Signs/Causes/Reasons for Overload trip - Motor troubleshooting

- blown fuse
- improperly sized fuse
- tripped/open circuit breaker
- failed capacitor
- overheating
- poor ventilation/lack of cooling
- high ambient temperature
- broken motor fan
- low voltage
- overvoltage
- voltage fluctuation, transient voltages
- power imbalance to the phases (not same power to each phase)
- insufficient torque
- belts too tight
- one phase drawing excessive amps
- one phase is open (single phasing)
- phase imbalance (voltage on one phase lesser than others)
- one phase drawing no (zero) amps
- open contactor contacts
- open motor winding
- low insulation resistance
- low resistances causing high currents
- vibration
- damaged stator
- loose wiring
- improper wiring combinations
- loose contactor contacts
- grounded motor
- shorted motor
- defective overload heater
- malfunctioning overload block
- overload relay failure
- overload protection not properly sized/not properly set
- motor sitting for long period of time (e.g. not operated during winter)
- seized motor
- rotor not turning
- shaft not turning freely
- shaft misalignment
- shaft too loose
- rotating parts contact stationary parts
- soft footing/foundation
- pipe strain
- moisture
- rust, contamination, dirt, accumulated dust
- bearing failure
- overlubrication
- inadequate or incorrect lubrication
- jam/obstruction inside/outside motor
- inadequate wiring/undersize wires
- undersized motor
- tripping of thermal protection/overload trip
- system alteration (e.g load increase, power supply changes, etc)
- new component added
- flowrate increase (airflow, water flow, heat load increase)
- operating a motor at 10% to 15% above rated speed
- harmonic distortion causing high frequency voltages or high current
- wear, incorrect fit
- shaft voltages/currents while rotating
- variable frequency drive (VFD) has improper pulses generated

How ddc works: HVAC Furnace direct digital control

HOW DDC WORKS

CENTRAL WORKSTATION (control, monitor, manage)

-         talks to global controllers/building controllers

-         send, receive, process, store, print the data

-         check component and system status

-         check trends and monitor performance of equipment

-         change set points, schedules and settings

-         ASCENT COMPASS - Alerton

GLOBAL CONTROLLERS (integrate devices)

-         talks to field controllers/zone controllers

-         connects/provides gateway to allow communication

with devices made by different manufacturers

-          integrates different devices

-         ACM, BCM, VLX - Alerton

FIELD CONTROLLERS (control terminal units)

-         operates actuators, fans, blowers, pumps

-         field controller for VAV, AHU, Fan coil unit, chiller

cooling tower, boiler, terminal unit

-         VLC, VAV - Alerton

     

SENSORS

-         provide input, send signal to controllers

-         display room setpoints and fan status

-         display room temperature, outside air temperature, relative humidity

-         MICROSET - Alerton

HOW CONTROLLER WORKS

 

Receive Input Information From Sensors

Process Input Information

Respond with an Output Action

Receive Feedback when set point is met

Respond with another Output Action

Example:  How a Furnace DDC works?

1.      Thermostat (Sensor) calls for heat

2.      Thermostat switch is closed, sends voltage signal to control board

3.      Control board (“Brain”) receives and processes input signal from thermostat

4.      Control board closes contactor, inducer fan motor starts

5.      Air flow switch/Sail switch closes to confirm air flow supplied by fan

6.      Control board will activate the Spark Igniter

7.      Control board activates Gas Valve

8.      Burner ignites

9.      Flame Sensor detects flame

10.   Spark Igniter deactivates

11.   Control board energizes Indoor Fan Blower motor

12.   Furnace supplies heat to the structure (room, home, building, etc.)

13.   Thermostat temperature set point is met

14.   Thermostat opens switch, sends feedback signal voltage to control board

15.  Control board shuts off the Gas Valve and Induced draft fan

   

   

HOW BUILDING AUTOMATION SYSTEM (BAS) WORKS

 

BAS uses an integrated network of Workstations, Global Controllers, Field Controllers, Sensors, Gateways, Routers, Repeaters, Cables and other associated components that are designed and programmed to provide the following building services:

1. Networking
2. Control, Monitoring and Alarms
3. Data collection
4. HVAC – Heating, Ventilation, Air-Conditioning
5. Real-time Adjustments of Setpoints, Percent valve openings, etc
6. Scheduling, Remote Operation and Remote Access
7. Changing Modes, e.g. Economizer mode (to save on energy costs)
8. Load and Demand Control
9. Fire Protection
10. Security
11. Lighting management
12. Energy Management

 

 

Refrigeration System Sequence of Operation

REFRIGERATION (COOLING) CYCLE:

