Catatan Kecil - 1

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:

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

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 = h_l - h_e                                                 (4)

where 

NRE = Net Refrigeration Effect (Btu/lb)

h_l = enthalpy of vapor leaving evaporator (Btu/lb)

h_e = 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 = h_lc - h_ec                                          (7)

where 

h = heat of compression (Btu/lb)

h_lc = enthalpy of vapor leaving compressor (Btu/lb)

h_ec = enthalpy of vapor entering compressor (Btu/lb)

Volumetric Efficiency 

μ = 100 w_a / w_t                                   (8)

where 

μ = volumetric efficiency

w_a = actual weight of refrigerant

w_t = theoretical weight of refrigerant

Compression Ratio

CR = p_h / p_s                            (9)

where 

CR = compression rate

 p_h = head pressure absolute (psia) 

p_s = 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 = P_c / E_r         (1)

where

P_c = energy consumption (kW)

E_r = 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 = E_u / E_a         (2)

where

COP = coefficient of performance

E_u = useful energy acquired (btu in imperial units)

E_a = 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 47^oF and 17^oF (8.3^oC and -8.3^oC) 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 = E_c / P_a                                    (3)

where

EER = energy efficient ratio (Btu/Wh)

E_c = net cooling capacity (Btu/h)

P_a = 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