steam pressure in a public building

jacobsond

This is my 1st season maintaining and repairing so bear with me. Kind of a long post.I don't mean to sound uneducated but I am. Working at a college. We have a central heating plant 80lbs steam going to the buildings. Most of the AHUs have steam coils. The newer ones are hot water. Most buildings have and exchange for baseboard hot water.We have 4 on our crew not counting boiler operators. The guy that did my job moved into instrumentation. He has told me I know more about steam than he does. The other guys have only been on staff a few years so not much experience on the crew. Boiler operators have been here the longest. Some 20 yrs. Only know the heating plant. Now for the question. We are running 8psi on the low side. Is that a good pressure to run on the low side. The supply lines are 2.5 to 3. I cant ask anyone here because I don't think anyone knows and I'm not ready to ruffle feathers. I know someone will get upset and just say that's what we have always ran. I have been watching Dan's webinars. I am learning a lot. I now know I must buy his books. He indicates anyone running more that a couple pounds may just be covering up for a poorly designed system or not properly maintained. I know maintenance is an issue because I'm doing it. Hoffman F&Ts all over. Sized to the line I believe. I'm the 1st guy that wants to test them all with something other than the IR gun. We have a thermal camera that no one ever used except me now. We have a new UE 10,000 ultrasound and the grease caddy that no one wants to use except me. Greasing has gone from every bearing gets 3-4 pumps a month to the whole campus this last run I needed 6 shots total. AHU bearings never sounded so good. One building that has been blowing steam out the condensate vent for 6-7 yrs. The fix was to vent out the sided on the building. 3hrs in the tunnel under the building with the UE following the sound found a blowing disc trap in two entryways. Now remember the question after the long post. Is 8 psi a good pressure to run on the low side?

Pumpguy

One question I would want the answer to is what is the steam TEMPERATURE needed at the steam to hot water heat exchangers?

Since there is a direct relationship between steam temperature and steam pressure, knowing that temperature requirement will tell you the needed steam pressure.

EBEBRATT-Ed

Commercial steam is sometimes different from residential boilers.

8psi isn't bad but it depends on how the system was designed.

The only way to tell without knowing the original design is to lower the pressure and see if it still heats the farthest radiator.

So drop it a lb or so and ggive it at a week during cold weather before you lower it any further.

And yes, as @Pumpguy mentioned we don't know what pressure the hot water hxs were selected at

But 8psi probably isn't excessive for a college with long runs

Steamhead

EBEBRATT-Ed said:

.......The only way to tell without knowing the original design is to lower the pressure and see if it still heats the farthest radiator.

So drop it a lb or so and ggive it at a week during cold weather before you lower it any further.......

That's exactly what I'd do. Once you've found the lowest pressure that will work, keep it there.

If you lower the pressure and find that just one unit doesn't work, fix that unit instead of raising the pressure.

Then watch for the fuel savings.

pecmsg

Commercial buildings I’ve worked in had
Less then
1#
and
5#,s
Special applications 15#,s

dopey27177

Good you came to the Heating helper.

I did consulting work for Princeton University and Bard university up state New York.

What I found is the maintenance staff tries to avoid explaining what is happening in the heating systems.

They fear the retribution that will befall them from the engineers that work for the university.

My interface with the engineers taught me that their knowledge for the most part is out of text books and design. Most of them have never left the office to fix a problem, nearly all of them don't know that free publications are available for proper design and trouble shooting.

See the attachments as they will help you understand what you will be working with.

The one pipe steam system does not show a hot water generator.

If the steam fired hot water generator is installed it will need a separate steam supply at steam pressures from 5 to 10 psi.
Just like the two pipe steam system.

It is important that you get the specifications ( blue prints and typical drawings and installation instructions) for each building..

Copy all name plates on equipment and write the manufacturers for ratings and maintenance instructions.

I hope the drawings taken from my book (steam the Perfect Fluid for Heating and some of the Problems) will help you.

