Help with using Navien in a primary/secondary loop

olemanplumbing

need to circulate up to 20 gpm in open radiant system thru a Navien NPE 240 A (rated for 4 gpm)....can I use a  manifold loop to create a primary loop for the navien and then run the radiant system as a secondary loop

this is my first time here...I could do a drawing of the whole system and scan it in I think...

Zman

Open???

Open radiant is an evil, evil thing.

Open systems become a breading ground for all thing biological, Including legionella.

I have seen systems that are full of slimy organic film that are hooked right to the homes domestic water supply.We are talking about multi million dollar homes. Do not do this. Radiant heat should be a closed system.

If you are really insisting on using a tankless heater as a boiler (another bad plan), put a plate heat exchanger between the 2 systems.

Boilers cost more money because they are designed for the work load.

Carl

Rich_49

On board pump

in the Navien is only capable of 5 GPM .

HomeOwner1

NPE is not a boiler (CH is the boiler)

I don't think they make a boiler by itself. Just a combi unit.



The combi works well in our place. Three 1/12 HP pumps hooked up to our primary 1" loop in our place feeding 6 3/4" home loops. Always heats up our loops just fine even when all running at the same time.



Stick with the CH ASME 210 ro 240 unit if you choose to do this. Stainless steel and actually made to run as boiler. Also get the outdoor temp sensor for modulation.

Zman

Navien

Homeowner1,

Do you work for Navien?

This question has been asked before with no response.

It sure seems like you are more than a compulsive homeowner and you are essentially posting advertisements for Navien (rule 3).

Carl

HomeOwner1

No

You guys sure hate combi systems!

Gordan

Why would you need 20 gpm?

Sure seems like a lot of flow...

Gordy

20 GPM?

I'm with Gordan, but with out the particulars hard to judge.



Also with Carl on the open system Taboo unless seperated by an HX, and Tankless use as a boiler in general.



I think some constants/Variables, and math need to be done along with the heat loss of course.



I'm also wondering if homeowner1 will be so glee to share his postings when his combi is failing in the future as to what happend, and why so we can all learn from it.

SWEI

20 GPM

Implies a ∆T of 20F at full fire (100% efficiency.)  Given that we still don't have any efficiency curves from Navien, I'd guess perhaps 17-18F in the loop?

olemanplumbing

More info on the primary/secondary loop

Here is more info on what I am trying to do...first I am a plumber of 40 years but have only done a little bit of radiant and boiler work...so am learning as I go...by the way thanks for the above input incl the comments from Carl..

My customer is building a 3500 sf house in north GA...He has purchased a wood boiler, 400 gal. storage tank, loading unit with pump, also a 100 gal heat exchanger with 64' of 1 1/4" SS coil,...we have installed about 3600' of 1/2" pex in four zones...the supply & return manifolds are 1"

We estimate the heat load around 100K BTU and using the formula GPM=BTUH /delta T x 500 this works out to 100K/10 x500 = 20 GPM ( I was told to use a delta T of 10 degrees for radiant floor heating.

Right now there is no backup system...I asked the wife was she going to load wood when her husband was good ...she said no.....so I figure we need a backup system.

There is a propane tank on the property and I have installed many tankless for DHW and a one for a radiant floor system about 3 years ago....seems to be working fine.  I have made a drawing which I can scan in on the next post....and this is what led to my first post 'Help with using Navien in a primary-secondary loops'....I am trying to avoid keeping the 100 heat exchanger hot 24/7 especially during the 6 months a year when there is no heat load.

olemanplumbing

Primary/secondary loop on tankless

Here is the scan of my drawing....I don't know if the tankless manifold kit will work...I originally thought I could run the return right thru the tankless but then found the flow rate needs to be around 4-5 gpm....so with up to 20gpm on the coldest days the plan needed the 1 1/2" manifold kit ...thanks for your comments and time to help...

don't know if file is attached?  having trouble getting drawing right sideup

Rich_49

Open Loop

as stated by others is a horrible idea . I see you have a 400 gallon storage tank there for the wood boiler and another tank w/ HX being used to heat water for domestic and heating .

