Head, Friction and Cast Iron Radiators

Brad White_185

is, as Mike pointed out, essentially zero, whether tall or short. The piping leading to and from those, however has some resistance.

It has to- no resistance means no flow and then where are you, Gwen?

Exactly! And without a paddle.

The term "viscous friction" is a broad term which means, "if you use glycol or anything but water, take that into account".

Most piping tables are based on water and that at 60 degrees usually. Not a huge difference to speak of between that and heating temperatures, just a base line.

Assuming the system is a closed system, there is no need to take into account system height into the friction or pump head side of the equation. (Expansion tanks and relief valves if the system is rather tall, yes, but not the circulator.) All water that goes up displaces what goes down like a Ferris Wheel; the height cancels out in a perpetual siphon. Much as Mr. Siegenthaler said.

If you can take a good guess at the pipe sizes and approximate heat losses of the structure, I can help you size the circulator.

One thing which may be of benefit to you is, (assuming that replacing the circulator is part of your plan), variable speed drives. These neat devices can infinitely compensate for variables in the calculations, not a substitute for poor guessing but to absorb unknowns. Say your system starts up and heats well. You can still turn down the circulator to save energy to a point where you begin "not to keep up". Then kick it up a notch and you have optimized your pump energy use.

Flow is a forgiving variable you know- cut the flow in half and you will still get about 90 percent of your output capacity. Use that to your advantage!

Brad

Radiator Ranger

Water System - Head, Friction and Cast Iron Radiators

Hi All -

I'm trying to do load calcs. on a system that was installed ~ 30 yrs. ago (into stick frame buildings that were built in the 1930's) and which was never specd. i.e. no heat load calcs. or circuit load estimates and no as builts. We've now got 130+ heated buildings on 2 sides of a river. There is about 55' difference between the north and south side of the river (from the well house). Most of our emitters are cast iron radiators. There are circ. pumps, heat exchangers and crossovers in there too but my questions today are really radiator related.

1) How can I determine how much resistence cast radiators represent in a circuit?

2) If designing a system with cast iron radiators would a choice to install emitter units w/ overall height of 24" or less measurably effect energy use within the system Could I possibly downsize the pumps if good emitter choices are made?)? OR Would it be useful to keep emitters low or of low resistence by some other radiator design feature i.e. some wall units have huge interior cavities (compared to other radiators).

3) What are the benefits/ consequences of installing cast iron wall radiators in places in the system with flow problems (because they have large interior spaces which appear to offer less resistence or friction in the line).

These questions are directly related to reading the following statement from Siegenthaler p. 148

"To maintain a constant rate of circulation in any fluidfilled piping loop, the circulator need only replace the head loss due to viscous friction."

How can I determine the viscous friction that currently exists within the system?

I saw Dan Holohan speak in Lynwood, Wa. last week - it was by far the best mtg. of the week for me. So interesting to learn about central heating history and the effects on society and energy use. It was well worth my time - what a pleasure, what a resource - I love that guy - Thanks Dan!!

For a little more info. our current catalog has a breif article about our heating system at the end of the issue: www.breitenbush.com.

Radiator Ranger

Water System - Head, Friction and Cast Iron Radiators

Hi All -

I'm trying to do load calcs. on a system that was installed ~ 30 yrs. ago (into stick frame buildings that were built in the 1930's) and which was never specd. i.e. no heat load calcs. or circuit load estimates and no as builts. We've now got 130+ heated buildings on 2 sides of a river. There is about 55' difference between the north and south side of the river (from the well house). Most of our emitters are cast iron radiators. There are circ. pumps, heat exchangers and crossovers in there too but my questions today are really radiator related.

1) How can I determine how much resistence cast radiators represent in a circuit?

2) If designing a system with cast iron radiators would a choice to install emitter units w/ overall height of 24" or less measurably effect energy use within the system? Could I possibly downsize the pumps if good emitter choices are made?)? OR Would it be useful to keep emitters low or of low resistence by some other radiator design feature i.e. finned-tube units, some wall units have huge interior cavities (compared to other radiators) etc.

3) What are the benefits/ consequences of installing cast iron wall radiators in places within the system with flow problems (because they have large interior spaces which appear to offer less resistence or friction in the line).

These questions are directly related to reading the following statement from Siegenthaler p. 148

"To maintain a constant rate of circulation in any fluidfilled piping loop, the circulator need only replace the head loss due to viscous friction."

How can I determine the viscous friction that currently exists within the system?

I saw Dan Holohan speak in Lynwood, Wa. last week - it was by far the best mtg. of the week for me. So interesting to learn about central heating history and the effects on society and energy use. It was well worth my time - what a pleasure, what a resource - I love that guy - Thanks Dan!!

For a little more info. our current catalog has a brief article about our heating system at the end of the issue: www.breitenbush.com.

Thank You,
Gwen

Mike T., Swampeast MO

At any rational flow rate, head loss/friction in a standing iron radiator is considered to be zero.

Are you certain the system originally used circulators--especially on the radiation side of the heat exchangers? While a bit late, in the 1930s gravity systems were still used. Gravity systems have utterly enormous pipes. Even a fairly small structure will have mains that look big enough to heat an elementary school. In the case of systems designed to operate under gravity but now under forced circulation, head loss in the piping (again at any rational rate) is essentially zero.