Power is supplied to Timer Motor

Timer Motor controls time for Cooling and Defrost cycles

Room Thermostat Closes when the temperature rises above setpoint

Control Board will activate the Refrigeration/Cooling Mode

Timer Motor is on Refrigeration/Cooling Mode

Defrost Heater is Off

Defrost Limit Switch is Off

Defrost Termination Solenoid is Off

Defrost Termination Thermostat/Fan Delay Switch is On

Evaporator Fan Motor is On

Liquid Line Solenoid is energized

Liquid Line Solenoid Valve Opens to allow liquid refrigerant to Evaporator

Low Pressure Control/Switch is Closed

High Pressure Control/Switch is Closed

Overload Protection is Closed

Compressor Contactor Coil is Energized

Compressor Runs

Condenser Fan Motor Runs

When Desired Room Temperature is reached

Room Thermostat Opens

Liquid Line Solenoid is De-energized

Liquid Line Solenoid Valve Closes

Compressor continues to run to allow Pump Down of refrigerant

Low Pressure Control/Switch will Open

Compressor Contactor Coil will De-energized

Compressor will turn Off

Condenser Fan Motor will turn Off

When defrost time is reached by the Timer Motor

Defrost Mode/Cycle begins



===============



DEFROST CYCLE/MODE:

Compressor Pump Down process

Timer Motor will be on Defrost Mode/Cycle

Defrost Heater is On

Defrost Limit Switch is On

Defrost Termination Solenoid is On

Defrost Termination/Fan Delay Switch is Off

Evaporator Fan Motor is Off

When defrost time is completed and Evaporator warms up

Defrost Termination Thermostat Closes

Low Pressure Control Closes

Compressor starts

Condenser Fan Motor Starts

Refrigeration Cycle Starts

When Evaporator coil temperature cools down

Fan Delay Switch will Close

Evaporator Fan Motor will turn On

Refrigeration cycle continues until the next Defrost Cycle is set by Timer Motor

Advantages Disadvantages of Pneumatic, Hydraulic, Electrical-Electronic systems

The following relates to general Pneumatic, Hydraulic, Electrical-Electronic systems
as well as Control Systems which uses the systems mentioned.



Pneumatic Systems advantages:
- cheap initial installation
- air availability
- ease of transfer through piping
- ease of power and speed transmission
- ease of use
- ease of maintenance
- safe, explosion proof
- clean
- works in wide temperature range
- reserve compressed air can be stored



Pneumatic Systems disadvantages:
- more energy cost compared to hydraulic
- easy to leak
- hard to find leaks
- noise
- condensation/moisture
- needs drying to avoid condensation
- control of speed needs additional devices
- control of position difficult
- does not work underwater
- does not work in extreme temperatures
- requires bigger cylinder to handle the same load as in hydraulic



Hydraulic Systems advantages:
- high horsepower-to-weight ratio
- maintains constant torque and force
- hydraulic power can be transmitted in long distances
- motion reversal is fast
- handles strong, heavy loads, shock forces
- lesser overall wear because of oil lubrication
- does not generate sparks
- smooth operation/lifting/movement of loads
- costs less energy to operate
- leaks easier to find
- operates in hot environments



Hydraulic Systems disadvantages:
- more expensive initial installation than pneumatic system 
- noisy
- risk of contamination
- requires more energy to operate
- requires more maintenance
- heavier components, parts
- hydraulic fluid dangerous to humans
- hydraulic fluid not environment friendly



Electronic/Electrical Systems advantages:
- high accuracy
- quiet
- longer life
- no moving parts
- lesser maintenance
- more reliable
- high efficiency
- higher energy savings due to better energy management
- less drift and recalibration problems




Electronic/Electrical Systems disadvantages:
- expensive initial cost
- complexity of algorithms/troubleshooting
- risk of radio frequency interference
- risk of fire hazards due to arcs, sparks
- risk of electricution, short circuits, grounds

8-minute run time for 3/8 cordless drill 18 volts

Example:
18 volts Lithium-ion
3/8 inch chuck
Max. Torque: 400 inch-lbs/33 ft-lbs/45 N-m
No Load RPM : 0-400 / 0-1,300 rpm
Clutch Settings : 15 position
Length : 7.7 inch
Weight : 3 lbs
Battery Charger: 45-Minute Fast Charger
 


Cordless drill run time depends on:
- Battery voltage: More volts, More run time

- Battery capacity: More amp-hours, More run time

- Drill Efficiency: More efficient, More run time



How long cordless drill run in a single charge?
?


