Please help with my new construction, thinking about mini split ductless system
First of all this is my first post in this great forum. Been reading many threads here, but the more I read the more I am confused...
Here's my situation. We are building a house in Fremont, California. Weather here is fairly mild (average summer temp highs is around high 70s to low 80s, go up to the 90s maybe 1-2 week the most. It's fairly dry here so humidity is not a problem. The house is about 4300 sq ft of living space, 3 stories on a steep hill, with the lowest being the garage, main level and the upper level is about the same size (~2100 sq ft each level). And because we are on such a steep slope, the house is step like stairs and with crawl space.
Now to our HVAC questions. On the heating side, we planned to install radiant flooring. We do need an AC system, but I am thinking about the ductless system (like mitsubishi or the Daikan), since our thinking is that by doing this we can get away with ducting, and these ductless mini split system seems very efficient and well build. On the other hand, I have read that people seem to use the ductless more for smaller space and/or retrofit. Is it a bad idea to eliminate all ducting for a new construction? Budget is also a big factor here, and it seems that the equipment itself will cost more for the ductless system, but I am hoping the installation cost will be cheaper and therefore the total installed cost will be less. Is that true?
So I am thinking either:
1. Full ductless mini split system for the whole house with various zone control. I like the ability of cooling each zone individually, and with no duct work I am hoping the total installed cost will be less than a typical ducted system. In addition no ducts sounds great as my floor plan on the main floor is very open.
2. Get a typical system with two condenser units. One will be located in the attic for the upper floor. The other one will be in the garage level, have the duct work in the garage ceiling so that the main floor air vent will be on the ground (so that I don't have to run the ducts through the main floor). Not sure if this system will cost more because of all the ducting work, and not sure how a unit in the attic will work (noise, venting to the outside, etc).
Some concerns I have with the ductless system is that, if I don't have any ducts, how do I get the systems for enhancing indoor air quality? I have read about these whole house fan, ERV/HRV, electronic air cleaner, circulating fresh air throughout the house, etc... Do all these need a duct systems? How does a ductless system do that? In addition, people seem to recommend sealing the house as tight as possible (using spray foam), but that also means I need some fresh air to circulate the house. Can you open the windows to achieve similar effect?
Lastly, can you tell me some rough system cost comparison between the mini split ductless and the traditional AC system? I know it varies, but I want to get some ideas before I go talk to contractors. Is there some HVAC contractors recommendation in the San Francisco Bay Area? There are just so many contractors but not sure which is good (both quality and value).
We don't discuss pricing.
An ERV/HRV can have its own duct system if you want ductless splits.
A mini split system will probably cost less, but it will certainly be more "visible", and a little noisier than a well designed duct system. Air distribution is also limited to a point source, single fan per zone. The open floor plan may allow for this, but it's difficult to obtain even temperatures everywhere. Would a separate one be in each bedroom, for instance?
Using an ERV/HRV on its' own dedicated duct system for fresh air is possible, especially with your weather, but it is less than ideal, because the air it will supply will not be fully conditioned. (IE warm air coming in during hot weather).
Here's the big picture - cheaper systems builds in compromises. I would personally not want to see mini-split terminal units (the indoor units) in my own home, plus the afore mentioned noise and distribution issues. Depends on what you want to live with, I guess.
One thing to note - you could get heat pump mini-splits - that would likely handle your heat load and eliminate the need for the radiant system - avoiding extensive cost. But then again, now your heat system will have the same compromises already mentioned. Radiant is very nice....
Last edited by larobj63; 11-02-2008 at 11:13 AM.
This is my opinion, but I think ductless are ok for single room or for small applications. If you are doing new construction, I would put in a central system(s). I wouldn't want big ugly pieces of plastic hanging from rooms in my home, if I had no other choice, I would, but given the choice, no way would I use one. There is nothing the matter with them and they work well, I just think they are ugly, you might as well put in window units, it will be even cheaper than ductless.
You bring up a good point.
That many people fail to consider.
Will a ductless system, decrease sell value later. When prospective buyers look at it and think, they look ugly.
Originally Posted by bmathews
The only time I have used them is in server rooms radio towers where looks are not important if I was building a new house I would go the extra mile and put in central system this will look right and if and when you do sell your home it will help the resell value of it but dont get me wrong the mini splits are apretty popular item.
I'd suggest that you think about central Heat Pump systems, one for each floor. That is what I had designed for my own home. Although, much smaller than your home, this was the best overall solution for me. Depending on what system you choose, it is less costly than putting in a number of ductless split systems. Your architect or engineer can probably help work through this question as well. The previous poster made a good point about not having to put in radiant heating with a heat pump. By the time three or four ductless systems are plumbed, wired and commissioned, you are probably paying at least as much as for a floor of central air with a heat pump.
As previously mentioned the aesthetics issue is something to consider. For a home of your size you would need numerous mini-splits. If that is the route you want to take you may want to consider full split systems from Daikin, Mitsu or Sanyo.
Each of these manufactures have VRV/VRF (Variable Refrigerant Volume/Flow) systems in which up to nine indoor units can be connected to a single outdoor unit. The indoor units can be either ducted or ductless so you could do both within the home and use what would work best in each area of the home.
These are not mini-splits but use some of the same technology which provides very efficient operation. The outdoor unit has an inverter compressor that can run as low as 25% of system capacity and can actually over run and have output greater than the rated capacity. The heat output is much greater compared to a typical heat pump at low ambient temps. The indoor units can be sized for the area they are servicing (sizes range from 1/2 ton to 4 tons) and are fully variable in output ranging from 10% of rated capacity to its maximum output.
All of it can be run from a single control device with a small sensor in each zone (the size of a match book). The controller can be tucked away in a closet.
These systems are highly sophisticated, efficient, and provide advanced levels of comfort.
There are many options when using VRV technology, and yes you can go either ducted or ductless. for example, you may put several bedrooms on one Zone with a concealed ducted unit. doing it this way wold still allow you to have zoning, but now run the whole house. There are other options, such as concealed wall cabinets that could be used in an entryway for example, or even under large windows. This technology is quickly becoming accepted and is in use in many applications. You can also bring your fresh air to the ducted units if you like, we have done that on occasion in hospital settings. I would take a good look at the full line catalog and decide for yourself what is mst important. I personally like the idea of thee systems as they are energy conscious, quiet, zonable, easy to install, and cost competitive in most cases. They also have the ability to give you a second source of heat if required, and when dereg occurs you may actually be forced to think about alternatives depending upon price per therm.
I think minisplits are great. But this is the wrong application. Minisplita are really popular overseas in small living areas. They are mostly used here in sunrooms and additions. you should think about a conventional split systems since you are concerned about IAQ. (you will not be impressed with the mini filter in the mini splt.)
Originally Posted by flange
I just sat through the diamond training for mitsu VRV set-ups a few weeks ago.
Me thinks they are awesome, especially in commercial settings where simultanious heating/cooling might be needed (I realize mitsu has a line that does not offer simultanious heat/cool for less $), but me also thinks this is expensive stuff for resi applications, no?
I'm asking, not attacking. I'm an ME - so I don't get good numbers for everything like you guys do....
Another great option for open floor plans with not much room for ductwork is High Velocity Systems like Space-pak or HI-V. The small duct work can go in wall cavities and reach places ordinary ductwork can't. The outlets are also small, unobtrusive, and have architectural diffuser options.