True vs. Published Steam Radiator EDR

random12345

Apologies if this has already been answered somewhere. Has anyone ever come across any studies that have attempted to compare a steam radiator's published EDR as stated by the manufacturer with the true EDR that has been measured using modern techniques and instruments? Only relevant thread I've found on here was this one: https://forum.heatinghelp.com/discussion/comment/1753657#Comment_1753657. @Nick_Castrads seemed to think that an ARC Corto's EDR could actually be 20% less than advertised.

Jamie Hall

Intriguing question, and no I'm not aware of any such test. Part of the problem -- which should be obvious but like so many other tests isn't -- is that the conditions under which the measurement was taken would have a tremendous influence on the result, and so would have to be rather carefully specified.

The actual measurement itself would not be difficult at all, since what you really want as a result is how many BTUh the radiation is capableof; the power. There are a number of ways this could be measured, but the most obvious --and much the simplest -- would be to simply measure the rate at which it could condense steam.

random12345

Yes, that is the method. I thought Dan may have mentioned it somewhere, but don't remember.

Steamhead

There were actually two different versions of the Corto. The original version is here (scroll down for the chart):

https://heatinghelp.com/heating-museum/american-radiator-companys-corto-1922/

The later version is shown in @DanHolohan 's "E.D.R." and is consistent with other large-tube rads of that era, such as the National Aero.

The difference is obvious when you look at the section spacing. The original Corto had a section width of 2 inches. The later version had the standard 2-1/2" width.

And the earlier version did have lower ratings per section. For example, where the standard 5-large-tube, 38" tall rad was rated 5 square feet per section, the earlier Corto was only rated 4-1/2 square feet per section. So the Castrads guy might have had the earlier version.

random12345

Good point. From his post, it looks like he was comparing to the later version. Maybe it was actually the original you linked to? Either way, I'm still unsure how accurate the standardized ratings really are. When did manufacturers switch away from the paint method and start measuring condensation rates I wonder? Seems like they would need to send their rads to someplace like UL or ETL that would have a standardized test method. The dip in paint was probably something they could do in house for cheap.

Jamie Hall

To add to my comment -- as in so many things, "you're mileage may vary". There are a lot of variables besides surface area which go into the potential power of a radiator. Some of them in the radiator design -- those can be captured by tesring for actual power. But others, such as room placement, the finish applied, whole bunch of things.

If you're counting on the rating being accurate to better than 10 percent, you're dreaming.

random12345

All true. Completely agree. I guess what I'm concerned about is the possibility that cast iron rads were systematically overrated by the manufacturers either to make them look better or simply due to inaccurate testing and measurement.

ChrisJ

I doubt my calculations on EDR for my radiators was very accurate.

They're Kohler steam / hot water radiators from the mid 20s and I never saw any actual published data on them.

So everything I used was "hurry up good enough"

Seems to have worked though.

random12345

I guess in the grand scheme of things, it's not that important. But the lower the pressure the faster the steam velocity. Rads heat up faster and the thermostat reaches setpoint more quickly...in theory. The closer the match between the boiler's steam output and the system EDR, the lower the pressure will be.

ChrisJ

random12345 said:

I guess in the grand scheme of things, it's not that important. But the lower the pressure the faster the steam velocity. Rads heat up faster and the thermostat reaches setpoint more quickly...in theory. The closer the match between the boiler's steam output and the system EDR, the lower the pressure will be.

Well
I came up with 392sqft if memory serves.  That's 94,000 but/h

My boiler has an output of 104,000.

It can run for over an hour and not build more than a few inches of water column so I guess I did pretty good.


But
I'm also pretty confident I could drop the output by 25,000 and still not have balance issues.


The steam in my system moves slower with 104,000 output than it did with 125,000.  That was a big part of why I did it.  To make the system easier to control.

And I'm sure it would move even slower with less boiler. 

random12345

How is that possible? Higher pressure -> lower velocity no?

ethicalpaul

You have to look at a lot of variables. That statement is kind of over-broad.

I think it’s meant to be a simple statement to convince people that oversized systems running at higher pressures are bad (which I agree with).

Pressure at the boiler is what pushes air out of the system at the start of a cycle and the higher that pressure is measured, the faster the steam is moving down the main.

likewise, in the next “phase”, pressure measured at the boiler is what pushes air out of the radiators. The higher the pressure, the faster the radiators fill with steam.

ChrisJ

random12345 said:

How is that possible? Higher pressure -> lower velocity no?

Let's say you have 2 boilers on identical systems and lets assume your radiators are cool and vented fast.

You have a 104,000 btu/h output boiler.
And on a second identical system you have a 125,000 btu/h output boiler.

You feel the smaller boiler will feed steam faster through the same size piping? It can only provide so much steam so fast.


Like Paul said, I think Dan wrote that comparing a system running well at 1/4 PSI vs one running bad at 5 PSI. He's trying to get the point across that higher pressure isn't better.

