With the current chilly weather, I'm mulling over the best (most
efficient) way to keep my place warm. I work (or rather did) from home,
so weekdays normally see me here pretty much all the time. Weekends I
may be away for the weekend, or again pretty much here all the time.

I have gas-fired CH, via combi boiler, no HW tank. I live in an old
(1880's) property (small hall off which toilet, bathroom, kitchen,
livingroom off which 2 bedrooms), the upper of two maisonettes.
Insulation in the roof, though not to all that high a standard. No
insulation in floor, so I get the benefit of heat from downstairs when
it's running. Double glazing throughout, one external door not d/g. I
have a CH temp control on the boiler (and separate one for HW). It's a
non-modulating boiler. Property is quite large for room sizes but
sloping ceilings help reduce actual volume, and the rads are well sized
for the rooms. No TRV's but programmable room stat located in the hall.

The wall construction is somewhat unknown. I suspect brick for some
walls, either brick or brick/timber/lathe&plaster construction for
others - it's possible they're just timber/lathe&plaster throughout a
lot of the walls but not drilled into them to find out. Internally
everything apart from kitchen broom cupboard is drylined/plasterboarded
due to condensation/damp being a problem previous to my occupancy.

I'm not about to start adding insulation/upgrading
doubleglazing/replacing front door etc, so suggesting I stop more of the
heat from being lost in the first place *isn't* a useful OR valid
suggestion no matter how well-founded you think it might be.

Now, after all that background, the question. Since I'm not out all day
at work, I'm not sure what the most efficient way of heating the place is.

Should I:

Turn the boiler temp down, and keep the room stat at a fairly constant
setting and just a couple of degrees cooler at night, so that the system
is circulating fairly warm water around on a more frequent basis (on the
basis that eventually the heat lost from the house will equal the heat
the boiler is putting in near enough, with the CH running for long
periods with less frequent firing of boiler).

This would presumably avoid having to shove heat back into the walls etc
during the heat-up phase in the mornings.

Or:

Turn the boiler temp up, and set the room stat to drop significantly
overnight, with a blast of heat in the morning, then lower level during
the day, then another blast of heat in the evening. This means the
place will have cooled down significantly overnight, and the boiler will
be working hard to get the place back up to temp in the morning, it'll
cool slightly again during the day (I just wear jumpers cos it's easier
to regulate my heat with clothes depending on what I'm doing than it is
to turn the heating up and down all the time!), heat it back up during
the evening again before effectively switching it off over night.

This means the boiler's heating up the fabric of the house twice a day,
and then keeping the heat constant.



Now, I originally thought that it was easy to work out, and if the place
spent longer not needing to be heated (ie, overnight/during the day if
I'm wearing warm clothes) then it worked out more efficient to do the
latter, but I'm starting to wonder now.

Heat loss would be the same through the fabric, presumably it'll lose
heat faster when the difference between inside and outside is greater,
in which case keeping a lower overall temp would be more efficient (and
this is actually what I've done already, reduced the room stat by a
couple of degrees, which is fine for me).

So do I match the heat loss on a fairly constant level, thus keeping the
place heated to a fairly constant level, or do I let the outside suck
the heat out of it overnight, then heat the place back up and start
maintaining heat in to counter heat loss?

As you can tell if you've stuck with this to the end, I'm a bit confused
as to what the best thing to do would be. I've googled and googled both
in web and groups to see if this has been discussed and any evidence
found on the different ways to keep a place heated, and can find nothing
that really explains it, just lots of home energy efficiency tips. I
guess I'm looking for an article that explains the physics of heating a
home, and looks at the differences between the two ways of doing it.

Any replies will be much appreciated, and thanks for sticking with it if
you got this far.

Velvet

With the current chilly weather, I'm mulling over the best (most
efficient) way to keep my place warm.

It will probably be more efficient to let it drop overnight, particularly as
your maisonette probably has low thermal mass. However, the difference might
not be all that great.

You really should install TRVs on all the radiators not in the thermostated
room. They could save you a lot of cash AND make you more comfortable as it
will prevent rooms overheating. It will also considerably reduce the
overshoot when heating from cold.

Christian.

Christian McArdle wrote:

With the current chilly weather, I'm mulling over the best (most
efficient) way to keep my place warm.


It will probably be more efficient to let it drop overnight, particularly as
your maisonette probably has low thermal mass. However, the difference might
not be all that great.

