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# Just Don't Get Modcon Boiler Pump Charts!

• Posts: 5,545Member
A BTU is a BTU

Your boiler has a Minimum fire it will only modulate down so far. It doesn't matter what you do with the gpm and delta t It is a fixed number. Your system can only absorb so many BTU's at a given average temp this is also fixed.

Your boiler will run more efficiently with a wider delta t.

Carl
"If you can't explain it simply, you don't understand it well enough"
Albert Einstein
• Posts: 462Member
I Think That

is what I am saying. A delta T of only 5, or so, is not going to make for a very efficient system.
• Posts: 45Member
How do you determine D/T

Hi,

Been trying to educate myself on these systems for the past month and a half.

What I can't seem to get is the 20-30* and more D/T's I am seeing, and reading about in my Alpine manual. I read, after the zone has stabilized, a D/T of 5-8* max.

I have done the measurements on the LCD screen, and also on the pipes themselves raped in black friction tape with an inferred gun. The readings were very similar. I just don't see where D/T's of 20* and more come from. Can someone explain what I am missing.

Thanks,

Tom
• Posts: 3,066Member
Pump

I don't know if your talking about your boiler side or system side. Can you clarify please. The two reasons why a small delta-t. Either your pump is oversized or your boiler is oversized. Lasers suck by the way. Suggest you invest in a digital strap on multi temp meter. Cooper makes one in the three Benji area. It will take 4 temps at once and calculate delta for you. I have one and it works like a champ.

The universal hydronic formula of GPM = BTU/HR / (DELTA-T x 500) is all the math you need.
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Posts: 45Member
Zone pumps

Chris,

Not to bore you but this is my situation:

Last Spring I had my heating system replaced with a new one.

Its a 2300sq/ft 1860ish Sea Captains house on Cape Cod.

Had a highly recomended plumber install the system.

Its an Alpine 150 and 4 Taco 007 zone valves.

He never did a heatloss and I wound up with a boiler that is over twice the size I need. I soon realized that he had no idea on how to size a boiler or how to set it up properly.

I have been reading all I can for the last couple of months to get up to spped and see what can be done.

The primary pump is the Grundfos UP 26-99. Probably way oversized also.

I will look for that Cooper strap on temp gauge. Wha does "in the three Benji area"  mean?

It sure looks like the Taco 007 is pumping way to much for the kitchen zone anyway.

Tom
• Posts: 5,545Member
Temp guage

Check out this one http://www.firedragonent.com/DM6802B.htm

I have had one for 2 years and it works well.

3 benji's = \$300

Carl
"If you can't explain it simply, you don't understand it well enough"
Albert Einstein
• Posts: 772Member
edited March 2013

Absolute Mechanical Co. Inc.

www.AbsoluteMechanicalCoInc.com
• Posts: 3,066Member
Suggest You Start

With a new heat loss room by room and then broken out zone by zone. I don't like zoning with pumps as you tend to over pump the zones. At first glance the best way to fix is going to be by adding a buffer tank for the boiler side, then change the zone pumps to zones valves and use a Taco Bumblee Bee as a system pump. Your ok with the 26-99 as your boiler pump. I'd get my system side under control first then play with the boiler pump. Is the boiler also doing DHW? Attached is the Alpine flow chart and I also put the Grundy 26-99 Curve on it.
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Posts: 45Member
D/T's

Thank you all for the replies.

Chris I did look at the Alpine chart but because of the D/T's I read I am way off the chart as to primary flow rates. I am way too low with D/T's ofonly 5-8*.

The P/S plumbing looks OK except for the zone pumps being on the return side not the supply side as shown in the manual.

The kitchen zone is slightly less than 100' ttal so using a head of 6' and the Taco chartI read 13GPM. That seems gawd awful high unless I am doing something wrong.

My thought was to replace the zone pumps with the correct sized ones after determining the correct size.

There is also a Superstor SSU-45 plumbed into the system.

Do you think by getting the zones flowing a the 2-4GPM rate it will help with the D/T's?

Tom
• Posts: 45Member
Heatloss

Chris,

I have done a Slant/Fin heatlosson the home so so have the room to room numbers.

Tom
• Posts: 45Member
Heatloss

Chris,

One other question if I may.

As I look at the Alpine manual why does the boiler head loss vary with D/T?

I thought the head loss was a fixed number due to flow restriction and did ot vary.

Tom
• Posts: 3,066Member

In the HX is dependent on the flow rate through it. The less flow the lower the head loss. You still need to maintain a minimum flow so you don't flash to steam. Giannoni HX's (Your Alpine) are tight and thus why the American mfgs thst use it size boiler pumps for a 20-25 degree delta. I'm a Viessman. guy and all our pumps are sized for a 40 as a boiler pump.
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Posts: 927Member
Are you still confused?

Hey Ced48, are you still struggling with the charts?
• Posts: 462Member
You Bet!

