Donate to Remove ads

Got a credit card? use our Credit Card & Finance Calculators

Thanks to johnstevens77,Bhoddhisatva,scotia,Anonymous,Cornytiv34, for Donating to support the site

Boiler efficiency

Does what it says on the tin
MrFoolish
Lemon Quarter
Posts: 2284
Joined: March 22nd, 2020, 7:27 pm
Has thanked: 553 times
Been thanked: 1115 times

Boiler efficiency

#461150

Postby MrFoolish » November 26th, 2021, 1:08 pm

I was watching a video about the efficiency of condensing central heating boilers. The point was made that for best efficiency, you want the return pipe to be as cold as possible so that the boiler will enter condensing mode. Failure to achieve this will reduce the efficiency and will cause excessive cycling which will reduce the life of the boiler.

(Apparently most boilers are oversized for the property, but there's not much you can do about this.)

Anyway, it made me wonder what to do about an unused room. Is the best approach:

1. Close the door to the room and turn off the radiator. After all, why heat a volume you are not using?

or

2. Turn the radiator on and open the door. You are providing an additional heat sink for the boiler, which will condense and run more efficiently, with less cycling.

I suspect the first approach is better, but I wonder if it might be a close run thing?

I do tend to see a plume of white vapour from my flue, which suggests it isn't condensing. And it cycles a fair bit.

staffordian
Lemon Quarter
Posts: 2298
Joined: November 4th, 2016, 4:20 pm
Has thanked: 1887 times
Been thanked: 869 times

Re: Boiler efficiency

#461156

Postby staffordian » November 26th, 2021, 1:18 pm

I suspect the answer is less to do with heating or not heating specific rooms, but more to do with correctly setting the temperature of the water in the heating circuit.

We can set this and set the hot water temperature on the boiler.

My preference (instinctive rather than scientific) is to set the heating circuit temperature relatively low, not just to encourage maximum efficiency of the boiler, but I also feel heating rooms more gently results in less see-sawing of temperature. I think having the heating water, and therefore the radiators, too hot leads to overshooting of the set temperature, then a longer wait for the room to cool before the cycle repeats.

My boiler (a Worcester Bosch) also displays a temperature whilst it runs, which appears to be the water return temperature, which presumably gives an indication of whether it 's likely to be running efficiently.

MrFoolish
Lemon Quarter
Posts: 2284
Joined: March 22nd, 2020, 7:27 pm
Has thanked: 553 times
Been thanked: 1115 times

Re: Boiler efficiency

#461159

Postby MrFoolish » November 26th, 2021, 1:26 pm

staffordian wrote:My preference (instinctive rather than scientific) is to set the heating circuit temperature relatively low, not just to encourage maximum efficiency of the boiler, but I also feel heating rooms more gently results in less see-sawing of temperature. I think having the heating water, and therefore the radiators, too hot leads to overshooting of the set temperature, then a longer wait for the room to cool before the cycle repeats.


Yes, I've also wondered about this. But does reducing the water temperature make it modulate down its ouput power (good) or just set a limit on the flow or return temperature (not so good)? I don't know.

staffordian
Lemon Quarter
Posts: 2298
Joined: November 4th, 2016, 4:20 pm
Has thanked: 1887 times
Been thanked: 869 times

Re: Boiler efficiency

#461165

Postby staffordian » November 26th, 2021, 1:44 pm

MrFoolish wrote:
staffordian wrote:My preference (instinctive rather than scientific) is to set the heating circuit temperature relatively low, not just to encourage maximum efficiency of the boiler, but I also feel heating rooms more gently results in less see-sawing of temperature. I think having the heating water, and therefore the radiators, too hot leads to overshooting of the set temperature, then a longer wait for the room to cool before the cycle repeats.


Yes, I've also wondered about this. But does reducing the water temperature make it modulate down its ouput power (good) or just set a limit on the flow or return temperature (not so good)? I don't know.

We need Mike4 here :D

I assume it modulates its output to maintain the set temperature, then shuts down when the set temperature is exceeded, whilst still pumping the water round. The circulating water would soon cool sufficiently for the boiler to fire up again, but presumably using relatively little gas as it works less hard to maintain this temperature.

scotview
Lemon Quarter
Posts: 1480
Joined: November 5th, 2016, 9:00 am
Has thanked: 602 times
Been thanked: 911 times

Re: Boiler efficiency

#461171

Postby scotview » November 26th, 2021, 1:49 pm

I think No 1 is the correct answer. This is effectively what zoned heating does. You only heat the rooms you need.

