Stelrad - Fit for the Future - Catalog - Page 17
Delta t
The effect
of temperature
difference on
low temperature
systems
(difference in heat emitter and desired room)
Correction factor table
1.267
60
55
50
45
40
35
30
25
20
15
10
5
1.132
1
0.872
0.748
0.626
0.515
0.406
Effect on heat emitter output
0.304
0.209
0.123
0.05
0
0.2
0.4
0.6
0.8
1
1.2
1.4
Limitations in the use of correction factors for low temperature systems.
It is true that the above correction factors apply when considering the relative sizes of a heat
emitter (panel radiator) when applied (in similar circumstances) to systems operating at
varying temperature differences (Delta t).
However, it is a comparator only. To ensure that the heat emitters provide the correct comfort
levels and work in a way that is consistent with both the building and the heat pump it is
important that the heat transferred to the environment (heat loss) is properly calculated. Both
the heat generator (heat pump) and the emitters (radiators) are selected with a suitable output
in accordance these calculations (heat losses).
Comparison of radiator size and outputs at Delta t 50 and Delta t 40
The following examples demonstrate how the size and surface area of a radiator need to increase
to achieve the desired output (BTU) of a radiator at Delta t 40 compared to a Delta t 50 output
that is achieved by a traditional boiler.
The correct output of a radiator at a lower Delta t (20 or 30) can be calculated by contacting an
MCS accredited installer, who will work out the correct size of radiator to suit your space.
As the Delta t ( temperature difference) can be half that of a boiler
when the flow temperatures of a heat pump are considered then
more than twice as much emitter (heat exchanger) surface area is
required. The heat emitter needs to be physically larger.
Example 1
RADIATOR AT DELTA T 50
Adjustment factors for a range of temperature differences
between the emitter (in this case a panel radiator) and
air in the living space (Delta t) is shown below.
Height
Length
Type
BTU
600
400
K2
2,365
Example 2
RADIATOR AT DELTA T 40
Height Length
RADIATOR AT DELTA T 50
RADIATOR AT DELTA T 40
Type
BTU
Height
Length
Type
BTU
Height
Length
Type
BTU
K2
2,652
600
800
K2
4,730
600
1100
K2
4.863
5,006
600
600
700
600
K2
3,005
700
1100
K2
700
600
P+
2,344
700
1400
K2
5,468
300
1000
K3
3,443
700
700
K3
4,844
1600
300
K2
2,780
1800
500
K2
5,053
At Delta t 40 the the surface area of the radiator needs to be larger. The surface area is determined
by height, width and the depth of the radiator. Here are a couple of examples.
Example 1
DELTA T 50
BTU : 2365
DELTA T 40
BTU : 2652
DELTA T 50
BTU : 4,730
H: 600
Type K3
>>>
W: 600
H: 1800
H: 700
>>>
16
DELTA T 40
BTU : 4,844
Type K2
Type K2
H: 600
W: 400
Type K2
Example 2
Type K2
H: 600
DELTA T 40
BTU : 5,053
W: 800
>>>
W: 700
W: 500
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