EXPANSION TANKS

Hugh Baxter

I'm responsible for a 60-suite apartment heating system. The building was built in 1956 and is heated by a 2,900,000 BTU Cleaver Brooks hot water boiler. It also originally supplied domestic hot water to the building. The hot water leaves the boiler via a 4" line and runs to the top of the building (36') and then splits into five lines to supply five zones. The return lines (2-1/2") terminate in 1-1/4 hp Armstrong pumps (5) and discharge into a common header back to the boiler. As far as I can tell the system contains approximately 800 US gallons excluding the expansion tank (which is very small), open and located on the roof i.e. at the high point of the system. During the winter we operate the system at 180 degrees F
We want to install closed (diaphragm) expansion tanks. At this height it appears that the tank(s) airside pressure should be about 22 psi. The volume I estimate should be about 200 US gallons. This seems quite large but the system does contain a lot of water.
I have two questions - are these estimates reasonably accurate and what would be the system pressure when the water has been raised to 180 degrees F.
I also realize that a system designed today would have the recirculating pump on the discharge side of the boiler. Would it be possible to replace the five pumps with circuit balance valves and check valves and put one circulator in the discharge line. I expect the circulator would have to move bout 200 US gpm.

Hugh Baxter

EXPANSION TANK/CIRULATOR LOCATION

I'm responsible for a 60-suite apartment heating system. The building was built in 1956 and is heated by a 2,900,000 BTU Cleaver Brooks hot water boiler. It also originally supplied domestic hot water to the building. The hot water leaves the boiler via a 4" line and runs to the top of the building (36') and then splits into five lines to supply five zones. The return lines (2-1/2") terminate in 1-1/4 hp Armstrong pumps (5) and discharge into a common header back to the boiler. As far as I can tell the system contains about 800 US gallons excluding the expansion tank (which is very small), open and located on the roof i.e. at the high point of the system. During the winter we operate the system at 180 degrees F
We want to install closed (diaphragm) expansion tanks. At this height it appears that the tank(s) airside pressure should be about 22 psi. The volume I estimate should be about 200 US gallons. This seems quite large but the system does contain a lot of water.
I have two questions - are these estimates reasonably accurate and what would be the system pressure when the water has been raised to 180 degrees F.
I also realize that a system designed today would have the recirculating pump on the discharge side of the boiler. Would it be possible to replace the five pumps with circuit balance valves and check valves and put one circulator in the discharge line. I expect the circulator would have to move about 200 US gpm.