You really should install TRVs on all the radiators not in the thermostated
room. They could save you a lot of cash AND make you more comfortable as it
will prevent rooms overheating. It will also considerably reduce the
overshoot when heating from cold.

Christian.



For the same reason as the insulation, I'm not prepared to installed
TRV's. I don't own this place, long term rent (though that's not as
certain to continue as it used to be due to changed landlords).

Don't find it overshoots much, one of the reasons I have the stat set a
couple of degrees lower than normal - the overshoot brings it up to a
nice temp rather than being overly hot for a bit.

Will have to go look up thermal mass for an idea on what my place would
be catagorised as, I think. The age, building materials and style mean
there often seems to be quite a lot of difference between how it behaves
and how it should, window placements and the sloping ceilings etc.

Ta for the reply though, given me something else to go investigate.
Much appreciated.

Velvet

----- Original Message -----
From: "Velvet"
Newsgroups: uk.d-i-y
Sent: 28 January 2004 10:01
Subject: CH - most efficient way to run in cold weather?


Snipped

Now, after all that background, the question. Since I'm not out all day
at work, I'm not sure what the most efficient way of heating the place is.

Snipped

Heat loss is proportionate to the insulation factor and temperature
difference between the inside and outside of the house. Hence if you turn
down your thermostat, you will lower the inside temperature and the heat
loss will be less. I'm sure there are small effects due to the way the
boiler performs, but I think the overall picture will remain the same - turn
it down, use less fuel. As you have a programmable thermostat you'd be daft
not to.

In very cold weather, you may need to program the boiler to come on a bit
earlier to get the place warm enough.

The lower the inside temperature, the more heat you'll gain from (or less
you'll lose to) the house below :-)

Alan Shilling
Remove packaging from e-mail address before replying

Alan Shilling wrote:

----- Original Message -----
From: "Velvet"
Newsgroups: uk.d-i-y
Sent: 28 January 2004 10:01
Subject: CH - most efficient way to run in cold weather?



Snipped

Now, after all that background, the question. Since I'm not out all day
at work, I'm not sure what the most efficient way of heating the place is.


Snipped


Heat loss is proportionate to the insulation factor and temperature
difference between the inside and outside of the house. Hence if you turn
down your thermostat, you will lower the inside temperature and the heat
loss will be less. I'm sure there are small effects due to the way the
boiler performs, but I think the overall picture will remain the same - turn
it down, use less fuel. As you have a programmable thermostat you'd be daft
not to.

In very cold weather, you may need to program the boiler to come on a bit
earlier to get the place warm enough.

The lower the inside temperature, the more heat you'll gain from (or less
you'll lose to) the house below :-)

Alan Shilling
Remove packaging from e-mail address before replying



Sorry, maybe I wasn't that clear. I know running the overall temp lower
leads to less heat loss, but my question was whether keeping it at (for
example) a min of 17C overnight (which would mean the boiler coming on
and off) would be more cost-effective than letting it cool down
overnight from the 19C in the evening to perhaps 14C before stat turns
it up to 18C for the morning blast of heat.

Bearing in mind I'd likely get no heat overnight from downstairs, since
I don't think they run theirs overnight, I lose a lot of heat quite
quickly, and I'm not sure if it's better to maintain the temperature,
albiet a bit lower, overnight, or just let it drop then have the boiler
firing for a long period in the morning to bring it back up to temp?

Added to this, I've got the option to changing the boiler temp (of the
water circulating in teh rads). I normally have it set to about a
third, not quite sure what that is in degree's C of water but I have
thermometers on the pipes at teh boiler exit/return so can find that out
if it would help. I turned it up to about 2/3 because it does take
quite a long time to warm up in the morning. Not sure if that will make
much difference as I only did that after I got up this morning.

Having already lowered the stat temp and got used to (and indeed finding
I prefer a cooler rather than warmer house most of the time, as long as
I don't have cold feet), I don't really want to drop it any further.
Handy bit about the programmable room stat is it gives me an easy
indication of what the current temp is, just by flicking the override
up/down and seeing when it stops/starts firing. This is how I know how
cold the house drops to overnight (sometimes I'm up before the next
programme on the stat kicks in, though that's rarer these days).

Ta for the reply though.

