primary secondary pumps explained?

[Winnipeg Jet]

Can someone enlighten me as to why having 2 pumps is better than one?
in other words, on my system i have a primary and a secondary pump, both pumps are on the hot water side but they are sort of connected to the cold water return from the slab via a "purge tee".It looks to me like while the pumps deliver hot water to the slab one pump also takes some of the return water and sends it right back to the slab as well.Kind of a crude mixing valve?
I have seen allot of systems that just use one pump, simple, hot water goes in and cold water comes out.
Interestingly the manufacturer that supplies the micro boiler for these "engineered systems" says the warranty is void on the boiler if you don't use a primary secondary system...Why?...why should it make a difference?
I think i would have been better off just using one pump and making the whole thing allot simpler.
I have been looking at the setup from Seisco and they have very similar type boilers running on one pump with no secondary.What makes their boiler any different?

 

[nehog]

Looks like your bypass valve is open, is that intentional or just how things were when you shot the image?

 

[Winnipeg Jet]

thats the way its supposed to run when its operational.
the handle on the tee is only supposed to be in the up position while purging the system of air.then its suposed to be horizontal.according to the instructions they gave me.

 

[tdkkart]

thats the way its supposed to run when its operational.
the handle on the tee is only supposed to be in the up position while purging the system of air.then its suposed to be horizontal.according to the instructions they gave me.

Huh?? We're talking the lower right yellow handled valve, the first one to the left of the cold manifold??

If that valve is open most of your water will do nothing but circulate the water in your loops, most of it never going through the heater.

It's no wonder your boiler is burning up, except that it should have an overtemp shutdown.

But, if that's the way it's supposed to run, I see no reason for the 2nd pump, it's nothing but a duplicate.

Edit:
Went back and looked at your pics from your previous post.
The plumbing makes no sense.
If the bypass valve is always open the lower pump will pump the majority of the water around in a circle, with the 2nd pump pulling only a small amount of water to the heater.

If the bypass valve is closed, the 2nd pump is redundant, no reason for it really.

I would double check with the installer, and the Hydroshar folks to see just how teh system is supposed to be plumbed. I don't understand the requirment for a secondary loop unless it's supposed to be a heat exchanger loop.
You definitely need some clarification.

 

[00si2]

I looked into this also and never completely understood it.

The only thing that i found out is the hydroshark boilers have a large pressure loss and the second pump is required to get enough flow.

I got my system running this winter and started out with a single pump. With one pump i couldn't get my return temperature within 50 degrees of the supply. I added a second pump and the increased flow and that bumped up the return temperature.

 

[Winnipeg Jet]

well thats pretty much what i thought also.Why have the valve in the horizontal position? Most of the water being drawn through the boiler would already be hot?
But, if you touch the pipe coming from the boiler its warm but definately not hot, as a matter of fact the temp guage right after the boiler has a hard time raching the temperature setting on the boiler.For example if i set the boiler to 110f the guage struggles to reach the 110 mark.
so assuming the hydro shark has a high pressure drop would running to pumps in series help? and eliminate that tee handle vavle altogether?When the system was running well last winter my temp at the manifold would be about 75 or so degrees entering the floor and about 60 to 65 degrees exiting it.That seemed pretty good to me.and thats with the boiler set to about 110.You would think that the guys at Energy products,hydro-smart out of elk river Minnesota would have engineered this thing correctly?
i am very tempted to switch out the boiler and just replace it with an on demand tankless and scrap the whole secondary pump arrangement.

 

[Fastback]

I'm curious, the system that you used for a reference, was it set up for a tank system?

 

[sneezer41]

Do not listen to these people do not listen to these people.

Sorry

Ya dunno what you are talking about.

I cannot see the entire setup, but primary secondary is a very standard way of piping a conventional boiler to do radiant heat. It allows a lower water temp to run in the floor loops while a higher temp that is better for the boiler is in the main loop. It also allows a mix of both high temp and low temp circuits.

Go to heatinghelp.com 'the wall' and ask actual experts how this looks to them. It could be wrong, I don't know.

