Another mini split question... help me climate control my barn... aka tell me what i'm wrong about...

[PirateToast]

Hello!

I'm working on finishing my barn and am trying to determine climate control now. It's a 48x32 barn with 11' ceilings in MN. It's pro rib exterior, R30 batt insulation, vapor barrier, and more pro rib on the sides. Installed by me (and I'm far from a pro). The ceiling will be pro rib, vapor barrier, and then professionally blown in insulation. I'll probably go overkill there.

I'd like to heat and cool this thing. Mini splits seem like a great, affordable option. But I have a lot of questions...

1. Am I wrong in even considering a mini split or is there a more cost effective way to do this?
2. If I go the mini split route... what size do I do? The websites seem to indicate 36K for 1,500 sq ft. I like the idea of overkill... so would 48K... or even 60K make it a safer bet to be effective? I've heard oversizing in modern mini splits isn't really an issue?
3. Do I want a single zone since it's just one big open space?
4. What kind of unit? Ceiling cassette? Wall mounted up high? Wall mounted floor?

Here are a couple I was looking at... would either of these make sense?

• https://hvacdirect.com/48-000-btu-1...ni-split-system-w-extreme-heat-id-135702.html
• https://minisplitsforless.com/colle...8-seer-mini-split-air-conditioner-ch-60lcfc-i

Thanks for any info, I just want to make sure I can actually control the temp...

 

[ratflinger]

Well $50 will get you an online Manual J (easy to use) and it's pretty accurate. The online one I used came to the same conclusions as the HVAC Engineer we hired for the Manual J.

It is true that over-sized minis are not as big an issue as with std AC units. What you need to worry about is the ability to heat that space, that will determine the mini you get. Cassettes will be the most expensive way to go. I'd think 2 wall hung head units would work fine.

 

[WildBill]

36k would cool it fine, but if it wasn't horrible to do financially I would probably go 48k for more heating capacity and get a hyper/high heat model. Your not going to find a cheaper way to cool it but you might possibly find cheaper heating depending on how much everything costs in your area. I have one wall mount 24k that shoots cold air the full length of my 24x36 shop. It works amazing for cooling, no insulation so it's not so great at heating when it's below freezing.

The ceiling cassettes cost more and you might have to use longer line sets, so keep that in mind. One 48k with two wall mounted units spaced correctly should work great with your planned insulation level.

 

[dcg9381]

1. Am I wrong in even considering a mini split or is there a more cost effective way to do this?

You're not wrong. Watch the performance curve on heating capacity, I assume that a good deal of it's use will be heating. These can heat just fine if they are designed for cold climates... And there are some (like mine) that don't work worth a darn below freezing.

1. If I go the mini split route... what size do I do? The websites seem to indicate 36K for 1,500 sq ft. I like the idea of overkill... so would 48K... or even 60K make it a safer bet to be effective? I've heard oversizing in modern mini splits isn't really an issue?

Manual J is the right answer.
Again, watch heating capacity because there is a curve.
With R30 you're pretty well insulated (assumes you don't have huge crappy roll up doors). 36k would generally be more than enough.
You can "oversize" these, but 60k is nuts. If you want to do that, do two units and run just one unless necessary.

1. Do I want a single zone since it's just one big open space?

They are kinda location specific. You'll be fine if you move the air (fans, etc). Multi-zone is a pain in the ***. Why not do 2 x 18K units? That'd be what I'd do.

1. What kind of unit? Ceiling cassette? Wall mounted up high? Wall mounted floor?

I mount mine on the wall. Keep it simple.
Mr. Cool units are the only "consumer" unit that kinda dumbs it down and makes it easy. I just did two for a buddy and they've got the connections down so they seal easily and are much better than the Daikin's I put in for refrigerant connections.

 

[PirateToast]

They are kinda location specific. You'll be fine if you move the air (fans, etc). Multi-zone is a pain in the ***. Why not do 2 x 18K units? That'd be what I'd do.

I've seen this or similar recommendations a lot. Why do people recommend multiple heads/multiple smaller units vs one big one/single output. Is it mainly for better distribution of the air?

 

[dcg9381]

Why do people recommend multiple heads/multiple smaller units vs one big one/single output. Is it mainly for better distribution of the air?

For me, looking at multi-head unit, they were a price multiplier. You could get 2 single units for less than you could buy a larger unit with 2 heads.

I don't think you could get them pre-charged in multi-head at the time, so there was that... HVAC ain't my favorite thing.

These definitely have an air distribution issue, it's pretty directional but can be solved if you move the air in your shop (fans). There's nothing wrong with a multi-head unit, I just wasn't willing to pay 3x. And like the OP, I went "over" on HVAC capacity, so I've got two units to knock the heat down, but can shut down to one unit to maintain...

 

[fitter30]

Doesn't matter heating or cooling have to decide if your going to unit off,setback the temperature or leave it at a certain temperature for sizing. Air is easier to heat. Mass is the hard part. Have lots of tools, machines, trucks or cement floor that's mass. Cooling air is the easy part humidity is harder.

 

[Jackfre]

Single or multi? They are all variable speed, will seldom actually turn off. Therefore they have constant circulation without the large peaks and valleys of a single stage unit. Yours choice will largely depend on your use of the space.

 

[barks]

Half of Minnesota doesn’t need A/C. Heat is the problem and mini splits, of which we have four, are marginal heaters at very low temperatures and start getting expensive. Figure out best heating arrangement—might be central furnace if gas NG is readily available.

 

[chinboys]

Get the Manual J survey done and perhaps a blower door test to determine what system(s), their initial cost of installation as well as their cost to run.
Determine if you want the interior of your space to always be in your comfort zone and how many hours of the day or what parts of the day you will be in it.
Research tax credits and rebates from the federal and state governments and your utility company.
Look for discounting or rebates from the manufacturers.

