Predicted loads vs. timestep

asked 2016-08-29 11:28:05 -0500

Rohini
683 ●2 ●9

updated 2016-10-18 14:25:52 -0500

__AmirRoth__

4436 ●5 ●17 http://bleedinggreenna...

I am looking at zone predicted sensible and moisture loads. When looking at the output I get the following results. I would have expected them to be similar. Am I missing some conversion constant? a) Predicted Sensible Load [W] (Monthly) 10 minute timestep run - 5596 1 minute timestep run - 21020 b) Predicted Moisture Load [kgWater/s] (Monthly) 10 minute timestep run - -0.036 1 minute timestep run - -0.20551

answered 2016-08-29 11:41:03 -0500

Archmage

7185 ●3 ●11

updated 2016-08-29 13:01:17 -0500

This sort of thing will happen if you have thermostat (and humidistat) schedules that have setup/setback or internal gains with "top hat" schedules that create an abrupt changes in zone loads. The HVAC system will attempt to recover from a change in loads over just one timestep, which takes more power for a shorter timestep. Such an experiment would need to use constant thermostat schedules and gradually ramping changes in internal gains.

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I do not have setbacks. Also, these runs have a unitary system.

Rohini ( 2016-08-29 11:45:38 -0500 )edit

I changed all schedules to not have variations. The issue still exists. The only other thing I havn't done is change the system to ideal loads system. Not sure if that makes a difference.

Rohini ( 2016-08-29 15:25:25 -0500 )edit

Also, these "predicted" load variables need to be compared over shorter reporting periods, at the timestep or hourly frequency. Because these are directional (load to heating setpoint or load to cooling setpoint) there are strange carryovers if the system moves from heating to cooling and back again over the course of the reporting period (which is this case is monthly).