Central heating power?

[Tim Ward]

If the house is cold and I turn the heating on it heats up at about one
degree C per hour. Which seems slow.

But if the outside is cold and I turn the heating off the house cools
down at about 1/3 decree C per hour.

Which suggests that the heating system is capable of putting out four
times as much power as is needed to keep the house warm in steady state.
Which seems like a lot.

Does this sound plausible? What ratio is used when designing domestic
heating systems?

[The Natural Philosopher]

Post by Tim Ward
If the house is cold and I turn the heating on it heats up at about one
degree C per hour. Which seems slow.
But if the outside is cold and I turn the heating off the house cools
down at about 1/3 decree C per hour.
Which suggests that the heating system is capable of putting out four
times as much power as is needed to keep the house warm in steady state.
Which seems like a lot.

No, its about right in a fairly low thermal mass house.

Post by Tim Ward
Does this sound plausible? What ratio is used when designing domestic
heating systems?

Really in a combi house, the instantaneous power required for hot water
usually comfortably exceeds the CH requirements, so you size for DHW.
With a system boiler, its really a wet thumb. Thermal calcs will tell
you you need say 8Kw to keep the house warm. You might pick a size above
that at sensible price.

Bearing in mind that peak requirements will be only needed at -5°C and a
40mph gale.

Which isn't very often. More typically people will want to be cosy at
0°C on a calm winter day, and will be prepared to run heating 24x7 if
its colder than that.

[Vir Campestris]

Post by The Natural Philosopher
Which isn't very often. More typically people will want to be cosy at
0°C on a calm winter day, and will be prepared to run heating 24x7 if
its colder than that.

My first house had heating like that. Once it got below freezing the
temperature in the house started to drop, even though the heating was
running flat out.

We had a cold winter. It go to -10 outside. We had to supplement with
electric heating, or else it would have gone from a normal 20 to +10
inside :(

You need to size for peak. What's the coldest on record for your area?

Andy

[Tim Ward]

Post by Vir Campestris
You need to size for peak. What's the coldest on record for your area?

Coldest I remember in Cambridge was some time in the 1980s when it was
supposedly something like -18 for a day or two.

[Roland Perry]

Post by Vir Campestris

Post by The Natural Philosopher
Which isn't very often. More typically people will want to be cosy at
0°C on a calm winter day, and will be prepared to run heating 24x7 if
its colder than that.

My first house had heating like that. Once it got below freezing the
temperature in the house started to drop, even though the heating was
running flat out.
We had a cold winter. It go to -10 outside. We had to supplement with
electric heating, or else it would have gone from a normal 20 to +10
inside :(
You need to size for peak. What's the coldest on record for your area?

The coldest I remember was the winter of perhaps 1981/2 when the place
my group of friends rented for a pre-Xmas party, and we also got snowed
in.

Ah yes... <https://en.wikipedia.org/wiki/1981%E2%80%9382_United_Kingdom_
cold_wave>

We were actually in south Wales, that week:

"Wales also recorded its coldest recorded December temperature
during the cold wave, with a temperature of -22.7 °C (-8.9 °F)
recorded at Corwen, Denbighshire also on the 13th."

[Theo]

Post by Tim Ward
If the house is cold and I turn the heating on it heats up at about one
degree C per hour. Which seems slow.
But if the outside is cold and I turn the heating off the house cools
down at about 1/3 decree C per hour.
Which suggests that the heating system is capable of putting out four
times as much power as is needed to keep the house warm in steady state.
Which seems like a lot.
Does this sound plausible? What ratio is used when designing domestic
heating systems?

When designing a heating system, the designer should calculate the heat loss
of the building. That will be in a certain set of conditions - eg average
minimum winter temperature outside at your location, humidity/wind,
draughts/chimneys, popular internal temperatures (eg 18C in bedrooms, 21C in
living rooms). That gives you a heat loss figure in kW. For example, for
my house when I did the numbers it was 5kW.

In other words, in those conditions you need 5kW running just to fight the
losses and keep it at steady state.

Of course, if you actually want to warm the place up from cold, you need
more than that. If your heating was outputting 5.1kW it would warm up, but
very very slowly[1].

