A buffer tank is a very important part of any Hydronic Heating System especially when using a heat pump.
Here are 6 reason for buffer tank:
1. Primary function keeping Hydronic circuit and heat pump circuit separate through use of a buffer tank makes sizing and operating circulating pumps for both circuits basic and straight forward. Otherwise pressure entering heat pump would vary or be difficult to control when different zone pumps activated if there was no tank.
2. Buffer tank has some storage capacity so heat pump is able to routinely cycle on and off better for lifespan, acts like a battery.
3. Allows heat pump to produce heat at a desired set output temperature instead of constantly modulating based on various conditions inside and outside house.
4. Controlling heat pump operation based off a delta call of buffer tank is much easier than trying to control operation based on hydronic t stat calls.
5. Gives easy ability to integrate backup electric boiler and DHW coil.
6. With advanced control set ups you could drain energy in tank during peak $/KWH times to save on HP operational costs. Also alows you to store energy in the day when the outdoor temp is usually greater giving you a higher COP.