CH Energy Requirements Estimate

[JohnW2]

Mid terrace is good unless neighbours are a nuisance somehow. First floor in three storey buildings better still.

Indeed.

That's not what the op wants however. Heat-Engineer and use the estimator not the in-depth survey option.

That's what I would have expected and, as I';ve said, even if it's 'arrogant', I think I would (if I wanted to - which I don't) probably be as capable of undertaking a fairly accurate survey/estimate as any heating engineer

Close enough or if the ceilings are not too high use L x B x 100 = watts

Thanks! That, of course, would give almost exactly the same as my 'by room' calculations, since my L x B is about 110 m², hence about 11 kW ! Given your caveat about that rule-of-thumb, that's perhaps a little surprising, given that the rooms are quite 'high' - reducing from about 2.95m on ground floor to about 2.4m on top floor.

Kind Regards, John

 

[JohnW2]

For me, with a non condensing, non modulating oil boiler, it does not matter if I use on/off zone valves (digital), or up/down TRV's (anagoge), the boiler will switch on/off, so the temperature will always form a sine wave.

I'm not really sure what yiou are talking about. No matter what sort of boiler one is talking about, the energy requirements are obviously much less if water is being circulated through just one 'zone' (say 20% of the radiators) than if it is circuited through all of the radiators!

 

[ericmark]

11% of the energy delivered from a condensating boiler is from turning steam in flue gases to water. So to do that the return water to boiler needs to be cool enough, and to control this takes time, so all needs to be by gradual analogue control.

Turning a boiler on/off can result in loosing 11% of the energy compared with turning it up/down.

 

[JohnW2]

11% of the energy delivered from a condensating boiler is from turning steam in flue gases to water. So to do that the return water to boiler needs to be cool enough, and to control this takes time, so all needs to be by gradual analogue control. Turning a boiler on/off can result in loosing 11% of the energy compared with turning it up/down.

I know all that, but you seem to be suggesting that a condensing boiler (certainly a non-modulating one) is not appropriate (or, at least, can't achieve the expected energy saving) if, as in my case, one usually only requires a small proportion of the heating system to be active at any point in time.

My house has about 30 radiators, of which I usually (need to) use only about six at any one time. Are you seriously suggesting that it would be more ';energy efficient' for me to have all 30 radiators 'on' when I only needed six (simply to reduce the temp of water returning to boiler)?

 

[JohnW2]

As a Victorian mid-terrace dweller, I can say that my heat demand isn't huge - around 3400kWh last year ...

I'm about to 'continue' this thread of mine ("watch this space"!) but, first, I've just noticed the above .

Thinking about it (which I just have ) such information is not very useful in terms of assessing the required radiators to heat a house. If one assumes (probably fairly modestly, 12 hours per day for 6 months of the year, that not over an average much above 1.5 kW(to haet the whole house), yet that's probably no more than one radiator

3,400 kWh per year is very low (maybe, as below, because you are terraced). However, even if one takes Ofcom's average for a 'mid-sized' house (11,500 kWh per year), that's still only an average of a bit over 5 kW - so maybe a couple of radiators!

I presume that the catch/flaw in attempting such calculations is that, whilst the heating may be 'on' for 12 hours per day, the rads will not be producing their full theoretical heat output for anything like that long ?

With both neighbouring houses occupied, 2/3 of my walls have perfect, or better than perfect insulation.

Similar with the house I'm talking about - so maybe very modest 'heating requirements are to be expected?

Kind Regards, John

 

[RandomGrinch]

Pressed post accidentally!

 

[RandomGrinch]

If one assumes (probably fairly modestly, 12 hours per day for 6 months of the year,

12 hours a day for 6 months of the year is an interesting assumption to make

Possibly off topic, but these are some of my thoughts.
There are so many factors at play.
My house is basically a two up, two down, with an 'extension' at the rear, containing the kitchen and bathroom. A very typical victorian terrace house in our area. (Completely off-topic, but if you've ever watched "Gavin and Stacey", ours would be Stacey's mum's house!).
Both of these rooms are small and don't require much heating.
The living room and dining room are open plan to the stairs.
The radiators in our bedrooms are set low.
Whereas Eric has been known to go on about smart TRVs and there being no necessity for room thermostats - in our case, a single room thermostat will suffice; if the downstairs living room is at a comfortable temperature, the rest of the house is too.

We are also a relatively young and active family; we are comfortable with a thermostat temperature set to 18.5C.
Sometimes we bump it up, and the night set back temperature is 17C.
Rather than setting a schedule, keeping the house at a fairly constant temperature seems to work for us.