Velvet

On Wed, 28 Jan 2004 16:17:29 UTC, Velvet wrote:

Sorry, maybe I wasn't that clear. I know running the overall temp lower
leads to less heat loss, but my question was whether keeping it at (for
example) a min of 17C overnight (which would mean the boiler coming on
and off) would be more cost-effective than letting it cool down
overnight from the 19C in the evening to perhaps 14C before stat turns
it up to 18C for the morning blast of heat.

Bearing in mind I'd likely get no heat overnight from downstairs, since
I don't think they run theirs overnight, I lose a lot of heat quite
quickly, and I'm not sure if it's better to maintain the temperature,
albiet a bit lower, overnight, or just let it drop then have the boiler
firing for a long period in the morning to bring it back up to temp?

I look at this in terms of simple input and output.

To get it to a given temperature in the morning, you either leave it on
all night or you don't.

Heat loss is greater if you leave it on (as the differential is
greater), so you lose more heat overnight if it's on than if it's off.
In both case you need to replace the heat lost. You have more heat loss
to replace if you leave it on.

QED. Turn if off!
--
Bob Eager
begin by not using Outlook Express...

On Wed, 28 Jan 2004 13:36:56 +0000, Alan Shilling wrote:

----- Original Message -----
From: "Velvet"
Newsgroups: uk.d-i-y
Sent: 28 January 2004 10:01
Subject: CH - most efficient way to run in cold weather?


Snipped

Now, after all that background, the question. Since I'm not out all day
at work, I'm not sure what the most efficient way of heating the place is.

Snipped

Heat loss is proportionate to the insulation factor and temperature
difference between the inside and outside of the house. Hence if you turn
down your thermostat, you will lower the inside temperature and the heat
loss will be less. I'm sure there are small effects due to the way the
boiler performs, but I think the overall picture will remain the same - turn
it down, use less fuel. As you have a programmable thermostat you'd be daft
not to.

In very cold weather, you may need to program the boiler to come on a bit
earlier to get the place warm enough.

The lower the inside temperature, the more heat you'll gain from (or less
you'll lose to) the house below :-)


The least heat lost from the house wil be the regime that runs the lowest
average temperature.
So you need to find what the lowest temperature you're content with for the
night-time (suggest 15C until you know better).
Like-wise anytime you are not there you need you need to find the lowest
temperature you would be happy with considering:
1) The house will take a while to heat up from the low temp.
2) You don't really want the house getting much below 5-10C becasue you
may get temporary condensation on objects with a high thermal mass until
the house is warmed up again.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html

Ed Sirett wrote:
On Wed, 28 Jan 2004 13:36:56 +0000, Alan Shilling wrote:


----- Original Message -----
From: "Velvet"
Newsgroups: uk.d-i-y
Sent: 28 January 2004 10:01
Subject: CH - most efficient way to run in cold weather?



Snipped

Now, after all that background, the question. Since I'm not out all day
at work, I'm not sure what the most efficient way of heating the place is.

Snipped

Heat loss is proportionate to the insulation factor and temperature
difference between the inside and outside of the house. Hence if you turn
down your thermostat, you will lower the inside temperature and the heat
loss will be less. I'm sure there are small effects due to the way the
boiler performs, but I think the overall picture will remain the same - turn
it down, use less fuel. As you have a programmable thermostat you'd be daft
not to.

In very cold weather, you may need to program the boiler to come on a bit
earlier to get the place warm enough.

The lower the inside temperature, the more heat you'll gain from (or less
you'll lose to) the house below :-)



The least heat lost from the house wil be the regime that runs the lowest
average temperature.
So you need to find what the lowest temperature you're content with for the
night-time (suggest 15C until you know better).
Like-wise anytime you are not there you need you need to find the lowest
temperature you would be happy with considering:
1) The house will take a while to heat up from the low temp.
2) You don't really want the house getting much below 5-10C becasue you
may get temporary condensation on objects with a high thermal mass until
the house is warmed up again.



I keep the house to a fairly normal cycle of heat even when I'm not
there for a weekend (tend not to be gone any longer than that) because I
have pets who, though they'd no doubt survive, would take a while to
acclimatise to lower temps, and then have to acclimatise to higher ones
again - and other pets who will simply end up with their own heaters
running constantly to keep them up to temp. With that in mind, the stat
never sets itself below about 12C at any time day or night, and while
daytimes are cooler than if I'm around, they're still no lower than 16,
with a burst of a couple of degrees of an evening.

