Mini-split heat pumps are an extremely convenient and efficient way to heat and cool your home. They are more efficient than traditional HVAC systems and can be installed without much disruption or mess.
I remember that when I was a child, my father repeatedly told the rest of the family to stop turning the thermostat up. Then, whenever we left the house, he would turn that thermostat down so we didn’t pay to heat an empty home while we were out.
Many my age recall similar stories because we all grew up when fossil fuel furnaces were the primary way people heated their homes. However, times have changed, and more and more of us are installing renewable energy systems in our homes to keep us warm in the winter and cool in the summer.
The technology might have changed, but has the advice on efficiently running our HVAC systems?
For those of us conditioned to turn off our HVAC systems when we leave the house, for however short a period, leaving a mini-split running 24/7 just feels wrong.
How can it be that leaving a unit running constantly uses less electricity than only switching it on when we need it?
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Can You (Should You) Leave Your Mini-Split on All The Time?
Mini-splits work best when they run non-stop throughout the day. Designed as a “set-and-forget” solution, they automatically adapt to conditions in the home to provide optimal efficiency. Adjusting the temperature or turning your system off when you go out typically makes mini-splits less efficient.
We admit we were initially skeptical, but the rest of this article explains why it makes sense to keep a mini-split system running all the time.
It also covers some related benefits of ensuring your system operates at maximum efficiency for as much time as possible. So read on if you’re interested in saving energy and keeping your home’s temperature comfortable at a lower cost.
For more tips on improving your home’s energy efficiency, check out our article on efficiency-improving upgrades with the best ROI.
How Do Mini-Splits Work?
Mini-splits are comprised of two main parts, an outdoor unit, called the condenser, and one or more indoor components, known as air handlers, evaporators, or head units.
The two units are connected by insulated copper refrigerant lines and electrical cables that supply power and allow the units to communicate with each other.
The refrigerant absorbs heat from the cold side of the system in the evaporator coil. It then travels along the refrigerant lines to the condenser, passing through a compressor, which helps concentrate the heat.
Upon entering the condenser, the refrigerant releases the heat it previously absorbed, which passes through the wall of the condenser coil into the surrounding air.
The compressor is the most energy-hungry part of the system and consumes far more electricity than the much smaller fans that blow air across the evaporator and condenser coils.
Modern compressors in mini-splits are usually inverter-driven, which is highly efficient and is the key to understanding how the efficiency of a modern mini-split can be most significant when left to run continuously.
Inverter-Driven Compressor Technology
Inverter-driven compressors can precisely control the rate at which refrigerant is pumped around the system, allowing a mini-split to generate precisely the right amount of heating or cooling to maintain your home’s temperature.
In contrast to traditional systems that adjust the level of heating and cooling simply by turning the compressor on and off, inverter-driven systems ramp speed up or down according to the heating or cooling load needed to keep the temperature at the right level.
Improved Mini-Split Efficiency
In older systems, the first few seconds after the compressor kicks in is incredibly inefficient compared to the steady-state scenario. As the compressor starts up, it must overcome the initial inertia from a standing start.
Imagine you are going for a spin on your bike. You intuitively know that it takes much more effort to go from stationary to 10 mph than to keep going at a steady speed.
If you want to travel on your bike at an average speed of 10 mph, you can achieve this by accelerating up to 15 mph and then freewheeling until you drop to 5 mph, at which point you pedal as hard as you can until you get back up to 15 mph.
The result is an average speed of 10 mph, but you’ll likely get tired quickly. Compare this to the effort it would take simply to pedal along gently at a constant 10 mph.
This pace would take far less effort, and you would need fewer peanut butter sandwiches to keep going at this speed all day long compared to the sprinting and freewheeling approach.
This is analogous to the efficiency benefits you get from an inverter-driven compressor compared to an old-fashioned on/off compressor.
The compressor uses much less electricity by exerting steady, less vigorous effort. If you ride your bicycle in the same energy-efficient way, you’ll need to pack fewer peanut butter sandwiches to keep yourself going.
Improved Temperature Control
There are benefits in terms of comfort from an inverter-driven compressor as well.
In an on/off system, the temperature tends to vary much more because the system allows it to go above and below the setpoint by a wider margin than inverter-driven systems.
The inverter-driven compressor ramps up and down according to how far off the setpoint the temperature is. As the setpoint is approached, the heat pump slows down and can even run in what amounts to a steady state.
This operation means your room never deviates too far from the setpoint temperature, making for a more comfortable experience.
Longevity of a Mini-Split System
Another benefit of inverter-driven compressor technology is that because it is not turning on and off continually and can run at a low-speed steady-state for most of the time, there is considerably less wear and tear on the system.
You might have the opposite effect if you are constantly fiddling with the temperature settings to reduce your costs.
Say you turn down the temperature when you go out for the afternoon and then turn it back up when you return.
Because you’re making your system ramp up unnecessarily to get back to the desired temperature, it will cause more wear on the components than if you just kept things ticking over at the slow speed required to maintain the set point temperature.
The result could be the premature failure of components.
Quieter Mini-Split Operation
If you turn your mini-split off or down when you go out, you’ll have a bit more noise when you turn it back up. Modern mini-splits are very quiet, though, so this is not too much of a problem, particularly with newer models.
However, it’s worth bearing in mind, especially if your outdoor unit is right outside your bedroom window or faces your next-door neighbor’s bedroom. Keeping noise nuisance to a minimum makes for more harmonious neighborly relations.
Unlike traditional HVAC systems, mini-splits that employ inverter-driven compressor technology can precisely control the amount of heating or cooling output.
Instead of turning on and off continually, they ramp up or down according to what is needed and are most efficient when operating steadily at the set temperature.
Turning mini-split systems on and off or changing the temperature every time you leave the house can make them less efficient than if you just leave them running at the desired temperature.
Mini-splits are “set-and-forget.” Once you’ve found the right temperature, leaving your system to run at that setpoint 24/7 will typically result in the least energy usage, better temperature comfort, less wear on its components, and quieter operation.
For more information on mini-splits, why not read our archive of articles about them?