Multiple Mini or one traditional

[mattlikesbikes]

Central TX.

We are building a shop/barndo here at our ranch. 36x46 with 26x26 as apartment. will get 1" CCF walls 2" roof. Metal, light colors. This will be a weekend place more than anything else.

Right now the apartment is setup as 3 rooms, open kitchen/living, bedroom, bunkroom. I am trying to sort out if that means i need 3 mini splits or if I can get away with fewer and still control temp in the rooms without the blower. Particularly when the doors to the rooms are shut.

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I see it as three options - 3 units, 1 multizone unit, normal HVAC system.

the multizone mini split seems to require me use an HVAC company, as does a traditional system. while three individual mini splits could be the DIY. Mini spilts, either option, seem quicker and easier. I do prefer the ceiling registers vs the mini split wall things.

I've got no idea what an HVAC company is going to charge to vac and charge a multizone system. I have seem some traditional HVAC's advertised locally at 3500-4500 installed for 3T (enough to cool the whole building).

So first question, Is it possible to get enough airflow from a single unit to cool closed door rooms? Is there a mini split option that gives you the ability to throw out 2-3 small ducts to push air into a single small room? What would you do?

 

[superex87]

One mini will not work with the doors closed. They do make a variation of the mini split called a concealed or ducted mini. It uses the same outdoor unit as a regular mini split but has a compact air handler. Based on the size and number of rooms I think a ducted mini split would be perfect. When creating the ducting I would recommend each room having a return duct back to the air handler. This will greatly improve performance when the doors are closed.

Are you trying to heat and cool the shop space as well? If so I would use a regular mini split for the shop space and a ducted mini for the living space.

 

[dcg9381]

Texas here - It appears to be less expensive and more efficient to do single units in many cases. What's your cost on a 3-head system?

Here's what I haven't tried: There are "in wall" blower systems that are designed to circulate air. To me, it appears that you could possibly get away with 2 systems - one for the main garage and on for the residential part of that building. Note, I'd want "push/pull" and I have not personally done it, but I've considered it for an apartment residence where I didn't want to spend money on 3 zones.

 

[Lonnies Performance]

Smaller individual units typically have higher SEER ratings than a larger multi-zone unit.

Also if one individual condensing unit breaks you have 2 left... not so with a multi-zone unit.

 

[yeldogt]

It's a question of load. You are trying to match the load.

Remember -- every system is rated under it's ideal conditions. And what's that ?

No system is going to get the full rating throughout the range ... Unfortunately -- the manufacturers don't report ratings at different loads and percentages.

Most people oversize equipment .... this is especially true with AC. Doing this causes two problems ... 1. poor humidity control as it makes the unit short cycle. With a VS system -- the unit does not operate in the zone where it's been highest rated.

This is even more of a problem when used for a space not always occupied -- most people really oversize the equipment thinking the best way is more capacity. I want quick hot or cool.

The multi head systems when properly sized allow for a couple advantages -- they allow for over capacity on the head side and often a better operating zone for the compressor. At my beach house we have 3 12k heads on a 30k compressor. This allows the compressor to be running most of the time closer to it's max efficiency .. but still allow capacity when needed.

The Mitsubishi system can run above 100 percent ... it's rare that you will need full output from all the heads. This is much better vs having three systems.

On my new vacation build I have a loft area that will not be used all the time -- so it's a not used area in a not used house. So -- I'm placing that smallish space on it's own mini (it also easier to get the lines to the compressor) I'm doing the kitchen addition with a twin -- again doing an 18k and 9k with a 24k compressor

 

[theoldwizard1]

We are building a shop/barndo here at our ranch. 36x46 with 26x26 as apartment. will get 1" CCF walls 2" roof. Metal, light colors. This will be a weekend place more than anything else.

With that amount of insulation, you will nee a LOT MORE HEATING/COOLING !

1" of CCF is a good start in the walls as it will seal up all of the cracks and gaps, but follow it up this typical roll/batt insulation. Same in the ceiling/roof, but I would go with an additional 6" of insulation.

Mini-splits with multiple air-handlers or ducting GREATLY REDUCES THEIR EFFICIENCY ! Ducting is worse. For good EVEN heating and cooling in your shop, you really need 3 air handlers, basically one in each corner.

A separate unit with one air handler would probably be adequate for the front room and middle 3 rooms if the doors were open most of the time.

 

[theoldwizard1]

The multi head systems when properly sized allow for a couple advantages -- they allow for over capacity on the head side and often a better operating zone for the compressor. At my beach house we have 3 12k heads on a 30k compressor. This allows the compressor to be running most of the time closer to it's max efficiency .. but still allow capacity when needed.

Your statements are correct, but 3 smaller individual units, even "slaved together" would be more efficient. A lot more expensive, but more efficient ! Likely take several years to pay back (maybe more).

