Guys, This is now my second or 3rd heating season with retrofit 3/8 Roth panel over concrete.

I'm in a 1800sq ft 1 floor ranch house on concrete slab

I still have trouble with my Den holding a 68Degree over night, not even coming close to design temp.(@45degree)

Design temp: 9
Room BTU: 5968


Floor is Roth over concrete slab, 1/4" hardboard with a radiant approved padding/carpet over the cardboard. (Less the 1R)

This morning with an outside temp of 45degree, thermostat set at 68, room is @ 66. I have my flowrate currently set at .8GPM for this room.

This morning, (I have flir gun) I show 83degree water temp into the manifold feeding the room, and a 75degree return temp.

I have a DIY'd Daikin Altherma (Full setup with DWH & Solar assist)

System has a built in outdoor-reset and I have tried setting different temps/outside to increase water temp, & also bypassing out-door reset mode and running straight 110degree water with no change.

Im on a warm Roof design with 10" open cell, with closed cell sealing soffit areas. I have 2"rigid foam around all walls, and last summer I dug up around house and added insulation in ground to footings.

I can't fund any air leaks or issues (using my flir). My Heat load calc must be wrong, but even by increasing my GPM or Water temp does not seem to help keep room @ temp during colder nights.

House is zoned into 3 radiant zones. (Only Den zone seems to have issues) Den is 40% windows, added different curtains this year to try and mitigate window's heat loss.. Still same as last year.

I just noticed that my full heat design was 21k BTU/HR, and the Altherma outdoor unit may be the 18 model (Heating Capacity 19,620 Btu/h)

I would say I was undersized.. but if on Den Zone is calling, the Altherma should have plenty of capacity to heat the one zone..

Idea's/Suggestions?? Much appreciated in advance!

If you changed your SWT from 85° to 100°F without effect, we all have a serious problem. Say your prayers.

Consider:

the usual btu/sq ft calculations based on temp and floor coverings
your flow rate/temp delta is only delivering 3200 btu
the slab will absorb a lot of heat until it eventually warms up

Use 110F water and more gpm and wait a few days.

It is a shame that most btu calculations don't consider thermal mass and temp variation effects. High mass radiators are sluggish.

The only thing I can get is that there is more heat loss in den then the Roth can produce with 3/8 Pex. Or no matter what temp/GPM combo for underloor, the floor itself absorbs a certain amount of heat, more then I can dump into room?

I have the following set on the Altherma

Weather Dependent set point
00:Low Abmient Temp:8.6
01:High Ambient Temp:66.2
02:Set point at low ambient temp:105.8
03:Set point at high ambient temp:77

Posted By jonr on 03 Nov 2014 10:25 AM
Consider:

the usual btu/sq ft calculations based on temp and floor coverings
your flow rate/temp delta is only delivering 3200 btu
the slab will absorb a lot of heat until it eventually warms up

Use 110F water and more gpm and wait a few days.

I was following an article I found:
http://www.taco-hvac.com/images/phc08_simplefacts.pdf

Should I still us the outdoor reset, or use straight 110degree water, then set the Den zone to aprox 1.6GPM (since you quote 3200btu/hr with delta t of 23degree with .8gpm) Can you provide formula? I'd like to understand the why's.

I actually had flow set to 1.6gpm as of yesterday, but changed to .8 when I read that article I referenced above. This was a reoccurring issues from last winter, wanted to start fresh for this season.

Posted By jonr on 03 Nov 2014 10:25 AM
It is a shame that most btu calculations don't consider thermal mass and temp variation effects.

The Roth panel is an insulated 1/2 panel, retrofit over slab. 2/3 of house, in same config/slab does not have same loss issues, and in fact I have another zone that has very similar heat loss (per heat load calc) without the same issue.

Concrete slab is not insulated below. How would I go about calculating the addition of the un-insulated slab below?

83F supply with only a 8F circuit temp drop would normally provide plenty of upward heat flux for a well-insulated slab and home. You must have unusually high downward slab heat loss and/or high room heat loss. Do you know the total R-value below the PEX? Do you know the total R-value above the PEX (e.g., are you covering it with carpets, hardwood floor, furniture or other insulation)? You will likely need to significantly increase the supply temp to overcome the deficient design. Who did the design and what guidance did they provide you?