A one system fits all if your electric rates are low is a multizone, frequency-driven inverter compressor that will ramp beyond 100% (they all do) ground to air heat pump. The SEER value is higher than that of a mini-split system.
You can go air to air for the heat pump. Its install costs are much lower as its SEER.

The multizone will allow you to cool or heat that specific volume where the evaporator is located.
Eventually, the other volumes outside of the area being cooled/heated will also reach equilibrium or you can activate the other zones as need. Also install a ceiling fan to help circulate the conditioned air.
Find your local Johnstone, Grainger, HVAC service company, HVAC distributor, etc and ask them what brands they are selling in volume.
Why?, you want your HVAC company to be able to get parts that are in stock should you need such in the future.
But most decent HVAC places can get almost anything or an equivalent in a few days.

 

[theoldwizard1]

IMHO ...

You will need AT LEAST 2 air handlers, 4 would be better. Either way, I would go with 2 compressors.

If you have things that can not freeze in the barn during a long power outage, you need a backup heat source or a big generator.

 

[theoldwizard1]

Half of Minnesota doesn’t need A/C. Heat is the problem and mini splits, of which we have four, are marginal heaters at very low temperatures and start getting expensive.

Not necessarily true !

You will pay more for heat pumps that can make heat below 0°F, but they do exist

 

[pcmeiners]

This spreadsheet has this year's national average utility costs and average national fuel costs. As to the OP question concerning heating and AC cost, there is NO fuel which produces heat or AC which is cheaper than a very efficient minisplit; an average efficacy minisplit heating cost is only beaten using wood, it even beats gas. Again for the OP, large multi head min-splits are much less efficient than smaller single zone,single head units. So your best off using multiple independent single zone low temperature units, also with using multiple unit you have redundancy. To give you an idea of size, my garage is 30x36, 1080 sqft, my low temp minisplit is a 12k low temp, very high efficiency Fujitsu, it has been down to 7°, up to 101° ( with capacity to spare), the unit has actually heated and cool my attached house (1250sqft) along with the garage for a year; my units can go down to -26° with 100% of the rated output. My garage has a second 12k minisplit, it has only been on for testing after the install, I like redundancy.
Your capacity needs depends greatly if you leave it on 24/365 or turn it on and off. Mine is on 24/365 (I hate rust from condensation), it costs so little it is amazing (@$0.17/kw).. Insulation values of my garage/home are only slightly above average.
If you turn the minisplit on/off you will need a much larger capacity unit to offset your garage's content mass...likely it will cost more for electric because the less efficient large multi-zone minisplit (multi-head) will cost more for electric. My unit is the AOUG12LZHA1 in the link below. Lastly, SEER or SEER2 is not the important efficiency rating for most of north America, HSPF (or it's newer version HSPF2) is the most important

https://www.goodlifehvac.ca/images/Fujitsu_LZ_Series.pdf

Google this..... HEAT-CALC-Vsn-D_1-09.xls ........ for the original not updated spread sheet


My electric bill for this June, that is with the garage heat pump going for
A/C (24/7), (2) 9k minisplits going for the attach home's A/C (24/7), big refrigerator (24Cuft), 50 gallon heat pump water heater, lighting etc. I am single which does make a difference.

 

[pcmeiners]

Half of Minnesota doesn’t need A/C. Heat is the problem and mini splits, of which we have four, are marginal heaters at very low temperatures and start getting expensive. Figure out best heating arrangement—might be central furnace if gas NG is readily available.

Your information is years old. Technology has advanced. Refer to the spreadsheet posted above.

 

[PirateToast]

Just to wrap this one up, I went with the 48K ceiling cassette minisplit. It's been working well for a month now.

Temps outside are -7 right now and its still holding strong. Tomorrow will be -20, which is at the limit of its range, but thatll be overnight and not super common. Im very pleased!

 

[ToolsRCool]

Great job on insulating, that will pay off every single year on both your heating and cooling efforts. I'm kind of on an island by myself on this, but I prefer natural gas heating through a 94% high efficiency furnace, and A/C via mini-splits. But, a mini-split unit will do both for you.

I have both types of mini-splits in my house, ceiling cassette and wall units, I threw away my central A/C in lieu of them. Bought the Mitsubishi units since I work there and get half off of them. In my opinion, the wall hanging units are best for what you want. You can set their height, and there are more adjustments on the airflow output vanes, you can adjust both vertical and horizontal flow, including sweeping, etc...... Install the wall units at least above-your-head and point the flow as horizontal as possible, as cool air will pour out of them and fall down like a waterfall, and you will feel it instantly. Do not floor mount, you will have to "fill" the room with cold air before you even start to feel it.

OK to over-size, you will just pay a little more up front. All motorized aspects of a mini-split are variable speed, the compressor, and both fans on the condenser and evaporator, so it will moderate itself as need be to optimize. Oversizing can help in times of drastic transients, like if you open a large overhead door, etc....

Highly recommend to mount your outdoor unit on the side of the building vs on the ground. They seldom need service, and it protects the unit from impact damage, string trimmers, animal urine, theft, everything. It also helps to greatly shorten the refrigerant line run between the indoor and outdoor unit.

You will have a condensate drain to handle on the indoor unit during the summer. I strongly suggest to just use a simple gravity drain of large diameter. I have ran through all brands of micro-pumps that tuck up behind the indoor unit, none last. Traditional large rectangular home furnace condensate pumps do have great longevity if you do need to use a pump, dump into that and then route it from there if you need to go that route.