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

Design Builder/Energy Plus simulation warnings and bad results

asked 2018-07-06 05:31:28 -0500

Fábio Batista's avatar

updated 2018-07-06 11:46:11 -0500

Hello everyone,

I am currently modeling a building using design builder (detailed HVAC). Broadly speaking, the HVAC system consists of a combination of FAHU's (100% outdoor air) and individual terminal FCU's (not ducted). The results concerning heating and cooling energy consumption are very high for the building (and climate) under analysis, particularly the cooling demand. I have already check all inputs and everything seems fine to me and in line with the existing project info. The simulation err file reports the following warnings:

1- * Warning * Part-load ratio cooling control failed in fan coil unit PISO2:BALANCESROOM FAN COIL UNIT * ~~~ * Bad part-load ratio limits * ~~~ * ..Part-load ratio set to 0 Environment=HOVIONE (01-01:31-12), at Simulation time=05/04 15:45 - 16:00

This warning is the one I believe is causing the cooling bad results. It occurs for all FCU's for many time steps of the year (3000-3500 times). For now the majority of the input data related to the FCU's is set to autosize since there is no project info/details yet. I have already checked the setpoints managers and tryied to impose different rated/nominal conditions but the warnings and the bad results are not solved. Any advice would be great.

2- * Warning * HeatExchanger:AirToAir:SensibleAndLatent "FAHU 01-C AHU HEAT RECOVERY DEVICE" * ~~~ * Average air volume flow rate is <50% or >130% of the nominal HX supply air volume flow rate. * ~~~ * Air volume flow rate ratio = 1.15. Environment=(...) (01-01:31-12), at Simulation time=01/01 00:00 - 00:30

This warnign pops up for all AHUs with heat recovery for 15-20 timesteps of the year (2 time steps/hour). These AHU's are 100% Fresh air units, therefore in design builder I turned heat recovery on, but not the recirculation. What do you think that may be causing this? May i ignore this warning?

3 - * Warning * Calculated design heating load for zone=(...) is zero. * ~~~ * Check Sizing:Zone and ZoneControl:Thermostat inputs.

This warning is reported for several zones but not for all. I have already checked temperature setpoints, which I have defined in the activities tab and everything seems fine. I am using simple HVAC data in detailed hvac. Do you think I should be using detailed hvac data option instead? May i ignore this warning? I also read on this forum the following:

"Verify that the people, light, equipment schedules are not 0 for the hours for the design runs." - which I have checked already.

Thank you all in advance.


edit retag flag offensive close merge delete

1 Answer

Sort by » oldest newest most voted

answered 2018-07-09 01:44:04 -0500

Dave's avatar

This is a difficult question to answer on a forum like this as there could be a range of reasons. Assuming you have a DesignBuilder licence I would suggest you raise a ticket on the DesignBuilder Support Desk who will review the model and identify the problem.

edit flag offensive delete link more



Thank you Dave! I will do it and then post their advice.

Fábio Batista's avatar Fábio Batista  ( 2018-07-09 02:58:16 -0500 )edit

Hello Fabio, did you ever get anywhere on this? I am modeling in Design Builder a DOAS with FCUs having variable speed fans, and am getting the exact same problem. I saw a related post on the Github developer site (FanCoil Capacity Control Issues #6208) that points to similar issues. Thanks!

TNZ Energy's avatar TNZ Energy  ( 2019-05-05 21:15:24 -0500 )edit

@TNZ Energy, Hi. Sorry but I can´t help you on this. I have modeled the DOAS+FCU system on many occasions and only once encountered this problem. As the project I was working on at that time was shortly after revised, I no longer had to model the DOAS + FCU system for that building, thus I actually never got anywhere on this issue. There is another post (here) adressing the same problem that may help you. Good Luck

Fábio Batista's avatar Fábio Batista  ( 2019-05-10 04:11:44 -0500 )edit

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

1 follower


Asked: 2018-07-06 05:31:28 -0500

Seen: 1,062 times

Last updated: Jul 09 '18