Chilled water for residential forced air AC systems?

Our 100+ yr old house currently has 3 separate forced hot air gas-fired heating units.
We would like to add central air sharing the same ductwork and blowers.
The "traditional" approach would be to add a separate compressor/evaporator for each of the 3 heating units.
I have seen that some high end remodels are using a single chilled water unit to supply coolant to multiply blower units and that this is somehow "better".
Can anyone comment on the pros/cons and appropriateness of using such a system residentially?
I am particularly interested in comparing initial cost (equipment & installation), efficiency, noise-level, and reliability.
I will be hiring a reputable HVAC contractor for the installation.
Thanks.
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It is a common method of commercial and industrial cooling. Big chiller located on a rooftop and cold water piped to various locations. It has the advantage of going long distances with no refrigerant lines and the charges in them. You may get better result talking to a commercial contractor than someone that only does residential.
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One house and 3 furnaces = high energy bills. Water AC system will not be cheap.
I'm not sure if this would will work, but you should look into a ground-linked heat pump system. I think some are water systems plus you might be able to use it to heat your house.
blueman wrote:

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blueman writes:

Where have you seen that?
Are you sure the water is not cooling separate compressors/evaporators at each air handler? Rather difficult to cool efficiently without a phase change.
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Not sure, but I think the OP is looking for a system like a "motel system" that circulates chilled water to all of the systems and a fan blows when a unit calls for cooling. He is looking for a system with a heat exchanger rather than a air-based system like a regular AC.
Richard J Kinch wrote:

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blueman wrote:

fantastic. after you do a room by room load calc and a room by room duct calc, you will know if your existing ducts and blowers are adequately sized for air conditioning.

"better" can have different conotations. for example, if you have to add a 400 amp panel to handle 3 freon based dx cooling systems, a single chilled water condenser might be 'better".

yes. with a freon based, dx system, most anybody can work on and provide parts for it. on a resi chilled water system, parts are propriatary, can be outrageously expensive, and very few people can work on such a system.

go with a high end freon based dx system.

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snipped-for-privacy@gonefishin.net writes:

We had a couple of HVAC contractors in for preliminary estimates and calculations. Their sense is that while not ideal (the ducts appear to be sized and located for the original system which seems to have been coal-fired gravity hot air), the cost of installing new ducts would be substantial in addition to the need to make a fair number of holes in the wall. This will mean that even after getting the calculations there will be some compromises in determining the tonnage relative to the heat load and duct capacity.
We will still like to get relatively high end AC units so that we get good efficiency, reliability, and noise performance.
One question though is whether we should hire an independent HVAC engineer to do the measurements and write the specs or whether we can "trust" a recommended "reputable" HVAC contractor to measure, spec, and install.

Sounds then like this is the way to go and as mentioned above we expect to pay for the high end since much of the cost in our project is labor (we need to have a bunch of ductwork in the basement replaced too).
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If I were you, I think I would find an AC installer who does more light-commercial work than residential work. I would lose the idea of doing chilled water because there are issues with that. I would see if anyone had any experience doing a zoned freon system. You put 1 compressor somewhere out of the way so it doesn't bother you. You run a manifold to either balance the system or to have electronic switcing to shut down systems that don't need cooling, and you put in 3 regular heat exchangers (evaporators) in your forced air system. Except the switching system, it would be pretty straight forward. There's no reason you can't move freon rather than chilled water. In fact, it might move more efficiently.
Oh, and hope and pray it doesn't need to be a 3-phase system. But it doesn't seem like it should. It's not that big.
BTW, every old gravity fed coal system I ever saw had pretty big ducts. So you probably have enough size -- maybe even too big. So check for leaks and make sure your blower is sufficient.
1 issue you will still have is that AC is must better coming out high than at floor level. So you might need some ceiling fans or something to help out. This might explain the high cost of ducting.
Good luck with it.
blueman wrote:

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I don't know if such a system would fit your needs, but it might be one more option to consider if it can be easily integrated with your home's existing ductwork. The big advantage is that it could also supply one or more independent air handlers for areas that require additional "spot" heating and cooling (or for which installing the necessary duct work would be too costly or impractical).
http://www.mitsubishielectric.ca/hvac/A01-20.html
Cheers, Paul

[....]
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writes:

What??? You want to slap in a system that isn't right and has lots of compromises, but yet you want to purchase high-end equipment? That is like saying you need a car for fishing and hauling the trash up the driveway but you are going to buy a BMW.
You already know you are going to get a system that doesn't work right and may not last long, but you want to spend lots of money? That is fucked.

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IMO, using the existing warm-air gravity ducting with ac would be a huge mistake. Most of that old style ducting is 10-12" in dia, and while they may be able to handle the cfm requirements, they will not provide the velocity that is required. Sure, you can still use the wall and floor penetrations and grills, just replace the gravity ducting with new product sized for the job.

a real problem with any engineer is they have no hands-on, real world experience. Most 'engineers' couldnt engineer their way out of a paper bag.
If you're worried about a contractor doing the job right, require a 'performance warrantee' from the installing contractor. Either they deliver what they promised & sold you , or they dont get paid......

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