Daiken or Mitsubishi Inverter Systems for Residential?
We are at the framing stages of a custom home in North Texas and are looking at the options for a/c and heat as we are trying to get US Green Building Council LEED's certification and efficiency is a consideration. Total cooling capacity between 10-12 tons.
We are considering (2) 4 ton residential variable refrigerant units from Daiken or Mitsubishi in addition to the concealed ductless units. The Mitsu is the S Series. The Daiken compressors are RXYMQ48MVJU. On the domestic front, we considered the Carrier hybrid system with 21 seer compressors.
Here are the questions we are trying to get answers to before finalizing the decision:
1. What are the differences in efficiency between the systems?
2. What is the availability of parts look like between the two foreign companies?
3. How well do they produce heat when there is an extreme change in ambient temperature and how cold is the a/c? Dallas ambient temperature can drop from 70-25 in one winter day and can go from 50 to 100 plus in the summer.
4. Any other differences that we should consider?
5. Any experience integrating the systems with whole house automation?
1. These systems do not have SEER ratings because of the many different indoor units that can me matched to it with capacities as low as 50% of the outdoor unit to as high as 130%. The best way to measure and compare to other manufactures is to look at the COP in both heating and cooling modes. That is simply energy in vs energy out (convert KW in to BTU, 3,414BTU = 1KW and divide into output). The Mitsu is not as efficient as the Daikin. Here are the kilowatts to produce the rated BTUs:
Originally Posted by MILTON01
Cooling 48,000 Mitsu = 4.97 Daikin = 4.73
Heating 54,000 Mitsu = 4.88 Daikin = 4.26
Mitsu Cooling COP = 2.82
Daikin Cooling COP = 2.97
These are the COP at the nominal rated capacity. Unfortunately, finding the ratings at part load, say when the compressor is only providing 18,000 BTUs is hard. But, since the compressor speed is slowed down in that situation then the energy being used drops even faster. I would expect the COP to be as high as high 4's to low 5's in part load operation.
2. Daikin has the largest US market share. Both should not be a problem though.
3. Because they can run at higher than rated capacity they will be better in those situations. But even more significant is the fact that these system run almost constantly to condition the indoor space. Therefore, they are constantly modulating the output to meet the needs of each of the zones within your home. Most run as low as 25% of nominal capacity, thus on a 4 ton system it will be running when there is only one ton of load. As the load changes it is already running and adapting with the changing load.
4. These are top systems and what the rest of world has be using for several years now. You can have up to eight zones with one outdoor unit. Each with its own cooling and heating specifications. Air handlers are rated as low as 7,500 BTUs, so even a small space can be a zone without all the air flow issues with ducted zoning that the typical system (Carrier) will have. May also want to consider the Sanyo Eco-i Mini. It is rated at 54,000 cooling and 60,000 heating and has even better COP.
5. These systems are smaller versions of commercial systems used in large buildings. In those situations they can gang together many outdoor units to feed all the indoor units. Hundreds of indoor units can be managed by computer based automation systems. Each of these that we are discussing here can be incorporated with computerized automation systems just like the larger systems.
If you go with the 4 ton systems seems like you may need three instead of two outdoor units. Good thing you don't have to worry about performance problems with oversizing as you do with typical systems. Three ton systems are also available from each of these manufacturers. See what your engineer says the load will be then match outdoor units accordingly.
If I'm not mistaken, Daikin has a base of operations in Carrollton. You might want to contact them to see about qualified contractors/installers for your part of the Metroplex.
The president of my RSES chapter has been to the Daikin facility in Carrollton for a tour and walked away very impressed. One of their representatives came to a chapter meeting of ours and explained the VRV system to us. Overall, the inverter driven systems are more flexible for squeezing heat out of the air due to the variable speed compressor (this is not a two stage compressor...it is truly variable in speed). These compressors, in a sense, can be "overdriven" somewhat to move more refrigerant to meet demand. Example: in summer, a conventional single speed compressor will pump a fixed amount of refrigerant when the system is operating under design conditions. Should design conditions be exceeded, the system has no reserve capacity...at the very time one needs more capacity, during an extreme environment, there is less. With the inverter driven compressors, they can move more refrigerant when conditions are beyond design, resulting in more capacity when it is needed. Although I haven't thought how it might work, there may be a similar strategy for winter heat pump operations.
I have lived in the Dallas area most of my life...I've seen the 70 to 20 degree drop scenario before, but I can't recall waking up in the morning to a temperature of 50, only to come home in the evening over 100. I do recall one day about two years ago here in Cowtown where it came close to doing that...45 in the morning and into the nineties in the afternoon. Weekend before last I recorded 55 in the morning and saw 87 by afternoon. It's not out of the question to see a 50 to 100 jump, but it's rare.
At any rate, those are not conditions you design a residential HVAC system for, anyway, for the very reason mentioned...rarity. You design for expected highs and lows over the seasons. If you are building your house to be thermally efficient, it will probably not experience temperature swings as sharp as a conventionally built structure. I do see you've mentioned between 10 to 12 tons...this must be a pretty large house to need that much tonnage, yes?
Thank you. This information was very helpful.