 

[yeldogt]

Your statements are correct, but 3 smaller individual units, even "slaved together" would be more efficient. A lot more expensive, but more efficient ! Likely take several years to pay back (maybe more).

Can't say I understand this ...

It's all about load -- match the load.

 

[dcg9381]

I don't understand it (slaved together) either. I found that 3 individual units were often less expensive (depending on size) than a mult-head unit.

Agree with others - I didn't catch that this is 1" CCF insulation - what's the R value on this? In Texas - I'd highly recommend that you spray foam the roof, 3" minimum... Walls, if you're framing them in, lots of insulation options. Your insulation is going to massively impact what HVAC systems you need.

 

[Lonnies Performance]

Keep in mind that 3 units may be oversized, but there no reason you have to run all 3 continuously.

I have 4 in my garage & typically run 2, except in extreme conditions.

 

[jjrbus]

After lots or research and asking questions I decided on 3 separate mini splits. I like the redundancy. If one goes out it is not panic time, nothing worse than the AC going out during a heat spell on a holiday weekend.

I have a mold issue on one of my 3 mini's, it is claimed that 2% have a mold issue. So might want to look into cleaning mini splits before pulling the plug. Unit is properly installed with no drain issues. Just draws mold like a magnet!

 

[yeldogt]

After lots or research and asking questions I decided on 3 separate mini splits. I like the redundancy. If one goes out it is not panic time, nothing worse than the AC going out during a heat spell on a holiday weekend.

I have a mold issue on one of my 3 mini's, it is claimed that 2% have a mold issue. So might want to look into cleaning mini splits before pulling the plug. Unit is properly installed with no drain issues. Just draws mold like a magnet!

It could be the way it's forced to operate .... oversized systems tend to stay wet ... you don't want a system that's trying to modulate so low .. the fan is also on low.

Obviously stuff fails ... but, IMO you design for proper function and load ... no for failure. If you have a critical system -- it would be two identical and rotate.

 

[theoldwizard1]

Your statements are correct, but 3 smaller individual units, even "slaved together" would be more efficient. A lot more expensive, but more efficient !

Can't say I understand this ...

It's all about load -- match the load.

Mitsubishi MSZ Single Zone heat pump have Energy Efficiency (SEER) in the range of 22 - 30.

Mitsubishi MxZ Multiple Zone heat pump have Energy Efficiency (SEER) in the range of 15 - 19.


Three 9,000 BTU MSZ units has a SEER of 30. One 27,000 BTU MXZ unit a SEER of 18.

 

[yeldogt]

Mitsubishi MSZ Single Zone heat pump have Energy Efficiency (SEER) in the range of 22 - 30.

Mitsubishi MxZ Multiple Zone heat pump have Energy Efficiency (SEER) in the range of 15 - 19.


Three 9,000 BTU MSZ units has a SEER of 30. One 27,000 BTU MXZ unit a SEER of 18.

But at what output ?

Three units running at 30% is not the same as 1 running in its sweat spot .. also -- some of the multi loss is the way they have to operate with flow to each head .. this is reduced when all are running.

The key is matching the load ... the multi are especially good at doing that and they give capacity when you need it. You have to match a single unit to the space -- with the multi ... you match the common load and see how the system will be used. That's how you can have 36k (3x 12k) load with a 30k compressor as I have done on three properties. I'm doing a 18k head in my kitchen with a 9k in another space .. on a 24k compressor. it's even possible to do a 18 and 12 -- depending on the situation and load. Kitchens can often have situations where extra capacity is required ... with a multi you don't have to oversize the compressor .. you take from the other heads when needed.

 

[mattlikesbikes]

The insulation on the roof is starter. I won't install batts, but may blow in above the apartment if we decide we need it. For the walls I will be doing fiberglass, both interior and exterior. The CCF is to get us a moisture barrier and start to insulate. But this place will see use just on weekends, and we won't be there with the intention of staying indoors. We also run our ac at 78ish, never lower. Also, heat of the summer, August and Sept, probably not out here that much.

I found a local HVAC guy that is cool to just purge and charge, so no longer stuck with some of the DIY only options. My wife really does not care for the wall mount look, so I think we may go with wall mount only in the two bedrooms, then a ceiling register in the livingroom. I'm going to do the math on those three units, vs going to the hybrid ducted system with a 5 duct plenum.

We will eventually throw a stand alone DIY unit in the garage/shop, cheap and cheerful there. Also, just to take the edge off.

