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Radiator placement



 
 
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  #1  
Old March 22nd 05, 02:53 PM
Beartums
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Default Radiator placement

My wife and I are having a discussion about radiator placement. We are in
the process of having our basement renovated. The rooms in the basement
have an 8-inch "shelf" about a foot and a half from the floor along the
outer walls of the building (part of the footing, since we had to dig down
to make the ceilings high enough). Currently, our contractor has placed
our hot-water radiators on the shelf under windows. My wife is convinced
that the radiators will never properly heat the rooms since heat goes up.
I believe that the room is actually warmed by being filled with heat
(otherwise, you would need radiators on all walls and even in the middle of
the room to heat the floor).

While I believe the optimal placement of the radiator would be on the
floor, the sizing of the radiator is MUCH more important, and the saving of
floor space in this case is more important that the minimal increase in
heating efficiency.

Can anyone add any comments or guidance on this issue?

tia

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  #2  
Old March 22nd 05, 03:14 PM
Joseph Meehan
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Default

Beartums wrote:
My wife and I are having a discussion about radiator placement. We
are in the process of having our basement renovated. The rooms in
the basement have an 8-inch "shelf" about a foot and a half from the
floor along the outer walls of the building (part of the footing,
since we had to dig down to make the ceilings high enough).
Currently, our contractor has placed our hot-water radiators on the
shelf under windows. My wife is convinced that the radiators will
never properly heat the rooms since heat goes up. I believe that the
room is actually warmed by being filled with heat (otherwise, you
would need radiators on all walls and even in the middle of the room
to heat the floor).

While I believe the optimal placement of the radiator would be on the
floor, the sizing of the radiator is MUCH more important, and the
saving of floor space in this case is more important that the minimal
increase in heating efficiency.

Can anyone add any comments or guidance on this issue?

tia


Time will tell, but assuming you will heat full time, then I would guess
it will work. The deeper you go the more even temperature and better
insulated the wall. Need the floor you have almost 8 foot of soil as
insulation. The wall above and just below ground will be the coldest.

At worse you may want to add some sort of fan to mix the air. It can be
a ceiling fan or a floor fan. It would not need to be large.

--
Joseph Meehan

26 + 6 = 1 It's Irish Math


  #3  
Old March 22nd 05, 04:03 PM
Edwin Pawlowski
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Default


"Beartums" wrote in message
Currently, our contractor has placed
our hot-water radiators on the shelf under windows. My wife is convinced
that the radiators will never properly heat the rooms since heat goes up.
I believe that the room is actually warmed by being filled with heat
(otherwise, you would need radiators on all walls and even in the middle
of
the room to heat the floor).

While I believe the optimal placement of the radiator would be on the
floor, the sizing of the radiator is MUCH more important,



It will work just fine. Way back in the mid 60's I worked for a major
manufacturer of heating products. Two of them were Window-line and
Sill-line systems. They are installed in buildings all over the country.
In your case, it may work better than the floor.


  #4  
Old March 22nd 05, 06:20 PM
Steve Manes
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Default

On Tue, 22 Mar 2005 13:53:32 GMT, Beartums wrote:
While I believe the optimal placement of the radiator would be on the
floor, the sizing of the radiator is MUCH more important, and the saving of
floor space in this case is more important that the minimal increase in
heating efficiency.


As you said, heat goes up, not out, so it probably doesn't make a big
difference. Most of the heat in that room will be cooler air dropping
from the ceiling (which is why ceiling fans work well even in the
winter).

I once had a basement apartment with steam heat. Since the boiler was
on the same floor but about 40 feet away, the radiators were mounted
up near the ceiling. It was the hottest apartment I ever had.

Steve Manes
Brooklyn, NY
http://www.magpie.com/house/bbs
  #5  
Old March 22nd 05, 10:21 PM
m Ransley
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Default

Radiators literally radiate radiant heat and with air convection will
heat fine. I hope a load calculation was done, the real issue is enough
btu. If you mix different types, cast iron and baseboard then you will
have an issue. But if it was planned by a pro who knows, [ many don`t],
you will be fine.

  #6  
Old March 23rd 05, 06:17 PM
[email protected]
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Default

Beartums wrote:

My wife and I are having a discussion about radiator placement... Currently,
our contractor has placed our hot-water radiators on the shelf under windows.
My wife is convinced that the radiators will never properly heat the rooms
since heat goes up...


Warm air rises, and cool air falls near exterior walls. Why fight nature?
IMO, a radiator near an exterior wall is less efficient, since it's in
slower air, since it has to fight downgoing air. It also loses more heat
to outdoors, keeping the wall warmer than a central radiator would and
making turbulent vs laminar flow near the wall, which increases the wall's
film conductance. Harry Thomason knew this, but we've mostly forgotten it.

