[asteroidburger]

A heat pump is an air conditioner that can run in reverse. In the winter, it provides heat; summer, it provides cooling.

It's greener because it's not burning fossil fuels (directly, anyway) vs. a propane / natural gas furnace, and it's more efficient than resistive heating.

[balfirevic]

> A heat pump is an air conditioner that can run in reverse

Is this really the correct terminology? I'd say every AC is a heat pump, whether or not it can run in reverse, because that's how it works. It pumps heat from a colder place to a warmer place.

If it has been crippled so that it can't run in reverse, that's crappy and unfortunate, but it makes it no less of a heat pump.

[RatchetWerks]

According to the HVAC industry it is the correct term, based on my experience.

I agree with your logic both modes of operation (heat/cool) are both pumping heat.

Cripple is a fairly strong word here. HVAC is hyper optimized for cost/simplicity at the expense of comfort and efficiency. Which kills me. The industry is also stuck in the 80s in terms of power electronics. Variable speed control on the fans and compressors are a BIG deal. Like 20k for the gear. Even though the BOM cost is dirt cheap. Look at Carrier Infinity if you are curious

MANY Megawatts worth of power would be saved if they just included a directional valve, some speed control PCB and electronic expansion valve

[balfirevic]

> Cripple is a fairly strong word here.

Well... I'm in Europe, so I don't know if I ever saw a heat pump that can't operate both ways :-)

[asteroidburger]

Until recently, they've not been as common here in the US. Fossil fuels are just so much cheaper for the end customer, and central HVAC units in homes are much more common here.

[RatchetWerks]

The US is somehow very ahead and very behind at the same time :)

[toast0]

> If it has been crippled so that it can't run in reverse, that's crappy and unfortunate, but it makes it no less of a heat pump.

Yes, it pumps heat, but it's generally not referred to as a heat pump if it doesn't have a reversing valve and all the accoutrements that go with it (coil defrost heater, etc). I wouldn't say not having all those parts make it crippled, a refrigerator/freezer isn't crippled because it can't heat food, although some commercial units can be set to keep cold food cold or hot food hot because they have reversing valves.

If you have utility natural gas at reasonable prices, gas fired heat can be very economical, and it might not be forseable that you would ever use electricity for heating, in which case a reversing valve is a waste of capital.

[Brian_K_White]

Kind of a pointless observation.

The words "air conditioner" don't literally mean much at all. It doesn't refer to a humidifier or a hepa filter for instance, yet the term air conditioner has a distinct meaning that is silly to try to pretend not to recognize.

Same for heat pump.

[balfirevic]

I view "heat pump" as a technical term describing how some heaters/coolers/dehumidifiers/clothes driers/fridges work. Wikipedia seems to somewhat agree with me, although article about heat pumps seems focused on space heaters and coolers.

> yet the term air conditioner has a distinct meaning that is silly to try to pretend not to recognize

Well, yes, in US it apparently means "heat pump based space cooler". Where I live it means "heat pump based space heater and cooler".

[icehawk]

Its more complex to have a reversible heat pump, because in addition to the reversing valve, you also need two metering devices and a bypass for each of them.