So the heating system is sized to be able to swing your house around faster.
For example, my heat pump installer calculated that as 8.5kW and the next
model up was 10kW. That also provides a bit of headroom in case the calcs
weren't perfect.

If you're on gas the upfront cost of installing a larger boiler is often
relatively minimal, so installers tend to oversize, often skipping the
calculations and going for a finger in the air. That's why people end up
with 24kW or 40kW boilers. Those also have to provide instant hot water, or
if you have a cylinder you need a boiler large enough to heat the water.

The heat is also limited by your emitters - you need to dump the heat into
your rooms, otherwise it just goes around and back to the boiler. So the
boiler output temp (condensing can be cooler, also heat pumps) and the size
of your radiators etc also sets how fast the system can swing your
temperature around.

Once your house has reached steady state your boiler will modulate - it
won't run constantly, it'll turn on and off to maintain the temperature.
That's fine, it's designed for that. Meanwhile you'll need full power when
heating water, so oversizing isn't wasted for that.

Theo

[1] it's actually a bit more complicated, since conductive losses depend on
delta-T so a cool house has lower losses than a hot one, and so the
temperature would ramp faster to begin with and then struggle as the house
warmed up.

[Mark]

On 18/12/2021 23:21, Theo wrote:

[snip]

Post by Theo
Once your house has reached steady state your boiler will modulate - it
won't run constantly, it'll turn on and off to maintain the temperature.
That's fine, it's designed for that. Meanwhile you'll need full power when
heating water, so oversizing isn't wasted for that.

Full power for a combi, yes.

Indirect (cylinder-based) HW systems typically have coils rated at
around 10-12kW, which is around half to two-thirds the capacity of the
non-combi boiler that supplies them. In that sitution the boiler is
commonly sized as much for the space heating as the HW requirements.

[Alan Jones]

Post by Mark
[snip]

Post by Theo
Once your house has reached steady state your boiler will modulate - it
won't run constantly, it'll turn on and off to maintain the temperature.
That's fine, it's designed for that.  Meanwhile you'll need full power
when
heating water, so oversizing isn't wasted for that.

Full power for a combi, yes.
Indirect (cylinder-based) HW systems typically have coils rated at
around 10-12kW, which is around half to two-thirds the capacity of the
non-combi boiler that supplies them. In that sitution the boiler is
commonly sized as much for the space heating as the HW requirements.

Thanks for the 10-12kW figures, that helps explain my learnt behaviour
when I need more hot water or to raise the house temparature quickly.

This is with an old boiler that my plumber says I can keep until we rip
out the whole system for the next generation. It is non-combi - a
stelrad ideal CF60 with 23kW in, 17kW out, although some of the losses
heat the utility/drying room and an attic over the garage!

Temporarily, I

(a) turn up the boiler stat (the one inside the boiler that senses the
incoming water temperature) from 2.5 to 3.5 to increase the temperature
of the circulating water from hot to very hot, and

(b) turn up the pump from "1" to "3" to get it round the pipes before it
cools, and to prevent any "boiling" from hotspots in the heat exchanger.

This boosts both the hot water heating and the radiator temperatures. It
is one of the things I will miss when we have heat pumps.

Strangely, when the boiler stat failed two winters ago, so the water was
too hot (limited by the boiler overheat thermostat), the gas comsumption
seemed to go down. That still doesn't make any sense to me. I would have
thought that running the boiler on hotter water would lead to a less
efficient exchange of heat, but I suppose a lot of other factors would
have changed as well - even the weather!

Alan Jones.

[The Natural Philosopher]

Post by Alan Jones
Strangely, when the boiler stat failed two winters ago, so the water was
too hot (limited by the boiler overheat thermostat), the gas comsumption
seemed to go down. That still doesn't make any sense to me. I would have
thought that running the boiler on hotter water would lead to a less
efficient exchange of heat, but I suppose a lot of other factors would
have changed as well - even the weather!

