Danfoss Planning Underfloor Heat Compendium

MAKING MODERN LIVING POSSIBLE

Planning Underfloor Heat

DANFOSS HEATING SOLUTIONS Handbook

Handbook Planning Underfloor Heat

Planning criteria

Standards for
underfloor heating

Essential requirements for all calculations:

• Detailed plan of building, construction of outer
walls, and size and type of windows.
These data are essential for calculation of the
heating load in accordance with EN 12831.

• Information on the type of ooring and its

thermal resistance R

dependent on the oor construction, particularly

, since the heat output is

λ,B

that over screed (in accordance with EN 1264 a

thermal resistance of R

living rooms is specied, in bathrooms R

m2 K/W. Other values up to a maximum of 0.15
m2 K/W are to be separately agreed.) R
m2 K/W.

= 0.1 m2 K/W R

λ,B

λ,B

for

λ,B

= 0.0

λ,B

= 0.0

• Building plans, building drawings and all room
data have to be shown. After the calculations,
the pipe layout and data are included in the
building plan.

• Danfoss forms for calculations.

The following standards have to be observed when
planning and installing oor heating:

EN 1991 Action on structures

EN 1264 Underoor Heating, Systems and

Components

Changes in building methods over the last few
decades have brought about lower requirements
for heating homes, so that Danfoss underoor
heating can meet respective heating requirements
for even physiologically acceptable surface tem­peratures. In some rooms, such as bathrooms,
additional heating may be necessary, as areas
under bath and shower cannot be heated and
a higher temperature is required (24° C instead
of 20° C). In such rooms the underoor heating
maintains the temperature in the oor while other
heat comes from sources such as wall heating,
heated towel rails, etc.

EN 13813 Screed Material and Floor Screeds

Local building regulations.

Professional information on interface

co-ordination when planning heated
underoor constructions (ref: BVF).

Estimated
pre-calculations

DIN 4109 Sound Insulation in the Building
Industry

ISO EN 140-8 Measurement of sound insulation
in buildings and building elements

The output tables of Danfoss SpeedUp and Basic
heating systems show output values for various
room temperatures as well as the temperatures of
the central heating water in relation to dierent
oor nishes. These tables give calculations of the
mean central heating water temperature with
which to run the underoor heating in order to
achieve the desired output.

EN 1264 is crucial for the construction of under­oor heating. With the inclusion of EN 13813

‘Screed Material and Floor Screeds’ three Basic

Danfoss constructions are possible.

The required excess heat source temperature
determines the supply temperature which is
described in more detail in the chapter ‘Calculating
the supply Temperature’. The heat ow densities
are distributed evenly over the edge and comfort
zones. The main central heating water tempera­ture is determined by the type of installation (see
output tables).

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max 29°C

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Handbook Planning Underfloor Heat

Standard heating load of
an underfloor heated
room

Thermal insulation to
avoid downward heat
loss

When making calculations for Danfoss underoor
heating the standard heat load Q
essential. For underoor heating in multi-storey

of the room is

N,f

buildings the heat gain of the shared oor can be
included into the calculations if there are no
restrictions on the work.
The heat output QH is generally calculated from
the standard heat load of an underoor heated
room Q
accordance with EN 4701 Part 3.

plus an extra calculation allowance in

H,f

QH = (1 + x)* Q

N,f

It is important to consider the thermal resistance
of the insulation below the underoor heating so
that the heat of the underoor heating radiates
mainly upwards.
In accordance with EN 1264, Part 4 there are three
dierent kinds of oor/storey constructions and
various minimum heat resistances.

Thermal Insulation R

A above rooms with similar use 0.75 m2 K / W

B above rooms with dierent

use*, unheated rooms (e.g.
cellar) and on ground oor

C above external air (-15°C) (e.g.

garages, passage ways)

* e.g. rooms above commercially used premises

1.25 m

2.00 m

Ins, min

2

2

K / W

K / W

Q

: Standard heating load of an underoor

N,f

heated room [W]

QH: Heat output calculation

If the heating system, such as an underoor
system, can raise the heat output by raising the
heat source temperature the extra allowance is is
zero. Thus the calculated temperature output
equals the standard heat load of an underoor
heated room.

The heat resistance R

layer is calculated as follows:

R

with a single insulation

λ.ins

S

=

λ,ins

λ

ins

ins

with:
S

: eective insulation thickness [m]

ins

λ

: thermal conductivity [W/m K]

ins

Maximum surface
temperature Θ

Fmax

Fluctuation in
temperature (W)

In accordance with EN 1264 maximum surface
temperatures for phsysiological reasons are set

as follows:

Comfort zone: 29° C
Edge zone: 35° C
Bathrooms: ti + 9° C = 33° C

Standard room temperatures of 20 or 24° C
in bathrooms result in a dierence in surface

The position of the heating pipe can further
inuence the output. Depending on the position,
varying surface temperatures can occur. Output
is higher above the pipes than in between. The
dierence between the maximum and minimum
surface temperatures is called uctuation (W).

W = θ

F max

- θ

F min

Larger distances between pipes cause larger
uctuation. Lower lying pipes slow down the heating
sy stem but the ‘ long w ay’ to the sur fac e dis tribu tes
the temperature evenly, the uctuation remains
small. Since the maximum oor temperature must
not be exceeded, larger uctuation causes greater
loss in output than a smaller uctuation. In the rst

temperature and room temperature of 9K (in
comfort zones and bathrooms) or 15K (in edge
zones). Limiting the surface temperature has
the eect of limiting the heat output of the
underoor heating. It is an important factor when
deciding whether to choose additional heating.
However, with modern insulation the heat output
in underoor heating is sucient in 99 of 100
cases.

case, average oor temperature is signicantly lower
than the maximum permitted temperature.

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Handbook Planning Underfloor Heat

1 2 5 20 K

W/m²

200

100

50

30

20

10

Characteristic base line

The Characteristic base line shows the relation­ship between the heat ow density and the
surface temperature (surface temperature minus
room temperature) when the heated area is
evenly heated (uctuation = 0).

Heat output q

Mean surface temperature difference

With a surface temperature of 9K above room
temperature an output of approx. 100W/m2 is
achieved, with an excess temperature of 15K a
heat output of approx. 175 W/m2.

Since the characteristic base line has idealised
physical parameters and is valid independent of
the system, no system, kept at the maximum
permitted surface temperature, can reach an
output of more than 100 W/m2 or 175 W/m2 in
edge zones.
Consequently the specic heat output q of the
oor surface depends on the dierence between
room and surface temperatures as well as the
transferability. The latter is dependent on the
room data, including the needs to air the room
and is described as heat transfer coecient α
here 11.1 W/m2K.

q = α

(θF - θi)

ges

ges

θF = Floor temperature °C

θi = Room temperature °C

Example:

At a room temperature of 20° C and a oor
temperature of 27° C a heat output of

q = 11.1 W/m2 K * 7°K (27° C - 20° C)
= 77.7 W/m2 would be achieved.

Heat source temperature

Installation types

The mean heat source temperature is a rm
component of many calculations. It is calculated
from the mean value of the supply and return
temperatures:

θm = θi + Δθ

H

The heating system Danfoss Basic comprises two
dierent installation types in edge zones and
three in comfort zone areas.

System Possible pipe distance in cm

BasicRail 8.8 (mean)

BasicRail 12 (mean)

BasicRail 20

BasicRail 25

BasicRail 30

BasicGrip and BasicClip 10

BasicGrip and BasicClip 15

BasicGrip and BasicClip 20

BasicGrip and BasicClip 25

BasicGrip and BasicClip 30

SpeedUp and SpeedUp Eco 12.5

SpeedUp and SpeedUp Eco 25

with:

ΔθH: Excess Heat Source Temperature

θi: Standard - Inside Temperature
θm: Heat Source Temperature

The SpeedUp and SpeedUp Eco heating systems
has installation types for the edge and comfort
zones. They dier in pipe distance.

