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What is Type III certification?
Maintaining, servicing, repairing, or disposing of low pressure appliances
How is leak detection different from other types?
Because a low pressure system operates below atmospheric pressure (in a vacuum) leaks in the gaskets or fittings will cause air and moisture to enter the system
What is the most efficient method of leak checking a low pressure unit?
- Pressurize the system by use of controlled hot water or heater blankets
- When controlled those are not feasible, use nitrogen to increase pressure
- Do not exceed 10 psig, which could cause the rupture disc to fail
How would you leak test a water box?
- Be certain the water has been removed before placing the leak detector probe through the drain valve
- To leak test a tube, use a hydrostatic tube test kit
- Systems with open drive compressors are prone to leaks at the shaft seal
When should crontrolled hot water be used to pressurize a system?
- For the purpose of opening the system for a non major repair
- Under EPA regulations a major repair mean involving the removal of any of the following components: compressor, condenser, evaporator, or any auxiliary heat exchanger coil
What are the leak repair requirements?
- Comfort cooling appliances containing more than 50 lbs should be repaired when leak rate exceeds 15%
- Commercial and Industrial process containing more than 50 lbs should be repaired when leak rate exceeds 35%
Describe the recovery techniques?
- A unit's high pressure cut-out is set for 10 psig when evacuating the refrigerant from a low pressure chiller and a rupture disc on a low pressure recovery vessel relieves at 15 psig
- Recovery from a system using R-11 or R-123 starts with liquid removal and is followed by vapor recovery
How would you prevent the freezing of water in a system?
- Water must be circulated through the tubes when evacuating refrigerant
- Most low pressure recovery machines utilize a water cooled condenser that is connected to the municipal water supply
- If a chiller is suspected of tube leaks, the water sides of the evaporator and condenser should be drained
What does the ASHRAE 3-1996 state?
If the pressure in a system rises from 1 mm Hg to a level above 2.5 mm Hg during vacuum testing, the system should be leak checked
What temperature should be attained when removing oil from a low pressure system?
- 130o F
- Fewer refrigerants are contained in the oil at this higher temperature
State some of the recharging techniques.
- Refrigerant is added through the lowest access point on the system, the evaporator charging valve
- However introducing liquid refrigerant into a deep vacuum will cause it to boil and may lower temperatures enough to freeze water in the tubes
- Intital charging is in the vapor tube, an R-11 system requires a vapor pressure of 16.9" hg or saturation temperature of 36o F
State the recovery requirements.
- Equipment manufactured after 11/15/93 must be certified and labeled by an EPA approved testing organization
- All equipment mst have low loss fittings to minimize refrigerant loss when hoses are disconnected
What are the required levels of evacuation for Low Pressure appliances? (before 11/15/93 and after)
- 25 inches Hg before
- 25mm Hg absolute after
- Once achieved, wait a few minutes and monitor the system pressure
- If pressure rises, there is refrigerant remaining in the system and recovery must be repeated
What are requirements of chillers using CFC-11 and HCFC-123?
- A purge unit
- Primary purpose is to remove non-condensables (air) from the system
- A centrifugal chillers purge condensing unit takes it suction from the top of the condenser, removes air from the system and returns refrigerant to the evaporator
How are systems protected from over pressurization?
- Low Pressure chillers typically use a rupture disc mounted on the evaporator housing
- The typical design burst pressure for a rupture disc is 15 psig
What is required for all ASHRAE saftey groups?
- Refrigerant monitor
- CFC-12, CFC-11 and HFC 134a are code grouped as A-1
- R-123 is code grouped as B-1
- All systems must be protected by a pressure relief valve, not in series