I had been looking at these off and on but for some reason thought they were a nitch item only. Today I found out that on most HVAC sites they are listed under minisplits. I found that for the cost of a third heat pump and air handler for my addition, at 14seer 2 ton, I can get a LG 54000 btu https://www.acwholesalers.com/LG/LMU540HV-54000-BTU-Ductless-Heat-Pump-Air-Conditioner-Inverter-Outdoor/30171.ac?catId=cat1251&mainCat=&subCat= inverter unit that will work down to almost single digits without strip heat. I find this interesting because in my current house I have two two ton heat pumps. Most of the summer and most of the winter they are oversized. However, some january nights it gets cold in here and in some hot july days it starts to overcome the units. So you have a humidity issue most of the summer as well as constant on offs. Overall, my untity bill isnt bad but I am looking to reduce it through envelope enhancements. Now, I had been looking hard at a geothermal unit but not looking forward to the ground loop install. I had looked at high efficency split heat pumps and air handlers but require one air handler for the whole house. I live in Virginia so I think a very efficent air-air would probably likely be close to a geo system in effiency. Looking at the LG or even Daikin system, I can easily oversize and not suffer efficency and other issues if I improve the envelope because of the inverter system. I get to choose between mini air handlers, wall mounted, and ceiling box units. I could easily go cheap wall mounted in my shop and a miniducted or ceiling box in the addition. I could then slowly purchase and retrofit the rest of the house into up to 8 zones. Finally, this outdoor unit uses the same 30amp breaker as one of my 2 ton units. My old 3 ton trane used a 50 amp outdoor. Seems like a lot less power? So, are my numbers off? Will I see close to the efficency of a geo in a mild VA climate. Is the total insulation cost too good to be true? Will this inverter heatpump really work as good and last as long as a traditional? Also, I have wifi thermostats now and do not want to lose them, will these units allow for any stat or just the LG or daikin specific?

Internet scuttlebutt has it that the LGs have some of the highest warranty recall rates of any of the vendors. Proceed with caution there.

Daikin is on the other end of the heap- very high quality all around, under-promising and over delivering on performance, and very high reported reliability. Some of that is installer certification, some of it is design, but world-wide Daikin is the largest vendor of variable refrigerant volume inverter drive HVAC, followed by Mitsubishi (the company that invented the technology), and Fujitsu. In the US Mitsubishi own's the lions-share of the market, followed by Fujistu, but it varies from local market to local market.

You probably need anything like a 4.5 ton multi-split like that LG under any circumstances, unless you have a whole wall full of unshaded west facing glass and a huge cooling load.

Having 8 zones is also way-sub-optimal, since the smallest heads from any vendor are in the 7000BTU/hr range, and likely oversized for most individual rooms. Dividing the output of a mini-duct cassette between a couple of rooms will usually work out better.

Older ducted non-inverter heat pumps had abysmal performance at 30F, and even worse under 25F. If your pair of 2-tonners were almost keeping up, there's no WAY you'd need anything like 4 tons of ductless for heating at VA type outdoor design temps. At +15F most multi-splits & mini-splits will be capable of delivering 15,000BTU/hr per ton of compressor at a COP=2 (at max-compressor speed, higher if modulating), whereas your old-school heat pumps would be crapping out at 20F at ~9000BTU per rated ton, at a system COP under 1.5. So while I can believe your heat load on the coldest nights might be over 35,000BTU/hr, I'd be very surprised if they're anything like 60,000BTU/hr (4-tons of ductless.)

And yes, in a VA climate, if properly sized, your seasonally averaged COP would be ~3.5, comparable to a typical (but not best-in-class) geothermal implementation.

But getting to the right solution starts with a real heat load calculation on the "after" picture of any window or insulation upgrades you're contemplating. Without it you could easily over or undersize the thing, which has efficiency and upfront cost consequences. Oversizing any head (or the compressor) by more than 50% ends up costing more and runs at lower efficiency. Ideally you'd never be more than 25% oversized, a point at which single-head mini-splits can sometimes beat exactly-sized units on efficiency, without losing too much to cycling & idling losses on the shoulder seasons.

Both Mitsubishi & Fujitsu have quite a range of multi-splits and cassette options in the 2-4 ton range, as well as Daikin. Stick with those three and forget the rest.

Air sealing the house and managing the ventilation rates can keep the summertime humidity well controlled in most homes cooled with ductless technology. In VERY high performance homes you may need a dehumidifier, but the Daikin Quaternity series has independently settable relative humidity and temperature setpoints, and can dehumidify without cooling the place if need be. They're pretty expensive (an $800-1000 cost adder compared to a standard Daikin mini-split of equivalent output & efficiency) and only come as single-head units, but it may be worth heating & cooling at least one large zone with a Quaternity, even if you used a multi-split approach for the rest, and that would pretty much guarantee that the latent loads won't outstrip the latent capacity of modulating multi-splits.