My previous experiences with letting a house cool to around 10C is that
it took hours, literally hours and hours, to warm back up again.
Possibly even longer than that - a day, maybe. It wasn't this place so
I'm not sure how much of that was the heating (different system, not
going to start an argument so won't say what it was).


I'm perfectly happy with the stat dropping to 11 or 12 overnight,
because at the moment (well, before this recent cold spell) it's never
got down beyond 14 or so. Me personally I don't mind if it drops below
that, cos I have a thick duvet and prefer a cold rather than hot room to
sleep in. But getting up in the morning I'm conscious of how long the
heating runs for to bring it back up to temperature, vs how often and
long it runs for if it's just maintaining the steady temp.

That's how I got to wondering which one actually does use more gas, and
therefore, costs more... and searched the web, but to no avail, no
concrete examples and theories that demonstrate the differences between
the two methods seem to exist. And whilst I'd give it a go as a home
experiment, I know the weather's too variable to make the results
worthwhile.

Oh well. Ta for the replies. Anyone else?

Velvet

On Wed, 28 Jan 2004 22:33:45 GMT, Velvet wrote:



I keep the house to a fairly normal cycle of heat even when I'm not
there for a weekend (tend not to be gone any longer than that) because I
have pets who, though they'd no doubt survive, would take a while to
acclimatise to lower temps, and then have to acclimatise to higher ones
again - and other pets who will simply end up with their own heaters
running constantly to keep them up to temp. With that in mind, the stat
never sets itself below about 12C at any time day or night, and while
daytimes are cooler than if I'm around, they're still no lower than 16,
with a burst of a couple of degrees of an evening.

My previous experiences with letting a house cool to around 10C is that
it took hours, literally hours and hours, to warm back up again.
Possibly even longer than that - a day, maybe. It wasn't this place so
I'm not sure how much of that was the heating (different system, not
going to start an argument so won't say what it was).


I'm perfectly happy with the stat dropping to 11 or 12 overnight,
because at the moment (well, before this recent cold spell) it's never
got down beyond 14 or so. Me personally I don't mind if it drops below
that, cos I have a thick duvet and prefer a cold rather than hot room to
sleep in. But getting up in the morning I'm conscious of how long the
heating runs for to bring it back up to temperature, vs how often and
long it runs for if it's just maintaining the steady temp.

That's how I got to wondering which one actually does use more gas, and
therefore, costs more... and searched the web, but to no avail, no
concrete examples and theories that demonstrate the differences between
the two methods seem to exist. And whilst I'd give it a go as a home
experiment, I know the weather's too variable to make the results
worthwhile.

Oh well. Ta for the replies. Anyone else?

Well...... you've introduced additional information that you have
animals who require an environment influenced by the room temperature.

If there are a significant number of them or more to the point their
enclosures and the energy requirements, then the cost difference of
energy for the house may well become irrelevant. If the heating for
the enclosures is electric, then that is costing 3-4 times the gas
cost anyway.

If economy is a real issue for you, then insulating the animal
enclosures makes sense.

I've done this for an enclosure housing two creatures who like to have
an environment of about 29 degrees and 80% humidity. It was a
challenging project, but I made a significant difference on
electricity use with insulation to avoid heatloss to the room.






Velvet

..andy

To email, substitute .nospam with .gl

On a purely practical and non-scientific test over the last two winters I've
left our heating on constant and turned the thermostat down to 20 at night.
(I don't think the scale is very accurate as we run it at about 25 during
the day - and the house is seldom too hot.)

It's a 1988 4 bed detached and we have no TRV's. The kids used to wake at
night and it was far more pleasant to deal with in a warm house, I also
appear at home at all hours of the day after site visits to do my
paperwork - nice to return to a warm house.

The result has been a very marginal increase in our gas bills, though not
enough to increase our monthly direct debit. The heating seems to be off for
the vast majority of the time during the night, and when I'm sitting at home
during the day. The seemingly endless hot water is also blissful!

"Velvet" wrote in message
...
Snipped

That's how I got to wondering which one actually does use more gas, and
therefore, costs more... and searched the web, but to no avail, no
concrete examples and theories that demonstrate the differences between
the two methods seem to exist. And whilst I'd give it a go as a home
experiment, I know the weather's too variable to make the results
worthwhile.

Oh well. Ta for the replies. Anyone else?

Hi it's me again, maybe I didn't provide a simple enough explanation - if
you run continuously you'll use more gas. This is because the average
temperature inside the house will be higher and hence the heat loss to the
outside will be greater (as I'm sure someone else has also pointed out).

You're probably thinking that there is some complex stuff going on here -
but there isn't. Think of your house as a box with gas going into it and
heat coming out. The hotter it is inside, the more heat comes out and the
more gas has to go in. You can reduce the gas going in by lowering the
temperature (overall or for a few hours at a time) or by improving the
insulation.
--
Alan Shilling
Remove packaging from e-mail address before replying

Andy Hall wrote:
On Wed, 28 Jan 2004 22:33:45 GMT, Velvet wrote:



I keep the house to a fairly normal cycle of heat even when I'm not
there for a weekend (tend not to be gone any longer than that) because I
have pets who, though they'd no doubt survive, would take a while to
acclimatise to lower temps, and then have to acclimatise to higher ones
again - and other pets who will simply end up with their own heaters
running constantly to keep them up to temp. With that in mind, the stat
never sets itself below about 12C at any time day or night, and while
daytimes are cooler than if I'm around, they're still no lower than 16,
with a burst of a couple of degrees of an evening.

My previous experiences with letting a house cool to around 10C is that
it took hours, literally hours and hours, to warm back up again.
Possibly even longer than that - a day, maybe. It wasn't this place so
I'm not sure how much of that was the heating (different system, not
going to start an argument so won't say what it was).


I'm perfectly happy with the stat dropping to 11 or 12 overnight,
because at the moment (well, before this recent cold spell) it's never
got down beyond 14 or so. Me personally I don't mind if it drops below
that, cos I have a thick duvet and prefer a cold rather than hot room to
sleep in. But getting up in the morning I'm conscious of how long the
heating runs for to bring it back up to temperature, vs how often and
long it runs for if it's just maintaining the steady temp.

That's how I got to wondering which one actually does use more gas, and
therefore, costs more... and searched the web, but to no avail, no
concrete examples and theories that demonstrate the differences between
the two methods seem to exist. And whilst I'd give it a go as a home
experiment, I know the weather's too variable to make the results
worthwhile.

Oh well. Ta for the replies. Anyone else?


Well...... you've introduced additional information that you have
animals who require an environment influenced by the room temperature.

If there are a significant number of them or more to the point their
enclosures and the energy requirements, then the cost difference of
energy for the house may well become irrelevant. If the heating for
the enclosures is electric, then that is costing 3-4 times the gas
cost anyway.

If economy is a real issue for you, then insulating the animal
enclosures makes sense.

I've done this for an enclosure housing two creatures who like to have
an environment of about 29 degrees and 80% humidity. It was a
challenging project, but I made a significant difference on
electricity use with insulation to avoid heatloss to the room.






Velvet


.andy

To email, substitute .nospam with .gl

That's an interesting point. In my situation, it's only one that'd
actually cost me more financially (potentially) - tropical fish tank. I
found somethign that gives an estimate of cost/month based on wattage of
thing, and hours run, which was quite handy. Need to establish what the
heater wattage is of course, then it'll be a stab in the dark for how
long it actually spends running.

The majority of the other critters wouldn't mind, but a couple of them
would be prone to getting far more chilled than they should, and lack of
'freedom to roam' if I'm not there means they can't use exercise as a
means of keeping body temp up. They don't have any form of heating, cos
there's absolutely no way to stop it escaping straight into the room.

I'm still really looking for a fairly simple explanation of the energy
used to heat a place from a colder temp, vs energy used to maintain a
temp. Someone somewhere must have done the research for this, I just
can't find it :-) I thought maybe there were lurking people here who
had the physics etc knowledge to calculate this sort of thing, I was
thinking it was something that people might know from sizing CH systems
since you have to generate enough heat to actually get the place warmed
up in the morning, but I think I'm realising that the efficiency isn't
looked at in an overall sense like this but more as an 'insulate as much
as possible then fit the most efficient boiler' - just seems there's a
bit bit of the puzzle being missed out, which is how to run the CH most
efficiently.

Off to google again for more physics based stuff I think!

Velvet

Alan Shilling wrote:

"Velvet" wrote in message
...

Snipped

That's how I got to wondering which one actually does use more gas, and
therefore, costs more... and searched the web, but to no avail, no
concrete examples and theories that demonstrate the differences between
the two methods seem to exist. And whilst I'd give it a go as a home
experiment, I know the weather's too variable to make the results
worthwhile.

Oh well. Ta for the replies. Anyone else?


Hi it's me again, maybe I didn't provide a simple enough explanation - if
you run continuously you'll use more gas. This is because the average
temperature inside the house will be higher and hence the heat loss to the
outside will be greater (as I'm sure someone else has also pointed out).

You're probably thinking that there is some complex stuff going on here -
but there isn't. Think of your house as a box with gas going into it and
heat coming out. The hotter it is inside, the more heat comes out and the
more gas has to go in. You can reduce the gas going in by lowering the
temperature (overall or for a few hours at a time) or by improving the
insulation.


Ok, but what about once the house (fabric of) has cooled. Surely you
end up pumping more energy/heat into it, some of which leaks out, some
of which is absorbed by the house fabric, and only then do you start
actually raising the temperature of the air within (once the house has
stopped sucking heat out of the air).

That's the crux of the question for me. The longer the heating is off,
the further it cools, and the more energy you need to put in to raise
the temperature again. It's the comparison between energy used to raise
it back to temp and energy used to maintain a temp that I wanted to find
out about.

Velvet

That's the crux of the question for me. The longer the heating is off,
the further it cools, and the more energy you need to put in to raise
the temperature again.

The efficiency will be higher letting it cool. The only effect that will
reduce efficiency compared to the alternative as that things get overheated
in an attempt to reheat the house to a comfortable level too quickly. This
is only likely to happen if the house is high thermal mass (i.e. thick stone
walls) and the cycling frequent. It would actually require a pretty
pathological set of parameters to make it less efficient, too.

Higher insulation would tend to reduce the heat losses, keeping the fabric
warmer for longer. This will reduce the differences between the two methods.

Christian.

Alan Shilling wrote:

"Velvet" wrote in message
...

Snipped

That's how I got to wondering which one actually does use more gas, and
therefore, costs more... and searched the web, but to no avail, no
concrete examples and theories that demonstrate the differences between
the two methods seem to exist. And whilst I'd give it a go as a home
experiment, I know the weather's too variable to make the results
worthwhile.

Oh well. Ta for the replies. Anyone else?


Hi it's me again, maybe I didn't provide a simple enough explanation - if
you run continuously you'll use more gas. This is because the average
temperature inside the house will be higher and hence the heat loss to the
outside will be greater (as I'm sure someone else has also pointed out).

You're probably thinking that there is some complex stuff going on here -
but there isn't.


There is tho.

In order to warm up the house fully - structure and all - you have to
actually make it hotter inside for a time. This *partially* offsets the
benefits of timed running.

With UF heating, I have found it simpler to run it 24 hours for the last
month. A complex predictive timeclock and stat is probably better, but I
haven't yet installed one.

The fuel burn rate seems very little different from running it timed.



Think of your house as a box with gas going into it and
heat coming out. The hotter it is inside, the more heat comes out and the
more gas has to go in. You can reduce the gas going in by lowering the
temperature (overall or for a few hours at a time) or by improving the
insulation.



Thsi takes no account of thermal interia. If teh time constant of the
building is anywhere over a few hours, it will stay warm and decay
agfter heating is off - a net gain for you, but rewquire a huge burn
first thing on switch on to restore. And take several hours to get fully
warm. By understanding this you can adjust your timeclock accprdingly,
but the option of switching off, and immmediately ceasing to lose heat
as the inside temperature plummets to zero when you leave for work,
followed by instant restoration to 22C or whatever the moment the boilre
fires up is not possible in practice.

The better the insulation and the more thermal mass there is the less
there is to gain from timed usage.

Velvet wrote:


I'm still really looking for a fairly simple explanation of the energy
used to heat a place from a colder temp, vs energy used to maintain a
temp. Someone somewhere must have done the research for this, I just
can't find it :-) I thought maybe there were lurking people here who
had the physics etc knowledge to calculate this sort of thing, I was
thinking it was something that people might know from sizing CH systems
since you have to generate enough heat to actually get the place warmed
up in the morning, but I think I'm realising that the efficiency isn't
looked at in an overall sense like this but more as an 'insulate as much
as possible then fit the most efficient boiler' - just seems there's a
bit bit of the puzzle being missed out, which is how to run the CH most
efficiently.

