Delta T: Question?

TAG

What does it point to when the Delta T is only a few degrees and not the 20 degrees --- viewed by many as ideal?

My new systems is up and running. The supply and return temps (using each manifold's temp gauges) are only a few degrees different ... maybe 5 (max) The 1k sf of retrofitted 3/8 plates finally got connected the other day -- they are now warming the living room nicely. They 1k sf slab and 3k sf of Warmboard are working as they should. It's all working too well (too warm) .. have to figure out the Viessmann heat curve a bit better!! It went down to 19 the other night. The main goal has been to get heat into the building for the ongoing construction.

The system has two of the same smaller Alpha II pumps -- one for the boiler loop and the second after the LLH for the system. I did play around with different setting --- both now running on "AUTO" : System Alpha display is "MAX" ... System Alpha is feeding the slab (8 loops) .... two Warm-board manifolds (7 & 5 loops) and the plates (11 loops). I did have some concern about only using the one pump as the numbers do look as if they get close to Alpha II limits -- but there is a larger Alpha pump? It must be pumping enough as everything is hot. Initially had everything running fully open to get it going. I'm not getting a huge flow (using the flow meters on the manifolds) --

I turned down the slab loops to around 1L from about 1.5L yesterday before I departed. The slab area of the house was a bit warmer VS the other areas -- as expected. The Warm-board is running a bit over 1.5L -- I did not crawl under to check the plates again ... but I had some flow across all the loops when I first looked. ...maybe 1L before.

Using my 1 year of engineering before moving to finance --- It would seem that I'm still getting too much flow. ? Or am I thinking wrong/ incorrect and the water is too hot and the flow too low?

hot_rod

The 20∆ you selected to design around is just that, a random number you used to calculate with. It could have been 18, 22, 17.5 Your system may never run at that delta.
Hydronic system are dynamic, conditions like temperature delta is constantly moving just as the heat load of the space is also dynamic, constantly changing.

If you want the long answer read the Idron ics that I attached.
Also a couple pages as it relates to radiant loops.

Basically the tighter the ∆ through any heat emitter the higher the average temperature of that loop or heat emitter. So as a result the output will be higher if the heat emitter is warmer.

Tight ∆ can come with a price, that being pumping power. If you are pumping your entire system with an Alpha then you have very low power consumption, that is a win.

If you have a lot of small zones you may experience short cycling based on both the small load and tight deltas.

If you watch your system from a cold start you will usually see a wide delta, maybe even beyond your 20 design. As the space warms, load lessens so will the delta. Just as the thermostat satisfies that delta may drop to 3, 5. And of course when the load is satisfied delta drops to 0∆.

Radiant slabs for residential typically design around a 10- 15°. Shop slabs may run a wider ∆.

https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_23.pdf

TAG

Hotrod -- You are always full of knowledge. Think I remember seeing your link on another thread (I did read at one time) and will reread (print out).

TAG

Turing down the slab loops to 1L did balance the temps -- the Warmboard is showing a bit more delta -- still less then 10. The slab maybe 5. I lowered the curve to .9 from 1 and the level to 10 from 14.

Will check again today ...