The Gorton #2 Saga Continued

jpf321

memory fuzzy ...

I think it was in the neighborhood of 28-35? SR should still have our notes ..



the convectors he has are of various widths .. the smallest in Bath and largest in Living Room.



for sizing they ask for cabinet height, element depth and width.

Mark N

Check My Math

SR's boiler has a net EDR of 360 sqft which equals 86400btuh.  The gross output is 1.33 times this amount or 115,000 btuh.  This means the output of the boiler is 1916 btu per minute.  This is equal to 7.98sqft of steam per minute.  In 9 minutes his boiler only makes 71.82 sq ft of steam.  His convectors have an EDR of 295 sqft,  it takes his boiler 37 minutes to make that much steam.  All I can figure out is that even though a convector might have the same EDR as a cast iron rad it must not condense steam the same way as the cast iron rad.



Mark

steam-rookie

Convector data

Its been another long day at work. I`m off tomorrow.

I will post all of the convector Data after I get a good nights sleep.

Thanks everyone for your help.  Tomorrow is convector day. sizes, pics, locations, and the EDR`s that JP and I calculated.  I will also try to throw in the sq. ft. of each room.   

Mike Kusiak_2

BTU vs. EDR

Mark, what you are not taking into account is 1 square foot of EDR is equivalent to  240 BTU per Hour. If you figure on a minute basis, it comes out to 4 BTU per minute, for each sq. ft. of EDR. So using your example, in 9 minutes the convectors could  require 295 EDR x 4 BTU/min x 9 min = 10620 BTU.  His boiler is capable of 1916 BTU/min so in 9 min it can generate 17244 BTU. So in reality, his boiler is quite oversized compared to the calculated connected EDR load, by a factor of 1.62.



 This is confirmed by his on off times when pressure cycling, which are  about 150 sec ON, 120 sec off, which correspond to a oversize factor of about 1.8 which is in the ballpark of the oversize obtained from JP's EDR calculations.

Mark N

Oversized

Mike thanks for the reply. What I think my problem is that I'm trying to figure out on the convectors work as compared to my cast iron rads. As best as I can figure the convectors heat very quickly then convection should keep cooling them so they can keep condensing steam. If air flow isn't optimal or the boiler is quite a bit oversized they can't cool fast enough to keep up therefore the steam that isn't condensed is able to close the air vent. Once this happens the boiler will keep cycling until the thermostat is satisfied.



Mark

Mike Kusiak_2

Yes, you've got it

The convectors ability to condense steam is dependent on its ability to transfer heat  to the air passing through it. If the airflow is blocked it will condense less steam than if air circulated freely and rapidly through the fins. Thats why the published EDR ratings for the same convector may be different depending on its placement or height in the enclosure.



If you put a fan under the convector and forcefully blow air through the fins, it will be able to condense even more steam, and therefore under those conditions may have an effective EDR far greater than the published rating. As long as the convector tubes are filled with steam at constant pressure, the convector can condense steam at a rate only limited by how fast the heat can be removed and transferred to the air flowing through it.



Once the convectors are at equilibrium and cannot transfer heat any faster under the present set of conditions, the pressure will rise and the pressuretrol will begin to cycle to limit the amount of steam generated to only the amount that can be condensed. Thats why, by timing the pressuretrol on-off cycles, you can determine how much oversized the boilers steam generating capacity is relative to the installed EDR's ability to condense it.

jpf321

SR

when you open up each convector .. make sure you have a vaccuum with brush attachement in hand so that you can vacuum off all your convector fins and cabinet openings .. the most important part of convectors is airflow and dirty fins or cab opening restrict air flow .. as do pieces of furniture or curtains in front of cabinets.



jpf