> we are comparing pears and apples
Yes.
The assertion that steady or set-back is better depends a LOT on Thermal Mass. And nearly as much on Appropriate Design.
Many newer US houses don't have much mass. And because the price of a furnace does not go up much with output, they often have a carelessly over-sized burner. It comes on strong, the house gets hot quick, it shuts down, over and over. Under 50% duty cycle on the worst day, and all that startup/shutdown loss on each cycle.
My house is pretty massive. It takes hours to cool a few degrees on the coldest night. The previous owner had thrown in a burner which was just too darn large. Too large for the ducts. The house air heated fast, 20 min tops. The walls can not absorb heat so fast, it takes hours (thermal conductivity and thermal mass of gypsum and heavy woods). So large airflow and over-temp followed by cold-wall chill.
I figured the house's actual cold-day need at 29KBTUh. I ended up with a 38KBTUh burner (half the size of the other). It runs long and steady. We set-back at night, but not real far because it is slow to pick-up again. On the coldest day/night it runs 19 of 24 hours. Inside air rarely gets 1 deg F off the set-point, except at pick-up and drop-back. On a cold day it takes 3 hours to drop 7 deg F, and 3 hours to make it up again.
IMHO, the "advantage" of a Modulating burner is that you can recklessly over-specify the output and let it burn part-power most of the time. But a small fire in a big firebox has consequences also.
My system is forced air. I figure the fan blower contributes about 7% of the total heat. Since electric is 3X the cost of propane, that's a point for thought. This is an extreme case since this is the smallest model of its range, and I think it has the next-up blower motor. Hot-water pumps use less electric but put only some of that in the water (my fan-heat goes 99% in the duct).
Yes.
The assertion that steady or set-back is better depends a LOT on Thermal Mass. And nearly as much on Appropriate Design.
Many newer US houses don't have much mass. And because the price of a furnace does not go up much with output, they often have a carelessly over-sized burner. It comes on strong, the house gets hot quick, it shuts down, over and over. Under 50% duty cycle on the worst day, and all that startup/shutdown loss on each cycle.
My house is pretty massive. It takes hours to cool a few degrees on the coldest night. The previous owner had thrown in a burner which was just too darn large. Too large for the ducts. The house air heated fast, 20 min tops. The walls can not absorb heat so fast, it takes hours (thermal conductivity and thermal mass of gypsum and heavy woods). So large airflow and over-temp followed by cold-wall chill.
I figured the house's actual cold-day need at 29KBTUh. I ended up with a 38KBTUh burner (half the size of the other). It runs long and steady. We set-back at night, but not real far because it is slow to pick-up again. On the coldest day/night it runs 19 of 24 hours. Inside air rarely gets 1 deg F off the set-point, except at pick-up and drop-back. On a cold day it takes 3 hours to drop 7 deg F, and 3 hours to make it up again.
IMHO, the "advantage" of a Modulating burner is that you can recklessly over-specify the output and let it burn part-power most of the time. But a small fire in a big firebox has consequences also.
My system is forced air. I figure the fan blower contributes about 7% of the total heat. Since electric is 3X the cost of propane, that's a point for thought. This is an extreme case since this is the smallest model of its range, and I think it has the next-up blower motor. Hot-water pumps use less electric but put only some of that in the water (my fan-heat goes 99% in the duct).
They frequently talked about buying, crunched the numbers and decided that renting is cheaper for them. She comes from a family of bankers and accountants so I assume they knew what they were doing.
Bankers and accountants know what they're doing
From what I can tell (and I've lived more of my adult life without central heating than with) most of the reliability issues are down to people who are good with boilers putting complex electronics in without understanding reliability engineering. Given the trials and tribulations my wife's sister is having with her boiler the training given to some service personnel also seems sadly lacking.
I have not followed the modern boiler technologies so I am completely out of date.
But here goes:
A boiler running constantly at one fixed energy rate will have a fixed efficiency. The manufacturer will find what energy input rate gives the highest efficiency. The manufacturer then uses that highest efficiency to compare to all their competitors.
Maybe it's changed now, but rarely did the manufacturers reveal efficiency rating for boilers that were operating at low energy rates.
My first boiler had a gas pressure governor that was set to input a fixed energy input rate. At the highest rate and the lowest rate the manufacturer gave efficiency values (the ratio of lowest to highest was not great - I'll guess at 7:10). But they did not give any efficiency rating for repeatedly On/Off boiler, (this was spark ignition and no pilot light).
In the winter I would turn it up to maximum rate to heat the house.
In spring/summer/autumn I turned it down to minimum to reduce the number of times it turned ON/OFF. This gave me the best efficiency from a boiler sized to meet maximum demand and thus massively oversized for warmer weather.
And I always ensured that the water heating coincided with heating ON to maximise demand and again avoid turning ON/OFF.