Originally Posted by mchild
You are welcome.
Originally Posted by MILTON01
One other point I failed to mention is the effect of the indoor units on the outdoor unit. You can connect indoor units that total 130% of the nominal outdoor rating (5 tons of indoor units to a single 4 ton outdoor). There is a benefit to doing this as the operating cost of the outdoor unit drops (higher COP) as you connect more indoor units to the outdoor, up to the 130% max.
As an example, the outdoor unit capacity at 95* OAT with 100% indoor unit connection is 48,000 with a COP of 2.97. With 130% connection the outdoor unit has capacity of 50,700 with a COP 3.07. Same situation in heating mode. Plus, these units have much higher output at lower temps than a typical system such that you may not need any, or very little, supplemental heat. These are some of the points shophound was mentioning.
I saw in your other thread that the cooling load is going to be 11 tons. What is your heat load? You may want to consider one of the commercial units - the big brother to what you are looking at here. Daikin has a 144,000 BTU unit that can have 20 indoor units connected. In can run as low as 10% (just over one ton) of rated capacity and has a minimal cooling COP of 3.70. It does require three phase electric. May be worth considering.
I have seen mitsu unit's in operation I was suprised they chose to 200% oversize the unit's. But the units decreased speeds well after startup as long as the remote control was were the airhandler could transmit to them.
Would stick with hard wire tstat that home ower could control at single point.
The nice clean install is to put the one controller for all the air handler units in a convenient but discreet location such as a closet. Network interface can be made too. Small, remote sensors can be installed in each zone. Hard wire it all.
Originally Posted by bzzline
I was impressed by the mini splits performance but not thermostats because you have to use the control they give you.
Zone control with a central system would be my choice for ease of maintance and durability. Energy savings would have to go to the mini splits
Vrv / Vrf
There are certainly a few factors to consider when contemplating VRF / VRF systems. The first is how much load you will require. Question to ask yourself....What is the largest area/s you will want conditioned at one time - there's your load. As has been previously mentioned there are diversity factors able to be calculated to match a smaller condensing unit with a greater capacity of indoor units and some systems can run as low as 8%.
Do you want heat pump or heat recovery system...Do you want the system to either heat OR cool and have the ability to simultaneously heat AND cool as required (2 pipe vs 3 pipe)
As mrchild has suggested a central control with individual thermostats (size of a match box) in each conditioned area is a great idea. There is the ability on some systems to operate up to 144 indoors with 365 day scheduling if required.
These systems are extremely popular outside of the United States (it's what I do everyday) and there is no reason to go for 2 x outdoor units when up to 136kW / 464000 btu's off one system or a single condensing unit capable of being located up to 160m (524) feet to the furthest indoor.
Do youself a favour and check out Mitsubishi Heavy Industries as well (Different from Mitsubishi Electric) Their latest range of KX6 systems are breaking new ground.
I work with both of those brands and have seen good results with each. To me, they are basically the same product packaged slightly different. In our part of the country though, the Daikin rep is definately more responsive and contractor friendly, which should give better overall results. It is my understanding that each has strategically located distribution in order to be able to get ant part out overnight if absolutely necessary. I wouldnt really know though, because so far we havent needed any replacement parts. These things suck the life out of a service business if installed correctly. The only difference that i am aware of is low ambient heating operation, the Daikin seems to offer better results for some reason...........
The difference being that these systems, with extensive self monitoring, will normally shut down before running in a self destructive situation. If the typical U.S. system were properly installed, including correct air flow and charge, then there wouldn't be much service required on them either. If someone does a hack install of a Daikin or similar system, it often won't even start. Hopefully, as the market embraces this technology we will see a thinning of the herd of hacks. No more beer can cold and a hand in front of a register to measure air flow.
Originally Posted by flange
Additional Questions Dailken/Mitsu/Sanyo
MCHILD, and the other posters thanks for the information. We had the loads recalculated under manual J to take into consideration blown in insulation, closed attic, low e-2 windows etc. and the loads come in at 7 tons, rather than 10-12.
Here are some additional questions:
1. With the 130% capacity of the outdoor units for these companies units, does this mean that 5 or 6 tons of capacity is sufficient and ideal?
2. How much more efficient are the 3 phase units, such as the 6 ton unit offered by Daiken? compared to running 2 3 ton 2 phase residential units?
3. Would you recommend a one compressor configuration for a two story house with 9 zones? It appears that some of the Sanyo units use two compressors, one as a backup.
4. Do any of these systems have occupancy sensors that set back the thermostat in a zone that is vacated?
5. Are their differences in the ability to connect an erv and whole house air filtration and the sophistication of these products from the 3 companies?
That will happen only if there's a herd of competent techs to supplant the hack ranks. The manufacturers of these systems would do well to offer training for those who will both sell and install the systems...many of them already do. To me, the only way the higher technology systems will make it is if the OEM is more involved with ensuring contractors and installers are properly trained on the equipment. They can't afford to let untrained Joe Pickup waltz into the parts house and drive off with a VRV system in the bed sitting next to a hacksaw and a beat up gauge manifold manufactured in the sixties.
Originally Posted by mchild