1. HVAC Test results Anish Gaikwad Parag Mitra
WECC LMTF Meeting Salt Lake City, UT 3 Oct 2017

2. Disclaimer and test information
The test is intended to add more data points to the present set of observations to refine our current estimates of parameters of the Motor D model
We have tested only two units and thus test results are not necessary universal
2 units tested so far-
2 Ton Trane unit, single speed (No VFD) with Trane Climatuff scroll compressor
4 Ton Armstrong unit, single speed (No VFD) with Copeland scroll compressor

3. Test setup Supply V/I Run/Start winding V and I
Programmable Power supply
Lab ambient temperature
Temp controlled chamber
Outdoor unit/ Compressor
Supply V/I
Run/Start winding V and I
Indoor/Outdoor fan V and I
Outdoor/ Indoor Temperature
Comp. Inlet/Outlet pressure
Indoor unit
Monitoring system

4. Test waveforms Rectangular sags Ramped recovery sags
POW
0, 90 degrees
Ramp
0.5 cycle (dip/recovery)
Sag levels
0.4, 0.45, 0.5 (pu)
Duration
2, 3, 4, 5, 6, 9, 12 cycles
Recovery
0.85 pu then 1 pu
Ramped recovery sags
POW
Ramp
0.5 cycle (dip)
Sag levels
0.4, 0.45, 0.5, 0.6, 0.7(pu)
Duration
3 cycles
Recovery
1 pu with 30 s ramp
Temperature : 85 F, 95 F, 105 F, 115 F
Relative Humidity: 36%

5. HVAC Stall determination
Note that it is not possible to measure the motor speed
For rectangular sags
For 0.85 pu real power is almost 3.5 times the base KW
kW consumption should be greater than 3.5 times the times the base KW at that outdoor temperature
Duration of the 3.5 times base KW period should be greater than the inrush current durations
Inlet
Outlet
For ramped recovery sags
Power does not jump as voltage recovers slowly if the motor restarts
The inlet and outlet pressure can be seen to equalize as the motor is stalled and not compressing any more
It is critical to define “stall mode” in the context of scroll compressors

6. Unit Description (Trane 2-Ton)
Manufacturer
Trane, Trane Climatuff (No VFD, single speed)
Size
2 Ton
Voltage rating
240V/ 60 Hz
Rated, Locked rotor amps
8.3, 58 amps
Refrigerant
R-410
Motor type
Cap. Start, Cap. Run
Cap. size
Start: 196 μF, Run 35 μF
35 μF
196 μF
Temp
Steady state amps 85
6.2 95
6.7
105
7.6
115
8.3

7. Cold start up of the unit (2-Ton Trane, Climatuff compressor)
Multiple cold restarts were performed:
Unit started between 5 – 6 cycles or 0.083s approximately
Input voltage (Volts)
5X scaled input current (Amps)

8. 2-Ton Unit: Summary of results (rectangular sags)
UV contactor tripped when voltage dropped below 0.45 – 0.4 pu.
Contactor dropout was independent of outdoor temperature
The A/C stalled only if the contactor dropped out and reconnected back
The A/C invariably stalls for voltage below the pu range. Vstall can be assumed to be in the range pu.
For the Vstall, the A/C invariably stalls for a sag of 2-3 cycles. Tstall can be assumed to be 2-3 cycles.
The values of Vstall and Tstall as indicated were consistent across all temperatures (85°, 95°, 105°, 115° F)
The unit started up for the rectangular sags at all temperatures and TOL did not operate
Reverse rotation of the compressor was not observed for this unit

9. 2-Ton Unit: Summary of results (30 sec. ramped recovery)
NOTE: These test were performed to gain deeper insights
Not meant to replicate an actual sag
For the ramped recovery tests, thermal overload operated only for 115° F for sag levels of 0.4, 0.45, 0.5 pu.
Unit takes longer time to restart at 115 F and therefore trips on thermal overload
The thermal overload operated 7-8s after the A/C stalled
Thermal overload operation is a function of both current and time for which the large current persists
When the A/C motor slows down, the start capacitor connects. The starting cap is large (196 μF) and causes the net current to be capacitive for a short period.
Capacitor helps in terms of providing the reactive power demand
In Motor D model, the Motor D draws large inductive current when stalled

10. Example: Stalling of A/C due to opening of contactor
Temp 105 F
POW 90
Vsag
0.4 pu
Duration
2 cycles
Vrecovery
0.85 for 1s then to 1 pu
Both sag and recovery have a 0.5 cycle ramp

