Central air vs mini split?

Jlamb

I would like some opinions on central ac vs Mini splits. Building a new home approx 2600 sq ft. I am partial to hydronic heating, but would like to have the ability to have AC. I want to be cost effective while being energy efficient as well. So it goes round and round with central ac conventional duct work ......or a unico system, which people have mixed reviews on. Heat pump system with an air handler, because I am not a fan of the cassets or heads. Everyone I have talked to says that mini split is the most efficient but I still cannot use that as a primary heat source in (Maine). So now I have the added cost of baseboard,panel rads, radiant etc. So my question is if you were building a new home what would be your choice for heat and ac?



Thanks

SWEI

If I had my druthers

I'd install radiant tubing in the ceilings (and perhaps a few bathroom walls) and a hydronic heat pump for both heating and cooling.  Then a VRF small duct A/C system sized to handle latent loads and MUA.

heatpro02920

My choice would be...

Gas fired furnaces with case coils, heat pump/cool condensers and mod/con powered radiant flooring and either a smart tank or a tankless water heater... Cost wise this is a pretty nice system...

you use the heatpumps in the shoulder seasons then the mod con radiant when the heatpumps get inefficient. Install case coils ontop of a decent variable speed 95%+ gas furnaces and configure the controls to use the furnaces if your radiant can't keep up or is out of service...



That system works well and the cost of a furnace and coil vs a a/c air handler is not much. Now If no expense is spared, I would install a couple waterfurnace series 7 units with a series 5 unit for water, variable speed pumps, monitoring system, ect ect ect... believe it or not with a 30 year mortgage you will save a ton of money if you can roll it in...



As far as mini splits and unico type systems go, no thank you, not in my home....



Rite now, my house is 4300 sq ft and we used a coal furnace to heat this year, I have a mod con and hydro air units, with heat pumps, ect... BUT this year I was trying out the coal and normally in heatpumps and running the propane we would have spent $6000 or so this season, but with coal we spent under $1500.... {tankless propane DHW with a hybrid used in the warm months...} My house is my frankenstien testing ground...

Harvey Ramer

Radiant!

You already like Hydronics. Go with it!



I would look into Radiant heating and cooling with a Daikin Quaternity for humidity control and indoor air quality.



Harvey

heatpro02920

I am so curious about radiant cooling

I have never done it, not very popular around here... where can I go to read more about it...

Harvey Ramer

Couple places.

Uponor is probably at the forefront of this. They an hour long webinar that discusses technical design. Healthy Heating I believe has information on it. Siggy has info on it. ASHRAE has design parameters published.



You should have a good understanding of psychometrics when designing a system like this. You need to separate the sensible and latent loads. Tube spacing also becomes more critical if you are doing radiant floor cooling. You need to space closely in order to satisfy the sensible load @ ASHRAE minimum design water temp. Radiant ceiling cooling is much more flexible. Either way you should monitor your water temp with a dewpoint control.



The Quaternity is able to maintain a humidity setpoint due to it's split coil and air mixing capabilities. I haven't done it yet but all the data suggests it would be an ideal fit for radiant cooling.



Harvey 

heatpro02920

thanks

gonna have to look into it..

Jack

The Mini-splits are a great idea

Retrofitting duct work to a building is like the Texas Chainsaw Murders. Mini-split heat pumps are an ideal compliment to a hydronic system. Carefully check the specs on each model of each manuf you consider. I would stick with Fujitsu, Mitsubishi or Daikin. I have a single 12kbtu mshp that cools my entire first floor here in CA. As well it provides excellent heat. In your circumstance you would probably run the mshp in the shoulder seasons and not run your boiler until you have a bit of a load on it. Your choice. Do your research and get the best experienced guy in your area.



I did a combination of mshp's here. a multi for the bedrooms upstairs (16.5 seer, 9 hspf), Downstairs, where we run it much more frequently I have the 12 (25 seer, 12 hspf). With the new remodel and kitchen addition I installed a 15 in the center. Depending upon air flow this summer I think I'll end up pulling the 12 and installing at at my daughters. We'll see.

Noman

low load house+ashp

I'd design small with open floor plan and spend a few extra bucks on insulation and air sealing. At that point two ductless minisplits should handle your load for most of the year. Electric resistance takes care of the rest. In green build circles there seem to be a growing consensus that strategy yields comfort and the best bang for buck.

Lots of articles over at Green Building Advisor on that strategy. Check out Marc Rosenbaum especially.

The new Mitsubishi FH series has fantastic cold climate ASHP performance. Mitsubishi is supposed to be working on expanding their hyperheat minisplits and adding multihead units, maybe by next year. That'll do three things--allow a single condenser to serve multiple heads, allow ceiling cassettes with hyperheat, and allow an HRV (mechanical ventilation) to be integrated.

Good luck on your project.