I'll be pairing a Nordic Geothermal EMW-55 GSHP unit to radiant floor heating in our new home. The basement will be radiant heat in the concrete slab while the main and upper floors are Warmboard. We're planning on a thermostat per floor controlling the flow for each floor. We will only use the system for heating. The house won't have forced air which means no cooling.

The builder is recommending the Honeywell Pro 1000 thermostat while the Nordic GSHP manufacturer says they like the Honeywell Pro 5000; perhaps more for forced air installs with both heating and cooling? What would you recommend for a thermostat on each level?

Thanks in advance,
Guy

keep in mind that the geounits should condition a buffer tank for a water to water application, and the buffer tank thermostat is the one turning on and off the geounit. The only thing your house thermostat does is turning on he circulation pumps. Both are fairly simple thermostats, may be the one for the house should have a outdoor reset....

Hey doc,

nice looking website you have there. I really like your WEL graphics.

Dean, Thanks for the pad on the back!

The response times between Warmboard and slabs are HUGELY different. Either the 1000 or 5000 would work fine with Warmboard, but something with a PID algorithm like the Tekmar 5xx series would be necessary to anticipate the delays due to thermal mass inherent in the slab would be better. With non-integrating standard T-stats running a slab there will be times when the room temp won't be very stable, both under & overshooting the setpoint temps. Warmboard doesn't have this issue- since it isn't working against a significant thermal mass, it's response time is the same order of magnitude as standard types of hydronic radiation, and under/overshoots will will be pretty much limited to just the hysteresis designed into the Honeywells.

PID (proportional-integral-differential) works by anticipating when to turn on/off the heat into the slab based on how far the room temp is above or below the setpoint, and how fast it's falling/rising over time to provide stable room temps. Standard T-stats just turn on at some low temp, turn off at a higher temp within a hysteresis band around the setpoint. Some have a small amount of fixed or even programmable anticipation, but that isn't sufficient to manage the thermal mass of a slab. Some PID thermostats have both air-temp & floor temp sensing to better refine it under rapidly varying load conditions, but in a below-grade basement that isn't likely to be necessary.

And what docjenser said about buffering the water, particularly for the Warmboard zones. The slab has enough thermal mass to keep the compressor from inefficiently short cycle times, but the Warmboard doesn't. A buffer tank will set a minimum compressor run time by both it's volume (=thermal mass) and temperature hysteresis, preventing short-cycling.

> may be the one for the house should have a outdoor reset...

If you are using a buffer tank, I believe that the temperature reset should be on the buffer tank thermostat. No sense in taking the efficiency hit of heating the buffer tank all the way to max temp if it is not very cold outside.

PID control is very old and somewhat outdated technology - I recall replacing code for it in the early 80s. Better controls learn from previous experience and immediately move to the correct control point.

Posted By jonr on 21 May 2010 10:02 AM
> may be the one for the house should have a outdoor reset...

If you are using a buffer tank, I believe that the temperature reset should be on the buffer tank thermostat. No sense in taking the efficiency hit of heating the buffer tank all the way to max temp if it is not very cold outside.

PID control is very old and somewhat outdated technology - I recall replacing code for it in the early 80s. Better controls learn from previous experience and immediately move to the correct control point.

"Smart" PIDs work by tweaking the coefficients as they "learn" the system, but it's still proportional-integral-derivative at it's core. (I'm not sure how smart the Tekmars are, but they're a lot better than non-anticipating systems when dealing with the long time constants of large thermal masses.)  The thermostat can't know apriori what the thermal mass is, or the BTU output of the boiler or the heat loss of the building- I wouldn't be surprise if the Tekmars are adaptive.

And I'm pretty sure standard t-stats are NOT adaptive.

two things to think about;
As to the thermostat choice PID is a great feature for all applications since it learns to adapt to conditions in the home. You will however want to consider how you change over from heating to cooling, most manufactures do not provide remote changeover when using a water to water. I say this because the geo unit is only looking at the buffer tank in a simple application with out any outdoor reset controller.
so to integrate a zone control application and if you are using it for cooling also then you have a challenge, to allow for the standard operation we are acccustomed to using, the mode button the thermostat which we use to change from heating to cooling.
Tekmar makes controls that have been usefull in doing this. You may need to use a thermostat that has seperate B and O terminals on it and Honeywell does not provide this on most of its thermostats, you would need these terminals to tell the system that you selected heating or cooling mode. WaterFurnace makes a hydro controller that has outdoor reset and auto changeover along with outdoor disable feature.
For the slab area(s) I would recommend using a Teckmar #509 stat which alllows for a minimum slab temperature and room sensing for temperature adjusment in the room or zone. The slab sensor is great because it allows you keep the slab at a minimum temp which is set at what you choose and this will also provide a quicker response for a heat call and it keeps the bare floor areas temperate or warm depending on your preference.
2. As to the buffer tank, warmboard or a mass like concrete you will want to select a buffer tank, ( believe most manifacurers suggest this) especially if you are spliting up the radiant project into zones. The buffer tanks purpose is to allow the geothermal unit to have longer run times. in a small zone call for heat, the geo units output is way more than what that small zone needs, using a buffer tank the zone calling for heat it takes the stored energy from the tank and when that heat is diminished then the geo unit heats the mass of water back up. This way the zone gets what it needs and the geo unit cycles are where they need to be.