Reset Buffer Protection et all

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  #41  
Old 01-08-12, 11:08 AM
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Illustrious?? Not!

I think we've gone around regarding the heat loss. There were some unknowns but pretty sure a ballpark was stated some time back, and it was 80k or less.

The GB142 needs the primary/secondary piping. This looks pretty good to me, what I can discern with aging eyes.

Major question is do you really need all that buffer capacity. 150 gal is a lot.

Here's the way to estimate, per Siegenthaler.

Vbt = t(Qh -qload) / (500 *dT)
Vbt size of buffer (gal)
t desired on-cycle (min)
Qh energy source output (BTU/hr)
qload rate of heat extraction from buffer (BTU/hr)
dT temp rise of tank between on/off cycles (F)

For example, say you want a 10 minute cycle time at 30k output at 20k load, with tank dT 20F.

Vbt = 10*(30000-20000) / (500*20)

Vbt = 10 gal buffer needed

Now see what happens when you play with higher output. Say 80k. Now Vbt = 60 gal.

All kinds of ways to play with this formula. Say you want runtime for that same 20k partial load with 150 gal buffer, at say 28.3k output.

t = (Vbt*500*dt) / (qh - qload)

t = 150*500*20 / (28300 - 20000)

t = 180 minutes runtime.

So for the buffer sizing, you want to look at partial loads, outputs, etc. I am going to guess that you definitely don't need 150 gal, and probably 50 would cover all the reasonable partial load states once you figure out what firing (modulation) rates should be needed. That extra 100 gallons represents a) a lot of work to heat and keep heated, and b) a slow continuous heat loss through the jackets -- it's a lot of surface area for those two (presumably) extra tanks.
 
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  #42  
Old 01-08-12, 11:18 AM
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Heat loss is aproximate as R-values are unknown.

Read my posts above:
12-31-11 8:16pm
1-04-12 6:15pm
 
  #43  
Old 01-08-12, 11:41 AM
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Hello All,

If the basement is to be heated, will the loss from the buffer tank/s go to waste or will it all be used to help heat the basement?

P1 runs continuous. Meaning only when there is a heat call?

To extend run times, feed the hot water into the bottom of the buffertank/s take the supply off the top.
Place the boiler sensor on the House Supply, after P2.

Thoughts?

Peter
 
  #44  
Old 01-08-12, 11:52 AM
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What are the 3 IDW for. Is there that much hw demand? If so, I am concerned about boiler sizing in this case. We normally do not talk about resizing the boiler for the indirect but if HW is the primary concern for the boiler I would reconsider that idea.
 
  #45  
Old 01-08-12, 12:10 PM
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Hello RBeck,
They are buffer tanks.
Not indirects.
The OP has them available for no extra cost and wants to use them, given that the boiler is at least half again oversized.


Peter
 
  #46  
Old 01-08-12, 12:23 PM
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These 3 tanks are new and on site, may as well use them to extend cycles.
3/4" in/out of 3x tanks works well with the system flow via the 1-1/4" system pipe.

P1 runs 24/7/180 via a Summer/Winter switch.
I want to de-stratify buffer tanks.

There is no external boiler sensor. This boiler has sensors on supply & return internally.

The tanks are easy to wrap with fiberglass, the little heat getting out will slightly help heat basement.
Basement is heated. See P3 useage in drawing.

rbeck these are buffer tanks with system water. The TT Solo 60 is for DHW.
 
  #47  
Old 01-08-12, 12:23 PM
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If I recall correctly, they are 50 gallon electric water heaters that are being 're-purposed'.
 
  #48  
Old 01-08-12, 12:31 PM
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When it's 55* outside & a small zone calls for heat, this boiler is probably 50x oversized.

Thus the buffer.

At 6,000' altitude it should modulate from about 33 -> 130MBH
 
  #49  
Old 01-11-12, 05:59 PM
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Still thinkin' about this...

