LG mini-split question

[ejm1961Tbird]

I am planning a detached, well-insulated, stick-built garage with room-in-attic trusses. The first floor will be 48'x30'x12'6" and the second floor will be 48'x14'x8'. I am looking at the LG multi-split tri-zone unit (LMU369HV) with three 12,000 BTU indoor units. Two units would go on the first floor and the third unit would go on the second floor. I live in temperate east Tennessee. I want the garage "comfortable" in the winter and summer; not as comfortable as my house, but I want to have this capacity if desired in the future. Please give me your thoughts on this plan -- the mini-split system, the size of the unit I mentioned for the size of the garage, or any other ideas for heating/cooling this space. Thanks for any advice.

 

[Jackfre]

I think you are substantially undersized and I usually say push the sizing to the lower end and work them, but your 12-6 ceiling height increases your cubes by a third over a "normal" room height. Making this decision based upon a guess is not cool. You need a real heat cool sizing. I may be all wet based upon your well insulated design but you need a pro sizing done.

 

[whatuusay1]

I'd agree - call acwholesale.com and work through a system size with them. It sounds a little small to me but that's just a guess. I just put in a single zone LG mini split - so awesome, you'll love it.

 

[ejm1961Tbird]

Then how about a 4 ton Rheem heat pump? Has 48,000 BTU heating capacity and 45,500 cooling.

 

[Markwithak]

You need a real heat cool sizing. I may be all wet based upon your well insulated design but you need a pro sizing done.

This would be your best starting point.

 

[cowboyjosh]

I normally don't like heat pumps, but then again I've lived in Colorado (cold *** climate) and Arizona (hotter then hell in the summer, but nice) and in both places when heat is needed I like natural gas, but in Tennessee your on the right track, as the mid South is the best geographic location for heat pumps. I would hazard a guess that like what others said you might be a bit undersized with the LG, and I second the opinion on checking on a regular Rheem, Ruud, Carrier, or whatever brand heat pump; might be more economical and provide a more even temperature environment.

 

[admiraljkb]

I normally don't like heat pumps, but then again I've lived in Colorado (cold *** climate) and Arizona (hotter then hell in the summer, but nice) and in both places when heat is needed I like natural gas, but in Tennessee your on the right track, as the mid South is the best geographic location for heat pumps. I would hazard a guess that like what others said you might be a bit undersized with the LG, and I second the opinion on checking on a regular Rheem, Ruud, Carrier, or whatever brand heat pump; might be more economical and provide a more even temperature environment.

I've got some personal experience with that, as I've got LG downstairs and Mitsubishi upstairs in my house, ripped out my gas heat to do so, and save about $100/month in the summer, and $100/month in the winter as well. The old style heatpumps like Rheem, Ruud, Carrier don't heat below 35F, while the inverter based mini splits like LG and Mitsu heat at full capacity at 5F as I can attest to last winter... The inverter based mini-splits also don't slam the electric grid with sudden on/offs like a conventional AC and heatpump. They are also picking up in Canada where it is much colder than the US (obviously...). These critters aren't your father's heat pumps.

@ejm1961Tbird - The LG listed at the beginning of the article is a newer model than mine, which is a LG LMU366HV. I'd attach a 12K and 18K downstairs, and an 18K upstairs. The system balances out as long as it doesn't ago ABOVE the total rating of 36K for cooling and 42K for heating. So if upstairs needs all 18K, it'll take it so long as the downstairs units aren't also requesting their rated amounts. I guess the other recommendation would be to go with a Mitsubishi for less headaches. I've had three sensor failures on 2 LG installations, and no failures on the Mitsu which has been installed for 6 months longer. I mean, sensors are easy to fix and still warranty items, but its still frustrating. Although, the nice part about the distributed nature of mini-splits, there isn't a complete heating/cooling failure when one inside unit goes out.

