Higher pressure in colder weather

ToddB

We are experiencing the first cold weather (low 20s during the day and single digits to low teen overnight) since I installed the low pressure gauge. To date, with daytime temperatures in the 30s and overnights in the 20s, I have found that I generally run for 18 minutes per hour at a maximum pressure of 0.05 psi. This week I have been running a bit longer (18 to 20 minutes) every 42 minutes. I have also found that the pressure is significantly higher (0.8 to 1.5 psi depending upon run time). In warmer weather the radiator vents do not generally close. Now they are closing and that is when I am seeing the pressure rise.



is this change in system operation simply due to the radiator vents closing?

Paul48

Comfort

That is how it works. With all the vents closed the system will build pressure.Your cycle time sounds good. Is everything heating evenly,no banging, and is the house comfortable?

Dave in QCA

Normal operation

Your observed pressure of 0.05 psi, or about 1 ounce is optimal condition during the partial steaming of your system.  In mild weather the system cycles are not long enough to fully heat the radiators and so you never reach a fully steamed condition.  As the weather gets colder, the steam cycles last longer and you get to the point that the radiators are filled with steam, all air has been vented, and the vents close.



Two things change at this point.  First, there is no more air to be vented and so the vents close, causing pressure to build up.  Second, and even more important is that at this point, there is no more cold cast iron condensation huge amounts of steam.  Now, while the condensation rate in the radiators is still very significant because it still takes a large amount of steam to maintain the temperature, the amount of steam being condensed decreases.



When the system's capacity to take steam from the boiler has reduced, the pressure will begin to rise.



High pressures are seldom necessary on domestic steam heating systems.  Since your system is getting even distribution to all radiators on the cycles with about 1 ounce of pressure, you already know that the system works great at those very low pressures.  If you want to save some money, you might turn down the pressure.  The pressuretrols are never accurate to the scale or dial.  You just about have to tinker with to find a point where the boiler shuts off as the pressure rises, yet comes back on as the pressure drops.  If you adjust it too low, it won't come back on at all.   Of course, a Vaporstat is excellent for low pressure operation.

ChrisJ

efficiency

This may be a dumb question but how does cycling a burner effect the boilers efficiency.



Meaning if you shut the burner off at 0.5PSI and fire it back up at some low pressure, and do this repeatedly, would it use more or less fuel than letting it run continiously at a slightly higher pressure?

ToddB

Yes...

the house is heating evenly and is comfortable. I find that the only noise that I have is expansion/contraction at two risers in contact with the floor. This happens even at higher temperatures and I need to address that. Some of the Gorton 1 main vents spit very slightly (two out of eight on two mains).



I have noticed that the condensate return is generally slow, but with a "normal" off cycle of 40 minutes or more it all comes back. With the shorter off cycle not all of it comes back, but the boiler operating water level does not drop. I am going to have the wet return looked at in the spring and have a drain installed.

ChrisJ

milk bottle

Cut some strips of plastic out of the side of an empty milk bottle and wash them.  Then put them between the riser and the floor where its rubbing.

ToddB

Thanks...

I have read that will work, but I have a rope saw or Dremel that I was thinking of trying to make the hole larger. They are first floor radiators and I have good access. At one location the riser is tight enough to have cause the wood to locally distort upward.

Paul48

Think of it this way

You had the boiler making steam. Now you shut it down and let it cool slightly. That's wasted energy. On the same priciple that a mod/con uses...once you have the water at a temp., it is easier to keep it there. It all starts with sizing, and having everything proper in the system.

ChrisJ

steaming

Hi Paul,



True, but as the pressure drops the water will continue boiling.  To me, this suggests it never stops as long as you fire the burners back up before the pressure completely drops.

Paul48

True

But boiling water does not necessarily mean steam. I may be wrong, but I believe it takes 5 times the btus to create steam, and that is the latent energy that you get heat from.If you think about, you know it's true because the pressure is dropping. Energy is being lost.

ToddB

If...

the maximum pressure that I am reading is 1.7 psi and it is running for about 2 minutes longer than it does during warmer weather, does it make any sense to readjust the pressuretrol (now set at 1.5 psi cutout)? I don't think so. I have noted a pressure rise from 1.0 psi to 1.7 psi in those last two running minutes.

Paul48

Same ...Only Different

Could you get the same results with 5 minutes less burn time, by increasing main venting.That's 20-25%. Just tossing that out. And, no, I don't see issues with the pressure.Maybe 5 minutes is unrealistic. How about 2 minutes, or 10%. That's money back in your pocket.

ToddB

Not sure

I probably can't drop the run time by 5 minutes and I don't think that I would want to. Right now the main vents typically close at 3 minutes. Both mains are about the same length so steam hits the vents at the same time. I am using four Gorton 1's on 30' long, 2 1/2" diameter mains. I went with the 1's because they fit nicely in the floor joist bays - the 2's are just too large and close to the subfloor.



I had read that a 20 minute continuous run time was good and that anything less was considered inefficient. I do not know the reasoning for the 20 minutes, but I thought that my run times were not too bad.



My only real concern at the moment is combination of the slow return of condensate and the short off cycles.

Paul48

Pressure

Are you shutting down on pressure?

ToddB

No

No, not even when it hits 1.7 psi does it shut down on pressure. I guess that the pressuretrol is not accurate as we already know. I never have had the pressure come up to this level before as I mentioned.

Paul48

Well

Then the short off cycles can only be cured by tightening the envelope.

ToddB

That makes sense

The house is brick and stucco and has the original double hung windows and plaster walls. The exterior walls appear to be uninsulated. All is in fantastic condition for the age (built in 1928) and the house has historic significance by association with a famous painter, so the likelihood of making any major invasive changes is slim. The windows do have decent storms, but even those cannot stop all of the drafts.



Thank you for helping this make sense.

SWEI

Envelope upgrades

which don't break preservation standards are entirely do-able for most every architectural style and era.



Finding appropriate professionals in major metros and high-dollar tourist destinations is difficult.  For the rest of us, it's bloody impossible.

Dave in QCA

Like finding a Steam Pro

Finding competant and qualified professionals who know how to work on historic buildings is similar in difficulty to finding a qualified steam pro.  The first challenge is knowning what you're looking for.  Once you know that, you begin the search and it is always amazing to discover the talent that is out there.

Paul48

House

Is it on any Historic Registry?