Hi there,
I'm trying to explore how does Energyplpus-based software tools, like BEopt, Designbuilder,etc calculate the heating load. For example, if the outdoor temperature is 20°C， does Energyplus use the outdoor temperature and the properties of building envelopes to predict the indoor temperature, and then use this temperature difference to calculate the heating load? Or it just set the indoor setpoint like 25°C, and for whatever the outdoor temperature is, it uses the temperature difference between outdoor temperature and the indoor setpoint to calculate the heating load and heat loss? Any helpful suggestions is greatly appreciated.
Hi Lu,
Energyplus has inbuilt equations and algorithms like TARP. It considers occupants behaviour, glazing material, internal and external gain, local climate, etc. The accuracy of your output depends solely on your input.
So the answer to your question is Energyplus does not calculate the heating/cooling load of a building by simply considering the room and ambient temperature. It considers the above mentioned factors and it runs the chosen algorithm based on your input.
Dear Lu,
There is other form documentation of Energy Plus there : https://bigladdersoftware.com/epx/docs/8-8/engineering-reference/
(if web interface is more preferable...)
There is more details provided how it calculates the heat flows thru building envelope with finite difference method and how the ground contact related losses is handled with existing algorithms and additional plugins.
From my own experience - heat flow obtained from software is not so often equal to steady-state solution [q=U*A*(T_int-T_out)] due to solar radiation, thermal mass effects on both sides of the envelope surfaces and radiant heat transfer (in cooling season periods) when the temperature difference is relatively low.
Do not know how it is important for you, but keep in mind that local thermal effects like thermal bridges is not included unless you add additional transmittance to overall U value.
Work on EnergyPlus began by modularizing (restructuring) code from the heat balance engine in IBLAST, a research version of BLAST with integrated loads and HVAC calculation (Taylor et al. 1990, 1991). Normally such restructuring would result in major rewrites involving a long development period and very extensive testing to ensure the new code performs as intended. To avoid this problem, we devised a process we call ‘Evolutionary Reengineering (ER)’ that incrementally moves the program from old unstructured legacy code to new modular code by incorporating new code with old. Throughout the process, existing code still works with user input data and is extended to generate parameters needed by the new code modules. In this way the new modules can be verified without having to completely replace the entire functional capability of the old program with new code before it can be tested. As the process proceeds, old routines are replaced by new routines and data structures. This makes the transition evolutionary and permits a smooth transition with a greater capability for verification testing.
The new eddition energy plus you should consider bondray condition for simulation
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