Heat always goes somewhere - it doesn't just disappear. What are the floor surface temps in the different rooms? I'll have more thoughts once you report on what happens after 3 days @ 110F and a higher flow.

Posted By sailawayrb on 03 Nov 2014 12:42 PM
83F supply with only a 8F circuit temp drop would normally provide plenty of upward heat flux for a well-insulated slab and home. You must have unusually high downward slab heat loss and/or high room heat loss. Do you know the total R-value below the PEX? Do you know the total R-value above the PEX (e.g., are you covering it with carpets, hardwood floor, furniture or other insulation)? You will likely need to significantly increase the supply temp to overcome the deficient design. Who did the design and what guidance did they provide you?

Un-insulated slab. The only insulation is the Roth itself. I did insulate the exterior foundation wall (rancher / no basement) this year with 2" rigid foam to try and add a bit of insulation.

I believe I have only about 1r of floor covering, (1/4" hardboard, + low R/radiant approved carpet)

How can I calculate what my uninstalled slab is absorbing, to try and compensate for it?

I actually worked with Rob/NRT, but now that business dissolved, and him at rockport, understandably I don't get the help I need/request now.

Is the den on a corner of the house?

You're probably losing at least half the heat going into the slab and out the bottom and that doesn't leave much to heat the room and then you have board and carpet on top.

Do you know the total R-value below the PEX?

It's 3/4" 90 PSI polystyrene with 3/8" PEX embedded, so there is all of 3/8" of foam under the tubing. That's maybe R-2 to R-3 and then the slab, so you can be sure the slab is getting plenty warm

I suggest that carpet + pad + air film is likely to be > R2.2.

I believe ICF has it right. Having more R-value above the PEX than below, is causing you to heat the slab/ground perhaps more than the room (i.e., 40-60% downward heat loss). Normally, one designs a HR emitter so it doesn’t produce more than 5-10% downward heat loss. I also suspect that the large percentage of window area you mentioned could also mean that the room heat loss was under-estimated as well. So I suspect this combination is causing your problem. Increasing the supply temp will eventually result in the room getting warmer, but you will be wasting a lot of heat given this HR emitter design.

Posted By sailawayrb on 04 Nov 2014 03:28 PM
I believe ICF has it right. Having more R-value above the PEX than below, is causing you to heat the slab/ground perhaps more than the room (i.e., 40-60% downward heat loss). Normally, one designs a HR emitter so it doesn’t produce more than 5-10% downward heat loss. I also suspect that the large percentage of window area you mentioned could also mean that the room heat loss was under-estimated as well. So I suspect this combination is causing your problem. Increasing the supply temp will eventually result in the room getting warmer, but you will be wasting a lot of heat given this HR emitter design.

Much appreciated, This makes sense now, if the R value below is less the above, heat goes to path of least resistance. So now instead of having a fast reaction mass, I have a slow reaction thermal mass, as it heats the slab for den. At least I have an answer as to why. The rest of house is ROTH with engineered floating hardwood floor.

I have an Air/water heat coil, would introducing the Air handler help satisfy the Den demand (As perhaps a second stage) for the slow reaction roth/slab?

It will help. If you have specs for it, you can calculate how much.

"You're probably losing at least half the heat going into the slab and out the bottom and that doesn't leave much to heat the room and then you have board and carpet on top. "

This is physically impossible unless you have high ground water.

Outdoor reset can be adjusted to account for nearly any thermal mass common in residential construction. We have many commercial properties, and snow melting systems without the benefit of any insulation. Sometimes it is not cost effective. Once the ground is charged the steady state heat load is quite predictable and surprisingly modest on larger structures with relatively low indoor design temperature e.g. parking garages and warehouses.

The shoulder months are the worst for HVAC control. I don't care where you are.

