Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
You're asking several different questions here, so I'll just address the ones on the differences between the loads reports in LOADS (LS-E, LS-F) and SYSTEMS (SS-A, SS-D), and how to find the fresh air load.
I do not recommend comparing the loads reports from LOADS to those from SYSTEMS because they're calculated very differently and serve very different purposes. The LOADS loads reports are tabulations of the heat flows into a space or building at the fixed reference LOADS temperature (Default is 70 F), with the heat flows assigned to heating or cooling depending on whether the aggregate loads that hour is positive (cooling) or negative (heating). The SYSTEMS loads reports give the heating or cooling input required for each hour into a zone to meet the specified set-point temperature. The differences are thus very striking: (1) the reference temperatures are quite different, (2) the LOADS loads has no deadband, (3) the attribution to heating and cooling are also very different, (3) LOADS loads can be disaggregated to building components, but SYSTEMS loads cannot because the SYSTEM simulation works only with loads at the space/zone level, and of course, (4) fresh air or any other load introduced by the SYSTEM simulation do not appear at all in the LOADS report. Therefore, trying to get a measure of the outside air load by comparing the SYSTEM to the LOADS reports is highly unreliable and can even be completely misleading.
However, there is a way to get the outside air load exactly, but it requires using the HOURLY-REPORT option in DOE-2 and then a little bit of postprocessing. In the HOURLY-REPORT specification, print out the Zone Temperature, Ventilation CFM, and Equipment Ontime for Heating and Cooling each hour. Then, you can calculate the Ventilation Air Load each hour as the temperature difference between the outside air and the zone times the CFM and the heat capacitance of air. I still remember that in IP as DeltaTxCFMx0.0128. If the Equipment is on, it would be obvious to attribute the Ventilation Air Load as either Heating or Cooling, but what to do if the Equipment is off? The best method I've found is to aggregate them as a cache and then assign them to whatever mode the Equipment next comes on. For example, if the building is off at night, the aggregate cache of Ventilation Air during those hours will be assigned as Heating Loads if that's the equipment that comes on next the next morning. You can think of that load as a morning pick-up load. If you throw away these ventilation air loads when the equipment is off, you will have underestimated their impact on the building load.
One last practical suggestion, you might also try the eQUEST-Users bulletin board because there seems to be a lot more eQUEST users participating there than here on Unmet Hours.
| | 2 | No.2 Revision |
You're asking several different questions here, so I'll just address the ones on the differences between the loads reports in LOADS (LS-E, LS-F) and SYSTEMS (SS-A, SS-D), and how to find the fresh air load.
I do not recommend comparing the loads reports from LOADS to those from SYSTEMS because they're calculated very differently and serve very different purposes. The LOADS loads reports are tabulations of the heat flows into a space or building at the fixed reference LOADS temperature (Default is 70 F), with the heat flows assigned to heating or cooling depending on whether the aggregate loads that hour is positive (cooling) or negative (heating). The SYSTEMS loads reports give the heating or cooling input required for each hour into a zone to meet the specified set-point temperature. The differences are thus very striking: (1) the reference temperatures are quite different, (2) the LOADS loads has have no deadband, (3) the attribution to heating and cooling are also very different, (3) (4) LOADS loads can be disaggregated to building components, but SYSTEMS loads cannot because the SYSTEM simulation works only with loads at the space/zone level, and of course, (4) (5) fresh air or any other load introduced by the SYSTEM simulation do not appear at all in the LOADS report. Therefore, trying to get a measure of the outside air load by comparing the SYSTEM to the LOADS reports is highly unreliable and can even be completely misleading.
However, there is a way to get the outside air load exactly, but it requires using the HOURLY-REPORT option in DOE-2 and then a little bit of postprocessing. In the HOURLY-REPORT specification, print out the Zone Temperature, Ventilation CFM, and Equipment Ontime for Heating and Cooling each hour. Then, you can calculate the Ventilation Air Load each hour as the temperature difference between the outside air and the zone times the CFM and the heat capacitance of air. I still remember that equation in IP as DeltaTxCFMx0.0128. If the Equipment equipment is on, it would be obvious to attribute the Ventilation Air Load as either Heating or Cooling, but what to do if the Equipment equipment is off? The best method I've found is to aggregate them as in a cache and that is then assign them to whatever assigned to whichever mode the Equipment equipment next comes on. For example, if the building is HVAC is shut off at night, the aggregate cache of cached Ventilation Air during those hours will be assigned as Heating Loads if that's the equipment that when heating comes on next the next morning. You can think of that ventilation load as a morning pick-up load. If you throw away these ventilation air loads when the equipment is off, you will have underestimated their impact on the building load.
One last practical suggestion, you might also try the eQUEST-Users bulletin board because there seems to be a lot more eQUEST users participating there than here on Unmet Hours.