Off to google again for more physics based stuff I think!




Heat required is the integral of temperature difference times the
calculated U values over the surface areas of the house PLUS the amount
of heat needed to raise the temperature of teh contained air mass and
structure to the same level.

However this is a 'once and only' heat 'loss' since once warm. it takes
no extra heat to keep it warm - its all about the insulation and air
change losses. And if you like it gives it back to you by staying warm
after the heating goes off.

The pertinent issue is whether you need to e.g. raise air temperature
significanbtly MORE to feel confortable in a room with a stone cold
concrete floor and icy thick exposed brickwork etc. etc.

The 'tmed' soulktion is most effective where heat loss is high and
thermal mass low. There there is very little retention of heat, and teh
internal temperature responds rapidly to CH heat input.

If insulation and mass is high, the system takes longer to respond if
driven by the rated boler outpurt, since this will be lower anyway due
to teh better insulation. In effect, it will take time to get up to
temperarture, teh boiler will run at peak output for a lomngish initial
period, and the rooms may need to be set hotter in order not to feel
cold until it does.

There are so many variables that its very hard to predict, but having
moved fom only moderately well nsulated house to one with big mases and
good insulation, the oil burn rate is very little extra on 24 hour
heating on the UF sections.

Upstairs where its studwork walls only, its timed, and these warm up
very quickly anyway.






Velvet

Velvet wrote:

Alan Shilling wrote:

"Velvet" wrote in message
...

Snipped

That's how I got to wondering which one actually does use more gas, and
therefore, costs more... and searched the web, but to no avail, no
concrete examples and theories that demonstrate the differences between
the two methods seem to exist. And whilst I'd give it a go as a home
experiment, I know the weather's too variable to make the results
worthwhile.

Oh well. Ta for the replies. Anyone else?



Hi it's me again, maybe I didn't provide a simple enough explanation - if
you run continuously you'll use more gas. This is because the average
temperature inside the house will be higher and hence the heat loss to
the
outside will be greater (as I'm sure someone else has also pointed out).

You're probably thinking that there is some complex stuff going on here -
but there isn't. Think of your house as a box with gas going into it and
heat coming out. The hotter it is inside, the more heat comes out and the
more gas has to go in. You can reduce the gas going in by lowering the
temperature (overall or for a few hours at a time) or by improving the
insulation.



Ok, but what about once the house (fabric of) has cooled. Surely you
end up pumping more energy/heat into it, some of which leaks out, some
of which is absorbed by the house fabric, and only then do you start
actually raising the temperature of the air within (once the house has
stopped sucking heat out of the air).

That's the crux of the question for me. The longer the heating is off,
the further it cools, and the more energy you need to put in to raise
the temperature again. It's the comparison between energy used to raise
it back to temp and energy used to maintain a temp that I wanted to find
out about.


In theory iots always less to time, because the energy you put in to
warm it up, keeps it warm after you have switched off teh heating. This
of course is a net waste and leads you to advance the timing so teh
house is warm when you get in and when you leave. In teh case of high
enough thermal inertia:heat loss ratio this results in the system being
on nearly 24 hours anyway.

So you might as well leave it on.




Velvet

Christian McArdle wrote:

That's the crux of the question for me. The longer the heating is off,
the further it cools, and the more energy you need to put in to raise
the temperature again.


The efficiency will be higher letting it cool. The only effect that will
reduce efficiency compared to the alternative as that things get overheated
in an attempt to reheat the house to a comfortable level too quickly. This
is only likely to happen if the house is high thermal mass (i.e. thick stone
walls) and the cycling frequent. It would actually require a pretty
pathological set of parameters to make it less efficient, too.



Yes. Experience shows that it is marginally less efficient to do 24 hrs,
but not nearly as much as 'simple theory' predicts.

And teh iusses are as you say, thermal mass to insulation level ratios.

There is a lower limit on thermal mass - and that is the enclosed air
volume of the house.

As insulation levels rise to the point where heat input is drastically
reduced, the rate of cooling of that air mass makes it almost silly to
stop heating it. Air change factors start to dominate the loss equations
anyway.

There are side issues to do with whether boilers are more or less
efficient dong long burns to heat up big storage elemnents, or lots of
short blasts to keep a fast responding house 'up to temperature'

So it is complex.