[edit]
I don't see a thermostatic valve, only instant flaw

p/s piping is to prevent condensation inside your boiler from rotting it in short order, thus the lack of warranty

 

[Winnipeg Jet]

I you guys want to see what the system looks like just type in menards flex pro panel on a ggogle search or look at the farmtek website they sell them there.
mine is an exact copy just i saved about 500 bucks soldering it together myself.

 

[Fastback]

Do not listen to these people do not listen to these people.

Sorry

Ya dunno what you are talking about.

Really?

Why would an instant on, on demand unit with no storage tank need a recirculation circuit?

 

[Fastback]

I you guys want to see what the system looks like just type in menards flex pro panel on a ggogle search or look at the farmtek website they sell them there.
mine is an exact copy just i saved about 500 bucks soldering it together myself.

I looked at that same deal myself, but it is designed to be used with a domestic hot water heater, at least the one in my local menards is.

 

[Winnipeg Jet]

my undestanding is it needs to recirculate the water through so the temperature inside the boiler doesnt get too hot.Thats probably why they void the warranty now if you dont use the 2 pump system.
i think im starting to understand this thing now.
and maybe i see why i just fried 2 boilers the darn things were maybe running too hot!
what should my water temperature be right after it leaves the boiler??if the boiler is set to 110, im thinking the water temp might be somewhere around 70 or 75 and not the 110 that i thought it should be.

 

[Possum]

They are tempra tank-less water heaters with a boiler sticker on them. They will tell you different, and that they are modified for boiler work with multiple different internal parts. Look up the part numbers for the shark and the tempra, they are the same except for a "B" suffix. The tempra readily gives specs for temp rise at certain flow rates. The sharks specs are top secret. What is the flow rate of your floor? I bet its way over the highest listed spec for any amount of temp rise for that 10kw heater. If its made to produce hot water at a few gallons a minute, how can it be expected to do double that with any temp rise? I am on the bandwagon that the two loops are a bandaid for low recovery rate and high pressure loses. I owned one for a week or so, just had to wait for the return authorization.

 

[Fastback]

If a Hydro shark can actually over heat itself and damage itself, then I would call it over priced **** and be done with it.

And, if thats the case then I recommend the $200 titan water heaters on Ebay, they can heat up to 4gpm and mine can easily make 170º with an inlet temp of 60º . And dont forget that a water heater like these insta-hot units are designed to start with incoming ground water temps, and that is typically much colder than any Delta-T.



A lot of overthinking happens with this stuff.

 

[stingry]

I cannot see the entire setup, but primary secondary is a very standard way of piping a conventional boiler to do radiant heat. It allows a lower water temp to run in the floor loops while a higher temp that is better for the boiler is in the main loop. It also allows a mix of both high temp and low temp circuits.

As I understand true boiler systems, this is a correct statement. Boilers are made to operate at higher temperatures and at a narrow inlet/outlet temp difference. The theory then is that the primary loop operates at this higher temp range and adds small amounts of very hot water to the secondary loop to make lower temperature water to flow thru the floor heating loops. I have two such systems in self-serve carwashes. They work quite well. I don't know the temp in the primary loop, but you cannot hold your hand on the copper pipe.

Here is a link to the instructions for the Hydroshark 3. http://www.farmtek.com/wcsstore/EngineeringServices/allbizunits/techdocs/109179_86.pdf

Page 18 shows the primary/secondary plumbing which you have. What I don't understand is why they reccomend the primary/secondary loop system. It operates in the 86 to 120 degree range, which is where you want to be with radiant floor systems. Traditional boilers operate at much higher temps. Seems to me that this is just a tankless water heater made especially for radiant systems. Why they require this system for their warranty is a mystery to me!!!

You could try closing the valve between the inlet and outlet to the floor loops, disconnect the primary pump and run the system as a single loop system and see what happens.

Cheers
Steve

 

[tdkkart]

Do not listen to these people do not listen to these people.

Sorry

Ya dunno what you are talking about.

