Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
After some analysis I found the following explanation: overheating in a thermal zone, as shown in the image below:
How did this happen ?
In the HVAC configuration a water-air heat pump cooling coil is used to heat a domestic water tank. The upper limit of the tank temperature is 60°C. However, when this maximum temperature is reached, operation of the cooling coil is not shut down by EnergyPlus, and the cooling coil produces heat at the water side, which EnergyPlus simply "dumps" into the zone where the water tank is located. Although no objects in the zone can be hotter than 60°C, this leads to temperatures of up to appr. 130°C. This is presumably the reason for the illegal humidity ratios warnings above.
After inserting a EMS programmed control that ensures shutting down the cooling coil whenever the water tank reaches maximum temperature, the problerm disappeared completely.
One could debate whether there is a flaw in EnergyPlus algorithms that allows such overheating to happen, including continued cooling coil operation despite water-side overheating, but with this explanation of EnergyPlus behavior this exception can be dealt with by the user.
(remark: The idf-model used is a derivative from an OpenStudio model, where the air loop and a unitary heat-pump system was modified)
| | 2 | No.2 Revision |
After some analysis I found the following explanation: overheating in a thermal zone, as shown in the image below:
How did this happen ?
In the HVAC configuration a water-air heat pump cooling coil is used to heat a domestic hot water tank. The upper limit of the tank temperature is 60°C. However, when this maximum temperature is reached, operation of the cooling coil is not shut down by EnergyPlus, and the cooling coil produces heat at the water side, which EnergyPlus simply "dumps" into the zone where the water tank is located. Although no objects in the zone can be hotter than 60°C, this leads to temperatures of up to appr. 130°C. This is presumably the reason for the illegal humidity ratios warnings above.
After inserting a EMS programmed control that ensures shutting down the cooling coil whenever the water tank reaches
maximum temperature, the problerm problem disappeared completely.
One could debate whether there is a flaw in EnergyPlus algorithms that allows such overheating to happen, including continued cooling coil operation despite water-side overheating, but with this explanation of EnergyPlus behavior this exception can be dealt with by the user.
(remark: The idf-model used is a derivative from an OpenStudio model, where the air loop and a unitary heat-pump system was modified)
