ac system for new home build

TEXASMG24July 5, 2012

Hello! First time poster--

I am currently working on the construction documents for our new house. We live in Texas (hence user name) and the home will be approximately 5500 sq ft, 4 BR, open floor plan on main floor. I assumed we would put central air for HVAC, but recently had a conversation with a 'mentor' of mine who is in the process of building, quite possibly, the most amazing house I've ever seen. He is going with Daikin ductless system for the entire (8,000 sq ft) house, and is very excited about the zone control and capabilities of saving energy in rooms less utilized. I know I'm one of those guys that like to crank down temp when I sleep and we will have a larger size home for the 2 of us until we start a family. Can I get some feedback on the split ductless system for a new home design? Pro/Cons/etc. Thanks for the assistance.

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Right now I have 7 high-wall indoor units in my house and 3 outdoor units (Mitsubishi). I canned the ducted system a year and a half ago.

Advantage: inherent zoning
Advantage: semi redundancy if one of three systems fails
Advantage: can drive part of system with a relatively modest generator
Advantage: No ducts, no duct losses, no pressure differentials induced by the system

Disadvantage: no simple way to add central air exchange
Disadvantage: no simple way to add central humidification or dehumidification

Other comments:
The default programming of the heat pump mode makes the units good ceiling heaters. As they approach the set point the blower speed goes way down so hot air gets stratified near the ceiling even though the louvers are pointed down. Setting the blower speed manually to a slightly higher speed fixed that. A ceiling fan would also fix that.

Conditioning a small room like a bathroom might require combining one room and a bathroom with a small ducted unit. Unfortunately, that will add cost. Jump ducts are also a possibility. NOte that some people (including some HVAC pros) think that directly conditioning bathrooms is not a good idea.

I have found the remote controls of the Mitsubishi not very flexible. You can set on and off times, but you can not really make true setbacks. I will be checking into their hard-wired controls. I would like to set back the bedroom and have it warm when my feet hit the floor in the morning! Other brands might be better. With Daikin, I suspect your control options will be very flexible, even with remote control possible via internet.

One thing you might want to keep in mind. I can say that the Mitsu (and perhaps all brand) multi are less efficient than the 1:1 units and they do not do as well as the single units with heating at low temperatures. For the former, I think it stems from the fact that the compressors only throttle back to a certain percentage of max. For example, a single unit might be rated at 9000 BTU. If you only need a little cooling, and assume that they throttle back to 10%, you can efficiently get 900 btu out of them running constantly with no on/off. Your tri unit is probably 22,000 btu and can throttle back to 2200 btu with the same assumption so your compressor will be flicking on and off more often which yields poorer humidity control and not as even cooling. This might affect your design. If you are going to use an indoor unit under partial load a lot, like a bedroom at night you might want to place that with a smaller outdoor unit rather than some random design. Please, keep in mind the relative nature of my comments. These things all work really well compared to window units and compared to central forced air.

Be sure to consider all of your alternatives for the installation. In addition to wall-hung, you can have floor mounted, short ducts to hidden units and ceiling-mounted. That all costs more though.

If you go mini splits, don't mount a wall unit above where you will have a bed. I saw advertising that showed that and planned that but changed my mind figuring that at low speed at night the cold air would sort of cascade down over the heads and be uncomfortable. I am glad that I changed my mind about it. I don't know if that problem would occur. See, however, "ceiling heaters", above.

You can do some interesting things with the Daikin. Are you going to incorporate water heating? I would like to know if good dehumidification can be achieved by heating one room and cooling an adjacent room at the same time at very low fan settings.

Don't be afraid to make some of the house with a central, ducted system and put minis in other parts. With the ducted system running an area that is up for a hour or two, once or twice a day, and mini-splits running areas that are used continuously for several hours (bedroom) or not used much at all (other bedrooms or ?) it could work really well. I suspect that with your open floor plan on the ground floor, a more conventional system will cost a lot less and there is not much advantage to installing minis.

    Bookmark   July 5, 2012 at 7:40PM
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ionized, great information. A system with both central air for the open plan and minis in the bedrooms might be the way to go. I'm still at the early stages on the plans and my research, I look forward to going through the process and learning more.

    Bookmark   July 6, 2012 at 11:28AM
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This is our first year with Fujitsu ductless mini-split air. After the pain of installation we have loved the system. In our open area which includes two story entry, two story living room, kitchen, two story family room and open stairway that goes from the basement to the second floor, we have two 18,000 btu units. One is a ceiling cassette placed at the highest point of the house. The other is a wall unit placed in a vaulted area of the family room.

