Danfoss Domestic Hot Water Application guide

Domestic hot water

Domestic Hot Water

Application guide

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Table of content

Our quality management
system
and compliances

Along with full compliance with EU

directives and product approvals

ISO 9001 TS 16949

ISO 14001 PED

Let DEVI do the work

1. Application overview 4

2. System Description 5

3. System design 7

3.1 Heat loss calculation 7

3.2 Product selection 9

3.2.1 Heating cable selection 9

3.2.2 Thermostat/Controller
selection 11

3.2.3 Accessories selection 14

4. Safety instruction 18

4.1 DO's 18

4.2 DON'Ts 18

5. Case stories 19

6. Technical support 19

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 electric cable heating systems and electric
pipe heating systems with over 70 years of experience. The development of
electric floor heating system takes place in Denmark, where the head office
is situated while heating elements (cables and mats) are manufactured by
Danfoss in EU.

Domestic Hot Water temperature

maintenance system

This design guide presents DEVI’s recommendations for design and
installation of Domestic Hot Water system. It provides guidance for a heating
cable layout, electric 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, self-limiting heating cables with 5 years of warranty.

1. Application
overview

Modern living requires buildings to
have hot water available whenever
and wherever needed – and prefer­ably immediately. The building regu­lations demand domestic hot water
systems to ensure best comfort and
efficiency as well as the Legionella
control measures.

DEVIhotwatt™ systems ensure con­tinuous and reliable supply of with
the possibility to disinfect Domestic
Hot Water (DHW). DEVIhotwatt™ is
a self-limiting heating cable that is
used for temperature maintenance of
hot water supply.

DEVIhotwatt™ systems compliments
domestic hot water systems and enables
the unique possibility to temperature
control and disinfect, both for circula­tion systems and uniquely also for single
pipe systems from source to tap.

DEVIhotwatt™ systems complies with
IEC 62395-2:2013.

Benefits

• Unique opportunity - allows the installation
of a single pipe hot-water system, that includes
thermally controlled and disinfected hot water
at the tap.

• Lower initial investment the electric
pipe tracing in DHW system without
circulation requires less pipes and insulation
(approximately 50%), less valves, less pumps
and installation labor compared to the
recirculating system.

• DEVI pipe tracing systems ensure hot water
in all taps and savings when a circulating pipe
system is unnecessary.

• DEVI heating cable reduces water waste as you
can get hot water immediately.

• Protection against Legionella – DEVI system
maintains water supply at the required
temperature level and provides disinfection to
combat the bacteria.

• DEVIhotwatt™ system is the Perfect solution
to be used in domestic hot water systems.
Including systems supplied by low temperature
district heating.

• Energy efficient - Self limiting heating cables
provide power where needed, adapting their
output according to the ambient temperature.
Less pipes and smaller boilers will in term mean
lower heat losses.

• The heating cable is flexible and easy to
install as it can be cut to length, right on site
and installed directly on the pipe system.

4 Application guide · Domestic hot water · ©DEVI

2. System Description

DEVI Pipe tracing systems
will be required in the
following cases:

• Low-temperature, heat
source is supplying DHW
at lower than 50 °C

• The ambient
temperature variation is
significant

• Tap is located so far
away that the hot water
temperature is not
properly maintained

1800

1600

1400

1200

1000

Since 1998 the EU Drinking Water
Directive (98/83/EG) in EN 806-2
has established standards for hot
water in pipes that should not drop
below 50 °C. The building regulations

as well as global trends are demand­ing DHW systems to provide the best
comfort, energy efficiency and the
Legionella mitigation measures.

General design principles aim to
provide uniform water temperature,
which should also enable tempera­tures to combat Legionella growth.

The general recommendation for
DHW is to maintain the heat source
temperature between 50-60 °C
(IEC 62395-2:2013).

Water heating is provided by central­ized or decentralized sources, Central­ized water heating systems (district
heating) often have large distribution
network that might contribute to
temperature inconsistencies.

Accord­ing to IEC 62395-2:2013 guidelines:
”For disinfection purposes min 55 °C
is typically required for hot water in­stallations fitted with mixing valves”.

In the case that the water temperature
of DHW systems cannot achieve the
recommended level, risks of possible
water waste and Legionella will arise,
therefore a supplementary electrical
tracing system is recommended.

The Legionella bacteria which is com­monly found in many types of water
worldwide. The bacteria can create a
potentially fatal type of pneumonia
commonly by inhalation.

The Legionella bacteria multiply best
where temperatures are between
20-45 °C and nutrients are available. A
method used to reduce the risk from
the Legionella bacteria, is to control the
water temperature, which is easy to do
with help of DEVI pipe heating system .

The DEVI pipe heating system for
DHW, maintains the water at the de­sired nominal temperatures or heats
(disinfects) it when needed.

1389

800

600

400

200

0

FranceGermanyItaly Netherlands Spain

Source: ECDC Annual Epidemiological Report for 2017 Source: ECDC Annual Epidemiological Report for 2017

664

1535

1018

393

Temperature and disinfection time

Tempera-

ture of

disinfec-

tion [°C]

55 2 h 00 minute

60 0 h 40 minute

65 0 h 26 minute

70 0 h 20 minute

75 0 h 10 minute

Time settings for thermal

disinfection

Recomended

70°C

60°C

50°C

40°C

30°C

20°C

Any disease Legionella Higher risk

At 70°C pasteurization process takes 20 min

At 58°C pasteurization process takes 50 min

At 50°C Legionella will no longer multiply

Ideal growth range

35-46 °C

growth range

5Application guide · Domestic hot water · ©DEVI

Heat tracing in DHW (Domestic Hot Water) systems

DHW system, single pipe system

(without circulation) - the cable
modifies its output and thereby
temperature according to the
conditions along the installation. This
means that the DHW system is heated
corresponding to heat losses, thus
maintaining and/or controlling the
temperature.

The more often the hot water tap is
turned on, the less the hot water tem­perature maintenance system needs to
be activated assuming a water supply
with a higher or equal temperature to
the respective requirement.

DHW system with circulation ­continuous circulation of hot water
to ensure that hot water is available
at any of the taps.

Self-limiting heating cable

In case of DHW with circulation - pipe
tracing can be installed to ensure
loop temperature. Thereby aiding the
system to maintain temperatures at
the required level.

DHW systems can also be installed to
secure pipes where circulation can't
be provided to ensure the wanted/
needed temperature.

The DEVIhotwatt™ pipe tracing in
DHW system without circulation
requires less pipes, less valves, less
pumps and installation labor com­pared to the Recirculating system.

• Approximately 50% less pipes – less
water volume in the pipes, thus
smaller boiler can be used.

• Energy consumption reduction, as
heat losses from the pipes will be
reduced by a significant amount.

Self-limiting heating cable

• Less maintenance cost, as less
mechanical parts and pumps.

• Saving water – DEVI pipe heating
system attached to the pipes keeps
water at the desired temperature
along the pipe system, so hot water
is immediately provided, when
demanded, and with minimum
water loss.

The DEVI pipe heating system insures
that DHW is supplied, independent of

the pipes length, and reduces the risk
of localized temperature fluctuations
by heating only where needed.

DEVI pipe heating system is insuring
automatic maintenance of the
required temperature 24/7.

6 Application guide · Domestic hot water · ©DEVI