AIR-TO-WATER (A2W) HEAT PUMPS DETAILS

AIR-TO-AIR (A2A) MINI-SPLIT HEAT PUMPS

  • Heating and Cooling only. No hot water production.

  • Refrigerant lines are run from outdoor unit to indoor heat distributors (e.g. “split”); this limits their application and requires specific HVAC expertise.

  • Very common and many HVAC install them

  • Cost: $5,000 to $15,000+ installed before any tax credits.

DO NOT USE BELOW

Buffer Tank

The buffer tank is the center of the system and actually it is the “thermal center” or perhaps a thermal battery, as it stores either warm energy or cool energy (liquid).

  • A buffer tank is filled with freeze protected non-toxic glycol and has four ports

  • Two ports (left in this case) are connected to the heat source which is the outdoor-mounted heat pump, and usually a back-up heat source (for temps below -15F)

  • The other two ports (right side of tank) are connected to the house distribution (e.g. radiant floor) to warm (or cool) the house

  • Buffer tank size typically ranges from 40 to 80 gallons

Illustration of a buffer tank with a gradient from red to blue, labeled "Buffer Tank" at the top and "40g" at the bottom, indicating capacity or volume.

Heat Pump

HEAT MODE
The buffer tank is heated by a heat pump (but it could also be a boiler or solar heating panel). In this case the target temperature of the buffer tank is 120 F.

COOL MODE
Or, a heat pump can operate in cooling mode The buffer tank target temperature is shown at 48 F:

Diagram showing a heating system with an A2W HP or other heat source connected to a buffer tank. An arrow indicates flow in heating mode aiming for a target temperature of 120 F in the buffer tank.

Distribution System

Diagram illustrating a heating and cooling system with a heat pump, buffer tank, and distribution emitters like a radiant floor or radiator. Arrows show the flow of heat or cool air between the components.

Then we add the distribution system, such as radiant floor to heat or cool the house.