existing air vent. That’s way too long.

The follow-up

The problem was the boiler cycling off before the air was out of the end of that longest main. Steam didn’t distribute to the end of that air-filled main. Without steam to the end of the main, no distribution occurs in the last risers or radiators.

After explaining the problem to the brothers, they agreed to update the venting. It may have been the first thing they agreed upon in years. I selected a combination of vents that would relieve the volume of air out of each main in about two minutes.

At this new air-venting rate, steam now makes its way out to the ends of the main well before the cycle-rate control shuts off the boiler.

Now there are no more cold radiators. The tenants are happy with even steam heat throughout the building. Silk Suit is happy with his modern control and lower operating expense.

Unfortunately, Work Shirt isn’t happy because his brother got his way.

Fortunately, my regular customer is happy because he didn’t have to replace the new control.

Me? I’m happy when systems work right. It keeps me out of the doghouse.

Patrick Linhardt is sales manager at Aramac Supply in Cincinnati. His book is “Linhardt’s Field Guide to Steam Heating.” To order, visit steamupairoutwaterback.com or call 513/703-5347.