Boiler operating pressure

[vi007]

If anyone can help me in understanding this term. Is this the pressure at the bladder tank? how can i calculate operating pressure at my boiler? design pressure is 125 psig and supply temp : 220 f and return: 180F.

 

[JohnGP]

Well, the simple answer is that "Boiler operating pressure" is the pressure that you operate your boiler at. But I think you knew that. Beyond that it is a bit hard to help with the info that you have given.

I'm not familiar with bladder tanks used with steam, but if you need steam at 220F, let's see, that's a bit over 104C - heck 120kPa will give you that (17psig). But then there are losses to consider, so you need higher pressure to overcome those, and ensure you still have steam where you want it (and not just condensate). Also, the higher the pressure the smaller diameter pipe you can use to transport the steam.

If the data you have provided is for the "bladder tank"(?), then I'm not sure what the steam side conditions need to be - the temperature change is a start, but you need also flows to work out the heat required.

 

[vi007]

I am asking about hot water boiler.I need to figure out the boiler operating pressure and relief valve setting at the boiler.
I know per ASME SECTION IV THE relief valve design pressure is 125 psig,but what will be the setting pressure?
what is the boiler operating pressure? i asked manufacturers about it and they say it has to be determined by hot water heating system design? can anyone help me please?

 

[JohnGP]

Oh Ok, that's different then, I haven't worked with ASME IV so can't help there. I don't imagine the requirements are too far different from ASME VIII where the first safety valve must have a set pressure no higher than the maximum allowable operating pressure of the vessel. But your Code should specify that.

The logical way to proceed is to determine the heating system design requirements, as has been suggested, then select the boiler size and operating conditions to suit.

 

[tim1984]

Why do you need to calculate the operating pressure ?

Is it not specified by the client ?

 

[TBP]

You need to calculate the "fill-head". How much pressure will you have after the system is initially filled? (Just enough pressure to drive out the air initially found in the system? That's simply a function of height above the boiler. Depending on the system, you'll need a few PSI more. If the boiler is in the penthouse mechanical room, there won't be much pressure on it. This works better for dissolved air removal, the boiler can have a 30# relief on it, etc. If the hot water boiler is in the basement of a building that got water lines running up 200 feet, NOW you'll have 100 PSIG on the boiler. This is why hot water boilers aren't usually located in the basement, except for residential, or 2 - 3 floor structures.

Try

http://www.bellgossett.com

for some really useful info on hydronic heating systems and their components.

 

[vi007]

we are the consulting engineers so we need to figure it out.