Re: [EnergyPlus_Support] Unexpected difference between 'Total Cooling Rate' (hourly) and rated cooling capacity

[Bereket Nigusse <nigusse_ba@xxxxxxxxx>]

Hi Neal,

Possible reasons for the differences:

 

(1) cooling coils delivered capacities can be greater than the design value when coils are run at condenser entering air dry bulb temperature less than the rated condition (tdb < 35.0) and when there is such a high zones cooling load. Check if the internal heat gains and outdoor air amount during the maximum coil output hour and the design day peak hour values are different. Zones with large glazing on south facades may experience higher solar heat gain on days other than the design day depending on location. 

    

(2) keep in mind that the gross total cooling capacity already includes the cooling sizing factor but not the fan heat effect. So, the ratio shouldn't be the same as the sizing factor.  Based on your assumption it should have been 1.0.

So, it is possible for this ratio to be greater than 1.0 but has no direct correlation to the sizing factor. I would look at the condenser entering air temperature and the zones load at the maximum cooling coil output hour and compare them with that of the design day peak hour values. 

  

Hope this helps,

Bereket

On Tuesday, January 28, 2014 5:02 PM, "Humphrey, Neal" <neal.humphrey@xxxxxxxx> wrote:

 

Hi,

 

Iâ??ve simulated the â??Small Hotelâ?? reference building, where Iâ??ve converted the HVAC system to air source heat pumps (using the templates for PTHP and UnitaryHeatPump as appropriate). Iâ??ve used autosizing for the coil capacities and airflow within the template. Iâ??m trying to extract the system sizing to get a comparison of energy use per ton, as well as view the hourly loads to compare to a GSHP model. However, the outputs for the cooling/heating coil sizing and the hourly loads are further apart than I expected.

 

Iâ??m comparing the maximum value of the â??COOLING COIL:Cooling Coil Total Cooling Rate [W](Hourly)â??  from my variable output for each coil to the Coil:Cooling:DX:SingleSpeed â??Rated Total Cooling Capacity (gross) [W].â?? I would expect the ratio of these to be about the same as the sizing factor (1.2) but they instead range from 1.5 to 1.8.

 

I used the 99.6% and 0.4% design days from the .ddy file, which does correspond to the hottest/coldest day. Would the rest of this difference simply come from the difference between actual and design schedule for internal gains (ppl, lighting, etc.)? Or am I misunderstanding these two variables?

 

Thanks,

Neal

__._,_.___

Primary EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx

The primary EnergyPlus web site is found at:
http://www.energyplus.gov

The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/

Attachments are currently allowed but be mindful that not everyone has a high speed connection.  Limit attachments to small files.

EnergyPlus Documentation is searchable.  Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.

Your email settings: Individual Email|Traditional
Change settings via the Web (Yahoo! ID required)
Change settings via email: Switch delivery to Daily Digest | Switch to Fully Featured
Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe

__,_._,___