The ceiling cassette works well to cool the open area of the living room, foyer and stair way. It also cools the office, bathroom and laundry room that are not open but are on the north and west side of the house. We just leave the doors open to those rooms and the cold air migrates in after it falls to the floor. The wall unit cools the two story family room and the kitchen. We have a wall of windows on our south and west side which generate a huge heat load. It does a wonderful job because the heat rises into the vault. We do have an external solar screen on the floor to ceiling windows and do have external solar screens on the ceiling skylights. Without solar screens these areas are 140 degrees. With they are about 110 so much easier for the AC to overcome.

We also have a ceiling unit in our master bedroom (12K btu). We placed it over the foot of the bed as far from our heads as we could but still get cold air blowing on us at night. I wish they included the ability to close up one of the ceiling vents. The only place we could have put it so it didn't blow on the bed at all was in the entrance hall to the bedroom. We weren't sure if it would cool enough there because the bedroom itself is vaulted and the hall is not.

In our master bath we have a wall unit (7K or 9K btu) placed high in a vaulted ceiling. This room has two skylights. The magnificent thing about the ductless is we can leave it off all day and then 5 to 10 min. after start up your fine being in the room because it is cooling so quickly.

Our 5th unit was in an upstairs south facing bedroom (7K btu). I'm not sure we needed this one on all but the hottest days. A similarly placed west facing bedroom stays cool enough from the ceiling unit in the highest part of the house. For us this is an unused guest bedroom so the door is open all day. It wouldn't probably work for someone sleeping if they wanted to close the door.

Our utility bills have been amazingly low with this system. We have had many days with over 100 degrees and our house has stayed completely cool. Sometimes I have to turn the temp up because the contrast with the outside is too much and the cold air falling around me gives me a chill. When I leave the house I can turn most of the units off. When we get home they very quickly cool the house. I think it is because the cool air falls around you while the hot air rises so you feel the cooling right away. Before getting the system I figured I would have to leave it on all the time. Our house has in-floor radiant heating in gypcrete so tremendous thermal mass. I figured if it got heated up the system wouldn't be able to cool it quickly but I was wrong.

These units are great at cooling but they do tend to create a draft. In order to work properly they have to throw the air away from themselves so it falls and doesn't go back in the intake vent. This is great in the main living areas as it feels good. However the bedroom ones are hard to place.

The zone cooling aspect is amazing. Especially in a big house. You can cool just the parts you use. The ceiling cassettes blend right into the ceiling. The wall units are not attractive but high up in the vaults you never even see them because they are out of the main line of sight.

The units contain filters so the air inside is often fresher than that from the outdoors as we are having alot of wildfires here this year. The units seem to keep the house pretty dust free. With no duct work dust doesn't seem to get blown around.

Our system advertised a quiet operation. It is simply setting the fan speed to the lowest setting. We don't do this as it seems to run the fan 100% of the time whereas on auto it turns the fan off when temperature is reached. We prefer this at night vs. running the fan on low the entire time. I wish it had a real quiet mode for sleeping.

So in summary I think they do a phenomenal job cooling efficiently and cost effectively. They are great in the big open areas if your vaults are configured in a way so the hot air rises to them. They are difficult to tolerate in the bedroom unless you like sleeping in a cold breeze. Even my dogs don't like sleeping under them. They tend to dry out your eyes, nose and mouth over night.

    Bookmark   July 8, 2012 at 4:40PM
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I should start by saying I don't own a mini-split system and so I have no personal experience with them.

My understanding is that they were originally designed as a way to provide something beefier than window units for living spaces without HVAC ducts. You see a lot of them on old buildings in countries around the Mediterranean.

In the US, they're not well known and not particularly well thought of. Even if they should be.

Are you going to put wall mounted gas heaters in your new house (think of a 50's era apartment)? No, of course not. So why would you put the AC equivalent of same, you may was well use window units, it would be cheaper. Though no less unattractive.

    Bookmark   July 8, 2012 at 7:01PM
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Mic111, where in the world are you? Did you have AC before?

"One is a ceiling cassette placed at the highest point of the house."

How are you going to get at the filter to clean it?

"We placed it over the foot of the bed as far from our heads as we could but still get cold air blowing on us at night."


" They are difficult to tolerate in the bedroom unless you like sleeping in a cold breeze. Even my dogs don't like sleeping under them. They tend to dry out your eyes, nose and mouth over night."

Would this be any different with a ducted system?

    Bookmark   July 9, 2012 at 11:21AM
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Hi Ionized,

To answer your questions. We did not have AC before. We do not have any duct work as we have in-floor radiant heating throughout. We are in Colorado. Our house had a swamp cooler. It is very common here. We only got the AC as there is development going on around us which causes dirt to be in the air that would have clogged up the swamp cooler. We have alot of wildfires here right now and they are advising folks to not use the swamp coolers so we are doubly happy to have the AC this year.

