Re: [EnergyPlus_Support] unable to reach set point temperatures in zones

["Jean Marais jeannieboef@xxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx>]

The thing to understand with radiant systems is that the energy is transfered to the air node via convection from the surface area. Even the radiative energy will go to other surfaces and only effect the zone air if it is convected into the air. So there are exactly 3 variables which effect the capacity of the system:

1) area of radiant surface (m2)

2) convection coefficient (calculated by e+, as per the default or model selected)

3) Temperature of the surface

Check these and make sure the active surface is not turning off due to high humidity.

The sizing routine effectively exchanges energy directly with the air such as to keep the setpoint at all times and is not subject to the same "lag" as the radiant system. Make sure your design day set point curve is a flat line and that all internal loads associated with it are also a flat line. This gives a nice steady state peak. Then use the sizing factors to "oversize" the system to get the pull down times to about 30 min for an air system like a fancoil. A radiant system is mainly bound by active area. It doesn't matter if you have a super big pump, and ice cold water. Oversizing is useless if you are area limited.

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Posted by: Jean Marais <jeannieboef@xxxxxxxxx>

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