Dear Forum, Although I have had occasional problems with EnergyPlus giving a fatal error due to DX cooling coil sizing problems, most have been associated with autosized coils. I have a project now which uses 11 different rooftop units, all with DX cooling coils. Three of them are giving me fits (problems). So far, I have:
- disabled the coil below a specified outdoor temp (<= 65F) using an EMS script
- raised the airflow 20% (for improved flow/watt ratio)
- reduced the coil rated capacity by up to 50% (for improved flow/watt ratio)
- disabled the coil completely (availability = always OFF) The only strategy which works is to disable the coil - and that isn't a very good representation of actual performance :)
The current problem coil has these characteristics: - 11,400 cfm VAV fan with minimum flow fraction = 0.7 - 385 MBH / 113 kw rated capacity - single stage coil
The Fatal error looks like: * Severe * PsyRhoAirFnPbTdbW: RhoAir (Density of Air) is calculated <= 0 [-2.69960]. * ~~~ * pb =[98900.00], tdb=[-400.80], w=[9.9866244E-006]. * ~~~ * Routine=Unknown, Environment=STORE 291 - STURGIS (01-01:31-12), at Simulation time=05/16 01:40 - 01:50 * Fatal * Program terminates due to preceding condition.
Can you suggest ways to correct this? Thanks in advance. The rooftop unit uses a digital compressor, which unloads very flexibly. Perhaps I should make the coil multi-stage?
