2-stage gas valve control - pressure or temperature?

PCapNJ

Hello Strictly Steam - longtime lurker here learning a TON from the books and discussions and now that I no longer have a commute, I have some spare time to dive in and tinker/improve my system. I bought my home 7 years ago and through research here found a local contractor to fix my near boiler piping from copper to a 3" drop header, vent my mains, and install a 2-stage gas valve (thinking I would save $$).

The contractor has since retired and the system is working well, but now I'm investigating to see if I can make it work more efficiently. Currently, my system is generating ~1oz of pressure through the cycle thus not activating my low fire. High fire is set at 6oz, then should go low fire until 2oz, and so on until demand is satisfied. I tested this on the benchtop with my pressuretrol (Honeywell) and vaporstat (Honeywell L408J1009)

Did I "overbuy" with the 2-stage gas valve? Is there a way to make it work using temperature instead of pressure (aquastat?) since lower pressure = good for steam systems?

My boiler is Mclein EG-45 that should generate 392 net steam and my radiators are 331 total EDR. 2 Gorton #2s on my main, then another at the end near my wet return (parallel flow).

Any thoughts are appreciated!

Jamie Hall

Not really, if it's all steam. It sounds as though you have managed to get lucky and come up with a system which just doesn't generate significant pressure during a normal run. Does it get to the 6 ounces during a very long run -- say you go wild and give it a 8 degree setback or something?

If not, I can't see that the two stage gas valve will gain you anything at all. Sorry about that...

PCapNJ

Yea, that's the crazy thing - on a really long setback, it stays very low... MAYBE getting up to 2-3oz at best. Which if I'm thinking correctly, means that the steam is being generated at a similar rate in which its condensing.

I see the pressure "breathe" a bit going to 2oz then back to 1oz but that's about it. I was wondering if I had a unicorn or not.

I previously thought to slow my venting at the rads to potentially generate some pressure, but learned in recent conversations that's wasting more gas/energy than running low pressure... since my system can do it. Am I thinking correctly?

Jamie Hall

Yup. If it stays low like that, sit back and enjoy!

mattmia2

Just make sure it isn't not generating pressure because it is leaking. How much water does it use?

EBEBRATT-Ed

I agree with @Jamie Hall
Leave it alone!!! Sounds perfect as is.

PCapNJ

mattmia2 said:

Just make sure it isn't not generating pressure because it is leaking. How much water does it use?

So I have a leaky drain valve that I need to fix before I can accurately observe my water usage.

I did artificially add pressure to the system (bike pump) while flipping my rad vents upside down and it held 6oz just decently but helped me find two stem leaks that I also have to fix. I was worried my boiler was cracked, but I'm 99% sure it's not the case.

dabrakeman

Just curious. You have a "continuation of the main" that comes back to the boiler and ties into a vertical that drops down into the wet return? You have a main vent there as well as at the end of the true main/mains? If so just thinking maybe you don't need the main vent back at the boiler and would be better off adding it to what you already have at the true ends of the main/mains. Unless there is a trap at the end of the main the vents back at the boiler just extend the time before steam starts getting to the radiators. Sounds like your system is working pretty good though. Do you do significant setbacks (~4+ degrees) or just run nearly constant stat temperature 24hrs?

PCapNJ

Thanks for the curiosity! I'm in the process of drawing up my setup as I'm curious about the decision on venting - it'll be more clear once I do that and share it. I do a 2 degree setback at night, but would want to kick up the daytime temp now that I'm home a lot, so trying to think of ways to make the system more efficient.

No traps, simple 1 pipe system with two mains, one 1.5" that feeds 2 radiators (counterflow) and the 2" main that feeds the rest (parallel). I'll likely start a new thread to separate topics and focus on feedback on my main venting overall.

My fear was that the 2-stage burner was overkill and wish I had studied more before making that decision, but you live and learn!

motoguy128

IT would work better if you have TRV’s to zone some areas and cause the system pressure to rise, and save energy by not over conditioning some spaces. For example, a spare guest bedroom or a kitchen and/or dining room (that might overheat when cooking or guests)

Jamie Hall

If you do use some TRVs, that will -- as @motoguy128 says -- cause the pressure to rise, and it might rise far enough to trip over to low fire -- which would save some gas. Make sure your low fire trip point is low enough, though!

motoguy128

The TRV’s will also cause the other radiators to heat up faster which may cause the thermostat to satisfy sooner, also, still saving heat.

Pressure normally only rises once vents close when a radiator fully heats. Another thing to watch for is radiators heating too fast because of too fast of vents. If steam fills a radiator too fast it mixes with air and doesn’t get as hot, thereby consuming less steam, whcih can increase pressure. This is why in some cases, slower radiator venting will actually LOWER steam pressures. It’s also why venting the main fast is so important, you need steam to get to the radiators as soon as possible to be consumed, then to fill up nice, slow and evenly.

Friction in the steam main is only <1”, so most pressure is created due to the rate steam is consumed compared to steam generation. It reaches equilibrium when the venting rate increases enough to consume the steam as fast as it’s made.