Condensing Boiler Setup/efficiency

matelodave

How about this then - you need a Viessmann boiler though http://www.advance-heating.co.uk/pdf/2008.03%20Vitotronic%20200%20Datasheet%20200%20GW1.pdf.

Baxi do something with theirs http://www.advance-heating.co.uk/pdf/2008.03%20Vitotronic%20200%20Datasheet%20200%20GW1.pdf

So some systems have the capability but I'm not sure if they can be retrofitted to older or even existing systems unless they've got the appropriate interfaces

sk240

I achieve permanent condensing mode in a very easy way, but your house will determine if you can do it or not.
I run my heating at 55'C so the return can never be any hotter than that!
It does run in condensing mode as I can regularly hear the drain syphon dump all the water.
I do however never turn off my heating, but my house is very well insulated (my annual gas bill is £350 :-) (3 bed semi)

matelodave

Yes that's the way to do it but as you say you have to run the heating continuously as do I with my heatpump. It has weather compensation and varies the flow temperature between 25 and 40 degrees to correspond with outside temperatures of 15 to zero degrees - it usually sits at around 30-35 degrees (= 10-5 degrees outside)

It's fine if you are at home all day but if you require fast warm up when you get up or get home in the evenings then a low temperature system may not be suitable, you also need to increase the rad sizing by at least 50%.

Mine takes 24 hours or more to get the place up to temperature if I turn it off when we go away, although I've discovered a holiday setting on my programmable thermostats that let me turn the system on the day before we return. We just set back the overnight temperatures by 3 degrees rather than turning it off.

Cardew

matelodave wrote: »

How about this then - you need a Viessmann boiler though http://www.advance-heating.co.uk/pdf/2008.03%20Vitotronic%20200%20Datasheet%20200%20GW1.pdf.

Baxi do something with theirs http://www.advance-heating.co.uk/pdf/2008.03%20Vitotronic%20200%20Datasheet%20200%20GW1.pdf

So some systems have the capability but I'm not sure if they can be retrofitted to older or even existing systems unless they've got the appropriate interfaces

Thanks for the links although you have put the same link for the Baxi.


After you have bought and fitted that Veissmann boiler and control unit, you can get some useful information by running it in different modes.


However what I want is some ballpark figures of a boiler before I buy.


I read the links in your other post as well. Not sure they answered my queries, but picked up some interesting points. One was the difference in efficiency between a light heating load and a full heating load.


The other was that you achieve a higher SAP(the Government’s
Standard Assessment Procedure) for energy rating by having a property with poor insulation where the heat loss is higher - which rather defeats the object.

Cardew

sk240 wrote: »

I achieve permanent condensing mode in a very easy way, but your house will determine if you can do it or not.
I run my heating at 55'C so the return can never be any hotter than that!
It does run in condensing mode as I can regularly hear the drain syphon dump all the water.
I do however never turn off my heating, but my house is very well insulated (my annual gas bill is £350 :-) (3 bed semi)

Your post has illustrated the point I have been trying to make.


Your method is driven by the need to keep in condensing mode and to achieve this you keep heating on 24/7 and run at 55C.


That indicates you consider that it is very important to run in condensing mode. However you cannot quantify how much more efficient running in permanent condensing mode will be than running CH at, say, 70C on a timed basis and accepting that for some of the time the boiler will not be condensing.


People who have work/school all day will normally have their heating to come on before they get up in the morning, go off shortly before the property is unoccupied; and back on before people return to the house. CH will then be off while occupants are in bed.


I would add that I have never seen any technical publication that advocates running a CH system 24/7 either with or without a condensing boiler and that includes the Energy Saving Trust latest advice.

nxdmsandkaskdjaqd

There have been some interesting posts containing some very usefully information.

I have had my boiler set to 55 degrees C flow for the last month, but I am now going to set this to 50 C in order to give me a 35 C return.

My heating engineer is due to visit in a weeks time to replace a manual gate value with an automatic gate value when the boiler goes into bypass. This should enable me to finally set everything up as I want it.

I was also interested to note that the boiler is more efficient on a light load, currently the boiler is running most of the time with a 8KW load (28KW boiler), so I should be mid 90's in terms of efficiency.

matelodave

There's a more info if you trawl the interweb and about all you can get is a feel for the efficiency drop off v temperature. Possibly, if you spoke to the boiler manufacturers directly, you might get a bit more info but I'd guess they'd consider it proprietary info.

I also was intrigued by the SAP conclusions, so is it better to flog the boiler flat out kicking it on & off or let it chunter away all the time at maximum efficiency.
I suppose it depends on how you need to heat your home, continuously or in short timeslots where the place only just gets up to temperature before it starts to cool down again.

We are back into the argument of whether there's more heat loss if you keep the house warm all day or let it cool down between heating cycles. There's got to be a cut over point where they balance out and one is better than the other and I'm sure that the amount of insulation would change that parameter.

Pincher

It's worth doing a little experiment, go away on holiday for a week with the thermostat set to say 14 degrees, and see how much gas is used if you leave it on 24/7.


At 14 degrees, the boiler is not even on most of the time, unless you have Swiss cheese for a house.

nxdmsandkaskdjaqd

This can be proved by modelling the thermal coefficient of the house. I am going to have a go for various models. Might take me a few days.

Cardew

nxdmsandkaskdjaqd wrote: »

I was also interested to note that the boiler is more efficient on a light load, currently the boiler is running most of the time with a 8KW load (28KW boiler), so I should be mid 90's in terms of efficiency.

I very much doubt you will approach 90% efficiency - those figures are only achieved in a laboratory.


You presumably heat DHW that isn't included in the SAP figures.


In any case how could you measure the efficiency of the boiler in your property? You can obviously measure the energy input(i.e. the gas used) but the heat output??


It is immensely complicated to measure heat output. Just for starters, you would need a Heat meter measuring water flow and change of temperature between boiler output and return.


Look at the Strathclyde University link provided by matelodave to see the complexity.