June 9 2022
The push is on to decarbonize buildings and that means code changes and incentives to move toward carbon- free electric homes accomplished by using heat pumps for: 1) Clothes-drying, 2) Water-heating, and 3) Air-conditioning/heating via either “Air to Air” (Heat
from outside air) or “Ground to Air” heat pumps (heat from underground)
WHAT IS A “HEAT-PUMP” A Heat-pump moves heat via refrigerant pipes from one area to another. It
DOES NOT CREATE heat as does as a space heater. The magic happens via high pressure pipes and low-
pressure pipes and also the type of refrigerant chosen for optimum phase change from liquid to gas in
both the high and low environments.
WHAT IS A “Mini-Split” A mini split is a descriptive term for its “small” unit size versus a whole house
central HVAC system. It is “split” into two sections, 1) the cassette unit inside and 2) the
compressor/condenser unit on the outside of the building. The term “ductless” means not integrated
into a central heating system, The potential to install the inside cassette unit anywhere makes it great
for remodeling existing homes/apartments because no ductwork is required. But 240VAC power is
required to the outside unit.
Using an electric (resistive) floor heater is 100% efficient because for every watt used, we get one watt
of heat out. The power companies love these because an electric heater appears as a direct short to
their wires. (High current at 1200-1400 watts near the maximum of your breaker).
A heat pump is 3 to 5 times more efficient than an electric resistive heater because we are grabbing
heat from the other side of an insulated wall and sending it to the other side, that is, using available heat rather than creating heat.
HEAT-PUMP DETAILS: A house has two different temperature environments: In winter we have a: 1)
warm indoors via insulation and: 2) cold outdoors. The heat-pump works because of the physics of gas to
liquid phase change. We can heat and cool gas-to-liquid in the warm environment and heat and cool
the same gas-to-liquid in the cold environment. The magic is the pressure developed inside the
refrigerant pipes by the compressor/condenser, and ALSO, the factory engineers decide on what
refrigerant they want to use I.E. the chosen trigger temperature of the refrigerant best suited to
naturally return to a liquid.
There are many different refrigerants that have a wide range of phase-change temperatures. CO2
changes to liquid at minus 87f for example and R-410A (most common) changes to gas at minus 55F. We
can change phase from liquid to gas in both the cold outside and warm inside environments due to what
pressure the gas is under and heat or cool the house. (Think how a spray-can will get cold while holding
your finger on the button) A cold winter day at -10F seems pretty warm to a -55F liquid. The Winter
limiting factor: If the outside temperature were to get colder than -55 than the R-410A gas would
naturally change state to liquid and the heat pump would no longer work.
The liquid state will lose its heat and turn very cold when it vaporizes. We pump the heat by
vaporization either throwing that heat to inside (heating mode) or to the outside (Air conditioning
mode) via reversing the electric Heat-pump pressure zones. I.E. Spay the can inside the house or spay
the can outside the house.
Summary of Phase Change: The “heating side” is under high pressure to confine the gas phase-
change at high