Jake

jacobsond

Thanks for the reply's. Steam supply at the buildings are running in the 250 range. Lots of old AHUs about 6 are in doghouses on rooftops but most have their own mech rooms that are running 80 degrees. No steam engineers left on staff. The guy that knows the most is hard to talk to and gets grumpy if you would ask a question like why do we run 8lbs. Steam trap maintenance has been not been done in years. I'm starting a program to get temperatures and sound Dbs on the traps. Really having a hard time with the Hoffman F&Ts. Trying to use the comparison method with the UE meter and not really having much luck. On my extra time I'm working on a building that has been banging for years. 30+ hoffmans on ceiling unit heaters 20 ft up in the shops. With the knowledge of this group and my willingness to learn and read I hope to become the go to guy on the steam system eventually.

pecmsg

Some of your questions can be answered here:

ethicalpaul

He gets grumpy because he doesn’t know why I bet. Good luck on your quest!

dopey27177

Pecmsg

sent you a reference guide and manual that will cover everything you will need to know in the engineering side of plant maintenance.

Much of the data you will not use because it is not related to what you are tasked to do, but there are items in there that will affect your steam systems and also how the steam systems will affect other mechanical equipment involved in space heating, laboratory needs, domestic hot water production etc.

There is 500 pages of data I wish I had available to me when I was working. (retired 25 years)

Hope my sketch of buildings using HPS for heat and hot water.

Oh incidently grumpy may not why but only knows just is.

Jake

Pumpguy

As far as the radiation in the individual buildings is concerned, if sized according to EDR rules, they need 215* steam temperature surrounded by 70* air to provide 100% of their rated heat output. That's steam at just under 1PSI.

So if you can get steam at 1 PSI out at the furthest run of the building, the only additional pressure needed is to make up for pressure drops through the system.

It is frequently stated on this site that the Empire State Building is heated with around 3 PSI steam pressure, although they do have a good vacuum on their return lines.

dopey27177

Why 8 psig steam.

Fan coil units may require 8 psig steam many use 2-5 psig. depends on the leaving temperature requirement to the a space with a unit that will fit into a specific location.

Heat exchangers producing hot water, heating air or other fluids. The coil size in the units need to put out a specific amount heat to perform a task. the steam temperature provides the heat needed. 1 pound of steam pressure equals 216 degrees, 8 pounds of steam pressure provides 235 degree temp.

Building heat to radiators and coils normally do not need steam at greater than 216 degrees and in vacuum systems steam temperatures as low as 150 degrees.

Some times in a steam heating system the zone valve is the pressure reducing valve. This is accomplished by
1. a zone valve smaller in size than the the low pressure steam main.
2. a zone valve full size but has smaller internal trim. ( smaller hole (orifice) than the pipe size)

To use smaller pipes in steam supply the steam pressure must be increased. Steam is a compressible gas and here is an example:
Steam at 8 psig is 238 degrees F and occupies 18 cubic feet of space
steam at 125 psig 353 degrees and occupies 3 cubic feet of space

These items were taken from my book Steam the Perfect Fluid for Heating and some of the Problems.


Jake

jumper

Pipe lay out can be a big deal when some terminals heat outside air and others do not. Cold temperatures can cause lower pressure. So intelligent piping helps steam circulation. And unintelligent.... Way forward to determining ideal pressure is to make a diagram of piping layout. Generally low pressure works fine with good circulation.

jacobsond

We got the go ahead to start some testing. While we still have some winter left going to lower at least 1 building down to 6 maybe lower and go from there. The supervisor is going to try to get the operators to agree to a 60lb boiler output. Maybe less. That will be a next winter thing. Our goal is to lower the pressuer for each building and have only the pressure we need to heat. Piping may warrant an 8lb pressure may not. Maybe we can go down to 4 or less.

