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AIR CONDITIONING & HEAT PUMP SYSTEMS
A/C - HEAT PUMP CONTROLS & SWITCHES
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A/C DIAGNOSTIC FAQs
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AGE of AIR CONDITIONERS & HEAT PUMPS
AIR CONDITIONER BTU CHART
AIR CONDITIONER COMPONENT PARTS
AIR FILTERS for HVAC SYSTEMS
AIR FLOW MEASUREMENT CFM
AIR HANDLER / BLOWER UNITS
BACKUP HEAT for HEAT PUMPS
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING
BOOKSTORE - Air Conditioning "How To" Books
CAPACITORS for HARD STARTING MOTORS
CIRCUIT BREAKER SIZE for A/C or HEAT PUMP
CLEANING & Legionella BACTERIA
COMPRESSOR & CONDENSING COIL, A/C
CONDENSATE HANDLING, A/C
CONTROLS & SWITCHES, A/C - HEAT PUMP
COOL OFF HEAT Thermostat Switch
COOLING CAPACITY, RATED
COOLING COIL or EVAPORATOR COIL
DATA TAGS on AIR CONDITIONERS
DEFINITION of HEATING & COOLING TERMS
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DUCT SYSTEM & DUCT DEFECTS
DUST, HVAC CONTAMINATION STUDY
EDUCATION, HVAC SCHOOLS
ELECTRIC MOTOR DIAGNOSTIC GUIDE
EVAPORATOR COIL or COOLING COIL
EVAPORATIVE COOLING SYSTEMS
EXPANSION VALVES, REFRIGERANT
FAN, AIR HANDLER BLOWER UNIT
FAN AUTO ON Thermostat Switch
FAN, COMPRESSOR/CONDENSER UNIT
FAN CONVECTOR HEATERS - HYDRONIC COILS
GAS DETECTION INSTRUMENTS
GAUGE, REFRIGERATION PRESSURE TEST
HEAT LOSS (or GAIN) in buildings
HEAT LOSS (or GAIN) INDICATORS
HEAT LOSS R U & K VALUE CALCULATION
HUMIDITY LEVEL TARGET
INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS, A/C SYSTEMS
LOST COOLING CAPACITY
LOW VOLTAGE TRANSFORMER TEST
MANUALS & PARTS GUIDES - HVAC
MOTOR OVERLOAD RESET SWITCH
MOLD in AIR HANDLERS & DUCT WORK
NOISE AIR CONDITIONER / HEAT PUMP
ODORS in AIR HANDLERS & DUCT WORK
OPERATING COST, AIR CONDITIONER
OPERATING DEFECTS, AIR CONDITIONING
OPERATING TEMPERATURES, AIR CONDITIONER
PORTABLE ROOM AIR CONDITIONERS
PRESSURE READINGS, REFRIGERANT
REPAIR GUIDES A/C / HEAT PUMP
REPAIR & DIAGNOSTIC FAQs for A/C
REFRIGERANTS & PIPING
RETROFIT SIZING for A/C or HEAT PUMPS
SEER RATINGS & OTHER DEFINITIONS
SPLIT SYSTEM AIR CONDITIONERS & HEAT PUMPS
THERMOSTATS, HEATING / COOLING
THERMOSTATIC EXPANSION VALVES
WATER COOLED AIR CONDITIONERS
WINDOW / WALL AIR CONDITIONERS
WINDOW / WALL A/C SUPPORTS
Heat pump COP, definitions, efficiency, true electricity cost calculations. This article defines heat pump COP (coefficient of performance) and explains why the operating efficiency of heat pumps varies as a function of outdoor temperature. We include a table of factors used to convert electricity costs to true electricity costs as a function of outdoor degree days in the heating season - a calculation that makes comparison of heat pump operating costs with those of other heating methods much more accurate. Illustration at page top provided by Carson Dunlop Associates.
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What is the COP or Coefficient of Performance of Heat Pumps?
The COP or coefficient of performance describes the ability of a heat pump to extract heat from outdoor air down to some low temperature, typically 25 degF. for modern equipment. The COP determines how effective a heat pump can be at providing heat during cool or cold weather.
The COP or co-efficient of performance for a heat pump can be expressed as a curve showing energy consumed to operate the equipment versus the amount of heat energy provided to the building.
Because COP curves show that we cannot continue to make effective use of a heat pump at very low or very cold outdoor temperatures, a backup heating system is required where heat pumps are installed in cold climates.
Illustration provided by Carson Dunlop Associates.
[Click any image to see an enlarged version and to read details.]
Watch out: As we explain in details at HEAT PUMPS, GROUNDWATER, you can't tell which COP and EER measurement for groundwater based heat pump systems is "right" without additional data describing the testing conditions.
The balance point in a COP curve for a heat pump describes the point beyond which it is not efficient to continue to run the equipment to try to heat a building - because we are obtaining less heat energy to put into the building than the energy we are using to operate the equipment.
Illustration provided by Carson Dunlop Associates.>
Heat Pump operating cost variables & COP Calculations
Where a heat pump is used to provide part of the building's heat requirements, the efficiency of the air-to-air heat pump will be less at lower temperatures.
Spies (1971, 1977)  notes that heat pump efficiency when outdoor air is warm is quite different from at cold temperatures, making its use of electricity more complex.
The coefficient of utilization may be as high as 3.0, falling to 1.0 as outdoor temperature approaches 10 degF. In 1971 when Spies wrote that note for the Small Homes Council, few heat pumps worked at temperatures that low, Also that this was in 1971, newer equipment is capable of efficient heat extraction from colder air. Spies provided a calculation to transfer heat pump efficiency or COP into electrical costs when comparing heating fuel type cost alternatives:
Example: If you live in a climate in which the average number of degree days in the heating season is 4000, then to compare heat pump operating costs (using electricity) to other fuels and heating methods,
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