Looking at our daily consumption on the smart meter readings, there's a
pretty strong corellation between the weather and the energy consumption.
The colder it is the more it takes. For example the last two days (cold and
foggy, average about 4C) have been about 30kWh while Thursday (10C) was
16kWh. With a baseload of about 12kWh that shows quite a difference
(although some of that will have been different consumption of hot water).
So a 'warm' winter versus a 'cold' winter is likely to dwarf any minor
difference in boiler efficiency.

I burn twice as much oil between November and March as I do for the
entire rest of the year.
Average temp here is 9°C, and house runs at about 18°C, so there is a 9
°C thermal differential.

Go down to zero and heat loss doubles. Go up to 18°C and it needs no
heat at all.

Energy versus temperature is a massively steep graph.

Theo

[Roland Perry]

Post by Tim Ward
If the house is cold and I turn the heating on it heats up at about one
degree C per hour. Which seems slow.
But if the outside is cold and I turn the heating off the house cools
down at about 1/3 decree C per hour.
Which suggests that the heating system is capable of putting out four
times as much power as is needed to keep the house warm in steady
state. Which seems like a lot.
Does this sound plausible? What ratio is used when designing domestic
heating systems?

Have you considered using thermostatic valves, and having them at a
higher temperature in your living rooms. It should e possible to warm
the house up one or two rooms at a time (as a kind of domino effect)
much faster than 1 degree per hour.

[Tim Ward]

Post by Roland Perry
Have you considered using thermostatic valves, and having them at a
higher temperature in your living rooms. It should e possible to warm
the house up one or two rooms at a time (as a kind of domino effect)
much faster than 1 degree per hour.

There are (newly replaced) thermostatic valves throughout. There is no
radiator in the main living room - there's a gas fire there, and obvs
that heats that room up much faster than the rest of the house. It was
boiler sizing I was curious about.

This curiosity arose when I returned to the house which had been left at
ten degrees whilst we'd been away and noted how long it took to warm backup.

[Alan]

Post by Tim Ward

Post by Roland Perry
Have you considered using thermostatic valves, and having them at a
higher temperature in your living rooms. It should e possible to warm
the house up one or two rooms at a time (as a kind of domino effect)
much faster than 1 degree per hour.

There are (newly replaced) thermostatic valves throughout. There is no
radiator in the main living room - there's a gas fire there, and obvs
that heats that room up much faster than the rest of the house. It was
boiler sizing I was curious about.
This curiosity arose when I returned to the house which had been left at
ten degrees whilst we'd been away and noted how long it took to warm backup.

Guess that's where the modern fad for internet connected controllers come
in to play. You don't worry if your house takes three hours to warm up,
if you turn it on three hours before you get home :-)

Not that I've fallen for that marketing yet....

[Tim Ward]

Post by Alan
Guess that's where the modern fad for internet connected controllers
come in to play.  You don't worry if your house takes three hours to
warm up, if you turn it on three hours before you get home :-)

Internet connected thingies tend to depend on the manufacturer keeping
the web site running, and there are regular stories of IoT suppliers
dropping support for things whilst the devices still have many years'
life left in them, either because they've gone bust or because they just
CBA to support old stuff any more (like my mother's ***@iler).

So for a remote reading thermometer I built my own, with a Raspberry Pi
and a bunch of sensors and wrote my own web site code. But really it
should be easier than this.

For remote reading oil tank level gauges, if you don't feel it's
sensible to drill holes in the tank yourself and put bits of amateur
wiring inside (which we don't), there's not a lot of choice - none of
the sensor manufacturers will tell you what their protocol or API is,
you have to use their server, and your guess is as good as mine as to
whether that will remain working for the lifetime of the oil tank.

Back to remote control for central heating ... how's about

* a Raspberry Pi which polls commands from your own REST API[#]
* the web server with the REST API and the UI
* electric motor which drives the dial on the room stat via friction
* a camera to see where the dial is
* a temperature sensor to confirm that the house is warming up

?

The only potentially tricky bit sounds like writing the image processing
code to look at the camera output and see whether the motor has turned
the thermostat wheel far enough yet. But I'm sure the Raspberry Pi
community can point one at a library for that.

