Radiant slab issues

NealFoley

I’m trying to tweak the temp control of a radiant slab in a commercial food space. During the day there is a lot of solar gain so the slab turns off. Likewise as work progresses the room heats up. Then at night the cool slab has to make up its loss and isn’t getting as warm as necessary over night. However, on dark days the slab over run during the day can make it quite hot. The slab doesn’t have any probe in it. It runs off a standard non programmable thermostat. What sort of thermostat should I use to fix this?

kcopp

Can you find a way to carefully get a sensor into the floor ad hook it into a thermostat that does both? Also what boiler heats this?
Does it have a weather responsive feature on it that would moderate the water temps?

hot_rod

That I that may be a challenge to get good control over.
Id look at managing the solar gain somehow, proper shading, motorized window blinds?

in a bind a sensor could be put on the return from the slab to try for better control 

Turning a big flywheel like that on and off is not a good control logic

Some applications don’t lend themself to high mass radiant heat

Maybe it idles at a floor warming temperature with a quick responding heater for faster pickup?

nibs

We have a similar situation, not commercial but High thermal mass and a simple thermostat.
What we found is that by programming the boiler to ramp up slowly, and keeping the boiler output temperature fairly low tends to even out the system, a small gathering of about 8 people (outdoor temp about 20F) was enough to shut down the boiler until they went home.
It is very unusual for our boiler to run more than once per day, at about zero F the system runs with a delta T of 9 or 10 deg F. We tried a few different places for the thermostat and also played with the balancing valves on the loops, Havent had to touch the balancing valves for a few years and we adjust the thermostat in the fall and spring by about one degree, keep meaning to tune the thermostat to narrow the range between the demand temp and the shut off call, maybe one day will get around to it. Hope that helps

NealFoley

kcopp said:

Can you find a way to carefully get a sensor into the floor ad hook it into a thermostat that does both? Also what boiler heats this? Does it have a weather responsive feature on it that would moderate the water temps?

No way to get sensor in floor as there are few places to get one. I could lay a sensor on floor under a table where it isn’t disturbed. This is heated off of a secondary loop of a wood boiler set up. No outdoor modulation. 

NealFoley

Is there a thermostat or controller that could cycle the pump for the radiant loops on a schedule? Like exercising pumps during the off season? I’ve thought to try with a simple programmable thermostat… cycle on higher temp for 30 minutes a couple of times a day and use a hold temp to control overnight. But it needs to be automated to take the forgetful human element out of it. 

nibs

You could do that with a timer wired to the thermostat, timers are cheap.
Curious what temp is the water leaving the boiler?.

NealFoley

nibs said:

You could do that with a timer wired to the thermostat, timers are cheap. Curious what temp is the water leaving the boiler?.

Water leaves the boiler about 190. Waiting on a couple of cheap digital thermometers with probes to verify temp at the radiant loop and mix down temp. The mixing valve is set for 130 I think. 

cmalinowski

I'm a noob to all of this radiant floor heating, so take it for what it's worth. What is the deltaT. 190F seems very hot to me for a slab, but I truly don't know. What is the return temp to the boiler? I find it odd that dark days and nights are completely different. Any chance the thermostat is in a place that gets to temp at night, but not in the day, like near a door opening? If you have people moving in/out of a door all day and cold air hits the thermostat, it may think the room is cold and fire the boiler and heat up an already heated room. At night, it doesn't get that "interference."

How big is the space? Do you have a way to track temp near the thermostat on a constant basis and keep a log to get some data? What are "cold" and "warm?" What is the thermostat set to? Is it constant, or is it turned down at night? Are there ovens and such that fire during the day to help heat the space? Are there days when people aren't there contributing to heating, like holidays or something? This might be a good test to see if the empty space on a cloudy/dark day acts similarly to your nighttime situation.

The reason for all of the questions is that it sounds like the issue may not be (just) the thermal impact. If dark days overrun the slab, but night doesn't even heat it up enough, I don't get it.

I'm sure this can be worked out simply enough. Maybe just moving the thermostat, or something similar. I like the idea of lower heat for longer periods of time versus the high heat and short boiler run. Just makes more sense to me. If my pipes are close to the surface, and spread apart, high heat may heat up the slab right around the pipes and generate enough quick heat to turn the room up to temp, but not keep it there since the pipe and slab may cool off quickly since you may only be heating a fraction of the slab. Slow heat, I would think, might more evenly heat the slab and keep the whole system more "constant".

