Multizone HVAC: The Ductless System

Multizone systems can be big, complicated, and a challenge to cram into small spaces. If you’re using hot and cold water for your heating and cooling, you need to install valves and actuators everywhere, possibly install a whole second set of pipes for a “dual pipe” system that meets any need, and make sure you can pump enough water to satisfy the beast. In forced air applications, you would have to tear apart your ducts to add the controls and fans, then spend ages locating and sealing every leaking part. This nets you a working system, but it could be better and easier.

 

The Central Problem

We tend to centralize our HVAC hardware as much as possible. You do all your heating and cooling in one place, then send the air or water around the building. It makes a lot of sense. You only need one or two boilers for most places, even industrial settings. Put it all in one place and save on energy costs and complexity, except when you want granular control.

With a central heat or cooling source, you need to add tons of controls to manage the flow hot and cold air. You’ll lose a lot of energy by sending air and water around too. Leaks in air ducts and pipes radiating heat into the open air pose annoying losses in efficiency. There’s only so much you can do to fight nature’s hell-bent desire to make everything even out.

What if we changed how we centralize things?

The entirely decentralized system would require an air conditioner and heater in every room. That’s a little too far in the other direction. Such systems lose out on efficiency and require a good window or hole in the wall to be available. What if we replaced all the ducks and water pipes with refrigerant pipes?

 

The Decentralized, Centralized System

A ductless system is different in that you replace the often single indoor unit with several. These can be installed in the floor, ceiling, wall, anywhere you would normally install a vent or air conditioner. Each indoor unit is connected to a shared condenser coil outside. With careful design, this yields efficiency, simplicity, and reduced installation cost. In principal, it could even be considered the ideal installation for retrofitting an older building where a ducted system would not fit.

The advantages all come from a mix of centralizing the big parts, shrinking the smaller ones, and preventing energy from moving until we’re ready. The single big outdoor coil is able to produce tens of thousands of BTU without requiring as much power as an equivalent number of indoor stand alone units. That larger outdoor coil can also get better airflow than window units thanks to its large cooling fan and being near totally exposed to the open air.

Meanwhile, on the inside, pipes of refrigerant run to the individual evaporator coils. Air and water systems are happy to leak and give off or take in energy from their environment. This is especially true for water. It’s great at temperature changing due to its density. That’s bad for efficiency. Luckily for our split systems, refrigerant is actually a little stubborn about the temperature changes. You need a thermal expansion valve to make the condensed refrigerant evaporate, to make it absorb more heat. We don’t experience as many losses pumping refrigerant around as we do pumping air or water around.

This hybrid of a central system and independent components allows each room or area of the building to have a separate temperature control. Conference room needs to be cooler? Get fresh refrigerant from the outdoor unit, cool just that room. Boss wants his office warmer? The indoor unit holds a higher temperature and doesn’t run as often.

The alternative would be a centralized system directing air and water around with a complex series of valves and ducts. That’s more wires, parts, and complexity, which probably isn’t worth the effort unless you’re operating tends of thousands of square feet of office, warehouse, or industrial space.

 

The Ideal Solution

In my opinion, the split-system is probably the way to go for most small businesses, offices, and small buildings being retrofitted for a new system. You get the zone control built-in, you get reduced complexity and maintenance, and if one indoor unit fails, you’ve still got cooling in the rest of the building. If “one” indoor unit fails on any other central air system, you’re going to sweat it out til’ a new one is installed.

Your situation of course may be different. Every situation and installation is unique. Differences in building construction, local contractors, and end-user preference will dictate your best upgrade options.


The Wrap Up

What did you think? Did we get something wrong? Got something for us to cover next time? Let us know in the comments below.

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