Circulator Sizing for Indirect

Users who are viewing this thread

mattk22359

New Member
Messages
5
Reaction score
0
Points
0
Location
NH
I'm trying to finish specing out the components I'll need to convert my tankless coil to an indirect water heater. At the moment I am trying to properly size the circulator pump. I was hoping someone could check my work. All calculations were taken from the article on circulator sizing on this web site located here: http://www.comfort-calc.net/circulator_sizing.html.

I first calculated Equivelant Feet Pipe as follows: (assuming 1" copper):

16' Copper (est.) x .042 = .672 EFP
1 - Tee (side port) = 4.5 EFP
4 - 90* Elbows = 10 EFP
2 - unions = 1.5 EFP
-----------------------------------
16.67 EFP

16.67 EFP x .04 = .67 Feet Head

So assuming a Superstor Ultra SSU45 which has 7.9 Feet Head @ 10gpm (recommended flow rate)

If I assume a 1.5 Feet Head for the boiler that would be:

Boiler = 1.5
Plumbing = .67
SSU45 = 7.9
---------------
10.07 Total Feet Head @ 10gpm

If this is correct then using the the Taco Pump curves as shown here http://www.comfort-calc.net/Piping/Taco_pump_curves.JPG in order to maintain the Superstor's 10gpm recommended flow rate I would need at
least Taco 0012 assuming it is better to have a little more flow rather than less then spec as indicated on Taco's own web site here: http://www.taco-hvac.com/uploads/FileLibrary/curves003-008.pdf and here: http://www.taco-hvac.com/uploads/FileLibrary/curves009-0014.pdf

Thanks in advance for any additional insights/help/guidance you'd be willing to share.
 

Dana

In the trades
Messages
7,889
Reaction score
509
Points
113
Location
01609
You're probably going for overkill here- unless you have enough boiler output that you need higher flow to protect the boiler there's no advantage to higher flow rate. Install enough pump to keep the boiler's delta-T down to the 20-25F range and you'll be getting about as much output out of the system as you would at higher flow, which would only result in a lower delta-T on the boiler, not more first-hour gallons out of the system.

If your boiler's output is, say, 108,000BTU/hr and you're designing for a 20F delta-T, that means you need 108K/20=5400lbs/hr of water pump rate. A 8.34lbs/gallon that's 5400/8.34=647gallons/hr which is 10.8gpm. For a 25F delta-T you only need 8.6gpm, and for a 30F delta-T, 7.2gpm.

As the flow rate drops the head also falls, and it's faster than linear- at 7gpm the head is roughly only about half what it is at 10gpm. At 8.5gpm it's about 70-75% of what it is at 10gpm, so a Taco 007 would be more than enough pump to keep the delta- under 30F, and it would run close to 25F. A Taco 0010 would lower the delta to close to a bit over 20F. A Taco-0012 would be overkill, raising the flow to something like 14-15gpm, and the delta-T down to ~15F for no benefit.

Methinks a Taco-007 would be fine here. You'd be giving up at most a few percent of first-hour gallon performance due to lower-than-recommended flow on the SS. If you're concerned that the boiler is ultra-sensitive to high delta-T, go with a Taco-0010, then kick yourself when it turns out your head calc ran a bit high. :)
 

CattleDog

New Member
Messages
42
Reaction score
0
Points
0
Location
Portland, Oregon
take a look at Grundfos 15-58

If you are trying to span between a taco 007 and 010 take a look at the small Grundfos three speed. At 10 feet of head you can get 6 gpm on medium and 10 gpm on high with a 15-58.

You will have some adjustment possibilities to tune the delta T across the boiler if the equivalent feet of pipe calculation is not exactly matching the real system.
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks