Danfoss Cold Store Protection Systems Application guide

Cold Store Protection Systems

Cold Store
Protection Systems

Application manual

Intelligent solutions
with lasting effect

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Index

Let DEVI do the work

General information 4

1. Frost heave prevention system 5

2. Protection against
condensation on floors 13

3. Freeze protection of
doors and gates 16

4. Frost protection of
pipes in cold stores 19

5. Frost protection of
drain lines of cooling equipment 23

6. General installation guide 24

7. Case story 28

DEVI - an abbreviation of Dansk El-Varme Industri - was established in
Copenhagen, Denmark, in 1942. As from January 1st 2003 DEVI has become
a part of the Danfoss Group - Denmark's largest industrial Group. Danfoss
is one of the world's leading companies within heating, cooling and air­conditioning. The Danfoss Group has more than 23.000 employees and
serves customers in more than 100 countries.

DEVI is Europe’s leading brand of electrical cable heating systems and electric
pipe heating systems with over 70 years of experience. The production of
heating cables takes place in France and Poland while the head office is
situated in Denmark.

Cold stores, Ice stadiums and alike

This design guide presents DEVI’s recommendations for design and
installation of frost heave prevention systems and frost protection for
cold room doors, drain lines, and fire protection sprinklers and pipes. It
provides guidance for a heating cable layout, electrical data and system
configurations.

Following DEVI’s recommendations will ensure energy efficient, reliable and
maintenance free solution for constant wattage heating cables with 20 year
warranty.

Our quality management
system
and compliances

ISO 9001 TS 16949

ISO 14001 PED

Along with full compliance with EU

directives and product approvals

General
information

In cold stores, ice stadiums, etc. the
temperature is always within the
range of –20 and –30 °C, however
cold leak occurs even if the floor
is insulated properly. This means
that materials which are in contact
with the soil, such as foundation
and floor areas, will absorb the cold
and let the ground freeze. Water,
contained in the soil, will change
volume when turning into ice and
can cause substantial damage due
to frost erosion.

Furthermore, in areas where very
cold dry air meets warm moist
air, the moisture contained in the
warm air flow may settle on the
cold surface and turn into ice. Ice
conduces unwanted freezing of
elements such as cold store doors/
gates or door frames and can cause:
damage to the door structure,
weather stripping, disabling closing
the door tightly and leading to
increased energy consumption, etc.
Another problem, that occurs in a
drainage system of refrigeration
equipment, is condensation
freezing and inability of free water
flow.

DEVI offers reliable and energy
efficient cable heating systems to
prevent frost heave and ensure
frost protection of doors drain
lines and firefighting piping. DEVI
has supplied various range of such
systems to 5 continents over many
years.

Benefits

• Eliminate risk of foundation damage – ice buildup

in the foundation, which can result in problems
such as: uncontrolled movement or elevation of
the building foundation causing damage to the
construction. DEVI prevents frost heaving damage
in commercial freezers & ice stadiums by eliminating
the possibility of such ice buildup.

• Investment safety – reduces the possibility of cold
storage stock loss or destruction of the building due
to the damaged foundation.

• Reduced energy loss - smooth operation of doors,
protects the construction and prevents energy loss
through untightly closed doors.

• Safety of working environment - prevents slippery
floors and ensures frost protection of firefighting
pipes and sprinklers.

• Power saving solution – DEVI uses Advanced
Controls to ensure power saving by: minimizing
running time of the system, while maintaining the
appropriate foundation temperature to prevent its
freezing.

• Space saving – as compared to alternative
solutions, DEVI system is less complicated, easier for
planning & installation and requires no extra space.

• Lower initial costs – competitive solution with
over 50% lower cost of the system, comparing to
Pumped Fluid solution (Glycol) in pipes built into
the foundation.

• No Environmental Concerns – DEVI electric
heating systems do not pose any environmental
hazards, e.g. glycol leak into the soil. DEVI systems
use electric heating cables instead of glycol-water
mixture.

• Lowest ownership costs - 20 years of full warranty
from Danfoss Group and 50 years of expected
lifetime for all DEVI serial resistive heating cables.

4 Application manual · Cold Store Protection Systems · VGLUB102 · ©DEVI

1. Frost heave prevention system

1.2. System Description

The main object of heating, in the
Frost Heave Prevention System,
is to provide frost protection of
foundation in premises where
temperature is constantly
maintained below zero (cold
storages, ice stadiums, etc.).

Installation of an indoor frost
protection system is required
and electrical heating cables
embedded in concrete is a
solution to prevent frost heaving.
Frost heave can cause floor slab
cracking, damage to support
structures and foundations. In
such cases underfloor heating is
needed in order to avoid freezing
or other related problems and
prevent destruction of foundation
structures.

Frost Heaving

As the soil temperature under
a freezer drops below zero,
the moisture contained in the
soil freezes up and expands
significantly.

This ice formation results in
floor cracking and its change of
elevation or “heaving”.

Ice formation can lift up columns,
push over foundation walls
and rip open roofs. Almost all
components of the cold store can
be repaired, whilst the major part
of space is still used for storage,
but this doesn’t apply to the floor.

The problem cannot be solved by
insulation alone.

The heating cable in this case
is located below the main floor
insulation of the cold storage,
typically in the sand backfill or in
concrete screed.

For safety reasons: two identical
parallel heating systems should be
installed (main and reserve).

5Application manual · Cold Store Protection Systems · VGLUB102 · ©DEVI

1.2. Products

Heating cables

To prevent ground freezing the
heating system may include the
following resistive (constant wattage)
heating cables:

DEVIflex™ 6T, DEVIflex™ 10T,
DEVIflex™ 18T;
DEVIbasic™ 10S, DEVIbasic™ 20S.

DEVI resistive heating cables allow
safe, efficient and economical cold
store installation.

Note. The number at the end of the
cable’s name refers to its specific
output in W/m, at voltage of 230 V
or 400 V. Letter “T” means twin
conductor cable (Twin), letter ”S” –
single-conductor cable (Single).

DEVIflex™ is a twin conductor heating
cable for installation in concrete
floors, pipe heating etc. The cable
complies with IEC 60800:2009 class
M2, and is designed for applications
with the high risk of mechanical
damage. It is supplied in readymade
sets with 2,3 m cold lead (supply
cable), sealed joints and end muff.

Cable diameter is Ø 6,9 mm.

The cable is available for 230 V power
supply.

Cables of 6, 10 or 18 W/m (230 V)
linear output are available.

Available cable length:
DEVIflex™ 6T: 30 - 200 m;
DEVIflex™ 10T: 2 - 210 m;
DEVIflex™ 18T: 7 - 170 m.

DEVIbasic™ is a single conductor
heating cable complying with
IEC 60800:1992 and intended for
installation in concrete floors, for
pipe heating etc. It is supplied in
readymade sets with 2x3 m cold
leads and sealed connection muffs.

Cable diameter is Ø 5,5 mm.

DEVIbasic™ 20S is available for 230 V
and 400 V power supply voltage.

To decrease linear output (W/m) the
400 V cable can be connected to 230 V
means – in this case the cable linear
output is 6,6 W/m.

Available cable length:
DEVIbasic™ 10S, 230 V: 21 - 407 m;
DEVIbasic™ 20S, 400 V: 56 - 229 m.

Fixing

In case of heating cables application,
it is recommended to use fitting
bands to fix the cable to the floor,
e.g. DEVIfast™ metal galvanized
fitting band. It should be attached
to the floor (e.g. nailed down) in
parallel lines usually at intervals of
100 cm or using one meter of fitting

DEVIflex™ DEVIbasic™

band per each square meter of cable
installation. The same applies to
DEVIclip™ C-C and Montagestege™
plastic bands.

For quick cable fixing to reinforced
mesh DEVIclip™ Twist plastic fixing is
recommended.

For cable fixing to metal columns etc.
Alutape adhesive aluminum tape is
recommended.

6 Application manual · Cold Store Protection Systems · VGLUB102 · ©DEVI

Thermostats

For control of Frost Heave Prevention
System the DEVIreg™ 330 (-10…+10 °C)
thermostat with DIN rail attachement
is recommended. Additionally a wall
mounted DEVIreg™ 610, IP44 can be
used.