Whilst timed CH in older less well insulated houses of lightweight
constrctions is definitely a huge saveing, its by no means clear ij teh
fcvase of modern well insulkated stuff.

My sister, in Sweden, has no concept of time clocks. The CH is switched
on in the autumn, and off in the late spring, and thermostats control
the house temperature. Thats all triple glazed 8"" rockwool no cold
bridges stuff.


Higher insulation would tend to reduce the heat losses, keeping the fabric
warmer for longer. This will reduce the differences between the two methods.


Exactly.



Christian.

"Velvet" wrote in message
...
With the current chilly weather, I'm mulling over the best (most
efficient) way to keep my place warm. I work (or rather did) from home,
so weekdays normally see me here pretty much all the time. Weekends I
may be away for the weekend, or again pretty much here all the time.

I have gas-fired CH, via combi boiler, no HW tank. I live in an old
(1880's) property (small hall off which toilet, bathroom, kitchen,
livingroom off which 2 bedrooms), the upper of two maisonettes.
Insulation in the roof, though not to all that high a standard. No
insulation in floor, so I get the benefit of heat from downstairs when
it's running. Double glazing throughout, one external door not d/g. I
have a CH temp control on the boiler (and separate one for HW). It's a
non-modulating boiler. Property is quite large for room sizes but
sloping ceilings help reduce actual volume, and the rads are well sized
for the rooms. No TRV's but programmable room stat located in the hall.

The wall construction is somewhat unknown. I suspect brick for some
walls, either brick or brick/timber/lathe&plaster construction for
others - it's possible they're just timber/lathe&plaster throughout a
lot of the walls but not drilled into them to find out. Internally
everything apart from kitchen broom cupboard is drylined/plasterboarded
due to condensation/damp being a problem previous to my occupancy.

I'm not about to start adding insulation/upgrading
doubleglazing/replacing front door etc, so suggesting I stop more of the
heat from being lost in the first place *isn't* a useful OR valid
suggestion no matter how well-founded you think it might be.

Now, after all that background, the question. Since I'm not out all day
at work, I'm not sure what the most efficient way of heating the place is.

Should I:

Turn the boiler temp down, and keep the room stat at a fairly constant
setting and just a couple of degrees cooler at night, so that the system
is circulating fairly warm water around on a more frequent basis (on the
basis that eventually the heat lost from the house will equal the heat
the boiler is putting in near enough, with the CH running for long
periods with less frequent firing of boiler).

This would presumably avoid having to shove heat back into the walls etc
during the heat-up phase in the mornings.

Or:

Turn the boiler temp up, and set the room stat to drop significantly
overnight, with a blast of heat in the morning, then lower level during
the day, then another blast of heat in the evening. This means the
place will have cooled down significantly overnight, and the boiler will
be working hard to get the place back up to temp in the morning, it'll
cool slightly again during the day (I just wear jumpers cos it's easier
to regulate my heat with clothes depending on what I'm doing than it is
to turn the heating up and down all the time!), heat it back up during
the evening again before effectively switching it off over night.

This means the boiler's heating up the fabric of the house twice a day,
and then keeping the heat constant.



Now, I originally thought that it was easy to work out, and if the place
spent longer not needing to be heated (ie, overnight/during the day if
I'm wearing warm clothes) then it worked out more efficient to do the
latter, but I'm starting to wonder now.

Heat loss would be the same through the fabric, presumably it'll lose
heat faster when the difference between inside and outside is greater,
in which case keeping a lower overall temp would be more efficient (and
this is actually what I've done already, reduced the room stat by a
couple of degrees, which is fine for me).

So do I match the heat loss on a fairly constant level, thus keeping the
place heated to a fairly constant level, or do I let the outside suck
the heat out of it overnight, then heat the place back up and start
maintaining heat in to counter heat loss?

As you can tell if you've stuck with this to the end, I'm a bit confused
as to what the best thing to do would be. I've googled and googled both
in web and groups to see if this has been discussed and any evidence
found on the different ways to keep a place heated, and can find nothing
that really explains it, just lots of home energy efficiency tips. I
guess I'm looking for an article that explains the physics of heating a
home, and looks at the differences between the two ways of doing it.

Any replies will be much appreciated, and thanks for sticking with it if
you got this far.

If not a condensing boiler have the boiler stat full on, or near to. Don't
go for night setback temps. If a condensing boiler have boiler stat as low
as possible. Trial and error if not auto modulation controls.