But I think I know what I am going to do as far as pumps and piping. I still do not understand where the delta t numbers in the charts come from, or their useful meaning. I had assumed that the boiler makers were being way over cautious when recommending boiler pumps. This is however, hurting the efficiency of how these primary/secondary piped systems function.
• Posts: 7,356Member
∆T numbers on charts

Are simply the result of dividing BTUs by 500 and again by GPM.  Based on what I see, the manufacturers assume far more external (loop) head loss than what we build.  If you know what you're doing, just use the head loss curves for the HX and pick the smallest pump that gets the the job done (I use 5F below ∆T alarm level) at full fire.
• Posts: 462Member
So, I Divide 44,000 BTU's

by 500, then by GPM, in this case 3. I come up with 29.33, right? Is this the delta t number, and what does it mean?
• Posts: 462Member
Also, What Do You

think of running 3.5 GPM thru a small baseboard loop and thru the boiler, no primary/secondary? The boiler being a Lochinvar 55, 44,000 BTU net. Boiler chart says 3 gpm with 35 degree delta t. The 3.5 GPM would be controlled by a Quicksetter balancing valve, so there would always be that flow rate. Water temp could be controlled by the outdoor sensor, but that's it.
• Posts: 462Member
By the Way,

I know what delta t means, I just don't understand how it is used in sizing a primary loop in this boilers.
• Posts: 3,066Member
That's Fine

You'll move 3.5gpm but your boiler rise will continually change. As the emitter or room begins to satisfy and not absorb the btu/hr out of the conveyor belt your boiler rise will decrease and the burner will back off until obviously setpoint. Your designing for your rise for the coldest day of the year just like a heat loss. Outdoor reset helps..
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Posts: 4,492Member
ced48

How did you come up with the 3.5 gpm for the baseboards? Generally, that would be a 35000 btu loop.
• Posts: 45Member
I agree

Hi,

I am also having have a dificult time understanding where the 20-30* D/T is coming from. I certainly don't see it on the LCD of my Alpine. I see maybe 5-8* after a zone stabilizes.  As I read at the manual, the flow rate through the boiler is inverse to the D/T. The greater the D/T the lower the flow rate required. Is not the D/T they are talking about the diference between the input and the output temps to the boiler?  At the 3-5* I see I am way of the chart as the lowest published D/T is 35 at 7.9gpm*. I have measured the temps with a IR gun and get similar readings. This is driving up "WALL" so to speak. Can someone clear this up for us?

Thanks,

Tom
• Posts: 462Member
Paul-

I have about 75 feet of baseboard in the loop, which is split into two equal circuits, with a common supply and return.
• Posts: 462Member

Right now, the loop, with the two circuits, as well as an old steel boiler vessel, is be pumped with a good old Taco 007. The system works fantastic, as is, but the boiler has to go from the basement to the first floor. This is thanks to "Sandy", otherwise I would not be doing this conversion, that I hope turns into an upgrade, rather than the alternative.
• Posts: 4,492Member
OK

Roughly 1.7 per split. Just wanted to make sure it wasn't an arbitrary number.
• Posts: 3,066Member
BTU/HR

Your leaving out one factor in the equation btu/hr.

gpm = btu/hr / (delta-t) x 500

Smaller the delta-t the less btu/hr the boiler is putting out. Temp rise is not constant that's why it is a modulating boiler. Only constant is flow. What goes in a tee must leave a tee and the boiler is a tee. Small delta means your emitters are not pulling out the btu/hr, your boiler flow is much higher then your system flow and or a combination of both.

Forget the boiler for a minute and let's talk about the system side. What is the over all heat loss, how many zones and what is the heat loss of each zone? What is each zones delta-t?
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Posts: 462Member

1 zone, single split loop, 2 equal circuits, I assume something like a 20 degree delta t. I know the boiler is oversized, but it's as small as they get. I figure if I set the ramp up at 70 percent, i should be just fine. With the boiler able to modulate down to about 8.8 net Btu's, short cycling should not be a problem.
• Posts: 45Member
edited March 2013
Chris

The D/T seems to be roughly about the same for each zone.

The downstairs zone minus the kitchen has 46' of standart slant/fin. There is another 50 or so feet of semi insulated piping running to and from. The two rooms that add up to the 46' are actually 2 zones fed by one thermostat. I did that so as to help unload the oversized boiler.

I turned the thermostat for the test up and the others down. Ran the boiler at 150*. After the boiler stabilized at 150 the return temps were running about 4-5* cooler. It did have a hard time keeping 150 at min mod and was creaping up a degree every 30 sec or so but so was the return temp.

The primary circuit is feb by a Grundfos 26-99 FC set to the lowest speed.

Please clarify that the 20-30* D/T I should be able to see  on the LCD scree on the boiler when set to read In and out temps is that correct?

