jjhpf said:
Any one know a good link to review pros and cons of both?
jim
Do the search, you will find lots of debates on the topic, each has its pros and cons, and every situation puts it's own balance on them, so one has to make a tradeoff as to which will work better for a particular setup.
In short...
Pressure - Pro
1. Can be run to a higher temperature than Non.
2. Heats more efficiently - no HX losses (at least on boiler loop)
Pressure - Con
1. Comes in large, bulky, non-flexible tanks - can be difficult or impossible to get in and out of some locations, Tanks are heavy, can be difficult to move.
2. Requires very high volume (expensive) expansion tanks - much larger than Non.
3. Limited range of tank size choices
4. Hard to install in-tank HX's for things like DHW, or glycol loops
5. Pressure vessels, which can be problematic in some code jurisdictions (i.e. MA, among others)
6. Because of tank design, can be a challenge to plumb, modifying tank to add / change plumbing is possible, but difficult / expensive.
Non-Press - Pro
1. Flexible - can be built to fit into almost any space, and in any size
2. Because it can be made on-site access to get materials in is seldom a problem.
3. Easy to do almost infinite numbers of in tank HX coils
4. Adding / changing design easy
Non-press - Con
1. Requires careful design / build to get tank that will hold water safely
2. Can't be run to as high a temperature as P.
3. Somewhat less efficient because of physics of HX operation
4. Requires somewhat more attention to controlling water loss / evaporation.
Gooserider