Reading Vitodens 200W B2HA Return Temp.

Robert_H

Any way to read the return water temp in the coding? Ive been logging system data a few times a day since startup and noticed that the return water temp that I read  on the boiler gauge I installed has been between 118 and 122 degrees which seems high to me based on boiler temps from 124-129. Not the Delta t I was expecting. But them I don't really know what to expect.

 I'm wondering it the gauge is really out of calibration and just want to verify it.   With return water temp being such a big deal in condensing boilers I would think it would be monitored in the system at some point. I cant find it in the service manual but it may be called something else .

Out Door Temp, Boiler Temp, Flue Temp and Common Supply Temp (LLH sensor I think) are all right up front under "information", " General".

CMadatMe

Return Temp?

Loaded question...Boiler return or system return? The boiler does not display return temps. Your boiler side delta-t will always be a moving target dependent on what gpm the system side is pulling out of the boiler/primary side. Your boiler pump is a fixed speed pump moving a specific x gpm each and every time it comes on. So if it is moving 6gpm and your system side is only taking 2, the other 4 has no place to go except right back up into the boiler return.



What which boiler? What's your boiler pump? What is your system side total flow rate and each zones flow rate? Did you notice this when only 1 zone was on, all zones?

Robert_H

Boiler Return

is what I was thinking.



42000 BTUH Load, Right now I am only heating the first floor and basement so the total load is  10kish less.



System;

Vitodens B2HA-19

Using ODR

Viessmann Low Loss Header .

Cast Rads with TRVS

One small radiant ceiling, two loops, about 120 ft long each

Rads oversized to match Radiant Ceiling temp. No mixing or zone valves.



boiler loop has a taco 0015 three speed on low.



System Loop has a B&G Eccocirc (auto version) at lowest setting, which feeds a System Manifold,  from there, Home Run piping to rads and ceiling manifold.

Ceiling manifold feeds two loops. (small 99sqft room)



Design system flow is 4.2 GPM with no branch having more that .5 except the basement rad which calculates to 1.5.



Data sample from a colder day

ODT    10

Boiler T    133

Flue T    126

CST    133

Boiler Ret    125

Manf Sup    132

Manf Ret    118

Manif Δ    14

Ceiling Sup    131

Ceiling Ret    109

Ceiling Δ    22

dRad    121

bRad    121

kRad    116

lRad    123

hRad    123

baseRad    125



#Rad is just the different radiators measured dead center top with a cheap IR thermometer. krad is a not cast, it's a tall steel column radiator.

All the TRVs are wide open for now while Im balancing things.



Boiler return is from a boiler gauge installed after the boiler circulator about a foot from the boiler inlet.



CST is common Supply Temp which I think is the LLH temp. But so far that's only hearsay I cannot find it in any Viessmann documentation.



Manf is  the system manifold, a Viega with temp gauges

Ceiling is a Roth two port manifold with guages

CMadatMe

Wrong Boiler Pump

The 0015 is not a recommended boiler pump and if you look at it's curve and the pressure drop in the HX you will see that the pump will exceed the max flow rate of the boiler...Rigth pump is a Grundfos UPS15-58 as recommended in the manual. You'd being working with a boiler flow rate of

3.5gpm with the UPS15-58 on speed 1..



If you cannot expel the boiler/primary side flow rate, no matter what type of condensing boiler into the system side, you end up with elevated boiler return temps, ie, small delta. Now, say thank you to Americanization of European technology. This boiler across the pond utilizes a variable speed boiler pump but not here in the great old USA cause we have to dumb down technology so its affordable to all..

Robert_H

Per the Technical Data Manual that came with the boiler

The recommended boiler pumps are: Grundfos UPS 15-58 (3-speed), Taco 0015, Wilo Star S 21 FX.

Regardless, I think your saying that I am overpumping in the boiler loop and I would be better off with the Grundfos. Ill have to compare curves and digest that.

Thanks

Robert

CMadatMe

Really?

Think you better read a little more. It's a blanket statement for the 19/28/35 still have to look at the individual pumps curves..Hopefully my notes on Page 13 helps ya and your able to see them. Yes, this is the draft version TDM before the final was released so it may not be the same as the published.. Nothing changed from the HX pressure drop and flow rates.

Robert_H

Thanks for passing along your notes Chris. And your help!

I plotted the 0015 15-58 curve together and, as you pointed out, the 15-58 is clearly the better choice. Not by much though. I think I will still be over pumping except on design day. Im going to rework my boiler loop head lose just to be sure.

The only thing I see that really covers a low flow and low head system like mine is a B&G ecocirc vario, etc. Is that a better choice or should I stick with something Viessmann recommends in case there is ever a warranty issue?

SWEI

Warranty determination

should one arise, will ultimately come down to actual flow provided, and someone will have to prove that one way or the other.  If you have the flow, you have it -- no matter what pump was used.  Same story if you don't (excessive loop resistance, boneheaded piping configurations, etc.)

Robert_H

"boneheaded piping configurations"

Love it!

CMadatMe

Its A Fixed Speed Pump

You'd be flowing on the 35 degree rise 3.5gpm no matter what they temp is outside. How do you think you'd be over pumping the HX?

Robert_H

Becuase If I do the math

On design day my heat loss is 42K and GPM requirement is 4.2. on a 30 degree day both are lower; GPM 3.3 and on a 50 degree day GPM is 2.7.  So I have different GPM requirements depending on the ODT.



Based on your response it's obvious I am looking at this wrong.  and that on the boiler loop I shouldn't be concerned with the system load vs GPM. The flow rate stays pretty much the same on the primary loop regardless of the load.  I should determine GPM from page 13 (based on Delta T) then with the GMP determine the head from the tables on Pg 10. Then with Head and GPM choose the circulator.



Do I have that right?



Something that doesn't make sense is that  if "flow limitation" is the Maximum flow Limitation, whys dose the table provide options to exceed the limitation, like 6.1 @20dT and 4.9 for 25dT?



Is the head loss provided in the page 13 tables just for the boiler or is it for a "typical" for a primary loop?



Sorry for being so dense. I appreciate the time you have taken to help me out.

CMadatMe

The Head Loss

Shown is for the pressure drop in the HX only! System flow rate doesn't change based on outdoor temp, water temp in the boiler does, it would if the boiler had a variable speed pump controlled by the boilers logic.. But we like to Americanize things on this side of the pond. Maybe you should call the place you purchased it at and get some professional help.



Boiler should have been piped primary secondary utilizing a low loss header period..