Hardwired, communicating thermostat with in-floor sensor for radiant heat

[ReasonablePerson]

We are looking for a thermostat to use with our Elk M1 system for zone control with radiant floor heat. The thermostats we find that have a 2nd temperature sensor to maintain the floor temperature are not communicating and i have not seen that any compatible with the Elk have floor temperature control.

A radiant floor heat thermostat should call for heat like normal except when the floor temperature gets to the max floor temp at which point it should stop calling for radiant heat and either do nothing or start calling for aux heat (via forced air in our case). when calling for cooling it should turn off the floor and call for cooling (comes via forced air again) but not let the floor temperature drop below the minimum setpoint. It should also keep in mind that the gypcrete floors change temperature very slowly.

this is hydronic heat so all the calls are low voltage (i.e., high current, line-voltage version not required)

True, true, this could be done with a standard thermostat and bunch of elk temperature probes along with a couple of rules in the Elk for each zone. however, i have more zones than Elk inputs that can measure temperature and since this is a fairly important task i didn't want it easily messed up. After all, next time my wife may marry for money or looks rather than intelligence and i don't want husband #2 to destroy the house if he can't figure this stuff out.

thanks

 

[Del91574]

I've always really seen/done hydronic radiant heating by monitoring the inlet and outlet temperature on the piping, then plugging in values with help of the HVAC/mech contractor to work on the BTU's being dropped into a room with an in room stat only controlling how fast or slow the water is entering/leaving the loop.

 

[ReasonablePerson]

We are going to have wood floors, so slab temperature is the #1 priority. The system would only have flowrate (and therefore delta-T) control if variable speed pumps or proportional valves are used. That isn't out of the question but right now we are only budgeting for standard on/off zone control valves (and controlling the open time per hour) so we will only have binary control on the flow. Input temperature is fixed and kept to a minimum for efficiency (geothermal).

 

[tmbrown97]

I'm thinking this might need a combination of items... primary would be any ol' communicating thermostat - something like an OmniStat II can handle multi-stage heating pretty easily. The part it'll struggle with is what to do when max temperature is reached - I think you'll need a separate circuit to cut off the heat call when max floor temp is reached. It would handle the call for stage 2 heat the same as any heat pump - by temperature differential or perhaps if it's just taking too long to reach the desired temperature.

Other members here have replaced their entire thermostat with a CAI Web Control board; no reason you couldn't build this little bit of logic into one - they can handle like 8 temperature inputs, a humidity sensor, and control about 8 outputs - so you could get pretty trick with one.

My concern is that I'd think a good radiant floor system would learn the characteristics of the floor... so for example, if the desired temp is 72, you don't want these floors to max heat until 72 is reached, otherwise the temperature may continue to rise way past that point.

 

[KenN]

Just curious, is this an existing radiant heating setup or are you installing new? I ask because my understanding of modern hydronic systems is that there is no need for slab/floor temperature monitoring if they're designed correctly. The designer should be doing a surface temperature calc and use the results to figure the spacing of the pipes so that the floor temp isn't above 85F.

I moved into a newly built house with hydronic a couple months ago, so I just went down the the basement to have a good look and there is no floor temp monitoring. I'm pretty curious about these things though, so I looked up a few things and here's what I found of interest;

http://www.radiantcompany.com/faq/#damage

http://www.healthyheating.com/Radiant_Design_Guide/Infloor_Radiant_Design_Guide.htm

Hope this is useful!

 

[Dean Roddey]

The Elk probably won't interface to it, but we recently added a driver for the Tekmar series of thermostats, which provide built in support for room and slab temps. It seems to be a pretty solid system. There's a central gateway box that the thermos all come back to, and there are a number of models of thermos with different features.

 

[ReasonablePerson]

Just curious, is this an existing radiant heating setup or are you installing new? I ask because my understanding of modern hydronic systems is that there is no need for slab/floor temperature monitoring if they're designed correctly. The designer should be doing a surface temperature calc and use the results to figure the spacing of the pipes so that the floor temp isn't above 85F.

I moved into a newly built house with hydronic a couple months ago, so I just went down the the basement to have a good look and there is no floor temp monitoring. I'm pretty curious about these things though, so I looked up a few things and here's what I found of interest;

http://www.radiantco...com/faq/#damage

http://www.healthyhe...esign_Guide.htm

Hope this is useful!

It is new construction with a gypcrete floor, professionally designed but just with non-communicating thermostats (uponor). When using a slab, the control is somewhat different than when using under floor tubes as in your first reference. As Work2Play mentioned, overshoot is a real problem with slab floor radiant due to the thermal inertia of the slab; which is why the slab temperature sensor is so important.

 

[KenN]

Sounds reasonable. Is it important to you to have the slab temps wired in so you can see them? If not, then an alternative might be to bring the wiring into a box and hardwire some relays to switch the heating sources. You lose the ability to see what heat source is used via your Elk system, but then again, it's generally pretty clear when the forced air furnace starts to run!

