3.2. Large building application
Let us consider a large building, in which a daily consumption of
50,000 L is demanded. Extrapolating the previous performance (see
Table 4), this consumption can be supplied by using 31.500 m of ¾00
hose during winter days (35 C), the most limiting condition. In this
case, the recirculation loop allows us to choose a low-cost LDPE
hose, for which the cost is 3500 dollars including a plastic manifold
used to split this very long hose in many parallel lines used to
reduce the hydraulic restriction. The extra cost related to the
recirculation loop (two on/off valves and a small pump) is largely
balanced by the saving cost on hose material, since HDPE hoses cost
twice that LDPE ones.
The design of the huge tank deserves some special consideration.
Firstly, let us remark again the advantage of this system, in
which the tank does not need to be installed onto the roof and so,
concerns related to mechanic loads over the roof structure can be
avoided. Second, this large volume could be provided by two tanks
instead of a single one; the complexity introduced is minor and can
be counterbalanced by the higher flexibility obtained; for example
one tank could be used for keeping a larger water inventory on
lower temperature and the other for storing a smaller inventory of
hotter water. This configuration is suggested by the great difference
in performance obtained regarding to Tp.
The total cost of the system is estimated (without tank) in less
than 5000 dollars. The cost of tank is dependable of the pattern of
using. For example a school with fully diurnal demand would