  Think about using the HX for just DHW , use the buffer tank as a hydraulic separator (it is) and plumb in your boiler / combi of choice properly sized for this system .  I agree with everything stated above and would add that the Combi that you are thinking of will not adequately heat this volume of water . 

  Just plumb everything on the secondary side of the storage tank as it own zone , heat zones and DHW zone as a priority zone possibly .  Using the tank that is there makes Pri / Sec . very uncomplicated .  It is a buffer tank and the biggest concern will now be is that tank sized properly . The system as a whole should function much more efficiently .

Just pipe the supply and return to the tank in other words

Zman

Piping

You need to get away from the heating system that is open to the domestic.

I don't understand why you are wanting to heat with a tankless.

I am assuming that the wood boiler is non pressurized?

If you want your radiant to work perfectly, you need outdoor reset.



I would set this up as a typical 2 boiler in parallel system. From a control point of view the wood boiler would always be the lead boiler. I would tie the wood boiler into the system using a flat plate exchanger and 0-10 vdc injection pump.The lag boiler would be a modulating condensing boiler like a triangle tube prestige 110 or a lochivar firetube. A tekmar controller designed to control 2 modulating boilers will control both boilers using outdoor reset to get the optimal temp to the floors. The controller will see the injection pump as boiler one. For domestic water, use your 100 gallon indirect piped and controlled as a priority. The owner can stock the wood boiler as they like. If there is enough heat in the storage to meet the heating and hot water needs, the controller will inject the heat as needed. If the storage tank is cold, the condensing boiler will take over.



Carl

olemanplumbing

redraw w/radiant on closed system

the closed system is planned to be 12 PSI and I didn't draw it but an outdoor reset with  tempering valve would go in before pump 3 (taco 0013 vdt) for the radiant.

The HX is 119 g with 63' of SS 1 1/4" coil and also  has 4 -1 1/2 ports

I will redo drawing with the radiant coming off the HX as a closed loop..

and include how the NPE 240 A might provide DHW and keep the HX hot when heat is needed.  One of my goals is to have option to have DHW and not keep 119 g HX hot.  Thanks for your input...

olemanplumbing

New drawing closed loop

Carl.. thanks for your input...I am not familiar with all the terms in your description but please look at the drawing I will be submitting..

.I do like the tankless 240A which is 199K BTU, A is for built in recir pump, and no standing loss from a tank

the drawing is a little messy but now a closed loop system and using the tankless as backup for the radiant and DHW.  Thanks for your input...

Zman

Hot water

I really don't understand the practice of using water heaters for space heat. Sure they cost less up front. They won't last as long and will require more service along the way. I am guessing you don't use a Subaru for a work vehicle? Why not? It would do the job ( for a while).

Instantaneous heaters run a whole lot of short cycles. This drags the overall efficiency way down. A properly installed indirect is well insulated and will only cost a few dollars a month in heat loss.

It looks like what you have drawn will work. You may run out of hot water if you have a large slab call for heat at the same time as a long domestic water need. This will generally happen on a holiday. A domestic priority would be nice.

Let me know if you want more details on my design. It looks like you have already decided how you will proceed.

Carl

olemanplumbing

new drawing closed loop

Carl & Rich....thanks for taking the time to help and give your input.  I like the closed loop on the radiant...you have really helped with a better design....earlier I had just got lost down a rabbit hole.

On the closed loop system still using the tankless as backup I am not sure if the piping is correct for the tankless pump to recir hot water to the HEX tank.....it seems right but I would like a second opinion.

the tankless can deliver 11gpm at a 35 degree rise for DHW, the  builtin recir pump is rated 4gpm

Carl if it is not a lot of work I would like to look at your design but frankly the customer is not going to spend a lot more money...we have the HEX tank and probably cannot return to NH...

Zman

4gpm

I think your bottleneck is the 4gpm. Even if you upsize the circulator, you will have a heck of a time pushing more than 4 gpm through a 3/4" pipe. If you really 100,000 btu, that would be a delta of 50. I guess you could make that work if you could set up a domestic priority.

