Re: [EnergyPlus_Support] Re: Tolerance and Unmet Hours

Qianmin

On Mon, Oct 17, 2011 at 12:14 AM, Jean marais <jeannieboef@xxxxxxxxx> wrote:

You may have understood this wrong.

If your Cooling Setpoint is 25 deg C, then your systems will try and achieve 25. When they fail to achieve 27 (I.e. 25 + tolerance) for any given time, that time will be binned to Time SetPoint Not Met.

This means (if you report with "timestep" interval instead of hourly the room temperature and the Time SetPoint Not Met you can check this) that each timestep that your system does not manage 27, the time will be recorded. The system is aiming for 25 and failing even 27.

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Qianmin Zhang <zqianmin@...> wrote:
>
> Dear All,
>
> I'm confused about the way energyplus count the unmet cooling/heating
> hours. The default tolerance for temperature is set to be 0.2C, and we
> increase it to 2C to reduce the unmet hours. I thought the unmet hours
> is calculated by using space temperature and setpoint temperature, so
> I report the zone mean air temperature to represent the space
> temperature and pot it with unmet hours.The cooling setpoint is 25
> during occupied, and 35 during unoccupied.2C tolerance for cooling
> should give us the up limited temperature of 27C during occupied time.
> From this graph, my system is able to keep the zone mean air
> temperature below 26C, lower than 27C, but E+ report the unmet cooling
> hours during this time. Did I use the wrong variable? If not zone mean
> air temperature, which variable should I report to examine the unmet
> hours?
>
> I don't think the temperature tolerance used to calculated unmet hours
> will matter the energy usage. But, when I run two simulations, one
> with tolerance of 1.1C and one with tolerance of 2C for cooling, their
> total energy usage is not the same number, and I didn't change any
> other input at all. The simulation with 2C tolerance gave me about 3
> KBtu/ft2 less energy consumption.
>
> I have another question about SizingPeriod:DesignDay. I'm using the
> weather file for Yuba City, and want to use the summer design day and
> winter design day at this location. But, in my file, both of these two
> day typs are for Sacramento, how could I get the summer design day and
> winter design day information for Yuba City, or from my weather file?
>
> Graph of mean air temperature with unmet cooling hours, weather file,
> and my idf file are attached. Thank you, and any help will be
> appreciated!
>
> Reagrds,
> Qianmin
>