What is the relationship between internal temperature and heat loss
from a building? In particular if the outside temperature is 0 deg. C
and the internal temperature is, say 18 deg. C what percentage
increase in heat loss would occur if the internal temperature is
raised to say 20 deg.C? Does an increase in the internal temperature
translate to the same increase of external skin temperature, that is
is the heat transfer linear across the interface?

I appreciate that boundary conditions are important but for the sake
of the exercise let us assume the building in in a sheltered location
in a city.

Although I don't think it is relevant to the question, assume the
construction to be brick cavity walls and insulkated, loft is
insulated and windows double glazed.

On a staright linear relationship I suppose the answer is about 10%
but I suspect it is not as simple as that, hence the question.

"Edward W. Thompson" wrote in message
...
What is the relationship between internal temperature and heat loss
from a building?

Complex. It depends upon the u-values of the building materials used and
even in buildings of similar construction, the proportion of different
materials can change the overall value for a surface. Exposure also affects
the loss - a north facing wall in an exposed location loses more heat than a
south-facing wall in a sheltered one. As rooms are rarely all at the same
temperature, you also have to factor in heat transfer between rooms.

Try this programme:

http://www.quinn-radiators.co.uk/downloads_heatloss.php

Colin Bignell

nightjar cpb@ wrote:
"Edward W. Thompson" wrote in message
...
What is the relationship between internal temperature and heat loss
from a building?

Complex. It depends upon the u-values of the building materials used and
even in buildings of similar construction, the proportion of different
materials can change the overall value for a surface. Exposure also affects
the loss - a north facing wall in an exposed location loses more heat than a
south-facing wall in a sheltered one. As rooms are rarely all at the same
temperature, you also have to factor in heat transfer between rooms.

Try this programme:

http://www.quinn-radiators.co.uk/downloads_heatloss.php

Colin Bignell


For conduction and convection ( when the temperature difference is small
and the air flow forced - probably applies in this instance) the rate of
loss of heat is proportional to the temperature difference.

So if its 0 deg outside reducing the internal temp from 20 to 18 will
reduce rate of heat loss by 10%.

Although not a totally accurate statement of the situation I would
suspect it is good enough for this query !

Edward W. Thompson wrote:
What is the relationship between internal temperature and heat loss
from a building? In particular if the outside temperature is 0 deg. C
and the internal temperature is, say 18 deg. C what percentage
increase in heat loss would occur if the internal temperature is
raised to say 20 deg.C?

Basic O-level physics. Newton's law of cooling states "the rate of heat loss
of a body is proportional to the difference in temperatures between the body
and its environment".
So the difference is 2/273 or about 0.73% more heat loss. The outside
temperature is irrelevent.
--
LSR

Edward W. Thompson wrote:
What is the relationship between internal temperature and heat loss
from a building? In particular if the outside temperature is 0 deg. C
and the internal temperature is, say 18 deg. C what percentage
increase in heat loss would occur if the internal temperature is
raised to say 20 deg.C? Does an increase in the internal temperature
translate to the same increase of external skin temperature, that is
is the heat transfer linear across the interface?


yes.


I appreciate that boundary conditions are important but for the sake
of the exercise let us assume the building in in a sheltered location
in a city.

Although I don't think it is relevant to the question, assume the
construction to be brick cavity walls and insulkated, loft is
insulated and windows double glazed.

On a staright linear relationship I suppose the answer is about 10%
but I suspect it is not as simple as that, hence the question.

It is precisely that simple.

To a very good approximation.

Obviously hot outside walls induce more convection and therefore a bit
more heat loss. As does wind..

LSR wrote:
Edward W. Thompson wrote:
What is the relationship between internal temperature and heat loss
from a building? In particular if the outside temperature is 0 deg. C
and the internal temperature is, say 18 deg. C what percentage
increase in heat loss would occur if the internal temperature is
raised to say 20 deg.C?

Basic O-level physics. Newton's law of cooling states "the rate of heat loss
of a body is proportional to the difference in temperatures between the body
and its environment".
So the difference is 2/273 or about 0.73% more heat loss. The outside
temperature is irrelevent.
Probably the least correct answer anyone has posted on here ever.