There is a catwalk between some bedrooms that goes right under the ceiling cassette that is at the highest point in the house so that one is easy to get at to clean. One of the wall units requires an extension ladder so will not be so easy to change the filter on. We have some smoke detectors and lights that also require an extension ladder. My next house will have normal height ceilings.

I never had a ducted system that sets up a breeze like the ductless mini-split. The breeze is great in the main parts of the house. Not great in the bedroom or the office that is in a bedroom as it is uncomfortable to sit in. Perhaps other brands do not blow as hard as the Fujitsu. I suspect our master bedroom is over sized at 12K and should have been the 9K ceiling unit. I could have over ridden the installers measurements but didn't want to make a mistake and get one that was undersized. And the office upstairs gets partially cooled by the ceiling cassette that is up there so probably doesn't need the 7K that is in that room. However they didn't make a wall unit less than 7K. We are pleasantly surprised how the ceiling cassette in the main open area manages to cool the adjacent rooms both upstairs and downstairs as long as we leave the doors open. We are very pleased to not have gone with the installer who wanted to install a 24K btu up there. The two 18K btu units do a better job distributing the cold air through out the main living area. In addition they are on separate outdoor units so if one ever develops a problem we will have the other to cool the main part of the house.

I am considering getting a canopied bed. Another possibility is to try and put some type of air deflector around the unit but that will be unsightly.

    Bookmark   July 9, 2012 at 12:29PM
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Ionized - while I know you really like your minisplits, do you really think that makes sense in new construction?

Especially combined with a central system. That seems crazy especially when the OP needs heat and may have NG available.

Also with a really large house, central a/c allows economies of scale that would save a lot on install cost vs minisplits. There is nothing mini in Texas....

    Bookmark   July 10, 2012 at 7:16AM
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David_cary, I think you are right about many and possibly most situations. I also think that homeowners, builders and HVAC pros should consider all the alternatives because the mini-splits can be a real asset in some situations. Combining them by using a central system in parts of the house while using mini-splits in others might be really useful if you want to control parts of the house separately. The savings could be pretty high in a home office situation, for example. Another thing to consider is that a central system that can do everything that some minis can be comparatively expensive. That level of zoning is going to be expensive isn't it?

In this thread we have two situations that minis seem to have worked well in two very different situations. I have a home that was retrofitted with AC ca 1950 and then added onto twice after that. The duct system is a mess. (Note that I have not yet completely decommissioned it and the gas furnace is still usable in 6 of 7 rooms.) We have small rooms. Our lifestyle is such that sometimes we are only cooling one, two or three of the seven rooms at any time and rarely over 4. I am in a primarily cooling environment and I need a lot of humidity control. I might go back to heating partly with gas next winter since the costs have gone down so much, I want to keep the gas for other purposes I don't make the minimum monthly usage. A couple of years ago, the gas costs were much higher and calculations showed that heat pumps were the clear winner. Personally, I think the shale gas thing is not going to last that long, but we don't need to get into that.

Mic111 has a very different situation and is pretty happy as well. They are a predominantly heating environment or at least mixed and no latent load (dry eyes at night). The rooms are large and it is an open floor plan with rooms two or three stories high. Radiant, in floor heat is a real advantage and ducts are not necessary for that and might not be installed even if cooling was considered in the original build. They seem to have some trouble with drafts, but that might not have been a problem with a better installation.

The most difficult thing to take into account might be the lifestyle of the homeowners and how to plan for that.

Mic111, about that problem with blowing on the bed, a deflector might not look as bad as you think. You could also consider trying to partially disassemble the device and putting some sort of partial diverter inside of it. You might end up blocking half of 1/4 (one side) of the unit and that amounts to only 12% of the flow.

    Bookmark   July 10, 2012 at 4:46PM
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Thanks for the suggestion. I thought about calling Fujitsu to see if internally blocking one of the vents would void the warranty. Just haven't gotten around to doing it yet. I also feel bad for one of my dogs who sleeps on the floor across from the foot of the bed. She would then be getting even more air. As it is she often creeps off to sleep at the doorway out of the draft. Our other dog sleeps on the bed. Usually he likes to stay down by our feet but with the AC going he will keep moving up till he is even with our heads. We don't keep it very cold. It is set at 76 at night to keep it from coming on too much. But at any temperature when it blows it blows cold and creates a draft.

Your right in that maybe an installer who could have installed the unit in the attic and run the ducts would have avoided this situation. But no one in our area had any experience with that particular unit nor were they interested in doing it. As it was I was struggling to find anyone who had experience with these at all.

And yes we are very happy with the units. Cooling power is unbelievable and the cost is very low to run them. Zoning is amazing. Every area can be set differently and turned on and off as needed. No issue cooling an area down immediately. Plus virtually no noise outside. I can hear the neighbors units and not ours at all. Were on 1 acre lots so the neighbors aren't that close but their ACs are noisy compared to ours. We also have the redundancy with the heating system due to the heat pump functionality in the AC. Could be very valuable if on a cold day our heat system goes out for some reason. This would keep the radiant heating piping from freezing.