All thermostats are equipped with
wire temperature sensors –
NTC 15 kOhm @ 25 °C with 3 meter
long cable.

DEVIreg™ 330 DE VIreg™ 610

To provide correct temperature
measuring the sensor cable should
be of e.g. 10 m, to measure the
temperature in the heated area
(depends on the local conditions). 10
m long sensor is available, but needs
to be ordered separately.

Note! For safety reasons: installations
in cold storages should contain
two independent circuits (main
and reserve) controlled by separate
thermostats.

Products - general overview of Frost Heave Prevention Systems

Product Options Description

DEVIflex™
Resistive heating cable

DEVIbasic™
Resistive heating cable

DEVIbasic™
Resistive heating cable

Assembly kits

DEVIreg™ thermostat DEVIreg™ 330 (-10…+10 °C) -10…+10 °C, 16 A, IP20, DIN rail

DEVIreg™ thermostat DEVIreg™ 610

Temperature sensor 10 m, PVC

Temperature sensor 40 m, silicone covered

Fixing

Fixing DEVIclip™ Twist

Fixing Alutape

DEVIflex™ 6T, 230 V;
DEVIflex™ 10T, 230 V

DEVIbasic™10S, 230 V;
DEVIbasic™20S, 400 V

DEVIbasic™ on drum,
0,0134 - 34,1 Ohm/m

DEVIcrimp™ assembly kit
DEVIcrimp™ CS2A/CS2B

DEVIfast™ Metal
DEVIclip™ C-C
Montagestege™ 6 mm
Montagestege™ 8 mm

Twin conductor, 100% screen.
6, 10 W/m (230 V).
DIN IEC 60800:2009 M2

Single conductor, wire screen.
10 W/m (230 V), 20 W/m (230 V/400 V).
DIN IEC 60800:1992 M2

Single conductor, wire screen.
Max. 20 W/m; max. 400 V.
DIN IEC 60800:1992 M2

For single conductor cable.
For twin conductor cable

-30…+50 °C, 10 A, IP44,
on wall/pipe installation

Wire sensor, Ø 8 mm, IP65,
NTC 15 kOhm @25 °C

Wire sensor, Ø 5 mm, IP67,
NTC 15 kOhm @25 °C

25 m pack; galvanized metal, fixings every 2,5 cm.
10 x 1 m; plastic, fixes cable Ø every 1 cm.
1 m; plastic, fixes cable Ø 5,6-6,5 mm every 2,5 cm.
1 m; plastic, fixes cable Ø 6,6-8 mm every 2,5 cm

Bag with 1000 pcs.;
Ø 17 mm; fixing cable to reinforced mesh

Glued aluminium tape 38 mm x 50 m;
0,06 mm; max. 75 °C

For details please refer to the DEVI Catalogue.

7Application manual · Cold Store Protection Systems · VGLUB102 · ©DEVI

1.3. System design

The heating cable for the Frost Heave
Prevention System is located under
the main floor insulation of the
cooling facility, typically into sand
backfill or concrete screed (fig. 1 and
fig. 2).

Heating cable should be placed
under the insulation layer of the
floor to offer frost protection. Cables
should be placed directly on top of
the hardened concrete only, as an
option can also be separated from
the floor surface with the damp
proof membrane. The cables should
be installed at least 5 cm below the
insulation. The floor construction
must comply with local norms and
regulations.

Installed output

Under normal conditions calculated
values of heat loss aren’t very high,
e.g. 3-8 W/m² only. However it is
recommended to use 15-30 W/m²
as a standard value or at least 15 W/m²
for frost protection installations. In
any case an output value should
be calculated and correspond to
downward heat loss.

The foundation cooling rate
depends on:

• the rate of heat/cold emission
through the floor;

• soil/ground temperature;

• interior temperature of the cold
room or surface temperature of ice
stadiums etc.

