This doesn't add up. The drain water is, by definition, cooler than the boiler water. Looking at the diagram, cold water is heat exchanged with the drain water which means it will be heated but to less than what a boiler does.
This heated stream is then pumped directly to the shower to be mixed with the boiler water, which should cool it a bit. Anyone else find this odd?
Personally I'd redesign the system to put the exchanger upstream of the boiler water inlet which means that the boiler would need to expend less energy to heat the water going to the shower head.
The idea is that, instead of using cold water to mix with your boiler water, you use cold water that has been slightly heated by the heat-exchanger. This allows you to use less water from your boiler.
This heated stream is then pumped directly to the shower to be mixed with the boiler water, which should cool it a bit. Anyone else find this odd?
Personally I'd redesign the system to put the exchanger upstream of the boiler water inlet which means that the boiler would need to expend less energy to heat the water going to the shower head.