Run time calculation
actual screws driven: 160 screws (3 inch size) per charge
assume: 3 seconds to drive per screw

Run time = 160 screws x 3 sec/screw

Run time = 480 sec

Run time = 480 sec/60 sec per minute

Run time = 8 minutes

Pressurized Cylinder Projectile

OXYGEN, NITROGEN
Oxygen and Nitrogen cylinders typically have 2500 psig pressure
Oxygen is one of the three elements of the Fire Triangle (Fuel, Oxygen, Heat/Spark)
Oxygen cylinders are usually green in color
Nitrogen cylinders are usually black in color


ACETYLENE
Acetylene cylinders typically have 250 psig pressure
Acetylene is a highly explosive fuel gas used for brazing and welding
Acetylene burns at over 3,000 C/6,000 F (one of the hottest burning fuel gas)
Acetylene cylinders are usually maroon in color
Acetylene chemical formula is C2H2
Pressure relief valve set at 400 psig


ACETYLENE CYLINDER PROJECTILE FORCE

Example: 6 x 20 inch --- small cylinder

Diameter = 6 inch
Radius = 3 inch
Height = 20 inch
Cylinder pressure = 250 psig
Weight = 22 lbs
Capacity = 40 cubic foot of acetylene gas (120 times compressed vs. empty)


Capacity of cylinder without gas = (pi/4) x D^2 x H

Capacity of cylinder without gas = (pi/4) x 6 in^2  x 20 in x 1 cubic foot/1728 cubic in

Capacity of cylinder without gas = 0.33 cubic feet (empty)


Full capacity comparison = 40 cu ft/0.33 cu ft = 120 times compressed


Cylinder Total Surface Area, TSA

TSA = 2 x pi x r x h  +  2 x pi x r^2

TSA = pi x d x h  +  2 x (pi/4) x d^2

TSA = pi x 6 x 20  +  2 x (pi/4) x 6^2

TSA =  377 + 57

TSA = 434 sq. in.


Total Cylinder Projectile Force = Pressure x Area  + Cylinder Weight

Total Cylinder Projectile Force = 250 lb/sq in x TSA  + 22 lbs

Total Cylinder Projectile Force = ( 250 x 434 )  +  22 lbs

Total Cylinder Projectile Force =  108,500 lbs + 22 lbs

Total Cylinder Projectile Force = 108,522 lbs

Total Cylinder Projectile Force = 54 tons approx.

*** Small pressurized cylinder with huge 50 ton force projectile !!!



PRESSURIZED CYLINDERS (PRESSURE VESSELS) SAFETY

WORKING
1. Before working with pressurized cylinders, check them first.
2. Check valves, regulators - broken, damage, leak.
3. Check hoses - wear, crack, leak, damage.
4. Pay attention to leaks, noises and unusual smell.
5. After checking, if you found any defects, don't use it.
6. Keep cylinders a distance away from the work area --- don't braze/weld directly in front of the cylinder!
7. Always wear personal protective equipment when working with pressurized cylinders.
8. Open quarter turn only, this is enough for most jobs, faster to close in case of emergency.
9. Know location of fire extinguishers and nearest exits when working with pressure vessels.

TRANSPORT
1. Don't drop - damages valves, etc.
2. Transport in upright position.
3. When transporting heavy cylinders, they must have a safety cap securely fastened and be in an approved cart with chains to secure the cylinders.

STORAGE
1. Store in upright position and ensure safety cap in place - to prevent tripping, valve damage, etc.
2. They must have chains to prevent from falling over.
3. Oxygen and Fuel cylinders must be separated with a minimum wall height of 5 ft or 20 ft distance away from flammable substances such as paint.


CYLINDER SAFETY DEVICES
1. Pressure relief valves
2. Fusible plugs (low melting point)
3. Pressure regulators
4. Safety cap


EMERGENCY ACTIONS
If you find a leaking cylinder, use your discretion, safety first!!!
If the leak is small and it is safe to close the valve, then immediately close the valve without endangering yourself.
If the leak is big, evacuate the area, close the door, pull the nearest fire pull station to sound the alarm, call Fire dept...

 

3 RHVAC REPAIR (body analogy): Superheat, Subcooling, Delta T

SUPERHEAT - WHAT'S GOING ON IN EVAPORATOR
High Superheat = Thirsty Evaporator (little refrigerant)
Low Superheat  = Flooded Evaporator

SUBCOOLING - WHAT'S GOING ON IN CONDENSER
High Subcooling = Flooded Condenser
Low Subcooling  = Starved Condenser (little refrigerant)


Body Analogy:
Body is Hot = Thirsty (high superheat)
Body is Cool = Drank plenty of water (high subcooling)



SUPERHEAT & SUBCOOLING

High Superheat & High Sub-cooling:
 -- restriction/blockage in coil, orifice or line set
 -- too little refrigerant in low side (suction line)
 -- too much liquid refrigerant in the high side (liquid line)
 -- Evaporator starved of refrigerant
 -- restricted TXV or drier
 -- check TXV bulb tightness
 -- check insulation)