I think the main issue with this type of system is the initial cost vs. central air when you already have ducting. With no ducts we didn't have a choice. Eventually we will work through the bedroom draft issue even if we have to buy a canopy bed. Some folks with central air can't cool their bedroom at all so I think most systems have their pros and cons.

Ionized, since you have had both can you compare the operating costs for mini-split vs. central air? I'm curious to know if it is cheaper with mini-split. I think we expected the worst so have been pleased that there is very little cost to operating the system but were coming from using a swamp cooler so don't don't have a point of comparison with what it would have been vs. central AC.

In terms of the point about the aesthetics. With a new build you could completely hide the system. We looked at several options that hide the units in the attic or the wall and you get just traditional looking vents. The only thing that prevented us from doing this was a lack of an installer to take it on. It is called the Slim Duct. Here is a link.

Here is a link that might be useful: Fujitsu Halycon System

    Bookmark   July 10, 2012 at 6:17PM
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Mic111, I can't really compare. The system I had previously was poorly (stupidly) designed, there were two, staged compressors 2 tons each) that were feeding a single, split evaporator. The blower was single speed. (Yea, right, how is that supposed to control humidity?) The duct system was messy too.

Even if both compressors were running at the same time, the max possible system efficiency was probably a SEER 10 at that time of installation. It would really be hard to compare. Duct losses are quite variable, but if the ducts are all inside the envelope, it does not matter that much unless you are causing pressure differentials.

You are better off in some ways that you could not go into the attic with small ducted units. Putting ducts outside the house envelope can cause a lot of problems. I don't know why the installer would hesitate. It is like installing a miniature central system. You must have a lot of old dogs that don't like to learn anything new. Fortunately, my installer is eager to do so. He's been teaching at a local trade school part time for over thirty years and he feels like if he does not keep up, he needs to quit.

    Bookmark   July 11, 2012 at 3:40PM
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Thanks ionized. This discussion caused me to dig out my installation manual and operations manual for my ceiling cassette. We can install a plate to block one of the vents. I wrote to Fujitsu yesterday to find out how to buy it. Then there is a programming mode on the wall unit to set it to three directions. Likely this lowers the fan speed. This is not supposed to be user programmable. The installer is supposed to do it but my installer flat out said they didn't know how so we ended up doing it for them by reading the instructions. I guess reading comprehension isn't everyone's strong suit. But I digress. Fujitsu may require to have a 'professional' install it. If so we'll have to pay for someone to come sit here while we do it ourselves as the last time the 'professional' programming duties consisted of powering the unit off and on while I programmed it.

    Bookmark   July 11, 2012 at 5:59PM
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It really seems like the mini spit system has a lot of advantages, even on a new home build. With my life style, I really like the idea of high zoning-- the house will be a little bigger than what we need for a couple years and I like certain areas cooled down. I'm curious why more new builds don't consider the ductless option? Especially if the technology has advanced to hide the units upon build and potential energy savings.

    Bookmark   July 14, 2012 at 6:18PM
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I'm guessing part of it is the cost. Our system cost $15.5K. Most of the bids were for $20-$30K. And this was only to do the part of the house we use. It would have probably been another $10K or so to do the rooms we didn't. In addition finding a contractor who knew what they were doing was really tough. So part of it may be unfamiliarity with the products.

We think we've solved our bedroom draft issue. I changed the ceiling programming from high ceiling to regular and then set the vents to the heat position so they don't throw the air out over the bed. It seems to be working but we've had to lower the temp. in the bedroom because it doesn't cool the whole room as well. Even so were happy with the results because we no longer have the air blowing on our heads. The dogs are not so happy. They are still trying to figure out new comfortable places to sleep at night.

    Bookmark   July 14, 2012 at 8:17PM
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Minisplits are far more expensive than central air.

Zoning sounds good in theory but it doesn't help that much with energy use. In a well insulated new home, that hot section of the house heats up the cooled area.

Zoning is typically about comfort and not energy use. When minisplits cost roughly twice as much as a basic central system, it is easy to see why they aren't done very much.

    Bookmark   July 15, 2012 at 3:14PM
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" programming from high ceiling to regular"
That must change the blower speed and maybe the focus of the air flow. It is really neat that they program that kind of stuff.

" When minisplits cost roughly twice as much as a basic central system,"
How did you arrive at that figure?

"Zoning is typically about comfort and not energy use."
I don't understand. If a well-designed residential HVAV system keeps all rooms at a comfortable temperature, why should zoning be desirable for comfort?

    Bookmark   July 16, 2012 at 9:43AM
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