d.dennerline said:
d.dennerline, on 09 Sept 2014 - 02:08, said:
The Carrier Greenspeed uses an Inverter compressor which improves it zoning capabilities, but the price will give you sticker shock.
As long as we're on the topic, what is the incremental cost for variable versus two stage? In case you guys are shy, I'll show you my numbers first, and then hopefully you guys will show me yours.
I presently have a very basic two zone (an upstairs and a downstairs) system. It came with the house and consists of a 5 ton Trane condenser and a 4 ton Trane condenser, both SEER 10, and each with their own air handler that doubles as an NG furnace. Single speed and no dampers. R-22, 15 years old, and probably ready for either replacement or some significant maintenance. The system heats and cools a 3,800sf two story house. It short cycles a lot, and the system is definitely unbalanced. I'm told the average lifespan for an AC system where I live is around 15-20 years.
IIRC from the quotes I previously received, the cost to replace it with a more or less identical (but not R-22) two-speed system (including new air handler furnaces) was about $10,000, or thereabouts. That would be reusing the existing flex ducting and no additional zoning. I don't recollect the incremental cost of adding zoning to it the system, assuming it's configured with two-stage condensers. Adding zoning to the current system would have obviously required by-pass dampers, and probably wouldn't meet our comfort objectives.
To replace what I have with a custom chiller system with 15 dampered zones would have cost around $18,000, according to the one bid I got for doing that. That would have been without heating, and it was somewhat unresolved as to how heating was going to be integrated with it, as I don't think the HVAC guy's proposed heating solution (leveraging ordinary residential-grade tankless hot water heaters) would have lasted very long because the duty cycle, though perhaps there are commercial grade tankless that could handle it. Heatpumps could be used, but that would be trading reduced system cost for higher heating costs. Perhaps that's acceptable, but I'd want to use a sharp pencil to figure it. It also assumed the existing ducting would be re-used, and it assumed I would be supplying the 15 z-wave thermostats (which cost about half as much now as they would have then), one for each of the 15 zones. It would have relied on a bank of three chiller condensers, operating in parallel and switching on as needed to balance cooling demand. It would have utilized an insulated buffer tank to mitigate short cycling. Although I didn't request it, the bid proposed the heated refrigerant at the condensers be evaporative cooled using water, not just air cooled as is more typical for residential. On average it probably would reduce energy costs somewhat, and would make for a quieter fan, but there must be good reasons (like maintenance) that's it's not more widely used, and it would have vendor-locked me even more in terms of servicing it.
Since then I found on my own true variable speed chiller units that operates 0%-100%, which I'm pretty sure would remove the need/benefit of a buffer tank, and only one would be needed even if other one or two stage chillers were operating in parallel. MSRP equipment cost on the variable speed chiller condensers I found is about $1,000 per ton, but when/if it needs servicing I'm not yet sure who I would call. I think there probably are options though. I'd probably be better off with some lower capacity chillers to operate in parallel with it, both for redundancy and to hit better efficiency rather than rely entirely on one variable speed chiller to cover the low-end of the load range, where (as discussed above by ano and lleo) efficiency may be poor. If I pursue it, I'll look into that efficiency issue more carefully.
Also, the notion of an ice bank to complement the chiller might be worth exploring, as those are now available "off-the-shelf" in standard units and look to be maintenance free and would undoubtedly reduce operating costs, though I'd haven't yet figured the NPV of adding it to the mix. However, if the ice bank(s) were big enough I wouldn't have any need for a variable speed chiller or a separate buffer tank, and I could probably get by with just one single speed chiller condenser that could be operated very efficiently (in some respects similar to the way a Toyota Prius works). By charging the ice bank at night, the system would also gain efficiency from the lower ambient temperature at night for cooling the heated refrigerant generated by the condenser during compression. When it comes to efficiency for a multi-zoned system, I suspect it would be very hard to beat the performance or the efficiency of such a chiller system.
I'd prefer to hire someone else to do a chiller system, if I were to do it at all, although unlike all other systems, it could conceivably be done either DIY or assisted DIY. That's because you can buy pre-charged outdoor standalone chiller units, and so there's no life safety issue about the containment or possible release of toxic refrigerants within the living space.
I also had a quote from Daiken of $40,000 to build one of their direct expansion systems to service 15 zones. With it, there would have been no ducting at all. Also, you could heat one zone and cool another without it being double the operational cost (not that the need for such a thing arises very often, but the topic arose as a humerous sidenote earlier in this thread). Mitsubishi quoted their system, and it was $35,000. Anyhow, those prices were non-starters from my perspective, and in any case they are no longer options for me now that I'm post-remodel.
