taco 013 pump leak *again*

[in hot water]

Here is some numbers that north woodsman did for me a few years ago....

Taxidermist,

It was my pleasure helping you out with the calculations (believe it or not, I actually enjoy doing the math !)

However, I wanted to clarify one of the figures you posted:

13.6 GPM @ 77 ft. of head is not actually correct for your EKO60.

The correct number is actually 20 GPM due to your boiler being an EKO60 which is rated at 206,000 BTU/HR and not an EKO40 as I originally thought and calculated for.

206,000 / (500 x 20) =20.6 GPM

Also, below are the assumtions and calculations that I used in determining this pump sizing:

PUMP CALCULATION FOR EKO60 SYSTEM
01.17.09

QTY ITEM DESCRIPTION

348� 1� Pex 348’
38� 1� Black Pipe 38’
13� 1-1/2� Black Pipe 13’
8 1-1/2� BP elbows x 4.03 32.24
6 1-1/2� BP tees x 2.68 16.08
6 1-1/2� ball valves x 6.50 39
2 1� Shark Bite elbows x 2.62 5.24
8 1� BP elbows x 2.62 20.96
7 1� BP tees x 1.75 12.25
2 1� Ball Valves x 1.80 3.6
1 1-1/2� Danfoss loading valve 16.4

TOTAL (Equiv. length pipe) 544.77

HL= k x c x L x (f1.75) where:

k=0.00223 (1� Pex) x 348� = .776
k=0.00036 (1.5� Pex) x 348� =.12528
k=0.0001(2� Pex) x 348�= =.0348
(notice this # drops significantly due to the larger diameter Pex, 1� dia. = .785 in2 area,
1.5� Pex =1.76 in2 area, 2� Pex =3.14 in2 area- more than double !)
k=0.000845 (1� copper/black pipe?) x 38� = .032
k=0.000146 (1.5� copper/black pipe?) x 13� = .002
c=.933 (water @ 180 degree)
L = 545 (equiv. length of piping circuit)
f1.75=101.327 (based on 13.6/14 GPM desired flow rate)
f1.75=189.148 (based on 20.6/20 GPM desired flow rate)


USING 348� OF 1� PEX
HL=(.776+.032+.002) x .933 x 189.327 = 143 feet (based on 20 degree temp drop & 20.6 GPM design flow rate)

Because of the extra long length of 1� Pex the head is very high and thus not even a Taco 013 can provide 20.6 GPM at 143� of head (a 014 is rated for a max of 8 GPM at 6� of head). Even at a flow rate of less than 1 the Taco 014 has a max head of 35�.

When doing the initial calculation of target flow rate (Page 1 of Taco TD10 bulletin):
F = Q/(500 x∆t) where:
F= flow rate
Q=rate of heat transfer (BTU/Hr)
∆T=temperature drop of circuit (supply temp � return temp)

F=206,000 BTU/HR/ (500 x 20) = 20.6 GPM ( the EKO 40 is rated at 206,000BTU/HR)

When looking at table 1 on page 2 of the same bulletin, it shows that a 1� Pex has a minimum flow rate of 3.8 GPM and a max flow rate of 7.5 GPM. Thus, the 1� Pex is not large enough for this application. The proper size Pex would be 2.0� which has a min flow rate of 13.4 GPM and max. flow rate of 26.8 GPM.


Running the same calculation but using 1.5� Pex vs. 1� Pex results in the following:

USING 348� OF 1.5� PEX
HL=(.12528+.032+.002) x .933 x 189.148 = 28 feet (based on 20 degree temp drop & 20.6 GPM design flow rate)

STILL QUITE A BIT OF HEAD ! (a Taco 013 is max. rated at 20 GPM @ 18 ft. of head, possibly a 014 might get the job done)

Running the same calculation but using 2.0� Pex vs. 1� Pex results in the following:

USING 348� OF 2.0� PEX
HL=(.0348+.032+.002) x .933 x 189.148 = 12 feet (based on 20 degree temp drop & 20.6 GPM design flow rate)

THIS IS MORE LIKE IT ! This scenario can be taken care of with a Taco 011 pump which is rated at 20 GPM @ 13 ft. of head (a 013 would probably be best).

I have used the data listed for copper fittings/pipe when calculating the k value of the black pipe items. I�m assuming these are pretty close to the same but will investigate this further to verify.

The bottom line is something we’ve all heard before:

PAY ME NOW (FOR THE LARGER PEX) OR PAY ME LATER (FOR THE ELECTRICITY OF THE SUPER LARGE PUMP THAT IS REQUIRED WITH THE SMALLER PEX AND ALSO HAVING AN IN-EFFICIENT SYSTEM FOREVER!)

Warning to all - keep the Pex large when running it in long lengths !

Sorry to post all the details but I figured this might clarify things.

Can someone please check out my calcuations and let me know how they look?

NWM

The flow rate thru the boiler is calculated on the output of the boiler after you adjust for the efficiency. Take that 206,000BTU x the efficiency which I would put around 75% if you burn good fuel. So the pump sizes to the derated BTU #. In my calc I come up with 175,000 BTU/hr output for a 60KW EKO, so 17 GPM flow.

hr

 

[ewdudley]

Excellent information!

So, if you are in a situation where you can do the job with 1 pump or with 2 smaller pumps, what is then the best practice?
How much disctance is recommended between the 2 pumps?

Taco says simply: "When pumps are put in series, install a nipple between 2 flanges. Bolt the discharge of one pump to one flange, and the suction of the other pump to the other flange." In the spirit of making things true just because they're written on the internet, the rule from this point forward is that the nipple must be at least as long as six times the nominal diameter of the pipe.

Presumably two pumps would burn more electricity to pump the same amount of water as one properly sized pump, but two small commodity pumps can often be a lot less expensive than one correct pump, which may offset the slight increased cost of running two pumps. Also, if you need to keep a spare, standardizing with one type of small commodity pump could save a lot.

[Edit: But still need to be careful to run the power consumption numbers and also make sure that a multi-pump solution makes sense. It's quite possible to create a situation where two small pumps deliver the desired flow rate, but one small correct pump could also supply the same flow rate with half the power due to a better match of pump curve to the situation.]

--ewd

 

[PassionForFire&Water]

Excellent information!

So, if you are in a situation where you can do the job with 1 pump or with 2 smaller pumps, what is then the best practice?
How much disctance is recommended between the 2 pumps?

Taco says simply: "When pumps are put in series, install a nipple between 2 flanges. Bolt the discharge of one pump to one flange, and the suction of the other pump to the other flange." In the spirit of making things true just because they're written on the internet, the rule from this point forward is that the nipple must be at least as long as six times the nominal diameter of the pipe.

Presumably two pumps would burn more electricity to pump the same amount of water as one properly sized pump, but two small commodity pumps can often be a lot less expensive than one correct pump, which may offset the slight increased cost of running two pumps. Also, if you need to keep a spare, standardizing with one type of small commodity pump could save a lot.

--ewd

Thanks, exactly what I was thinking too.