I’ve installed somewhat similar systems as this, but am not quite sure about this one. But let me take a stab at it.
As far as 188 gals @ first hour, I think that is the maximun output. 188 gals per hour… isn’t that about the same as 3 gals a minute? So in a “on demand” system, with domestic water being fed directly from the boiler, that might be how much hot water it can supply.
Most on demand systems have two temperature zones. One for the heating loops and one for domestic… which would require a lower temperature so no one gets burned.
By using the tankless system for domestic, the unit would have to operate every moment hot water is being called for. By using a storage tank, with high and low settings, the boiler has to work less often. It only has to heat the storage tank when necessary.
Another thing is, that if you want “instant” hot water, you can hook up your loop to the tank and it can circulate when needed.
If this is a single temp unit, or even if it’s not, the storage tank could aslo be used, along with a mixing valve to regulate the temp of the domestic water delivered. This is another way to reduce the frequency that the boiler has to operate.