I presume that the catch/flaw in attempting such calculations is that, whilst the heating may be 'on' for 12 hours per day, the rads will not be producing their full theoretical heat output for anything like that long

Getting back to the 12 hours per day -
We didn't start heating the house until late October, that was the first time that the temperature dipped below 18C (apart from the perfectly insulated party walls, the rear wall is south facing and gets an appreciable amount of solar gain).
Here is our gas usage, according to OVO (and I'm excluding 100kWh/month as the average standing amount of gas used for water heating and cooking - probably an underestimate)...

The Nest thermostat doesn't give the best information, but it does give a record of the amount of time it is calling for heat; here is last week's "Energy History"...

Even this isn't the full picture.
Nest may be calling for heat, but it doesn't mean the boiler is constantly firing; if the boiler return temperature was above the boiler thermostat setting, the pump would continue to run without the boiler firing.

Our boiler is also a non-condensing boiler. I don't have to worry about trying to optimise the boiler return temperature

so maybe very modest 'heating requirements are to be expected?

Yes, the heating requirements may be modest.
But what I have learnt from past experience (dealing with estates departments, office workers and classes of students) - comfortable temperatures are subjective; calculations can be attempted, but there won't be a universal solution.

 

[JohnW2]

12 hours a day for 6 months of the year is an interesting assumption to make

As you quote below, I did go on to qualify that assumption, but indicating the 'flaw' in it!

My house is basically a two up, two down, with an 'extension' at the rear, containing the kitchen and bathroom. A very typical victorian terrace house in our area.

The house I'm talking about (and currently sitting in!) is sort-of 'taller brother' of that - basically two-down, two up and two above them, with an 2-storey 'extension' (albeit I presume original) at the rear, containing the kitchen and another bedroom above it. When I first saw it,it had no bathrooms at all. Built in 1887.

The room I'm sitting in in the only one remotely warm at present - about 21 °C, but that's thanks to the 2kW fan heater which has been on for most of the past 16 hours! The outside temp is currently hovering around zero. The temp in the kitchen (which has easily the most 'outside wall' of any room) is about 5-6 °C (similar to the cavity of the fridge ), but the rest of the house around 9-10 °C, I presume largely thanks to the neighbours (and partially the fan heater). You can see why I'm designing a heating system

Whereas Eric has been known to go on about smart TRVs and there being no necessity for room thermostats - in our case, a single room thermostat will suffice; if the downstairs living room is at a comfortable temperature, the rest of the house is too.

My (ridiculously large) house at home is conceptually similar to that. Whilst we do have a few TRVs, primarily the heating system is split into 6 zones, each controlled by a wall stat and motorised valve - and with a non-condensing and non-modulating boiler.

Getting back to the 12 hours per day -...

Indeed!

We didn't start heating the house until late October,

Same with us at home. I think the '6 months' part of what I said is roughly right (at least, for us). I think we normally start heating in late October or early November and then carry on until March/April.

The Nest thermostat doesn't give the best information, but it does give a record of the amount of time it is calling for heat; here is last week's "Energy History"........
Even this isn't the full picture. ..... Nest may be calling for heat, but it doesn't mean the boiler is constantly firing; if the boiler return temperature was above the boiler thermostat setting, the pump would continue to run without the boiler firing.

Yes, that's essentially the 'qualification' I presented, and more straightforward with a simple on/off non-condensing boiler. Even if your heating is 'on' for 12 hours per day, the stat will be calling for heat for a lot less than 12h and, as you say, even when it is calling for heat, the boiler will not always be firing - which therefore may happen for only a small proportion of those 12 hours.

However,what is interesting is that 'averages are averages'. If one assumes that your heating system is 'on' for 12 hours per day, 6months of the year (probably not unreasonable assumptions), then your figures suggest that just one 1.5 kW radiator fed by a boiler that was running (and firing) continuously (no thermostatic control) should deliver as much total heat to your house as you present system is delivering - albeit not necessarily in 'the right places at the right times'!

Our boiler is also a non-condensing boiler. I don't have to worry about trying to optimise the boiler return temperature

Same with ours at home but, of course, with what I'm now designing (from scratch) I have no choice but to have a condensing boiler.

However, none of this helps me very much with my current attempts at a design exercise However, I realise that, in many senses, I'm 'over-thinking' (trying to be too clever) and that just throwing in rads 'which looked about the right size for each room' would probably result in a reasonable system (and a lot less mental effort!)

Kind Regards, John