TRV's for radiant slab?

billyboy

Seems many here love TRV's They work great on radiators.

But it seems some complain about control issues with a slab (overshoot etc.)

also, I like WIFI thermostats, lots of features, remote control, logging, etc.

My question: Has anyone tried to morph a zone valve so that it acts somewhat like a 2 stage TRV ?

Am thinking along the lines of: a low flow bypass around each zone valve (flow set with a globe valve)
This would allow a single Alpha to provide continuous circulation (reduced by say 75%) in multiple zones & provide full flow when thermostat opens zone valve.

SWEI

High quality, low cost proportional zone valves have been available for decades. The issue is the lack of off-the-shelf controls capable of managing them...

Firecontrol933

Overshoot in a slab system is caused by too much energy being put into the mass beyond the need to maintain the temperature of the space it's responsible for keeping at set point. Simple on off control of the movement of energy into the slab is the "fix" to solve a problem that should instead be resolved by supplying the slab with the exact temperature of water that it needs to JUST do it's job, no more no less.

The problem is people/customers tend to only consider a radiant slab system to be operating properly if the surface of the slab is nice and warm so that they can walk around on it in bare feet. This condition almost always means that too much energy is being supplied and the space will overshoot and the flow will have to be stopped while the excess energy is released to the space.

But I regress and am not answering your question. I have never seen nor tried what you are suggesting, but there are already many different kinds of valves that modulate around a steady state. A person just needs to decide what they want to do and then research already existing product that does exactly that.

billyboy

Firecontrol933:
your:
"should instead be resolved by supplying the slab with the exact temperature of water that it needs to JUST do it's job, no more no less."
Is a good plan

I use ODR via injection, but even with that I need to control the flow.



SWEI, like this:

http://www.supplyhouse.com/Macon-Controls-MAC-ZMC-DDC-Proportional-Normally-Closed-Electric-Zone-Valve-Actuator-with-3-3-Cable-24V
&
http://www.supplyhouse.com/Erie-VM2222P33A000-1-2-2-Way-NPT-Proportional-Non-Spring-Return-Zone-Valve-2-0-CV-24V

The only DDC controller Erie lists is for stuff like this:

"The T167 thermostats provide proportional control of
cooling fan coil damper and fan system."

Does anyone sell a 0-10vdc proportional controler outside of a new ModCon boiler?

So it looks like I need to start programming my Arduino microprocessors to do this?

billyboy

This seems close:
http://s3.supplyhouse.com/product_files/A350PS-1C - Product Overview.pdf

Zman

Outdoor reset is a must.
In my mind the next level of control should be indoor feedback and slab temp feedback.

The problem with reducing flow as you suggest is that the delta t between the supply and return will be very high resulting in uneven heat.

SWEI

Plenty of single channel PI/PID controllers out there. Put four or eight of them in a panel and you're easily 3x the cost you want to be at if you intend to transform a market.

billyboy

SWEI posted this in 2013:

"A stat with a proportional output paired with a proportional zone valve will do this. The mechanical version is called a TRV. The electronic version is unfortunately quite rare in residential systems. When using ODR with conventional on/off thermostats, it is necessary to shift the curve several degrees above optimal in order to give an on/off zone valve (or pump) sufficient authority. The result is a slow cycling over and under the setpoint rather than constant temperature like you get with a TRV. "

billyboy

Seems like every zone would have a different "perfect ODR"
and if perfect, it could never catch up if weather takes a "cold snap"

billyboy

Danfoss Floor Heat Valves look good (small zones)
Are they sold in USA?

SWEI

If the emitters are correctly sized, a single ODR curve can work quite well for the entire job. The tighter you tune the ODR curve, the more challenging setback and recovery become. This is where indoor feedback really starts to show its value.

billyboy

Zman, u got me thinking & researching.

At constant SWT & 1gpm, a flow reduction of 50% (.5gpm) will reduce heat output by about 10%.
A flow reduction of 75% (.25gpm) should reduce heat output by another 10 to 15%
So at 25% of original flow, still about 75% heat delivered.

Still as u said, the start of the pex loops would be hotter than the ends.

I see an easy way to reverse flows at system side of my hydraulic seperator using 2 Alpha pumps without check valves & a solid state timer, say a 15 minute cycle in east direction.

Gordy

billyboy said:

Zman, u got me thinking & researching.

At constant SWT & 1gpm, a flow reduction of 50% (.5gpm) will reduce heat output by about 10%.
A flow reduction of 75% (.25gpm) should reduce heat output by another 10 to 15%
So at 25% of original flow, still about 75% heat delivered.

Still as u said, the start of the pex loops would be hotter than the ends.

I see an easy way to reverse flows at system side of my hydraulic seperator using 2 Alpha pumps without check valves & a solid state timer, say a 15 minute cycle in east direction.

Keep it simple. Why reduce flow to have to do a more complex reversing flow setup to maintain panel comfort. Reversing flow is a method to fix a bad design usually when someone installs radical loop lengths.

As been said if the panels were designed properly for each zone one reset curve should cover the whole job. Where it gets complicated is different panel types requiring different water temps.

billyboy

Gordy, This was original why

This would allow a single Alpha to provide continuous circulation (reduced by say 75%) in multiple zones & provide full flow when thermostat opens zone valve.

It's difficult to have continuous circulation without having a separate pump for each zone.

So with reversing flow, it would require 2 Alpha's

billyboy

House will have 4 zones, all slab emitters.

DHW & boiler buffer tank function will be provided by a Viessman dual coil indirect.

Top coil will provide system heat.

Another attractive method, would have a Alpha in each zone providing constant circulation with 3-way zone valves diverting flow to bring in heat, this elemonates a pump to bring in heat.

billyboy

I was in the wrong part of the curve in my post above

(1/2" pex in slab @ 12" OC) 1gpm vs. .25gpm

"So at 25% of original flow, still about 75% heat delivered"

S/B

So at 25% of original flow, still about 55% heat delivered