Boiler downsizing with TRV's

Steve_15

Going to change old cast iron wall hung radiators with copper fin tube radiators properly sized for the load of each room in a school. The system is 2 pipe steam. Reason for changing radiators is they are falling off of the wall in all classrooms. They want to control each room individually. My questions are 1) What are the concerns with installing Danfoss or equivalent TRV's on each radiator set in the classrooms. 2) How do I properly size the boiler with the reduced load. (The school has been remodeled, and the boiler is not heating as much of an area as it used to). Not sure how to size with the TRV's. Do I size for maximum radiation load. If I do, will the boiler short cycle when not all of the radiators are calling because of overfiring? It is currently firing at 4,000,000 btu's and has a modulating valve train. Thanks for your help

Steamhead

Size your boiler

to the maximum load it will have to heat. This means a very cold winter day with all TRVs open. Just add up all the fin-tube and size the boiler from that.

If you use an outdoor reset controller, the boiler should not short-cycle so much. And be sure to install adequate venting on each steam main (the trap at the end may not be enough) so the mains fill with steam quickly. Depending on the size of the school that can mean a lot of Gorton #2 vents! But the results will be worth the cost.

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