Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
The message is telling you that the supply air temperature is close to the zone temperature (a small delta T). During sizing the zone air mass flow rate is calculated as: mass flow rate = design heating load / (Cp, air * (supply air temperature - zone temperature). So as the supply air temperature approaches the zone temperature the mass flow rate becomes unreasonable large. Within a 5C difference and larger than 2C is a warning (27 - 24.993 = 2.007) and within a 2C difference (27 - 25.001 = 1.999) is a severe. A typical range of air flow for HVAC is 300 - 500 CFM/ton. The small delta T here shows a very high air flow of 10x what is typical.
The first message shows 2.41854 m3/s / 5957.52 W = 0.000406 m3/s/W or 3025 CFM/ton The second message shows 0.0714982 m3/s / 175.39 W = 0.000408 m3/s/W or 3038 CFM/ton
| | 2 | No.2 Revision |
The message is telling you that the supply air temperature is close to the zone temperature (a small delta T). During sizing the zone air mass flow rate is calculated as: mass flow rate = design heating load / (Cp, air * (supply air temperature - zone temperature). So as the supply air temperature approaches the zone temperature the mass flow rate becomes unreasonable large. Within a 5C difference and larger than 2C is a warning (27 - 24.993 = 2.007) and within a 2C difference (27 - 25.001 = 1.999) is a severe. A typical range of air flow for HVAC is 300 - 500 CFM/ton. The small delta T here shows a very high air flow of 10x what is typical.
| | 3 | No.3 Revision |
The message is telling you that the supply air temperature is close to the zone temperature (a small delta T). During sizing the zone air mass flow rate is calculated as: mass flow rate = design heating load / (Cp, air * (supply air temperature - zone temperature). So as the supply air temperature approaches the zone temperature the mass flow rate becomes unreasonable large. Within a 5C difference and larger than 2C is a warning (27 - 24.993 = 2.007) and within a 2C difference (27 - 25.001 = 1.999) is a severe. A typical range of air flow for HVAC is 300 - 500 CFM/ton. The small delta T here shows a very high air flow of 10x what is typical.typical. To fix this, increase the Sizing:Zone heating supply air temperature.
The first message shows 2.41854 m3/s / 5957.52 W = 0.000406 m3/s/W or 3025 CFM/ton
The second message shows 0.0714982 m3/s / 175.39 W = 0.000408 m3/s/W or 3038 CFM/ton
