Mistakes were made, but any help would be appreciated

chevelle71

Well, like the title says mistakes were made.  I learned a decent bit with the search function, but am looking to firm up my plan before spending additional money...and potentially making more mistakes lol.

I have a 40x50 shop in PA, with a closed loop in floor hydronic system.  It has 6 loops of 1/2" pex-al-pex each around 300' plus or minus about 5-6'.  The heat source (takagi jr tankless water heater 😳) is about 25' in a horizontal run from my manilfold.  The basic flow path is, the water exits the water heater, passes through a check valve, then circulator pump, then enters 3/4" pex with oxy barrier, goes up about 10', runs about 25' horizontaly, then down 10' into my manifold, into the floor, out of the floor, into the return manifold, up 10' into 3/4" pex, 25' horizontally in 3/4" pex, down 10' in 3/4" pex, and back into the return side of my pump panel where is flows through some piping with an air eliminator and expansion tank, then into the cold side of the water heater.  I am using a single Taco 0013. 

I have attached a pic of my setup since it is hard to visualize, and a pic is worth 1,000 words.

My problems are, flow rate (usually 2.5 gpm) is too low and I keep losing flow rate over time (sometimes will drop to 1.0 gpm in a few hours, then i purge the system again and flow rate returns to normal).  Also, i keep plugging the small mesh strainer on the water heater.  The plugging material looks like paint from the circulator.  So, the low flow i believe is due to the water heater head loss and other losses in the system in addition to air in the system. I have purged the system multiple times for extended periods of times.  I dont get air out of the system, but flowrate increases after i purge it.  

Here is what I think needs to be chaged.

1 - should have used a boiler.  My goal is make the tankless water heater work for the next few months and then do a major rework over the summer.  I know this is not ideal, but if at all possible i like to try and make it work for now.  I understand this will be more expensive in the long run.

2 - install an actual air seperator and move expansion tank to outlet of water heater.  I have read both of these item should be installed between the outlet of the heater and suction of the pump.  Is that correct or no?

3 - install a higher head circulator to combat the head loss of the tankless heater and other losses in the system.  Can I install two circulators in series?  I would love to get 4gpm, but i will have 32' of head in the water heater alone.  Also, would you leave the circulator installed on the outlet of the water heater or move to the inlet?  

4 - install a larger strainer in the inlet side of the water heater.  I would assume this is the best place for it?  

5 - maybe install a high point vent.  If I can increase my flowrate then I may not have to do this since i should be able to move the air to a separator.  

What else am I missing?

If you made it this far, I want to say thank you for your time, and I appreciate your help.

EdTheHeaterMan

If you read up on Boyles Law and Henry's Law about dissolved gasses you may realize where the air is coming from. After you understand that you will see that every time you Purge all the water from the system you are starting fresh with dissolved air again. Get the air separator installed at the point with the hottest water and the lowest pressure then your system will almost self purge the air. You will need to use a primary/secondary piping system to accomplish that at low pressure ( 12 t o15 PSI ) If you try to pump away from the expansion tank on the hot side of the water heater, the water heated does not like that. The water heater wants the pump on the inlet (cold) side. So... two circ pumps are used. the primary pump on the system loop and the secondary pump on the boiler loop.

Another thing water heaters like is flow. The more flow the larger the flame. Think about it... if you are using a small amount of water (1 gallon per minute GPM) to wash your hands in a sink you need a small amount of heat to heat it. If you have 2 shower heads operating at the same time (2,5 GPM each) You need 5 times as much water so... 5 times as much heat. That is how the water heater works.

Finally, the water heater likes cold water coming in. If the water is returning from the loop already hot then the water heater logic board gets that input from the sensors and may decide there is a problem and **** down the burner

So Yes you made a mistake choosing a water heater to heat the radiant floor system.

Bigger pump... actually a higher head pump is suggested to get the GPM up to the minimum for the water heater to operate.

Stop replacing the water, Just add as needed once you get the air separator installed

Maybe operate at a higher pressure (the water heater is rated for a 125 PSI relief valve). Check the rating of the other components to see if they can handle say 40 or 50 PSI until you get the new boiler. This may keep the water heater happy until then.

