Not that simple. The air source outdoor exchanger must have much more surface area, since air has less heat capacity and thermal conductivity than water. Unless your water flow rate is super high, the water source exchanger will be more compact. I already posted a few links to point you in the right direction. I recommended a coaxial exchanger with turbo tube inside for a reason.
Plate heat exchangers that will stand up to refrigeration pressure aren't the same as the common ones found on the used market. Most of these are rated for maybe 10 bar, you need better pressure rating. The common units are also rated at a higher temperature difference than a heat pump can provide. Depending on specs, you will need to oversize the hx by a large factor. Plus the fouling issue.
A coaxial exchanger made with smooth tubing will need more overall length than one with ribbed or corrugated center tubing, which will drive up the materials cost. The issues of pressure drops, turbulence and spacing between the tubes make more difference for the worse as well. If you have a cheap supply of smooth (inside and shell) tubing and don't mind the extra bulk, go for it. But the easily copied designs pretty much all use high performance inside tubing to save weight and bulk.
|