Floor in cold store Floor in cold store

Reinforced concrete Reinforced concrete

Thermal insulation Thermal insulation

Concrete

Concrete

DEVIfast™ fitting

Sand backfill

Sand backfill

Reinforced mesh

Ground Ground

Fig. 1 – Heating cable in in the concrete screed Fig. 2 – Heating cable in the sand backfill

To estimate the required power
density in [W/m²] of the freeze
protection system, the thermal

Heating system output can be
determined from the following

formula:
resistance of multilayer floor
construction should be calculated.

P = Δt · U · 1,3 [W/m²],
While comparing actual values of all
layers the thermal resistance of each
layer, except the insulation layer,
should be neglected.

where

Δt – the temperature difference

between ground/soil and cold store

interior [°C];

U – the floor heat transfer factor,

typically for insulation only [W/m²·°C];

1,3 – safety factor.

For insulation U value can be

determined as follows:

U = λ/δ = (thermal conductivity

coefficient [W/m·K]) / (thickness [m])

Calculation example

A cold store has the following
parameters:

Cold store temperature: -25 °C.

Ground temperature: +5 °C.

Insulation: 0,2 m thick,
λ = 0,04 W/m·°C.

8 Application manual · Cold Store Protection Systems · VGLUB102 · ©DEVI

The U-value of the insulation:
U = 0,04 / 0,2 = 0,2 W/(m²·°C).

Δt = +5 °C - (-25 °C) = 30 °C.

Calculation of heating system output
per square meter:

P = 30 °C · 0,2 W/(m²·°C) · 1,3 =
= 6 W/m² · 1,3 = 7,8 W/m².

Output calculation is 7,8 W/m², but as

per recommendations, the installed

minimum should be 15 W/m²!

For example, three lines of DEVIflex™ 6T

per m² provide 18 W/m² output and

ensure cold store protection against

frost heaving.

C-C distance

There must not be any subzero
temperature gaps between the
heating cable lines! Otherwise it will
not prevent frost heave!

The temperature distribution in
geometry of cold store floor has to be
evaluated. The result depends on a
number of parameters, the main are
the following:

• thermal conductivity of the
ground;

• linear output of the heating cable;

• C-C distance.

The thermal conductivity of the
soil may vary significantly during
operation, hence in practice following
simplification rule is often used:

to ensure even heat distribution
with no cold gaps the maximum
central-central distance (C-C
distance) between the heating
cables should not exceed 50
cm (fig. 3). In other words, an
installation of minimum 2 meter
heating cable per m², is necessary.

C-C ≤ 50 cm

Fig. 3 – Heat/cold distribution and max C-C without cold gaps

It's very strongly advisable to always
place a second supplementary cable
loop with the same C-C distance.

For installations with max. C-C
distance of 50 cm power output
per 1m² for some cable types is the
following:

DEVIflex™ 6T – 12 W/m²;
DEVIflex™ 10T – 20 W/m²;
DEVIbasic™ 20S, 400 V connected to
230 V – 19,8 W/m².

Recommendations: the preferred
C-C distance between cable lines
is 33 cm. It allows implementation
of a simple rule for cable length
calculation – 3 m of cable per 1 m².

For example three lines of DEVIflex™
6T per 1 m² provides 18 W/m² (230 V)
output. It is applicable for almost all
types of cold stores, ice stadiums etc.

Minimum requirement: 10 W/m
cable should be installed with a C-C
distance of maximum 50 cm.

Safety

For safety reasons two identical
heating systems should be installed
in parallel – the main and the reserve
one.

Elements for such system are
following:

• two identical parallel circuits of
heating cable (main and reserve);

• two identical thermostats with
temperature sensors for each
cable;

• alarm signals in case of reserve
cables operation – light and
acoustic alarm;

• two separate power supply lines;

• separate fuses, RCD relays,
contactors, etc.

Please note that the reserve cable
system is obligatory for this type
of installations. Reserve cables are
usually mounted in parallel to the
main cable with a distance of
2,5-5 cm, to the primary system.

2,5-5 cm

Main cable

Reserve cable

The C-C distance is determined as a
median line between the main and
reserved cable, see fig. 4.

Note! One thermostat per heating
cable should be installed.

C-C C-CC-C

Fig. 4 – Main and reserve heating cables

9Application manual · Cold Store Protection Systems · VGLUB102 · ©DEVI