Two Small Chillers or One Large One?
The site only has 1-phase electricity; 3-phase requires a digital phase converter. For this discussion its pricing will be considered 1 (one).
Two chillers could be 1-phase, either 3-ton and 5-ton or 2 5-ton. A few offer a reverse cycle option. Right now, only one reverse cycle model offers an inverter-powered compressor (Daikin), however by next year 1 or 2 more should (Aermec, maybe Multiaqua). Cost ranges from 2x to 2.4x for 1-stage chillers, 3.6x for reverse cycle chiller with inverter-powered compressor.
One 8-ton or 9-ton single phase chiller has been identified from Drake. It has two compressors for 2-stages. Cost is 2.4x.
Carrier has a 3-phase 10-ton with a Copeland Digital Scroll giving 13 stages down to 20%. Cost with phase converter is about 3x.
Aermec and maybe some others should have inverter powered chillers (maybe reverse cycle) in the 10-ton range next year. Cost with phase converter will probably be 3x to 3.5x.
Is it better to have two 1-phase, one one-phase, or one more sophisticated 3-phase?
Need more info. Is this a critical setup, does the load change or is it constant? Look at efficiency. What is it for??
Its a residence. Sensible load around 70mbtu/hr but design conditions were exceeded 25 days this year. Distribution by forced air through air handlers, probably something like a Carrier 39SH or an EPS LV-E (VFD blower with 4 speeds). Hot water through a boiler and the chiller if it is reverse cycle.
Installation probably in September October, but the chiller could wait until March/April if necessary to get the right unit.
What are you replacing? When we replaced a residential Absorber Chiller with a mechanical chiller, we had to install an insulated tank to get the fluid mass up or it would never work right, The tanks we used were Fibreglass, it's been too long ago to remember the brand. We also had some problems on some jobs when we replaced an Old American Standard mechanical chiller. Does Carrier still make the "Chiller Mate?" This was a nice set up, the condensor sat on a raised pad that had the chiller coil inside it. Carrier supplied pre-formed Vapor and Liquid line to hook it all up. Will the utility provide 3 phase power to the residence ?
The utility would charge more than the system for 3-phase power. A digital phase converter is available for roughly half again the cost of the chiller: http://www.phaseperfect.com/products.htm. We would use the PT-380.
Some of the packaged units come with a tank inside the assembly, others add an outside tank. The piping is long enough in the house that one or two 50 gallon tanks would be enough. One tank manufacturer, who only makes ASME tanks (which way too much for this application) in a discussion of storage tank baffles suggested using a water heater storage tank with a small diameter elbow on the end of the inlet to redirect the water at 90 degrees.
The single units with inverter-powered compressors will probably offer better overall efficiency and more sophisticated integration into the overall system. They come at the cost of installation and maintenance of the digital phase converter and a lack of redundancy.
The two smaller units provide redundancy and use 1-phase power. They don't really have a staging advantage since the larger units have a variable volume compressor or at least two compressors. Their compact chassis are generally less efficient.
The Drake, at 8-tons, is the largest 1-phase available. It is basically two 4-ton compressors in the same system. However, it doesn't reach the efficiency levels of the best VRVs.
Another big issues in maintenance, both parts availability and technician availability. Carriers new small to mid-size commercial chiller should have virtually overnight availability on all parts and lots of technicians. Aermec, Multiaqua, and Daikin, no matter how large some of them may be world wide, in our area their dealers are either few and far between or non-existent. While most will not have seen a Drake, it is pretty straightforward and Drake's owner, URI, is nearby and well stocked.
The ideal solution would be two staged 5-ton reverse cycle 1-phase chillers with inverter powered compressors that can vary down to 20-25% of capacity, are in a typical US configuration with a large circumferential condenser coil and horizontal fan. The heat exchanger would be indoors, limiting glycol needs. It would be capable of chilling water to 20-25F for ice production. It would be made in the US with wide spread availability of both parts and trained technicians.
That doesn't exist.
The question then becomes where the trade-offs will be made.
all of those chillers are straight forward. There's nothing special about them. You can always go around the local dealers and contact other reps and well there is UPS. Anything overnight ed is at our shop by 10 am. If you are that concerned about parts talk to the manufacture about which parts they recommend you having on your self. Plus you could put a tap in your supply line for city water in case the chiller goes down. It is a little thing figure 2.4 gpm per ton. Our city water temps are around 55 degrees so that's perfect.
Can't the customer handle being down over night if there is a problem?? I am not familiar with residential but they might be uncomfortable for a bit no big deal. It's not a process chiller or data center
I am the customer...so no parts on the shelf. The Daikin residential chiller has no dealer who has installed; their current dealers focus on mini-splits or the VRV-III. Aermec is worse and the importer is in Canada. Ditto Multiaqua, but made in the US. Carrier commercial I would expect to find lots of people and ready parts availability. It seems to be a well designed chiller that covers a range of sizes including some smaller ones not otherwise handled. Unfortunately, the need for 3-phase move the price from the low end to the high end, and a) it is not reverse cycle, and b) the digital scroll won't match the efficiency of a inverted-powered scroll.