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Handbook Planning Underfloor Heat

Heat output curve
Limiting curve

Calculated heat flow
density

The heat output and the uctuation of the surface
temperature are dependent on several factors:

• Floor surface temperature

• Room temperature

• Pipe distances

• Thickness and thermal conductivity of the
load bearing panels

• Lateral heat output

• Thermal resistance of oor nish

• Composition of the layers

In accordance with EN 1264 all factors combine
into the following equation heat ow density q:

q = KH + Δθ

H

with:

q: Heat output [W/m2]

KH: Equivalent heat transfer coecient [W/m2 K]

(ocial DIN check)

ΔθH: Excess heat source temperature

When doing the calculations for underoor
heating, the calculated heat ow density is to be
worked out as follows in accordance with DIN EN
1264, Part 3 :

Q

q

=

des

N,f

A

F

with:
q

Calculated heat ow density [W/m2]

des

Q

Standard-heat load of an underoor heated

N,f

room [W]

AF Floor area to be heated [m2]

The heat output achieved from underoor
heating is

QF = q * A

F

with:

Δθ

H

θ

- θ

=

V

R

- θ

θ

V

θR - θ

i

i

In

with:
θV: Supply temperature
θR: Return temperature
θi: Standard-inside temperature

When keeping to maximum permitted tempera­tures, the above factors will give, apart from
uctuation, limiting curves (calculated according
to EN 1264, Part 2). The intersections indicate the
heat ow limits and the limits to excess heat
source temperatures.

The data for the heat ow densities of the edge
zones or comfort zones qR and qA can be calcu­lated from the output diagrams where the excess
temperature of the heat source applies.
The approved threshold of the heat ow density
(intersection of curves with limiting curve) must
not be exceeded. The approved density depends
on the thermal resistance of the oor covering
and the construction type.
If one value of the calculated and distributed heat
ow density (qR/qA) is above the threshold heat
ow density, the threshold density rather than the
heat ow density applies. The resulting decrease
in excess heat source temperature also reduces
the heat ow density of the other combination
type of installation.
If the standard heat load of a room heated with
underoor heating is greater than the heat output
of the underoor heating, additional heating for
the shortfall should be considered. Q

N,f

- QF.

with:
q

Calculated heat ow density

des

Q

Standard-heat load of an underoor heated

N,f

room

AF Floor area to be heated

where q is evenly distributed over the edge zone
(maximum 1 m wide) and the comfort zone:

A

R

q =

VGCTC202 © Danfoss 06/2009

A

* qR+

F

A

A

* q

A

A

F

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Handbook Planning Underfloor Heat

Calculation of excess
supply temperature

The calculated supply temperature for a room
with the highest calculated heat ow density is
assigned q
thermal resistance for oor cover of R
K/W. Higher values for R
account. Bathrooms will have R
The dierential temperature σ for the room to be

(except bathrooms) and given a

max

have to be taken into

λ,B

λ,B

= 0.0 m2 K/W.

λ,B

= 0.10 m2

calculated is dened as σ = 5 K. The installation
type is chosen so that q max fully achieves the
threshold heat ow density indicated in the
limiting curve. The maximum permitted excess
ow temperature is

Δθ

V, des

≤ Δθ

when

H, des

+

σ

Δθ

σ

2

≤ 0.5:

H

with Δθ

H, des

≤ Δθ

H, G

otherwise:

Δθ

V, des

= Δθ

H, des

σ

+

+

2 (12 Δθ

2

σ

)

H, des

In all other rooms which are operating on
calculated ow temperatures the dierential
temperature is calculated as follows, as long as

the relation:

σ

j

< 0.5

Δθ

H, j

is:

Δθ

: Excess heat source temperature of each room j

H,j

with:

σ j = 2 * [(Δθ

V, des

) – Δθ

]

H,j

otherwise:

4(Δθ

- Δθ

σ j = 3 * Δθ

*

H, j

[√

1+

V, des

3 * Δθ

)

H, j

-1

H, j

]

