New meets old

JasonA

I am the Construction Manger of a small portfolio of Residential and Commercial building all located within New York City. All of the buildings are over 100 years of age. All are heated by steam heating systems of various designs – a veritable living history of steam heating. The building in question is a 9-story former manufacturing loft building that is currently occupied by office tenants on the upper floors and until recently, retail use on the ground floor. We have a new tenant that will occupy the ground and basement floors. The new tenant intends to operate a nursery school.



The existing heating system is/was what appears to be a two-pipe, Paul system. There are remnants of the old vacuum lines and all of the radiators have double bottom tapings, generally 1-1/4” and 1-1/2”. There are even some radiators with these same tapings side by side at one of the radiator only. The vacuum piping is now gone and all of these radiators have had one-pipe air vents installed. All of the current and past tenants have left these radiators in place and are providing air conditioning to their spaces by split of packaged DX units.



The new tenant has proposed something completely different. The new proposed system does away with the existing cast iron radiators in favor of steam fan coil units mounted in new air handlers. The steam piping details indicate standard F&T traps and associated piping. This arrangement appears to have two main problems.



Problem number one is that the existing “return “ lines are going to have steam in them, shutting down the T portion of the F&T trap and not allowing any steam into the steam coils. Would a completely new condensate return piping system back to the boiler allow this system to work?



Problem number two is that the existing all cast iron radiator system is controlled by a Heat-Timer control that cycles the boiler based upon outdoor air temperature. This works acceptably for the current system but is going to be a big problem for the fan coil units. Because of the intended occupancy there is some outdoor make-up air required at all times. There will be continuous air passing over the fan coils regardless of the availability of steam. The units have the potential to shut down (often) via their freeze stats.



I am sending this off to our house engineer for review but I am afraid they know as much about Paul systems as the tenants engineer.



Thoughts?

ttekushan_3

Let me see if I'm getting this right.

This is a single pipe system and they're going to fan-coil everything and expect the coil to vent and drain into a single riser? How are they proposing to vent the coils? How are they proposing to stop the steam when heat is not required? And is one fan coil supposed to take the place of multiple radiators? If so, is the riser able to handle the load? And is the riser able to supply enough steam to the coil in the event of extremely cold make-up air? if not, the coil will suffer "steam stall" and probably freeze. Steam stall is when the steam is condensing so quickly that the supply of steam is inadequate, the "vacuum zone" falls somewhere in the middle of the coil and condensate fails to drain due to the vacuum holding it back, all the while ice cold make up air is blowing across the coil and potentially freezing the coil.



If they don't know what they're doing, everyone's going to be in a world of hurt when the whole thing has to be repiped.



Edit: rereading, this is a two-pipe with Paul vacuum air vent system? Wow. They're going to have to put an air vent at the top of the F&T, but I think that thermostatic element will get hammered to smithereens by steam existing in the return. They're going to have to valve it at both supply and return for control, and assure that there's a vacuum breaker to prevent the coil from vacuum damage.



And all this and they won't have any more radiant heat provided by the cast iron.



ANd you're right. The blower will blow cold between cycles.



The only way I've seen this work with continuous blower operation is with a continuous steam supply to a modulating steam supply valve on a real two pipe system. Best yet is to allow the fresh air to be modulated both on heat demand and outdoor temperature.



So they probably should drop new returns into a dedicated vented condensate receiver/pumping unit.



Dunno what they're going to do about all the cold air between cycles.

JasonA

Another way

My first suggestion is to leave the cast iron radiators at the front facade (the only place where there are any windows) and install electric strip heaters at the fan coils. Interlock the strip heaters with the condensers so they cannot operate concurrently. There is an up size to the electric feeders to the air handlers but there should be no need to increase the size of the electric service.