But, when it comes down to it, I have no idea

Good luck, though.

nibs

@NealFoley Surprised you are putting 130 deg water into the slab, I suspect that you would do much better at a lower temp. This morning with an outside temp of -10 F, my boiler was running at 110 F.
Are people mucking about with the thermostat?
Do you have balancing valves on the manifold?
How many loops do you have, can you slow water going through the loops that are in the most affected areas?
If the mixing valve is on the hot supply leg it can give problems, there is an article on youtube which has a good discussion on mixing valves. I just googled "mixing valve in hydronic system" & found it.

NealFoley

nibs said:

@NealFoley Surprised you are putting 130 deg water into the slab, I suspect that you would do much better at a lower temp. This morning with an outside temp of -10 F, my boiler was running at 110 F.
Are people mucking about with the thermostat?
Do you have balancing valves on the manifold?
How many loops do you have, can you slow water going through the loops that are in the most affected areas?
If the mixing valve is on the hot supply leg it can give problems, there is an article on youtube which has a good discussion on mixing valves. I just googled "mixing valve in hydronic system" & found it.

Nibs. My target for slab temp water is 90-120. There are no coverings so that’s not a concern. It Is a large open space with equipment on wheels and very wet. Ideally a slab temp of 90 is what I’d like to achieve. No one touches the thermostat. Because the space is wet I’ve had trouble locating and keeping functional thermostats running. I’ve since moved the thermostat into a different room and use a probe to get air temp. There really isn’t any way to get a probe at or in the slab.
I believe this is a single 300 foot loop of 3/4 pex. It was originally designed to receive waste hot water from food manufacturing processes but crucial piece of equipment was changed to a differently model that didn’t need to flush as much hot water and it was reclaimed a different way. It has been heated with an electric hot water heater for the past two years but rates more than doubled so it was not tenable. And at the coldest part of the year it struggled to keep up. The gundfos alpha circulator runs at’ less than a gpm.
I’ll look into the mixing valve issue. The one I got is leaking a bit and not ideal.

Zman

Outdoor reset on the slab should be your first move. That will help prevent the slab from overheating, the water temp will vary based on outdoor temp. A simple way to do that is by replacing your mixing valve with something like this and installing an outdoor sensor.https://www.supplyhouse.com/Taco-I075C3R-1-3-4-3-Way-Outdoor-Reset-I-Series-Mixing-Valve-w-Sensor-5203000-p.

If this was a living space spending a bit more on a Tekmar system with indoor temp feedback would make sense. I don't think I would bother in this application.

nibs

@NealFoley , I like and appreciate what you are doing. The system was designed to recover waste heat and now you are working to adapt it. Kudos.
You likely will have to think outside the box a little and experiment to get it to perform the way you want.
What kind of boiler are you now using to heat the slab, and is it programmable? Does the circ pump have speed settings?
Just a guess but I suspect that if you increased the gpm and lowered the temp in the loop you might get results closer to what you want.

NealFoley

Peakedtoosoon said:

Solar shading helps but it sounds like you need additional controls, like outdoor reset with room sensor influence or water delta T control. Night set-back would also help. Can't comment on install, without more detailed information, but the control set-up seems insufficient.

The boiler is an EKO40 gasification Wood boiler. Its minimum start temp is 140. I’ve used an EKO60 before that was hooked to a 1000 gallon heat storage tank with coils for heating tank and drawing off DHW and two heating zones. It worked amazing with very little issues. 

The setup I’m working on now is a temporary, direct connected system. Primary loop off of boiler with mixing valve set to return 140+ water to boiler. Boiler pump kicks on at 150. Idles at 185 at the moment. There are 2 secondary loops. One is to heat a poorly insulated milking parlor with an diy air handler made from a Toyota radiator. It pulls water off of closely spaced tees at primary loop temp. The second circuit is the radiant slab loop with a mixing valve. The boiler is on a shed at cellar level. The loop rises about 12 feet.  It’s fortunately still warm out while I work out the bugs. 

NealFoley

Zman said:

Outdoor reset on the slab should be your first move. That will help prevent the slab from overheating, the water temp will vary based on outdoor temp. A simple way to do that is by replacing your mixing valve with something like this and installing an outdoor sensor.https://www.supplyhouse.com/Taco-I075C3R-1-3-4-3-Way-Outdoor-Reset-I-Series-Mixing-Valve-w-Sensor-5203000-p. If this was a living space spending a bit more on a Tekmar system with indoor temp feedback would make sense. I don't think I would bother in this application.