HVACNUT

Check the max flow rate through your water heater vs the flow rate through a properly sized boiler and the 0013. And there's your air. 

EdTheHeaterMan

Here is a piping illustration that will work better than your current design. The boiler pump is building pressure on the inlet of the heater. The system pump is creating a low-pressure area in the same place as the high-temperature area. The expansion tank, pump location, and air separator location is the key to removing the dissolved air in the system.

Jamie Hall

We all have made, make, and will make mistakes. That's the best (although not always the cheapest!) way to learn!

You do need a higher head pump, and it should be -- as the folks have said -- before the inlet to the water heater, and the system expansion tank should be perhaps 10 inches before that. Try to keep the pipe straight between the tank and the pump inlet. If you do that, you may be able to get away with the same tank pressure as you have now. The air separator should go at the point of highest temperature... and lowest pressure... but that is a mismatch which you really can't fix with a tankless, since almost all the pressure drop is in the tankless. I think, on balance, that I'd try putting it at or near the expansion tank, where the pressure is lowest.

Nor can you fix the problem that the tankless wants cold -- or at least cool -- water coming in. When you repipe and rebuild later, with a boiler, and go primary/seconday, that problem will pretty much solve itself, but honestly at the moment for the winter, I'd not try to go primary/secondary, as that won't lower the water temperature getting to the boiler (it can raise it -- but not lower it).

Nor would I try two pumps in series. That rarely works well -- and then only when the two pumps are chosen so that at the flow rate through the system they are both working somewhere in the middle of their flow curves.

EdTheHeaterMan

Good idea @Jamie Hall, but getting the larger head pump will not be necessary if @chevelle71 just gets a second pump for the system. And it will work on the new boiler also. The existing pump looks like it could be a 0014 or a 0011 pump with a priority relay. that should be sufficient to operate the water heater pressure drop if it does not need to deal with the system pressure drop.

What do you think?

chevelle71

Everyone, thank you so much for the help!  I have done some reading and understand why my constant purging has not helped the situation and actually made things worse.  Based on some information above, here is what I am thinking.  

Option 1 - find a higher head and flow pump and change my piping so the pump discharge enters the cold side of the water heater and then exists. Flows through an air seperator and my expansion tank.  Looking at my piping, this would be pretty straight forward.  Install the pump so the discharge is up, turn my check valve around and route piping to tankless heater inlet.  Then i would have ample room on my hot discharge to install an air seperator in the horzional run over to the new hot side of my pump panel.  

Option two - everything above but i set it up with a primary and secondary loop.  This wouldn't be too bad since i have an area to install the two TEEs right now (see pic below).  The hard part for me would be figuring out what pumps to use.  I know my tankless heater will have about 32' of head loss at 4 gpm.  So, i would still need a bigger pump for the boiler circuit.  Then the loop circuit i have the 3/4 pex, fittings and manifolds.  I already have an 0011 and 009 sitting here, so one of those may work for that circuit.  I am thinking the 009.  The hard part will be getting 4 gpm through the heater.

Am i on the right track?  Also, what air seperator would yall recommend?  I am looking at Taco and spriotherm.

The only problem with my plan is the purge system will not really be functional, but i can work around that.

chevelle71

EdTheHeaterMan said:

Good idea @Jamie Hall, but getting the larger head pump will not be necessary if @chevelle71 just gets a second pump for the system. And it will work on the new boiler also. The existing pump looks like it could be a 0014 or a 0011 pump with a priority relay. that should be sufficient to operate the water heater pressure drop if it does not need to deal with the system pressure drop. What do you think?

Hello @EdTheHeaterMan, i currently am using an 0013.  

chevelle71

Also, on the wiring side, would I remove my tekmar 301p and install a 302p to turn on both circulator pumps at the same time when triggered by the thermostat?  

Jamie Hall

Your new option 1 would be simple enough, but... it places the expansion tank a long way from the inlet of the pump. All the way around the loop, in fact. Though most of your head loss is in the heater, not the loop, you will still have to run the tank -- and system as a whole -- at a much higher pressure to avoid the pressure going too low on the pump inlet -- which is very bad for the pump.

