Environmental Engineering Reference
In-Depth Information
of time. As a rule of thumb, requirements can be approximated based on a hot water
temperature of 45 ° C:
Low usage:
15 - 30 litres or 0.6 - 1.2 kWh per person per day
Medium usage:
30 - 60 litres or 1.2 - 2.4 kWh per person per day
High usage:
60 - 120 litres or 2.4 - 4.8 kWh per person per day
Storage Size and Hot Water Demand
The storage size V storage should be equal to about twice the total requirements of P
persons with a daily requirement V person per person:
V
.
=⋅ ⋅
2
P V
storage
person
Based on the hot water requirement Q person per person per day, the annual hot water
requirement Q HW for the supply of hot water can be calculated as:
Q
=⋅
365
P Q
HW
person
The storage size for a four-person household with an average consumption of 45
litres or 1.8 kWh of hot water per day would thus be:
V storage
360
=⋅⋅
2445
litres
=
litres
Typical storage sizes are 300 or 400 litres. A 400-litre storage would be more than
adequate in this case. A 300-litre storage falls somewhat below the calculated
requirement but is still suffi cient. The annual heating requirement is:
Q HW
.
=⋅
365 4 1 8
.
kWh
=
2628
kWh
Collector Size
Once the size of the storage cylinder has been established, the collector size A collector
is calculated. This calculation also requires the annual fi gures for radiation H solar and
tilt gains f orientation (see Section 5.4). With an annual solar fraction sf and an average
system effi ciency of 30% with systems using fl at-plate collectors, the collector size
A collector can be calculated as follows:
sf Q
Hf
HW
A
collector
03
,
solar
orientation
In this formula a solar fraction of 0.6 should be chosen for European climates (e.g.
Berlin or London) and 0.9 for very sunny climates such as California.
In the case of the above consumption, the collector size for fl at - plate collectors
should be calculated on the basis of a roof in Berlin orientated about 30 degrees
towards the south-southwest and tilted by 30 degrees. The annual solar radiation in
this case amounts to 1000 kWh/(m 2 a) and the southern orientation produces tilt
 
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