The Case of The Shocked Boiler

RayWohlfarth

This week's case, The Case of the Shocked Boiler, talks about how a boiler fails after only a few years. I hope you enjoy it.

https://youtube.com/watch?v=yDNDIUVTha4

hot_rod

Nice.
Curiosity would have me ask if the installation manuals showed any boiler protection piping options?

The Steam Whisperer

There is likely one other problem that contributed to the boiler failures besides cold shocking a hot boiler. The reverse is also true on multiple boiler systems... hot shocking a cold boiler. The 180F main loop water is pumped at full volume into a boiler that just turned on that is at room temperature. Again you have an 110F delta tee hitting the boiler. I am not sure if any of the boiler manufacturers are addressing this issue.

RayWohlfarth

@hot_rod The system had a blend pump which brought warm water into the return but I guess the amount of water in each zone was too much The building was six stories high and each zone covered a corner of the building. Thanks
@The Steam Whisperer Good point I always try making the downstream boiler as the lead and the upstream as the lag boiler, hoping to avoid that. Thanks

The Steam Whisperer

RayWohlfarth said:

@hot_rod The system had a blend pump which brought warm water into the return but I guess the amount of water in each zone was too much The building was six stories high and each zone covered a corner of the building. Thanks
@The Steam Whisperer Good point I always try making the downstream boiler as the lead and the upstream as the lag boiler, hoping to avoid that. Thanks

I would think installing a low limit control for the boiler pump ( assuming P/S piping) to hold the pump off until the boiler gets up to temperature would work with typical cast iron. For Mod cons and copper tube, it probably would be more complicated to provide shock protection. for a copper tube, I can picture a boiler loop pump that would run whenever the boiler is firing with a low limit limit control that would cycle on an injection pump when the boiler loop is up to temperature. For a modcon it would probably take a much more complex control logic that would use the same piping layout to provide the minimum flow for the boiler when its firing and use sensors to compare the system temp with the boiler loop temp to see if they are close before running the injection loop pump.

RayWohlfarth

Sounds like you had this issue in the past Thanks

EdTheHeaterMan

I just want to share with everyone that many of my old customers were SHOCKED when they found out I was not a Licensed Electrician

The Steam Whisperer

RayWohlfarth said:

Sounds like you had this issue in the past Thanks

I've seen a number of staged boiler failures that I think hot shock was a cause.

Long Beach Ed

Nearly every residential steam boiler in Brooklyn has a hot water baseboard loop piped into the base of the boiler. When its circulator turns on, a gallon of 60 degree water dumps into the base of a steaming 200 degree cast iron boiler. Yet, I've never seen one crack.

Why, Ray?

RayWohlfarth

@The Steam Whisperer I have never seen that but believe it could happen. Now I will be looking into that.

@Long Beach Ed I often wondered that myself but I believe the difference is the system I was talking about in the video was a hydronic and the one you are referencing is a steam system. I guess it's like when a boiler feed system injects feed water into a boiler. I saw a video once that shows what happens when water is injected into a steaming boiler. The boiler immediately stops steaming until the water warms up. That is why you see modulating feed water valves so the boiler keeps steaming. Thanks for watching and hope this helps

RayWohlfarth

@Long Beach Ed Here is the link to the old video that shows what happens when water is injected into a steaming boiler.
https://youtube.com/watch?v=tI3tWuSsX7c

Long Beach Ed

Thank you, Ray!

RayWohlfarth

welcome @Long Beach Ed

The Steam Whisperer

Thermal shock is not just temperature dependent, but flow dependent. Lots of cold water going into a hot boiler is a problem. Lots of hot water going into a cold boiler is a problem. Well balanced 2 pipe steam systems (especially orificed systems) with high mass radiation typically have returns at room temperature nearly year round. However, there is only about 1/50th the water flow as a hot water system. These returns temps are well into the condensing range all winter, but boiler condensation is usually not a problem, unless you have a top fired boiler.

RayWohlfarth

@The Steam Whisperer Your going to have to change your name to the The Steam and Hydronic Whisperer LOL Thanks