Pickup factor advice

delta T

Doing a steamer replacement, need some advice on the correct pickup factor. This is a 12 unit motel converted to apartments, total radiation is 701.6 sq. ft. one pipe system with condensate receiver, not enough vertical height for a good A dimension to get rid of the receiver. There are two 4" mains leaving the boiler room, one about 115' long, the other about 270' long. The mains and the dry returns are both buried in a ditch that runs under every unit, not big enough to crawl through, but I can stick my head in. The ditch is about 3' in from the outside wall, the pipes were wrapped (poorly) with yellow fiberglass batting when a major renovation was done a few years ago, but that is it as far as insulation goes. The majority of the mains are inaccessible now.

My question is this:

Does anyone have any experience dealing with long, partially/mostly buried steam mains, and if so what did you use for a pickup factor? My usual common sense is that I am probably paranoid and I should always err lower than I think, but this is a different case I think (see the paranoia?). I cannot see what the outside foundation wall is, owner is unsure. The original structure was built in the '20s though, so I am pretty sure I will be losing a TON of heat through the long main just through the foundation. Best guess would be it is un-insulated concrete, or stacked sandstone, both are common for the area and time period. Oh Btw, the mains do step down in size as they go as far as I can tell, I'm assuming the dead men sized it correctly, but most of the rads have been changed over the years so who knows what reality is now.

Any thoughts/advice greatly appreciated.

My EDR sheet is attached if anyone is curious, trying to decide between an IN11 and an IN12 for the new boiler. If my pickup is 1.25 the IN11 makes sense. If it is 1.33 the IN12 is a better fit. Better to err high on this? Think I am way off base?

Danny Scully

I’m a little confused...if your EDR IS 706 than an IN9 seems more suited for the application. Am I missing something?

delta T

Altitude deration at 6000'

delta T

@Danny Scully sorry, forgot to mention that, its on the attached sheet wrapped up in the formula for the required boiler input box. 4% per 1000' sure adds up!

Danny Scully

So you’re figuring a 16% loss? Still, IN10 is right there. Err high would be IN11 for me.

delta T

4% x 6 gives me a 24% loss no?

delta T

Product sheet from Burnham says "Ratings shown are for installation at sea level and elevations up to 2000'. For higher elevations, reduce ratings 4% for each 1000' above sea level. I know this is a perennial debate, but my understanding has always been that for atmospheric, you de-rate based on total elevation, not just elevation above 2000'. Let me know if I am wrong, or if there is enough of a fudge factor built in to the calculation that I can still ignore the bottom 2000'

Danny Scully

Maybe it’s worth calling US Boiler, I was calculating every 1000 ft over 2000 ft, but I may be misinterpreting it.

delta T

Yeah might do that. Might call the gas utility here and see what they say about the gas too.

Any good guesses on where to start with finding a good pickup factor? I would try and work backwards from the rads to figure what size the main is, but they are all replacement rads, mostly sized by what would fit in the room vs what should be there so all I can go off with any sort of reliability is the supply piping size to the rads. That will give me a pretty wide range for what size the main is and what lengths there are, not sure I could get a good number for how much loss I am going to get on the mains. What would you do?

Danny Scully

Well they build a 1.33 pickup factor into their ratings so I certainly wouldn’t go over that, especially if you’ve visually inspected the piping and found it to be insulated. What are your concerns with the insulation?

delta T

My biggest concern is the unknown. The insulation job is just paper backed fiberglass batting strips wrapped around it with some duct tape in a few spots. I have no way of verifying that they did actually insulate the whole thing or not, I can see the 30' or so in the boiler room, and another 10' out near the end of the main on the 270' one (they have a small section of flooring up in one unit that is currently being remodeled), and I can only see the other main in the boiler room. I may be over thinking this, but I just want to see what others think about the CYA factor. I hate installing something too big, but I don't want complaints when it gets cold either.

US Boiler says to derate based on total altitude above sea level, so 24% in my case.

Danny Scully

Use this line in your invoice, I created it just for you

“Boiler sized based off connected radiation and industry standard 33% pickup factor. Pickup factor assumes pipe/fittings to be insulated, as they can not be visually inspected in totality. The customer is aware and agrees that potential existing insulation deficiencies could lead to poor boiler performance. Furthermore, the customer holds (your company name here) harmless regarding this matter.”

delta T

haha I like it, believe me there will lots of disclaimers in this bid!

Steamhead

Where is this job located?

The Steam Whisperer

Those 2 4 inch mains are huge for that radiation load and will probably eat up a lot of steam. Also, how good is the main and radiator venting. Big main vents and small radiator vents will allow a smaller boiler to perform better. I think those big pipes fall under the unusual pick up factor, so a bigger boiler may be necessary.

delta T

@Steamhead the job is in southern Colorado, nearest city with a published design day temp (very similar climate) is Pueblo, CO with a 0 degree 97.5% design day.

@The Steam Whisperer The main venting is in the boiler room through F&T traps into the condensate receiver at the end of the dry returns. I am thinking of adding a few big mouths or Gorton #2's to the ends of the dry return before the F&T's to expedidite the main venting. Radaitor venting is a hodgepodge, going to replace them with different Gortons based on the distance from the boiler room.

Thanks all for the advice, I think I am leaning towards the IN12 which will give me 727 sq ft after efficiency (79.5%), altitude deration (24%) and a 33% pickup factor, or 756.8 sq ft according to the I=B=R steam output rating adjusted for altitude.

An IN11 will give me 684 sq ft after altitude deration according to the I=B=R rating, and may fall short.