11. Example: A/C motor deceleration and acceleration without stalling
Temp 105 F
POW 90
Vsag
0.5 pu
Duration
4 cycles
Vrecovery
0.85 for 1s then to 1 pu
Both sag and recovery have a 0.5 cycle ramp
Motor D won’t capture this spike if Vstall is set to 0.45pu

12. Example: Thermal overload operation on ramped voltage recovery
Temp 115 F
POW 90
Vsag
0.4 pu
Duration
3 cycles
Vrecovery
30 s ramp to 1 pu
Input contactor remains connected so the voltages do not go to zero
Input, run and start winding currents go to zero as the thermal overload operates
Pressure difference between discharge and suction valves starts to equalize
Thermal overload was observed to operate in s approx.

13. Example: Thermal overload operation comparison at different temperature
Vsag
0.4 pu
Duration
3 cycles
Vrecovery
30 s ramp to 1 pu
95 F
115 F
8s approx.
6.5s approx.
A/C takes longer time to restart at a higher ambient temperature and trips due to thermal overload

14. Unit Description: 4 Ton Armstrong, Copeland Scroll
Manufacturer
Armstrong, Copeland (No VFD, single speed)
Size
4 Ton
Voltage rating
240V/ 60 Hz
Rated, Locked rotor amps
16.5 , 117 amps
(24.3 amps for contactor sizing)
Refrigerant
R-410
Motor type
Permanent Split Cap
Cap. size
70 μF (comp) + 10μF (Fan)
Temp
Steady state amps 85
12.42 95
13.73
105
15.17
115
16.81
Start
Run
70 mfd
PSC

15. Cold start up of the unit (4 Ton Armstrong, Copeland compressor)
Multiple cold restarts were performed:
Unit started between cycles or 0.2s approximately
Input voltage (Volts)
5X scaled input current (Amps)

16. 4 Ton Unit: Summary of results (rectangular sags)
UV contactor tripped when voltage dropped below 0.55 – 0.5 pu (Note this is higher than the 2 ton unit)
Contactor dropout was independent of outdoor temperature
Once the contactor opens, the A/C won’t re-connect before 5 minutes (similar to trip due to thermal overload)
This is a standard recommended manufacturer set delay for protection against short cycling and reverse rotation. Confirmed by both HVAC contractor and compressor manufacturer.
This behavior cannot be captured by the present Motor D model
For a simulation study this means that once the contactor trips, the load is lost.
Better in terms of voltage recovery, but loss of load may mean possible overvoltage
For the rectangular sag, stalling of the A/C unit was not observed. The contactor tripped the unit before it stalled.

17. Example: A/C motor deceleration and acceleration without stalling
Temp 105 F
POW 90
Vsag
0.6 pu
Duration
12 cycles
Vrecovery
0.85 for 1s then to 1 pu
Both sag and recovery have a 0.5 cycle ramp

18. Example: A/C motor contactor opening
Temp 105 F
POW 90
Vsag
0.55 pu
Duration
3 cycles
Vrecovery
0.85 for 1s then to 1 pu
Both sag and recovery have a 0.5 cycle ramp

19. 2 Ton vs. 4 Ton comparison Description 2 Ton 4 Ton
Rated amps, Locked rotor amps
8.3, 58
16.15, 117
Type of motor
Cap start, Cap run
Current at low motor speeds can be capacitive at times
Permanent split cap
Current at low motor speed is inductive
Contactor drop out voltage pu
Reconnects on voltage recovery pu
Does not reconnect before 5 mins
Stalling
Stalls when contactor trips
Vstall , Tstall 2-3 cycles
No stalling
Trips due to contactor and doesn’t reconnect before 5 mins
Thermal overload
Operates for ramped recovery during higher ambient temperatures
No thermal overload operation observed

20. Conclusions
The 2 Ton unit test results indicates Vstall=0.45 and Tstall=0.032 (as suggested now) is within the realm of possibility
For both units, the temperature did not have any effect on the stalling for the rectangular sags
The 4 Ton unit never stalled for any rectangular sag
The contactor trip behavior of the 4 Ton unit cannot be captured by using the standard motor D parameters
Results indicate: Drop out voltage: pu, Reconnection voltage: 999 (high value)
Differences where observed in the operation of the TOL for the ramped recovery sags, with temperature (only for the 2 Ton unit)
TOL was found to operate at higher temperature