I am hoping I could get some help with designing a water chiller system. I know this is a boiler forum, but the design idea's are a lot alike and quite honestly can't find anywhere else to ask these questions. I will have a 5 ton AC condensor hooked up to a water coil then have air to water HX on top of each furnace/blower. The design of the house either requires 4-5 small HVAC systems or to seriously chop up the house for HVAC ducting. Using one main chiller will allow one AC condensor to drive all 4-5 of the small HVAC systems without having the need to have 4-5 AC condensors sitting outside. Due to the low delta temeratures I can't run a water to water heat exchanger, which means I need a pressurized storage. Operating temp of the water will be about 38-50 *F. The AC condensor would be run on a thermostat on the buffer tank, the room thermostats would only turn on their zone circulation pump. I have narrowed it down to two different designs. The first I do not know the name but it is pictured on page 11 of the following link. I would have a 40-100 gallon water heater inline on the feed to the chiller coil, this would be to prevent the AC condensor from short cycling. Problem with this design is I have to run the chiller circulator pump whenever any zone is running. The plus side is I can use a cheap water heater. www.caleffi.us/en_US/caleffi/Details/News/.../HydSep102508.pdf The second design would be to use a very large buffer tank that acts as a hydraulic seperator. All zones as well as the main chiller circuit would dump directly into this tank. This design would allow for the zone pumps to run with the chiller pump being off. The downside is I would need a non-water heater tank to allow either for multiple in/out taps or 1.5" plus taps. The tank is more of just a buffer, not a storage. 100 gallons will allow for a 8-9 minute recharge from 50 to 40 *F and theoretically a cooling time of the same length without the AC condensor running. I probably would not go over 250 gallons. I had run across this type of tank and figured it might work pretty well for design #2. http://www.ebay.com/itm/330688268931?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649 Thoughts, idea's, comments that I am just plain crazy? PS. I already have a 5 ton AC condensor, a chiller coil (Doucette Industries CC-500, thank god I bought that when copper was cheaper, it is a 110lb chunk of all copper), and Magic Aire water to air heat exchangers. Also have all the pumps (Taco bronze), just need to figure out a final design and find a buffer tank.