Max Heater Delta T - Help me understand.

Mplsavant

Hey guys. I have a Buderus GB142/24, serves an air handler zone, DHW and two slab heating zones, no AM10 since installed in 05' (working on getting installed). The manifold pump speed has always been set to 2 (med) since install. When a slab zone calls for heat, the unit begins to fire up pretty quickly, with the delta T being pretty large (guessing 30 degrees, varies of course based on when last heated up, etc).



The part I don't understand is the air handler zone. When it calls for heat, it stays around 100 degrees for 5 minutes, it is like it is not firing up to heat. The air handler run from the boiler to the First Co (HWC-2030) in the air handler is like 24 feet. Back from it to the boiler is about 12 feet. The delta T, guessing is like 10 degrees. I don't have a temp gauge yet. Buderus tech support said that it should be higher and thinks my pump is not size correctly.



What I truly don't understand is in the applications manual, pasted here, what exactly it means. I have some thoughts but would rely on the experts. I keep thinking the boiler is reducing the boiler output for some reason on the air handler zone. I have the unit at 100% (L--), etc. The heating temp dial is set to 170 degrees. Thoughts? Tried to paste the section from the application manual below. Otherwise it is on page 2 of this link. <a href="http://www.radiantheatproducts.com/pdfs/GB142%20Buderus_Application_Manual.pdf">http://www.radiantheatproducts.com/pdfs/GB142%20Buderus_Application_Manual.pdf</a>

Zman

Simultanious?

Does the problem occur when one load is present or only when both call?

It reminded me of this http://www.radiantandhydronics.com/Articles/Glitch_and_Fix/BNP_GUID_9-5-2006_A_10000000000001216751



Carl

CMadatMe

Air Handler

What you posted applies to the boiler pump not a zone or system pump. Are we piped pri/sec or utilizing the low loss header? Boiler is 75,000 btu/hr output. Spped 2 is providing a 7.5gpm flow rate based on a 20 degree delta-t.

Mplsavant

That does happen....

Zman, what you posted does happen (when slab and air handler zone mix). I am going to talk to my installer about some mixing valves. In this instance, I shut the slab zones off and was just having the air handler zone call for heat during the test I mentioned in my original post.



pic of current setup

Mplsavant

PRI/Sec or low loss

Not sure I understand the question. I posted a pic below which shows the setup. I understand the prim circ pump, on speed 2, gpm. The interesting thing is that the boiler should run full load, fire the air handler zone up more quickly because the delta T is not reaching the 45 degree difference in theory at which point the unit itself throttles itself back....(per the notes under the matrix in my orig post).

CMadatMe

Boiler Delta

Is based off the pump selected. Your running a Grundfos UPS15-58 on Speed 2. Chart clearly shows boiler delta is 20 degrees. Boiler btu/hr output is 75,000. This means your moving 7.5gpm out of the boiler loop into the secondary of system side.



What is the spacing on center of those two tees where boiler supply and return enter?Looks like 1" pipe so they should be no more than 4" apart.



Air handler zone most likely is eating up 3gpm providing the pump was sized correctly. What is the air handler zone delta-t? What was the heat loss for the radiant zones? What is the delta-t on the radiant zones?