GARN has Arrived! Close Approach HX

[bpirger]

The GARN 1500 has arrived! Now it is is time to get it all set up. I will connect the GARN through a HX and plumbed as a secondary loop. Attached is a planned overall layout sketch.

I'd like to maximize the heat I can suck out of the GARN, so I'm thinking I'd like to size my HX to get the "closet approach" temperature I can, within reason. My heating is all radiant in slab, so water temperatures of 100 degree is all I really need. I plan to heat DHW though, so this is a different story. I'm hoping to can go down to 120F in the GARN...though the DHW might charge a bit slow with this relatively low temperature.

I'm looking at the flat plate units from Flat Plate, now GEA PHE Systems. It seems like the 5x12-80 plate should get me fairly close, and it seems that this is significantly oversized. My heating load is less than 100K/HR, plus the DHW. But I've also broken the bank here, so if I can save a bit of money, I'd like to hear it!

WHat I don't seem to understand though is the various models of 5x12 units from GEA. I see the "FP" series and the GBE series. Is the difference here primarily working pressure? The FP up to 450psi and the GBE at 232? Both obviously are way beyond what I need. I understand the MPN series is for pools/spas and the like.

I found the detailed specs for the FP series, but not the GBE series. I believe the GBE series is the "economy" model for typical heating needs?

I see the GBE 5x12-80 plate for about $600. I also see it doesn't have the mounting studs. Do folks typically suspend these exhangers in a homemade mount?

Can you heat these things up too fast and cause damage? If a circulator turns on and pumps 195 degree water from the GARN at 15 gpm, can this cause any damage? I'd think I'd heat up my primary loop very quickly at this rate. I have 1 1/4" microflex after the HX to the primary loop.

Thanks!

 

[Hunderliggur]

I would put the Garn HX and boiler circulator in the boiler shed and pump the hottest water to the boiler shed. This would ensure you get the max temp for the heating loop. Depending on your working temp for the radiant, you may want to put a high flow tempering valve at the HX so that the return to the slab is not greater than your setpoint (135 or so). You definitely want the tempering at the DHW for scald protection.

 

[Kemer]

Congratulation's on the Garn I just received mine and I'm about where your at with the install.I got a 60 plate hx and variable pump for the garn side.

 

[bigburner]

issues - keeping the oil boiler hot [stack loss], over temp for radiant floor as shown. YA need Hottest water to DHW then the staple up, Then a another loop with a tempering valve for slabs. put another loop around the oil boiler so you can isolate it also, this means more pumps, but translates to better control. A low HX delta T is life when working with lower water temps, you loose a few degrees on a smaller size and then over time add some fouling of the HX you may have a hard time getting a good recovery on the DHW. My thoughts. PS there is no one who has ever done this that hasn't broke the bank and it just gets worse. every year you add something.

 

[bpirger]

Hi All:

Thanks!

All the radiant manifolds are feed with mixing pumps and controls off the primary....so they are temperature controlled that way.

The oil boiler in the primary loop is something I go back and forth on. It is a Buderus with a Riello OC-3 burner. It doesn't have a "stack" per se, i.e. it draws in cumbustion air from outside and vents through a local vent. So not the typical stack height draft/loss. Since oil is the backup, it seems like I might want to keep it "ready". If I plumb it is a secondary, it will presumably stay cold for a long time. So will the oil that sits out in the oil tank with the boiler. Does it matter? I don't know.....will the oil boiler by happier/more ready if it stays warmer? Seems like it....but maybe this is a waste of energy.

First off the primary loop is DHW, the the staple up, then the rest.....so they are in the proper order coming off the primary loop, though I didn't draw it that way! I should adjust....

 

[Hunderliggur]

If the oil burner is in a well insulated building, and there is not the stack loss (low temp force air exhaust), then keeping the oiler warm would keep it drier (less corrosion) and easier to start. Yes, it will cost a few BTUs and maybe some pump head, but not too bad. You could start that way and allow for diverting around it at a later time (unions can be your friend).