67 lines
4.4 KiB
Markdown
67 lines
4.4 KiB
Markdown
---
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tags: HVAC
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---
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# Why Mini Splits Stink
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In this general article, I explain why I don't generally like to use mini-splits.
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## The Positive Sides
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When people say mini-splits, in general we mean "ductless" style units. These can either be high wall, floor mounted, or ceiling mounted
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consoles. These units do offer really high efficiency and becuase they're "ductless" you don't have duct gains/losses.
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These units are common in many other countries and have been around for a long time. They do are generally quick and fairly easy to install,
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but are mostly a pain in the tail to work on.
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So, the plus side to these units are that they are really efficient, they generally have models that have a high-heat output for colder
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climates, although this option is becoming more prevelant in traditional unitary style heat pumps as well. You do not have heat gains or
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losses due to ductwork being in unconditioned spaces.
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## The Down Sides
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Most mini-split systems do not do the greatest at humidity removal. This is partially because they use proprietary algorithms to control the
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blower and compressor. They do achieve long run-times, which is often good for comfort stand points, however there is generally not a good
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way to control / hack them to work towards achieving good IAQ.
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These units offer next to no filtration, so in order to have filtration you need to utilize a stand-alone / portable filtration means. Which
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a lot of the portable filtration systems have problems of their own (come bundled with UV / PCO technology or other "space" technology that
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can lead to their own IAQ problems). It also introduces another fan, which may / may not be that efficient. In other words, when considering
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other items to make them more comparable to what a traditional system offers, are they really that much more efficient?
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These systems also do not have a good method of offering basic fresh air control / management, so other systems, such as an ERV need to be
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installed to handle the fresh air requirements of the building.
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The controls for these systems are often hard to understand / use. They do allow you to change fan speeds, but they control the compressor.
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The fans often run all the time, which is not necessarily a bad thing, but they don't really offer many ramping profiles or adjustments to
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change the blower speed when the compressor is off vs. on.
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These systems get dirty quickly, are generally a pain to clean properly, and are not easily repairable. Manufacturer support is often poor,
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the documents aren't always translated very well, and most technicians hate to work on them.
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# What about ducted models?
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But what about the ducted models? Well, the ducted models are a step in the right direction. You can use filters on them, although some of
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the manufacturer's do not recommend installing better / improved filter cabinets (like a 4-5" media filter), however we have done that
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successfully many times and always include media filters as an option on our installations, but you do need to make sure that they have a
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very low pressure drop, as they a lot are not designed for very much static pressure.
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The ducted models still generally have the same control problems, previously mentioned. If you read my introduction to the
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[coil-bypass-system](https://mhoush.com/posts/coil-bypass-overview/), you have a basic understanding that even most traditional systems /
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designers do not focus on the proper air-changes in a structure to maintain proper IAQ levels.
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You can't easily pair mini-splits with larger fan-coils because they are "communicating" style systems.
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## Conclusion
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Don't get me wrong, there are applications that are well suited for mini-splits. These are often applications like sun-rooms, garages, small
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server-rooms / network storage rooms, and many others. But in my opinion these are not at all my favorite and are generally really far down
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my list of options that I want to recommend to my clients.
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As an industry, I feel we need to step back and refocus on the pillars of IAQ. Filtration, fresh-air, and humidity control. The
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manufacturers / government should put less emphasis on chasing efficiency just to shoot ourselves in the foot and loose the qualities that
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make traditional / unitary style systems cover more if not all of the 3 pillars of proper IAQ.
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There's plenty that I did not cover and I'm sure I missed some things, but just needed to rant for a few minutes... Thank you for making it
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to the end!
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