Carl

Zman

Flow switch

You could put a flow switch on the domestic side that would disable the heating circulator.

That would give you domestic priority

olemanplumbing

tankless hot water

Carl are you saying that the tankless would not be able to keep up with the radiant needs (not deliver the BTUs) ..I was planning on using 1" copper to and from the Hex tank (although the outlet, inlet & return on the navien are all 3/4").

Also that the DHW needs might not be met when in the heating mode?

thanks again, cary

Zman

Priority

Cary,

My concern is that if you are under a full heating load, especially if you have a cold slab heating zone that has just fired up, the domestic water will suffer and the customer will complain.

I would control the system so that if there is a call for heat and hot water at the same time, the heat zone would temporarily cut out.

Carl

HomeOwner1

Why not just run a combi?

The combi units out there do all of the priority switching and logic out of the box. Why not just choose your favorite brand of choice that meets the BTU requirements?



Navien makes a combi boiler, Triangle Tube, many others, all at different cost tiers and quality.

olemanplumbing

combi tankless

'Please see the drawing above 'new drawing closed loop'...we have the 100 gal heat exch  and don't think it can be returned to NH.

the 240A is about half the price for the combi...also the combi produces 5+gpm of DWH and the 240 A produces 11+gpm of DHW..

.although the combi has 1" ports and its pump circulates 5gpm max vs the 240A has 3/4 ports and rated 4gpm max.

I just hope the design works with the 240A's reicir pump pumping enough BTU in the Heat Ex tank to meet the load...there is no slab but 4 zones of wood and tile bath floors (about 3000sf )

Zman

Btu

Cary,

Don't be fooled by the charts. A btu is a btu. If you apply the hydronic formula (gpm x 500 x delta t) all the products have the same capacity.

The only capacity problem I see is a simultaneous load issue. Do you have tubing in slabs?

Carl

HomeOwner1

Flow rates very close for Hot Water Side

NPE-A unit:

Flow Rate (DHW) 35⁰F(19⁰C) Temp Rise 11.2 GPM (42 L/m)

45⁰F(25⁰C) Temp Rise 8.7 GPM (33 L/m)

77⁰F(43⁰C) Temp Rise 5.1 GPM (19 L/m)



Combi Unit:

35⁰F(19⁰C) Temp Rise 10.9 GPM (41 L/m)

45⁰F(25⁰C) Temp Rise 8.4 GPM (33 L/m)

Flow Rate(DHW) 77⁰F Rise 4.5 GPM



We have a larger home than you have spec'd running the Navien 240 combi. Running baseboard in 6 loops with three 1/12 HP pumps. Runs fine. We were lucky to have very well balanced loops to start off with though. The old boiler was oversized but at least was installed correctly. I would have negated running the water heater model as a boiler if anyone recommended it to us.



I hear the Vitodens 222-F and Triangle Tube Prestige Combi are nice but flow rates are much less. Our friends are looking at these as an option for their smaller ranch home.



Good luck.

HomeOwner1

Flow rates very close for Hot Water Side

NPE-A unit:

Flow Rate (DHW) 35⁰F(19⁰C) Temp Rise 11.2 GPM (42 L/m)

45⁰F(25⁰C) Temp Rise 8.7 GPM (33 L/m)

77⁰F(43⁰C) Temp Rise 5.1 GPM (19 L/m)



Combi Unit:

35⁰F(19⁰C) Temp Rise 10.9 GPM (41 L/m)

45⁰F(25⁰C) Temp Rise 8.4 GPM (33 L/m)

Flow Rate(DHW) 77⁰F Rise 4.5 GPM



We have a larger home than you have spec'd running the Navien 240 combi. Running baseboard in 6 loops with three 1/12 HP pumps. Runs fine. We were lucky to have very well balanced loops to start off with though. The old boiler was oversized but at least was installed correctly. I would have negated running the water heater model as a boiler if anyone recommended it to us.



I hear the Vitodens 222-F and Triangle Tube Prestige Combi are nice but flow rates are much less. Our friends are looking at these as an option for their smaller ranch home.



Good luck.