I cannot see the entire setup, but primary secondary is a very standard way of piping a conventional boiler to do radiant heat. It allows a lower water temp to run in the floor loops while a higher temp that is better for the boiler is in the main loop. It also allows a mix of both high temp and low temp circuits.

From what I know, all the people that have replied to this post have ACTUAL FIRSTHAND EXPERIENCE in this specific type of radiant floor systems. They have them operating in their shops and homes. So therefore, they probably DO have an idea of what they are talking about.

What they are NOT talking about is a conventional boiler system, which the OP's system is not, nor does it contain a primary and secondary loops as plumbed, or does it need them unless the heater is an absolute *************. The system as plumbed worked fine for awhile and then quit. It needs a couple minor design changes but there's no reason it should not work again. Whomever designed and plumbed it did either screwed up, or simply did not understand what they were doing. I suspect a bit of both.


Edit:
I'd sure like to see what's inside the valave that looks like a bypass valve.

Reading the instructions in the link posted above:
http://www.farmtek.com/wcsstore/EngineeringServices/allbizunits/techdocs/109179_86.pdf

These instruction indeed say that the "purge Tee" (valve E) should be closed while filling, open when in operation. Without knowing for sure what's inside that valve I can't know which way the water is flowing.
I did not see any refernce to voiding the warranty if this 2 loop system was not used though??

 

[Winnipeg Jet]

the warranty part was on the box that the last boiler came in, it specificaly said that the warranty would be void if not used with primary secondary pumping system.Funny thing is i found an older instalation manual online that shows a one pump system similar to the seisco boiler setup, so for whatever reason stiebel eltron must have dettemined that the old system was inneficient or maybe it used to fry boilers who knows?

 

[Winnipeg Jet]

if you look at the picture of the system in that pdf that you have from farmtek you will see that my system is an exact copy except for the fact that the air vent is below the boiler and i suspect thats where i screwed up bigtime.The boiler needs to be relocated to an area that is lower that the air scoop and hopefully that will solve the problem.

 

[keweenawbee]

Here you go read up:

http://comfort-calc.net/primary-secondary_piping_tutorial.html

When that purge tee valve is open it is wide open and becomes the "closely spaced tees"

 

[sneezer41]

If the manufacturer says warranty is void without it, that is enough.


I have experience with primary secondary pumping, and understand how it works, and why it is required.

That is why the people saying rip it out are FOS.

I am unsure 'why' the manufacturer requires it on a modified water heater, but they do.

I will not comment on the exact layout of the system, but I will suggest the you go to heatinghelp.com, they will have the right answers by people who actually know what they are talking about

 

[keweenawbee]

It must be the extended duty cycle required when used as a boiler that is burning them up. They should be beefed up if that is the case. If they are flow controlled and temperature adjustable, they shouldn't have to rely on a return mix to operate properly.

 

[tdkkart]

Here you go read up:

http://comfort-calc.net/primary-secondary_piping_tutorial.html

When that purge tee valve is open it is wide open and becomes the "closely spaced tees"

Hmmm, that's a new one on me and something I have not seen anywhere else in all the radiant info I've read. It's a slick deal and may be cool to play with.

 

[tdkkart]

It must be the extended duty cycle required when used as a boiler that is burning them up.

The instruction manual linked above specifically says:

Warning: Not to be used with potable water systems

and

IMPORTANT! BOILERS ARE TO BE USED FOR RADIANT FLOOR HEATING ONLY!

They are fully intended o be used as BOILERS by the company that makes them.

Page #1 and Page #3
http://www.farmtek.com/wcsstore/EngineeringServices/allbizunits/techdocs/109179_86.pdf

 

[Frank The Plumber]

Do not listen to these people do not listen to these people.

Sorry

Ya dunno what you are talking about.

I cannot see the entire setup, but primary secondary is a very standard way of piping a conventional boiler to do radiant heat. It allows a lower water temp to run in the floor loops while a higher temp that is better for the boiler is in the main loop. It also allows a mix of both high temp and low temp circuits.

Go to heatinghelp.com 'the wall' and ask actual experts how this looks to them. It could be wrong, I don't know.

