I just setup a very similar system to rbeck's drawing - except it was a old gravity system boiler swap so we're talking one zone and a mess of cast iron rads. This diagram is also very similar to the one supplied with my Knight mod/con. It works like a champ I have to say. The boiler controls the all the pumps - the primary loop runs maybe 10 degrees or so warmer than the system from what I can tell. A single pump seems to move the water through the old system pretty well despite a lot of big pipe and volume. It takes FOREVER to fill the system with water and bleed all the rads... The heat is uncannily constant and even. The temp is rock solid at 68 degrees.

I removed a boiler rated at 240K and replaced with the Knight 105. All the electronics were built in and comes with the primary pump, outdoor reset, system sensor, etc. all standard + other goodies so it was a plug and play affair. It's been down in the teens and it's been pure comfort. Even my wife who thought I was crazy tells me this has been worth it based on comfort alone in our masonry 120 year old home. It's around 2700 ft/sq. I've probably reduced the amount of "iron" in the house by a half from what it used to be. (I've added insulation and replaced all the windows with double pane) I broke down the rads and reduced them from 11 sections to 6 or 7 and sprayed them all with auto paint - they look and work great. I've removed a few too - it was a cast iron jungle, I don't know how people put furniture in the place. Despite all my ignorance and meddling the place feels great.

The quality of heat has been perfect even when we were in the teens - the boiler ran at around 50 to 60% capacity. Haven't seen enough gas bills to know what the difference in cost was but we had one month cost us $600 last year. Regardless of that outcome, this has been one of the most satisfying improvements in terms of comfort to my home.

 

Why did you remove and reduce the size of the rads? What kind of return temperatures are you seeing at different outdoor temperatures?

rbeck's layout is very common for modcons. My Prestige is piped like that, Ultra's are supposed to be piped like that as well. Pretty well most except for the Munchkins, Vitodens and Buderus BG142 are laid out this way.

 

Nice drawing Who. What program did you use?

 

rbeck, I use Visio and Paint.

 

Is this piping suitable for NON-CONDENSING units that cannot accept return water temps below 140 F? Everything I've read from manufacturers websites seems to indicate that some form of valving is required between the system and boiler loops. The debate seems to be over what is required (e.g. TV valve, 2-, 3-, 4-way mixing valve, pump) and how do you purge/bleed it! Am I correct?

 

The thermic valve is extremely efficient and effective.
It only serves to keep the return
temps above 140 degrees. The diagram
below is how I piped my Biasi using a Danfoss TV
valve and a Tekmar 260 ODR controller. This
system allows FULL ODR reset range,
and also constant circulation in the
heating loop--if the burner fails the
water will keep circulating in the heating
system to delay the chance of freezing pipes.
The heating loops alway have full circulation
during a heating call, using a single circulator
with a TV valve would only allow flow to begin
in the primary loop once the boiler return reaches
140 degrees.

I can set the lower limit to 90 degrees and
still have effective boiler protection. Without
the TV valve I'd have to set the Tekmar Boiler
Min. setting to 150 degrees to prevent condensation.

Pete

http://i117.photobucket.com/albums/o...PS-diagram.jpg

 

with Who's and Radioconnection's Thermic Bypass in the proper place. Note the location of purge valve moved to other side of Thermic tee ... this allows the purge valve to work as designed in rbeck's original diagram.

 

I believe that rbeck's diagram and suggestions indicate that the "central heating secondary circulator" can be a variable speed pump to provide boiler protection. It would be worth thumbing through the tekmar brochures to see how that would be controlled (perhaps the 361 wired differently). Or call your local/regional tekmar rep.

Who makes an interesting, cool case. Only change I'd make is either move the PONPC (Point of No Pressure Change -- the expansion tank) to connect upstream of the circ, or move the circ downstream of the PONPC.

The great thing about hydronics is that there are so many options. The confusing thing about hydronics is that there are so many options.

 

On Trooper's last drawing, with the air scoop before the PS tees, what effect does this have on the PONC? I asked this on the Wall several months' back, and no one could give a definitive answer. Also, there is no air purging on the DHW side during the non heating seasons. (that's one reason mine was piped the way it was.)

Also, for a tank within a tank type DHW heater, how are you going to avoid an airlock when initially filling the system as shown?

:mask:

 

xiphias, from what I’ve read and learned, I too strongly advocate pumping away from the point of no pressure change (having the air eliminator, makeup water and expansion tank just upstream from the circulator pump). The reason I propose this layout as it is, was because I was trying to maximize the benefit of using the thermic valve.

The thermic valve can be placed on the supply of the return. On the supply, it stops the supply until the water temperature reaches 160°. It doesn’t really control the return temperature. If there’s a high temperature differential on the supply, the return could be low enough to condense and if the temperature differential is really low the boiler would lose system efficiency by not supplying water to the heating loop until it has a return temperature of close to 160°. Given that the emphasis on my design was to make the warmup loop as short as possible, placing the thermic valve on the return makes the most sense to me. In order to do that, the circulating pump needs to be where it is.

The air elimination / makeup water / expansion tank was put on the supply near to where the buffer tank connects. Therefore, the heating circulator will be pumping away. With the air elimination where it is, it does see the hottest water and the supply pipe is higher than the return for doing fills. Keeping the expansion tank and fill on the boiler side allows the indirect to remain functional even if during the summer the heating side is drained to make any changes or repairs.

With modern diaphragm tanks and micro-bubbler eliminators like Spirovents I don’t think “pumping away” is nearly as important as it used to be. If you look at piping diagrams for the Viessmann Vitodens you would actually see that it in effect pumps into the point of no pressure change.

I was trying to do the following with my layout. Keep the indirect path as short as possible since it has to work even when air conditioning is on. Keep the warmup protection loop as short as possible to maximize efficiency. Provide a buffer tank to maximize both run times and just as important off times for the boiler so that the number of heating cycles is kept down to extend the life of the equipment. The buffer allows full outdoor reset on the heating side (as does RadioConnection’s).

 

Your rationale on system construction is well-reasoned, as usual. I like it! You and radioconnection have a much better understanding/zen of the TV valve than I do.

Having been a "victim" of not pumping away, in spite of a Spirovent and a modern diaphragm tank, I will quibble about that, though. Air elimination has something to do with it, I agree. Get rid of the air and there are no bubbles to expand. But it's mostly about the pressure differential and how the pump achieves it. Perhaps mine was a limiting case. The fact that vast numbers of systems pump without problems into the expansion tank rather than away suggests that may be true. But I like to exploit the laws of physics whenever possible.

OK, manonano, how you holding up? Decided what to do yet?

 

Well, the heating supply pump, which operates far more often is actually pumping away and neither the boiler loop circ or the DHW circ is pumping into the point of no pressure change so it should be fine. Those circs are both a long long way from the PONPC.

Was your circ directly upstream and pumping into your expansion tank? If so, I'd still be gun shy about that as well...

 

No, just the classic pump on the return, and spiro/tank on the supply. I forget the exact numbers. Pressure differential was something like 4.x psi, nearly all of which was achieved by negative pressure on the inlet side. Abundant bubbles at the top of the system....

 

I wondered about that too... maybe there should be another air scoop ? (wouldn't need another exp tank though...) although, once the system was in operation for a while, it's doubtful that you would need it...

Fill and purge boiler first, then:
Close iso valve upstream of purge valve, close iso valve on boiler return. Open purge... water will flow through the DHW and out the purge valve.

The valve on the Thermic bypass line has to be open, because the water will be following that route ...