The given figure represents a two$-$pipe reverse return hot water heating system.

The heating load for the system radiators is as follows. The supply hot water

temperature drop is $10C$ and the total equivalent length of circuit $(1)$ is $130m.$

$1-$ The total heating load for the boiler Qb:

$24\mathrm{.}87kW$

$50\mathrm{.}12kW$

$27\mathrm{.}36kW2-$ The required pump capacity is:

$*$

$1\mathrm{.}1$ L$/$s

$1$ and $4$

$0\mathrm{.}65$ L$/$s

$1\mathrm{.}1$ kg$/$s

$3-$ The pressure drop per unit length. If an iron and bronze pump is to be used:

$*$

$350$ Pa$/$m

$442$ Pa$/$m

$240$ Pa$/$m

$20000$ Pa$/$m

$4-$ Diameter of steel pipe for section A$-$B:

$*$

$35$ mm

$25$ mm

$32$ mm

$40$ mm

$5-$ Diameter of steel pipe for section f$-$g:

$*$

$25$ mm

$23$ mm

$32$ mm

$20$ mm