Boiler protection loop

[Armaton]

Has anyone tried using a smaller diameter line for the boiler protection loop? Use 1 1/4" for pipe to and from storage, but use say just 3/4" from the output tee to the thermic valve? Still put in the ball valve, but much cheaper for 3/4" materials than 1 1/4". 3/4" should be able to allow enough flow to satisfy thermal protection, (both corrosion and overheat), and because of the inherent restriction of the smaller pipe water shouldn't JUST go round and round if you forget to close it down. Plus, if you set your pump launch temp at say 160 with a 140 degree valve, thermic valve may be more responsive and charge storage quicker. Just a thought. Waiting for the Guru's to burst my bubble!

 

[Hunderliggur]

I am NOT a guru, but...

Amount invested in the project = A lot
Amount you save on the protection loop (one smaller valve, 5' of smaller pipe) = A little

Plus, at 100F return, you will have 66% of your design flow in the bypass loop. I don't think it is worth the savings to loose the flexibility

The balancing valve will control the flow in the bypass when the thermatic valve is fully open. The water will take the path of least resistance. The balancing valve should be set and forget, not fiddled with..

 

[DaveBP]

I think it is a legitimate question.

I've often wondered what the difference is (in that particular part of the system) between a valved-down 1-1/4 pipe and a regular 1 or 3/4 pipe with the valve open more. Reducer bushings are pretty cheap compared to larger ball valves, especially if you're talking about quality brass or stainless. Copper pipe gets pretty wild in the larger sizes, too. It is normally a pretty short run from the supply line to the return, I would bet my $.125 that it wouldn't change anything but your total cost.

 

[ewdudley]

Assuming a moderately large boiler cranking out a for real 120000 btu per hour, for a 20 degF rise through the boiler -- from a mix temperature of 140 degF to a 'launch' temperature of 160 degF -- the mix flow would need to be 12 gpm:
You have: (120000 btu/hr)/((20 degF)*(500 ((min btu)/(gal hr degF))))
You want: gpm
12.0
And assuming that return temperature from storage was a rather cool 80 degF, then you'd need three parts 160 degF water and one part 80 degF water to bring mix temperature up to 140 degF, which would be 9 gpm through the bypass circuit. So 9 gpm through 3/4 inch pipe:
You have: 9 gpm/(pi (0.75 inch/2.0)^2)
You want: ft / sec
6.5
At 6.5 ft per second you wouldn't build up a whole lot of head through a short section of pipe, and at any system return temperature above 80 degF there would be less flow through the bypass.
So I'm with Dave, sounds like a low-risk way to save some. Plus if you're working in close quarters it could be a lot handier working with smaller components.

 

[maple1]

I think it is a legitimate question.

I've often wondered what the difference is (in that particular part of the system) between a valved-down 1-1/4 pipe and a regular 1 or 3/4 pipe with the valve open more. Reducer bushings are pretty cheap compared to larger ball valves, especially if you're talking about quality brass or stainless. Copper pipe gets pretty wild in the larger sizes, too. It is normally a pretty short run from the supply line to the return, I would bet my $.125 that it wouldn't change anything but your total cost.

Agreed.

 

[Armaton]

It really isn't the $35 that I would save on the original install, (even though I am frugal/cheap), ball valves aren't meant to be left "part way" so it isn't if I will have to replace it, it's when. So I figure when I do replace, it would be cheaper and easier with the smaller diameter. And if it worked the way I hoped, wouldn't need to leave it "partly closed" so may never have to replace. Thank you, Eliot, for the numbers.