Well talking with my wife she is onboard with getting the addition done first. Since it will be built with R30 walls and R50 minumim attic when I am done it only makes sense to do a smaller outdoor unit with that area first and then do the existing house later after the envelope upgrades. I am looking at daikin units. A 2.5 ton split system for close to 1000sft of area is a bit oversized. My heat load for the second floor at 0 deg is about 14000btu. The first floor will be less because the conditioned area is smaller. A ceiling cassette system in the big second floor room will be almost perfect. A traditional wall mounted unit in the shop will be approved since it is a work area.

The only downside is that the daikin internet stats do not work with cassette indoor units. They do work with the mini concealable ducted units but then the seer goes from 18 to 13 (dont ask me why.) Which seems like poor design and business. Why would I go with a ducted unit that has such a poor efficency. My existing 2 ton units are at 14 seer and 9 hspf without the resistance heating.

Some might say that the seer is reduced by the flower fan and duct losses, so would very short rigid duct runs actually have a higher seer than the quoted 13??? Also, is there another alternative for internet control for such a unit without donating my testicals? Finally, at even the lower SEER and HSPF, with a short duct length, inverter HP, and super insulating the ducts, will this still be more efficient than a traditional rheem 14seer split single stage? If so, how much?

Unless you live at the top of a high mountain 0F is a ridiculous heating design temp in VA. Most locations in VA will have a 99% design temp between +10F in the interior hills to 25F on the warm coast.

http://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/Outdoor_Design_Conditions_508.pdf

A tight house with a whole-wall R (not center-cavity-R) of R30 and an R50 attic will have a fairly long time constant, and you can probably use an even higher temp than the 99th percentile bin and do just fine. Yes, it gets down to 0F sometimes, but never long enough that the BTU shortfall of a unit sized exactly to load at the 99% design temp would ever be felt.

The issue with a standard split-system in a high-R house is the duct losses, air hander power, lack of modulating and the likely gross oversizing, no matter what the HSPF and SEER test numbers say. A mini-ducted modulating system will do better than a non-modulating long-ducted system in the real world. Ducted systems also drive air infiltration, adding to the instantaneous loads while operating, which is a situation easier to minimize with a mini-duct cassette than with a whole-house system.

Been doing a lot of research over the week. I will have real R30 walls with staggered studs. We got to 5 deg last winter and it sucked a couple of times. So, looking at a heat loss and the drastic differences between the addition and the rest of the house I am going to go with a 2 ton Mitsubishi. I want to install a ceiling cassette unit on the second floor room which is 24x24 with a second 24x14 room connected on the back of that with no wall dividing. The 24x24 portion is over the garage with r19 under it. The 24x14 portion will be over my shop and I will be insulating between the floors with R30 for sound purposes. The ceiling cassette will be a 15000 btu unit and the unit in the shop will be 9000 wall hanger. The outdoor unit will be slightly oversized most of the time but at 17deg it will produce exactly the BTUs that both units can handle. From what I have read, keeping the outdoor units at partial load is more effiecent anyway. I might even go with the 30,000btu unit instead of the 25,000 so I have the option of installing another head inside of the garage in case I want to do work in there.

As for the rest of the house I am going to keep my two two ton units for now. If the addition goes well then I will probably replace them on a 5 year plan. My mother desperately needs a new second floor hvac system in her house but will not hire someone to do it. I am confident I could roll in one day while she is at work, flush the lines, and drop in one of my 2 ton units. Her ductwork and sizing is not jacked up like mine.

Why mitsubishi? Well, in short because they support redlink. This is the only split mfg who has a standard that will let me easily link the system to the internet for control with little fuss. Each zone can be zoned with a $100 receiver.

My only concern at the moment is the airflow of the ceiling cassette unit. I know it is rated at 15000 btu and the heatloss of the two connected rooms is around 10000 btu, but they are in an L shape. If I put the cassette in a third of the way into the 24x24 room, will the bottom vent have enough velocity to adequately cool the backside of the 24x4 room? I know I will have two ceiling fans in there, one in each room...

Thanks... This is so much more exciting than the geo system that looked like cool returns but a money pit and headache with the drilling or excavating.

Without a head in the room, all bets are off. I would rather do one room correctly and hope to reduce the humidity in the other with a ceiling fan for help while occupied. Of course all advice is dependent on a room-by-room heat load. Windows are the key to cooling.

I will come up with a photo...

Ok so here is a simplified version of the plans. Forgive the door in the office closet bc that was not originally in the plans and I added it! So the red box in the office is the 15000btu cassette. There will be a ceiling fan at about where the words office and sitting are. R30 on all exterior wall when are the ones on the bottom top left and bottom right... R13 minimum between the old house and the new addition!

