Mini-Split vs conventional split

[AndyCBR]

Hello,

I've been using GJ for research on mini splits for a while. I've read countless threads and am still having a hard time making a decision.

24x24 well insulated attached garage here in South LA.

Options are:
1) Daikin 18,000 BTU (1.5 T) 15 seer mini split.
2) Goodman 18,000 BTU 13 seer (1.5T) conventional split system.

Pricing for DIY is actually very similar for both options with the mini split being just a tad cheaper due to the cost of the ductwork/return plenum/drain pan. The mini split adds up when you add the line set cover, wall bracket, good flaring tool, micron gauge, etc. If I went the conventional route I would probably just have an A/C company come out and solder/vacuum/fill/startup the system.

The mini split is certainly easier and I would suspect be much more efficient in the long run due to eliminating the losses from the ductwork in the attic. My attic is easily accessible but it is still a 125 deg F space in the summer where the air handler would have to do its work.

Cons to the mini split are the air filtering in a shop space and perhaps the long term reliability/ability to repair. IE after 5-10 years are you going to repair or just replace either inside or outside unit.

Both being equal tonnage I assume the conventional system would cool the space down a little quicker based on the dedicated return and supply grilles and better air distribution. Then again you would be fighting the attic temps.

Any insight or advice would be appreciated.

 

[pseudorealityx]

What is your heat source for the conventional unit? strip heat or heat pump?

 

[AndyCBR]

What is your heat source for the conventional unit? strip heat or heat pump?

I would use a 5k heat strip which is less than a $100 add on for the Goodman air handler.

Not efficient at all but I can count on one hand the number of times I actually needed heat this year. Between the insulation, lighting, a milk house heater and a sweatshirt it can get and stay 50-60 degrees which is comfortable enough.

The mini split heat pump or the 5k strip in the conventional would both be more than enough heat for my needs and I could probably get away with and AC only mini split but at 18,000 BTU there isn't much savings on the equipment.

 

[MushCreek]

A couple things- How did you arrive at the size needed? My 1400 square foot house in SC needed only 9K BTU, but it is very well insulated. Did you run a calculation, or just use the WAG method? You can buy a computer program for $50- I used HVACCalc. Secondly- That's pretty poor efficiency for a mini. My Mitsubishi is 26 SEER. Running the A/C in July only added about $20 to my power bill. Maybe you've already addressed all this- just trying to help.

 

[Jackfre]

I agree with MC that you are choosing a lower efficiency unit. Your issue with service on the mshp is correct but you can ease some of the evaporator issues by not tucking it to closely to the ceiling. Access eases all maintenance regardless of what is being serviced.
When you look at almost any shop environment I think they can all benefit from an ambient air filter box. I will run a JDS 2000 in the shop. I think there are many manuf of this equipment today and you could certainly build your own.
I'm not sure how you sized this, but look at the specs for all of the adjoining sizes for actual outputs. For instance, Fujitsu, because I have the '13 catalog here, has a 12RLS2that ranges, at 25 seer/12 hspf from 3,100-13,600 cool and 3100-22,100 heat. The 15 RLS2 at 21.5/12 is 3,100-18,400 & 3,100-23,900. My point, regardless of manuf is that you need the specs each unit. They will surprise you.

 

[AndyCBR]

A couple things- How did you arrive at the size needed? My 1400 square foot house in SC needed only 9K BTU, but it is very well insulated. Did you run a calculation, or just use the WAG method? You can buy a computer program for $50- I used HVACCalc. Secondly- That's pretty poor efficiency for a mini. My Mitsubishi is 26 SEER. Running the A/C in July only added about $20 to my power bill. Maybe you've already addressed all this- just trying to help.

1) Proper sizing based on some online calculators and my own Manual J is the one ton unit (12,000 BTU). However, the 12,000 BTU window unit I have can cool the space and keep it cool provided it stays running all the time. Something I don't do in my shop. Also, should you open the double door to move a vehicle in/out or bring in a hot vehicle it takes several hours to recover.

So the 18,000 BTU is a tad oversize which is no problem for the inverter mini split as they tolerate oversizing very well with the variable speed.

With the conventional unit you don't have much choice as most suppliers 1.5T is the smallest you can buy. If I went that route I would select the lowest of the 3 fan speeds and charge the unit based on that fan speed. This would increase dehumidification for a given run time and cut down on short cycling.

2) The only reason I compare the 15 seer MSHP is cost. The very high seer models are very expensive for a part time use space. And again, based on short term use the lower the seer the better to cut down on short cycling.

I could afford a very high efficiency MSHP but then I creep into the $2k+ range installed.

Thanks for the input and advice. All points to consider for sure.

I have briefly considered dropping down to the 12k BTU 15 seer Daikin as Johnstone Supply has it on sale this month for about $750 less the line set.

 

[thammel]

Say, Johnstone supply has a store not too far from me. How did you get the info on the sale? I checked on-line and the prices aren't shown. Seems like you have to open an account.

Thanks,
Tom

 

[AndyCBR]

Say, Johnstone supply has a store not too far from me. How did you get the info on the sale? I checked on-line and the prices aren't shown. Seems like you have to open an account.

Thanks,
Tom

Yes the pricing is on a Johnstone flyer you get in the mail (or in the store) if you have a wholesale account.

Some supply houses are pretty strict and won't take walk in sales unless you have a commercial account. They do check your commercial license and credit if you want an open account.

 

[theoldwizard1]

If you are looking for long term durability, I would go with Mitsubishi or Fujitsu. Better quality mini-split heat pump will make heat down to about 10F WITHOUT a heat strip.

 

[fastjohnny]

If you are looking for long term durability, I would go with Mitsubishi or Fujitsu. Better quality mini-split heat pump will make heat down to about 10F WITHOUT a heat strip.

-13 for the hyper heat Mitsubishi

 

[AndyCBR]

If you are looking for long term durability, I would go with Mitsubishi or Fujitsu. Better quality mini-split heat pump will make heat down to about 10F WITHOUT a heat strip.

I definitely looked at the Mitsubishi but the dealer I like is a Daikin dealer. I also learned that many of Mitsubishi's units are not made in Japan but Thailand, China, and/or S. Korea. Daikin's warranty also seems better than Mitsubishi.

As far as heating down to 10F it really isn't a consideration in South LA. I can count on one hand the number of times I have seen below 20 F and not sure the Southern part of the state has ever seen 10 F.

 

[91 zeee]

conventional system is more reliable and easier/less expensive to work on in the future when there is a problem. parts are more readily available. less efficient and bulkier though.

 

[PWC Repair]

If it's all open, why not just go with a PTAC?

 

[AndyCBR]

If it's all open, why not just go with a PTAC?

I would have to do some pretty significant wall demo and brick rework to fit the ptac sleeve in the wall.

Also my experience with ptacs are they can be loud and difficult to service. So all the downsides of a window unit with none of the advantages of a split system.

I ordered a 12k btu daikin mini split and it should be in this week. I'll probably do an install thread later.




Sent from my iPhone using Tapatalk

 

[theoldwizard1]

conventional system is more reliable and easier/less expensive to work on in the future when there is a problem.

So what is the weather going to be 100 days from now ?