Could you expand on your answer please 
New combi - do I need weather comp or stick with Hive?
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I have since first post found Hive TRV heads a lot cheaper, had the Hive thermostat been volt free I may have gone with Hive, although not OpenTherm the heat on demand system means it does not turn off just because one room is reaching target temperature, all rooms with Hive TRV heads fitted must also be at temperature, so the boiler can modulate with the return water temperature, so providing you use the Hive TRV heads it will be very similar to OpenTherm with the algorithm built into boiler deciding if worse or better, but clearly not as cut and dried as it was before the Hive TRV head hit the market.
Unless some one builds rows of houses for workers in a factory so work patterns are the same and fits a different heating system in each house, we really have no way to compare. I can tell you average electric used by my freezer easy, but working out average oil or gas used by central heating is a lot harder, I tried to work out if the Worcester Bosch gas boiler in last house was modulating or using mark/space ratio to control heat output, but can't put a clamp-on ammeter around a gas pipe, so simply don't know.
With a heating system that works, you take no notice, it works so why fix it, only when is does not work does one take any notice, I hope as winter arrives I will set the Thermostat and TRV's then forget, only if it does not work will I worry.
Unless some one builds rows of houses for workers in a factory so work patterns are the same and fits a different heating system in each house, we really have no way to compare. I can tell you average electric used by my freezer easy, but working out average oil or gas used by central heating is a lot harder, I tried to work out if the Worcester Bosch gas boiler in last house was modulating or using mark/space ratio to control heat output, but can't put a clamp-on ammeter around a gas pipe, so simply don't know.
With a heating system that works, you take no notice, it works so why fix it, only when is does not work does one take any notice, I hope as winter arrives I will set the Thermostat and TRV's then forget, only if it does not work will I worry.
Before I chip in with my sixpennyworth I'm not sure when you mention modulating whether you mean adjusting a boilers output between the maximum and minimum output settings or adjusting flow temperature according to demand.
Additionally, do you mean mark/space ratio control to be a description of TPI where the room control records heat up time and adjusts cycling to suit, spreading the ON periods as far apart as possible while maintaining the desired target temperature? It could be taken as the boiler's own anti-cycle delay between firings.
Fankly my personal opinion is that the differences in operation are minuscule as gas is so cheap. It is easy to show a calculation, an imaginary situation, where simple ON/OFF controls linked to a condensing boiler in non-condensing mode with a 5 minute anti-cycle delay operating three times an hour will be cheaper (by fractions of a penny) to operate than if the boiler ran continuously in condensing mode without cycling matching the load exactly.
eg 5kw put in in spurts is the same as five kw trickled in as 15 minutes of off time through cycling conserves more fuel than the latent heat harvested by condensing continuously even with cycling inefficiencies added and without operating flue losses included. The small overheat and underheat temperature changes with ON/OFF are hardly discernible in the comfort of the user as combination boiler users know very well.
Additionally, do you mean mark/space ratio control to be a description of TPI where the room control records heat up time and adjusts cycling to suit, spreading the ON periods as far apart as possible while maintaining the desired target temperature? It could be taken as the boiler's own anti-cycle delay between firings.
Fankly my personal opinion is that the differences in operation are minuscule as gas is so cheap. It is easy to show a calculation, an imaginary situation, where simple ON/OFF controls linked to a condensing boiler in non-condensing mode with a 5 minute anti-cycle delay operating three times an hour will be cheaper (by fractions of a penny) to operate than if the boiler ran continuously in condensing mode without cycling matching the load exactly.
eg 5kw put in in spurts is the same as five kw trickled in as 15 minutes of off time through cycling conserves more fuel than the latent heat harvested by condensing continuously even with cycling inefficiencies added and without operating flue losses included. The small overheat and underheat temperature changes with ON/OFF are hardly discernible in the comfort of the user as combination boiler users know very well.
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And how many houses have you worked on ?????
I was going to write more than I care to remember, hundreds and hundreds but in all honesty, not enough. If I were suddenly younger I'd do it again.
However with more time now to study boilers and controls, a calculator and with what I've learned from installing added to that my opinion is continually refined.
However with more time now to study boilers and controls, a calculator and with what I've learned from installing added to that my opinion is continually refined.
