Finding the volume of accumulators

[TSN79]

I'm calculating the size of the hot water accumulators for a condominuim. I know that the use of hot water is ~ 0,5 l/s (probability considered). The water is heated by an external hot water source through a heat exchanger. What I've done is to calculate the heat supply capacity using;

4,2*70*0,5 = 147 kW

I'm not really sure what to do with this number, or if I need it at all. How can it bring me closer to finding the required volume of the accumulators?

 

[FredGarvin]

What is the purpose of the accumulator? Is it for make up flow capacity? Shock absorption?

 

[TSN79]

It is to make up for flow capacity as you said, so one wouldn't have to heat up the water directly in an instant each time some is used.