Seems a bit OTT though, for avoiding being a bit cold for a few hours
once or so per year.

[#] Rather than a direct connection into the Pi, 'cos NAT.

[Roland Perry]

Of course the whole thing would be way easier if all heating were
electric and there was no need to control water circulation - and the
electricity, thanks to nuclear power, was almost too cheap to meter.

Absolutely! That was what was promised to us when I was growing up.

Some builders even sold "all electric" houses.

Just shows you can't trust government forecasts.

[The Natural Philosopher]

Post by Roland Perry

Of course the whole thing would be way easier if all heating were
electric and there was no need to control water circulation - and the
electricity, thanks to nuclear power, was almost too cheap to meter.

Absolutely! That was what was promised to us when I was growing up.
Some builders even sold "all electric" houses.
Just shows you can't trust government forecasts.

Just shows how powerful the oil lobby were. Windmills that don't work
that need gas backup - perfect.

Nuclear power that doesn't? Fund the greens!

Actually there is a line of though that says that since the fuel cost of
nuclear is so small, the electricity would have been standing charge
only to pay for the infrastructure.

[Roland Perry]

Post by The Natural Philosopher
Actually there is a line of though that says that since the fuel
cost of nuclear is so small, the electricity would have been standing
charge only to pay for the infrastructure.

Yes, that was the original promise, "too cheap to meter". We're still
waiting.

For the meter that's so cheap it's redundant?

[The Natural Philosopher]

Post by Roland Perry

 Actually there is a line of though that says that since the fuel
cost of  nuclear is so small, the electricity would have been
standing charge  only to pay for the infrastructure.

Yes, that was the original promise, "too cheap to meter". We're still
waiting.

For the meter that's so cheap it's redundant?

As I said, that realistically - and its perfectly possible now, and was
then - ta massive investment in nuclear power would be merely a capex
cost, and the actual O & M and fuel costs would be irrelevant, so once
you had built them with public money, there would be no need to charge
further for the product.

Obviously coal gas and oil were far happier shelling out to the Greens
to stop that.
And the grid infrastructure still had to be paid for.

I see that wholesale day ahead prices for electricity are up around 300
euros per MW/h in the EU.

No wonder we are burning coal and exporting electricity to them. Wind
and solar are essentially nil today, continent wide.

[Tim Ward]

Tho i do believe the reason why France has a lot of Nuclear energy is
that someone decided that Nuclear power electric heating was the way
to go, rather then coal and Gas?...

I got that impression from my winter visit to Japan. Loads of cheap
nuclear power, electric heating, so no need to bother much with insulation.

Then Fukushima happened, and they started turning off nuclear power plants.

It was cold.

[Peter Maydell]

Post by Tim Ward
I got that impression from my winter visit to Japan. Loads of cheap
nuclear power, electric heating, so no need to bother much with insulation.
Then Fukushima happened, and they started turning off nuclear power plants.

I think Japan's lousy housing stock has more causes than just that.
The houses having little intrinsic value and often short lifespans
doesn't encourage long-term investments like insulation. And, as
everywhere else, builders will build the cheapest rubbish the
regulations will permit them, because they're not paying the
ongoing heating/cooling bills...

-- PMM

[Owen Scarrott]

Post by Tim Ward

Tho i do believe the reason why France has a lot of Nuclear energy is
that someone decided that Nuclear power electric heating was the way
to go, rather then coal and Gas?...

I got that impression from my winter visit to Japan. Loads of cheap
nuclear power, electric heating, so no need to bother much with insulation.
Then Fukushima happened, and they started turning off nuclear power plants.
It was cold.
--
Tim Ward - 07801 703 600
www.brettward.co.uk

Norway has same thing. Cheap hydro so everyone uses elec for everything. No gas grid across the country. Now they are connecting their grid to Germany's And power prices are set to move up aggressively. Seems crazy, but it is plausible oil demand will rise in Norway as more isolated dwellings install oil tanks and or biomass (wood/

[The Natural Philosopher]

Post by Roland Perry

Of course the whole thing would be way easier if all heating were
electric and there was no need to control water circulation - and the
electricity, thanks to nuclear power, was almost too cheap to meter.