I really like this idea. Not in the budget on this temporary set up. But once the final version goes in I will use this idea. The system has been in operation for 5 years. The first two years it was just a 50 gallon electric hot water and a thermostat operated pump. It worked but was costly. We are waiting to add another building and heated space and proper boiler. Meanwhile we changed to a heat pump water heater and that worked nicely for a couple of years. In the shoulder season the temp could be lowered and recovery time was acceptable. It helped save money. Last year with rising electricity rates we added a panel radiator to the system to remove an electric radiator. It worked but was costly. Hence this year going with a wood boiler to cover the food factory and have heat in other spaces. Not ideal as the boiler will idle a lot except on coldest days. But this is an extreme budget solution so we can focus on getting buildings built and a proper system in—which was supposed to happen in 2020… 

hot_rod

I had that same EKO in my last shop, a great little boiler. You must be working with Zenon at New Horizon, quite the character.
I,m pretty sure the controller has our door reset function in it? Check with Zenon , the spec sheet indicates it has weather responsive control. I never used the function on mine it was piped to a 500 gallon buffer tank.

As for your floor temperature, if the surface is 90 degrees and the room air temperature is say 65, you are getting 50 btus/ sq ft of heat out put. The math is 2 btu/ every degree difference between ambient and floor surface. So to lessen over heating or fly wheeling from that slab, look to lowering the SWT.

To a degree you can do that with the reset, but be aware of return temperature to the boiler. And the temperature you need for the fan coil.

I added a return protection pump/ valve on my EKO, because the 500 gallon tank kept it running too cold and creating creosote issues. A large slab would also do that.

The best piping would be to use a mixing valve with out door reset like the Taco I-valve, run the boiler hot and efficiently fun the radiant with better control.

NealFoley

Bob, this unit is second hand. Been abused. Overheated and bulged the outer jacket. But it works! I got a new controller because the original 2008 controller was way to manual. I’ve got the return mixing valve set to 140 ish I think—by feel. Outdoor reset for the boiler is something I’ll have to look at. I want to keep this as primitive as possible because I’ll have to tear out everything in the spring to start the new building. 

Having a devil of a time getting air out of system and dialing in gasification. The air controls are heavily worn…. 

hot_rod

Wood needs to be really dry for gasification boilers. Cut it a year in advance if possible. It's tough to get green or wet wood to allow good gasification.

The type of wood has a lot to do with ash removal, which was an every other week chore for me as I burned whatever wood fell down on the property, even walnut! which created a lot of ash. Ash piles up around and behind that ceramic gasification block in the bottom.

Door gaskets in good shape? About 5 years on those is normal. The red silicone coated door gasket work best. Adjust the door hinges and latch as the door gaskets age to keep a tight seal.
You will feel air leaking around the door or in a dark room with a flashlight you can spot door leakage.

Have you removed the back cover and rodded and brushed those tubes? That helps the burn also. I made a 36" long brush for my cordless drill to scrub those tube. Find burner brushes online. I think a 1-1/4 copper fitting brush is about the size you need.
If they plug solid it is a bear to get them cleaned. A long drill bit, 36" is about the only way to unplug them, drill down through the ash, with a shop vac running to pull it out.

That boiler is made in Poland by ship builder welders, extremely robust steel, thru rods and welding, they can take a lot of abuse.

I sold a trailer load of 40 and 60Kw units, some Atmos and PK Pyros around my area, most ended up with 2 or 3 owners as folks tired of the wood burning ritual and LP was cheap.

NealFoley

Bob, I run a Sawmill so I’ve got tons of slab to burn. I can store three days worth in the shed, it’s plenty dry. Got a good mix of softwood slab and hardwood cord wood. 

I’m actually thinking of lowering the pump start temp. I’ve only ever run the EKO 60 flat out to chart the storage tank. Without that, on this smaller boiler, perhaps I need to start pump at 110 not 150 and only heat until 175. That will still allow flywheel gain on the boiler before overheating and keep the primary loop pump running longer. 

NealFoley

I have the heat exchangers a good clean before firing up. Door gaskets are a year old and I’ve tightened up everything. 

hot_rod

I tried slab wood from a nearby mill one year. It was a pain in the ash, no offense. Old timer wood burners claim the bark is what causes so much ash. Tough on chain saws also with embedded dirt from skidding. I suppose dry enough the bark starts to fall off?

I found that buffers are almost a must. That boiler is most efficient, burning cleanly at full speed. But rarely does the load match full speed multi hour burns. The buffer lessens fire tending and allows you to have long off burn cycles, and pull a mixed temperature from it easily. Less overheating or dry fire potential which may have caused the damage on the one you bought?

I found old LP tanks to make my buffers. Started with a 160, went to 300, and eventually a 500. Plenty of tanks became available as NG made it way to my neck of the woods. A buck a gallon was typical price. Craigslist ones were yours for hauling sometimes.

It is a balance with wood boilers and radiant. The boiler likes to run 180 +, but the radiant wants below 120 typically.