The questions I need to ask:
Do modern boilers that have a large turn down ratio manage a good efficiency when turned down?
Do the manufacturers reveal the efficiency numbers for a range of fully ON to fully turned down.?
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Modern cars, both diesel and petrol turn off the fuel on zero accelerator. Cruising on partially open uses more fuel than running ON/OFF and maintaining the same average speed, provided the maximum acceleration is limited to avoid wasting fuel.
Petrol engines run against a throttle. The engine efficiency is low when producing low power against a nearly closed throttle. The efficiency is best when the BMEP is high. This usually occurs over a range of rpm and throttle that stays away from max throttle and max revs and also has to avoid low revs and low throttle. This affected the way we drove older petrol cars that maintained a minimum fuel flow rate when throttle was closed.
It was this realisation that resulted in fuel consumption competitions where the competitors carried a "judge of fact" who policed the "no travelling in neutral" rule.
Neutral then medium power in that good area of efficiency gives a better overall fuel consumption. It was banned from the competitions.
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My understanding is that the boiler has temperature sensors for water in, water out and external (which I assume means the air intake). The boiler maximum power seems to vary according to outside temperature, so on warmer days it takes a lot longer to heat up the water (40-50 minutes instead of the usual 10 mins). The room temperature does not vary very much, so this (if sensed by the boiler) would not tell the boiler very much.jean-paul said:
I believe modern boilers retain reasonable efficiency when turned down, but the numbers are rarely published. There would be little point in making modulating boilers if they were less efficient than simple boiler cycling.AndrewT said:
> There would be little point in making modulating boilers if they were less efficient
Dubious engineering can be excellent Marketing. Some of the annoyances of central heat are due to the very wide range of output needed from a warm October to a cold February. "It makes sense" that a variable fire "must be better".
However it is shown that cars get best medium-MPH MPG by alternating 90% BMEP with coasting in neutral.....
Page 'Advantages of Modulation' discusses some of the trends (by a maker of modulating boilers). It is complicated, but efficency generally drops at low firing rate.
Further down that page they have grey-graphs which seem to compare modulating, staged, and on/off modes, with equations. I did note that they are comparing "1 MM BTUH" (1,000,000 BTUh) boilers which are 25+ times bigger than my whole house heat; by geometry, standby losses may be larger on a smaller gizmo.
A site I mostly trust posted 'Are modulating burners really worthwhile?'
For non-US thinkers: 3,412 BTUh is 1KW. I heat a Maine house with a 11KW gas fire, but sold as 38,000 BTUh. This is warm-air, no real storage. For hot water radiators I would (be forced to) buy a larger BTU and run intermittent while the heat seeped out.
Dubious engineering can be excellent Marketing. Some of the annoyances of central heat are due to the very wide range of output needed from a warm October to a cold February. "It makes sense" that a variable fire "must be better".
However it is shown that cars get best medium-MPH MPG by alternating 90% BMEP with coasting in neutral.....
Page 'Advantages of Modulation' discusses some of the trends (by a maker of modulating boilers). It is complicated, but efficency generally drops at low firing rate.
Further down that page they have grey-graphs which seem to compare modulating, staged, and on/off modes, with equations. I did note that they are comparing "1 MM BTUH" (1,000,000 BTUh) boilers which are 25+ times bigger than my whole house heat; by geometry, standby losses may be larger on a smaller gizmo.
A site I mostly trust posted 'Are modulating burners really worthwhile?'
For non-US thinkers: 3,412 BTUh is 1KW. I heat a Maine house with a 11KW gas fire, but sold as 38,000 BTUh. This is warm-air, no real storage. For hot water radiators I would (be forced to) buy a larger BTU and run intermittent while the heat seeped out.
Are you aware that a CPAP can be fitted with both output air heating and moisturizing?
Johan-Kr
Isn't this always the case ? It the house is well insulated it would be the same but in a way lesser degree. It would be silly to heat a house that has many leaks and it not insulated with many kW as it costs more over the lifetime of the house in energy costs than it would have cost to proper insulate it from the beginning. I have seen some illogical situations in different countries which are truly laughable if they weren't so sad.
Confusing, "boilers" here are electro water heaters and the standard is natural gas heating + hot water which are called "combi heating". Please explain "boiler", just for my understanding. I can spend many words but a type number of the boiler is enough.
Secondly do you have a room thermostat at all and what Vaillant type is it ? To be honest I think you have a system with outside temp sensor. It will heat up the radiators with a predefined temperature of the heated water. Probably radiators with regulator valves are used to keep a constant room temp. You said something about an error code of the outside temp sensor. In my experience with Vaillant a broken cable or sensor would cause a "sensor error" and/or a 0 degrees Celsius symbol. In many cases the system would see a fake 0 degrees (for instance when it is 10 degrees outside) which will make modulating to throttle up resulting in higher consumption than would be necessary.
