What's this sudden change in radiator to condensate temperature relationship mean?

ariccio

Tonight I noticed something a bit different on the data logger, so I pulled the data, and sure enough, the pattern changed around 4pm:

Whereas before the condensate temperature would slowly approach the radiator output temperature (before eventually tracking), now it's started spiking up faster than the radiator outlet temperature. What the heck is this? Steam coming backwards through the returns?

delcrossv

Bad trap?

ariccio

Hmm. I wonder if it happened to go bad just now - lemme see if I can tell when the boiler fires next. Glad I didn't put the stethoscope away!

mattmia2

either bad probably main trap or the boiler is surging or priming and liquid water from the mains is heating the returns

ariccio

I'm learning an awful lot. I've listened into the trap many times over the past week and I'm not quite sure if it's leaking or if it's failed. It's not quite clear with the stethoscope, I can hear a faint whistle but it's certainly not an obvious hiss like it is on a few blown traps I've listened in on.

There's no "main" trap on this two pipe vacuum steam system thankfully, but what does surging or priming mean exactly? I know that surging can mean the water level in the boiler fluctuates wildly, but where does that mean it goes? Not sure what you mean by liquid water from the mains… unless you mean steam that's condensed in the mains and been flung through the radiator instead of down a drip trap?

The most interesting thing so far was the few very cold days over the weekend when the apartment (and some other apartments) were very uncharacteristically cold. I kinda wonder if it has to do with people elsewhere actually turning their radiators on for once. An interesting pattern showed up in the early morning hours for two days that I don't know what to make of:

You can see how different it is, not catching up to the supply temp there! And the rad out + condensate temps still eventually converging. I'm not sure what to make of that. The radiator stalled (steam bound?) from steam in the returns? Or just very little steam reaching this radiator?

ethicalpaul

This is surging/priming. It is boiler water getting thrown into the mains and possibly into radiators.

https://youtu.be/WSRvvNQ5WLc

mattmia2

Surging is water being thrown out of the boiler as a liquid because there is a film of oil on top of the water and stem is having trouble emerging from the surface of the water so it suddenly erupts as a burst instead of gently leaving the surface continuiously.

Priming is the water in the boiler foaming because of the water chemistry usually involving having detergent added to it.

Both will cause liquid water to be thrown in to the mains from the boiler instead of just mostly steam with a few droplets of water. The water will tend to collapse the steam and will corrode the steam mains over time.

mattmia2

What does the temp look like on different parts of the radiator. Is it heating the space adequately? Looks like there isn't enough steam to completely fill the radiator or the cycle ends before it completely fills the radiator which ideally is what you want as long as it heats adequately.

ariccio

I don't have a way to datalog the temperature gradient across the radiator more than these three data points.

That one weird morning of the 14th the apartment was unusually cold!

ariccio

I've been thinking about this for a few days, how does this "stall" the radiator like I observed? I'd assumed the water would just get purged through the traps?

Sidenote: I've seen cool sight glasses like that on McMaster-carr, but I didn't see one that looked like it had enough durability to trust 😒

mattmia2

the liquid water cools the steam and collapses it in to water so water in the mains kills the steam. it also usually causes water hammer when it collapses.

ethicalpaul

it's plenty durable, and stainless. It will outlast me and the other pipes.