Mini split basics - Printable Version

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Mini split basics - Jack Houpe - 03-11-2023

I feel responsible for many people jumping on the band wagon of replacing their basement air units with mini splits, it is wonderfully quiet and the direct transfer of energy from the evaporator means minimum btu loss giving you a more comfortable conditioning of the coach inside air. That being said there is some thought that needs to be done before you jump into a the mini split transformation. I've listed some of the important factors I feel you need to understand before leaping into the mini split bandwagon. This is for the folks who don't know squat about HVAC, I am a electronic tech who loves mechanical devices, when I was in the USN I worked on aircraft and on an airplane you have many things controlled by electric devices like hydraulics, pneumatics and even air conditioning so this my background and I am not a HVAC engineer by schooling. 

Filtered air is a must, you must clean or change your air filter on mini splits its usually on the evaporator but in the case of ducted air or cassette units sometimes it could be remote, these units must have air filters and they must be cleaned often for them to work correctly. You cannot install a cassette or ducted unit without it as the evaporator core will plug up. We have cleaned our filters twice since we've been living in it Florida for 2.5 months and they were dirty, pets add to this. 

Return air is important and it should be only the coach inside air, no air taken from the outside, without recirculation of inside air your just robbing BTU's. 

BTU sizing, this is a gray area with me now as the 4 tons of original basement air was inefficient and we bought this coach in the fall so its hard to say just how much tonnage to use, many factors apply here, windows window treatments (U factor) blinds, solar shades, exposure to the sun, outside air temp, and humidity all effect this equation. In our installation we went with 3.5 tons. 12,000 BTU is one ton so we installed 42,000 btu in place of the 48,000 btu units in the basement, 100 degree day in Arkansas sitting in the sunlight will tell if we did it right or not. One comment here was the bigger the better and with mini splits thats more than likely the correct answer, with conventional heat and air systems you want to size it just right so that the unit stays on long enough to remove the humidity from the air, to big a unit will turn off to quickly and will not remove the moisture from the air and you'll have mold issues. To small unit will not cool the air enough and never turn off, on a inverter mini split it the compressor doesn't turn off and on like the old type compressors in the original basement airs and the evaporator will always have some amount of Freon going through the expansion valve thus removing moisture. Inverter is the future in HVAC, I found it interesting when Tom mentioned how long its been around.

Condensation drainage, it must be be gravity flow or you must use a condensation pump if one is not built into the unit, without this or if the job is done poorly then you will have a flood inside your coach. On wall mounted units I use both left and right drain ports so if your sitting unlevel it will drain.

Thermostat or remote placement is important if you lay it in the window with sun on it your going to freeze or if you set it on granite your going to be hot. I moved the wall mounted thermostat for the ducted unit above the refrigerator and it was a world of difference in comfort control. 

Evaporator placement, wall mount, ceiling mount, floor mount and ducted mount all have pros and cons, hot air rises so in the winter a floor mounted units will be more comfortable and cold air falls so in the summer a ceiling mount will cool you off more quickly. Most people on our forum have aqua hot for heat so its your choice for what and where you decide to mount the evaporators. On our coach I don't think I would change a thing, we have one mounted low and 2 mounted high.

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RE: Mini split basics - Latitude 28 - 03-11-2023

Jack,
Great write up on your experiences with the mini splits!

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RE: Mini split basics - Jack Houpe - 03-12-2023

(03-11-2023, 03:57 PM)Latitude 28 Wrote:  Jack,
Great write up on your experiences with the mini splits!

Thanks Steve, I thought it might help people who are doing this transformation avoid problems.

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RE: Mini split basics - Jonestead - 03-12-2023

Jack, what a great explanation! Especially for those of us who don't really speak HVAC/electricianese (yet...lol). Your experience and helpfulness is very much appreciated

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RE: Mini split basics - Jack Houpe - 03-13-2023

Thanks Arch! Good speaking with you yesterday.

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