I believe that the room is actually warmed by being filled with heat
(otherwise, you would need radiators on all walls and even in the
middle of the room to heat the floor).


Warm air rises over hot spots, slides along the ceiling to cooler spots,
drops to the floor, slides back to hot spots, rewarms and rises. Warm
ceilings radiate heat to the rest of the room with a surprisingly high
linearized conductance: 4x0.1714x10^-8(460+70)^3 = U1.

While I believe the optimal placement of the radiator would be on the
floor, the sizing of the radiator is MUCH more important, and the saving
of floor space in this case is more important that the minimal increase
in heating efficiency.

Can anyone add any comments or guidance on this issue?


We might keep a room with an 8'x8'/R16 = 4 Btu/h-F exterior wall 70 F on
a 30 F day with a central radiator that heats C cfm from 70-dT to 70 F,
where CdT = (70-dT/2-30)4 = 10-dT/8. If 70 F air flows down a 8' wide
virtual duct that extends 1' from the wall into the room and 70-dT air
flows out the bottom and C = 16.6x1x8sqrt(8dT), dT = 0.163 F, the wall
loses (70-0.163/2-30)4 = 159.67 Btu/h, ignoring the turbulent flow. A
radiator below might make it lose (70+0.163/2-30)4 = 160.33 Btu/h. No big
deal, altho the difference is larger for windows with less insulation.

OTOH, warmer walls allow lower room air temps, for the same comfort level.
A cube with 5 70 F walls and a 70-0.163/2 = 69.919 F wall and a radiant
temp of 70-0.163/2/6 = 69.986 F would need 70.0104 F room air for equal
comfort compared to 70 F air and 70 F walls, according to ASHRAE 55-2004,
so the loss from the warmer wall outweighs the gain from cooler air.

With 180 F water in 5 Btu/h-F-ft fin tube, the central radiator might have
159.67/(5(180-69.84)) = 0.29' of tube in slow-moving air near the floor.

But the bouyancy force of a column of warm air in some sort of chimney
above a tube can move air by fins at a higher velocity and raise their
water-air conductance. If a foot of fin tube has a conductance of 5 Btu/h-F
= A(2+V/2) in V = 0 mph air, its effective area A = 2.5 ft^2. (I counted 43
2"x2" fins per foot, about 2.4 ft^2, including both sides.) Fin tube near
the floor in a closet or stairwell or inside wall with an A ft^2 vent at
the bottom and top and an 8' height diff between them and a dT temp diff
from room to chimney air should make C = 16.6Asqrt(8dT) = 47Asqrt(dT) cfm
flow with velocity V = 0.01136C/A = 0.533sqrt(dT) mph, so 1' of 180 F tube
would lose (180-69.84)2.5(2+0.533sqrt(dT)/2) = 551+73.4sqrt(dT) = cfmdT
= 47AdT^1.5, ie dT = ((11.73+1.56sqrt(dT)/A)^(2/3). With a 2"x12" slot,
A = 0.167, so dT = (70.4+9.36sqrt(dT))^(2/3). Plugging in dT = 10 on the
right makes dT = 21.5 on the left. Repeating makes dT = 23.4, 23.7, and
23.7, so 2.6 mph air might come out of the top vent at 69.8+23.7 = 93.5 F,
moving 47(0.167)23.7^1.5 = 906 Btu/h of heat, so we only need 159.67/906
= 0.176' of fin tube, ie 40% less than fin tube in free air.

The closet might be a nice place to dry clothes.

Nick

  #7  
Old March 23rd 05, 06:27 PM
RicodJour
external usenet poster
 
Posts: n/a
Default

wrote:
Beartums wrote:

My wife and I are having a discussion about radiator placement...

Currently,
our contractor has placed our hot-water radiators on the shelf under

windows.
My wife is convinced that the radiators will never properly heat the

rooms
since heat goes up...


Warm air rises, and cool air falls near exterior walls. Why fight

nature?
IMO, a radiator near an exterior wall is less efficient, since it's

in
slower air, since it has to fight downgoing air. It also loses more

heat
to outdoors, keeping the wall warmer than a central radiator would

and
making turbulent vs laminar flow near the wall, which increases the

wall's
film conductance. Harry Thomason knew this, but we've mostly

forgotten it.

I believe that the room is actually warmed by being filled with heat


(otherwise, you would need radiators on all walls and even in the
middle of the room to heat the floor).