 

[Neurorad]

Here is the Aube hydronic stat list

http://www.aubetech.com/products/list.php?noLangue=2&noFamille=1&app=7

 

[ElkUserMT]

[sup]I did quite a bit of looking into this recently. Conventional thermostats will not work in hydronic applications due to the delay in the hydronic loop responding to the call for additional heat. For this reason there are limited options if looking to interface with an Elk system.[/sup]

[sup]The system I am looking for a vacation home uses "warmboard" subflooring instead of gypcrete. I need to be able to control seven different zones and also interface with a heat pump / AC system. [/sup]

[sup]In my research I came across the following thermostats that I plan to use:[/sup]
[sup]
Hydronic Thermostats: Aube TH140-28-01-B/U Hydronic thermostats ($47)
Main System heat pump + a/c Thermostat: Aube TH-144HP-N-2H1C ($113)
Indoor/Outdoor Sensor: Aube AC-144-02 ($33.27 Amazon)[/sup]

[sup]The key with these is that they incorporate an analog input to trigger the pre-programmed vacation mode setting. This will allow me to have a normal operating temperature set up which will raise the temperature a day before arrival, and the vacation mode will utilize the heat pump to keep the place at a minimum temperature with better efficiency. The outdoor sensor is used to cut out the heat pump below 15F and revert to using the hydronic system / boiler to provide minimum heat.[/sup]

[sup]I will be able to trigger all of the thermostats into vacation mode using a single Elk M1 output / relay or if I would like to be able to move certain zones in/out of vacation mode I can use multiple outputs and groups.[/sup]

[sup]I did not come across any way to get full temperature monitoring and control of the temperature through the Elk. This was the next best thing that I could find and the Aube thermostats seem pretty capable.[/sup]

 

[beaumeri]

I'll be starting up my radiant "Hydronic" floor heating shortly (2" concrete with water pipes in it) and the vendor supplied my with Aube TH135-01-B with is pretty much the same as the TH140 you are looking at without the programming part. When I asked my vendor about the programming part he told not to worry about this as hydronic flood takes long time to rise in temperature and to cool down so daily adjustment would not really do any good or save energy.

I'll be looking at the TH-144 for my heatpump / AC as I have not selected any thermostat yet for it (I'm running a basic one put in place by the installer).

I like you idea and will be looking to do the same thin using the vacation mode.

 

[picta]

We have a zoned hydronic heating system with gypcrete layer and stone and wood flooring. It uses HAI Omnistats2000 to control each zone, and this was the main reason I went with HAI controller after using Elk for many years. The HAI thermostats have Energy Efficient Control that is adjustable for slow reacting systems like radiant, and also heat and cool anticipators. It takes a bit of adjustment for each room, but in the end the systems works great. The house had Aube thermostats before remodel, and IMO the HAI units are better (but that comes at a cost of course), but they did the job also. The problem was they were not communicating and when one of the floor sensors failed, there was no easy way to replace it.

 

[ReasonablePerson]

We have a zoned hydronic heating system with gypcrete layer and stone and wood flooring. It uses HAI Omnistats2000 to control each zone, and this was the main reason I went with HAI controller after using Elk for many years. The HAI thermostats have Energy Efficient Control that is adjustable for slow reacting systems like radiant, and also heat and cool anticipators. It takes a bit of adjustment for each room, but in the end the systems works great. The house had Aube thermostats before remodel, and IMO the HAI units are better (but that comes at a cost of course), but they did the job also. The problem was they were not communicating and when one of the floor sensors failed, there was no easy way to replace it.

Picta-when they put the sensor in the concrete or gypcrete, it is a good idea to put it in a piece of PEX tubing with a cap over the end to keep the concrete out. run the other end of the tube either up to the thermostat, down to the crawlspace or other accessible area. this way the sensor can be replaced.

 

[picta]

Picta-when they put the sensor in the concrete or gypcrete, it is a good idea to put it in a piece of PEX tubing with a cap over the end to keep the concrete out. run the other end of the tube either up to the thermostat, down to the crawlspace or other accessible area. this way the sensor can be replaced.

Sounds good to me. Unfortunately we did not have a say on that as it was installed by the previous owner.

 

[mikei-ma]

Couldn't you use a PID controller with RS-485 / Serial control? watlow makes a version of their pid with a rs485 connection like those that most of us use in our our espresso machines. It intimately monitors rate of rise in the espresso boiler, I can't imagine it would be that different to monitor slab temperature.

Here's a link to the Watlow Series 96 user guide, it looks like it just might be the right solution. I found this link to a scratch/dent list from pidkits.com that mentions rs-485 and serial models for a less expensive option to ordering new.

Mike