You also mentioned most boilers being oversized. With a zoned heating approach you can reduce the work the boiler has to do the majority of the time.

We have a 4 zone system. BG recommended a 28 kW boiler (whole house load calculation) but we installed a 15 kW boiler (no need for gas pipe upgrade). It works perfectly and most of the time and it is firing at a low rate. This small boiler has a much more efficient turn down ratio and that is how it is used 80% of the time.

When we occasionally need the whole house warm it just takes a little longer to heat up, I can live with that.

Sorry if I maybe didn't specifically answer your water temperature/condensing question.

staffordian
Lemon Quarter
Posts: 2298
Joined: November 4th, 2016, 4:20 pm
Has thanked: 1887 times
Been thanked: 869 times

Re: Boiler efficiency

#461206

Postby staffordian » November 26th, 2021, 3:32 pm

scotview wrote:You also mentioned most boilers being oversized. With a zoned heating approach you can reduce the work the boiler has to do the majority of the time.

We have a 4 zone system. BG recommended a 28 kW boiler (whole house load calculation) but we installed a 15 kW boiler (no need for gas pipe upgrade). It works perfectly and most of the time and it is firing at a low rate. This small boiler has a much more efficient turn down ratio and that is how it is used 80% of the time.

When we occasionally need the whole house warm it just takes a little longer to heat up, I can live with that


I think one of the calculations, if not the key one, when sizing a combi boiler is the maximum rate at which hot water might be required. A house with a couple of baths and two or three showers would probably warrant a boiler a fair bit more powerful than one for a similar sized house with just one bathroom, when a smaller boiler would be more than enough for the space heating requirement of either property, and would heat the house more efficiently than the more powerful one

scotview
Lemon Quarter
Posts: 1480
Joined: November 5th, 2016, 9:00 am
Has thanked: 602 times
Been thanked: 911 times

Re: Boiler efficiency

#461219

Postby scotview » November 26th, 2021, 3:59 pm

staffordian wrote:when sizing a combi boiler is the maximum rate at which hot water might be required.


Yes, you are correct. My example was for an open vented system with hot water cylinder and a standard condensing boiler. This allows for the traditional condensing boiler to be downsized whereas a combi is rated for max hot water requirement.

9873210
Lemon Slice
Posts: 985
Joined: December 9th, 2016, 6:44 am
Has thanked: 226 times
Been thanked: 296 times

Re: Boiler efficiency

#461334

Postby 9873210 » November 27th, 2021, 1:54 am

A boiler should be sized for the "design day", which is the coldest day of the year. On any other day it is over sized and needs to modulate in one way or another*. If it can't do this efficiently then it's a poorly designed system. Of course there are many badly designed systems.

If you're futzing with the system you need to consider how it will perform on that coldest day.

* either by time slicing or reducing the gas flow.

MrFoolish
Lemon Quarter
Posts: 2284
Joined: March 22nd, 2020, 7:27 pm
Has thanked: 553 times
Been thanked: 1115 times

Re: Boiler efficiency

#461354

Postby MrFoolish » November 27th, 2021, 8:57 am

It strikes me as funny, there's a massive push for so-called smart meters on domestic electricity. But electical systems are relatively simple in that all power consumption eventually gets converted to heat (it's physics). So if an appliance is getting hot it is noticeably clocking up your bill; if it runs cool you can pretty much ignore it. Or you can just look at how fast the wheel is spinning in your meter. You don't need a smart meter!

But gas heating is a lot more difficult to assess. You just don't know how much wasted energy is going out of the flue.

I can't help but feel we have our eyes on the wrong ball.

scotview
Lemon Quarter
Posts: 1480
Joined: November 5th, 2016, 9:00 am
Has thanked: 602 times
Been thanked: 911 times

Re: Boiler efficiency

#461405

Postby scotview » November 27th, 2021, 1:16 pm

MrFoolish wrote:
But gas heating is a lot more difficult to assess. You just don't know how much wasted energy is going out of the flue.

I can't help but feel we have our eyes on the wrong ball.


I've attached a graph of one of our heating zones, from the Heatmiser app. You can see the heating come on around 6 am and then again around 9pm. It is surprising how quickly the zone heats up even with the 15kW boiler. The room isn't heated through the day so no gas is burned needlessly. The door is normally closed, so I suppose this illustrates point 1 in your original query.

Pity that Boris wants to rip out these fully functional and highly effective heating systems.

