primary / secondary loops

Bob_94

I have to ask a dumb question. Did you check to see if the suppply and return sensors are wired to the correct terminals? Maybe they are reversed.

Bob

Tombig_4

primary / secondary loops

So I have a primary and secondary loop installed on my new mod con boiler.

Why is the supply higher than the return? Logic tells me it
should be the other way around.

At all times the supply is colder than the return by up to 7 degrees or they are equal (when the system temperature is equal at all radiators).


->- return sensor--|tees|--air--circ--supply sensor ->-

1) return sensor
2) closely spaced tee's lead to primary (boiler) loop
3) Honeywell air separator + expansion tank + cold supply
4) B&G 100
5) supply sensor

Dan Sedens

Can You Post Some Pics?

It would really help myself and others assess what is going on with your system.

k

request for pictures

I don't have any easy way to do that at the moment. (I tried making a pathetic little ascii drawing).

The design is straight out of page 16 in the weil mclain ultra manual.
http://www.weil-mclain.com/downloads/ug3_boiler_manual.pdf

The only difference is that my supply sensor is on the house side of the circulator, not the 'closely spaced tee' side.

Let me start with an easier question: in a primary/secondary loop is the supply side always a few degrees lower than the return side on the secondary (house) loop except when they are equal? I am measuring at 36 inches on either side of a closely spaced tee.

I don't have any worries about my primary (boiler) loop. When firing the boiler delta t is 19-21 degrees. At low fire it's a 6-7 degree delta t. And nothing seems wrong with the system, in fact it seems perfect. I'm just confused at the supply temp reading, I expected it to be higher than the return temp reading.

Timco

Heat rises, so supply pulls from top. as for the P/S, the point of the mod con is to get cold return temps, and with p/s piping, you have insured you will never get that and it will not condense. Best to pipe direct return with a mod con to get the cold return temps and make it condense. CI boilers need p/s protection when zoned so they do not condense...see a pic of my latest mod con at 'be brutally honest' thread.

Tim

Timco

You mean the supply of the secondary loop? The supply pulls some water from the return pipe due to the close spaced tees, and will always be pretty even in temp, but not cooler. Supply is supply, period.

Tim

k

Tim,

The point of the p/s circuit is to allow independent flow rates in each of the primary and secondary circuits. The point of the closely spaced tees is to provide a hydraulic separation to allow for this independent flow. The p/s piping allows condensing to occur in the boiler when water passes through it at temperatures less than 140 deg. Mine is currently condensing nicely and modulating as expected. In fact, I'm blow away at all the water that drains from it.


There are a few reasons to get a mod/con. It is not cast iron, the radiators are. The heat exchanger in the WM is an aluminum exchanger designed in Italy by a company who's been making them for 15 years (I read that on this board).

I realize that at design temperature of 0 degrees outside this boiler will not condense, it cannot. But just like any boiler you cannot put 'cold' water into it since you need to maintain the 20 degree delta tee out. If it had cold water in it, it would never be able to heat to a reasonable temperature. For example, 100 degrees in requires 120 out. But 120 degrees will only work on the mildest of spring and fall days. You can't take 100 degree water in and put 180 degree water out, the boiler is not that large.

Furthermore most manufacturers will highly recommend a p/s system and some may not offer warranty repairs without p/s piping for the simple reason that you guarantee ample flow through the high head mod con heat exchanger without needing to calculate flow in the completely hydraulically seperate secondary (house) loop.

Condensing boilers condense and modulate most in the early and late heating season. In the cold of winter they are quite similar to conventional boilers, except they still extract more heat from the flue making them more efficient in all conditions.

Timco

You have my apologies. I am mixing P/S piping up with a HX. I see your points. I did not mean to imply "cold" temps in return, but "return" temps, which of course rise. As for the boiler, I did not mean to imply it was CI, just that CI boilers use P/S for protection. P/S does allow for different flow rates.

k

>will always be pretty even in temp, but not cooler.
That's what I thought, but the temperature readouts are clearly showing the supply side is several degrees cooler than the return, until they are equal.

Where the new piping meets the old we change from 1.25" copper to 4" iron. Now I could believe that the heat shoots into the iron and up to the top floor very quickly and leaves push some cooler water down behind it. Do you think that is what's happening?

Derheatmeister

Correction!

Your quote on: "In the cold of winter they are quite similar to conventional boilers, except they still extract more heat from the flue making them more efficient in all conditions."

That is correct but this all depends also on your Heat emitters:

If your heat emitters are "over sized" then your boiler will condense even in the winter!

It also depends on your Insulation/Window upgrades/thermal mass of the building..

Even in some of the "Old Style" rads system it works petty good!.. Heatmeister

jp_2

cold water in a mod/con

your mod/con can certainly take cool water. during the heating season the water really couldn't be much below room temp, so I wouldn't call it cold water.

its my understanding the idea behind the mod/con is constantly supplying heat to the system as it looses heat. therefore the delta T would be what the system currently needs. I see no reason to artificially keep a higher boiler temp.
the system will provide the temp it needs, provided its initial set up right. if the system temp goes out too cool it will return to be 'bumped up' til heating is provided.

have you seen your system running constant(hours on end) at 180F? what are the radiator temps when boiler runs at 180F?