Just threw my intial HVAC plan in the toilet last week after discovering some big drawbacks with the service just last week at the last minute. Service issues with some serious money needed to install the needed ductwork has got me now looking at something totally different now. The pressure is on as I am now scrambling to get a new system designed and priced. I have just talked to a few guys in the past day or so about a VRF system. The one I am looking at is also a Heat Recovery unit that can move heat to one part of the house to another if need be thru refrigerant lines. I am sure that this is a new concept to most out there, but that past of a system never really occurred to me other than just using the old fashioned duct work and a fan do it as I think I might have one section of the house that may overheat in the winter. Regardless, that is not my main concern. Getting around some of this large amount of ductwork that was required for my initial forced air system is now my goal. The house is not that small. 3800 sq. ft. Though 800 sq. ft. of that is unfinished or mechanical room/storage, but it still needs to be heated I guess. Now 60% of the lower floor (1800 sq. ft.) is under or almost completely under grade as its a walk out basement with ICF block walls supporting the main floor above it. The house is almost a complete identical stack footprint with another 1900 sq. ft.on main level. I have only a few small north windows and a couple on the east and west sides. But a large amount of on the south side. I have it set with the eves/window combination now to really get the sun in the winter which we usually have plenty of here in the winter. But none in the south for two plus months to either side of solstice. So cooling is not a main concern, but secondary. The walls are either 2x6 or 2x8 , 24 inch on centers. My consultant friend of mine has calced the house out to around 46,000 k BTU at a design temp of -4. Thanks for looking. What do you guys think about these VRF systems? I think this new Trane line just came out a few years ago I am looking at, 6 ton 4TVR0072.

Posted By beetle55 on 28 Jul 2014 09:57 PM
... My consultant friend of mine has calced the house out to around 46,000 k BTU at a design temp of -4. .... I am looking at, 6 ton 4TVR0072.

If the load calc came out to 46K BTU (~4 tons), then why are you looking at a 6 ton unit?

Because the output at my design temperature fell to about that load and that was the smallest one they make in that series, however I have since learned that its a 3 phase system and the cost of the converter and the system doesn't make economic sense so its not an option any longer anyway. I am now looking at a 5 ton Mitsibushi PUMY series VRF. Every had any experience with that?

Posted By beetle55 on 09 Aug 2014 08:25 PM
...I am now looking at a 5 ton Mitsibushi PUMY series VRF.

I'll restate the question again.  If the load calc came out to 46K BTU (~4 tons), then why are you looking at a 5 ton unit?  Note that the load calcs generally have a pretty generous fudge factor built in, so adding more fudge to the calc just wastes money both in higher initial equipment costs and generally higher operating costs.

Also, 46k BTU seems kinda high for your load based on your proposed home size and design. Where are you located?

Your house design appears to be similar to mine, although I have ICF from footings to rafters with a full walk-out basement facing the south. I have ~1600 sq ft heated & cooled in the basement and ~2200 sq ft heated & cooled on the main floor. I will have ~R50 blown in the attic. I'm located in Arkansas near the top of Zone 3. My peak heating / cooling load came out to ~26,000 BTU.

Yes with the VRF unit you want to check it's efficiency with outside temp. If it is going to be under 17 deg most of the winter it might be a good idea to oversize or size based on the VRFs actual heat rating for temps outside. I have a traditional heat pump, two of the, and the house was 1900sft before our addition. In theory the load calc said about 3 tons in the winter. I put in two two ton units because the actual amp draw and price were minimal. I can tell you that with these cold winters we have had that 4 tons is not actually 4 tons but more like 1.75 when it is below 17deg and around single digits. This is why we have strip heat. Now, with VRF you will not have strip heat built into the unit. VRF also is not just on off and all of the mitsubishi units have DC inverter compressors. I am looking to put in a couple of small H2I units in my house and eventually put in a larger multi head unit when it is time to replace my two existing heat pumps in another 5 years or so (if it is close to the 10 year mark I can actually get some decent money for them.)

