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

Nominal capacity in Heating Coil

asked 2016-09-16 04:19:51 -0600

Vmoreno's avatar

I input nominal capacity in a water heating coil definition of a AHU. I input Rated inlet/outlet water temperature and Rated inlet/outlet air temperature, too.

In a AHU sizing i input the Design supply air flow rate.

The results show that nominal capacity of the water heating coil is greater than nominal capacity specified.

Why does this happen?

How can i to fix the nominal capacity of the water heating coil?

edit retag flag offensive close merge delete


Did you set the Performance Input Method to Nominal Capacity?

Adam Hilton's avatar Adam Hilton  ( 2016-09-16 09:32:48 -0600 )edit

Yes, you are right.

Vmoreno's avatar Vmoreno  ( 2016-09-16 13:32:22 -0600 )edit

1 Answer

Sort by ยป oldest newest most voted

answered 2016-09-19 16:42:47 -0600

Hi @Vmoreno, if you have entered a nominal capacity (aka "hard-sized" the coil), then EnergyPlus will use that value. If you enter "Autosize", then you are asking EnergyPlus to calculate the EXACT capacity that's required on the heating design day using the rated conditions you set. In the HVAC Sizing Summary table report, the "Calculated" values are what EnergyPlus is autosizing, and the "User-Defined" values are what you have entered.

It sounds like you have a case where the auto-sized capacity is greater than the hard-sized capacity you entered. There can be a number of reasons why this could happen, such as different design day conditions, rated coil inlet / outlet conditions, etc. If there's a large difference, you should re-examine how you calculated your nominal capacity.

edit flag offensive delete link more


Thanks by your reply. If I input the coil heating capacity, I don't known why E+ doesn't use that value. This is the problem.

Vmoreno's avatar Vmoreno  ( 2016-09-20 13:45:34 -0600 )edit

Hi @Vmoreno, EnergyPlus does use the heating coil capacity you enter. It's just providing you a warning that the heating coil capacity it calculates is a different value from what you enter. This is also true for any other input field that can be autosized in EnergyPlus.

Aaron Boranian's avatar Aaron Boranian  ( 2016-09-20 14:44:27 -0600 )edit

If I see the simulation results, the heating coil heating rate (w) shows that it value is greater than nominal capacity specified.

A colleague advise me that this issue is been studied:

Vmoreno's avatar Vmoreno  ( 2016-09-20 15:46:13 -0600 )edit

Your Answer

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

Add Answer

Question Tools

1 follower


Asked: 2016-09-16 04:19:51 -0600

Seen: 679 times

Last updated: Sep 19 '16