[edit]
I don't see a thermostatic valve, only instant flaw

p/s piping is to prevent condensation inside your boiler from rotting it in short order, thus the lack of warranty

Correct. The boiler operates at a higher temperature and the floor loops run at a separate temperature, the primary cycles water to be made readily available for the cooler floor loop, without the higher temperature you are prone to condensation issues which will oxidize the boiler heat exchangers. You would rust out the heat exchangers in short time.

 

[Frank The Plumber]

Correct me if I am wrong but I am not seeing any temperature gauges on this set up.

 

[charger891]

from the picture your boiler is higher than the pressure bleed off valve on the tank, definately lower your boiler or raise the valve, by having the boiler at the highest level you will be traping in air into your boiler, valve won`t remove air if lower than one part of the system.

 

[3x9RT/SE]

Here is a couple of pics of my system,high eff NG modulating boiler,controled by a six zone Argo box,2 hydro air units,and radiant floor heat in my garage that has 5 250' loops.
You will see on the return side of the boiler,there is a Taco 011 pump,and just past my check valve on the supply side there is a T that connects back onto the return side.
As some have siad here,the job of that primary pump is to ensure water IS flowing thru the bolier,as it holds less than six quarts of water,and not to overheat.
On my supply manifold,there are 5 zones(Grundfos 3 speed pumps),and the last one , ball valve,goes over to my floor heat pump station that I built.The pump for this cannot "push"up against the thermostatic mixing valve(80-120 degree),but has to circulate the system(floor loops),and as warmer water is needed,the valve opens some and lets the water from boiler enter,hence allowing left over water to return to boiler.That pump is a Taco 007.
The slab temp is controlled by a Uponor slab/air sensing T stat(I leave it just on slab)set at 64 degree all winter.
Very easy system,can't say enough about the boiler to,money well spent!!!!

 

[Winnipeg Jet]

yes there is a temp pressure gauge right after the boiler on the hot side and 2 temp gauges on the hot and cold manifolds.

 

[Winnipeg Jet]

the manufacturer advertises that this system should easily keep a 900 square foot building heated and actually for my garage 720 sq ft they suggest a 7kw boiler would be adequate.
and it did work quite well last year.Also why do i get glycol slowly dripping out on my air scoop valve, its not allot but is is a drip now and then.Is this because my vent is lower than the boiler?I already have moved my electrical and i am waiting on the boiler to redo the plumbing so i can position the boiler below the vent.I just hope they will warranty this second unit? If not i will have to purchase something else, i am wondering if i could just put a 10kw Bosch tank less water heater in its place for now. They got them at Menards for around 200 bucks.As was suggested by someone else this unit just looks like a repackaged tank less with a boiler sticker on it?otherwise i will have to shell out for a real boiler.I was considering a seisco mini boiler or?Again my fingers are crossed hoping they just send me another one.

 

[keweenawbee]

The instruction manual linked above specifically says:

Warning: Not to be used with potable water systems

and

IMPORTANT! BOILERS ARE TO BE USED FOR RADIANT FLOOR HEATING ONLY!

They are fully intended o be used as BOILERS by the company that makes them.

Page #1 and Page #3
http://www.farmtek.com/wcsstore/EngineeringServices/allbizunits/techdocs/109179_86.pdf

Yeah that's the schpeel, but I too have looked at the parts blowups. I also have noticed that Steibel Eltron keeps an arms length away from their "distributor" that markets these things. All inquiries for these devices as "boilers" are referred to the MN outfit that markets, imports, or whatever they do with them. One other thing I have noticed is that the small 7.5 KW Hydroshark II and III are exactly identical, the replacement parts list is an exact duplicate. They may have changed firmware programming but that's it. They did do some hardware mods on the bigger ones.

 

[BBQ&Love]

My old friend Dan Holohan wrote an easy to understand book on Primary Secondary. If anyone wants to educate themselves on the subject go to heatinghelp.com and order the book.

Also, go post the picture at heatinghelp.com and ask for their input. You will have professionals analyzing your setup.