What I have not seen however is any actual efficiency ratings for part loads on the inverters. For example, the mitsubishis that I want to install are 30.5 seer and something like 12 hspf. Those tests are done at full load. However, seeing some of the actual amp draws people are getting during part load I tend to think that the units are more efficient part load pulling only like 3 amps and having the full surface area of the larger coils. Now what gets really interesting would be comparing actual part load numbers to a larger unit vs multiple smaller. On paper it looks more efficient to do multiple 30.5 seer units. The bigger units might very will be more efficient than their 18.5 seer rating at part loads and you get the advantage of almost always running part load unless every single head in the house is cranked to 100%. If you size each head to compressor, or dont install one of the heads at all, you in theory would never run 100% with your system.

I would also install two smaller units before installing a DC inverter. The mitsubishi H2I citi multi with H2i, the only multi zone H2i that I know of, looks nice but requires a three phase converter or three phase service. Not what most homeowners are looking for. Also multiple outdoor units would be nice in case one breaks. You no longer have strip heat to you could be SOL in the winter if all of your splits are out. This kind of happened when getting the siding done here, one of the members of the siding team tried to slide between the outdoor condenser unit and the wall. He actually slid it out quite a bit and the refrigerant lines were coming out of brick and going to the units. One of the units had the refrigerant line start leaking. By the time I got home it wasnt heating my second floor at all. I of course caught something was wrong when my wife got home before me and texted me. I then checked the temps on my phone and at that point it was about 8 deg lower than it should have been. Anyway, my second floor got to about 40deg that night because the outside temp was 6 deg. If we had not had two units we would have had to stay somewhere else or frozen to death.

I agree that there is a lot to be said for some redundancy - so you and the house can survive one unit failing.

I recently found that LG seems to make a nice looking 28seer unit that almost matches spot on with the Mitsubishi units. They are $400 cheaper and the WiFi attachment is cheaper or free. However they don't have the WiFi option for their vrf multi splits. With the Mitsubishi units I could install a couple of high seer units and then fill out the rest of the zones later with a multisplit. In theory you could do the same cheaper with the LG but not have WiFi on the multi.

Industry scuttlebutt has it that the LG units of a few years ago had unusually high warranty repair claims. I'm not sure how much of that is design vs. manufacturing/QC vs. installer training issues, or if the situation has improved. Their efficiency numbers are very good, especially when viewed from a price/performance point of view, but it doesn't take many repairs to eat up any price advantage.

It's not as if Mitsubishi/Fujitsu/Daikin units never have problems either, but their US support networks are bigger, and the reliability reputations are better.

I would like to see current info before purchasing. The system that I am looking at lets you hook the outdoor unit to USB and run a ddiagnostic program provided by LG and see exactly what faults are what and how the thing is running. This makes some repairs easier. I know that I can not do this from my Rheem unit. It does have some trouble shooting features on board but nothing like that. If it is a minor repair I would swap the part myself. Anything requiring messing with the soldiered tubing would definitely be a call to a tech. However, knowing what's wrong ahead of time would cut down on labor costs and getting rodded by the tech. When I did both rheems I had a local firm come out and do the once over and refrigerant. Both were quick and I felt I got treated fairly. When the siding team bumped the condenser units and let all the r410 out, they called a different group. The first thing they wanted me to do was to pay them extra change to move both units 24 inches from the house. I quickly explained that the manual recommended 10 inches or more on that side and I had put it at 12 or a little more but close enough so if the gutters overflowed in the winter the fan couldn't freeze up. The guy got quiet quickly and said it was a state thing but I saved about a grand by not letting them do it. So it is very good to have a very good onboard second opinion.

I also wonder why the warranties are so short on the ductless. The only thing I can figure is that they expect more diy installs and there is a lower profit margin for the install. It could also be that they don't last as long. Personally, anything like that which lasts 10 years now would probably be worth the money to upgrade. My neighbor had a nice carrier unit put in that he paid around 3 grand to get done since they had to split to two zones like we did. His lasted about 10 years before the unit started getting large chunks of ice on the outside and the renter would scrape it with a shovel. For whatever reason he went ahead and got carrier to replace it. The renter told me that the electric bill got worse. That would probably be an exception in almost any other case. I know mine dropped $100 a month just by going with Seer minimum units.