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Topic Title: Energy Minder
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Created On: 06 December 2012 11:42 AM
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 06 December 2012 11:42 AM
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jcm256

Posts: 1796
Joined: 01 April 2006

Is that true, condensing boilers or heat pumps are most effective at running at lower temperatures - around 30 to 40 degrees instead of the standard 70 to 80 degrees,"

I though the opposite was the case, I have only a two pipe system to an outside boiler kept the boiler turned high (just under the limit for "too hot" tap water) thinking that the higher temperature causes a lower return temperature therefore optimising the condensing feature. Of course, I am not going to purchase one of these Energy Minders at that cost and then get hot water so low that it would not do for a hot water bottle. However, just in case did anyone fit one for a two-pipe system, was it any good.

http://www.meteorelectrical.co...ting-system/801478660

Regards
jcm
 06 December 2012 11:47 AM
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OMS

Posts: 18943
Joined: 23 March 2004

Well a heat pump will always be more efficient, the closer the source and sink temperatures get - so ground source is better on a cold winters night as the ground is warmer than the air - at mid season, in the day, an air source would be more efficient as the air temperature exceeds the ground temperature

For a condensing boiler, a lower flow and return is better, but you may have a higher flow and a greater temperature drop from flow to return

Ideally, you want the return temp to be constantly lower than the condensing temperature

Regards

OMS

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Failure is always an option
 06 December 2012 01:03 PM
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AJJewsbury

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Is that true, condensing boilers or heat pumps are most effective at running at lower temperatures - around 30 to 40 degrees instead of the standard 70 to 80 degrees,"

As OMS says, for a condensing boiler to run in condensing mode the return temp needs to low - from memory around 57 degrees. Typically rads are designed to loose around 10 degrees (delta T). Making the flow hotter will obviously cause more heat to be lost from the rad (for the same room temp) - slightly increased delta T, but the return temperature will still be higher. So design might be for 65-degree flow, 10 degree delta T, and so 55 degree return. If you ran it at say 80 degrees, delta T might be say 12 giving a return of 68 degrees - meaning that the boiler would be too hot to condense the products of combustion, so be less efficient.

The efficiency of a heat pump is directly related to the temperature difference - there's a formula for maximum theoretical efficiency based on the temperature rise - most practical heat pumps achieve about half that though. So in general the lower the output temperature the better the efficiency. Many aim at around 40 degrees and feed and underfloor heating or run with compensators to run the HP at the lowest temperature that'll deliver the required amount of heat.

- Andy.
 06 December 2012 01:32 PM
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OMS

Posts: 18943
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Usual design approach would be a much bigger deltaT, F&R - approx 20C with say 70/50C F&R giving a mean water temp of 60C , and then bigger rads to compensate for the lower MWT and smaller deltaT to the room

Weather Compensated circuits will almost certainly get the return down to well below the condensing temp to maximise the latent recovery

Regards

OMS

-------------------------
Failure is always an option
 06 December 2012 05:15 PM
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jcm256

Posts: 1796
Joined: 01 April 2006

Thanks for the replies, am sometimes asked all sorts of questions on boilers, you have sort off boiled it down to larger more efficient radiators as well to make the condensing boiler more efficient.
Thanks again.
 06 December 2012 05:22 PM
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OMS

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Not neccesarily more efficient radiators - just bigger to get the same heat output based on a lower mean water temperature and thus a lower deltaT to the room. The efficienct comes in the lower return temp being generally always below the boiler condensing temperature

Regards

OMS

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Failure is always an option
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