Gpm per loop

big willy

Are there tables or guides for this. I have never seen them before but it would be nice to know when you will run out of heat energy at a given gpm and temp with diferant materials.

big willy

Gpm per loop

I want to use an on demand Noritz for a small staple up job with aluminum transfer plates. I know the head is very high through a on demand and the flow is low as a result. I will get 4 gpm total with the pump I intend to use. I have five loops all under 200 feet. With 140deg water can I achieve 80 deg floor temps at just under 1 gpm per loop. Its hardwood floor. Also I have seen the threads about using on demands for boilers go wild. I don't want to focus on that. I am using it because It has to go outside and It fits the guys budget.

hot_rod

1 gpm

is a bit high for 1/2 pex 5/8" yes, easily on 3/4".

hot rod

Glenn Sossin_2

Charts

bigwilly

Since I don't know exactly what size loops your ran, I will assume all 5 loops are the same length. You said you required a total of 4 gpm. This means each loop would carry 5gpm/4loops = .8 gpm/loop. We take the longest loop length, let us assume they are all the same for balancing - 200ft and find the friction for the flow rate at a given water temp.

See the attached chart - pex head loss. Your head loss through the pex is 200ft x .0247hd/ft = 4.9fthd. To this value, you need to add the head loss through the Noritz unit, and the leader piping to the manifold supplying the pex loops.

I will assume, since you referred to a budget, you are using the N-063. Refer to the attached chart - At 4 gpm, the head loss through this exchanger is approximately 24ft.

Now you need to add leader head - the friction loss between the Nortiz unit and the manifold location. I don't know what that is, but lets say the manifold is 10ft away and you ran 3/4" L copper to it. Look at the attached chart for copper. - loss press drop 12. This shows head loss values based on 100ft. Using the assumption, the manifold is 10ft away, that would be a total of 20ft so your leader head loss would be .20 x 4.81 = .962. It is a common practice to add 50% for fittings, valves, etc. so your lead pex loss would become approx 1.44.

Now we add them all together. Loss throught the Noritz exhanger was 24ft, leader loss was 1.44ft, and the pex circuit loss was 4.9ft for a total of 30.34ft of head.

Now you can try and find a pump to do this. Refer to the 2 pump charts - Taco & Grundfoss. I plotted out your requirement. With Taco, you would probably require a model 0013. With Grundfoss, you fall right on the line of the UP26-99F.

This is why some of the wall hung heater applications fail - the pumps installed on these systems are too small. The instantaneous water heater units are designed with very narrow passage ways (resulting in high head loss) because they are expecting 40 -50 psi or more inlet pressure. Wall hung boilers are designed differently -they have wider passage ways in the exchangers resulting in much lower head losses.

All is not lost - a few other points. Although you didn't say, I am assuming you figured the gpm requirement based on a delta T of 20F. This means your heat load was 40,00 btu's at design conditions - the coldest day(s) of the heating season.

Did you consider a using a wider delta T. Consider what would happen if you raised the supply temp by 5F and lowered the return by 5F. Note, you will have the same average supply temp - the heat output should be the same. Now you have a delta T of 30. Look what happens to the flow rate required to produce your 40,000 btu's of heat. It drops from 4gpm to 2gpm. It's cut in half.

Now go back and recalculate your losses for 2gpm instead of 4gpm and you will get a whole different picture. This flow rate is still high enough to fire the Noritz unit and your head loss will drop from 24ft to less than 7ft through the heater. Now when your recalculate everything, you can can probably use a Taco 008 or a Grundfoss UP15-42 / 15/58 and make a serious dent in your pump costs.

You don't always have to design around a delta T of 20. Raising the supply temp slightly, and allowing a slightly lower return temp can have a wonderful effect on lowering gpm and head losses.

I know this was probably a lot to digest, but you asked for the charts- this is how you would use them.

Hope this helped you.

Good luck

Glenn

big willy

Thank you Glenn

My flow is bassed on what I can get from the noritz with this pump (ups 15/58). I used the Noritz 7.5 and the pump can produce 4 gpm with the head loss through the heater. I have about four feet total of 3/4 L before my manifolds and the loops start their. the loops are all about 200 feet with the eception of the entry hall loop that is only about 120 feet. I will use your charts from their. I do expect a very wide delta T and may have to use primary secondary pumping to increase my flow through the loops. Thanks again for the charts. Having real numbers instead of guesses sets the mind at ease.

Glenn Sossin_2

Diagram

Willy

I glad you understood and will use the charts.

I am sending you a piping diagram we just did for a customer out in Kansas. It was for the NH-150 boiler though. Conceptually, you could do this and substitute the water heater for the boiler.

Keep in mind there is another issue here. The primary loop helps to insure adequate flow through the unit, don't need such a high head pump. The problem - you may find you need a buffer tank inserted into the primary loop. The heater may not be able to downfire low enough under light load conditions. The buffer tank will help reduce the boiler from cycling, help to prevent an overshoot in temperature and going off on high limit should there be a very low load.

Just an alternative idea.

Good luck

Glenn

big willy

Start up

this mourning went well. Kinda. The loops are giving me about 80 deg floors at 140deg WT. The bad part is the GC layed 3/8 ply over the 5/8 to raise the floor level and shot a couple of two inch staples through a pipe. It was under presure but didnt start to leak until I started the system. The other thing is one of the loops in the dinning room wont move more than a trickle of water. I am sure there is a kink somewhere in my line But finding it is the trick. The tube went in and the fire sprinkler guy and electrician came behind us. I hope we didnt kink the line and miss it before walking away from the open floor. It's not like I want to point the finger but it makes me stupid to think me or my guys might have left a line kinked in a open floor.

Weezbo

you can find how far the kink is into the slab easy enough,

by using a thawing tool that is easy to make. interested?

Tim Doran_4

Surface temp is a function of resistance

The surface temperature achieved is a function of the water temperature, spacing, floor assembly thermal resistance, room set point and load. Temperature overcomes resistance and flow overcomes load. You need to plug in the missing pieces to get your answer.

Tim D.

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big willy

Staple up

Its between floors I have an outline of the area of the cooler loop using a infrared thermometer. I could start removing drywall down stairs but I would like to keep the destruction to a minumum. If your gizmo will work for staple up yes I am interested Frankly im interested anyway. I do enough in slab work that that day will also come.

big willy

I have enough

heat in the floor top meet load now I knew I needed to acheave a minumum of 78 deg avrage floor temp. I do need to fix the loop with the kink though its killing my recovery time. luckly we are just begining the winter season so they are comfortable still.