More research done. The difference between the 1.79 ton unit and the 2.5 ton unit is 8000btu.

The 2.5 ton unit also has less input wattage at full capacity than the 1.79 ton.

The 2.5 ton has 17.5 seer and 10.5 hspf

The 1.75 ton has 18 seet and a 8.9 hspf.

I guess the more important numbers for sizing variations is the capacity variation available with the inferter

1.79 ton varies from 7,800-20,000 btu

2.5 ton varies from 12,600-28,400 btu

So the difference on the min end is 4800 btu. Not a huge difference when divided between two floors. Plus I get the extra 8,400 btu of capacity for the winter. However, at 17 deg outside that number drops to 3500btu since the bigger unit caps out at 18000btu at 17deg.

I think the extra 3500 btu could be necassary when it is very cold. This worries me since the theoredical heat loss is 14000 btu at 0deg. Real world numbers will likely be higher with a margin for error. This way the room should remain warm even on those cold virginia nights we got this past winter of around 9 deg.

HSPF and SEER are somewhat squishy numbers. The max capacity at 45F outdoor temps is only slightly more than at 20F for a ductless, but the efficiency at 20F at the max modulation is about half what it is at the smaller load at 45F. (With ducted heat pumps it's an even sharper cutoff on both capacity and efficiency.)

Knowing the output at your actual 99% outside design temp is a critical part of the design. To really design these things you need the extended temperature & capacity charts, not an single-number, but keep in mind that the efficiency at part-load soars. A COP of 2 or 2.5 at your 99% outside design temp is pretty inconsequential if the COP when operating at your average winter load is 4+.

Check the 3rd party tested capacity and efficiency graphs of a couple of popular one tonners:

http://www.nrel.gov/docs/fy11osti/52175.pdf

And using 0F as an outside design temp for any VA location is just nuts- odds are it's something like +15F:

http://www.energystar.gov/ia/partne...ns_508.pdf

Yes, it might get to 0F sometimes, but not for long enough for the shortfall to make a substantial dent in the room temp. During the cold-snap of the century you might have to leave the lights on or turn on a space heater, but sizing the ductless heat pump for the load at 0F in a location where the 99% bin is +15F leads to higher expense up front, and cycling losses during the shoulder seasons.

Looking at the numbers that I keep running, it looks like the 20000btu system will be more than enough... However, adjusting the heat load calc to 15 deg does not change the loss numbers that much. Probably because of the thicker walls. I just found that there is a similar 24,000btu system available that fits my 15 deg design temp btu for btu almost exactly at 15 deg. At 0 deg it might fall short but I think with R30 walls it would take at least a day at 0 deg to begin to have an issue.

I dont know why the pictures I posted will not load but the room, that I am for the sake of things calling two rooms, is shaped like a giant P. The front half is 25x25 and over a two car garage with r19 in the floor. The rear half is 14x25 and over a workshop which will also have R30 between the floor mostly for sound purposes but will be conditioned. Their is a staircase that comes from the first floor in to the center between the two large rooms on the second floor. No wall between the 25x24 and 14x25 spaces. The walls in all areas, except the unconditioned garage, will be R30 and ceiling will be somewhere in the area of R50. I might consider insulating the roof deck further to keep heat out so if I do that there will be r15 between the second floor rooms and the r50 attic just to prevent rapid heat loss into the uninhabited space. Since I am not going to have ductwork in the attic now I am strongly considering just doing r50 cellulose on the ceiling to minimize heating and cooled square footage. I am looking at one ceiling cassette in the large p shaped 25x25 and joined 14x25 room or rooms and I will have one wall mounted unit in the workshop underneath. Since the unit I am looking at can use three heads I will have the option for a third unit inside the garage if I ever decide to do work in there. It is also possible that my new heat pump water heater will be located inside the shop or the garage. The only reason I am leaning towards the garage is because it never gets too warm or cold in there. I comfortably workout in there in shorts and sweats in the winter so it never drops below 40 without an insulated door. I plan to insulate the door. However, I have been getting mold spots on the wall in the summer and could possibly benefit from having the dehumidification inside.

My concern is with the large second floor. My calculations show that the 15000 btu ceiling head unit will meet the 14000 btu heat load almost exactly. Placed in the larger 25x25 section with one vein pointed into the 14x25 section. I would have a ceiling fan in each 25x25 area and the 14x25 area. I am just slightly concerned that the large room will not be satisfied by the airflow of one unit even if meeting the BTU demand. I dont want hot and cold sections of the room. I guess in theory with 15000 btu being jammed into a r30 area capped with r50 this wouldnt happen... but. My wife absolutely does not want a wall unit in the room on the second floor so the Isee adjustment feature would be out. I could be sold on a wall unit but I would need a real good reason to convince her.