Pick up Factor calculation/real life

STEAM DOCTOR · August 2022

Siphoning this conversation off of another thread. Looking for real life pick up Factor calculations. We need volunteers. People with actual steam systems. We need two basic facts. First is the EDR of your radiators. Second, is detailed piping information. Pipe size and length of your mains. In addition pipe size and approximate length of the piping going to each individual radiator. For example, if you have 1.25 inch piping going to a first floor radiator. That is approximately 10 ft of 1.25 in pipe. We would need the total radiator piping. There is a bit of a fudge Factor for fittings and valves. Don't remember that factor, if there is one, off the top of my head. And I would assume we need to add a little bit for header piping. Once we have that information, we can calculate heat loss of piping and figure out what percentage it is relative to radiator EDR. Once we have enough case studies, we can have a better handle on real life pickup Factor. Everyone and anyone is welcome and encouraged, to add or comment or correct etc do anything stated above. Why make assumptions when we can work with real life information? Some arbitrary factors may not be exactly what they seem.

Jamie Hall · August 2022

Hey @STEAM DOCTOR -- take a look at the note I tacked onto the end of the thread you spun this one off of! If I have the time I can get you at least some of the numbers you are looking for for Cedric -- but not today! Well, some of them right away. Total system EDR, not counting the piping, is 1485 which is, nominally, 346,500 BTUh. Cedric is firing at a nominal 2.75 gph, for a gross input of 379,500 BTUh. The nominal efficiency is around 83%, which suggests that the net output should be 312,500 BTUh -- but the 2.75 gph is based on nozzle size, and honestly I don't know what @Charlie from wmass has the pressure set at, so I'm not sure what the real firing rate is. If it is set at 120 psi, that would be 3.0 gph from a 2.75 gph nozzle-- which would exactly match the demand with that efficiency. But what are piping losses? I can only give you a guesstimate, and I don't have the time to go out there with a tape measure!... perhaps another 150 square feet? Most of that's insulated, though... but not heavily. But most of it is in spaces which are a good bit cooler than the nominal 70 used for that 240 BTUh/EDR figure, which makes a difference. If we suppose that maybe the pump pressure is set at 140, that would be 3.3 gph -- which would almost exactly match the nominal EDR demand counting the piping -- in other words, a "pickup factor" of pretty darn close to zero.

Which, by the way, matches experience: Cedric will cycle on pressure (7 ounces per square inch), but only on very long runs (45 minutes or more, more or less), and even then the cycles are long (about 10 minutes on, 1 minute off) indicating a very close match of supply to demand.

ChrisJ · August 2022

I have this handy.

https://photos.app.goo.gl/WDg1CnH8yNysGgbb7

STEAM DOCTOR · August 2022

@ChrisJ I might have missed it but I did not see pipe size listed.

STEAM DOCTOR · August 2022

@Jamie Hall I saw your other post. 100% spot on. But I guess we generally assume or guess that the heat output of the piping adds another 33% on to the heat output of the radiators. So let's just take measurements, as best we can, of the heat output of the radiators and the heat outputs of the piping and see if 33% is within a reasonable guesstimate.

STEAM DOCTOR · August 2022

So far, we have documentation from @kcjones. Piping heat output adds 11%

The Steam Whisperer · August 2022

One other big impact is the type of radiation. Fin tube heats up very quickly, so the pick up factor should be lower than with cast iron. There's also a big variance in thermal mass of cast iron.... old column rads have alot more mass per square foot EDR than newer large or small tube radiators.

That 11% sounds about right. Remember the pick up factor on hot water is only 15%.

STEAM DOCTOR · August 2022

Agreed. We're never going to get a truly accurate number. Jamie may have mentioned this in his post. The climate obviously plays a role. The radiators are relatively warm rooms. The mains tend to be in relatively cool basements. The radiator risers tend to be in very cold exterior walls. The header piping tends to be on top of a very hot boiler. I'm just trying to get a relative guesstimate. And maybe the Divine 33% is a bit heretical.

ChrisJ · August 2022

STEAM DOCTOR said:
@ChrisJ I might have missed it but I did not see pipe size listed.

I have no idea why I never added those details.

The mains are 2".
Most of the runouts are 1 1/4" except the main bathroom, top of stairs and small bedroom are half 1 1/4" and then half 1". They did the horizontal runs larger.

I'll try to update the drawing when I have time.

BobC · August 2022

About 13 years ago i ran the calculations for my system. I live in a small (1100sq ft) two story house with 6 rooms. The EDR of all my radiators is 198 sq ft. This house is 100 years old and the old Yankee builders were not about to oversize anything, any nickle they parted with bellowed long and hard.

The header comes out of the boiler and circles the center chimney so it's only 14 ft long and the riser is probably 6 ft long. This means the radiator leadout's are long - 10 to 20 ft ea. The calculated area of all the piping (header, main and radiator leadouts and risers) is about 10 sq ft.

That means my piping accounts for about 5% of the system EDR

Pick up Factor calculation/real life

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