just wondering what you guys are running for water temps into your slab. I have a outdoor reset and i find that i over heat. my house is very well insulated. the zones will demand at night and during the day indoor temps are 72-74 when set at 70. this alllows the slab to cool and need a big boost back up the next night. i would rather it hover around 70 so that the zone would demand alittle in order to keep the slab a bit warm so it wouldnt take so much effort to heat it back up
radiant temp
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I heat the concrete slab in my shop, slab set at 61F constant, and the actual range is 61-63F. No reset, so inside air temp varies between about 63F on the high side and down to about 55F or a little lower in below 0F outside temps. Concrete takes a long time to respond. My supply temp to the slab is 100F constant. I have the impression that, at least with concrete slab, a supplemental heat source to take care of the cold days is a good thing to have; else, potential to overheat or underheat, depending on how fast the outside temperatures move. Maybe some of the more sophisticated outdoor resets with accurate future weather forecasts can do a better job at maintaining a constant indoor temperature.
im just trying to figure out how to stop it from overshooting. its energy wasted. I put the max on the outdoor reset at 115 degrees.
Bad LP
Minister of Fire
I recall the setting on my Taco mixing block is 105 max. The first floor of the house maintains to the degree whatever is set on the t'stat.
Karl_northwind
Minister of Fire
Hello everyone. My first post, so I hope I understand the problem you are having correctly.
When I put the tubing in my slab, I also installed a tekmar slab sensor that will provide feedback to my thermostat in order to avoid excessive slab cooling. It looks like the Tekmar 079 could be used here, as it states it is suitable for a retrofit situation. I did this because that area gets a lot of sun during the day and there is also a wood stove in the room.
Not sure if this might help your situation, but the thread caught my eye.
Just so you know, my radiant is not yet operational so I can't tell you how well the sensor works......
When I put the tubing in my slab, I also installed a tekmar slab sensor that will provide feedback to my thermostat in order to avoid excessive slab cooling. It looks like the Tekmar 079 could be used here, as it states it is suitable for a retrofit situation. I did this because that area gets a lot of sun during the day and there is also a wood stove in the room.
Not sure if this might help your situation, but the thread caught my eye.
Just so you know, my radiant is not yet operational so I can't tell you how well the sensor works......
With odr and mixing vlvs, I have it set to supply highest of 120 at 2nd fl manifold, when 10 or below outside.
Avg 100-110, when above 10 outside..
Dt from 120 down to 85-90 on return manifolds, or from 100 down to 80.
Have very long runs to 2nd fl, running through the far partitioned section of the basement , which is usually in the 50s...thus the 120 at manifold.
Avg 100-110, when above 10 outside..
Dt from 120 down to 85-90 on return manifolds, or from 100 down to 80.
Have very long runs to 2nd fl, running through the far partitioned section of the basement , which is usually in the 50s...thus the 120 at manifold.
varadhammo
Member
What thermostat do you have? A good radiant-specific pwm thermostat does a great job at maintaining an air temperature setpoint, even if your reset curve is set steep, no slab sensor necessary... And IMHO it's good to set your outdoor reset curve a bit steep, gives it a bit extra for windy days. I've been using several of these wirsbo stats with slabs, excellent results: http://www.supplyhouse.com/Wirsbo-U...-Thermostat-WT-1-Heat-Only-Two-wire-2063000-p
BTW I send 110F constant to the slab, no reset. Room temp is always within 1 degree of the setpoint.
BTW I send 110F constant to the slab, no reset. Room temp is always within 1 degree of the setpoint.
Karl_northwind
Minister of Fire
cpeltier
Member
I use Outdoor Reset and run my temps low so they can also use warm water from a Heat Pump source. I also use PWM thermostats with PID controlled cycle rates to provide smooth room heating without overshoot or undershoot. No need for a slab sensor to control the PWM thermostat. I find that the wall mounted Tekmar or Honeywell thermostats work great. The key is PWM not a Bang On/Bang off thermostat with hysteresis.
As far as water temperatures are concerned it all comes down to calculating your Outdoor Reset temperature curves based on your coldest day and the design criteria used for designing the radiant slab. I have one house that operates at 118F at -25F and another that uses 130F at 10F for an indoor room temperature of 70F. The first house has 1/2" tubing spaced 4-6" apart with lots of tile. The second 12" spacing with tile, and area carpets. It all comes down to the BTUs/ft^2 required by the room. Calculating that is an entirely different exercise but trail and error with different Outdoor Reset slopes should get you close.
my thermostats are honeywell pro 1000. i find that when they do hit 70dg (setpoint) that it keeps asking for alittle while longer.
cpeltier
Member
The Honeywell Pro 1000 is a simple Bang On/Bang Off thermostat. It will lead to over and under shooting with radiant heat. The Tekmar 518 can replace that for low cost and implements a PWM algorithm. I've used the Honeywell Prestige thermostats with radiant and they work well for a lot more money.
Talk about Bang, Bang, I don't even have a thermostat! Just a switch than turns the alpha and ivalve on or off. What I do have are TRV's on each loop of my infloor radiant and I run on constant circulation with ODR. IMHO, you can't beat the simplicity and comfort of low temp radiant, constant circulation, TRV's and ODR. Hydronic Nirvana. Plus batch burning with gasification and thermal storage.....Yeah, I LOVE my setup.