Jamie Hall

Oh dear. Well, I don't have time this morning to write an essay... but let's just leave it that pushing the air out isn't the only thing or even the primary thing which controls steam movement in a cold main line...

ethicalpaul

Absolutely Jamie. The main also has to be heated, and during that, the steam is consumed (and therefore very slowly advancing). Something that will happen faster the more steam is produced, just like in Chris's example.

ChrisJ

Jamie Hall said:

Oh dear. Well, I don't have time this morning to write an essay... but let's just leave it that pushing the air out isn't the only thing or even the primary thing which controls steam movement in a cold main line...

That's correct.
The boiler is.

random12345

@ChrisJ and @ethicalpaul Appreciate the input. Good points. I should have been clearer that I brought up this topic in the interest of maximizing energy efficiency. I was looking at the steam velocity equation: I didn't realize velocity increased in proportion to flow rate. I understand what you're getting at now. At the same pressure, the bigger boiler will always get the job done faster, and that remains true even if the pressure is slightly higher. Velocity is much higher in the smaller pipes as well because of that exponent in the denominator. At the same time the 125k btu boiler is burning over 20% more energy per second, and that higher pressure must impose an efficiency penalty. It can't not. So the question is, how much extra fuel is burned by the larger boiler assuming that the system pressure will be higher? I will take a crack at this later...
https://tlv.com/global/US/calculator/steam-velocity-through-piping.html?advanced=on
https://heatinghelp.com/systems-help-center/how-to-calculate-steam-velocities/

ChrisJ

random12345 said:

@ChrisJ and @ethicalpaul Appreciate the input. Good points. I should have been clearer that I brought up this topic in the interest of maximizing energy efficiency. I was looking at the steam velocity equation: I didn't realize velocity increased in proportion to flow rate. I understand what you're getting at now. At the same pressure, the bigger boiler will always get the job done faster, and that remains true even if the pressure is slightly higher. Velocity is much higher in the smaller pipes as well because of that exponent in the denominator. At the same time the 125k btu boiler is burning over 20% more energy per second, and that higher pressure must impose an efficiency penalty. It can't not. So the question is, how much extra fuel is burned by the larger boiler assuming that the system pressure will be higher? I will take a crack at this later...
https://tlv.com/global/US/calculator/steam-velocity-through-piping.html?advanced=on
https://heatinghelp.com/systems-help-center/how-to-calculate-steam-velocities/

I don't have those answers.

My point was there's a fairly large tolerance on how mismatched the radiators can be and not really matter.
As long as boilers are sized reasonably well, and not grossly oversized they seem to do well.

That's why I try to get others to use 10-25% over for sizing rather than the typical 33% and worst case try not to ever go over 30-33%.

The times we see major issues is when a boiler is 50-100% oversized.

ethicalpaul

Pipe diameter IMO is never a limiting factor for steam velocity in a residential system that is piped anywhere close to correctly. Those charts aren't for us.

The things that affect the "steam time to radiators" that we care about are the size of the boiler (and this is of course hopefully set by the radiation or it's already installed so it's not much of a variable), the temperature of the pipe (affected by insulation), and amount of venting.

Get the right sized boiler for your radiation, insulate your mains if you want, have appropriate venting, and don't sweat "efficiency" which I believe you are kind of misusing anyway in your post above.

gerry gill

Radiator sizing and EDR are usually somewhat subjective anyways. For example- btu/240 = sq.ft. edr is a 'rule of thumb' that will only get you close if you are around sea level. Even there its still b.s.
Nowhere in that equation is the temperature of the steam based on elevation or even the average temp of steam in the radiator which is 95% of the temp of the steam at the boiler.
I tend to size radiators with warren websters charts in the 1922 book titled steam heating. Its on this site someplace. I have a couple hard cover copies here at the shop. Radiators themselves are all different when it pertains to EDR. a 60 sq. ft 4 column radiator will do a poorer job of heating than a 60 sq. ft. two column. I know I probably just opened a can of worms.

ChrisJ

gerry gill said:

Radiator sizing and EDR are usually somewhat subjective anyways. For example- btu/240 = sq.ft. edr is a 'rule of thumb' that will only get you close if you are around sea level. Even there its still b.s. Nowhere in that equation is the temperature of the steam based on elevation or even the average temp of steam in the radiator which is 95% of the temp of the steam at the boiler. I tend to size radiators with warren websters charts in the 1922 book titled steam heating. Its on this site someplace. I have a couple hard cover copies here at the shop. Radiators themselves are all different when it pertains to EDR. a 60 sq. ft 4 column radiator will do a poorer job of heating than a 60 sq. ft. two column. I know I probably just opened a can of worms.

Sometimes opening cans of worms is a good thing.


A lot of things said are wrong or don't make sense.  Even in books.

Sometimes they don't make sense but turn out to be right anyway.  But the only way to find out is question it and not blindly assume it's right.

EBEBRATT-Ed

Like @gerry gill mentioned the more columns in a radiator the slower it heats. It's like a hot water fin tube baseboard if you run the return line over the fin tube it slows the output and stacking fin tube in a commercial enclosure you don't get double the out put of one row of fin tube