I think you are missing ICF's point Badger. The slab and the soil are acting as a huge heat sink given the relatively low heating BTUs being applied to this HR emitter. It's not really appropriate to compare a dumb HR snow melting system where your only goal is to get slab surface temp above 32F to a residential or commercial HR floor heating system. It is true that if you increase the heating BTUs and/or continue heating long enough, you will eventually be able to get the temp high enough to actually heat the room. However, this residential HR floor heating system will be very challenging to control, it will waste much heat, and it will cost way more than it should to operate.  What is really sad here is that the current heating BTUs being applied would have likely been more than adequate if the HR emitter design was done properly.

Posted By jonr on 04 Nov 2014 05:35 PM
It will help. If you have specs for it, you can calculate how much.

Air handler is controlled by an "ECM Modulator" http://www.fanhandler.com/ - Regulates fan speed by coil output temp and duct pressure.

Daikin P/N# EFWT024AEVLU

By part number, its a 2 ton BTU @ 800CFM. - ECM Modulator is modifiable to output temp/duct pressure. I believe I'm currently set about .7WC for cooling when all zones calling. (I have a magnehelic plumbed to plenum)

Posted By BadgerBoilerMN on 04 Nov 2014 06:50 PM
The shoulder months are the worst for HVAC control. I don't care where you are.

Came home this evening to all Den windows open and temp @ 75degree.I have a small house and its zoned (Heat & cool) into the 3 main areas. 1:Bedrooms,2:kitchen/dining/sitting, 3:Den,


Something else that I should bring up is I have a "smart" thermostat - Omnistat2 rc-2000. This ties to a home automation controller. These thermostat's have settings for ECC & Anticipator controls. I have played with this in past with a slight understanding of how they work.

Would adding a modulating Grundfos pump (alpha) help with even out with my heating demand?



I also added some pictures of my DIY install. (I have East/West solar heat for solar assist for DHW & 4.7km Solar PV)

What did you do to finally get adequate heating, increase the supply temp, just wait a couple days, or both? Where are the pictures?

Posted By sailawayrb on 05 Nov 2014 08:20 AM
What did you do to finally get adequate heating, increase the supply temp, just wait a couple days, or both? Where are the pictures?

I didn't get adequate heating.. it got to 65degree yesterday.. with Thermostats set at 70.. it was 75 @ 7pm when I got home.

Currently have the Daikin set to outdoor reset values to modulate water temp. I think the system had way overshoot... (Its 74 this morning, with outdoor temp of 55). First time it goes below 45 again over night, I'm sure I'll have trouble meeting demand again. Perhaps I should start with another Heat load calc for den.

Links show up in IE, but not chrome.. so here is outside links

http://www.bitteroldsoul.com/pictures/house/daikin1.jpg
http://www.bitteroldsoul.com/pictures/house/daikin2.jpg
http://www.bitteroldsoul.com/pictures/house/daikin3.jpg


Keep in mind, I'm complete DIY'er.. hence why I still haven't finished insulating pipes..

Well first off, we love DIYers…checkout the DIY software and info on our website sometime!

Yes, you will be challenged to control this HR emitter. Outdoor reset is better than nothing, but it won’t provide the magnitude of anticipation necessary to adequately control and maintain the desired indoor temp, especially if you have significant and variable solar heat gain. You will need a controller that uses the slab temp and that has more anticipation feedback than outdoor temp. In short, given the long lag time associated with changing the slab temp, you can’t wait until the outdoor temp actually moves before you start modulating the heat to the slab.

I suppose the good news here is that you have an Omni automation system. The Omni can be hooked to the internet allowing you to parse the outdoor temp forecast. If you are fluent with basic control theory (e.g., PID) and with coding Omni macros, you should be able to build a control algorithm that will accomplish the job. We use Programable Logic Controllers (PLCs) in this capacity for our integrated passive solar and HR heating system designs.  However, you will still be wasting a lot of heat. So in the end, you might want to consider just getting more insulation under the HR emitter to better isolate it from the uninsulated slab.

I calculate up to ~4500 btu from your air handler with a 85F supply temp. That's going to heat your den much better/faster than 3200 btu with much of it going downward (until it warms up).