In a direct DHW system, precipitation of limescale can occur when water is heated, clogging pipes and boilers. This system is only suitable for soft water areas and can damage equipment. An indirect DHW system uses a heat exchanger to prevent this issue, making it more common and allowing boiler use for central heating. It requires a secondary circulation to avoid dead legs in pipes.

12. In a direct DHW system, there are chances where
precipitation of limestone will occur when heated.
This precipitation will then clog the boiler and the
nearby pipework. Therefore, direct system is only
suitable to be used in areas of “soft” water. This
system could lead to damages or even explosion and
is not suitable for hot water central heating.
Direct Hot
Water Supply
system

13. DirectHot
WaterSupply
system

14. Types of Direct DHW
system:
Various fuels and systems of
design can be used to heat the
water in this system, including the
following
• Electric Water Heating
• Gas Storage Heaters
• Boiler-Cylinder System
• Instantaneous System

15. Instantaneous
System

16. The indirect dhw system is probably the
most common form of dhw and allows a
boiler to be used for central heating
purposes
Water from boiler in primary pipework
passes through cylinder containing heat
exchanger to heat up water
The closed circulation of water can prevent
clogging. Secondary circulation is required
to prevent dead legs.
Indirect Hot Water
Supply system

17. IndirectHot
WaterSupply
system

18. Types of Indirect DHW
system:
Various fuels and systems of design can be
used to heat the water in this system,
including the following
• Vented Storage Hot Water Supply
System (Indirect/Direct Heated
Cylinder)
• Unvented Storage Hot Water Supply
System
• Indirect Hot Water system with
Expansion Vessel

19. Vented Storage Hot
Water Supply System

20. Unvented Storage Hot
Water Supply System

21. Indirect Hot Water System
With Expansion Vessel

24. These
heaters
are
fuelled
either
by
gas
or
electricity
a n d
h e a t
t h e
water
only
when
required.

25. These heaters are
located near a sink
a n d h a v e a
capacity not more
than 15 litres. The
stored water is
h e a t e d b y a n
electric element
until the water has
expanded enough
to discharge from
t h e d i s c h a r g e
spout.

28. INSTALLATION
Considera>ons:
• Type
of
materials
for
pipe
• Type
of
hot
water
supply
system
Types
of
Pipe
materials
available:
• Copper
Pipe
• Cross-­‐Link
Polyethylene
(PEX)
• Polybutylene
(PB)

29. W
Maintenance
• Temperature
check:
-­‐
principal
loops
-­‐
subordinate
loops
-­‐
localized
loops
-­‐
monthly
inspec>on
• Water
soNening
-­‐
removes
minerals
from
hard
water

30. • Water
sample
inspec>on
-­‐
to
ensure
no
contamina>on
-­‐
weekly
inspec>on
• Chlorine
inspec>on
-­‐
disinfec>on
of
bacteria
-­‐
annual
inspec>on
• Calorifiers
inspec>on
-­‐
removes
inspec>on
hatchs
-­‐
annual
inspec>on

31. Vented
Water
Hea>ng
Systems
Advantages
Disadvantages
Less
complicated
Requires
the
support
of
cold
water
storage
tanks
Low
cost
upon
purchase
Easy
to
maintain

32. Unvented
Water
Hea>ng
Systems
Advantages
Disadvantages
Doesn’t
need
cold
water
storage
support
Incompa>ble
power
showers
Provides
hot
water
to
any
draw
off
points
High
installa>on
cost

33. Direct
Solar
Water
Hea>ng
Systems
Advantages
Disadvantages
More
efficient
Cannot
be
used
with
hard
water
Flexible
collector
installa>on
Requires
an
automa>c
drain
valve
Less
risk
of
overhea>ng

34. Indirect
Solar
Water
Hea>ng
Systems
Advantages
Disadvantages
Good
freeze
protec>on
system
Risk
of
breakdown
at
high
temperatures
Less
problem
with
hard
water

35. CASE
STUDY
1

40. PROBLEMS
FACED
• Pipe
leakage:
Common
causes:
PH
value
of
water
(only
affects
metal
pipes)
Water
velocity/pressure
• Check
valve
failure:
Common
causes:
Water
velocity
Back
siphonage

41. FUTURE
IMPROVEMENTS
recommend
the
hotel
to
s>ll
keep
the
previous
water
hea>ng
systems
just
as
a
back
up
for
when
it
is
not
sunny,
thus,
giving
the
hotel
an
interchangeable
water
hea>ng
system.

42. CASE
STUDY
2

44. Initially, this hotel uses an electrical water heating system. But after some
time, due to some inefficiency due to the electrical water heating systems,
the hotel manager decides to upgrade its system by replacing those electrical
heaters with 21 thermosiphon solar water heaters, which in turn,
• reduces the hot water demand by 50%.
• it also reduces the overall energy consumption by a stunning 80%
• also adds up to approximately 1200 litres of additional storage capacity
Due to its success, the hotel, later adds another 4 additional units.