 

[Fastback]

This is the inside of a $200 10kw Titan scr2 water heater, it is as basic as a hammer. Mine looks just like this but mine shows the heating elements residing in a galvanized pipe.

I use this and if it dies I will just buy another, or just fix it with bits from radio shack and menards...

I guess my point is that if those hydro sharks are complex enough to take a dump so easily maybe you could look at other options...it's just hot water flowing through what sounds like 100' of pex right.

 

[keweenawbee]

Best guess I heard here is scaling. I had a tankless for my camp shower, after 3 seasons it took 5 minutes for any water to appear at all on the output. After about 6 hours under pressure it would finally put out enough for a "water saver" shower head. Finally chucked it. If the flow sensor has minimal smarts the flow reduction from the scaling might not be factored.

You can save a another 50% without the "boiler" sticker

http://www.pexsupply.com/Stiebel-Eltron-DHC-E8-DHC-E-8-Electric-Tankless-Water-Heater-7400000-p

 

[Jackfre]

The PS loop is SOP in the low temp heating business, whcih your radiant certainly is. As noted it provides two functions. It allows the boiler to operate at a higher temp, preventing condensation in the boiler due to the low return temps. This is a real issue with cast iron and steel boilers. As well it remoces the pressure drop of the extended system loops from the boiler. This necessitates the second pump.

I represent a condensing boiler and we provide a large, 3"x16-18" copper "low loss header". It has made installation and service of boiler vs system issues much simpler. Your closely spaced T's perform largely the same function, just not as well.

 

[Winnipeg Jet]

wow that link you posted for that stiebel water heater is exactly the same boiler they sent me last week that had a hydroshark sticker added to it.
i'm sure its exactly the same thing.
interesting

 

[koditten]

You mention that you have glycol leaking out your vent. Is you system totally glycol or glycol/water mix. Strait glycol has poor heat transfer characteristics. Maybe not enough heat is being sent into the liquid. Just tossing darts here.

 

[Winnipeg Jet]

no its not pure glycol i would say its about 60-40, 60 glycol 40 water i should probably make it 50-50 or 60-40 the other way, only thing is if i ever were to lose power for more than a week"highly unlikely" but if ever it happened i want to make sure i am protected to 30 below or better for my location up here in Winterpeg.
Good news today the boiler is back to the supplier and he says he should be able to warranty it! ill keep you guys posted.

 

[Winnipeg Jet]

Also today while i was talking to the rep for hydro-shark boilers i asked him what the difference was between the "boiler unit" and the tankless hot water heater that looks identical to it.He says the boiler model has beefed up Triads?
not sure what that is but it is made to withstand heavier and more repeated duty cycles, so he says.

 

[keweenawbee]

I am sure he said "Triacs" which is a solid state high voltage/high current AC relay/transistor. I was up at their MN HQ picking up the 7.5 KW and after I persistantly asked to speak with someone who knew something about these things an "engineer" finally came out and was very defensive (he said he doesn't normally talk to customers). I still think this is a scam to bump up the price. He said basically that the "response curve" of the firmware programming is different for the boilers. I am tempted to buy one of the 7.5KW POU water heaters and operate them side by side in parallel or something and see if they respond differently. I used to program ROM's for microprocessors as a hobby and I do see how response characteristics could be modified but I would think the details of the differences would be proudly published by now. I will try to find a replacement parts list for the water heater version and report back.

I just got a trade e letter that mentions the new Rheem tankless check it out

http://www.housingzone.com/cb/article/product-week-rheem-integrated-heating-water-heating-system

 

[nehog]

The triacs are likely what has been failing on these boards. They are basically like a solid state relay (and they are used in common lamp dimmers, but used differently there). So if the boiler has heavier ones, that makes sense.

And it makes sense that maybe the thing is tripping on and off too much which is causing problems with them.

I wonder if it makes sense to see if the flow rate is correct for that unit, or maybe it is too low? Also, I'd recommend setting the glycol to water ratio to what the maker recommends (which, IIRC, is 40/60, not 60/40). If you have poorer heat transfer that might lead to short cycling as well.