Thermal Equations & a few questions...

....jc

Folk's,
Can anyone give me a pointer to online Thermal Equations? I would like to be able to calculate things w/o bothering you guys!

Q1 - Given 180* water temp and Slant Fin 15 baseboards, how many feet of basebaord can be reasonably fed with a 1/2" pex line?

Q2 - Given 180* water temp and 1/2" copper pipe(maybe 6 - 8' long), how many BTU's can be delivered per hour at 1 gpm & at 3 gpm?

Thanks,
....jc

Unknown

I can...

25 feet of 1/2" Slant/Fin Fineline 15 will give you a drop in water temperature of 20°, if your flow rate is above 1 gpm.

Figure the second question from here...

http://www.slantfin.com/spec-fineline15.html

The values and pipe capacities are from here....

http://www.heatinghelp.com/shopcart/product.cfm?category=2-14

Noel

....jc

Thanks Noel...

The element in the baseboard is actually 3/4" but is fed by a 1/2" pex pipe. I'm trying to calc how many feet of this baseboard can be in one zone.

The 2nd question relates to a friend's installation. He has a Buderus boiler with a built in indirect W/H. I can't remeber the size or model. Aside from all of the internal connections(feeding the indirect), all he has for output from the boiler(to serve *everything* else in his structure(2 floors of radiant heating) is a 1/2" copper pipe that feeds a fancy manifold. I am trying to figure out how many BTU's per hour, that the 1/2" pipe can possibly provide. I think the pipe is too small, but an 'expert' told him to use the 1/2".

Thanks,
....jc

Unknown

15,000 btuh

at 20° F Delta T.

Not a lot.

1/2" pex is less than copper, by a little. I don't remember exactly how much less.

Noel

Tim Doran_2

Baseboard Calc

To calculate the max lenght of fin you can use:
max gpm x desired delta T x 500 if using 100% water / output per lineal foot @ 180 degrees.

In the second part of the question, is the copper tube the heat emitter?

Tim D.

....jc

Thanx for the replies!

Tim,
The 1/2" pipe is the sole output(except for the built-in indirect) from the boiler to a 'mixing console' which supplies all of the zones for the structure. What I am trying to figure out, is that if the boiler is say an 80,000 btu output, and all of that output is confined to that 1/2" line, how many btu's could the unit possibly supply. My near boiler piping is 1-1/4", his is that 1/2" line, which feeds at least 4 zones. His fuel expenses are high, and I am thinking it's because of that small feeder line.

Thanx,
....jc

Unknown

You're right

He has a problem.

If he has a much higher difference between the supply and return, it gets closer to handling it.

At an 80° F delta T, he's moving 60,000 BTUH.

If it's baseboard, and no mixing devices, and going out at 180° and coming back at 100°, he has probably got balance problems as well.

It just ain't right, Pa.

Noel

....jc

Baseboard is mine - Boiler is his...

Folk's,
The 2 questions represent 2 different systems/scenarios.

I was unable to find the thermal equations listed above. Any better pointer?

Not being a Heating Pro, the term Delta T is very confusing. I assume it means the difference in temperature. The problem that I have is: Difference between what and what. I mean if I'm trying to calc a length of baseboard with 180* water as input, what would a likely Delta T be?

Thanks,
....jc

S Davis

Delta T

Most of the time we design a high temperature baseboard system for a 20 degree delta T(or difference) Between supply and return water temp. The other part of the equation is flow you need 1 gallon per minute to move 10,000 BTU's of heat at a 20 degree delta T, so you would use a pressure loss chart to find out how much flow you can get through a given length of pipe while staying below a velosity of 4 feet per second because above that you can have noise problems.
If you need pressure loss charts you should be able to get them from your supply house, Grundfoss, B&G and Taco all have them for pump sizing.
Pump sizing is the other part, you need to make sure your pump is sized for the pressure loss of the system loops.
The pump curve charts will tell you how much flow or(GPM) gallons per minute the pump will move at a given pressure loss.
I hope I have not confused you more.

S Davis


Apex Radiant Heating