Low Superheat & Low Sub-cooling:
 -- orifice too big
 -- no orifice in the unit/orifice is stuck and refrigerant is by-passing it
 -- Evaporator flooded with refrigerant
 -- TXV opened too much


High Superheat & Low Sub-cooling:
 -- Undercharged on both sides (suction line & liquid line)
 -- find the leak


Low Superheat & High Sub-cooling:
 -- Overcharged on both sides (suction line & liquid line)
 -- remove, adjust charge




TROUBLESHOOTING: SUPERHEAT, SUBCOOLING, DELTA T

1. LOW CHARGE
 --- High superheat
 --- Low subcooling
 --- Low indoor TD
 --- Low suction pressure
 --- Low head pressure
 --- Low compressor amp draw


2. OVER CHARGE
 --- Low superheat
 --- Normal indoor TD
 --- High subcooling
 --- High suction pressure
 --- High head pressure
 --- High compressor amp draw


3. LOW INDOOR AIR FLOW
 --- Low superheat
 --- Low suction pressure
 --- Low to normal head pressure
 --- High to normal subcooling
 --- High indoor TD
 --- Minimal effect on current draw
 --- Low evaporator air flow
 --- dirty filters
 --- dirty evaporator coil
 --- Evaporator coil may freeze up


4. LOW OUTDOOR AIR FLOW
 --- Low subcooling
 --- Low indoor TD
 --- High superheat
 --- High suction pressure
 --- High head pressure
 --- High outdoor TD
 --- High current draw
 --- dirty condenser coil
 --- bad condenser fan


5. RESTRICTION
 --- High superheat
 --- High subcooling
 --- High head pressure
 --- High amp draw
 --- Low suction pressure
 --- Low indoor TD


6. WEAK COMPRESSOR VALVES
 --- Low superheat
 --- Low head pressure
 --- Low indoor TD
 --- Low current draw
 --- High subcooling
 --- High suction pressure




CRITICAL TEMPERATURE DIFFERENTIALS (depends on refrigerant):

Evaporator Delta T --- NOT to exceed 20 F

Condenser Delta T --- NOT to exceed 30 F

Evaporator Superheat --- between 20 F and 30 F

Condenser Subcooling --- NOT to exceed 15 F



Note:
Delta T conversion (degrees F to C)
Subtract first and then convert

F = 1.8 * C

C = F/1.8


Example:
T1 = 75 F
T2 = 90 F

Subtract:
Delta T = T2 - T1
Delta T in F = 90 - 75
Delta T in F = 15 F

Convert Delta T in Degrees F to Degrees C:
C = F/1.8
Delta T in C = 15/1.8
Delta T in C = 8 C




TYPICAL VALUES (depending on refrigerant):

SUPERHEAT: 10F - 15F --- short suction line lengths (less than 30 ft.)
SUPERHEAT: 15F - 20F --- longer lengths (between 30 and 50 ft.)

SUPERHEAT: 12-15 degrees F --- when ambient outside air temp is 75-85 degrees F
SUPERHEAT: 8-12 degrees F --- if the ambient temperature is 85 degrees F or over

Superheat with TXV: Nominal 10 degrees F at evaporator outlet
Superheat with piston: 8 to 20 degrees F at suction service valve

Superheat with TXV/cap tube: 8°F to 20°F
Superheat with electronic expansion valves & solid state controllers (newer systems): 5°F to 10°F

Subcooling: 8 to 12 degrees F
Sub-Cooling: 12-15 degrees F

EVAPORATOR DELTA T: 15F - 20F --- airside delta T across the evaporator 
EVAPORATOR DELTA T: 15-18 degrees F

AIRFLOW ACROSS EVAPORATOR: 350 to 400 cfm per ton of cooling capacity

Rule-of-thumb charging:
 -- Units come charged with refrigerant for 15 ft lineset
 -- Add 0.6 oz refrigerant per foot over 15 ft




UNIT COSTING:

$500 - $700 per ton capacity

example: 2.5 Ton Air-Conditioner (18 SEER) costs $2000
example: 120 Tons costs $60,000




INSTALLATION & LABOR COST Estimate:
Unit cost X 2

Heat Pump example:
4 tons unit for 4 bedroom (2500-3000 sq ft) house
4 tons unit cost: $3000 (18 SEER, 10 HSPF) heat pump
Installation Labor cost: $6500




APPROXIMATE TONNAGE SIZING:

500 sq ft per ton
50  sq m per ton

Area conversion:
10 sq ft = 1 sq m




Capacity conversions:
1 Ton = 12,000 Btu/hr
1 Ton = 3.5 kW
1 Ton = 4.7 HP



See also:
1. Basics of Refrigeration and Air Conditioning
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#RX#