Energy myth-busting: Is it cheaper to have heating on all day?

Spies

martastik said:

Is there any chance of a energy/money saving guide for those of us 'lucky' enough to have air source heat pumps?  They are not moneysaving unless configured properly, which I suspect most installers aren't smart enough to do (beyond turning them on and checking they work).  From what I understand, they are supposed to be running all the time, albeit at a lower constant temperature.

You might be best to post a new thread asking this question over here https://forums.moneysavingexpert.com/categories/green-ethical-moneysaving 

richardc1983

martastik said:

Is there any chance of a energy/money saving guide for those of us 'lucky' enough to have air source heat pumps?  They are not moneysaving unless configured properly, which I suspect most installers aren't smart enough to do (beyond turning them on and checking they work).  From what I understand, they are supposed to be running all the time, albeit at a lower constant temperature.

Follow HeatGeek on youtube https://www.youtube.com/@HeatGeek

Also, you could ask the question on their FB page. https://www.facebook.com/heatgeek 

https://www.youtube.com/watch?v=odMXRDd2nQg 

bilbomacuser

One thing missing from the article is the fact that a high proportion of condensing boilers have been poorly installed and / or use controls that don't allow the boiler to condense.  For example even controllers that appear to be modern such as Hive, actually act like old fashioned 'on-off' thermostats and don't allow condensing boilers to work efficiently.  In contrast, controllers that use opentherm will automatically adjust the 'flow temperature' according to weather conditions.  Any controller that causes a boiler to turn on or off without adjusting the flow temperature is not going to get the advertised efficiency of the boiler.  Therefore the argument of whether heating the house gradually leads to greater efficiency and/or maintaining a constant temperature only applies to decent installations.  Any system with an on/off controller (such as an old fashioned thermostat, or a Hive system) will surely be better of being turned off when nobody is at home.

bilbomacuser

QrizB said:

limecc said:

I just read the mythbusting guide and don't see it mentioned that to get a condensing boiler to actually condense there should be a wide temperature differential between the flow out of the boiler and the return to the boiler.

Why, exactly?

If the return temperture is 50C, for example, what difference does it make if the flow temperature is 55C or 75C?

Although a boiler will start to condense if the return temperature is below 54 degrees C - it will only retrieve a very small amount of energy back at 50 degrees C.  The efficiency becomes progressively much greater if the return temperature is 40 degrees C, or 30 degrees C, or 25 degrees C.  With a flow temperature at 75 degrees the chance of the return temperature being low enough to retrieve much energy from condensing is minimal.  

A good system will have flow temperatures of 30 degrees C in mild weather to get good efficiency.

QrizB

bilbomacuser said:

Any controller that causes a boiler to turn on or off without adjusting the flow temperature is not going to get the advertised efficiency of the boiler.

That will depend on what flow temperature the boiler is set to.

You don't need Opentherm, although it's one way of automating it. You just need to turn the knob on the boiler.

bilbomacuser

QrizB said:

bilbomacuser said:

Any controller that causes a boiler to turn on or off without adjusting the flow temperature is not going to get the advertised efficiency of the boiler.

That will depend on what flow temperature the boiler is set to.

You don't need Opentherm, although it's one way of automating it. You just need to turn the knob on the boiler.

For a combi-boiler - yes you could manually adjust the temperature on the boiler - but it's never going to be as good as a system that is continually optimising flow temperature.

For a boiler that heats hot water, it has to be able to adjust the temperature according to what it's doing - eg. 65 degrees when heating a hot water cylinder, 30 degrees for radiator flow temperature on a mild day, 40 degrees on a slightly colder day etc.  Turning down the temperature on the boiler manually  for a system with a hot water system risks legionella.

Qyburn

Setting aside the fact that you've bumped a year old thread, weather compensation and on/off controls are in no way incompatible. I've been involved with, and programmed a number of systems like that, predating modulating boilers.

On the original premise, there's no doubt whatsoever that a house heated 24/7 loses more heat than one that cools down and warms back up as needed. That's been known since 1701. The only reason that setback vs fabric protection continues to be debated over the last 50 or 60 years is because some people are confused by the peculiarities of some heating systems.

Reed_Richards

If you have a heat pump and use it to maintain a constant temperature 24/7 then if it is "well-balanced" it can do this by operating efficiently and constantly at a water temperature which only varies to compensate for changes in the outside temperature. 

If you ask the heat pump to heat up a bouse that has cooled overnight by a few degrees it will need to raise the water temperature whilst it is doing this and it will operate less efficiently during this time.  So although you have undoubtedly saved energy by allowing the house to cool, it is at least theoretically possible that you will use more extra energy heating it back up than you have saved.  This is indeed very peculiar and and confusing.  I have no idea what the reality is but it is murky situations like this that allow the debate to continue.       

FreeBear

bilbomacuser said:

QrizB said:

limecc said:

I just read the mythbusting guide and don't see it mentioned that to get a condensing boiler to actually condense there should be a wide temperature differential between the flow out of the boiler and the return to the boiler.

Why, exactly?

If the return temperture is 50C, for example, what difference does it make if the flow temperature is 55C or 75C?

Although a boiler will start to condense if the return temperature is below 54 degrees C - it will only retrieve a very small amount of energy back at 50 degrees C.  The efficiency becomes progressively much greater if the return temperature is 40 degrees C, or 30 degrees C, or 25 degrees C.  With a flow temperature at 75 degrees the chance of the return temperature being low enough to retrieve much energy from condensing is minimal.  

A good system will have flow temperatures of 30 degrees C in mild weather to get good efficiency.

The lower the flow temperature, the greater the surface area of radiator required to achieve the same amount of heating. So whilst a 30°C flow temperature will achieve very high efficiency, you need about ten times the radiator size.

I've tried running a 30°C flow temperature, and it just doesn't provide any worthwhile heat. Instead, I've settled on a maximum of 55°C, dropping down to 40°C as the house reaches the thermostat set point. This gives me a return temperature of ~38°C which should give an efficiency of around 95% on paper.

cardriver98

its a personal decision, so i decide to only use my halogen heater when it is really cold. otherwise its pj's and dressing gown and bed socks.  strip off when you get home,  into night attire,  and take that warmth with you.  no need for hotwater bottles and electric blankets.