I've done the wood boiler dance for over 30 years now. Finally last fall I turned into a city slicker, went 100% NG and some solar. It's a young mans sport processing wood, I miss parts of the wood gathering ritual.

psb75

If you own a sawmill and you are going to "build new" you really should look into a Garn wood boiler. It's a gassifying boiler and you don't need extra heat storage vessels. It's a batch burner and nothing like an outdoor wood boiler. Very good with EPA emmissions. It needs DRY wood though.

NealFoley

psb75 said:

If you own a sawmill and you are going to "build new" you really should look into a Garn wood boiler. It's a gassifying boiler and you don't need extra heat storage vessels. It's a batch burner and nothing like an outdoor wood boiler. Very good with EPA emmissions. It needs DRY wood though.

GARN only sells for commercial installations now. Fortunately we are. I’ve already looked into it and was going to get one. The $18k price tag is steep and the space requirements large. The rep lives a few miles from me.  Unfortunately the build time didn’t coincide with our cash flow. I’m also looking into a froeling and a biomass next Gen. boiler. I saw a dual fuel model and set up recently. 

propmanage

Hello and good morning, It’s always been my understanding that slab heat only works properly with a consistent temperature like say 65-70 degree loops and that’s why the zones and loops and building envelop are so important for the loops coming back to the manifold to be balanced properly.

The idea is for all of the space seating table chairs walls to also become a consistent temperature. You can use low loop temperatures because everything in the space becomes the same temperature so very little is pulling btu’s from your body. A non slab typical heating set up with heat on / off thermostat goes cool pulls btu’s from your body until the thermostat is calling for heat again.

In a commercial space slab system lots of people coming and going it’s a little more difficult to maintain and keep the btu’s so design is much more important. The entrances would need have some type of make heat to prevent a loss of btu’s and less air changes . These slab spaces are not usually designed to fluctuate like traditional set ups they need to keep air changes consistent. With that said and to late to redesign you may need to have a thermostat set up with your mixing valve for minimum and maximum temperatures as the solar gain heats the loop lowers and vice versa.

I’m not sure if I explained it properly I hope the idea comes across and possibly helps ?

Glenn_Venco

The most effective, least costly way, would be to repipe as an injection system. Use a Tekmar 356. It will adjust the temperature of the water sent out to your slab via the injection pump in real time based on outdoor, boiler, and radiant mix temperatures . Suggest you make your slab constant circulation - this way any solar gains are distributed evenly throughout the slab. The only way the slab will get heated water is from the injection pump. It is much more reliable long term than a modulating mixing valve. Essentially you are programming an outdoor reset curve for your slab that will adjust the speed/time of the injection pump. This will react not only to the outdoor temperature, but the temperature of the water circulating in the slab. You may have to adjust the curve a few times along the way, but it will eventually make the space more comfortable and potentially save on fuel.

NealFoley

Glenn,  thanks! I’ll research this option for the new system and slabs we’re installing next year. I’ll have the same issue with them. And I can fix issues with current set up. 

Right now I’m having a hard time getting the flow I need through get slab. Can’t seem to get more than 1gpm. I’ve bled the circuit several times.  It may be because there’s a panel radiator before the slab on the same loop. I should have made it last because the room it serves doesn’t need to be that warm. 

tanklessman01

NealFoley said:

nibs said:

You could do that with a timer wired to the thermostat, timers are cheap. Curious what temp is the water leaving the boiler?.

Water leaves the boiler about 190. Waiting on a couple of cheap digital thermometers with probes to verify temp at the radiant loop and mix down temp. The mixing valve is set for 130 I think. 

hot_rod

The Euro designs are state of the art technology, wood and bio is still big business in Europe.

Consider two separate boilers if you dual fuel. The fossil fueled one and a gas or LP for the second stage. Too many compromises in dual fuel technology

tanklessman01

nibs said:

We have a similar situation, not commercial but High thermal mass and a simple thermostat. What we found is that by programming the boiler to ramp up slowly, and keeping the boiler output temperature fairly low tends to even out the system, a small gathering of about 8 people (outdoor temp about 20F) was enough to shut down the boiler until they went home. It is very unusual for our boiler to run more than once per day, at about zero F the system runs with a delta T of 9 or 10 deg F. We tried a few different places for the thermostat and also played with the balancing valves on the loops, Havent had to touch the balancing valves for a few years and we adjust the thermostat in the fall and spring by about one degree, keep meaning to tune the thermostat to narrow the range between the demand temp and the shut off call, maybe one day will get around to it. Hope that helps

Timer and temperature probe on the return loop with a switching relay to run circulating pump and activate the boiler as needed, just as you would do with a hot water recirculation loop.
This might help maintain the the temperature you want at the slab loop.
İt's been nearly 30 years but I remember 94deg. F being the maximum temperature for radiant floor heating for people to walk on it without any health risks. You should verify it..

