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MN Renovator · 01-22-11, 10:43 AM

I've been looking at the mini-splits and started tossing numbers into the AHRI Certification Directory Variable-Speed Mini-Split and Multi-Split Heat Pumps section and air conditioner section.

There seems to be a huge disconnect amongst the way that efficiency works in these units. It seems that with standard central air units, to get better efficiency you need a cooling-only unit, which includes the Nordyne central-air inverter setups too. The inverter mini-splits have the highest SEER of any non-ground source air conditioner in the entire directory with 9,000 nominal BTU units at 26 SEER and 12,000 nominal BTU units at 25 SEER. Both Fujitsu but Mitsubishi, Toshiba Carrier, and LG have some that are close. For heating, I look at the ratio between low heat(14f) and high heat along with looking for a high HSPF since a very large portion of the winter heating in Minnesota is single digits and we dip lower fairly often which might cut the unit off completely.

It seems that SEER and HSPF both drop with SEER to closer to 20 or slightly lower if you want a size or sizes larger than these tiny ones. I've monitored my heating and for the Fujistu's minimum temperature rating of 5 degrees, I could probably keep my house up to temperature just with that tiny unit even with defrost cycles, I'd still need natural gas backup. The problem is at temperatures under 14 degrees, the only way I would save over a 90%+ efficient furnace(very cheap natural gas here) would be to use it in the room or area of the house I am in, such as the bedroom and allow the rest of the house to drop lower under setback.

If I had one, it would be upstairs in the master bedroom(where I sleep and don't mind surfing the net in on my laptop) and in my room I could aim it so it goes out the door and down the hall and with the second bedroom door open the airflow might reach to help with cooling if convection didn't do a decent job already. If the 12k unit couldn't keep up in the summer, I could section off(either partially or completely) the upstairs easily(smallish vault section opening for the stairs) and just cool that area and allow the rest of the house to get to a higher temperature and just use the central air for when I have people over or want to use the rest of the house but I'd probably only doing this during the hottest month of the summer or whenever the mini-split becomes undersized for the area. I once told someone about the 25 SEER unit and that I was interested, they thought 25 SEER was amazing but once I told them the capacity and price they shot the idea down quickly as being 'a very expensive way to cool just one room'. I think convection airflows are a bit more powerful than people imagine. He also hasn't seen my floorplan and why I think it would work well.

01-22-11, 10:43 AM	#295
MN Renovator Less usage=Cheaper bills Join Date: Nov 2010 Location: Minneapolis, MN Posts: 939 Thanks: 41 Thanked 116 Times in 90 Posts	I've been looking at the mini-splits and started tossing numbers into the AHRI Certification Directory Variable-Speed Mini-Split and Multi-Split Heat Pumps section and air conditioner section. There seems to be a huge disconnect amongst the way that efficiency works in these units. It seems that with standard central air units, to get better efficiency you need a cooling-only unit, which includes the Nordyne central-air inverter setups too. The inverter mini-splits have the highest SEER of any non-ground source air conditioner in the entire directory with 9,000 nominal BTU units at 26 SEER and 12,000 nominal BTU units at 25 SEER. Both Fujitsu but Mitsubishi, Toshiba Carrier, and LG have some that are close. For heating, I look at the ratio between low heat(14f) and high heat along with looking for a high HSPF since a very large portion of the winter heating in Minnesota is single digits and we dip lower fairly often which might cut the unit off completely. It seems that SEER and HSPF both drop with SEER to closer to 20 or slightly lower if you want a size or sizes larger than these tiny ones. I've monitored my heating and for the Fujistu's minimum temperature rating of 5 degrees, I could probably keep my house up to temperature just with that tiny unit even with defrost cycles, I'd still need natural gas backup. The problem is at temperatures under 14 degrees, the only way I would save over a 90%+ efficient furnace(very cheap natural gas here) would be to use it in the room or area of the house I am in, such as the bedroom and allow the rest of the house to drop lower under setback. If I had one, it would be upstairs in the master bedroom(where I sleep and don't mind surfing the net in on my laptop) and in my room I could aim it so it goes out the door and down the hall and with the second bedroom door open the airflow might reach to help with cooling if convection didn't do a decent job already. If the 12k unit couldn't keep up in the summer, I could section off(either partially or completely) the upstairs easily(smallish vault section opening for the stairs) and just cool that area and allow the rest of the house to get to a higher temperature and just use the central air for when I have people over or want to use the rest of the house but I'd probably only doing this during the hottest month of the summer or whenever the mini-split becomes undersized for the area. I once told someone about the 25 SEER unit and that I was interested, they thought 25 SEER was amazing but once I told them the capacity and price they shot the idea down quickly as being 'a very expensive way to cool just one room'. I think convection airflows are a bit more powerful than people imagine. He also hasn't seen my floorplan and why I think it would work well.