How would you repipe this?

Mike East

but I do not understand why this system will not work as is (with the by-pass closed). What is going on here? Are you not getting flow to certain zones at all? (purging) Or, is the water temp going out to the circuits cooler then the out going boiler water temp? If what I think could be happening is happening, then you may be getting some backflow across the by-pass. I do not know how much head there is in the heat exchanger of this boiler but it could be enough to cause the return water to move backwards across the by-pass rather then going through the boiler to get reheated. It is not to say that this is the prefered piping system on this job, but it should be able to function. If this guy is truely your friend, you might be able to save him some dough by simply installing a check valve and a properly set diff. pres. by-pass valve on the by-pass. On the other hand, I am sure that piping this system primary secondary will work and you can be confident that you are maintaining what ever the minimum flow requirement is for the boiler.

Craig R Bergman

Customer installed

system does not work. He is running system with 50% glycol.
I will add a plate exchangerand Circulator to the garage loops, lower to 30% glycol and run water in basement slab.
My main area of concern is the return piping. Will the system work with the returns dumping into a 1" return line or should the return line start at 1/2" go to 3/4" then 1"?

I am thinking about manifolding the three zones, adding zone valves and getting rid of two of the circs.

Your thoughts?

Bergy

Mike East

Why doesn't it work?

What do you mean the system doesn't "work"? What is it doing or not doing?

principal

The drawing looks pretty good to me. Make sure the loops are power purged and vent the circs if applicable. Make sure the bypass valve is closed (not sure why you need it anyway with the 'lectric boiler)
Edit - having another look at the picture, I guess maybe the bypass loop is not so much a "boiler bypass" (can't see it working that way) but more, a differential bypass setup

Weezbo

try closing the valve on the by bass loop

if that works,...then install a check valve in the return to help Keep the fluids from getting dizzy. just wondering how this system is Balanced ....

*~/:)

Craig R Bergman

The return piping

is my main area of concern. There are NO circuit balancing valves, just ball valves. Will the returns, all at 250', balance themselves or will the 1" return not allow that?

I am going to pipe the boiler Primary/Secondary because it's min flow rate is 5.2 GPM. That flow rate would require at least 2 zones calling.

Bergy

jp_2

equal loops

if as you say the loops are all 250', they will self balance.

Ted_9

piping

You could also reverse return the radiant maifolds.

Why is there a bypass? Is there a circ. not shown in the drawing? It doesn't look like the by pass does anything.

Craig R Bergman

Who knows???

Another bit of bad advise given to the customer by the "friend of a friend of a friend who knows this guy..."

Bergy

Craig R Bergman

not a friend

A new customer. Bypass is closed, and has been. I'm still not sure why it's not working. He ran it for a week and the best it would do was 85* output. I suspect the main problem is not enough PEX in the slab. Tubing is 16" O.C. The Garage slab will require a 20* Delta T. With that I'll need 2.5 GPM @16 Ft/Head going thru two loops. The Basement's 6 loops require 5.4 GPM @ 8.3 Ft/Head and a 10* Delta T.

Bergy

Mike East

85 deg supply?

I am concerned that it has nothing to do with the boiler piping. The boiler may be under sized. To diagnose, consider running only one small zone, if the boiler is able to bring the supply water temp up to the set point then start making other zones call, if the boiler is undersized, at some point it will not be able to maintain set point. That will tell you that the boiler is under sized. If the boiler can not even reach set point with just one small zone calling, then there is another problem with piping, flow, or something else.

Paul Rohrs_4

Electric Boiler

Why a bypass loop on an electric boiler? We arent worried about sustained flue gas condensation or return water temps. As I see it, each zone pump is the boiler pump.

I would repipe for a dedicated primary loop and secondary zone pumps. Bypass loop not needed.

Regards,

PR

Paul Rohrs_4

Even better

would be to use a Caleffi Hydrolink. It really simplifies piping.

Regards,

PR

Rod Kotiga

I'm with Mike on the boiler might be to small. Your glycol idea will help a little too. How many btus is this boiler capable of and what's the square footage of what your trying to heat ?

Rod

Paul Rohrs_7

7.9 GPM total ??

If that is accurate and with a 20 Delta T, that makes your needs 79,000 btus or 23KW. Is that a 23KW boiler?

I was looking more at the piping layout that load/demand.


Edit: 2.5 gpm @20 Delta T and 5.4 gpm at a 10 Delta T = 52,000 btu / 3413 btu's per KW - 15KW. Hopefully it is a 15KW boiler and that is just calculated with 100% water. I need to calculate at 50% glycol, which upsizes the boiler again....time for me to slow down a bit.

What KW is the boiler?




Paul

hot_rod

you need a heat load calc number

first off. Then the sizing gets easier.

Cold garage slabs can really suck some BTU's if they are tubed and pumped to allow it.

It may be you are short of horsepower. As others suggested close off the garage loop to see if the boiler will maintain the other zones.

Make sure the bypass ball valve is in fact turning off.

Lowering the glycol % will help move some heat also.

hr

Craig R Bergman

Boiler size

15KW

Bergy

Craig R Bergman

The Numbers...

After running the heat loss I have...

Garage. 600 Sqft. 2 Loops @250' Each. W/30% Glycol 23,894 Btu/hr @ 20* Delta T. 2.5 GPM(Total)@15.9 Head Loss.
(Because of the head loss I can't do a 10* Delta T.)

Basement. 1592 Sqft. 6 Loops @250' Each. W/100% Water 28,194 Btu/hr @ 10* Delta T. 5.7 GPM(Total)@8.6 Head Loss.

He has a 15KW (51180 Btu) boiler, so the boiler is under sized by 908 Btu/hr. The BTU requirements are higher than normal because of the Bubble/Foil/Bubble under-slab.

I am going to re-pipe the boiler Primary/Secondary. I will seperate the garage with a plate exchanger and reduce the glycol to 30%. Again, my main area of concern is the return piping. Will it work as shown in the drawing, or will I need to modify that as well?

Bergy

Mike East

Primary Secondary Piping

See attached drawing for my .02 on how to repipe this primary secondary.