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Re: [EnergyPlus_Support] Question on run time fraction
The runtime fraction (RTF) is the fraction of time the compressor
operates during a time step. Your question below sounds like the same
thing to me "Does it represent the fraction of the time step
that cooling would be on, or is it the rate at which the compressor
cycles". And looking at the runtime fraction examples you gave, 0.1 is
only 10% runtime fraction or approximately 10% of the DX coil capacity,
this unit is over-sized for the load. Make your coil smaller so the RTF
is higher and near 0.9 at the design load..
brianjbaker66 wrote:
>
> We are interested in using Energy Plus to look at typical heating
> and cooling system runtime at different load conditions. The model
> comprises a single story residence with a constant volume
> residential forced air furnace (FURNACE: HEATCOOL), a DX cooling
> coil (COIL:DX:CoolingBypassFactorEmpirical), and an electric
> resistance heating coil (COIL:ELECTRIC:HEATING). We are modeling the
> system using a cycling fan schedule.
>
> To estimate compressor runtime over the simulation time step (one
> hour time step), it is appropriate to use the cooling coil runtime
> fraction? We have run simulations using different internal and
> ambient load profiles and the runtime fractions vary from 0.02, 0.06
> and 0.1. There is some confusion about what the runtime fraction
> actually represents. Does it represent the fraction of the time step
> that cooling would be on, or is it the rate at which the compressor
> cycles. Any feedback or advice would be appreciated. Thanks
>
> Brian Baker
>
>
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