Multi-zone radiant and Delta T pumping

DaveL

OK, I am thinking some of you can cite your experiences of applying Delta T pump control to this type system.

My application will be residential, 6 radiant zone manifolds w/zone valve (gyp-krete over framed floor, with tile or eng. hardwood) served from a buffer tank, using single system pump. I will use OAR to reset the buffer tank temp with manual mix valve to system pump; letting supply temp to system adjust as the buffer tank does.

My thinking is the best solution is to use a DT controlled variable speed system pump.

Another question - Is Taco the only option for DT ECM pumping in the small 6-9 GPM capacity?

SuperTech

Last time I checked Taco was the only one. Unless you want to use PSC circulator with a separate control, I believe Tekmar offers one that will accomplish this
I'd just go with the Taco. The VT2218 is a great product, I have two of them on my boiler and I've been happy with them.

hot_rod

I think the constrained delta may not work well with the reset buffer and floating mix temperature.

DaveL

Hot Rod, what would you think best? An ECM system pump in proportional control curve mode? b

hot_rod

I like delta P mode with zone valves. The mode choice depends on the piping somewhat.

Idronics 16 has some good, non biased info on selecting the best settings.

hot_rod

https://www.caleffi.com/sites/default/files/caleffi/uploads/files/idronics_16_na.pdf

Dave H_2

In my own home I use two delta T circs with all radiant floor, modulating boiler and modulating mixing valves. A VT2218 and a 006VDT drive everything.
The reason for two is its a two temp system; the VT2218 does most of the house and has 5 zones on it, all under floor radiant, water temp design of 125F. The 006vdt is one zone, slab on grade, water temp design of 105.
I have the delta in the circs set for a 15 degree delta, that's the only constraint.

Everything is running great for the last 8 years. This boiler condenses all day long, and no one complains upstairs.

Dave H.

hot_rod

> @DaveL said:
> Hot Rod, what would you think best? An ECM system pump in proportional control curve mode? b


Some additional reading on how heat transfer works, some formulas,
And typical system examples. Plug in your own numbers and see what the results show.

The delta T you read across a circuit or system is basically showing you the amount of heat energy being transferred. The hydronic formula can put numbers to that heat transfer, plug you delta readings into the formula to show heat transfer

When the load is high the delta would be wide, closing down as the load gets satisfied

While a system will design to a specific delta to size everything it may never or rarely operate at that delta as the load is constantly changing. Left alone the system delta will move along with the changing load, thermal equilibrium is the term for that

I feel it’s best to allow the delta to move around and adjust the SWT with indoor and outdoor recent to get a nice stability. Properly adjusted a system with reset may be constant circulation,heat energy matching heat loss with varying temperature control. Most all boilers have those reset functions available for this ideal operating condition.

Euro systems commonly let the circulator run constantly vary temperature and use TRVs for zoning, read up on how Viessmann has been implementing this control logic successfully for decades

Regulating heat output by varying flow is a very non liner especially at low load low flow conditions.


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

DaveL

Makes good sense - Thank you again!