Calculating steam pressure

JBFBMech

I am working in a school that is running at 7 psi. I feel like the pressure is way too high. The boiler is 3,733 EDR and the steam main is 6”. What other information do I need. I don’t want to turn down the pressure and then they start having issues. We don’t service the boiler only the piping.

pecmsg

You need the Design Data from the original plans!

Was it designed for less then 5#'s 5, 15, 30# steam

Ironman

If you have only CI rad's on the system, the required pressure should probably 2 psi or less. But, if you have AHUs, heat exchangers, etc., more pressure may be necessary.

If you're not having any issues, I wouldn't touch it until it could be confirmed how much pressure is needed.

The old saying: "if it ain't broke, don't fix it".

JBFBMech

Some cast-iron radiators. Mostly convectors. There are no heat exchangers. Most of the convectors have actuators that operate off of compressed air. But I don’t think any of those are still operational. The biggest complaint they have is uneven heating. They would probably never let me change it anyway I was asking more for my own information. I would think it would save a lot of money to run at 2 pounds.

ratio

Improper operation is a hallmark of not operating the system the way it was intended to operate. You'd think more people would understand that.

Tell them to get someone in there who understands steam to take a look at it. A few pics posted here will get you a good start on figuring out what's going on. It's nearly always cheaper to repair than replace.

pecmsg

What do they have for Hot Water?

JBFBMech

Just a 50 gallon gas natural draft water heater.

JBFBMech

“Improper operation is a hallmark of not operating the system the way it was intended to operate. You'd think more people would understand that.
Tell them to get someone in there who understands steam to take a look at it. A few pics posted here will get you a good start on figuring out what's going on. It's nearly always cheaper to repair than replace.”

No one is looking to replace anything. I understand steam. A system this size is not what we typically work on. I was just asking the question to see if I could help them or not.

STEVEusaPA

Ironman said:

...
The old saying: "if it ain't broke, don't fix it".

I like,
"If it ain't broke, you can't fix it. But you can make it worse".
-first heard from George L.

EBEBRATT-Ed

a lot of commercial job run higher pressure. If it is gravity return and just basic steam heat ...the corner school house...which is just like a big residential job then running 1-1.5 psi sounds ok.

If it is a larger system with condensate tanks and boiler feed pumps & steam traps you will usually find them running more pressure.

On these, boilers are generally oversized burners are two position or modulating flame and to keep the burners from short cycling they run the pressure up and down.

Doesn't make it right but not much you can do. boilers sized for the coldest day......then oversized

JBFBMech

Thanks. It is exactly as Ed describes. Powerflame burner, low and high fire pressuretrols, condensate pumps, boiler feed tank etc. I will leave it alone.

ratio

JBFBMech said:

No one is looking to replace anything. I understand steam. A system this size is not what we typically work on. I was just asking the question to see if I could help them or not.

Sorry, I guess that came across a little snarky. What I mean is that often system pressure is adjusted further away from proper operation in an attempt to cure a problem. Sometime you can convince people of that, sometimes not.

And the repair/replace comment was just a general thought in case it came up with the owner.

Dave in QCA

If they are complaining about uneven heat, it sounds like the pneumatic system may need some repairs. Thermostats, pneumatic valves, and a compressor. Pretty simple stuff, a little routine maintenance and they will run forever. A maintained pressure system is pretty dependent on an operating control system.

JUGHNE

I have 2 old schools almost exactly that size. Both were running at 7PSI as yours. Dropped the pressure down to the 2 PSI range and nothing but improvements. Both have F&T's and cond pumps.

Also a hospital with 3,300,000 input. Dropped from 7 PSI to 5 with no problems. It has converter heater exchanger and some F&T's that require lifting the condensate.

As far as finding the original prints/data, I have that for the hospital; stamped and signed by the mechanical PE, the boiler notes includes the statement: "Operate at 15 PSI"

Try that setting with a 15 PSI pressure relief valve!
So it was best to ignore the PE's request.

EBEBRATT-Ed

I am all for running lower pressure...if you can. If the boilers are oversized and the burners can't be down fired you pretty much screwed. Lower pressure the controls work better, is better for the steam traps etc

Sometimes you have to do the wrong thing and run the pressure up a bit to prevent short cycling. It's not the best, swing the pressure up and down as the boiler cycles aint the best for the traps or controls.

If you have multiple boilers shut 1 down. Install an overflow trap on both boilers so the idle boiler won't fill with condensate through the seam line. Configure the controls so 1 boiler opearate by installing a manual lead-lag set up. The lag boiler will only fire when the lead boiler fails or cant maintain pressure