 

[mattlikesbikes]

Looking at a two zone concealed duct, 18k, so 12 to the living/kitchen and a 9 split between the bedrooms. end up doing double plenum on each, so a vent in each room, and then two vents in the big room. Then two returns from the main and one return from each of the bedrooms. no AC in the bathroom, just an open door most of the time and a vent fan/heater.

https://iwae.com/shop/18k-btu-22-5-...tem-2-zone-concealed-duct-9k-12k-ha11726.html

 

[Jagmandave]

I prefer multiple Minis.....mine's the one in front!

 

[kj_mustang]

1" of closed cell foam is not a full vapor barrier. All the literature I have read is it needs to be 1.5" to 2.5" depending on manufacturer. Having a good installer is key also.

 

[jjrbus]

It could be the way it's forced to operate .... oversized systems tend to stay wet ... you don't want a system that's trying to modulate so low .. the fan is also on low.

Obviously stuff fails ... but, IMO you design for proper function and load ... no for failure. If you have a critical system -- it would be two identical and rotate.

Designing for failure was only a consideration, there was much more to it. Makes sense to me!

The mold issue, after loads of web surfing, I am starting to suspect the plastic used in the blower wheel. Thinking some are more porous than others allowing the mold to get a foothold. There is no mold on the coils, no mold in the pan and very small amounts of mold near the blower wheel. This is not only me but I have viewed many blower wheel cleaning videos, all similar.

 

[Jackfre]

You could use the Tjernlund Airshare to handle the adjoining rooms. Keep the doors open during the day and if closed run the Airshare off a light switch. Position it high or low, your choice. Short sun the door or install a pass through duct to facilitate circulation. I represented Fujitsu in a six state area for 14 years and we used thousands of these fans with mini-splits. They are excellent, they work and they are much less expensive than another evaporator.

 

[yeldogt]

You could use the Tjernlund Airshare to handle the adjoining rooms. Keep the doors open during the day and if closed run the Airshare off a light switch. Position it high or low, your choice. Short sun the door or install a pass through duct to facilitate circulation. I represented Fujitsu in a six state area for 14 years and we used thousands of these fans with mini-splits. They are excellent, they work and they are much less expensive than another evaporator.

I have seen them used -- even as exhaust fans. But what about room to room noise transmission? Not the fan noise .. just general noise.

I encountered those little fans back in the 80's -- Japan. Many spaces got heated with these tiny unvented gas heaters -- attached with a hose to the gas supply.

scary little things and scary set up

 

[Jackfre]

When I was back east in the Rep business Tjernlund was one my lines. It was in the company going back to '58. They are excellent people. Representing Rinnai and Fujitsu I did thousands of these single unit jobs with the problem of moving air into adjoining spaces. Tjernlund (pronounced Churn-lund), developed the Airshares to hit this market. The cfm is not high and as you know from experience the audio side will vary by application. We found them to be excellent and rarely had a complaint. Those complaints were almost always meathead related.
When you speak of your time in Japan and the way they heated spaces I have to agree that it is so very different from our methods. The little vent free units, one I sold here, the Rinnai 229 was 2-5kbtu. In Japan they pipe gas around the home and have "gas receptacle." I say receptacles as an American would think they were and electrical outlet. They are very slick. The heater has a flexible hose and as you attach it, your thumb pushes open the hinged door and a magnetic connection grabs the hose. It is very secure. When you wish to move the heater you grab the hose at the connection an your thumb pushes on the door/cover that rotated out of the way on connection and pushes on it an the gas line disconnects. Very, very slick! When you think that the Japanese live in much smaller homes it is a solution which works for them and the products worked very well. Strange to us, but very effective.

 

[yeldogt]

When I was back east in the Rep business Tjernlund was one my lines. It was in the company going back to '58. They are excellent people. Representing Rinnai and Fujitsu I did thousands of these single unit jobs with the problem of moving air into adjoining spaces. Tjernlund (pronounced Churn-lund), developed the Airshares to hit this market. The cfm is not high and as you know from experience the audio side will vary by application. We found them to be excellent and rarely had a complaint. Those complaints were almost always meathead related.
When you speak of your time in Japan and the way they heated spaces I have to agree that it is so very different from our methods. The little vent free units, one I sold here, the Rinnai 229 was 2-5kbtu. In Japan they pipe gas around the home and have "gas receptacle." I say receptacles as an American would think they were and electrical outlet. They are very slick. The heater has a flexible hose and as you attach it, your thumb pushes open the hinged door and a magnetic connection grabs the hose. It is very secure. When you wish to move the heater you grab the hose at the connection an your thumb pushes on the door/cover that rotated out of the way on connection and pushes on it an the gas line disconnects. Very, very slick! When you think that the Japanese live in much smaller homes it is a solution which works for them and the products worked very well. Strange to us, but very effective.

Yes, That's how they worked. Encountered mostly when invited to a private home or a tradition inn/ spa for Japanese. Some were less secure -- the hose would push onto a valve ...