Image

88V8
Lemon Half
Posts: 5769
Joined: November 4th, 2016, 11:22 am
Has thanked: 4097 times
Been thanked: 2560 times

Re: Boiler efficiency

#461414

Postby 88V8 » November 27th, 2021, 2:39 pm

MrFoolish wrote:But gas heating is a lot more difficult to assess. You just don't know how much wasted energy is going out of the flue.
I can't help but feel we have our eyes on the wrong ball.

Maybe, but that ball is going to be abolished so no one's going to spend much time improving its roundness now.

I suspect that most ch systems are sub-optimal. I designed and installed two, yes, just two, but the amount of calculation required... the heat loss from each room, the air changes, sizing the rads, the pipes, the boiler... I can't believe that the average installer does all that stuff.

As a result most of the rads will be oversize, the pipes will be the smallest they can get away with, and the control system will either be pretty dumb as mine was - tank stat, one room stat - or too intelligent for the owners.
My nice simple 1982 gfch system required no additional capital outlay in the 29 years we lived there, leaving aside two valve actuators, the boiler never needed servicing... so I bet that in overall cost terms... running costs, capital, repairs... it compared well with a modern system.

And of course... many owners will likely sabotage whatever intelligence there is by putting furniture in front of the rads or drawing curtains over them, or indeed not drawing the curtains at dusk, and wandering around in their shirtsleeves with the stat cranked into the 70s.

We're all doomed.

V8

MrFoolish
Lemon Quarter
Posts: 2284
Joined: March 22nd, 2020, 7:27 pm
Has thanked: 553 times
Been thanked: 1115 times

Re: Boiler efficiency

#461440

Postby MrFoolish » November 27th, 2021, 6:05 pm

88V8 wrote:Maybe, but that ball is going to be abolished so no one's going to spend much time improving its roundness now.


I don't reckon they will abolish gas fired boilers in the near future. It's pretty obvious most people don't have the right pipework or radiators for heat pumps. Can you imagine the political flack if people are left without effective heating systems? More likely there will be some sort of push towards hydrogen IMO.

staffordian
Lemon Quarter
Posts: 2298
Joined: November 4th, 2016, 4:20 pm
Has thanked: 1887 times
Been thanked: 869 times

Re: Boiler efficiency

#461454

Postby staffordian » November 27th, 2021, 7:50 pm

MrFoolish wrote:
88V8 wrote:Maybe, but that ball is going to be abolished so no one's going to spend much time improving its roundness now.


I don't reckon they will abolish gas fired boilers in the near future. It's pretty obvious most people don't have the right pipework or radiators for heat pumps. Can you imagine the political flack if people are left without effective heating systems? More likely there will be some sort of push towards hydrogen IMO.

There is much debate about how clean hydrogen is (around it's production rather than it's combustion), but I'd be inclined to agree that there will surely be strong efforts made in that direction given that there is already the distribution infrastructure in place.

Mike4
Lemon Half
Posts: 7084
Joined: November 24th, 2016, 3:29 am
Has thanked: 1637 times
Been thanked: 3792 times

Re: Boiler efficiency

#461456

Postby Mike4 » November 27th, 2021, 8:08 pm

staffordian wrote:
MrFoolish wrote:
88V8 wrote:Maybe, but that ball is going to be abolished so no one's going to spend much time improving its roundness now.


I don't reckon they will abolish gas fired boilers in the near future. It's pretty obvious most people don't have the right pipework or radiators for heat pumps. Can you imagine the political flack if people are left without effective heating systems? More likely there will be some sort of push towards hydrogen IMO.

There is much debate about how clean hydrogen is (around it's production rather than it's combustion), but I'd be inclined to agree that there will surely be strong efforts made in that direction given that there is already the distribution infrastructure in place.


There isn't, according to a good friend on mine who is a big-wheel chemical engineer somewhere important!

He is askance at the proposition to use the existing gas network for hydrogen. He reckons hydrogen will seep through all plastics and quite a few metals. He suggests the proposals will come to nothing when the politicians realise that if you pump 10 cubic meters of hydrogen into a gas main, you'll only get (say) five cubic metres out at the other end. The difference having passed straight through the walls of the polythene gas main pipe.

Another serious and possibly insurmountable problem according to another chemical engineer (customer of mine), is hydrogen leaks are capable of self-igniting. He was telling me the other day that the friction of hydrogen passing through a restriction can heat it enough to cause spontaneous ignition. Gas leaks that randomly sprout a burning flame seem an unacceptably bad idea to me.

