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8.4 DHW TANK SELECTION AND
INSTALLATION
●
This DHW tank is designed for heat pump type heating system.
DHW shall be selected according to the requirements in this
instruction and on-site use requirements.
●
If the selection, installation and wiring are not carried out
according to the requirements in this instruction, we would not
be responsible for the problems caused by the DHW tank.
●
Hot water may cause serious burns. Test water temperature
with hands. Use after the water is mixed till proper temperature.
●
Connecting of water pipe with tap water pipe should be
operated by qualified staff using proper piping material
according to local regulations and standards.
●
When the high domestic hot water temperature can be
a potential risk for human injuries, a mixing valve (field
supplied) shall be installed at the hot water outlet connection
of the DHW tank. This mixing valve shall secure that the
hot water temperature at the hot water tap never rise above
a set maximum value. This maximum allowable hot water
temperature shall be selected according to the applicable
legislation.
8.4.1 DHW tank selection
When selecting a tank for DHW operation, take into
consideration the following points:
- The volume of the tank has to meet with the daily
consumption in order to avoid stagnation of water.
- Fresh water must circulate inside the DHW tank water
circuit at least one time per day during the first days
after the installation has been performed. Additionally,
flush the system with fresh water when there is no
consumption of DHW during long periods of time.
- Try to avoid long runs of water piping between the tank
and the DHW installation in order to decrease possible
temperature losses.
- lf the domestic cold water entry pressure is higher than
the equipment's design pressure, a adequate pressure
reducer must be installed to ensure that the maximum
pressure is NOT exceeded.
1 Storage capacity
The storage capacity of the DHW tank depends on the daily
water demand and the combination method. The daily water
demand is estimated with the following calculation formula
for consumption:
D
(T)= D
(60 °C) x (60-T
i
i
Where:
Di (T):
Water demand at T temperature
Di (60°C):
Domestic hot water demand at 60 °C
T:
Temperature of the DHW tank
Ti:
Temperature of the inlet cold water
- Calculation of Di (60 °C):
The standard consumption, expressed in daily litres per
person and determined by technical installation regulations
of each country, is used to calculate the domestic hot water
demand at 60 °C, Di(60 °C). This quantity is then multiplied
by the expected number of users of the installation. In the
following example, the domestic hot water demand at 60 °C
has been considered as 30 litres per person, in a detached
house with 4 residents.
/ T-T
)
i
i
19
SPACE HEATING AND DHW
- Calculation of T:
The temperature of the DHW tank refers to the temperature
of the accumulated water inside the tank, prior to operation.
This temperature is usually between 45 °C and 65 °C. It has
been considered as 45 °C in this example.
- Calculation of Ti:
The temperature of the inlet cold water refers to the
temperature of the water being supplied to the tank. Since
this temperature is usually between 10 °C and 15 °C, it has
been considered as 12 °C in this example.
- Example:
Di(T)= 30 x 4 x (60-12 / 45-12) = 174.5 litres/day
174.5 x 2(*) = 349 litres/day approximate demand of hot
water
(*) It is recommended to multiply the calculated consumption by two,
in case that the installation is in a detached house. This is done to
ensure a steady supply of hot water. In the case of a multifamily
installation, it is not necessary to increase the forecast of hot water
demand, given the lower simultaneity factor.
2 Coil Face Area
The coil face area is a key parameter for DHW tank. To
improve the heating efficiency, the coil face area should be
adjusted according to the capacity.
The coil face area should be no less than the values listed in
the table below.
Storage Capacity(L)
100
Coil Face Area(m
2
)
1.5
Smaller coil face area will lead to worse heating efficiency. In that
condition, the heat pump will start and stop frequently which causes
more time and more power consumption to heat up the DHW tank.
150
200
250
300
1.5
1.8
1.8
2.0
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