Please note that there are many ways to make a heating system and that your system may be very different from those of others. I try to understand the working of the system, regardless of where it is.
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@AndrewT. Modern diesels have throttles too. Modern diesels are an abomination. BMW have made petrols with no throttle as well.
I think there is considerable confusion here due to the very different ways heating works in different countries. I was never fond of US style blown air systems especially the ropy ones that were popular for a while in UK.
But in UK parlance 'boiler' is whatever heats the water for central heating*. Generally systems here are either radiator +storage tank for hot water or combi. Thermal store systems have started being used a bit and I know a couple of friends who swear by them. By this I mean similar to the Scandinavian style where you heat a large tank of water overnight on cheap rate electricity then use that to heat the house during the day.
I have an oil combi which is remarkably clockwork. If it wasn't a rental I would be looking at changing a few things.
*One house I had used a rayburn for the main heat in the winter with storage heaters in the bedrooms. It ran continuously for about 6 months of the year consuming about 700kg of coal and a tree in that time. It would often boil the water in the tank.
I think there is considerable confusion here due to the very different ways heating works in different countries. I was never fond of US style blown air systems especially the ropy ones that were popular for a while in UK.
But in UK parlance 'boiler' is whatever heats the water for central heating*. Generally systems here are either radiator +storage tank for hot water or combi. Thermal store systems have started being used a bit and I know a couple of friends who swear by them. By this I mean similar to the Scandinavian style where you heat a large tank of water overnight on cheap rate electricity then use that to heat the house during the day.
I have an oil combi which is remarkably clockwork. If it wasn't a rental I would be looking at changing a few things.
*One house I had used a rayburn for the main heat in the winter with storage heaters in the bedrooms. It ran continuously for about 6 months of the year consuming about 700kg of coal and a tree in that time. It would often boil the water in the tank.
Noticed that. I slowly get the impression that designing and installing low carbon footprint very high efficiency systems in well insulated homes is a local hobby here but not elsewhere. Might be the high energy prices ?
I see what you mean with differences as a thermal store system here is mainly used when one has collectors on the roof to heat up water. Without collectors a thermal store system makes not much sense when one has a combi heater as it has a small buffer tank which heats up quick. At least that is with quality systems that are manufactured here. Costs less gas too. Have seen quite a few separate systems and even then equipped with thermal storage AND hot water circulation costing many a m3 of gas during the night just so that the owner can have immediate hot water. At a price. A modern combi delivers hot tap water in seconds without wasting gas (or worse: electricity) all night .....Must admit that there more systems than I can count and complexity is becoming larger. In Germany 600 litre tanks with all in- and outputs for every single heat source are being promoted.
BTW what is wrong with modern Diesels ? I only drive Diesel cars and only know off cokes forming in common rail engine types of certain brands.
I see what you mean with differences as a thermal store system here is mainly used when one has collectors on the roof to heat up water. Without collectors a thermal store system makes not much sense when one has a combi heater as it has a small buffer tank which heats up quick. At least that is with quality systems that are manufactured here. Costs less gas too. Have seen quite a few separate systems and even then equipped with thermal storage AND hot water circulation costing many a m3 of gas during the night just so that the owner can have immediate hot water. At a price. A modern combi delivers hot tap water in seconds without wasting gas (or worse: electricity) all night .....Must admit that there more systems than I can count and complexity is becoming larger. In Germany 600 litre tanks with all in- and outputs for every single heat source are being promoted.
BTW what is wrong with modern Diesels ? I only drive Diesel cars and only know off cokes forming in common rail engine types of certain brands.
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Building regs here are equally tight. Modern builds are sealed and require ventilation fans and heat exhangers to not asphyxiate the residents!
Edit: there was a plan for new homes to be 'zero carbon' by 2016, but that was scrapped in a rare piece of govt common sense, much to the annoyance of those feeding at that particular trough.
Modern diesels are just too damn complex. Too much to go wrong (DPF, adblue systems). Injectors running at pressures that can cut sheet steel (2500Bar in the latest generation). Not compatible with hybrid drivetrains etc.
I just got rid of a 1.9Tdi passat with nearly 450,000 km on the clock. Talking to my garage he said the new 2.0 diesel from VAG can easily need £700 of fixes to emission equipment to get through annual inspection and the engines wont last nearly as long as the old clockwork ones.
Formula one cars have a better BSFC than road going diesels. Albeit over a VERY limited operating range
Edit: there was a plan for new homes to be 'zero carbon' by 2016, but that was scrapped in a rare piece of govt common sense, much to the annoyance of those feeding at that particular trough.
