Also interested in the difference in normal operation mode and “aux” or “emergency” mode.
Note: I have googled, the responses just aren’t in layman terms and I’m not understanding.
It’s basically air-conditioning in reverse. The compressor increases pressure and concentrates heat on the refrigerant flowing to one coil while a fan moves air through it, heating the air and cooling the coil. This now cooled refrigerant flows to the metering device. These can be as simple as a stopper with a tiny hole or a dynamically adjustable valve. Passing through this restriction drops the pressure and spreads the heat back out, lowering the temperature of the refrigerant as it flows into the second coil. A second fan moves air through this second coil, this time raising the temperature of the coil and cooling the air. The refrigerant now flows back to the compressor, repeating the cycle.
In a heat pump, the first hot coil would be connected to indoor air. And the second cold coil would be using outdoor air. On a standard heat pump unit there is a “reversing valve” which changes the direction of the flow. Making the outdoor coil the hot one and the indoor coil the cool one. This produces air-conditioning.
As you can see in both instances very little heat is actually produced, but rather it’s moved. Heat is moved from outside to inside in heat pump mode and the opposite for cooling mode.
Since we are moving heat that’s already there, that’s why heat pumps struggle to produce enough heat when it’s very cold outside. Most units will have a less efficient source of backup heat that actually generates heat rather than moving it. Running this along with the heat pump is “Aux” heat. Emergency is running this backup heat alone.
Source – Former HVAC Service Tech
Thanks so much for that information! Very good detail.
Quick question, is it ok to run ONLY in Emergency mode? In very cold situations, the heat pump simply doesn’t cut it. When I switch over to E-Heat it works like a charm. Is it bad to leave it on that mode?
There is nothing wrong with leaving it in that mode. It shouldn’t be called “emergency heat”, since this confuses people, thinking it shouldn’t be used regularly (like an emergency doughnut spare tire). There is some outside temperature below which your unit will struggle to pull any heat from the cold air outside (every unit is different). In certain months, many people switch over to emergency heat because it is more efficient to turn the heat pump off, since it is essentially wasting electricity. My unit has an outside thermometer to automatically disable the heat pump below a set temperature- I usually set mine around 45 degrees.
Emergency heat is electric. It turns on automatically when there is a 2 degree difference and the heat pump can’t keep up. It’s expensive to run in this mode. Won’t hurt your heat pump but will hurt your bank account.
You typically don’t want to run in emergency heat all the time because it takes more energy to produce that heat than the normal heat pump would. It’s usually reserved for very low outside temperatures, when a heat pump can’t run as efficiently as it would otherwise. Basically a heat pump is great until it reaches a certain temperature outside, at which point it becomes more cost-effective to use your emergency heat, which is typically electric heat strips (think of the inside of your toaster, and imagine a fan at the bottom blowing the air up).
Sorry, can’t flair. On mobile.
Download “BaconReader” bro; Lets you add flairs on mobile.
Two things first: When you compress a gas, it gets hotter, when you decompress a gas, it gets cooler. Going from liquid to gas is even better.
With that in mind, let’s look at a heat pump. We have four main components: A compressor, two heat exchangers, and what’s called a working fluid, which must be a gas at the lowest temperature you plan to deal with.
The compressor compresses the working fluid into a liquid, which heats up in response. The working fluid moves through the first heat exchangers and dumps a bunch of that heat off into whatever you are heating, or outside if you’re cooling.
The working fluid then travels through a one-way valve into the second heat exchanger, where the now cooler liquid working fluid boils off. Boiling is the same as expansion, so as a result, the gas cools off, and absorbs heat from the heat exchanger, which absorbs heat from the environment, the opposite of the first heat exchanger.
The now warm, gaseous working fluid flows back into the compressor, and the cycle begins anew.
In this way, by changing where the air from each heat exchanger goes, you can change the temperature of the environment around it.
It’s basically an air conditioner that can be turned around. When it’s an AC it blows cold air and hot air is pumped outside. When it’s a heater it blows hot air and cold air is pumped outside.
Don’t know what sux or emergency mode would mean other than they operate at their maximum capacity to warm or cool asquickly as possible.
Nic_the_Burner answered it nicely, but lemme tell you about a DIFFERENT type of heat pump!
So thermoelectrics are awesome. They operate on the Peltier-Seebeck effect. If you apply an electrical voltage to the thermoelectric, you get a temperature difference between the two sides. Now let’s say you put a fan blowing over the hot side; the heat gets sucked away by air. But if you keep an electrical voltage constant, the thermoelectric will constantly be trying to keep the temperature difference and so the only way to do this is to “pump” the heat.
Think of it like this, you have a water pump and you’re sucking water out of a lake and into swimming pool with a leak in it. You can put water into the swimming pool, but it’ll slowly leak out. So you need to constantly pump water into the swimming pool to keep the water level where it is.
Moves heat from outside to inside when the thermostat calls for heat. Moves heat from inside to outside when thermostat calls for cool. Works on refrigeration.
Aux heat is for a 2nd source of hear (natural gas, LP, oil or electric). Emergency is a 5 or 10 kilowatt heater strip inside the unit that turns on (when set by default) when the thermostat call is 2 degrees or greater than actual room temp.
Thermostats can be programmed multiple ways to show Aux heat and em heat to be the same heat source.