140301aB - Load Calculations Flashcards
What are the 4 temp range categories and their respective ranges?
- Med temp 28F to 40F
- Low temp 0F to -20F
- Ultra Low Temp (ULT) -40F to -120F
- Cryogenic Temp -58F to -148F
What is medium temp used for?
Dairy, meats, deli, etc
What is low temp used for?
Frozen meat, vegetables, dairy, and ice cream
What is ULT used for?
Laboratories, pharmaceuticals, biological samples, vaccines, and the production of certain metals and for temperature testing
What are some applications of cryogenics? How do they reach these temperatures?
Used by engineers and scientists to study the effects of very low temps on materials. MRI, NMR spectroscopy, FLIR cameras, etc. Liquid nitrogen and liquid helium are used to reach these very low temps
What is capacity and how is it measured? What is a ton of cooling equal to?
Capacity is a measure of a system’s ability to reject heat, measured by the NRE in tons of cooling, nominal BTUh or kWatts. 1 ton of cooling is 12,000 BTUh or 3.517kW
What is the purpose of any refrigeration system?
Remove heat from where it is not wanted and send it to where it is not objectionable
What does the configuration of a refrigeration system refer to?
The type of system, eg: cascade, air cooled, water cooled, ammonia absorption, centrifugal chiller, etc
What 3 terms might a system’s category include?
- Residential (Domestic)
- Commercial
- Industrial
Define the 2 main categories of HVAC and what they include
- Packaged Units: RTUs, Computer rooms, heat pumps
2. Built Up systems: split ACs and ductless splits
Define: Design Balance Point
The temperature at which the heating or cooling capacity of a unit matches the rate of heat or cooling loss in that building
Define: Direct Expansion System (DX system)
A refrigerant vapour compression system utilizing an evaporator in direct contact with the medium it cools (air, water or glycol etc) also known as dry expansion system
Define: Enthalpy
The amount of heat in 1lb of a substance starting from a zero base point and at a universally accepted temperature. -40C/F is the base point for refrigerants
Define: CPR Valve
Crankcase Pressure Regulator Valve. Operates on basis of CRO, close on rise of outlet. As crankcase pressure rises, valve closes to prevent compressor motor from overloading on pull down or while coming off defrost. Begins to open again once outlet pressure starts to drop
Define: EPR Valve
Evaporator pressure regulator valve. Operates on ORI basis, opens on a rise of inlet pressure, closes on a drop in inlet pressure. Keeps evaporator at a set pressure/temp, above the SST/pressure of a rack system
Define ORD Valve in relation to head pressure control
A Valve piped in between comp discharge and condenser outlet (receiver inlet) but after ORI. Part of head pressure control system with ORI Valve
Define ORI Valve for head pressure control
valve piped downstream of condenser and before ORD connection and receiver. Opens as condenser pressure rises, otherwise allows ORD to bypass hot gas to reciver
Define OROA Valve
Combination ORI and ORD valve used in head pressure control, has 3 ports and controls condenser flow to receiver based on condenser outlet pressure
Define packaged unit
a single unit containing all components, high and low side
Define Refrigerant
A substance able to change from a gas to liquid and back again and that has the ability to carry heat
Define RTU
rooftop packaged unit that can heat, cool, and provide fresh filtered air to a space
Define temp difference (TD)
the diff in temp between two substances such as temp of air in space and refrigerant in the evap
Define VRF unit
a unit that uses one condenser with multiple evap units. Compressor speed control changes the refrig flow to the evaps
Define Volumetric Capacity
performance rating of a certain compressor based on capacity
How can you categorize refrigeration applications? 6 points
capacity category configuration remote install purpose temp range
What functions can a computer room AC perform?
Cooling, humidification and dehumidification and filtration
What extra components do heat pumps have compared to an AC system
they have a reversing valve/three way valve and some models have an accumulator
What are the different types of heat pumps? 3 total
air to air
water to air
ground to air
What is a built up system? 4 points
- a system built on site
- customized to the requirements of the job
- Allows the amount of cooling to be altered
- Gives designer flexibility to mix and match components based on requirement
What is evap selection based on? 5 points
Capacity Setpoint SST Space limitations temp diff TD
What TD would an evap need to maintain humidity?
+/- 1Fdegree
What if equipment is sized too large?
It will not run long enough to maintain a constant temperature
What if equipment is sized too small?
it will run longer to try and maintain setpoint, sometimes not shutting off
What is a balancing graph useful for?
Balancing condenser and evaporator capacity
What are some variables in refrigeration compressor selection? 3 categories
-overall capacity
Evap:
- Setpoint
- SST/low pressure
- suction line press drop
- suction gas temp
Compressor:
- comp ratio
- displacement
- volumetric efficiency
- voltage
Condenser:
- condenser size
- temp of condenser medium
- quantity of condensing medium
How many evaporators and compressors should you plot on a balancing graph when seeking the design balance point?
at least 3
What are the selection criteria for refrigeration condensers? 5 points
- BTU/h capacity
- quantity of cond medium
- temp of cond medium
- low side pressure/SST
- compressor size
Why is condenser correction factor (CCF) vital to know?
So we can calculate how much higher the cond capacity must be in relation to the evap