Closing in on some design options. Will be sitting down with designer next week to review loading and numbers more. I am replacing a 3.5 ton and 1.5 ton HVAC units. All the heat is currently done through oil boiler via hot water coils in the supply ductwork. Figure this is in the 165-175* delivery range. Looking to go with one water-to-water unit and hydronic storage and transport for cooling/heating. Anyone with experience (positive/negative) they've had with replacing oil boiler with geo at lower water temperatures. Attached drawing shows a rough concept.........Trent

We have used Multi-Aqua and Enertech hydronic fan coils before with good results. The Enertech units have an ECM fan. Both have charts that show down to 100 or 110F performance. We do it this way instead of several packaged units, many benefits in my opinion, but some may argue against me saying it is more complex or costs more money, which both can be true!

If you do stick with hydronic, as someone recently pointed out, you should use outdoor reset on the buffer tank temp.

Thanks for advice and input. I was concerned whether low temp hot water would be adequate for heating loads. It seems that that is surmountable with adequate sizing. My only real strong hesitance on hydronic is the shoulder months and the loss of flexibility in the crazy mid-Atlantic days where you may want heat in the overnight and AM and possibly cooling later on. Along with that is the master slave relationship with the parents unit in the apartment. Really need to see where costs break out and quantify the value of a split unit flexibility.

Before any consideration of design a heat load calculation is a must.Buffer tanks are designed based on smallest zone being utilized at any given time.Your design is much more complicated that needed.Rethink your apartment into a stand alone system.

Low temp hydronics must be carefully designed whether or not it is fan assissted

MT
a near perfect match is the Hydro-Temp (.com)
Hydrozone zoning Hot and Chilled fluids from the HVAC Air system that most likely (politely a fact) HAS NOT been seen by most posting if any at all. Add-on desuperheaters are hybrids like a coil in line with the air coil for fluid conditioning.

Energy Star (TM) compliant - of all that is needed.
Comes with standard (all have for tax credits, as a refrigeration add-on) -hybrid desuperheater DSH - as you have indicated off a W:W , now to be zoned and plumbed in your drawing.
Unlike your picture, picture one less =DHW tank, onw w:unit gone and vertival upflow HVACGT-HYDROZONE + a hybrid desuperheater to meet E-Star...

But may I suggest full size desuperheating (DSH-Priority) eliminating the one DHW tank, as Hydro-Temp DHW 100% Priority "INSTANT" HW requires just one tank, a small one at that.  Engineers that have the first net zero school with 1/3 solar as others, are using this in major quotation on prints and for the past 6 years.
~ UNLESS you want a dual-fuel back into a coil in a water tank or take the existing hydronic coil, put it above a vertical upflow HVAC geothermal...

Recently DONE: Oil Boiler to gas, replacing with an  IBCboilers.com  system that has as posted -outdoor sensor, DHW and other zone programming also built in on touch screen w/buttons.  (can do solar too later as a hybrid) Dual fuel: for as emergency-supplemental that requires so little generation, electrically (?)  with the GT System. Twice: one was 13000 sq ft radiant and 2 4-Function Hydro-Temp each "size 7.4" by ratings, and dual compressors with 4 ht 3 cool staging

Hydrozone is the w:w heat exchanger off the aircoil for proven zone-control (like for yours) of other airhandlers.

Ask if who quotes you to quote that as well.
Call 800- 382 3113 just requesting to talk with anyone.
 It also comes with up to 4 zone wireles, diagnostics and programming controller -
can share or independently be zoned , from that same vertical upflow HVAC-GT to your apartment fancoil.

A single stand up system, no w:w unit in the room (as it is that too) and can be 4-function just like any desuperheating, but larger such that in Cooling the loop pumps are OFF.= 100% recovery in reclaim-mode , putting hot water ni to your tank.

 which , whether the  vertical upflow fan in the main unit is on or off, you can, again can control with the apartment fancoil.

W:AIR Heating and cooling
W:W
W:DSH Hybrid and full condensing 100% HW

Air coil:refrigerant
W coil: refrigerant heat only
W coil to refrigerant HYDROZONE HT and CL
One circulator built inside, comes with DSH built in or Full size 1/6hp bronze
4-Zone programmable board, wireless IRD Palm(tm), logging, tracking, diagnostics, extra relay programming dry  switch to 3 power-on / power-off on board to use for 14 settable functions

Better pay-rate (choose your utility supplier if not yet, when you can)
Better pad (building  improvements)
Study the loads and a/c needed again
Better plumbing, ducting sealing, etc, distribute as needed (like registers not disturbing walls where undesirable losses occur)
Better production HVAC-HW-Recovery, systemically tiny as possible

20 manufacturers of GT and HtP and Radiant/radiation-HX (heat exchang(er)) with assist as you shop

....outdoor senser could be implemented but you may also find NO FANCOIL BUFFER is not at all needed. ( 2 tanksLESS )


JP

www.GEOPros.com