Absolutely! That was what was promised to us when I was growing up.
Some builders even sold "all electric" houses.
Just shows you can't trust government forecasts.

Tho i do believe the reason why France has a lot of Nuclear energy is
that someone decided that Nuclear power electric heating was the way to
go, rather then coal and Gas?...
But i believe that they are some 4 GW odd short right now perhaps
explains the extra Gas being burnt?..

yes, two reactors are down for the winter, on account of I think
corrosion being found.

http://www.gridwatch.templar.co.uk/france/

Thanks for the plug, but this is far more worrying. Coal phased out,
nuclear on the wane, no renewables at all cos it's high pressure and the
sun aint shining

https://www.energylive.cloud/

typical ex power station UK gas and coal are around 60 euros per MWh, so
the net result of relying on renewables and russian gas has been to push
energy prices up around fivefold

[Fevric J. Glandules]

Actually a motorised radiator valve on some sort of CANBUS on one wire
system or even wifi works fine.
All the bits are in place...and the smart home hubs is really just a
rubbish attempt to make it work.
What you do is have some sort of wifi stat in every room and some sort
of wifi equipped motorised valves. The rest, is then as they say , just
software.
Now that WOULD probably save on heating. You could set the temperature
of the rooms you were in, and leave the others icy.

A friend did do this to his house IIRC, though whether WiFi or some
other technology I can't remember.

One feature was that you could set some rooms to not have the authority
to turn the boiler on, and would have to wait for e.g. the living
room to do it.

[The Natural Philosopher]

Post by Fevric J. Glandules

Actually a motorised radiator valve on some sort of CANBUS on one wire
system or even wifi works fine.
All the bits are in place...and the smart home hubs is really just a
rubbish attempt to make it work.
What you do is have some sort of wifi stat in every room and some sort
of wifi equipped motorised valves. The rest, is then as they say , just
software.
Now that WOULD probably save on heating. You could set the temperature
of the rooms you were in, and leave the others icy.

A friend did do this to his house IIRC, though whether WiFi or some
other technology I can't remember.
One feature was that you could set some rooms to not have the authority
to turn the boiler on, and would have to wait for e.g. the living
room to do it.

As I said, if you have room stats and motorised vales under software
control - it becomes merely a matter of trivial code hacking

[Fevric J. Glandules]

Post by The Natural Philosopher

Post by Fevric J. Glandules
One feature was that you could set some rooms to not have the authority
to turn the boiler on, and would have to wait for e.g. the living
room to do it.

As I said, if you have room stats and motorised vales under software
control - it becomes merely a matter of trivial code hacking

Yebbut there's trivial code hacking and then there's trivial buying
a system that already does it.

[Theo]

Post by Fevric J. Glandules
A friend did do this to his house IIRC, though whether WiFi or some
other technology I can't remember.
One feature was that you could set some rooms to not have the authority
to turn the boiler on, and would have to wait for e.g. the living
room to do it.

The various 'smart TRVs' can do this. I played with some Radbot ones, which
claim to detect room occupancy (via light levels) and only heat the room
when it's occupied (or a boost button is pressed). They were a bit limited
since they don't have a master controller which can call for heat. I think
other systems (eg Hive) can. Most valves are battery powered so it's not
wifi but more commonly 433 or 868MHz RF or Zigbee for power reasons
(although the control box is then on your network via wifi or ethernet).

What I would instead do is do it wired - these actuators:
https://www.heatingcontrolsonline.co.uk/multifit-thermal-actuator-24v-low-voltage-p-433.html
and then wire them back to an underfloor heating wiring centre:
https://www.underfloorstore.co.uk/category/wiring-centres
and then you have centralised control, rather than relying on individual
TRVs making their own decisions.

Theo

[tony sayer]

In article <fuk****@news.chiark.greenend.org.uk>, Theo <theom+***@chi
ark.greenend.org.uk> scribeth thus

Post by Theo

Post by Fevric J. Glandules
A friend did do this to his house IIRC, though whether WiFi or some
other technology I can't remember.
One feature was that you could set some rooms to not have the authority
to turn the boiler on, and would have to wait for e.g. the living
room to do it.