Using electronic timer as nibs suggested, with dip switches can keep the pump off when it is not needed.
Dip switches can help you intermittently turn system On and Off 24/7 regardless of what thermostat says or Sun's solar heat creates.
İt only cares for what the temperature is in the slab loop.

I hope this helps 

NealFoley

hot_rod said:

The Euro designs are state of the art technology, wood and bio is still big business in Europe. Consider two separate boilers if you dual fuel. The fossil fueled one and a gas or LP for the second stage. Too many compromises in dual fuel technology

After doing more research I’m strongly leaning towards a froling s3 with storage and dhw. Perhaps Solar to help in the summer. 

hot_rod

if it is worth doing its worth doing right. I would design around a buffer both to handle the wood boiler and solar needs some storage.

Here is a tank idea that work best for me after a handfull of versions over the years.

I ended up with a used 500 gallon lp tank, welded some legs to stand it upright.

I had 5- solar thermal collectors and the wood boiler connected to it.
I left an air bubble up top for expansion, and a drainback space for the solar. unless you have a constant summer heat or DHW load, I highly recommend drainback for the collectors.

The same water in the tank flowed through the radiant, some radiators and a plate HX for DWH. An LP boiler would back up if no solar or wood was available. But it only heated a small top portion of the tank. Just enough to assure DHW via the plate HX

It was piped as a 2-pipe buffer so all the pumps had hydraulic separation also.
Size the tank to the solar and amount of time for the wood boiler to buffer.

psb75

Froling S3 is about your only option from Europe these days.

hot_rod

It has been a few years since I have been following the wood boiler players. Tarm at wood boilers.com is still in the game, newhorizionscorp looks like he still imports Euro boilers. EconoBurn was a U.S. built gasification boiler, they seem to still be around.
Troy Boiler works in NY was building a Austrian design boiler under license,
I don’t see that one around anymore.

I’d like to try one of these wood stove boiler concepts. A small amount is boiler, but it could be more manageable on the hydronic side. I like the fire in the living space also.

NealFoley

psb75 said:

Froling S3 is about your only option from Europe these days.

New horizons imports biomass brand Polish boilers. They replaced the Orland Ekos. They seem better than the Eko but they still use the same lame controller, so no go. Froling seems like it’s around the same price for a better unit all around. 

NealFoley

tanklessman01 said:

nibs said:

We have a similar situation, not commercial but High thermal mass and a simple thermostat. What we found is that by programming the boiler to ramp up slowly, and keeping the boiler output temperature fairly low tends to even out the system, a small gathering of about 8 people (outdoor temp about 20F) was enough to shut down the boiler until they went home. It is very unusual for our boiler to run more than once per day, at about zero F the system runs with a delta T of 9 or 10 deg F. We tried a few different places for the thermostat and also played with the balancing valves on the loops, Havent had to touch the balancing valves for a few years and we adjust the thermostat in the fall and spring by about one degree, keep meaning to tune the thermostat to narrow the range between the demand temp and the shut off call, maybe one day will get around to it. Hope that helps

Timer and temperature probe on the return loop with a switching relay to run circulating pump and activate the boiler as needed, just as you would do with a hot water recirculation loop.
This might help maintain the the temperature you want at the slab loop.
İt's been nearly 30 years but I remember 94deg. F being the maximum temperature for radiant floor heating for people to walk on it without any health risks. You should verify it..

Using electronic timer as nibs suggested, with dip switches can keep the pump off when it is not needed.
Dip switches can help you intermittently turn system On and Off 24/7 regardless of what thermostat says or Sun's solar heat creates.
İt only cares for what the temperature is in the slab loop.

I hope this helps 

I had one of these pid temp controllers. Inkbird ITC-308 Digital Temperature Controller 2-Stage Outlet Thermostat Heating and Cooling Mode Carboy Homebrew Fermenter Greenhouse Terrarium 110V 10A 1100W https://a.co/d/7ThPr9V  I had been using it to monitor room temp near floor to run pump. Instead I’ve switched the probe to the outgoing slab pex and dialed in the floor mixed temp to 95. It seems to be keeping the space at 68 overnight which is perfect. I have it set to more or less run continually, with the upper limit set to 110. I may dial that down and lower floor temp a bit. It’s been cloudy with little solar gain at the moment. During production yesterday the temp got up to 79… but went down once heating processes were done.