Calculation heat source
temperature

For calculating the size of the circulating pump
the mass ow rate is determined as mH (ow rate
of heating water in kg/s). It is independent of the
total output (oor heating output, and heat losses
to other rooms) as well as dierential temperature.

mH =

* q

A

F

σ * C

R

1 +

(

W

R

- θ

θ

o

i

q * R

u

)

u

+

u

with CW = 4190 J/kgK

The partial heat transfer resistance of the oor

construction Ro (upwards) encompasses both the

thermal conductivity and thermal resistance
upwards:

1

Ro =

with1= 0.093 m2 K/W

+ R

α λ

α

S

u

+

λ ,B

u

The sum of the downwards thermal conductivity
and downwards thermal resistances is:

Ru = R

λ, ins

with R

+ R

λ, oor

= 0.17 m2 K/W

α, oor

+ R

λ, render

+ R

α, oor

The mass ow rate mH can also be expressed
when converted as the ow rate VH:

m

VH =

with ρ = 0.998 kg/dm

H

ρ

3

To determine the ow rate of a heating circuit the
ow rate of the room VH must be divided by the
number of heating circuits:

V

VHK =

Number of heating circuits

H

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Handbook Planning Underfloor Heat

Pressure loss

For the calculations and size of the circulating
pump it is important to calculate pressure loss. In
order to calculate pressure loss the total length of
the pipes IHK and supply and returns have to be
determined. Here it is important that the length
of the supply and return pipes FEED is double the
distance of room to manifold (supply and return).
Depending on the laying type the following

values are relevant:

lH = Pipe length of edge zone layout plan * AR

+ Pipe length of comfort zone layout plan * A

The mean length of the heating circuit IHK is
calculated thus:

I

IHK = FEED +

Here it must be mentioned that the area layout
and the number of heating circuits are determined
by the type of screed, i.e. the heating circuits must
be compatible with the screed sections.

Number of heating circuits

(

H

A

)

The pressure loss diagram (cf. pressure loss
diagram for Danfoss composite pipe) shows, via
ow rate per heating circuit V
resistance as pressure loss Δp per m. To calculate
the total loss of a heating circuit, this value has to
be multiplied by the length of the heating circuit.

ΔpHK = Δp * l

Individual heating circuits have dierent lengths
and dierential temperatures and show dierent
loss of pressure. Pressure compensation ensures
that all heating circuits are supplied with
sucient water. The ow adjustment is made on
the return valve by determining the ow per
minute (i.e. the volume ow [l/h] of the individual
heating circuits is divided by 60 [min.]).

The total water volume within an underoor heat­ing system is calculated by the length of all
heating circuits IHK multiplied by a factor of 0.113
(l/m).

, the pipe friction

HK

HK

Correlation between flow
rate, pressure loss and
differential temperature:

Threshold values

The smaller the dierential temperature:

• the higher the volume ow

• the higher the ow speed of the medium and

• the higher the pressure loss

• The maximum supply temperature must not
exceed 55° C for wet cement and calcium
sulphate (CAF) screed

• Heating circuits should not be longer than

100 m, 110 m maximum.

• The optimum length is 120 m.

• Pressure loss of 250 mbar must not be
exceeded since the circulating pump, apart
from maintaining the pressure head, has to
cope with pressure losses in the heating
circuits and in the whole system (in manifold,
its valves, supply and return pipes, mixing
valves, etc.).

• The maximum supply must not exceed 50° C

for gypsum plaster.

Raising the dierential temperature causes a
reduction in ow rate.

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Handbook Planning Underfloor Heat

Floor Heating
Quick Planner

Quick and easy dimensioning of the floor heating system

The proper dimensions for oor heating systems
can be calculated in a matter of minutes by using
the Internet-based Danfoss Floor Heating
Dimensioning Programme.
With a few, basic inputs, this easy-to-use software
will provide all the necessary information regarding

system design, product selection, and commis­sioning. This makes the Danfoss Floor Heating
Dimensioning Programme a very valuable tool in
both the bidding and the implementation phases.

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VGCTC202 © Danfoss 06/2009