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Convert Joule to Wh, when 'Reporting Frequency' is different from 'Hourly'

asked 4 years ago

rainbow's avatar

updated 4 years ago

I'm running some simulations by asking EnergyPlus (through the IDF) to output Output:Meter,Electricity:HVAC (an output meter which measures the electric energy consumption in Joule).

If I choose an 'hourly' reporting frequency, like this:

Output:Meter,Electricity:HVAC,hourly; !- [J]

I guess that I can obtain Wh from J in this way:

Wh = J / 3600 s,

E.g.: 4 J ==> 0.11111 Wh

But, if I choose a reporting frequency equals to 'timestep', like this:

Output:Meter,Electricity:HVAC,timestep; !- [J]

where 'timestep' = 4 (so there are 4 timesteps per hour, hence I have 15-minutes timesteps):
how can I convert that value of energy measured in Joule (but "sampled" every 15-minutes) to a value measured in Wh?

Is it sufficient to divide it by a factor of 3600, and then divide it by 4 (n°timesteps per hour), to finally obtain an energy value expressed in Wh?

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answered 4 years ago

Your equation converting J to Wh is correct for the hourly output from EnergyPlus, which could be rewritten as

Whhourly=Jhourly1hr3600s

If you compare the timestep output to the hourly output, you will see that EnergyPlus is already accounting for less energy consumed each timestep. For example, if the hourly HVAC electricity use was 400J, using 4 timesteps per hour would give a timestep output of 100J (assuming constant HVAC consumption). Because of this, you should use the same equation above for converting the J timestep output from EnergyPlus into Wh.

Whtimestep=Jtimestep1hr3600s

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Ok, thanks for your clarity!

rainbow's avatar rainbow  ( 4 years ago )

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Asked: 4 years ago

Seen: 672 times

Last updated: Sep 19 '20