My buddy always laments that his heat pump doesn’t work well when the outside temperature is running cold.  That’s because he has what can be called an ancient device (more than a decade old).  There have been major improvements in the devices, which is why the recent tax law changes all provided tax credits to install heat pumps.   Because now they work over a wide range of temperatures.

Heat pumps were invented more than a century ago (around 1850) and began finding uses in our homes in the 1960s.  Basically, as its name implies, a heat pump gathers heat from one location and dumps it in another.  (It also works for cooling, where it gathers heat from inside the abode and sends it to the ambient air like an air conditioner.)  The difference nowadays is the refrigerant (which have very low boiling points- say -25C)  within the heat pump; it circuits the system, soaking up heat and releasing heat as it goes.  (These devices are powered by electricity.)

So, stage 1.  The refrigerant flows through a heat exchanger, where the outside air warms up the refrigerant to boil it, converting it from a liquid to a gas.

Stage 2 is where the vapor gets compressed.  Squeezing the vapor into smaller volume, the pressure increases (remember PV=nRT?) and its temperature.  (Now, it is warmer than the indoor temperature of the home).

Stage 3 passes the vapor through another heat exchanger.  The warm gas (around 40 C) transfers some of its heat as it passes through the room (usually assisted by a fan), and as it transfers heat, it cools and begins to condense back into a liquid.

Now, we’re at stage 4, where the refrigerant passes through an expansion valve, where the pressure is radically reduced.  This cools the refrigerant (again- PV=nRT explains the situation), where it is once again able to absorb more heat and repeat the process.

This is not a perfect system.  As the temperature difference between outside and inside locations increases, it takes more energy (work) to gather heat from the outside air and disperse it into the home.  As such, efficiencies drop.

Since R22 (Freon) has been eliminated in the US, we now use R410A (which is not only better for the ozone layers, but it’s boiling point is significantly lower than R22) so it can absorb more heat at lower temperatures.

Besides the refrigerant change, the compressors can reach higher pressures using less energy.  (Many compressors are variable speed, so they can ramp their power usage up or down).  And, the heat exchangers are bigger and more efficient, so they, too, can provide better temperature modification.  300 to 400% efficiencies [that means they put out three to four times as much energy as heat compared to their energy consumption] are not uncommon.)

All these improvements aren’t cheap.  (Again, that’s why there are 30% tax credits via the Inflation Reduction Act.)   We can expect to drop between $3K and $6K for a unit- and many need multiple units to accomplish our task.

Is it time for you to consider installing one?

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