solar thermal collector for zone reheat

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Dear all,

I've been trying to simulate a solar thermal system for reheat in EnergyPlus but encountered lots of problems.
The laboratory building requires 6 ach at all times and strict temp and RH control. The original arrangement has a gas boiler providing hot water at 80 degree c to reheat coils sitting in zones. As a result of high humidy level and reduced sensible load at night, the reheat energy shoots up horrendously, though reheat is also needed during day time. The idea is to have a large solar collector array to cover the roof space and a storage tank to store hot water for night use. The size of the collector and storage system needs to be optimised to match the hot water need. But to kick start, the solar collector is simulated as one whole piece (shading surface:detached, around 1000m2) and parametric data is taken from the E+ dataset. I have managed to get all the connections right by following the example file: a mixed heater's (no heating capacity storage tank) source side connected to the solar collector and use side to another mixed heater (auxiliary heater) and to the rest of the hot water plant. But after running it a few times, I've got very strange results. The solar collector's efficiency is extremely low, e.g. 0.00001 but outlet temperature goes up to 200 degree c (steam?). The storage tank remains unfortunately cold. I suspect the large solar collector I put in the model (around 1000m2) is only functioning as a parametrically standard one (2 to 3 m2) and the rest area is functioning as a bypass. I tried to put in a small collector, same size and parameters as that's specified in the example file, and found the output more sensible.
In addition to ways to correct my input to get sensible output, another question is in the case of such a system how should it be sized in terms of tank storage capacity and solar collector size and output temperature to better match the mostly night reheat need.
Any comments are appreciated.


WU Xuchao

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Joined: 2011-10-02
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