Zman

Hydronic formula

The reason the 2 appliances  numbers are almost the same is that they have almost the same output BTU. The first one is 196k the second 189k.

delta t x gpm x 500 = BTU/hr

Works every time and you don't need the chart.

Carl

olemanplumbing

drawing using tankless w/100 gal HX

homeowner1..tha's good to know...thanks for your info

carl...what is the device to set DWH as a priority...did not see anything on my searches?  thanks

Also found out yesterday the internal pump on the navien A probably cannot be controlled by an aquastat....so after much searching found a ups 2699 bfc 3 speed and using the middle speed it is close to 4gps @23' which is what navien wants for recir water thru their unit...which I can use as an external pump controlled by the heat exc tank temp.

thanks again for all the input...cary

attached is my latest drawing:

olemanplumbing

performance analysis of tankless to HX tank ??

Radiant estimated need in above drawing was 20 gpm at delta t of 10F = 200gpm degrees (I just made up that term) when all 4 zones are open.

NPE (199K) can produce 4 gpm at delta t of 70F =280gpm degrees and assume efficiency of 119 gal HX with 63' of 1 1/4" SS coil at approx. .714 =200 gpm degrees

so it seems to me that the above design with tankless could provide enough BTU's in the HX tank to maintain a 10 degree delta t @ 20 gpm for the radiant system at maximum demand

no one can tell me the heat transfer efficiency of the HX coil...although the company selling it said it could do a 50 degree rise thru the coil.

I am close to deciding the above non-traditional design because I am attached to the neat use of the tankless vs having the customer spend an additional $1500 for a propane boiler and install it between the 400 gal storage and 119gal HX...thus keeping the 119 gal HX tank hot during the 6 months of no heating load but would have a more traditional design with a proven track record.

Zman

Decisions

Cary,

I think you should either do this as you are intending or do it the way I posted originally. Did the drawing come through?I would use the exchanger tank you have as a hot water indirect and pipe the two heat sources in parallel.

The way I did it will probably cost an extra 3K-4K  but will work better and last longer (my humble opinion)

I think what you are considering will work. For the priority I would use a flow switch to temporarily turn off the heat when the domestic water calls http://www.pexsupply.com/Taco-IFS01BF-1-Brass-Flow-Switch-w-Flexible-Paddles-Single-Switch

Carl

olemanplumbing

drawing

Carl the drawing is 2 posts above...thanks also for the tip on the flow switch

olemanplumbing

controls

what device is needed to turn control pump 2 between the storage and HX tanks in the drawing... pump 2 on when T2 (HX tank) is less than T1 (storage tank)  and then pump 2 off when T2  (HX tank) is = to or less than T1 (storage tank)



once again thanks for all the help...I'm just babe in the woods when it comes to all this....but I am learning..

Zman

Brand?

Do you have a brand preference on controls?

What were you thinking for t-stats and zone controls.

It would probably be easier to find a brand you are familiar with.

Carl

Zman

Difference Setpoint

This would be my preference



http://www.pexsupply.com/Tekmar-156-Difference-Setpoint-Control-On-Off-7954000-p

olemanplumbing

controls

Carl, thank you for the tip on the difference set point control.. I read the manual and it seems to do just what I wanted...and more.

Now my next challenge is to find a device for controller 2 which is to turn on pump 4 when the HX tank is below a certain temp ( maybe 120F) and off at a certain (temp maybe 160F) maybe the same device treating the tankless as the source ??

• also it needs only to work when pump 3 is on (during the heating season) because there is no need to heat the HX tank with the tankless when only DHW is called for.
• 
  
  
  
  I'm beginning to think this might can work....thanks for your help, cary
  
  I need help...Please see drawing above on Sept 24....I am not used to controls and am looking for what to use to control the pump between the navien and the HX tank  also for pump 3 which is the radiant pump controlled by the thermostats and zone valves...am putting this system in next week...thanks cary

olemanplumbing

zone controls

I don't have a brand preference but any help you can give on tstats and zone controls for controller 3 which will also turn on the taco 0013 pump would be greatly appreciated....