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Old 01-06-2010, 03:38 PM   #31
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Hi & Low Limit setting - Oil boiler, forced HW - Cast Iron radiators


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Originally Posted by Scuba_Dave View Post

So....I'm confused
Low return water temps for prolonged periods can cause several different problems.
most common. Is the boiler gunks up with damp soot.


Lots of cold fire boilers are set up like yours.
Can be a little harder to clean.

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Old 01-06-2010, 03:53 PM   #32
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Hi & Low Limit setting - Oil boiler, forced HW - Cast Iron radiators


Ah, OK
We have gone from 3 tanks of oil the 1st year down to 1 to 1.5 tanks of oil since then
I think as a result its been much easier for our Oil guy to clean
I know he's surprised at how little oil we use
At 1st maybe he thought we were filling up from someone else
But we found him the 1st year & have stuck with the same guy
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Old 01-06-2010, 05:35 PM   #33
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Hi & Low Limit setting - Oil boiler, forced HW - Cast Iron radiators


I am confused what valve needs to be shut. When adjusted always stays the same. What expense? two tees some pipe and a valve? Saves about 9 - 12% in large water volume systems. Nothing to sneeze at.
Boiler protection
Increased comfort
Fuel savings
Where are the negatives?
See link
http://www.comfort-calc.net/Bypass_P...laination.html
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Old 01-06-2010, 06:18 PM   #34
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Hi & Low Limit setting - Oil boiler, forced HW - Cast Iron radiators


I see what you mean now.....but

From the site:
Quote:
The savings is minimal
and my boiler is going on 23 years old
So I don't see a problem
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Old 01-06-2010, 07:17 PM   #35
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Hi & Low Limit setting - Oil boiler, forced HW - Cast Iron radiators


Going from a 130 return temp to a 120 return water temp won't save much on a residential system.

As a DIY change, cost is minimal. For those that have to pay someone, it is costly.

While a boiler bypass will maintain proper flow through the system.
Slowing water flow to .5GPM through the boiler doesn't not give full BTU to the house, and can cause heat problems. With boilers that are sized to the load of the house. In which case the bypass valve must be shut to get the full BTU to the house.

If the boiler is oversized. It won't have a problem.
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Old 01-09-2010, 04:23 PM   #36
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Hi & Low Limit setting - Oil boiler, forced HW - Cast Iron radiators


You could not reduce the flow to .5 gpm through the boiler or the boiler would grossly short cycle. But let's not confuse gpm flow with btu's. The btu into the home is going to stay the same. If the boiler is 80K for instance and the flow is 100 gpm or 5 gpm there is still 80k btu's to the home. The more gpm going through the boiler the lower the delta T. More gpm means less btu;s per gallon. Reduce the flow and that means more btu's per gallon thus higher water temperature. There are three thins to think about in hydronic heating, they are BTU's, gpm and water temperature.
You can change the flow through the boiler to achieve a different delta T but the btu's to the system do not change. The output from the radiation may change as water temp will change.
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Old 01-09-2010, 08:10 PM   #37
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Hi & Low Limit setting - Oil boiler, forced HW - Cast Iron radiators


Actually. Changing the GPM through the boiler can lower or increase the BTU delivery to the house.

Low water flow through the boiler will cause a higher stack temp(the higher the stack temp, the more BTUs that are in the combusted gasses). This is because not as many BTUs are being absorbed by the water.

Too high of a water flow, and the water isn't in the boiler long enough to pick up the heat/BTUs.

The .5GPM I refered to in my other post. Was to have been typed as .5GPM per 10,000 BTUs of boiler rated output. This would be a 40 rise through the boiler(on paper).
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Old 01-10-2010, 08:02 AM   #38
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Hi & Low Limit setting - Oil boiler, forced HW - Cast Iron radiators


Your analogy is correct but minimal change in btu's not going into the home as compared to need for boiler protection. The flow through the boiler can be whatever it is but the btu to the home is the same other than the small amount lost in the vent.
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Old 01-10-2010, 08:10 AM   #39
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Hi & Low Limit setting - Oil boiler, forced HW - Cast Iron radiators


Whats minimal will remain debatable.

Lowering allowable/safe entering water temp by 10 is only a 7% savings(on paper).
So if you lose 4%(just a % picked out of the air) heat transfer efficiency in the boiler. You don't really get much of a savings from the lower entering water temp.
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Old 01-10-2010, 01:15 PM   #40
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Hi & Low Limit setting - Oil boiler, forced HW - Cast Iron radiators


Quote:
You don't really get much of a savings from the lower entering water temp
.
The greatest temperature transfer is at the greatest temperature difference. So the cooler return water will allow a greater temperate transfer from fireside to water side. The boiler bypass in testing saves approx 9 - 11% dependent on water volume. Decrease water temperature and increase fuel savings. Heat less water as all the gallons in the system are not going through the boiler.
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Old 01-10-2010, 01:39 PM   #41
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Hi & Low Limit setting - Oil boiler, forced HW - Cast Iron radiators


So your saying that you get greater savings(9 to 11%) by having a 10(120) cooler entering water temp with a 10(160) hotter leaving water temp.
Then with a 10(130) warmer entering temp with a 10(150) cooler leaving water temp.

If your getting that savings. The savings might be from a more even heat through out the house. From having the lower water temp at the beginning of the heat call. And the customer is turning the thermostat down a or 2. But not from a boiler efficiency improvement alone.

What is your combustion efficiency improvement on these units that are saving 9 to 11%?

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