We're planning a 3600 sf, slab-on-grade, aging-in-place house in Minnesota, about as cold as St. Paul. It's very well insulated, tight, and includes exceptional windows. Energy modeling software (BEopt, so also Energyplus, on which it is based) consistently shows that energy use (Btu's; not cost, which would involve prices of fuels) is much higher for hydronic systems than for forced-air. I'm not asking about installation cost , or COST of running the system, but how much ENERGY is used to run hydronic vs forced air in the same structure. Pump and fan energy is also separated out by the software, so this is not what I'm writing about.
What I have consistently heard is that energy use in hydronic systems is always less than with forced air for the same building, but this software is saying the opposite. It reports this result regardless of efficiency of gas or electric boiler. Using a modulating 150-degree gas boiler is much better than others supplying 180 degree water, but even that still uses much more energy than just about any forced-air system. BEopt doesn't allow for true low temperature supply with hydronic, so that's also not part of this comparison. It's modeling baseboard hydronic.
Eventually I'm hoping to also compare ground source, low temperature radiant with other possibilities. Before that, however, it seems to me that I need to consider whether something is wrong in what I'm seeing in this result: hydronic consistently taking more energy to run than forced air.
Energyplus, and therefore BEopt, have been validated with quite a number of real world buildings, so it's unlikely that the software is completely off-base in what it is reporting. In the other choices that BEopt offers, it generally seems to be quite accurate when I add energy-saving features to the models I have constructed. Sadly, it also very accurately estimates the foolish, high energy use of the home which we unfortunately occupy now!
So what I'm asking is: can it be true, disregarding COST of fuel, that energy use by a hydronic system exceeds that of forced-air (after pump and fan energy use is factored out) in the same building?!
Thanks for any observations on the subject!