Is a manual J calculation expected to overpredict heating load?

asked 2022-08-22 21:14:22 -0600

janken's avatar

updated 2022-08-25 12:01:18 -0600


Background: I am trying to model the heating and cooling loads for my future home using EnergyPlus. My hope is to investigate different building construction methods and window options that allow us to build a pretty-good house. In short, a house that is well-insulated, but also affordable. The climate zone is 5A.

Approach: I am an EnergyPlus beginner, so I wanted to verify or benchmark my results using a CoolCalc Manual J prediction of heating and cooling loads. I tried to match the size and construction in the two approaches as closely as possible.

Problem: My EnergyPlus model matches the cooling loads of CoolCalc pretty closely (11124 BTU/h from eplus versus 13189 BTU/h from CoolCalc), but the heating loads do not match: eplus predicts 12905 BTU/h versus CoolCalc's 23890 BTU/h.

Question: Is the Manual J prediction expected to overpredict by this much, or should I keep looking for an error in my IDF file?

Any pointers would be appreciated, thank you!

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