Looking at the square footage listed and based on my experience, a 36K btu mini-split will _keep up_ ok, given the nature of mini-splits to run at low levels continuously, versus the sudden start and stops of regular AC/furnaces (which require higher ratings to do the same job). However, if you let had it off altogether, it would definitely take longer to catch up. Last I looked there weren't good measurement guides for the newer mini-split technology. That's part of the reason I've got massive, MASSIVE overkill with two 36K's in my house, which is the same square footage as your new garage. I can cool the house to refrigerator temps in like 30 minutes. One 36K could take care of an open 2,000 square foot space easy. Mitsu also has a 48K compressor that can support a maximum of EIGHT inside units. I'd go that route now if I had the chance.

Cheers
Jeff

 

[ejm1961Tbird]

Thanks for the great feedback, I appreciate it!

 

[RKA]

One thing I'd be a little concerned about is airflow. Looking at my Fujitsu 24K, it seems the throw is about 25 ft IIRC (I think that's a little optimistic) and the 18K is less than that. Based on that, I'd probably want a minimum of 2 units upstairs and another 2 (or better, 3) downstairs. Plan on some fans for the main level to push that heat back down. I have 11 ft ceilings and there is a 5F differential at least from the top and eye level (it's even colder nearer to the slab). The fan evens that out nicely and might be sufficient to get by with two heads downstairs (if you ran them year round).

I have no idea on the sizing though...I was thinking 12K x 5 units, but looking at Jeff's post, even that might seem to be oversized. You're going to spend a lot of money here...I'd spend a few extra for a proper load calc to get you in the right neighborhood, then upsize a bit if you want.

 

[ejm1961Tbird]

I will certainly go with the load calculation before such a big investment, but it is nice to get these ballpark estimates during the planning stage. Thanks.

 

[Jackfre]

Much good advise here. Another thing to consider. The use of multi's is fine, but be aware that they are not as efficient as a single condenser/evap. For instance the Fujitsu multi I have upstairs is a 16.5 Seer and I think 9-9.5 HSPF. The single 12 I have downstairs is 25 seer/12HSPF (heating season performance factor). If you have an area in the space that is going to be primary and is walled off, you may want to consider going with the highest efficiency system in that area and the multi's elsewhere.

Given that they are two distinct areas, I'd suggest an upstairs/downstairs configuration. Gives you better control. The suggestion to buy Mitsu over LG is spot on in my experience. The two top lines are mitsu and Fujitsu. I say that having competed in this market for years.

The reason that the minis draw so little power on start-up is that the system opens the expansion valve in the condensor to equalize pressures in the system. Therefore, the compressor can do a soft start, not having to push against the head pressure. $oft $tart $aves dollar$

The proportional load previously referred to is correct also. make sure you stay within the manuf guidelines on this, but you can oversize total evap capacity vs rated condenser capacity and it will share the load as needed. If the upstairs isn't calling you can have more capacity downstairs. Pretty cool.

I just visited my daughter in her new home in LA. First house for her. 1000 sq ft. Attic mounted horiz gas and conv. ac. the utility had red-tagged the furnace on age. The ductwork in the attic was thrashed and her husband and I pulled it all out. That was fun, but I'm now going back down to put a 24k unit in with 2-7kbtu evaps in the two end bedrooms and a 12 in the lr, dr, kit area. Looks like I have another house

Good luck on this. Keep us posted!

 

[admiraljkb]

I will certainly go with the load calculation before such a big investment, but it is nice to get these ballpark estimates during the planning stage. Thanks.

NP for my part. Just happy to relay my experience if it helps someone else. Keep in mind I'm more concerned about 100+ degree heat in the summer, and much more mildly concerned about a few 20 degree days in the winter. Of course, this last year Dallas got killed with extremes of a brutal winter and summer both, and the mini-splits performed admirably with both with the house being really comfortable and the overall utility bill still ended up being cheaper than heating with natural gas. I was a bit off on my own when I did mine (taking educated guesses for sizing and a couple of SWAG's that luckily turned out to be *mostly* correct later...), but if you can find a Mitsubishi dealer who is used to dealing with Mini-splits and trained on them, it'll help a lot (regardless of which mfg you put in, mine did the final hookups on my Mitsu and then 2 different LG's). A conventional HVAC dealer is a bit out of their element on these unless they've gotten re-trained for how mini-splits perform. In practice, they're just very different for sizing, placement, etc etc. For instance, the sizing charts I used off ACWholesalers seem tuned for conventional HVAC and are oversized for Mini-splits, not that oversizing a mini-split is bad like it is on conventional HVAC, but you can probably do it cheaper by not having to overbuild.

