AC
When does the fan typically run at high speed?
When the outdoor temperature is above 85°F.
What does the evaporator do during operation?
It absorbs heat.
What does the condenser do during operation?
It rejects heat to the outside air.
How much air do air-conditioning systems normally move per ton of cooling?
400 cfm
The Air-Conditioning, Heating, and Refrigeration Institute (AHRI) rates condensers with what air temperature passing over them?
95°F
Which instruments are used to measure electrical operating conditions?
A volt-ohmmeter and an ammeter.
What evaporator boiling point does a high-efficiency air-conditioning system typically operate at?
45°F.
What is the normal evaporator superheat at the outlet for a standard-efficiency system under design conditions?
About 10°F.
What type of power do most residential air-conditioning units operate on?
230 volts, single-phase power
What is the typical evaporator boiling point for a standard air-conditioning system?
40°F
Why can high-efficiency condensers sometimes cause low system pressures on cool days?
Because they can be too efficient, lowering condensing pressures more than desired.
What are the three major power-consuming devices on an air-conditioning unit?
The indoor fan motor, outdoor fan motor, and compressor.
At what temperature do most occupants set their air-conditioning systems?
Around 75°F.
Air-conditioning systems are rated at what standard indoor and outdoor conditions?
95°F outdoor temperature, 80°F indoor dry-bulb temperature, and 50% indoor relative humidity.
What does the EER (Energy Efficiency Ratio) measure?
Steady-state performance without accounting for warm-up periods
What are ratings called when they are not completely accurate?
Nominal ratings.
What does a larger EER rating indicate?
Greater equipment efficiency.
What is the typical running speed of a four-pole motor?
About 1800 revolutions per minute (rpm).
Why do high-efficiency systems have higher operating efficiency?
Because they operate at lower head pressures due to a larger condenser surface area.
Why is SEER considered a more accurate rating system than EER?
Because SEER measures performance over the entire operating cycle
A 4-ton air-conditioning system that requires 5 kW of input power has what EER?
9.6
Why must humidity be considered part of the evaporator load?
Because the evaporator absorbs both sensible and latent heat.
What does Enthalpy measure?
Total heat content of the air.
The study of air and its properties?
Psychrometrics
What is the standard atmospheric pressure?
14.696 psig