Replacing outdated central A/C

I live in a 4 story house with a typical split system Central AC installed around 1991\. Our outdoor compressor died and the coolant is no longer on the market. There is a huge air handler on the top floor. We are considering a renovation of the upper level and our architect wants to reclaim the space that the air handler takes up. He recommends using small air handlers, one per floor, at a cost of about $20k per floor. Does anyone have any experience with a system like this? I’m concerned that it doesn’t make use of the existing ductwork or wiring and it seems really expensive. What are your thoughts on modernizing old central AC systems? Does anyone have an alternative recommendation for central AC?

lauranyc

in Heating and Air Conditioning 9 years and 8 months ago

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dorkofwindsor | 9 years and 8 months ago

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80k? I hope you are going for the win of a design competition. That sounds like it is a total gut of your existing HVAC system (and then some, since presumably your walls will be open). At the end of the day you can only weigh the design with and without the additional cost. I am not sure this is something i would consider unless it was a top of the line reno on a $5+ million house. One thing to consider is that if you are opening up walls on every floor, you may not really have a choice because ducting might need to be moved anyway – and that changes the performance of the whole system. An HVAC system is designed as a complete design and every time you move / extend / make new corners or reduce the ducting, it affects how hard the compressor works, humidity (very important) etc. That would be an important fact to know. OTOH, if the ducts could stay as-is and you can definitely live with the layout that keeps the HVAC and you are not made of money – then i would just compare his designs with and without and weigh the cost. Not rocket science, just straight up cost benefit.

steam_man | 9 years and 8 months ago

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lauranyc, As nyc_sport mentioned, Mitsubishi does indeed have an air handler which would be installed using your existing ductwork and use a new condenser outdoors. Here’s the thing to remember though, Your ductwork was designed to feed from the current air handler’s location to all the floors/rooms it serves,. Your new air handler location will most likely be opposite the old one (in the basement I assume) So therefore your ductwork will have to change quite a bit. Def not something I’d be interested in doing given the cost involved versus the options available. I’d be happy to discuss the project with you in further detail. We are certified Mitsubishi installers. Feel free to look up our contact information in the Brownstoner Local Pro directory under Heating and Cooling Contractors. The company name is Molten Mechanical Metal Works.

nyc_sport | 9 years and 8 months ago

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The split system and ducting is not mutually exclusive. I have a Mitsubishi split system in my apartment, two outdoor units, 3 HVAC zones, with the air handlers in two bathroom ceilings and above the laundry room. The air handlers feed ducts. But this is not a small task as a retrofit, as you need power and t-stat wiring to the air handler, condensate drains, and need to access the existing ductwork to feed and isolate each zone, and you likely will require some new return ducting. However the zoning makes this much more comfortable and efficient, and likely will provide fa better air filtration. And, the heat pump can provide useful auxiliary heat if you have some cold spots or, as we use it, to get the place heated up quickly after having been away for the weekend. Whether that is worth $80K, I dunno.

nick521 | 9 years and 8 months ago

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There are multiple Split DX options, the one proposed by her architect, one indoor unit per floor (could be ductless or ducted) or her current setup which is a central ducted system. @Lauranyc, even if you weren’t redoing your top floors, you’d still have to replace your current system since your compressor died. Your system is using R-22 which is no longer being manufactured, new refrigerants are more environmentally friendly and more energy efficient. Deciding factor should be cost and also maintenance as both options will be more energy efficient than the current setup. Central vs Individual zone: If your central unit breaks down, your whole house is down. if one of your floor unit breaks down, only that floor is down. Individual, you can turn off unoccupied spaces and save energy

daveinbedstuy | 9 years and 8 months ago

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You either have a split system or a ducted system. It sounds like it’s a split system and the ducts you speak of are just the fact that the tubing and wiring is run to the blower units. Further clarification is necessary. I’ll let others speak to the current costs of new split systems.

nick521 | 9 years and 8 months ago

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Split DX systems have evolved over the years and are very energy efficient, they are great for new construction and some retrofit projects. 20k per floor seems very high, how many zones does that imply? Daikin has a multi-zone system where you can have one outdoor unit for up to 8 zones (indoor units).The Split DX system does add electrical cost and additional refrigerant piping to each floor/each indoor unit. @Lauranyc, I agree with you, for your needs, I think that you should just replace your existing air handling unit with a new efficient one and new matching outdoor unit. The new air handling unit may end up smaller than your current one. Also, you can also add some zone control for better energy efficiency. Do check the state of your existing ductwork as well, make sure they were properly sized and can still be used though. But to be on the safe size, I would request a quote of both system to compare. You might need to consult with a mechanical (HVAC) engineer or contractor. Hope this helps a bit. B.

lauranyc | 9 years and 8 months ago

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I understand the appeal of a split system for new installations, but we already have all the ductwork. Does that make sense for us?

thetinkerswagon | 9 years and 8 months ago

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he may be talking about a split system, something which has been written a lot about here on Bstoner. you can research old posts or wait for replies, but the consensus will be that the split system is the way to go. Steve