"The Natural Philosopher" wrote in message
...
LSR wrote:
Edward W. Thompson wrote:
What is the relationship between internal temperature and heat loss
from a building? In particular if the outside temperature is 0 deg. C
and the internal temperature is, say 18 deg. C what percentage
increase in heat loss would occur if the internal temperature is
raised to say 20 deg.C?

Basic O-level physics. Newton's law of cooling states "the rate of heat
loss of a body is proportional to the difference in temperatures between
the body and its environment".
So the difference is 2/273 or about 0.73% more heat loss. The outside
temperature is irrelevent.
Probably the least correct answer anyone has posted on here ever.

Well the first bit was nearly right, he forgot the air had to be moving and
it's the temperature of that air (the "environment") that counts. If he'd
actually used this he would have seen that the new heat loss would be 20/18
or 1.11 times the old or 11% more.


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

"Bob Mannix" wrote in message
...
"The Natural Philosopher" wrote in message
...
LSR wrote:
Edward W. Thompson wrote:
What is the relationship between internal temperature and heat loss
from a building? In particular if the outside temperature is 0 deg. C
and the internal temperature is, say 18 deg. C what percentage
increase in heat loss would occur if the internal temperature is
raised to say 20 deg.C?

Basic O-level physics. Newton's law of cooling states "the rate of heat
loss of a body is proportional to the difference in temperatures between
the body and its environment".
So the difference is 2/273 or about 0.73% more heat loss. The outside
temperature is irrelevent.
Probably the least correct answer anyone has posted on here ever.

Well the first bit was nearly right, he forgot the air had to be moving
and it's the temperature of that air (the "environment") that counts. If
he'd actually used this he would have seen that the new heat loss would be
20/18 or 1.11 times the old or 11% more.




Something I don't understand here about the linear relationship of heat
loss.
For example: a heater maintains a room at 20 deg C when it is zero outside.
If you put in a second heater I'm pretty sure you wouldn't be able to
maintain 40 deg C


mark.

On 25/03/2008 12:55, mark wrote:

Something I don't understand here about the linear relationship of heat
loss.
For example: a heater maintains a room at 20 deg C when it is zero outside.
If you put in a second heater I'm pretty sure you wouldn't be able to
maintain 40 deg C

But there you're talking about loss from the heater into *its*
environment (the room), as well as loss from the room to its environment
(the outside world).

mark wrote:
"Bob Mannix" wrote in message
...
"The Natural Philosopher" wrote in message
...
LSR wrote:
Edward W. Thompson wrote:
What is the relationship between internal temperature and heat loss
from a building? In particular if the outside temperature is 0 deg. C
and the internal temperature is, say 18 deg. C what percentage
increase in heat loss would occur if the internal temperature is
raised to say 20 deg.C?
Basic O-level physics. Newton's law of cooling states "the rate of heat
loss of a body is proportional to the difference in temperatures between
the body and its environment".
So the difference is 2/273 or about 0.73% more heat loss. The outside
temperature is irrelevent.
Probably the least correct answer anyone has posted on here ever.
Well the first bit was nearly right, he forgot the air had to be moving
and it's the temperature of that air (the "environment") that counts. If
he'd actually used this he would have seen that the new heat loss would be
20/18 or 1.11 times the old or 11% more.




Something I don't understand here about the linear relationship of heat
loss.
For example: a heater maintains a room at 20 deg C when it is zero outside.
If you put in a second heater I'm pretty sure you wouldn't be able to
maintain 40 deg C


You would.



mark.

Andy Burns wrote:
On 25/03/2008 12:55, mark wrote:

Something I don't understand here about the linear relationship of
heat loss.
For example: a heater maintains a room at 20 deg C when it is zero
outside.
If you put in a second heater I'm pretty sure you wouldn't be able to
maintain 40 deg C

But there you're talking about loss from the heater into *its*
environment (the room), as well as loss from the room to its environment
(the outside world).

Oh..in the sense that its not going to do the job if the radiators are
only at 35C? :-)

"Edward W. Thompson" wrote in message
...
What is the relationship between internal temperature and heat loss
from a building? In particular if the outside temperature is 0 deg. C
and the internal temperature is, say 18 deg. C what percentage
increase in heat loss would occur if the internal temperature is
raised to say 20 deg.C? Does an increase in the internal temperature
translate to the same increase of external skin temperature, that is
is the heat transfer linear across the interface?

I appreciate that boundary conditions are important but for the sake
of the exercise let us assume the building in in a sheltered location
in a city.

