Should you choose a portable air conditioner, or a portable air conditioner that also functions as a space heater? If you’re looking to save a little pocket change and cut down on household clutter, the latter might be a good choice for you.
But how does it work? How does an appliance designed to cool the air also provide heat? It’s actually quite simple, as this article will help you to understand.
To start with, you should know that the term “heat pump” – in scientific lingo – refers to any device used to move heat from one location to another. There are many types of heat pumps (see our article on thermoelectric cooling to learn about solid-state heat pumps). In this sense, air conditioners, refrigerators and freezers are all heat pumps typically used to make things cold by moving heat elsewhere.
In professional HVAC lingo, a heat pump is specifically a single device that can be used to provide both heating and cooling to the same space. But in a very practical sense, a heat pump works exactly like any air conditioner does – only the cycle can be reversed so that the cold air goes outside, and the hot air stays inside!
The Refrigeration Cycle
To get a better insight into how this all works, it helps to understand the basics of the vapor-compression refrigeration cycle . Whether you’re talking about a portable air conditioner or central AC, the mechanics are the same. A chemical refrigerant “carries” thermal energy (heat) from one part of the system to the other, and then releases it.
Four major components make this happen:
- Compressor – The compressor squeezes the refrigerant (such as refrigerant, though refrigerant is used less frequently today then other more eco-friendly coolants), and turns it into a hot, high-pressured gas that gets pumped into the condenser.
- Condenser – The condenser is a long coiled tube (like on the back of your refrigerator). As the refrigerant moves through it, heat is dissipated into the environment (usually helped by a fan). As it cools, it turns back into a liquid before being passed into the expansion valve. In a central AC, the condenser is located outside the house, so the heat stays outside. In a portable unit, the heat from the condenser coils is vented outdoors through the exhaust hose.
- Expansion Valve – The expansion valve further lowers the pressure on the refrigerant, returning it to a liquid state before pumping it into the evaporator.
- Evaporator – The evaporator is another long coil. Inside this coil, subjected to less pressure, the refrigerant begins to turn into a gas. As it evaporates, it pulls heat from the air to use as energy to power the transformation from liquid to gas. As the gas absorbs the heat, the cold air that is produced by the process is blown into the room by a fan.
Then the cool, low-pressure gas from the evaporator is returned to the compressor, and the cycle begins again.
So, in short, the air conditioner takes the heat from one side of the system (the inside) and transfers it to the other side of the system (the outside).
From Air Conditioner to Heater
Can the process of heat transfer be reversed? Yes! The addition of a single component – a reversing valve – is all it takes to reverse the flow of thermal energy through a heat pump system.
When put in heating mode, the reversing valve is flipped, and the flow of refrigerant through the system changes direction. The hot condenser coils now become the cold evaporator coils, and vice versa. Instead of venting the hot air outside, it is the cold air that gets expelled while the warmed air is pumped into the room.
Is a Heat Pump a Better Heater?
So why would you choose an air conditioner with a heating option over a regular space heater? Aside from the previously-mentioned space-saving benefits (having fewer appliances in the house) there is a very real economic and environmental advantage to using a heat pump:
A heat pump uses less electricity.
As evidence, let’s compare a couple NewAir products. The NewAir AC-14100H air conditioner heater uses less than 1000 watts to produce 10,000 BTUS of cooling, and it is only slightly less efficient during heating. In contrast, even a highly-efficient resistance heater like the NewAir AH uses 1500 watts to create only 5120 BTUs of heat. That’s an increase of 50% more energy used for only half the heating power.
The reasons for this are scientific. Resistance heaters convert energy to heat by sending electricity through a resistor. While 100% of the electricity used is converted into heat, it still takes a lot of energy to heat a whole room.
A heat pump, however, takes advantage of the natural properties of thermal dynamics to move heat from one place to another. The electricity used by the system is used only to power the compressor and the fans – not create heat – so far less energy is needed.
This means that you are going to spend far less money on your electric bills using a heat pump than you would using a separate space heater, and get more heat!
Is a Heat Pump a Better Heater?
Because they use significantly less electricity, heat pumps are becoming a popular choice for whole-house heating and cooling systems. But portable air conditioner heaters are a great choice for people who cannot install a whole house system (say in an apartment) or who only want to supplement heating and cooling in one or two rooms.
There are a couple of things to keep in mind:
One, a portable unit needs to be vented outdoors whether it is operating in heating or cooling mode. Instructions for installing the exhaust hose and window kit come with every unit.
Two, even in heating mode a portable unit will still “condition” the air – that is, remove excess humidity. This means that you will need to drain the condensation tank periodically.
Three, the heating mode won’t be as effective if the ambient temperature is under 45°F. The closer temperatures are to freezing, the less and less efficient it is to try and simply move heat one way or another. If you are supplementing existing heat from a furnace, this shouldn’t be a problem, because the portable heat pump recycles the inside air that is already warmed.
With your portable air conditioner heater installed correctly, it can provide you year-round comfort for your indoor climate, effectively and efficiently.