rbl671
Mechanical
- Mar 17, 2018
- 1
Morning all - new here and looking for help. I can't get my head around this.
Carrier Heating and Cooling specs their 25VNA8 Infinity Series 5 stage inverter heat pumps at cooling down to 40° OAT with their communicating system control and the ability to operate down to 25% of capacity in stage 1. It turns out this is not true and they left out an important part of the specification.
Their software seems actually uses a staging matrix.
At 60° or higher the unit will cool in stage 1.
At 59° to 55° the unit will only run in stage 2 or more.
At 55° to 45° the unit will only run in stage 4 or 5.
We have zoned systems in place based on their specifications and found this winter and early spring that the systems will not work because of excessive CFM delivery with higher staging and high static pressures. At 60° when the equipment stages down as spec'd the system is perfect. The zone trunks are designed to handle a maximum of 700 CFM (150% of design need) but in stage 2 the system wants to deliver 900 CFM and at stage 4, 1200 CFM ... it won't work obviously and the noise even if it did is unbearable.
Carrier now claims that the reason for the stage matrix (which is not documented anyplace) is because the lower OAT and low staging (compressor RPM) the oil will separate from the refrigerant gas because of reduced velocity and subsequently starve the compressor for lubrication. I know the oil mix is different in R-410 than like the old R-22 but this does not seem to ring true to me.
The evaporator is usually 8-10 feet above the compressor and I can not imaging how the oil could separate from the gas and not make a return to the compressor. This is what I can't get my head around - how is this possible. If anything I would think the compressor would be flooded. The Infinity Control can modulate the condenser fan to maintain head temps so the oly player here is the velocity of the refrigerant. Unfortunately Carrier will not provide any data to support it so we are essentially on our own.
Help me understand this please!
Carrier Heating and Cooling specs their 25VNA8 Infinity Series 5 stage inverter heat pumps at cooling down to 40° OAT with their communicating system control and the ability to operate down to 25% of capacity in stage 1. It turns out this is not true and they left out an important part of the specification.
Their software seems actually uses a staging matrix.
At 60° or higher the unit will cool in stage 1.
At 59° to 55° the unit will only run in stage 2 or more.
At 55° to 45° the unit will only run in stage 4 or 5.
We have zoned systems in place based on their specifications and found this winter and early spring that the systems will not work because of excessive CFM delivery with higher staging and high static pressures. At 60° when the equipment stages down as spec'd the system is perfect. The zone trunks are designed to handle a maximum of 700 CFM (150% of design need) but in stage 2 the system wants to deliver 900 CFM and at stage 4, 1200 CFM ... it won't work obviously and the noise even if it did is unbearable.
Carrier now claims that the reason for the stage matrix (which is not documented anyplace) is because the lower OAT and low staging (compressor RPM) the oil will separate from the refrigerant gas because of reduced velocity and subsequently starve the compressor for lubrication. I know the oil mix is different in R-410 than like the old R-22 but this does not seem to ring true to me.
The evaporator is usually 8-10 feet above the compressor and I can not imaging how the oil could separate from the gas and not make a return to the compressor. This is what I can't get my head around - how is this possible. If anything I would think the compressor would be flooded. The Infinity Control can modulate the condenser fan to maintain head temps so the oly player here is the velocity of the refrigerant. Unfortunately Carrier will not provide any data to support it so we are essentially on our own.
Help me understand this please!
