Steaming

JUGHNE

Fred & Ray, my experiences with orifices has seemed to be successful.
In a house that had no trap guts left in it, orifices were installed in the steam valve unions. Sized for 80% of EDR at a certain pressure. The returning condensate from these radiators is actually cool.
The orifice limits the flow of steam to where it all condenses within the rad. Regardless of how long the boiler runs as long as the pressure stays within the design pressure, in this case ounces. Possibly if the tstat was set to 80 or above then more of the rad would heat across, this I don't know. But it seems the steam flow matches the condensing rate of the rad as 20-30% of it stays cool. I have mentioned before we have had record low temps and my phone has not rung with complaints.

Did a schoolhouse like this, only it already had TRV's on most rads. Again, all trap elements were removed.
You allow teachers and kids the ability to operate the temp control and you know it is going to go to full open to fully closed.
The orifices will keep the steam out of the return.

In both cases more venting was added to the system rather than relying on the air to be vented thru the orifice into the dry return and then to the cond pump vent.

The house system has end of main air vents and dry return air vents. I don't think the return air vents see any steam at all.

Phil53

Just curious, could graduated packless radiator valves act like an an adjustable orifice as long as they're not fully opened?

The Steam Whisperer

Yep, it's the same concept. In fact the graduated valves may have been sized to limit steam just like an orifice. The Moline system used graduated valves.

ChrisJ

The Steam Whisperer said:

Yep, it's the same concept. In fact the graduated valves may have been sized to limit steam just like an orifice. The Moline system used graduated valves.

Have you found TRVs to be a viable solution to throttling single pipe radiators in large buildings? Would it allow you to reliably use a significantly undersized boiler vs the installed EDR?

The Steam Whisperer

I haven't had any large buildings with one pipe steam install TRV's on a large scale, only some two pipe systems that had orifices too.

Steamhead

How are you guys sizing your orifices? 80% fill at what pressure? Reason I ask is I just looked at a system that turned out to be a Hoffman Vapor that some idiot converted to hot-water, and (of course) it doesn't heat well. We're looking at changing the original system back to Vapor and leaving the addition as hot-water.

Dave in QCA

I have used Tunstall's cup type orifice plates. I size them from their table, which shows the range of EDR at various pressures. I have always used the 0.5 lbs (8oz). When doing a Moline system, which were intended to operate on 6 oz, I choose the next larger orifice if it's at the upper end of the range on the chart.

My own system controls with a 2 stage burner between the pressures of 7-11oz. Since I have working traps I don't know if I would be passing any steam into the returns, but I doubt it. On the Moline system, they work just great. Or course, the obvious thing is, sizing the boiler to maintain the pressure within the parameters of the orifice sizing is key.

Attached is the Tunstall chart.

The Steam Whisperer

It depends on the system and how it will be operated.
If we are trying to retain or convert to a gravity return, we will size to 1/2 psi drop so we will have plenty of stacking height on the radiator return main drops. If we are planning on running outdoor reset of the steam pressure, we design for a 3 psi pressure drop. Tunstall recommends 4 psi, but 3 seem to work fine and that's what we have charts for. The only complaint we have seen is there is a slight whistling when running at high pressures through the 3 psi orifices. With a properly sized on/off boiler or with outdoor reset, this won't happen very often.
We size the orifices based on the radiation capacity and the heat loss of the structure. We usually find that we can met the heat loss on the design day with the radiators only 60% filled, so that ends up being our design load for the system and we size the boiler accordingly. We only had one system that ran a bit short on capacity during our -20F days a month or so ago, so we know we are hitting our target pretty well because design day is only -4F.
The new replacement boilers installed with the new orifices are usually about 2/5 to 1/2 the capacity of the previous boiler. I have been using a 15% pick up factor for sizing the boilers, not the 33% since the orifices reduce the start up load dramatically from the studies I've read. I believe Henry Gifford, in New York, has also been using a 15% pick up factor for quite some time.

We have mixture of heating plants firing into these systems. Most are on/off which we've cut the firing rate to better match the new load. Some are new boilers that are sized to the heat loss running on/off, a couple are running outdoor reset and a few stage fire thier boilers as needed ( either with a two stage thermostat or manually by building personnel)

jumper

Steve Minnich said:

Let me add some more information -



Again, large buildings with large boilers; 750mbh to 4000mbh. Hundreds of them so the potential savings would be epic.



Industrial Combustion modulating burners with tight control, 1.2 psi max.

In the seventies there was a lot of interest in saving energy. Many large buildings in Toronto had "incorrect" boilers. Built on brick fireboxes as if for coal although they were oil fired. And then when converted to gas lost even more efficiency from less radiant heat transfer. Some owners replaced the boiler with multiple smaller units. Strategy was to run minimal number (one) at certain hours when residents are expected to be away or dressed or sleeping. Can steam heat work okay with grossly undersized boiler provided that whole system is heated up sufficiently twice a day? Owners believed that they saved on gas bills.

Perhaps it's odd but there were reports that the strategy did not work well for hot water heated buildings.

Tinman

@ratio - But, what I’m suggesting is a properly sized steam boiler both for the NEW connected EDR and the heat loss of the building.

JUGHNE

This chart was sent to me by "Fizzkids"??.
It would let you fine tune orifices as needed.
I did get Tunstall union cup orifices predrilled with 1/16 pilot hole.

I did a 1918 house with 382 EDR connected. It was an old Kelmac system with all trap components/guts removed, most valves were inoperable, which I replaced with standard type.
Any components that may have been in the basement, venting air perhaps into the chimney had long been gone.
Having no idea of what the operating pressure should be, I used the 18 oz column for 80% of EDR. As it turned out the system would run 8-12 oz. Used a HG vaporstat (one of 3 that I acquired). Figured if cold areas I could up the drill size. Never have had to. Attic insulation had been added, upgrade from 1918. Search this site for "Kelmac" system for more info.

Also did a 1933 school with 3781 EDR connected.
All trap guts were removed if orifice was installed.
I used 32 oz column and did none more than 60%, some 50%.
Room by room I made my best guess on how much heat was needed. Looking at wind exposure, outside walls and the number of windows closed up, dropped ceilings etc.
All remaining windows had a good upgrade and size reduction. (scientific...huh?).

Again we have had record lows and there is adequate heat in these rooms.

Dave in QCA

@JUGHNE Thank your for posting your steam orifice table. I find it interesting that the orifice sizes from this chart are much larger than on the Tunstall chart. In fact, if a look up an orifice from the Tunstall table, for an example, if I look up a 40 EDR radiator, I find the range 37-42 @ 8 oz. The punch size that Tunstall uses for their orifice for this range is .238. This corresponds to an EDR of 18-20 @ 8oz on this chart with orifice size 15/64" (.234"}.

I know that Tunstall has their orifices sized in a manner to make sure that no steam leaves the radiator even with a continuous steam cycle. But, the difference still seems to be more than I would expect.