Mod-Con Piping for efficiency

johntrhodes81

All,
It seems like all the mod-con boilers specify primary/secondary piping with closely spaced tees or hydraulic separators. But to maximize delta-T's between the boiler supply and return, to improve efficiency/condensing, shouldn't at least theoretically the system be piped primary only like an old style cast iron boiler? Maybe with a variable speed pump of pressure differential bypass valve. I drew up the 2 methods on the attached pdf. I am interested in peoples thoughts. I am about to replace a oil fired cast iron boiler with a gas mod-con (Navien NHB-80).

Thanks,
John

Rich_49

Forget the Navien , use this
http://www.htproducts.com/UFT-Boiler.html , and this
http://www.taco-hvac.com/vr2218/index.html .

Forget the P/S piping , keep the flow rate above 1 gpm by whichever means you see fit and enjoy your system .

Nice drawings though . In either case move the system circ to the supply pumping away from the expansion tank . Look into the meat of your Navien Manual for the minimum flow rate through the HX . once you identify tyhat see what your system side flows will be throughout operating temps . Once you discover the system side will rarely if ever exceed the flow that the boiler requires you will know that your chances of returning low enough temp water for a significant amount of time have evaporated .
Step 2 . Really look at the HTP UFT , realize you don't need P/S , DPBV and all the complexities and cost that go with them . Navien is suspect at best as can be found through internet research . UFT is competitively priced and is just a much better offering from an American company .

Eastman

I don't know Rich. The last time I suggested someone experiment with a boiler deltaT pump didn't turn out too well. Have you tried this configuration yourself?

johntrhodes81

Thanks for the suggestions. The HTP UFT looks interesting and has the features that attracted me to the Navien NHB-80.
John

4Johnpipe

Eastman

@4Johnpipe
This is working for you? What delta is it running at?

njtommy

That's the problem Hatt!
We need to be able to get really low gpms.
From what i have seen. I can't seem to get lower then around 6 gpm with either the bumblebee or the Vt2218
Time to break out the circuit setters i guess.

NYplumber

I crossed this bridge a few years ago when the bee came out from taco. I did this on a firetube style hx. The boiler condenses real well and doesnt short cycle. No buffer. The dt pump tries to keep the boiler at condensing almost all the way through the heating season. The outcome is a boiler that almost never has visible vapor as well as long boiler cycles. And this is a 5:1 lochinvar whn boiler. One of the kickers that this boiler has is ramp setting. I think Viessmann built that in to the boilers logic (rather then make it user adjustable) but other then them and lochinvar, i dont know others that have ramp settings. Slowing flow through the boiler usually hinders the boiler from going into high fire, so that is a form of ramp setting. As the boiler picks up return temp, the fire can modulate closer to full throttle ,if that makes sense.

Cycles 4859
Run hours 6575

Propper design and control.

Piped primary secondary btw. I cant imagine piping this system direct since it is a direct return distribution system from 20 years ago and 1gpm would mean water short circuits through the closest radiators. System is set for a 10dt. Boiler set to a 40 or 50 if i recall.

Just a thought, if you throttle the flow of a boiler loop too low (in order to keep the wide dt at low fire), it will have difficulty at best when in full fire since dt will be very wide.

Rich_49

@Eastman . Yes , we do have this running , a few of them actually . No problems , program the circ and boiler Delta the same and there are no problems . This boiler is not what we have had available gents , enjoy the freedom it allows us .

@njtommy . The head of your system must be too low , at low head the circ performance curve and your system curve intersect at a different point . Find the sweet spot and you'll flow what you need . Plotting the system curve against the pump curve at different conditions will allow you to make it the best it can be throughout the heating season .

@NYplumber . As with any system being reworked or components being replaced , one must pat close attention to what type piping is existing and how it responds to what you are doing . This boiler (UFT) may in some cases benefit from P/S due to conditions in the field or designer / installer choices . How many folks have the knowledge to use any boiler properly is the problem . The UFT controls the firing rate by what you program (or default) and has immersion sensors that tell the valve what's going on in real time . It has a boost function that some can access and use but in my opinion boost is a band aid . Figure out where the boiler MAY need to go during record cold events and know where it will need to be at shoulder conditions , set your curve appropriately and adjust in a visit or 2 after your customer gives you feedback .

As seen in the picture posted by @4Johnpipe we have these piped direct with VT2218s and are seeing no issues whatsoever . It has been cold and we have been in WWSD . They are installed in zone valve jobs (pictured) and constant circ systems piped 2 pipe reverse return with panel rads ( bypasses ) w TRVs with a properly sized Main . No other devices to limit head or the like . It is nice when you can install NEW stuff and make everything work just right , retrofits do vary as we all know . After careful consideration of what you are working with , the choices are yours .

njtommy

@ Rich it would just be nice to get the smaller zones run at a 20 degree delta on the warmer days.

njtommy

I had a nice new magnehelic once. I left it in a ceiling somewhere in Nj. Along with a tape measure and sharp markers.

SWEI

Plenty of Magnehelics on eBay -- even Capsuhelics, though mostly in lower pressure ranges.

Eastman

@SWEI
Didn't you try a deltaT boiler pump configuration a couple years ago?

4Johnpipe

@Eastman Its running at a 20 degree DT...with a VR for the indirect.

njtommy

@4Johnpipe nice looking job.
On aside note. The webstone valves and flange kits are awesome and makes jobs that much cleaner.

4Johnpipe

Thanks @njtommy ...I have a few critiques as I probably always will. My preference is the Caleffi auto fill valve. This one needed to get done asap which is why it's absent. I'm going to start stocking an extra one of those as they make dialing in system pressure a no brainer...

Eastman

@4Johnpipe

Glad to see some positive results.

hot_rod

4Johnpipe said:

Thanks @njtommy ...I have a few critiques as I probably always will. My preference is the Caleffi auto fill valve. This one needed to get done asap which is why it's absent. I'm going to start stocking an extra one of those as they make dialing in system pressure a no brainer...

Thanks John for the Caleffi support. Look into our Boiler Trim Packages, all the components in a box for less than the pieces. Including nice brass nipples with the expansion tank, like you wisely used.

4Johnpipe

Yes we've used them too. It's a much better deal as long as it fits and is in stock. I think we are converting our supplier to Caleffi....