The Benefits of Variable Speed Components in Air Conditioning

You may have already heard about the efficiency of variable-speed compressors. These features represent the latest in HVAC tech, a variable speed compressor is a gigantic leap forward for achieving optimal power savings and comfort indoors.

Still want to know the difference between variable speed, two-stage, and “traditional,” single-stage air conditioning, here’s the simple answer: Variable speed is the best. Hands down.

Read along and we’ll give you the complete low down on this topic.

How a Single-Stage AC Compressor Works

Most homes with AC use a single-stage compressor. Though past their prime now, these compressors were the standard for decades, and they continue to represent the majority of AC units we service in the Charlotte, North Carolina area.

A single-stage AC compressor cycles on when indoor temps exceed the temperature setting on your thermostat. For example, if you set the thermostat to 72 degrees, the air conditioner will run anytime indoor temperatures hit 73 degrees or above. After the AC cools the house back to 72 degrees and the compressor will turn off again.

Note that single-stage compressors always operate at 100% capacity. They run at full blast and cycle on and off all throughout the day.

 Whether single-stage, dual stage, or variable speed, our technicians can help you select the right system.

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So How Does a Variable Speed AC System Work?

Variable-speed AC compressors work differently. To maintain an indoor temperature that matches the setting on your thermostat, they operate continuously at less than 100% speed – often as low as 25% or 30% capacity. This in turn makes them run for much longer cycles than single-stage AC units. In the hottest months of the summer season, they may run all day!

So in contrast here are the major differences in compressors:

• Single-stage compressors blast your house with cool air and turn themselves off when the desired temp is achieved.
• Variable-speed compressors blow a steady stream of cold air into your home to maintain the desired indoor temperature. They rarely turn off.

Where Does a Dual Stage (2 Stage) Fit In?

A dual-stage or 2 stage compressor fits somewhere between single-stage and variable speed units in terms of how it functions. Though it doesn’t operate at a range of minor increments of capacities like a variable speed unit, it does vary its output level.

A single-stage AC offers one speed: high. A two-stage AC offers two speeds: high and low.

A dual-stage unit runs at full capacity when you need it to and at a lower level when you don’t. Dual-stage units don’t run as continuously as variable-speed AC, but they do cycle on and off less frequently than single-stage systems. This allows their efficiency and achieves comfort level to be noticeably higher.

How Does a Variable Speed Compressor Achieve Greater Efficiency?

So you may be wondering with the heat, why you would want an air conditioner that takes longer to bring the temperature down in your home and has to run continuously?

One of the major benefits is a variable speed compressor’s longer run times dehumidify your home more effectively than the relatively shorter cycles of a single-stage unit. One of the biggest drawbacks of single-stage compressors is that they’re not running continuously. Humidity raises whenever the AC isn’t running, making you feel hotter and more uncomfortable. This feeling is especially noticeable when an air conditioner is oversized, as they often are. This is sometimes referred to as “short cycling”.

Some homeowners may compensate for this problem by lowering the temperature on their thermostats, which brings us to the other benefit of variable speed units: cost.

A single-stage compressor floods your home with cool air before it turns itself off. Then it starts again when the indoor temperature increases. Most of your air conditioner’s current draw occurs when it first cycles on, not while it’s running. In summer months when a single-stage compressor turns on and off a lot, a process known as “short cycling.”

Starting Takes More Energy Than Keeping It Going

With knowing a stage compressor tends to short cycle, they usually draw more electricity than a variable speed unit that turns on and stays on (at a low speed) for hours. As a result, the single-stage AC is less cost-effective to operate!

A comparison of all three types:

• Single-stage AC Units don’t dehumidify continuously, forcing you to lower the temperature setting on your thermostat more than you usually would. They also turn on and off a lot, which raises your electric bill.
• Dual stage compressors don’t turn on and off quite as much. For this reason they are more efficient than single-stage units, but not as efficient as variable-speed units.
• Variable speed HVAC units run continuously, effectively dehumidifying the air inside your house. This allows you to feel more comfortable at higher temperatures and don’t have to set your thermostat to as low a temp. And since they don’t turn on as often they draw less power,  this allows variable speed AC units lower your utility costs.

Added Benefits of Constantly Circulating Air

You guessed it, more efficient cooling and lower energy costs aren’t the only benefits of a variable speed compressor.

If you’re worried about indoor air quality, opting for a two stage or variable speed unit can help clean the air circulating around your home, resulting in less airborne particulates for you and your family to breath. Since they dehumidify indoor air more effectively than a single stage unit, a more efficient system helps you:

• Decreased risk of mold growth in damp areas
• Decrease in airborne particles
• Create conditions that are inhospitable to pests

And since variable speed units run more frequently, they also filter your indoor air better. Air is more often cycled through your return ducts – and your air filters – thus lowering the volume of air contaminants. Variable speed units are also quieter than single stage compressors. If you’re used to cool air gushing into your home like a sudden gust of wind, you’ll probably be surprised by the variable speed unit’s more mellow, consistent air flow.

Should You Upgrade to a Variable Speed AC?

Of course now that you understand the differences among single stage, dual stage, and variable-speed compressors, you may be wondering if it’s time to upgrade. Before you rush out and do that, here are two things to keep in mind:

1. Variable speed and dual stage compressors, like most energy efficient HVAC equipment, do have a higher price point than single-stage units.
2. It doesn’t make economic sense for some to upgrade if their current HVAC Unit is working fine. It may be best to wait until your old one wears out.

All the technology and cutting edge components of a variable speed compressor cost more because they provide an objectively better air conditioning experience. When you’re weighing your options for a new system, you’ll have to consider whether updating to a unit with a variable speed compressor aligns with your budget.

But don’t fret, there still might be ways to lower humidity, improve indoor air quality, and improve perceived comfort without purchasing a dual-stage or variable-speed compressor. Here’s what we always recommend to our clients:

• If you’re current system is failing and you’re in the market, variable speed is the way to go.
  Already thinking about replacing an existing air conditioner? Assuming a variable speed is in your budget, you should definitely get one! You’re family will feel more comfortable throughout the summer, and your indoor air will be much improved. At the very least you should consider a two stage compressor for improved comfort and efficiency.
• If your old single stage air conditioner isn’t quite old enough to justify replacement, consider a whole-house dehumidifier.
  By installing a dehumidifier inside an existing single-stage system, you still can enjoy some of the benefits of a variable speed system without replacing any equipment. The dehumidifier will keep your relative humidity at a more comfortable level, improving indoor air quality and enabling greater comfort at higher temperatures.
• If it’s time to replace your whole HVAC system and you are fine with your single stage unit, stick with what you know. If replacing an old 8 SEER single stage AC with a new 14 SEER single stage AC still results in a much more efficient system. If your indoor humidity is consistently below 55% and you don’t suffer from poor indoor air quality, you may not really notice the benefits of a variable speed system

If you’re weighing the options of different system types, give us a call. We’ll evaluate your system and help make recommendations for purchase. After all, we want to keep you cool all summer long. Just schedule a visit with one of our technicians to talk about how we can help with your air conditioning needs. Would you like to learn more options? Our techs can help you out. Give us a call 704-684-5339