Posted By sailawayrb on 05 Nov 2014 09:55 AM
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.

Unfortunately I'm not very program literate when it comes to the Omni.. Of course now, with it being warming outside the house is now 75 without heat on.. so its hard to figure out what is working and what isn't.

Posted By jonr on 05 Nov 2014 11:27 PM
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).

Thanks, I will try and figure out how to program to have a second stage on thermostat activate secondary loop pump.

Would adding the air handler for second stage heat be helpfull or hurt for the rest of the house(zones)?

Two things tom.

First, the den was designed for 1.2 GPM at 115 at 10 degree outdoor. Your flow and your water temp may not be to spec, both sound low by your report..

1- If you have a 15 degree delta T at 45 degree outdoor, you definitely need more flow. This room should have 10 degree drop only at design.

2- If you're falling short all the time that means the reset curve is set too low, period. How much too low depends on whether you get to the appropriate flow spec or not first.

Try to get the flow up over 1 GPM for the room, see where you are at, and then adjust the reset curve up as best you can.

This room does require higher water temps than the rest of the house: if you can bring your air handler in for stage two, you could keep the reset curve low and increase efficiency of the altherma all season, that's nice.

Sounds right, BOTH more flow rate and more heat... Really not all that that different from this other recently reported situation:

New to Radiant Heat, Have a Problem

Rob, just in case you weren’t aware, this person was also looking to make contact with you a couple weeks ago too:

Looking for Rob at NRT