Mini-Split HVAC Systems – Heating and Cooling On Demand
It’s very simple. With ducted or ductless mini-split systems, you only pay for and use as much or as little heating and cooling as you need at any given time in any given room? How does it work?
In technical terms, there are three primary components to making this possible.
1. An inverter-driven scroll compressor inside the outdoor unit (a.k.a. condenser, compressor) that adjusts its rotation speed, and the electrical draw, to precisely match the load requirements within each zone of the house or building.
2. Quiet, low-wattage fans in the “mini” air handlers and outdoor units modulate their speed to match the need of individual zones (air handler) and whole system demand (outdoor unit)
3. Dual electronic linear expansion valves (LEV) that adjust the amount refrigerant being delivered to all air handlers, and within each air handler, based on what each zone or all zones are calling for.
In practical terms, it’s similar to a pay-as-you-go cell phone, where the user only pays for the minutes used. No more, no less. . With this technology, the users heat and/or cool as much or as little as they want, and only pay for what they use.
Let’s Break it Down
The inverter-driven scroll compressor in the outdoor unit adjusts the amount of electricity, and the linear expansion valves adjust the amount of refrigerant, the hot and cold liquid that is used to condition the air being supplied to each zone, to deliver exactly the amount of heating and cooling needed at any given time in any given room and/or zone. No more, no less. The system only uses the energy it needs to do this, whether its a little or a lot.
The mini air handlers (a.k.a. indoor fan coils), which range in capacity from 6,000 btu/h to 24,000 btu/h for residential, and up to 96,000 btu/h for commercial applications, are selected through a process that is based on the heat loss and gain calculations, a.k.a. load calculations. How many air handlers, how much air needed, and how that air is delivered to each room or zone, are the remaining steps in the HVAC Design process.
Outdoor units can have as few as one (1), and as many as eight (8) air handlers in residential applications, and up to sixty-four (64) units in commercial. This is what gives these systems their name “mini-split” heat pumps, since conventional split systems have one outdoor unit and one indoor unit to serve individual or multiple zones. The “mini” refers to the multiple air handlers that are not only smaller in capacity, but also in physical size.
IMAGE LEFT – Typical Wall-Mounted Ductless Air Handler
IMAGE RIGHT – Typical Concealed Ducted Air Handler
The air handlers can have ductwork and be concealed in a ceiling, attic or floor cavity to serve up to three or four rooms. OR, they can deliver the air without ducts with wall-mounted or recessed (in wall/ceiling) ductless units. Either way, these air handlers deliver air with a fan that is generally quieter than a human whisper.
They just make sense
Everything about these systems are variable, efficient, quiet, great for good indoor air quality, and extremely effective. What more would you want in an HVAC system?
Contrary to what you might be thinking, or know, these systems can and DO work in all climate zones. They’ve been used in Europe, Asia, Canada, and South America for decades, and have proven themselves to be reliable. HVAC companies rave about how few call backs and/or repairs that there are with these systems.
Generally, they can be as much as 30%-50% more efficient than conventional systems. Though they’re rated efficiency (at full capacity) ranges from 14 to 20 SEER, they rarely ever run at full capacity. This makes their real world efficiency seem higher. In fact, an alternate efficiency rating, called Integrated Energy Efficiency Ratio (IEER), is used to more accurately factor the variability of the equipment in to the rating.
A final technical note: Conventional outdoor units (heat pump or air conditioner) draw about 25-40 amps of electricity when in use.
The maximum amp draw on mostresidential mini-split outdoor units is 18-20 amps. Again, because of the variability, and the fact that the system is never on full capacity, the amp draw is usually much lower…maybe around 10 amps or lower….
To the left is a graph showing just one of the many ways that the mini-split systems are better at minimizing energy use.
If you need more information about these systems, or are considering them for your new or existing home, don’t hesitate to contact us. We have experience with these and many other types of systems, and can design a system that suites your needs…precisely.
written by Chris Laumer-Giddens, Architect, HVAC Designer, Residential Builder, HERS Rater, Building Science Professional, EarthCraft TA
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