The second option is much better. Put the expansion tank near the inlet to the primary loop pump. If I read the head required and flow data correctly, though, it looks to me as though a Taco 2400-45-3P might be required for the primary loop...

chevelle71

Jamie Hall said:

Your new option 1 would be simple enough, but... it places the expansion tank a long way from the inlet of the pump. All the way around the loop, in fact. Though most of your head loss is in the heater, not the loop, you will still have to run the tank -- and system as a whole -- at a much higher pressure to avoid the pressure going too low on the pump inlet -- which is very bad for the pump. The second option is much better. Put the expansion tank near the inlet to the primary loop pump. If I read the head required and flow data correctly, though, it looks to me as though a Taco 2400-45-3P might be required for the primary loop...

Thank you @Jamie Hall.  Two quick questions, when you say primary loop, are you taking about my boiler loop or floor loop?  I could see this high head unit for the water heater, but the floor side I am coming up with around 17 ft of head at a 4gpm target (300ft of 1/2 pex, call it 100ft of 3/4 pex, manilfold, some 90s and other fittings).   Also, would the circulator you recommend work at such a low flow rate?  It looks like the curve starts around 5gpm.

EdTheHeaterMan

For the price of that pump and the amount of flow on the pump curve, (it's at least 80% to 90% of the 0013), I would try the 0013 on the boiler loop. The system loop should also work with a less expensive pump. How many BTUs are needed for the slab? another 0013 will give you about 150,000 BTUs. The 2400 will get you near 200,000 BTU. which I believe is the total of the water heater input.

If this gets the heat to work, then you know that a 200,000 boiler is enough. if it does not get you there, then you may need a bigger boiler. If the boiler runs at less than full at design temperature, then you can get a smaller boiler in the spring. Whatever you decide, all these parts will work on the new boiler.

BTW you have a water heater expansion tank. The boiler expansion tank models are factory charged to 12 PSI. Adjust your tank pressure to the operating pressure of your system. The tank must not be connected to your system's pressure when adjusting the air pressure charge. Look that one up too!

chevelle71

@EdTheHeaterMan thank you again.  My heater is a 120k btu that can turn down to I think 12 or 15k btu.  I think the design load was right around 100-110k btu and then when the slab is up to temp, i require aroun 18-20k btu to maintain temp.  The shop is 40x50x14 with r38 on the ceiling and r19 in the walls.  

I will do some additional research on the expansion tank.  I know it was charged to 12psi when i started.  

EdTheHeaterMan

chevelle71 said:

Jamie Hall said:

Your new option 1 would be simple enough, but... it places the expansion tank a long way from the inlet of the pump. All the way around the loop, in fact. Though most of your head loss is in the heater, not the loop, you will still have to run the tank -- and system as a whole -- at a much higher pressure to avoid the pressure going too low on the pump inlet -- which is very bad for the pump.

The second option is much better. Put the expansion tank near the inlet to the primary loop pump. If I read the head required and flow data correctly, though, it looks to me as though a Taco 2400-45-3P might be required for the primary loop...

Thank you @Jamie Hall.  Two quick questions, when you say primary loop, are you taking about my boiler loop or floor loop?  I could see this high head unit for the water heater, but the floor side I am coming up with around 17 ft of head at a 4gpm target (300ft of 1/2 pex, call it 100ft of 3/4 pex, manilfold, some 90s and other fittings).   Also, would the circulator you recommend work at such a low flow rate?  It looks like the curve starts around 5gpm.

4 GPM will only give you 40,000 BTU of heat transfer at a 20° drop over the system. You can't get much more than 50,000 BTUs even with a greater temperature drop. As a rule of thumb you will get about 10,000 BTU of heat transferred for every 1 GPM. With six 1/2" loops at 300 ft. you will want to move more than 4 GPM at least 6 GPM. A more powerful pump can do more. So a smaller pump is definitely possible but you will want to overcome the 300 fr of 1/2" plus the manifold and air separator near boiler piping pressure drop. I think you can try a Taco 008 0r 0012. Maybe a 007 might even work. but you will want to go to 1" piping from the manifold to the boiler connection. the boiler can be connected with 3/4" of 1"

If everything stays 3/4" you will be choking the flow.

chevelle71

@EdTheHeaterMan thank you again.  I will make the adjustments and run some numbers.  One last question, is it ok if the air eliminator and expansion tank are installed in this location (see pic below)

chevelle71

Also, here is the pressure drop chart on my water heater.