Noah
Noah
Bad LP
Minister of Fire
cpeltier
Member
Noah's solution is essentially a bang on/bang off with the TRVs.
Tythib - If you can set the ODR curve down in temp so that thermostat stays on all of the time for a given outdoor temperature you will match Noah's setup and it will minimize the overshoot in those conditions.
However, passive solar gain can be a problem and in very cold temperatures the ODR curve is typically non-linear. This means In Maine as Bad LP surmised, this setup probably won't work. If you set it up at 25F outside then it will overshoot a 45F outside and you will be cold at 0F. Unless of course you have a sophisticated ODR control that can do a characterized heating curve!
Tythib - If you can set the ODR curve down in temp so that thermostat stays on all of the time for a given outdoor temperature you will match Noah's setup and it will minimize the overshoot in those conditions.
However, passive solar gain can be a problem and in very cold temperatures the ODR curve is typically non-linear. This means In Maine as Bad LP surmised, this setup probably won't work. If you set it up at 25F outside then it will overshoot a 45F outside and you will be cold at 0F. Unless of course you have a sophisticated ODR control that can do a characterized heating curve!
my odr is set at 0dg for a design outdoor temp and the indoor design is 68dg. woke up this morning and its 72 in my house. set at 70dg setpoint. I even limited the water temp going in to 105dg and it didn't help. it seems to me that the zones only demand once at night and then the house will be warm all day into the next night until it demands again. boiler pretty much idles all day. I could imagine that the slab has cooled allot by the time it demands again. Is it right to think that the slab should be staying at one even temp instead of spiking.
Karl_northwind
Minister of Fire
I would reduce the h20 temp. are you using a tekmar controller or what other sort of equipment to adjust the temp? or are you using a gas boiler with internal adjustment?
assuming you're running close to design conditions like the rest of us (-17 here this AM, design is -9) you're probably overshooting a lot at 115. adjust the peak temp down about 5 degrees F at a time. if it's slab on grade, well insulated all the way around, you're probably going to end up at about 100F.
assuming you're running close to design conditions like the rest of us (-17 here this AM, design is -9) you're probably overshooting a lot at 115. adjust the peak temp down about 5 degrees F at a time. if it's slab on grade, well insulated all the way around, you're probably going to end up at about 100F.
cpeltier
Member
You have a high mass radiant slab which is very slow to respond and once it does it's like a freight train - slow to get rolling and hard to stop. The easiest solution is a PWM thermostat and your done.
Otherwise you can lower the ODR curve some more. 105F sounds low but I have a system that's similar at 0F and I'm pulsing the slab with water or it will overshoot. At some point if you lower the entering water temp enough your room heat loss will match the output of the emitter.
Karl_northwind
Minister of Fire
he said up above that he set it to 115, which is definitely too high. I suggest dropping it a bit at a time. The PWM function of the stat isn't going to stop a massive overshoot, only make it less bad than a non pwm stat. the heat is still in the slab coming out for hours before the air temp rises enough for the stat to see. also, if it's been shooting heat in for hours, with no sun in the room, and then sun hits in the morning, the slab is charged for no solar gain, plus solar gain=large overshoot.
cpeltier
Member
I believe he means at the design temperature of 0F the zone water temp is 115F. I'm not sure what his current outdoor temp is but I agree the ODR curve does seem high for a well insulated house. I don't know that he has passive solar gain but if he's overshooting in the morning it could very well be. There's no way to stop solar gain in a high mass radiant system that I'm aware of other then implementing a custom weather predictive control (EasyIO) or using complex scheduling between slab and air temperature readings based on time of day (Tekmar). Getting the ODR curve as close to the heat loss of the house is important to minimize swings and maximize run time of the circulation pump.
The hysteresis built into the Honeywell Pro 1000 thermostat will call for heat a degree or so above the set point and once the room temperature reaches that, will wait until the room temp drops a degree or so below the setpoint to start heating again. Usually you will experience a nice sine wave temperature profile in the room around the differential with undershoot and overshoot.
Tekmar has a good essay on the topic: http://tekmarcontrols.com/images/_literature/e0006_06.pdf
What do you guys recommend my ODR be set at(room temp, outdoor temp, ect.) I live in fort kent maine. Always cold. The outdoor design temp right now is 0. I am definitely looking at the Wirsbo thermostats to aid. just sucks its a brand new house and replace thermostats I just paid for sucks. I really think my system could use a lot of fine tuning. but my contractor doesn't seem to interested in spending the time. his only recommendation would be to lower the indoor design temp.but it hasn't helped at all. I have a three speed circulator that controls the feed into the house which is setting at the top speed. my boiler is an okefen pellet boiler. Sitting here right now and my house is 73-75 dg set at 70
cpeltier
Member
Fort Kent! Could you be any further north in the lower 48? I lived in Orono for a while and I thought that was cold. Your official design temperature is -13F but I see it got down to -28F in January. What controls your ODR? I would set the design temp to -25F if you can and leave everything else alone and see what happens.
cpeltier
Member
This should increase the slope of the ODR curve and lower the temperature to the loop assuming this controls the radiant loop temperature.What kind of boiler do you have? Are your radiant loops run directly off the boiler or through a floating action mixing valve, an manually adjustable mixing valve or a variable speed injection pump?
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