For me, I see these as two elements for the boilers overall control/feedback system - I'd expect (assume through lack of knowledge!) that the boiler will modulate its gas-flow/burn rate/whatever is the measure, to achieve a target flow temp; in turn that target flow temp will be managed dependant upon demand, external temp if WeatherComp is in the mix, etc.
Does that make sense?
Any calculation of the heat loss from a building requires the U value of the walls to be taken into account as well as the difference in temperatures either side of the walls,.
How does a boiler acquire the U value of the building it is heating. The U value would be necessary if the boiler was to calculate the amount of heat needed to achieve the required temperature inside the house.
How does a boiler acquire the U value of the building it is heating. The U value would be necessary if the boiler was to calculate the amount of heat needed to achieve the required temperature inside the house.
I believe that is the gap learning thermostats fill - whilst they don't have the defined U-value, they can determine a measure that roughly equates it by measuring how a room/house heats up based on internal/external temp's and heat rise over time.
Whether using specific u-value or real-world measurements is better is a different question.
Whether using specific u-value or real-world measurements is better is a different question.
Yes but that's not what happens. The boiler has a temperature control, if there's demand that's what it will work to. It may be able to modulate the amount of fuel being burned to maintain that temp without hugely overshooting but the temp is the temp and set on the boiler panel.
Modulating thermostats or external sensors take over the temp control on the boiler and adjust the flow temp to as low as possible while maintaining the desired comfort level.
The reason is a condensing boiler becomes marginally more efficient if it is operated at cooler temps because the cooler the return from the system the more efficient it becomes.
So boiler can control fuel, external control takes over temperature.
External sensor aligns flow temp with weather, modulating stat aligns flow temp with internal demand.
Better control systems can incorporate both.
On/Off thermostats interrupt an electric supply to the boiler, modulating controls use a varying signal (WC) or digital protocol (modulating stat).
U values are a separate issue, they determine the size of emitter based on calculated heat loss either intermittent or steady state.
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I wish I knew the answers, as one reads one finds opinion varies as to how the boiler works, and to be far likely different makes have different ways of working, so likely there is no real one size fits all answer.
So if we look as a good boiler that can auto modulate 28 kW to 6 kW in the heart of winter it fires up at 28 kW output and the water heats up each radiator as all TRV's are wide open, as the room heats up, so the TRV closes, forcing more water through the ones which are still open, and finally opening the by-pass valve.
As the boiler sees the return temperature raising, it starts to modulate, and the modulation is controlled so the return water gets cooler as the boiler modulates more and more, so by time it has reached the lower limit of 6 kW the boiler is running cooler than when running at 28 kW so as the boiler starts to cycle, the heat inside it is at a minimum so less heat is lost out of the flue each time it turns off.
And the cycle times are also altered, so if after enough time for water to circulate has lapsed the return water is still hot the off time is increased, and vice versa, however what it can't do is turn completely off, as only way it knows if required is to circulate the water.
There are other problems, in that the time allowed before circulating water temperature is sampled is not published, and likely some boilers don't reduce return water temperature as the boiler modulates, so as to if the modulation is enough to ensure latent heat is extracted from the flue gases is unknown by person setting it all up. As said likely varies make to make.
However it seems likely having the thermostat control the modulation is a better system than using return water temperature, but although with a single make and model of boiler one may be able to state a X% saving using a modulating thermostat, over a range of makes and models one can't really say what method is best.
The Hive system would if the thermostat had volt free contacts work with nearly any boiler, OK it does not have volt free contacts so is limited, but the idea of having a thermostat which turns on when the TRV heads say heat is required removes the problem of boiler cycling when no heat is required, and when it is required in any room it will be on, which is arguably better than Nest which has open therm but as it stands the wall thermostat controls the TRV, instead of the TRV controlling the wall thermostat.
What I was however impressed with was how the Energenie TRV actually controlled the room temperature, I expected the heat from the radiator to cause the unit not to control room that well, however it says it has two sensors one for water and one for air and the water one compensates the air temperature reading, and it works, so set at 20°C actually gets room to 20°C.