BullDog
Lemon Quarter
Posts: 2443
Joined: November 18th, 2021, 11:57 am
Has thanked: 1965 times
Been thanked: 1196 times

Re: Boiler efficiency

#461535

Postby BullDog » November 28th, 2021, 9:23 am

Mike4 wrote:
staffordian wrote:
MrFoolish wrote:
I don't reckon they will abolish gas fired boilers in the near future. It's pretty obvious most people don't have the right pipework or radiators for heat pumps. Can you imagine the political flack if people are left without effective heating systems? More likely there will be some sort of push towards hydrogen IMO.

There is much debate about how clean hydrogen is (around it's production rather than it's combustion), but I'd be inclined to agree that there will surely be strong efforts made in that direction given that there is already the distribution infrastructure in place.


There isn't, according to a good friend on mine who is a big-wheel chemical engineer somewhere important!

He is askance at the proposition to use the existing gas network for hydrogen. He reckons hydrogen will seep through all plastics and quite a few metals. He suggests the proposals will come to nothing when the politicians realise that if you pump 10 cubic meters of hydrogen into a gas main, you'll only get (say) five cubic metres out at the other end. The difference having passed straight through the walls of the polythene gas main pipe.

Another serious and possibly insurmountable problem according to another chemical engineer (customer of mine), is hydrogen leaks are capable of self-igniting. He was telling me the other day that the friction of hydrogen passing through a restriction can heat it enough to cause spontaneous ignition. Gas leaks that randomly sprout a burning flame seem an unacceptably bad idea to me.

Everything you say there is true. I would also add that the gas turbine driven centrifugal compressors used to compress the gas and move it around the country cannot be used on pure hydrogen either. Of course, such trivial details matter little to the idiots making the grand pronouncements and policies. They know they will be long retired before any of the really serious issues have to be faced.

staffordian
Lemon Quarter
Posts: 2298
Joined: November 4th, 2016, 4:20 pm
Has thanked: 1887 times
Been thanked: 869 times

Re: Boiler efficiency

#461549

Postby staffordian » November 28th, 2021, 10:36 am

BullDog wrote:
Mike4 wrote:
staffordian wrote:There is much debate about how clean hydrogen is (around it's production rather than it's combustion), but I'd be inclined to agree that there will surely be strong efforts made in that direction given that there is already the distribution infrastructure in place.


There isn't, according to a good friend on mine who is a big-wheel chemical engineer somewhere important!

He is askance at the proposition to use the existing gas network for hydrogen. He reckons hydrogen will seep through all plastics and quite a few metals. He suggests the proposals will come to nothing when the politicians realise that if you pump 10 cubic meters of hydrogen into a gas main, you'll only get (say) five cubic metres out at the other end. The difference having passed straight through the walls of the polythene gas main pipe.

Another serious and possibly insurmountable problem according to another chemical engineer (customer of mine), is hydrogen leaks are capable of self-igniting. He was telling me the other day that the friction of hydrogen passing through a restriction can heat it enough to cause spontaneous ignition. Gas leaks that randomly sprout a burning flame seem an unacceptably bad idea to me.

Everything you say there is true. I would also add that the gas turbine driven centrifugal compressors used to compress the gas and move it around the country cannot be used on pure hydrogen either. Of course, such trivial details matter little to the idiots making the grand pronouncements and policies. They know they will be long retired before any of the really serious issues have to be faced.


Good points well made. It looks like the current distribution network is on borrowed time then.

I wonder if there is any scope for repurposing the pipes as conduits for internet fibre where that is not already in place?

The other thing which pizzles me is why the likes of Worcester Bosch are working on hydrogen powered boilers. It seems the only way they might work if a piped network is not possible is if users had a tank such as propane (or is it butane?) users currently do.

Mike4
Lemon Half
Posts: 7084
Joined: November 24th, 2016, 3:29 am
Has thanked: 1637 times
Been thanked: 3792 times

Re: Boiler efficiency

#461565

Postby Mike4 » November 28th, 2021, 11:44 am

staffordian wrote:
The other thing which pizzles me is why the likes of Worcester Bosch are working on hydrogen powered boilers. It seems the only way they might work if a piped network is not possible is if users had a tank such as propane (or is it butane?) users currently do.


Me too, I'm pizzled too.

I simply can't reconcile the dash for hydrogen given the two problems I outlined, with the apparent willingness of firms like Worcester and Baxi to be developing hydrogen-burning products. They MUST be aware. There are only two possibilities I can think of.

