[EnergyPlus_Support] Re: ZoneHVAC:LowTemperatureRadiant:VariableFlow

["luke_dorna" <luke.dorna@xxxxxxxxx>]

You might want to look into using the room air model three node displacement ventilation in the radiant case. Because energyplus defaults to well mixed, these radiant systems may be trying to condition the entirety of the zone, not just the occupied stratification. 

What's glazing configuration? I once had a radiant system in a room with a lot of glazing, and the sun would actually raise the temperature of the radiant slab, causing it to play catch up when cooling mode kicked on. 

Which radiant system, the ceiling or floor, is the priority for cooling mode? It could be by that modeling two floors as a single zone only one system is trying to condition the space and the interior partition is keeping the radiant cooling from getting to the other space. It thinks the set point is not met, so it keeps pumping in energy. 

Keep us posted. 


--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "aleagerman22" <agerman@...> wrote:
>
> I have a 2-story single zone residential home which I'm modeling with
> two distinct HVAC systems. One is a forced air system using a single
> speed heat pump with ductwork in conditioned space (no losses accounted
> for). The other is a hydronic system which uses radiant floor on the
> first floor and radiant ceiling on the second to distribute both heating
> and cooling. The distribution system is tied to a water-to-water heat
> pump and a ground loop. All other envelope characteristics are
> identical.
> Operating efficiency of they hydronic system in both heating and cooling
> is 1.5-1.75 higher than the forced air HP. Provided this increase in
> system efficiency along with similar distribution efficiency I would
> expect to see significant savings for the hydronic system. However, I
> end up with similar heating energy and 35% higher cooling energy for the
> hydronic case. Cooling energy delivered to the space is 2.5x greater for
> the hydronic case (both systems have the same capacity). I calculated
> this difference in delivered energy from the "HVAC Input Sensible Air
> Cooling" for the FAU and "HVAC Input Cooled Surface Cooling" for the
> hydronic case, is this correct?
> It seems to me that the radiant distribution delivery to the zone isn't
> performing correctly. During a heating or cooling event the two systems
> are turning on at similar times and have similar runtimes but the
> hydronic system apparently delivers a lot more energy to satisfy the
> load at a higher energy cost (based on the COPs input). I tried 1)
> making the model 2 zones and 2) eliminating the radiant ceiling and
> doubling the heat transfer area of the floor. Neither of which helped.
> Does anyone have any advice?
>




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