Although I don't think it is relevant to the question, assume the
construction to be brick cavity walls and insulkated, loft is
insulated and windows double glazed.

On a staright linear relationship I suppose the answer is about 10%
but I suspect it is not as simple as that, hence the question.

Its a straight line as far as insulation goes.
However probably not as far as ventilation goes.
So about 10% is a good guess unless its very draughty.

Bob Mannix wrote:
"The Natural Philosopher" wrote in message
...
LSR wrote:
Edward W. Thompson wrote:
What is the relationship between internal temperature and heat loss
from a building? In particular if the outside temperature is 0
deg. C and the internal temperature is, say 18 deg. C what
percentage increase in heat loss would occur if the internal
temperature is raised to say 20 deg.C?

Basic O-level physics. Newton's law of cooling states "the rate of
heat loss of a body is proportional to the difference in
temperatures between the body and its environment".
So the difference is 2/273 or about 0.73% more heat loss. The
outside temperature is irrelevent.
Probably the least correct answer anyone has posted on here ever.

Well the first bit was nearly right, he forgot the air had to be
moving and it's the temperature of that air (the "environment") that
counts. If he'd actually used this he would have seen that the new
heat loss would be 20/18 or 1.11 times the old or 11% more.

Oops. I thought it seemed a bit low. But there's definitely some calculation
I remember where the external temperature surprisingly "cancels out" . Not
this one though! Sorry.
--
LSR

On Tue, 25 Mar 2008 12:14:44 +0000, a particular chimpanzee, The
Natural Philosopher randomly hit the keyboard and produced:

LSR wrote:

So the difference is 2/273 or about 0.73% more heat loss. The outside
temperature is irrelevent.

Probably the least correct answer anyone has posted on here ever.

Oh come on! Drivel, reclaim your crown!
--
Hugo Nebula
"If no-one on the internet wants a piece of this,
just how far from the pack have you strayed?"

On Tue, 25 Mar 2008 12:13:18 +0000, The Natural Philosopher
wrote:

Edward W. Thompson wrote:
What is the relationship between internal temperature and heat loss
from a building? In particular if the outside temperature is 0 deg. C
and the internal temperature is, say 18 deg. C what percentage
increase in heat loss would occur if the internal temperature is
raised to say 20 deg.C? Does an increase in the internal temperature
translate to the same increase of external skin temperature, that is
is the heat transfer linear across the interface?


yes.


I appreciate that boundary conditions are important but for the sake
of the exercise let us assume the building in in a sheltered location
in a city.

Although I don't think it is relevant to the question, assume the
construction to be brick cavity walls and insulkated, loft is
insulated and windows double glazed.

On a staright linear relationship I suppose the answer is about 10%
but I suspect it is not as simple as that, hence the question.

It is precisely that simple.

To a very good approximation.

Obviously hot outside walls induce more convection and therefore a bit
more heat loss. As does wind..


Thanks to all for your input.

mark wrote:
"Bob Mannix" wrote in message
...
"The Natural Philosopher" wrote in message
...
LSR wrote:
Edward W. Thompson wrote:
What is the relationship between internal temperature and heat loss
from a building? In particular if the outside temperature is 0 deg. C
and the internal temperature is, say 18 deg. C what percentage
increase in heat loss would occur if the internal temperature is
raised to say 20 deg.C?
Basic O-level physics. Newton's law of cooling states "the rate of heat
loss of a body is proportional to the difference in temperatures between
the body and its environment".
So the difference is 2/273 or about 0.73% more heat loss. The outside
temperature is irrelevent.
Probably the least correct answer anyone has posted on here ever.
Well the first bit was nearly right, he forgot the air had to be moving
and it's the temperature of that air (the "environment") that counts. If
he'd actually used this he would have seen that the new heat loss would be
20/18 or 1.11 times the old or 11% more.




Something I don't understand here about the linear relationship of heat
loss.
For example: a heater maintains a room at 20 deg C when it is zero outside.
If you put in a second heater I'm pretty sure you wouldn't be able to
maintain 40 deg C


mark.


Yes if the room was surrounded on all sides by a zero degree environment
of moving air!
However in practice the room is bounded on most sides by other rooms at
say 15C so the rate of heat loss through those surfaces is going up
(40-15)/(20-15) times ie 5x.