1) The two chemical engineers whose comments I mention are simply wrong.
2) Worcester, Baxi etc know about the problems and are doing it because they have been asked to/told to by guvvermint, and are therefore going through the motions for political reasons.

Actually there is a third possibility. 80% methane and 20% hydrogen could work according to my friend. Something to do with the relative vapour pressures of the two gasses being the same ratio but inversed. Now the gas engineers will know about this and will have told the politicians that a 80/20 mix of methane/hydrogen can probably be made to work in the public network, so maybe this is the 'hydrogen solution' they are actually working towards and the 80/20 bit gets lost when politicians talk about it. But I don't know for sure.

staffordian
Lemon Quarter
Posts: 2298
Joined: November 4th, 2016, 4:20 pm
Has thanked: 1887 times
Been thanked: 869 times

Re: Boiler efficiency

#461573

Postby staffordian » November 28th, 2021, 12:04 pm

Mike4 wrote:
staffordian wrote:
The other thing which pizzles me is why the likes of Worcester Bosch are working on hydrogen powered boilers. It seems the only way they might work if a piped network is not possible is if users had a tank such as propane (or is it butane?) users currently do.


Me too, I'm pizzled too.



:oops:

Note to self.

Poof reed my pists a bet butter

quelquod
Lemon Quarter
Posts: 1017
Joined: November 5th, 2016, 12:26 pm
Has thanked: 195 times
Been thanked: 188 times

Re: Boiler efficiency

#461585

Postby quelquod » November 28th, 2021, 12:34 pm

“ Actually there is a third possibility. 80% methane and 20% hydrogen could work according to my friend. Something to do with the relative vapour pressures of the two gasses being the same ratio but inversed. Now the gas engineers will know about this and will have told the politicians that a 80/20 mix of methane/hydrogen can probably be made to work in the public network, so maybe this is the 'hydrogen solution' they are actually working towards and the 80/20 bit gets lost when politicians talk about it. But I don't know for sure.”

But mains gas is already somewhere north of 90% methane so this sounds a fairly minimal improvement on emissions, together with the anticipated pollution from hydrogen production itself. (And there are no asses in gases ;) ).

BullDog
Lemon Quarter
Posts: 2443
Joined: November 18th, 2021, 11:57 am
Has thanked: 1965 times
Been thanked: 1196 times

Re: Boiler efficiency

#461591

Postby BullDog » November 28th, 2021, 12:47 pm

staffordian wrote:
BullDog wrote:
Mike4 wrote:
There isn't, according to a good friend on mine who is a big-wheel chemical engineer somewhere important!

He is askance at the proposition to use the existing gas network for hydrogen. He reckons hydrogen will seep through all plastics and quite a few metals. He suggests the proposals will come to nothing when the politicians realise that if you pump 10 cubic meters of hydrogen into a gas main, you'll only get (say) five cubic metres out at the other end. The difference having passed straight through the walls of the polythene gas main pipe.

Another serious and possibly insurmountable problem according to another chemical engineer (customer of mine), is hydrogen leaks are capable of self-igniting. He was telling me the other day that the friction of hydrogen passing through a restriction can heat it enough to cause spontaneous ignition. Gas leaks that randomly sprout a burning flame seem an unacceptably bad idea to me.

Everything you say there is true. I would also add that the gas turbine driven centrifugal compressors used to compress the gas and move it around the country cannot be used on pure hydrogen either. Of course, such trivial details matter little to the idiots making the grand pronouncements and policies. They know they will be long retired before any of the really serious issues have to be faced.


Good points well made. It looks like the current distribution network is on borrowed time then.

I wonder if there is any scope for repurposing the pipes as conduits for internet fibre where that is not already in place?

The other thing which pizzles me is why the likes of Worcester Bosch are working on hydrogen powered boilers. It seems the only way they might work if a piped network is not possible is if users had a tank such as propane (or is it butane?) users currently do.

I wouldn't bet against a hydrogen blend coming to fruition. Though the issues highlighted remain, just at a more manageable level. We used to manage towns gas generally OK which has a lot of hydrogen and carbon monoxide. Before my time, but pror to natural gas use in the UK, I understand town's gas was generated in gas works in every town and distributed locally rather than nationally which is of course, a different proposition.

One worrying factor that seems unaddressed at the moment though with hydrogen/methane mix in the national pipeline system is that of hydrogen embrittlement of steels.


Return to “Building and DIY”

Who is online

Users browsing this forum: No registered users and 10 guests