Question-and-Answer Resource for the Building Energy Modeling Community
Get started with the Help page
Ask Your Question

Questions related to the cooling load calculations and selecting the right equipment size.

asked 2023-09-16 19:15:08 -0500

awadhi's avatar

updated 2023-09-18 09:21:08 -0500

1- How does the BEopt determine the AC tonnage size ? Does it follow manual J and select the 99% design load? If so, what about the solar heat gain. Does it use the highest solar heat gain day throughout the year or it uses the solar heat gain at the 99% design day ?

2- In case it uses the 99% design load, let's say for example it is 4 ton. Is the 4 ton capacity rated at outdoor temperature 95F ? Meaning that at higher ambient temperatures the unit will deliver less cooling capacity ?

3- What curve is being used in BEopt to account for the unit performance degradation? Is it similar to the NREL curve published in 2013 "Improved Modeling of Residential Air Conditioners and Heat Pumps for Energy Calculations".

4- Can I track the unit cooling capacity every hour ?

5- What is the indoor wet-bulb temperature when we change the indoor setpoint (e.g., 70F, 71F, ...). And if it is changing, are we able to monitor the indoor wet-bulb temperature ?

edit retag flag offensive close merge delete

1 Answer

Sort by ยป oldest newest most voted

answered 2023-09-19 09:36:25 -0500

  1. Yes, it follows ACCA Manual J/S using the 1%/99% design temperatures. Corresponding design loads, broken out by component (windows, walls, ducts) can be viewed in the End Use graph. I'm not sure I understand your question about solar heat gain, it follows the ACCA methodology (which is not using the highest solar of the year nor the value from a specific design day).

  2. Correct. The reported capacity is the nominal/rated capacity and the AC will have reduced output capacity at higher temperatures.

  3. Yes, it uses those curves for 1-speed and 2-speed systems.

  4. If you request timeseries output, you can see the cooling energy delivered for every timestep.

  5. BEopt v3 does not report the indoor wetbulb temperature. You'll have to take the EnergyPlus input file, add a request for that output variable, and re-run it directly in EnergyPlus.

edit flag offensive delete link more

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Training Workshops


Question Tools


Asked: 2023-09-16 19:15:08 -0500

Seen: 84 times

Last updated: Sep 19 '23