EdTheHeaterMan

It will work but you lose the Hottest water and lowest pressure in the same location. You will make the boiler loop the primary loop (nothing wrong with that) but you will need to operate at a higher pressure. and lose a "Primo" air separation location.

EdTheHeaterMan

So I did an illustration based on hypothetical numbers where the pressure drop across the boiler is about 7 PSI pressure drop and the pumps developed about 8 PSI pressure difference from inlet to outlet and the system pressure drop including near boiler piping is 8 psi. You can see that there is a low-pressure area on the way into the system pump where the hottest water is entering the system (primary) loop. So if we put a gauge at various points in your system...

This happens at the air separator.

By placing the air separator and expansion tank ay your suggested location the numbers change slightly and it appears that the idea will work. there is one small issue at the intersection of the two loops. this is where the pressure drop across the common pipe may cancel out the pressure drop of the other loop. I'm not sure how this will affect the system operation. If the system pump is stronger than indicated there will be no issue because the net effect will keep the water moving in the proper direction. If the boiler pump is stronger than the system pump the flow may reverse in the common pipe. I'm not sure that is a problem. A true fix is an exchange tank in lieu of the close tee configuration of the primary-secondary design.

Bob @hot_rod forgot more about this than I know. Hopefully, he will chime in at some point.

But I am looking for an easy fix, for now, and I think your plan is OK for now.

EdTheHeaterMan

Based on your chart. you are only going to get a 20 temp rise at a max flow of 6GPM so the taco 007 will do fine on the system loop.

chevelle71

@EdTheHeaterMan The only challenge i can see is trying to get 6 gpm through my water heater with a 34psig/79' of head pressure drop...if i am looking at the chart correctly.

hot_rod

You will only be able to pump you way out of some of the issues. You may never get to 6 gpm.
But the issue with plugged strainers may not go away.

With high pressure drop boilers the hydraulic separators really are the best option, providing 4 critical functions and allowing different sized circulators to get along.
As Ed mentioned, there will be reverse flow in those close tees.
Some additional reading.
https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_15_na.pdf

Zman

I would repipe it like this in anticipation of the boiler change. Use the 0013 you have for the boiler loop. There really is not
a pump you can afford that will move 79' at 6 GPM. The good news is that with primary/secondary, you should be able to get a little better than 4 GPM out of the 0013 and live with a higher delta T.

chevelle71 said:

@EdTheHeaterMan thank you again.  I will make the adjustments and run some numbers.  One last question, is it ok if the air eliminator and expansion tank are installed in this location (see pic below)

Jamie Hall

chevelle71 said:

@EdTheHeaterMan The only challenge i can see is trying to get 6 gpm through my water heater with a 34psig/79' of head pressure drop...if i am looking at the chart correctly.

The problem isn't the system loop -- one of the Taco 007 models will handle that just fine. As you point out, though, @chevelle71 , the problem is the hot water heater. And you are looking at the chart correctly. I don't have current catalogues for pumps; from what I'm finding in the Taco literature (excellent website, by the way) they don't appear to have anything which matches that.-- and I don't know who does. McMaster Carr lists some high head pumps which will exceed the flow and head you need, and which could be throttled -- but they don't come cheap. Much as I dislike pumps in series, you may be better served by just that. The Taco 2400 series isn't really suitable; you'd be off the low end of the flow range, and rather thus inefficient. The 1900 and 1600 series are also pretty inefficient at that flow and head combination.

hot_rod

Normally I would have the exp tank at the suction side of the boiler pump. However with that much heater pump, you may end up popping the relief. may be better to have the tank near the system pump.
I’d like the air sep right at the boiler for the hottest point in the system.
A hydraulic sep would give you air removal at the best location,put the expansion tank in the ideal position, possibly keep the heater strainer clear, and also give you magnetic separation.
The large diameter of a sep 4 for instance, allows that highhead, or multiple seriesed heater circulators to get the flow they need.
It would also facilitate the boiler upgrade, down the road.