Why have steam boiler run at 85 PSI and have regulator drop to 30 PSI a few feet away??

JUGHNE

During the last storm and flooding in my state, I was sitting with my wife for 4 days in a fair sized hospital.
I did get a tour of the boiler room while there. They said they don't get many requests for that and later said any who visit are some strange people.... .

They have 3 large steam boilers. They are staged for firing as the pressure drops.
The main lead boiler was running at about 85 PSI.
They then drop the pressure to 30 PSI for HW heating via converter/heat exchangers that are located near the boilers.

Being a visitor/tourist I didn't want to question this set up very much.
I understand the needed higher pressure for high temp/more BTU's heat transfer or lifting condensate.
But apparently 30 PSI is enough to do this.
To me it seems they could run the boilers at 40-50 psi and still get what BTU's are needed at 30 PSI.
The gas train is hi/low or modulating, not sure.
I have been to places where the pressure seems set quite high and when asked why, the answer is because that is where it always has been....the boiler pro set it there years ago.

I am just curious of this situation.

Henry

I have seen similar situations by misguided engineers who opt for instant hot water using a flat plate heat exchanger at plants and hospitals.

JUGHNE

I believe the main load for these boilers is heating the buildings via hot water. DHW, probably, I don't know for sure.

But as long as the 30 PSI is maintained for the second stage, wouldn't the 85 not be necessary. What is gained by the 85 versus 40-50 PSI? (there are 2 more boilers that could come on line if needed).

kevinj_4

I think they may also have sterilizers and such on the line.
It may also depend on other uses as the pressure thru the regulator should be stable if they need close control.

One hospital we take care of had more need for high pressure in the past so we have high pressure boilers and the nozzles are sized for that. So we keep the pressure up to work with the piping and nozzle size.

If you reduce to much the velocity rises as low pressure boilers have larger nozzels.

Intplm.

At a facility that I worked in a long time ago, they had large Cleaver Brooks boilers providing steam. The steam in the facility was divided into three different pressures for different needs in the facility. They were categorized as High pressure (80 to 120 psi), Medium pressure, (30 to 80 psi) and low pressure steam, (30 to 0 psi).

These different pressure requirements all had a different purpose in the running of the facility. Space heating, process heating, domestic hot water heating and conditioned space etc.

Was a long time ago and I haven't heard of, or come across this type of setup since. And since @JUGHNE post. Thanks for the trip down memory lane.

Leonard

Bit odd, but other thing I can think of is if burner fails there's more stored energy in the hot water ( higher temp) so it can provide heat (coast) for a bit longer.

But sterilizer explanation sounds more plausible. Think I've seen ~ 240 or 260 deg sterilizer (electric) in dentist office. Guessing that's more for quick ("guaranteed") heat up of metal instruments than killing power.

JUGHNE

Thanks for all the replies. Hopefully I don't visit the place again as a paying customer.

EBEBRATT-Ed

I agree with @kevinj_4,

Many hospitals have a large steam load for sterilization, laundry and kitchen cleaning as well as DHW and heating

HVACNUT

Most dry cleaners boilers run at 90 psi cut out so I can see a hospital having a need for high pressure. Gotta blast those bed sheets.

pecmsg

It is Stored Energy. Steam in Hospitals is Critical as such you CANNOT loose steam. With 90#'s in the boiler that gives the engineers or BMS system time to bring the back up boiler on line and get to a operating pressure greater then 30#'s before running out of steam!

Same reason as there's generally 3 boilers. 1 Primary, 1 standby and 1 back up.

Standby maintains 180 - 200° water temp.

jumper

pecmsg said:

It is Stored Energy. Steam in Hospitals is Critical as such you CANNOT loose steam. With 90#'s in the boiler that gives the engineers or BMS system time to bring the back up boiler on line and get to a operating pressure greater then 30#'s before running out of steam!

Same reason as there's generally 3 boilers. 1 Primary, 1 standby and 1 back up.

Standby maintains 180 - 200° water temp.

Another way to store thermal energy is with "molten salt". That avoids high pressures. Google "molten salt boiler".

Intplm.

jumper said:

pecmsg said:

It is Stored Energy. Steam in Hospitals is Critical as such you CANNOT loose steam. With 90#'s in the boiler that gives the engineers or BMS system time to bring the back up boiler on line and get to a operating pressure greater then 30#'s before running out of steam!

Same reason as there's generally 3 boilers. 1 Primary, 1 standby and 1 back up.

Standby maintains 180 - 200° water temp.

Another way to store thermal energy is with "molten salt". That avoids high pressures. Google "molten salt boiler".

@ jumper Wow that blew my mind ! Never heard of that before.
At first I thought it looked like an absorption chiller.

Dave in QCA

For a period of 17 years, 1982-1999, I was in charge of a small hospital complex, 100,000 sq ft. The boiler room was a 1968 addition. The boilers were set up to run at 60-70 pounds. The driving reason for that operating pressure was the sterilizers in central sterile supply. Since that pressure was available, it was also used for domestic water heating. The first setup was tube bundles in large storage tanks, then replaced with Aerco coil type heaters without storage. There were two domestic water systems, one for 120F tap water and one for 180F in the laundry and the kitchen. High pressure steam was used for a couple of tube in shell bundles for a hydronic heating system in the 1968 section of the complex. 10 pound steam was fed back to the older sections of the building that had steam convectors and coils in air handlers. A 10 pound line went to an air handler room in the 1968 air handlers and a 25 pound line went to the kitchen area for steam kettles and a steam oven cooker. Then, there was a mechanical room in a 1982 addition. They ran a 60-70 pound line down there and put a pressure reducing station to reduce pressure to 10 pounds for the air handlers and a hydronic tube bundle. Hi pressure went up to the sterilizers which were conveniently directly above the mechanical room.

The boilers were a matched pair of 338 HP Kewanee scotch marine, 2 pass boilers. Either one would carry the complex in the worst weather, so one was resting and ready to go with a moments notice. It was a good job and I learned a LOT while I was there.

EBEBRATT-Ed

For good reasons hospitals are usually done right