Patrick, your boiler has ODR built in, and is a mod/con... so, why not just do this? The ODR will operate on the boiler, you'll get the benefit of probably condensing most of the time. The buffer tank temp will simply follow the boiler.

To wit, I offer the stripped down model:



And the other idea we kicked around, with the buffer in the return only... which seems to make a lot of sense to me for a lot of reasons...

 

Last edited by NJT; 01-11-12 at 06:29 PM.
  #50  
Old 01-12-12, 08:35 PM
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NJ Trooper,

For a clean slate design your #1 is the best. Examples are numerous, Boiler Buddy, etc.
4 ports provide hydraulic seperation between boiler & system, total asynchronous operation of both, cool water to boiler to cause more condensing (at least at the start).

With my given 2 port buffer tank setup, your #2 with buffer on return works well, extends both on & off cycles. With the cool water from the return, it would seem to make more sense than having the buffer before the system load,
BUT

I have read feedback from a DIY type who very Carefully Monitored his own system where he moved his buffer between return & supply. Same load, flow, etc. etc. and the buffer in the supply caused longer cycles by about 15%

Possible reason is in how most modcon computers reacts to supply / return temperatures, cool temperature return at the start causes modulation to ramp up say 100% fire, this shortens the burn time vs. warmer water coming back AND can lower efficiency.

Some experts think that the burner modulation ratio has a higher impact on modcon effeciency than the commonly repeated: return water temperature is everything. It is both, I will post a graph.

With buffer in supply design, small zone calls MAY be satisfied drawing heat out of the buffer without firing the boiler. With a Time Delay Relay in the T-T circuit, the odds go up on this.

I'm still unsure if the zone panel end switch is the best way to control T-T.
I would somehow like to draw the buffer down more, say 30* before firing boiler.
I haven't figured out how to use a 30* delta aquastat for this as ODR shifts the buffers upper temp.





 

Last edited by Buffalobillpatr; 01-12-12 at 09:32 PM.
  #51  
Old 01-12-12, 09:48 PM
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I'm still unsure if the zone panel end switch is the best way to control T-T.
I would somehow like to draw the buffer down more, say 30* before firing boiler.
I haven't figured out how to use a 30* delta aquastat for this as ODR shifts the buffers upper temp.
Wouldn't the draw-down be highly (if not totally) dependent on the differential?

I know that the Tek's have either 'auto-diff' or 'manual'... and I'm pretty sure that you can go at LEAST up to a 30 diff.

Not too familiar with the AM-10 but if it allows a MANUAL diff, you could just set it and forget it... no?
 
  #52  
Old 01-13-12, 01:09 AM
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"Not too familiar with the AM-10 but if it allows a MANUAL diff, you could just set it and forget it... no?"

I wish I could. I have read everything I can find on the GB142 & AM10.
If this is possible, Buderus has hidden it well.
 
  #53  
Old 01-13-12, 05:04 AM
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It would seem that the benefit of lower return temperature giving us the extra heat from latent heat would out way the efficiency loss. Taking heat from the flue gasses that normally would end up outside is a benefit. You can gain about 9% from latent heat dependent on water temperature that will fluctuate. The more btu's produced that end up in the water that heats the home is the most efficient. It is not all about efficiency but cost to heat the home.
The buffer on the return will benefit also in modulation as the micro-zones call and the tank is not cold water it is usually warm. So at the beginning of the cycle we feed luke warm water and pick up the tank temp as the system runs longer. We will modulate the boiler quicker than cold return water back to the boiler.
 
  #54  
Old 01-13-12, 11:18 AM
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I just found this info:

Joe from Buderus,
"The DHW differential is fixed at seven degrees. It cannot be changed. On a call for DHW the GB142 will go to max temperature of 194 degrees."


http://cul-tech.com/Documents/Doyle%...ter_Heater.pdf
page 19,
System Heat Request (via T-T) shows a fixed +11* to -11* (Supply vs Target) for a 22* differential

This is Great IMO, 150gal x 8.3# x 22* = 27,350 BTU per burn minimum + any system draw.
 
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