Modern diesels are just too damn complex. Too much to go wrong (DPF, adblue systems). Injectors running at pressures that can cut sheet steel (2500Bar in the latest generation). Not compatible with hybrid drivetrains etc.
I just got rid of a 1.9Tdi passat with nearly 450,000 km on the clock. Talking to my garage he said the new 2.0 diesel from VAG can easily need £700 of fixes to emission equipment to get through annual inspection and the engines wont last nearly as long as the old clockwork ones.
Formula one cars have a better BSFC than road going diesels. Albeit over a VERY limited operating range
actually in the 8 years I had the Passat it wasn't that bad, mainly cos I decided to drive around the failed dual mass springs. I can clutchless shift the gears and double declutch as required. I only got rid of it because the wife couldn't handle that aspect and a new clutch would cost 3x the car value.
Again you twist my meaning to suit your own beliefs. Since this seems to make you happy, I will not contradict your misunderstanding.
> I was never fond of US style blown air systems
Most suck. They get done with little understanding and no figuring. Loud, drafty, hot/cold.
A good forced-air system is a thing of pleasure. Tedious to figure, and can be expensive to install properly; as bad as any good system.
A particular advantage in large parts of the US is that air-conditioning goes in the same ducts (slight compromise). While it does not get HOT on my neck of land, it can stay very damp.
> in UK parlance 'boiler' is whatever heats the water for central heating*.
For historical reasons, in the US we call it a "boiler" also. We have a VAST history of actual steam heat. I have lived with steam heat in two houses. It is interesting. At its best it is not bad. But many were installed without good figuring. Lifestyles and insulation have changed since most were installed, so most are now grossly over-sized. And all the "common sense maintenance" has been forgotten.
Fashion moved to Hot Water, but the same type "boiler" was installed just with a lower thermostat. The difference in pressure and temperature did not warrant new castings or product numbers.
People here say that "Hydronic" (forced hot water in radiators) is best; yet the selection of "boilers" is very limited. Ignoring boutique stuff, there's basically one house-size model.
Most suck. They get done with little understanding and no figuring. Loud, drafty, hot/cold.
A good forced-air system is a thing of pleasure. Tedious to figure, and can be expensive to install properly; as bad as any good system.
A particular advantage in large parts of the US is that air-conditioning goes in the same ducts (slight compromise). While it does not get HOT on my neck of land, it can stay very damp.
> in UK parlance 'boiler' is whatever heats the water for central heating*.
For historical reasons, in the US we call it a "boiler" also. We have a VAST history of actual steam heat. I have lived with steam heat in two houses. It is interesting. At its best it is not bad. But many were installed without good figuring. Lifestyles and insulation have changed since most were installed, so most are now grossly over-sized. And all the "common sense maintenance" has been forgotten.
Fashion moved to Hot Water, but the same type "boiler" was installed just with a lower thermostat. The difference in pressure and temperature did not warrant new castings or product numbers.
People here say that "Hydronic" (forced hot water in radiators) is best; yet the selection of "boilers" is very limited. Ignoring boutique stuff, there's basically one house-size model.
I think it is you who are taking my words out of context (by adding two different quotes) but have it your way. Believing is done in church, there is nothing to believe in heating/cooling just plain facts.
You said "heat seeping out" which gives the impression that there are leaks as heat or cold is not supposed to be seeping out AFAIK but maybe I don't understand high tech heating/cooling. Just meant that I have seen much illogical situations in other countries where energy waste was part of the design (or it was a non issue) so it occurs to me that design parameters are sometimes quite different. This could be such a situation.
Maybe you could elaborate some more on the subject and reply to the answers as that is what communication is about. Maybe you could imagine that using as little words as possible might not work out OK with foreigners.
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For decades the normal practice in the UK for domestic heating 'engineers' was to fit radiators which are too small and boilers which are too big. This is beginning to improve, yet it is still difficult to find boilers which are small enough to match a well-insulated house. Unfortunately there is now a strong trend towards combination boilers, which need high power for domestic hot water and so have to throttle back for heating purposes. My boiler can produce something like 28kW for hot water and 19kW for heating, when the house actually only requires 12kW for heating. Fortunately the boiler can modulate down to about 25%.PRR said:
I accept that modulating boilers will be less efficient at lower powers. I am not convinced that they will be less efficient than frequent on/off control. Anyway, we can only buy what is available.
We had an old boiler (claimed efficiency 80%) with TPI thermostat and a timer. Now we have a new condensing boiler (claimed efficiency 90%) with on/off temperature programmer (and a larger radiator in the lounge). The programmer can do TPI but I disabled that when the boiler started complaining about short cycling. We now have a warmer lounge and use about 12% less gas. The boiler itself, other things being equal, should use 12% less so it seems that replacing the controls has achieved sufficient improvement to cope with the larger radiator.
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