Pick Up Factor when sizing new staem Boiler

MP1013

I'm sizing a replacement boiler for a 8 family brownstone. which is 4 stories with 2 apts per floor. I' ve taken off all the EDR in the building. Im trying to decide whether to use 1.33 or 1.5 as the pickup factor. Each apt is identical and no radiators have ever been removed or changed. Each apt uses 3 radiators in 3 of the rooms and uses (1) 2"riser and (1) 1 1/2" riser only to heat each of the smaller two bedrooms. No radiators ever existed in these rooms. Generally when I see radiators removed or not original I would use 1.5 PUF. , but here everything is original. I I know the boilers ability to make staem has to match the systems ability to conensate steam. Using 1.3 PUF brings me 43,000 BTU's below a particular boilers DOE. Using 1.5 brings me only 1800 btus' above. Thus I would increase the boiler 1 size which would cost the owner more money to install and I would think to run. Im more inclined to use 1.3 PUF. Would like to know your thoughts.         

gerry gill

i'd use 1.33

i can't remember when the last time i used a larger pickup factor was.

Brad White

In a recent thread,

we had a good discussion about that.



http://www.heatinghelp.com/forum-thread/135810/Measuring-edr-When-to-include-pick-up



You do of course understand that the "net EDR" value already takes into account the 1.33 factor. You need not add for that.



In your example, if one boiler has a 43 MBH deficit and the other has you low by only 1800 BTUH, that small amount would not concern me. That is, if I grasp what you are saying.



In a short-hand way, factors that would lead me to calculate (at least look at) a larger pick-up factor are:

1) Larger pipe sizes, such as an 8" header being fed by a new 3" header.

2) Lack of insulation and/or an inability to insulate piping

3) Deep setbacks and sporadic use requiring a quicker pick-up, such as a church.

4) Particularly long pipe runs.



In these cases you might compare the amount of piping and convert it to EDR and see if that exceeds the +33% factor. Some systems actually do require higher factor but they are rare and have not exceeded +50% at least in my experience. If in doubt, take a stab at it. At least you will know more than the next person.



My $0.02



Brad

MP1013

Pick up Factor

Brad ,

I think you missed my point a bit. I did a EDR Take off on the entire system and came up with hypothetically  1000 sg ft. I have always used Dans formula of multiplying the load by 1.5 than times that by 240 to convert that to BTU output. I than use the DOE of boiler spec to get my size. I use this because 99% of the times radaitors have been removed or changed. In this particular case nothing has been changed at all. Evert apt has the same 3 radiators and the same 2 riser pipes that provide heat. If I use 1.33 the boiler would be smaller, if i use 1.5 it would take me 1800 BTUS past that particular boiler and move me up one size which would cost the client more momey to install. Does that 1800 BTUS warrant me moving up one size just to satisfy it.

Brad White

Missing Info

Maybe I am a bit slow on the uptake. When you say you did an EDR take-off, do you mean that you just measured the radiators? Or Radiators PLUS the piping?



The history of modifications, I do not see how that factors into things; the reality governs



Normally, just the radiator EDR is matched to the stated boiler nameplate "net EDR output" and this number includes the 1.33 SF and presumes the proverbial average installation including the piping. If you take the piping AND radiation as EDR, no factor need be applied. I think it is just a matter of terminology and approach to get to the same number..