retiredguy

If I was the boiler operating engineer, I would keep the main boiler plant steam pressure at the 80 PSIG it is now and would not change it until the system has experienced a very very, long and deep cold snap. Lowering the boiler's steam pressure may be possible but you could produce a lot of carry-over (wet steam) if under a very high load the boiler's pressure collapses and the boiler has to play catch- up for the steam load. Can you post a few pictures of the boilers and related piping and list the name, size and model numbers of the boilers? Do you know how much make-up water the boiler needs? What burner is on the boiler, Water tube or fire tube. Does the condensate system use a deareator? Also, how many buildings are heated by this steam plant. See if the school has any of the original engineering drawings for the steam system and try to find out who or what company did the original and any subsequent engineering work. Then contact them to see if they retained any of the engineering documents. If you can't find any of the original documents you could get the manufacturers name and model # of the fan coils and see if they can tell you the design inlet steam pressure, and the expected temperature rise. Your question as to the 8 PSIG being correct is that it depends on many factors. For me, I would want to study the whole system a lot more before I randomly reset steam pressures. Last item, where are you located?

nicholas bonham-carter

I would try a reduced pressure for a while, but you will need to watch things carefully, and be ready to restore the old settings, if the results don't pan out.--NBC

jacobsond

Im sorry I know nothing about the boiler. There are 3 all very old. One has been retrofitted with new burner and plans for another. We burn natural gas with oil backup. As far as what pressure the plant puts out that is their business. If the plant engineer wants to try lowering it it is between him and the facilities manager. Between me and my crew lead we feel we should be able to adjust the building pressure to what the building needs. We will take full ownership of any changes and repair or adjust as needed. We both question the 8lbs and there is nothing on the books to why and no one knows. We have an computer automation guy that watches all the building temps and outputs of the AHUs. We will know what the changes do.I hope we can obtain better running systems and get some efficiency. I feel at 8lbs we may be masking issues by the higher pressure. I have no problem making sure all the components of the system are functioning normal. Maybe we can even start testing traps every year instead of well never. We are entering spring now so temps will be average 10 at night and 20-30 during the day. We wont get a real good feel about the changes,but if there is no noticeable decline in heating capability we may be on the right track. It will be a long process. 30 or so buildings. We get to experiment on 1 for now. Baby Steps I guess.

dopey27177

firstly the pressure leaving the boiler plant is normally set by the original design of the district heating pipe sized transmission lines.

The smaller the pipe the higher the steam pressure must be to supply the amount of steam needed to heat a building.

In the building there must be a steam reducing station for the building heating. And possibly another for the hot water generator and or unit heaters.

I sent you two comments about your possible problems, On Feb 1 there are steam pressure reducing stations that may be applicable to your buildings and on Feb 2 another comment about your heating system.

You did not acknowledge that here may be your operating point for corrective action.

Now you are speculating to lower the boiler operating pressure to 60 PSIG. At 60 PSIG you are still sending steam into the building at pressures that are to high to heat the building. Therefore you still need steam pressure reducing stations.

It is fantastic that you are trying to make all the needed repairs to the unit heaters and that you have to make an added effort to repair or replace the traps because they are so high up in the air as to be nearly impossible to get at.

I will still state that you need to view the original blue prints or specifications to see what the design steam pressures for heating each part of the buildings heating systems require.

Jake

jacobsond

Thanks for all the reply's. I'm trying to wrap my head around this system and get it operating better. Facilities is pushing for a lower main pressure and I am asking questions about building pressure. No one has come up with an answer to why we run these pressures and I am not near smart enough.

I am not sure if the original plans are even available anymore.

I don't want to run a building at 8 just because we have bad traps and that was the fix. Then set the 30 buildings to 8 because that is what we do. The info sent is very informative.

I would like to push for an expert to come and inspect our system and recommend actions for our system. Of course money is always the issue.

Is there a consultant in the MN,ND area that could give us a quote? Maybe we could use our energy grant to help pay.

With all my other duties on the systems crew I don't have much other than repair.

2 more leaking coils I need to get to now. If we could have lower pressure would that be easier on the old coils?

dopey27177

If you are talking about coils on unit heaters they are designed to operate in your case at 15 PSIG. So, for the unit heaters that is pressure. You can google the unit heater manufacturer and get all the info needed on them. Remember, make, model number and serial number.

Building heating if with radiators and convectors, google the zone valve manufacturer, supply the same data. especially the serial number. The serial number shows the valve
manufacturer the internal trim size which then allows them to to tell you the design inlet pressure.

Jake