[jhayward]

> To be pedantic, nothing is more energy efficient than electric heat.

No, this is not true, if you are referring to electrical resistance heating.

Heat pumps transfer energy from one source to another. For home heating, for instance, they are about 5 times more efficient than resistance heating.

[Xarodon]

I think our misunderstanding comes from different meanings of the word efficient (or applying it in different contexts). I think the more accurate word you're looking for economical. Heat pumps for heating may be 5x more economical (use less energy overall, but they aren't as efficient with it), but resistance heating is 100% efficient (if we look at the efficiency after the electricity has left the socket, all that energy turns into heat inside your house; 100% efficient.)

And while heat pumps are transferring energy, there is loss due to inefficiencies. If you're trying to transfer heat from inside to outside, especially when outside is hotter than inside (like in almost every AC scenario), you need to spend energy to compress a refrigerant, cool it, move it inside (meanwhile it's gaining heat during the entire transfer process) and then use it. Also, components like the compressor and radiator fan aren't 100% efficient, and will be giving off heat.

[jhayward]

Well, I suppose you can invent your own language, but that is no where near the industrial or scientific use of the term "energy efficiency".

A heat pump will consume 1/5th the electricity to maintain a given room temperature as compared to resistive heating, including all system losses outdoors.

That is how energy efficiency is defined. Energy consumed to create the outcome vs an alternative.

[Xarodon]

What I wrote isn't hard to understand, I'm sure you understand what I'm getting at.

If you want to be obtuse, be my guest.

P.S - I should've just used "efficiency", that is the correct word, not "energy efficiency"

[SigmundA]

You may be technically correct, but just barely, all of the energy put into a heat pump is turned into heat, not only does it move heat it also adds it own and that conversion is 100% efficient. Now a 100% of heat generated by the compressor may not make it into the space being heated but most of it is along with a bunch it pulled from the outside environment.

Honestly you are the one being obtuse. Efficiency can be measured many ways, but in the case of heating and cooling I think everyone would agree the efficiency that actually matters is energy efficiency for both economic and environmental reasons.

[sbradford26]

Yes a heat pump for heating is very efficient when the outside temperature is above a certain temperature(aka there is heat to pump). But running a heat pump as an air conditioner is not nearly as efficient. In the case of heating any losses in the system usually add more heat into the system which is beneficial, when cooling though losses still add heat to the system which is the opposite of what you want.

[SigmundA]

In the case of geothermal heat pumps they work well regardless of outside temperature and are even more efficient at both heating and cooling.

The nice thing about cooling, its greatest demand typically coincides with the best time to collect solar energy. Solar is perfect for offsetting the a/c, they are a great combo in sunny warm climates.

[Xarodon]

Ground source heat pumps, AKA what most people call 'geothermal', have their own inefficiencies.

In the winter, when you're using it to heat, it collects heat underground and brings it up to be concentrated and released into your house, this concentration costs energy. Though in the grand scheme of heating your house, any heat generated inside your house isn't a loss. Due to the fact you have to have buried pipe which you pump liquids through, you'll lose some efficiency to head loss and gravity. Those loses happen outside your house too.

Ground source heating is a lot more economical as it uses far less electricity than resistance heating for the same BTU output (because it's "stealing" heat from somewhere else), but it's not more efficient. But if you ask anyone who has to heat their house in the winter, electric heat is the most expensive. It may be efficient, but electricity isn't cheap.

As for cooling, Ground Source Cooling would be more efficient than a conventional AC (as it's not compressing and then evaporating a refrigerant on a coil).

The nice thing about cooling, its greatest demand typically coincides with the best time to collect solar energy. Solar is perfect for offsetting the a/c, they are a great combo in sunny warm climates.

I hadn't ever thought about the double effect of solar panels on your roof protecting your house from heating up by absorbing the sun, and then using that power to cool your house further. That synergy makes me smile.

[SigmundA]

You seem to be implying its not more efficient on a technical level because its "stealing" heat while a heat strip is just converting electricity to heat with no loss. But that doesn't matter its free heat in the environment. Heat pumps are literally over unity and have over 100% efficiency, but its usually specified as their coefficient of performance which is a number usually 3-5, meaning they move 3-5 times as much energy as put into the system.

Bottom line 1500w heater puts 1500w into the room 100% efficient, a 1500w heat pump will put 4500w or more into the room 300% efficient or more, they both use the same amount of electricity.

[sbradford26]

Geothermal definitely helps overall efficiency. Sadly the upfront cost is still pretty high.

Also solar helps in other ways because it makes it so less heat is absorbed into the roof of the house.

[SigmundA]

Geothermal is not only more efficient its actually viable in below freezing weather. Air source heat pumps outside coils will freeze up with ice once the temperature goes low enough causing them to stop functioning.

The ground temperature 30 feet down is basically stable year round and well above freezing just about anywhere on earth. This allows them to function even mid winter in cold climates while air source heat pumps much switch over to more conventional heating.