Steam boiler w/indirect coil pressure drop

STEAM DOCTOR

Hi and hope that everyone is doing well. I have installed a number of indirects with steam boilers over the years. I have primarily used techtanium indirects( that's what my supplier has in stock) with satisfactory results. Virtually endless hot water. I am looking to move away from TT due to larger then acceptable number of coil failures and horrible customer service. I never paid much attention to coil head loss/pressure drop. As I started looking into various indirects,  I took notice of the wide range of pressure drops. How does one figure pressure drop/circulator sizing in these applications? The starting pressure (when using a steam boiler) I not much above zero. Obviously,  keep the circulator as low as possible.... I did install a Burnham stone lined indirect (number) of years ago and results were good. The Burnham alliance has a rather high pressure drop. Any thoughts and ideas would be greatly appreciated. 

Jamie Hall

The pressure drop of concern is that of the piping and the indirect. Unless you have a lot of piping, it's the indirect. Presumably you are using boiler water directly? If so, be sure to pump away from the boiler. Then the fact that the boiler pressure should be essentially atmospheric makes no difference.

So... find the pressure drop through the indirect at the flow you want and pick the pump to fit.

STEAM DOCTOR

@Jamie Hall  Thanks for responding. Using boiler water directly. Pumping away and keeping circulator as low as possible. My challenge is figuring out how to size circulator. I am very familiar with pump curves and pump sizing charts. My issue is that pump charts assume certain pressure. 12 psi or whatever. My application involves 2 psi or less. Can I still use the regular pump charts? Thanks. 

Jamie Hall

Yes. Consider. What the pump curve or chart is showing you is what the flow will be -- on the curves it is on the horizontal axis -- for a give pressure -- on the vertical axis. That pressure is what the pump will add to the pressure at its inlet for a given flow. So let us consider a pump -- in fact, a Taco 007, a nice common circulator. At 10 gpm, it will add just about 7.5 feet of head, or around 4 psi (not much -- but it's a circulator. At 20 gpm it will add about 2 feet. Conversely, if the head loss in the circuit it is pumping in is 8 feet total, it will pump just about 8 gpm.

If your chart is limited to one pressure, that's still the pressure difference between the inlet to the pump and the outlet.

The pressure -- head -- added and the flow are both completely independent of the actual pressure -- all we are interested in is the pressure difference between point a and b.

The only time that one becomes interested in the actual pressure --gauge or absolute -- at the inlet is if one is worried about whether it is high enough to prevent cavitation in the pump. Which, if you are pumping away from the boiler, is not going to be a problem. Usually...

STEAM DOCTOR

@Jamie Hall Thanks

Snowmelt

Hey steam doctor can you show me a picture of your indirect water heater with steam boiler , I want to do that at my moms house…….. she also has a wet zone, baseboard in a added on room

ethicalpaul

You want your mom to have to pay to heat up a (relatively inefficient) steam boiler all summer? I never understand this.

EBEBRATT-Ed

@ethicalpaul

Any difference between a indirect with a steam boiler versus a HW boiler? I don't see any difference other than one being an open loop and one a closed loop. Temp is maintained in the indirect, not the boiler

@STEAM DOCTOR

I agree with @Jamie Hall

The boiler pressure drop is negligible. The resistance of the coil and the connected piping is all you need in my opinion