Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
In cooling mode, the system capacity will continue to increase as the condensing (water-side) temperature decreases. This is because the sub-cooling at the condenser increases yielding more capacity, and at a lower compressor head pressure which reduces power consumption (higher COP). On the air-side, as entering air temperature decreases, the system SHR reduces. Meaning that less sensible capacity is available while more latent capacity is available (lower "sensible" COP, don't confuse this with "total" COP). Something else also happens at lower condensing and entering air conditions. The compressor suction temperature/pressure is lower. The translates to a lower refrigerant density, which for a volumetric pump (compressor), means the refrigerant side mass flow rate is lower.
So multiple things are happening as the operating temperatures are reduced. I can't tell from these graphs where the data came from. But I would lean towards graph 2 as being more representative, although the magnitude is still in question at this point.
| | 2 | No.2 Revision |
In cooling mode, the system capacity will continue to increase as the condensing (water-side) temperature decreases. This is because the sub-cooling at the condenser increases yielding more capacity, and at a lower compressor head pressure which reduces power consumption (higher COP). This agrees with graph 1.
On the air-side, as entering air temperature decreases, the system SHR reduces. Meaning that less sensible capacity is available while more latent capacity is available (lower "sensible" COP, don't confuse this with "total" COP). Something else also happens at lower condensing and entering air conditions. The compressor suction temperature/pressure is lower. The translates to a lower refrigerant density, which for a volumetric pump (compressor), means the refrigerant side mass flow rate is lower.
So multiple things are happening as the operating temperatures are reduced. I can't tell from these graphs where the data came from. But I would lean towards graph 2 as being more representative, although the magnitude is still in question at this point.
| | 3 | No.3 Revision |
In cooling mode, the system capacity will continue to increase as the condensing (water-side) temperature decreases. This is because the sub-cooling at the condenser increases yielding more capacity, and at a lower compressor head pressure which reduces power consumption (higher COP). This agrees with graph 1.
On the air-side, as entering air temperature decreases, the system SHR reduces. Meaning that less sensible capacity is available while more latent capacity is available (lower "sensible" COP, don't confuse this with "total" COP). Something else also happens at lower condensing and entering air conditions. The compressor suction temperature/pressure is lower. The This translates to a lower refrigerant density, which for a volumetric pump (compressor), means the refrigerant side mass flow rate is lower.
So multiple things are happening as the operating temperatures are reduced. I can't tell from these graphs where the data came from. But I would lean towards graph 2 as being more representative, although the magnitude is still in question at this point.