Warm air rises over hot spots, slides along the ceiling to cooler

spots,
drops to the floor, slides back to hot spots, rewarms and rises. Warm
ceilings radiate heat to the rest of the room with a surprisingly

high
linearized conductance: 4x0.1714x10^-8(460+70)^3 = U1.

While I believe the optimal placement of the radiator would be on

the
floor, the sizing of the radiator is MUCH more important, and the

saving
of floor space in this case is more important that the minimal

increase
in heating efficiency.

Can anyone add any comments or guidance on this issue?


We might keep a room with an 8'x8'/R16 = 4 Btu/h-F exterior wall 70 F

on
a 30 F day with a central radiator that heats C cfm from 70-dT to 70

F,
where CdT = (70-dT/2-30)4 = 10-dT/8. If 70 F air flows down a 8' wide
virtual duct that extends 1' from the wall into the room and 70-dT

air
flows out the bottom and C = 16.6x1x8sqrt(8dT), dT = 0.163 F, the

wall
loses (70-0.163/2-30)4 = 159.67 Btu/h, ignoring the turbulent flow. A
radiator below might make it lose (70+0.163/2-30)4 = 160.33 Btu/h. No

big
deal, altho the difference is larger for windows with less

insulation.

OTOH, warmer walls allow lower room air temps, for the same comfort

level.
A cube with 5 70 F walls and a 70-0.163/2 = 69.919 F wall and a

radiant
temp of 70-0.163/2/6 = 69.986 F would need 70.0104 F room air for

equal
comfort compared to 70 F air and 70 F walls, according to ASHRAE

55-2004,
so the loss from the warmer wall outweighs the gain from cooler air.

With 180 F water in 5 Btu/h-F-ft fin tube, the central radiator might

have
159.67/(5(180-69.84)) = 0.29' of tube in slow-moving air near the

floor.

But the bouyancy force of a column of warm air in some sort of

chimney
above a tube can move air by fins at a higher velocity and raise

their
water-air conductance. If a foot of fin tube has a conductance of 5

Btu/h-F
= A(2+V/2) in V = 0 mph air, its effective area A = 2.5 ft^2. (I

counted 43
2"x2" fins per foot, about 2.4 ft^2, including both sides.) Fin tube

near
the floor in a closet or stairwell or inside wall with an A ft^2 vent

at
the bottom and top and an 8' height diff between them and a dT temp

diff
from room to chimney air should make C = 16.6Asqrt(8dT) = 47Asqrt(dT)

cfm
flow with velocity V = 0.01136C/A = 0.533sqrt(dT) mph, so 1' of 180 F

tube
would lose (180-69.84)2.5(2+0.533sqrt(dT)/2) = 551+73.4sqrt(dT) =

cfmdT
= 47AdT^1.5, ie dT = ((11.73+1.56sqrt(dT)/A)^(2/3). With a 2"x12"

slot,
A = 0.167, so dT = (70.4+9.36sqrt(dT))^(2/3). Plugging in dT = 10 on

the
right makes dT = 21.5 on the left. Repeating makes dT = 23.4, 23.7,

and
23.7, so 2.6 mph air might come out of the top vent at 69.8+23.7 =

93.5 F,
moving 47(0.167)23.7^1.5 = 906 Btu/h of heat, so we only need

159.67/906
= 0.176' of fin tube, ie 40% less than fin tube in free air.

The closet might be a nice place to dry clothes.

Nick


An excellent example of why you should keep calculators away from
people with internet access and too much time on their hands.

All of your calculations mean nothing with respect to heating a room
evenly. Efficiency and comfort are not necessarily the same thing.

R

  #8  
Old March 23rd 05, 06:40 PM
pjm@see_my_sig_for_address.com
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Default

On 23 Mar 2005 09:27:00 -0800, "RicodJour"
wrote:

wrote:
Beartums wrote:



The closet might be a nice place to dry clothes.

Nick


An excellent example of why you should keep calculators away from
people with internet access and too much time on their hands.


Amen, my brother !

All of your calculations mean nothing with respect to heating a room
evenly. Efficiency and comfort are not necessarily the same thing.


His calculations are meaningless in EITHER domain. Nick has
one skill set, and one skill set only - piling bull**** upon bull****
upon bull****, and falsely claiming that he can 'prove it by some book
he saw'.

Oh - and writing inane little pretend-programs that suppose
and propose to support his babble.


  #9  
Old March 23rd 05, 06:47 PM
m Ransley
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Posts: n/a
Default

Nick your numbers mean nothing , Do you live in a house, have you ever
worked on one, have you ever done any heating or remodeling. Im suprised
you dont tell them to flood the floor for humidity like you have been
doing.

 




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