For installation, what I did was run all the electrical and refrigerant lines and the physical installation of the units and compressor, and then had the dealer do the final inspection to make sure I hadn't goofed (I had minor ones of course) and then they made the final connections. Saved a couple of grand that way. Another tip that comes to mind, is mount the compressor ON the side of the house/garage. This does three things:

1. Make sure you get as much heat as possible in the winter
2. Save the compressor from "yard crew" damage.
3. A LOT Less Dust/dirt/debris to clean from the compressor (or in my case cottonwood "cotton")

The above is a lesson learned the hard way. My Mitsu is on the ground in the line of fire from the mower and string trimmer as well as the cottonwood, and my LG on on the side of the garage nice and safe. The ground is a terrible place for one of these nice "thin/flat" compressors if you have a choice of mounting it on the wall. I'm going to get the new mount up, and then get my HVAC guys out to do the disconn/reconn to get my Mitsu next to the LG compressor.

The other thing I would do now, is with two compressors outside, I would split the units upstairs and downstairs across the compressors for better redundancy. When I put the Mitsu in originally, I was going to leave in the conventional HVAC since it was gas heat and that was needed more downstairs. I just needed something really efficient and cost-effective to better deal with the rooms upstairs which was unbearable in the Texas summer, particularly my office which needed to be on its own zone. It turned out to work so unbelievably well, I did rip out the conventional HVAC 6 months later rather than hassle with replacing it only to get something that didn't work as good as the mini-splits. Given the remodeling that has occurred, the required ductwork rework and all that was way too expensive , time consuming and still wouldn't have done the job. Mini-splits are really easy to install in comparison and surprisingly cost effective. I ended up plopping the LG in pretty quick after the experience with the Mitsu install. BUT, if I'd done the whole thing at one time, I'd have put the main inside units on each floor on different compressors, so if one compressor goes out, the upstairs or downstairs would still have at least minimal heating/cooling.

I agree with RKA, with really tall ceilings and large open areas, a couple of ceiling fans will help balance things out, in spite of it generally being said that ceiling fans aren't needed with mini-splits. But lets face it, each situation is different. Not needing a ceiling fan is true in a smaller space (bedrooms and my kitchen), as I removed 4 ceiling fans afterwards as they weren't needed and were just taking up space and attracting dust. But in the main living area downstairs, and the family room upstairs, the ceiling fans are still needed to move air around so it circulates evenly through the house. My 18K wall mount throws air a good 20 feet out, but without a ceiling fan it doesn't get distributed to areas to the direct side and behind it. The biggest oversize I did was in the kitchen and master bedroom. 18K and 12k ceiling cassettes respectively (cassettes being the reason I did LG downstairs...). The former "necessary" to still be able to cook in the kitchen on a 110 degree day (something that was impossible with conventional HVAC), and the latter necessary to freeze the room at night and keep my wife comfy... Actually I think 12k would have worked in the kitchen, I just had some extra tonnage to blow, no wall place for another 9K unit, and "spent" it there.

And a thanks to Jackfre. Nice to have second opinions from someone with a lot more experience on these. I hadn't thought about the disadvantages of multi's, although I do like the redundancy of them. If the downstairs area is complete open, maybe a single large ceiling cassette would work?

 

[ejm1961Tbird]

WOW! You guys have a lot of great experience and advice. Thanks for sharing. I hope others who are planning the heating/cooling for their shops get a chance to check out your feedback. Cheers.