Reff: dari wikipedia:
Air conditioner equipment power in the U.S. is often
described in terms of "tons of refrigeration". A "ton of
refrigeration" is approximately equal to the cooling power of one short
ton (2000 pounds or 907 kilograms) of ice melting in a 24-hour period. The value is defined as 12,000
BTU per hour, or 3517 watts.[14] Residential central air systems are
usually from 1 to 5 tons (3 to 20 kilowatts (kW)) in capacity.
|
This is different from the electrical power used by the AC
unit. In fact, they have an efficiency rating called SEER (Seasonal Enery Efficiency
Rating) for AC units.
From wikipedia on SEER:
From wikipedia on SEER:
The SEER rating of a unit is the cooling output in Btu
(British thermal unit) during a typical cooling-season divided by the total
electric energy input in watt-hours during the same period. The higher the
unit's SEER rating the more energy efficient it is.
For example, consider a 5,000-British-thermal-unit-per-hour (1,500 W) air-conditioning unit, with a SEER of 10 BTU/W·h, operating for a total of 1000 hours during an annual cooling season (e.g., 8 hours per day for 125 days). |
The annual total cooling output would be:
5000 BTU/h × 8 h/day × 125 days/year = 5,000,000 BTU/year
With a SEER of 10, the annual electrical energy usage would be about:
5,000,000 BTU/year / 10 BTU/W·h = 500,000 W·h/year
The average power usage may also be calculated more simply by:
Average power = (BTU/h) / (SEER) = 5000 / 10 = 500 W
If your electricity cost is 20¢/kW·h, then your cost per operating hour is:
0.5 kW * 20¢/kW·h = 10¢/h
5000 BTU/h × 8 h/day × 125 days/year = 5,000,000 BTU/year
With a SEER of 10, the annual electrical energy usage would be about:
5,000,000 BTU/year / 10 BTU/W·h = 500,000 W·h/year
The average power usage may also be calculated more simply by:
Average power = (BTU/h) / (SEER) = 5000 / 10 = 500 W
If your electricity cost is 20¢/kW·h, then your cost per operating hour is:
0.5 kW * 20¢/kW·h = 10¢/h
Compression Work
Compression work can
expressed as
W = h q (1)
where
W = compression work
(Btu min)
h = heat of compression
(Btu/lb)
q = refrigerant
circulated (lb/min)
Compression Horsepower
Compression horsepower
can be expressed as
P = W / 42.4 (2)
where
P = compression power
(hp)
W = compression work
(Btu min)
Alternatively
P = c / (42.4 COP) (2b)
where
P = compression power
(hp)
c = capacity (Btu/min)
COP = coefficient of
performance
Compression
horsepower per Ton
p = 4.715 / COP (2c)
where
p = compressor horsepower per Ton (hp/Ton)
COP = coefficient of performance
COP - Coefficient of Performance
COP = NRE / h (3)
where
COP = Coefficient of
Performance
NRE = Net Refrigeration
Effect (Btu/lb)
h = heat of compression
(Btu/lb)
Net Refrigeration Effect
Net refrigeration effect
can be expressed as
NRE = hl -
he (4)
where
NRE = Net Refrigeration
Effect (Btu/lb)
hl =
enthalpy of vapor leaving evaporator (Btu/lb)
he =
enthalpy of vapor entering evaporator (Btu/lb)
Capacity
c = q NRE (5)
where
c = capacity (Btu/min)
q = refrigerant
circulated (lb/min)
NRE = Net Refrigeration
Effect (Btu/lb)
Compressor Displacement
d = c v / NRE (6)
where
d = compressor
displacement (ft3/min)
c = capacity (Btu/min)
v = volume of gas entering
compressor (ft3/lb)
NRE = Net Refrigeration
Effect (Btu/lb)
Heat of Compression
h = hlc - hec
(7)
where
h = heat of compression
(Btu/lb)
hlc =
enthalpy of vapor leaving compressor (Btu/lb)
hec =
enthalpy of vapor entering compressor (Btu/lb)
Volumetric Efficiency
μ = 100 wa /
wt (8)
where
μ = volumetric
efficiency
wa =
actual weight of refrigerant
wt =
theoretical weight of refrigerant
Compression Ratio
CR = ph /
ps (9)
where
CR = compression rate
ph =
head pressure absolute (psia)
ps =
suction pressure, absolute (psia)
The chiller efficiency
depends on the energy consumed. Absorption chillers are rated in fuel
consumption per ton cooling. Electric motor driven chillers are
rated in kilowatts per ton cooling.
·
KW/ton = 12 / EER
·
KW/ton = 12 / (COP x 3.412)
·
COP
= EER / 3.412
·
COP
= 12 / (KW/ton) / 3.412
·
EER
= 12 / KW/ton
·
EER
= COP x 3.412
If a chillers efficiency is rated at 1 KW/ton,
·
COP = 3.5
·
EER = 12
Cooling Load in - kW/ton
The term kW/ton is
commonly used for larger commercial and industrial air-conditioning, heat pump
and refrigeration systems.
The term is defined as
the ratio of energy consumption in kW to the rate of heat
removal in tons at the rated condition. The lower the kW/ton the
more efficient the system.
kW/ton = Pc / Er
(1)
where
Pc =
energy consumption (kW)
Er = heat removed (ton)
Coefficient of Performance - COP
The Coefficient of
Performance - COP - is the basic parameter used to report
efficiency of refrigerant based systems.
The Coefficient of
Performance - COP - is the ratio between useful energy acquired and
energy applied and can be expressed as
COP = Eu / Ea
(2)
where
COP = coefficient
of performance
Eu =
useful energy acquired (btu in imperial units)
Ea =
energy applied (btu in imperial units)
COP can be used to
define both cooling efficiencies or heating efficiencies as for a heat pumps.
·
Cooling - COP is defined as the ratio of of heat removal to energy input
to the compressor
·
Heating - COP is defined as the ratio of heat delivered to energy
input to the compressor
COP can be used to define the efficiency at
single standard or non-standard rated conditions, or as a weighted average
of seasonal conditions. The term may or may not include the energy consumption of
auxiliary systems such as indoor or outdoor fans, chilled water pumps, or
cooling tower systems.
·
higher COP - more efficient system
COP can be treated as an efficiency where COP of 2.00
= 200% efficiency. For unitary heat pumps, ratings at two standard
outdoor temperatures of 47oF and 17oF (8.3oC and -8.3oC)
are typically used.
Energy Efficiency Ratio - EER
The Energy Efficiency
Ratio - EER - is a term generally used to define cooling
efficiencies of unitary air-conditioning and heat pump systems.
The efficiency is
determined at a single rated condition specified by an appropriate equipment
standard and is defined as the ratio of net cooling capacity - or heat removed
in Btu/h - to the total input rate of electric power applied -
in Watts. The units of EER areBtu/Wh.
EER = Ec / Pa
(3)
where
EER = energy
efficient ratio (Btu/Wh)
Ec = net
cooling capacity (Btu/h)
Pa =
applied electrical power (Watts)
This efficiency term
typically includes the energy requirement of auxiliary systems such as the
indoor and outdoor fans.
·
higher EER - more efficient system
