Adjusting ΔT

Alan (California Radiant) Forbes

We are replacing a boiler with an existing 1" supply and return. The heat loss calculation for the area comes out at 125,000 BTU's and at a 20°ΔT, the pipe size should be 1¼". How can I adjust the ΔT higher to make the 1" pipe work?
The radiant heat was done with ½" copper tubing.

SeymourCates

Since you can't pump 12.5 GPM through 1" (without a hydraulic mining pump), the DT will automatically climb when you connect it all up. You might flow 9 GPM depending on total pipe length and pump sizing. In that scenario, the DT will be 27.8. You'll get quite a drop in the AWT which begs the question if the emitters can deliver the 125K at the reduced AWT.

Alan (California Radiant) Forbes

Thank you, Mr. Cates. I've got an Alpha2 as the system pump and maybe it will figure it out for me.

SeymourCates

Ahh.........no, it will not figure it out for you.

The Alpha2 will give 9 GPM at 9.5' head. The question is what is the head for the system side @9 GPM? If it is more than 9.5' (likely), you can't get 9 GPM from that pump. The flow rate will drop and the DT will widen. That might still work for you...........depending...........

SeymourCates

Actually, after running the numbers, you'll be fine if the equivalent length of 1" is 150 feet or less. You will get 10 GPM @ 9 feet which matches the capacity of the pump. That gives you a DT of 25.

Alan (California Radiant) Forbes

Then I should be able to figure out the pressure drop of the system by the flow rate, no?

SeymourCates

You figure it with two variables: Equivalent length and flow rate.

Jamie Hall

Alan (California Radiant) Forbes said:

Then I should be able to figure out the pressure drop of the system by the flow rate, no?

Or if you have the pump curve handy, you can enter with the flow rate and read the pressure drop off the curve. That would be the pressure drop of the whole circuit, of course.

SeymourCates

Unfortunately the pump curve cannot determine the pressure drop of the whole circuit. The technician must calculate that based upon the variables of equivalent length and flow rate. Once the pressure drop of the circuit is already known, it can be utilized in the pump curve to determine the resulting flow rate.

Gordy

^i like this guy

Jamie Hall

SeymourCates said:

Unfortunately the pump curve cannot determine the pressure drop of the whole circuit. The technician must calculate that based upon the variables of equivalent length and flow rate. Once the pressure drop of the circuit is already known, it can be utilized in the pump curve to determine the resulting flow rate.

I beg your pardon? If you measure the pressure differential across the pump -- perhaps with a pair of pressure gauges at the inlet and outlet of the pump, or a differential manometer, you can use the pump curve to determine the flow through the pump. Conversely, if you measure the flow through the pump, you can use the pump curve to determine the pressure differential across the pump.

It's true enough that if the circuit doesn't exist, then someone has to calculate the pressure drop of the circuit based on the design circuit parameters and the desired flow rate -- or the flow rate, based on the target pressure drop and the design circuit parameters.

This is not rocket science; it's elementary engineering hydraulics and people do it all the time.

I was, however, making the perhaps naive assumption that the circuit actually existed.

Gordy

I knew what you meant Jamie, but your post was a bit illusive to the method.

Yes you can take a circ, pressure gauges, on inlet, and outlet to determine the head, and flow rate with the given Circ on its chart. However knowing the unkown to size the circ to begin with saves some money if the wrong pump size is selected.

SeymourCates

@Jamie Hall

Yes, sorry mate, I was under the assumption that the circuit did not already exist and that the OP was going to install same. Of course your method is fine if one has the equipment and the taps to determine pressure at the inlet and outlet of the circ. I do note that it is relatively rare to find such a convenient setup. There was a vendor offering isolation flanges with taps although they were pricey IIRC.

Harvey Ramer

Is it ceiling radiant or floor radiant?
If it is ceiling, the higher dt should not be as much of an issue. Adjust your supply temp upwards till you get the right amount of radiation.
If it is a radiant floor, the dt becomes much more important from a comfort standpoint. Based on what you are describing, I would turn the 1" supply and return into an injection loop. Basically, connect the supply and return together at the manifolds and add a second pump for the radiant. Bring the 1" supply and return into the manifold piping with closely spaced tees. Control the pump on the (now injection loop) with a tekmar 356 to provide variable speed mixing with odr. Bump up the supply water temp until the radiant loop achieves the the required water temp for design day with the injection pump running at 100%.

Gordy

May I ask why 1 1/4” pipe is out of the equation? Keep costs down?

EBEBRATT-Ed

I like @Harvey Ramer idea about using two pumps and an injection loop.

Why are we making this difficult? Run the loop as is and install a 1 1/4 circuit setter and measure the flow with a flow meter. Then use the pump curve from the existing pump to determine head andflow. Convert it on the B & G wheel to what you need and select a new pump

Your talking about needing 12.5 gpm through 1" which is good for normally about 8 gpm.

Yeah you need a little bigger pump but it won't need a

"1" (without a hydraulic mining pump), as @SeymourCates mentioned.

Little high on velocity but it will work

SeymourCates

@EBEBRATT-Ed

Yes, agreed, it's not catastrophic at 12.5 GPM. A Taco 0014 would do 12.5 feet @ 12.5 GPM.

None of the Alphas would make it, however.

Zman

You are talking about the difference between 3.27 and 5.11 fps.
There is nothing wrong with pushing 5.11 in a closed heating system. If it were new construction, you would naturally use 1 1/4", I would not tear out existing piping over it.
It will take a bit more pump. If you have the equivalant of 50', that would be about 1.5' of additional head.

hot_rod

I agree 1" can handle that 12 gpm. A growing chorus suggesting 5 fps is acceptable in hydronic design. Mostly Canadians

Right around that 5 fps is when you can start to hear some velocity noise, It is also about the velocity where dirt and rust particles start moving easily
I'd use it at an absolute max flowrate for the special circumstances.

The Caleffi Quicksetter is a simple, inexpensive way to view and adjust flow, and it can double as an isolation on the circulator.

Gordy

If it were a ceiling radiant which with 1/2” copper I doubt. Anything over a 15* delta is noticeable depending on tube density.

Canucker

> @hot rod said:
> I agree 1" can handle that 12 gpm. A growing chorus suggesting 5 fps is acceptable in hydronic design. Mostly Canadians
>
> Right around that 5 fps is when you can start to hear some velocity noise, It is also about the velocity where dirt and rust particles start moving easily
> I'd use it at an absolute max flowrate for the special circumstances.
>
> The Caleffi Quicksetter is a simple, inexpensive way to view and adjust flow, and it can double as an isolation on the circulator.

Crazy Canucks.

Alan (California Radiant) Forbes

I just wanted to post the original plans that called out a 1½" supply and a 1" return. I was there doing the plumbing 28 years ago and remember the radiant going in. The oldtimer (now dead) doing the radiant was ornery and now, I'm the ornery oldtimer in his footsteps. His name was Charlie Pistante and is a radiant legend in these parts.

EBEBRATT-Ed

The other day I went back to a job I worked on in 1978 UGH That's almost 40 years. Fun to go back though!