But in the same way as now I have Nest and Energenie I am not going to change to a different system, some one who has Hive is also unlikely to change to another system. In neither case is another system likely to be that much better to it be worth changing. However the real question is not the wall thermostat, but the TRV heads, is fitting linked heads going to be that much better than independent heads to be worth changing.
So in my case, if I was to replace the cheap eqiva head at £15 each with a Energenie head at £40 each will it in real terms give me better control with a more steady temperature or less oil cost? I am about 6 heads short to do every radiator, which should I get?
So if we look as a good boiler that can auto modulate 28 kW to 6 kW in the heart of winter it fires up at 28 kW output and the water heats up each radiator as all TRV's are wide open, as the room heats up, so the TRV closes, forcing more water through the ones which are still open, and finally opening the by-pass valve.
As the boiler sees the return temperature raising, it starts to modulate, and the modulation is controlled so the return water gets cooler as the boiler modulates more and more, so by time it has reached the lower limit of 6 kW the boiler is running cooler than when running at 28 kW so as the boiler starts to cycle, the heat inside it is at a minimum so less heat is lost out of the flue each time it turns off.
And the cycle times are also altered, so if after enough time for water to circulate has lapsed the return water is still hot the off time is increased, and vice versa, however what it can't do is turn completely off, as only way it knows if required is to circulate the water.
There are other problems, in that the time allowed before circulating water temperature is sampled is not published, and likely some boilers don't reduce return water temperature as the boiler modulates, so as to if the modulation is enough to ensure latent heat is extracted from the flue gases is unknown by person setting it all up. As said likely varies make to make.
However it seems likely having the thermostat control the modulation is a better system than using return water temperature, but although with a single make and model of boiler one may be able to state a X% saving using a modulating thermostat, over a range of makes and models one can't really say what method is best.
The Hive system would if the thermostat had volt free contacts work with nearly any boiler, OK it does not have volt free contacts so is limited, but the idea of having a thermostat which turns on when the TRV heads say heat is required removes the problem of boiler cycling when no heat is required, and when it is required in any room it will be on, which is arguably better than Nest which has open therm but as it stands the wall thermostat controls the TRV, instead of the TRV controlling the wall thermostat.
What I was however impressed with was how the Energenie TRV actually controlled the room temperature, I expected the heat from the radiator to cause the unit not to control room that well, however it says it has two sensors one for water and one for air and the water one compensates the air temperature reading, and it works, so set at 20°C actually gets room to 20°C.
But in the same way as now I have Nest and Energenie I am not going to change to a different system, some one who has Hive is also unlikely to change to another system. In neither case is another system likely to be that much better to it be worth changing. However the real question is not the wall thermostat, but the TRV heads, is fitting linked heads going to be that much better than independent heads to be worth changing.
So in my case, if I was to replace the cheap eqiva head at £15 each with a Energenie head at £40 each will it in real terms give me better control with a more steady temperature or less oil cost? I am about 6 heads short to do every radiator, which should I get?
Would it not be worth making that a separate zone, with its own zone valve, so you are not providing heat the the entire house?
Good grief, you're paying around 4.8p a kw NG. If you run the boiler at condensing temperatures lower and longer to reduce cycling and harvest latent heat you might reduce that to 4.6p.
Thing is if you ran the boiler at higher non condensing temperatures with 3 anti cycle delays of 5 minutes each the fuel saved when off for 15 minutes can be greater than the latent heat harvested.
Boilers running lower and longer have continuous flue losses. Against cyclical inefficiencies and standing losses they can be greater.
Go out, enjoy the day and your health, you're using more energy writing this and buying more equipment than you'll save.
Thing is if you ran the boiler at higher non condensing temperatures with 3 anti cycle delays of 5 minutes each the fuel saved when off for 15 minutes can be greater than the latent heat harvested.
Boilers running lower and longer have continuous flue losses. Against cyclical inefficiencies and standing losses they can be greater.
Go out, enjoy the day and your health, you're using more energy writing this and buying more equipment than you'll save.
Quick update - boiler is going in as I type this. So far so good, except installer really doesn't want to install the WeatherComp sensor. Apparently he's spoken to Intergas technical who have advised him against it, as "sometimes the heating just won't work". Struggling with this but defer to both the installer's and Intergas' own far superior knowledge and experience.
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