I m not sure if the plumber plumbed the primary circuit wrong, It looks correct per the manual. The only difference is the zone pumps are in the return line not the feed line.

Do you think a Hydrolic seperator would be a better choice for a P/S plumbed mod com?

Tom
• Posts: 3,066Member
Zones Are Over Pumped

The zone delta is a system issue not a boiler issue. Boiler can't do nothing for you for that. The conveyor belt is moving btu/hr (flow) too fast around the zone and the emitter cannot take it away. I'm not a believer in zoning with pumps unless those were Taco Bumble Bee's or Alphas.

If your zone supply is leaving 150 it should be returning from the zone 130. That's the standard 20 degree delta. So, if you were moving 1gpm through that zone you'd be moving 10,000 btu/hr. Think about each zone, what was the heat loss of each zone and at what water temp at design did you need. Then find the ODR chart in the manual, find the outdoor temp that matches what's happening now and see what your supply water temp should be. You should also measure the emitters and calculate the needed water temp at design. One hundred fifty degrees on a 40 degree day is pretty hot water. After that deduct 20 degrees and that should be the return providing the zone pump is correct. Get your zones under control first. Since you have an installed system we have to work backwards from the system side to the boiler not the boiler to the system side.
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Posts: 7,356Member
Lochinvar WHN055

Has an output driven by boiler ∆T.  If you use a circulator with a 0-10V input it will modulate flow to maintain ∆T.
• Posts: 3,066Member
Really

The rep has been up my butt maybe I should take a look at it. Does it have an onboard pump it communicates with or do you have to add it? Thanks..
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Posts: 45Member
Chris

All three zones are plumbed with Taco 007 pumps including the Superstor.

The formula seems to shows that lowering the GPM in a zone will increase the raidiated heat thus lowering the return temp. I see the Slant/fin chart shows greated BTU's at 4GPM than 1GPM which is confusing.

So basically what you are saying is that if one lowers the flow rate in a zone it will  raise the D/T. At this point I guess I need to carefully measure each loop for actual length from and back to th boiler apply the corrections for each elbow and valve etc, and get the head for that zone. One question here, as it is pumped P/S do I not need to add in the head of the boiler itself? Then apply that to the charts and pick a pump that gived the correct flow rate of 2-4 GPM in the zone. It seem it would be nice to make pumpsthat you could dial in the exact rate you want.

• Posts: 3,066Member
No No No

Let's start by doing the heat loss, room by room and the. find the heat loss of the zone. Once yu know the zone heat loss we can then calculate the required flow rate.
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Posts: 4,492Member
Yep

Taco Delta T circ, or Taco Bumblebee
• Posts: 3,066Member
Yes

That would be the non math approach.
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Posts: 7,356Member
just a 0-10V output

as far as I know.

The problem IMO is cost and availability of appropriate pumps.  Residential-sized smart circs available here thus far have not offered external control inputs even as an option.  Compared with a standard (F3) 00 circulator, Taco wants ~105% more for a VSF3 and ~138% more for a VDT3.

I've setup some ganged mod/cons where we just paralleled the boiler 0-10V input with the pump 0-10V input and tweaked the pump controller settings to make it approximate the boiler curve.  Not ideal, no separate PID loop, but it still works better than 99% of what we see out there.
• Posts: 3,066Member
Here Is How You Get A 40 Boiler Rise

This is basically a Viessmann Vitodens 100 WB1B10-26 and even a Navien CH-210. My system side is running on the standard 20 degree delta. It's your design day and everything is calling. This is when my system flow rate is greater then my boiler flow rate. The trick is even though the boiler is making 180 look at the supply temp out. Can you heat the space? At this snapshot in time the boiler is making 4x40x500 = 80,0000 btu/hr.

If anyone wants the spread sheet just email me and I'll send it your way. I have it the opposite way as well. When boiler flow is larger then system flow. Spreadsheet makes it easier then using the calculator. You can't upload spreadsheet here sorry..
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Posts: 45Member
Chris

Sorry if I missed it but yes I  have a done a Slant/Fin heatloss for the house and do have room by rooom and thus zone heatloss numbers.

Tom
• Posts: 3,066Member
Don't Leave Us in Suspense

Share them?
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Posts: 3,066Member
edited March 2013
Tom

Here is your Alpine. I used the 13.8gpm boiler flow rate based on the pump curve of the GRUPS26-99. I made an assumption that your system flow needed in this snapshot is 8gpm using 150 degree boiler water temp. Tried to mimic what your seeing. Am I close?

13.8 x (6x500) = 41,400 btu/hr

Your better off changing the boiler pump to a Taco 00R (0015) Speed 1 - It will get your boiler flow rate down to the 8gpm 35 degree rise so you can scrub out the btu/hr in the boiler. Still need to get your zone pumps under control though.
"The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
• Posts: 462Member