The various 'smart TRVs' can do this. I played with some Radbot ones, which
claim to detect room occupancy (via light levels) and only heat the room
when it's occupied (or a boost button is pressed). They were a bit limited
since they don't have a master controller which can call for heat. I think
other systems (eg Hive) can. Most valves are battery powered so it's not
wifi but more commonly 433 or 868MHz RF or Zigbee for power reasons
(although the control box is then on your network via wifi or ethernet).
https://www.heatingcontrolsonline.co.uk/multifit-thermal-actuator-24v-low-
voltage-p-433.html
https://www.underfloorstore.co.uk/category/wiring-centres
and then you have centralised control, rather than relying on individual
TRVs making their own decisions.
Theo

Neat idea those but the wiring!!

Months worth of work hiding that up how long do the batteries last?...

[Tim Ward]

Post by Tim Ward
If the house is cold and I turn the heating on it heats up at about one
degree C per hour.

Now in a different house, which has similarly been left with the
thermostat down low whilst unoccupied. It's heating up at about one
degree per hour, but oil this time rather than gas. So that seems to be
a standard design!

[The Natural Philosopher]

Post by Tim Ward

Post by Tim Ward
If the house is cold and I turn the heating on it heats up at about
one degree C per hour.

Now in a different house, which has similarly been left with the
thermostat down low whilst unoccupied. It's heating up at about one
degree per hour, but oil this time rather than gas. So that seems to be
a standard design!

Its enrirely a function of te construction.

If you have lots of concrete and block and brick *inside* the insulation
- if yu have any - then it will take at least that long to warm up and
you probably should run the heating 24x7.

If its modern cardboard and wood interior construction it will heat up
much faster.

[Tim Ward]

Post by The Natural Philosopher
If you have lots of concrete and block and brick *inside* the insulation

This house has single walls (no cavity) with, now, an insulation layer
on the outside.

[The Natural Philosopher]

Post by Tim Ward

Post by The Natural Philosopher
If you have lots of concrete and block and brick *inside* the insulation

This house has single walls (no cavity) with, now, an insulation layer
on the outside.

There you go. Lots of 'thermal mass' to heat up before the air gets warm.

[Vir Campestris]

Post by The Natural Philosopher
Its enrirely a function of te construction.
If you have lots of concrete and block and brick *inside* the insulation
- if yu have any - then it will take at least that long to warm up and
you probably should run the heating 24x7.
If its modern cardboard and wood interior construction it will heat up
much faster.

My garden office is pretty well insulated.

On Monday morning it's perishing.

This evening I don't have the heating on - it's taken 3 days to recover
from (my three day) weekend.

Andy

[Tim Ward]

Post by Vir Campestris

Post by The Natural Philosopher
Its enrirely a function of te construction.
If you have lots of concrete and block and brick *inside* the
insulation - if yu have any - then it will take at least that long to
warm up and you probably should run the heating 24x7.
If its modern cardboard and wood interior construction it will heat up
much faster.

My garden office is pretty well insulated.
On Monday morning it's perishing.
This evening I don't have the heating on - it's taken 3 days to recover
from (my three day) weekend.

This place has warmed up now - we've been here since Saturday and I
haven't been cold the last day or two.

[Paul Bird]

Post by Vir Campestris

Post by The Natural Philosopher
Its enrirely a function of te construction.
If you have lots of concrete and block and brick *inside* the
insulation - if yu have any - then it will take at least that long to
warm up and you probably should run the heating 24x7.
If its modern cardboard and wood interior construction it will heat up
much faster.

My garden office is pretty well insulated.
On Monday morning it's perishing.

No stone(?) no thermal mass. No stored heat. Cold

Post by Vir Campestris
This evening I don't have the heating on - it's taken 3 days to recover
from (my three day) weekend.
Andy

[Vir Campestris]

No stone(?) no thermal mass. No stored heat.  Cold

Timber framed, well insulated, but full of things.

It takes 3 days to get cold, and a day of 2kW to get warm again.

Andy