Natural vs Conventional AC: GHG Emissions

Objective:

Comparing GHG Emissions of AC using conventional vs natural refrigerant 

Outcome:

 Students will learn the detrimental effect of conventional ACs through emissions calculations and also will learn about the alternative natural refrigerant that can be used in ACs which has much less emissions. 

Requirements:

Laptop, calculator

Prerequisites:

 Fundamental knowledge about the carbon footprinting methods and different scope of emissions, and of different refrigerants and their global warming potential.

Procedure:

Decide and assume on a few constant parameters such as building type and volume of the space, amount of tonnage for the building, energy cost and penalty, capital cost and refrigerant type.

Data assumed:

Library Building: 130×82 feet, 10 feet 6 inch height per floor, 5 floors

Tonnage required: 84 TR direct expansion chiller system

Energy Efficient Ratio (EER) of the system: 2.93

Usage: 3000 hours/year use

Energy cost: 13.25 INR/Kwh

Energy penalty: 300 INR/Kva/month

1. Conventional AC Case: 

Refrigerant: R22 (which is used in conventional ACs)

Global Warming Potential: 1810

Calculations:

Step1: 

• Derive power consumption for the required tonnage – Tonnage to Kw

1 TR = 3.517 Kw 

84 TR = 295.4 Kw cooling output

• EER = 2.93

EER = Cooling output/Input electrical energy (W)

Input electrical energy = 295.4 / 2.93 = 100.8 KW input

Step 2: Determine annual energy consumption for calculated electrical input 

100.8 Kw x 3000 hours/year = 302457 KwH/year

Step 3: Calculate annual GHG emissions for energy consumption

• Scope 2 emission i.e. Indirect electricity emissions

0.96 kg CO2 emissions/KwH (Avg. India Grid electricity emission factor)

0.96 x 302457 = 290.4 MT CO2/year

• Scope 3 emissions (AT&C loss emissions)

0.29 kg CO2 emissions/KwH (Avg. India Grid AT&C losses emission factor)

0.29 x 302457 = 87.7 MT CO2/year

Step 4: Determine Non-energy emissions for Refrigerant use life-cycle (Scope 1 emissions)

REFRIGERATION AND AIR CONDITIONING, Volume 3: Industrial Processes and Product Use, Chapter 7: Emissions of  Fluorinated Substitutes for Ozone Depleting Substances, 2006 IPCC Guidelines for National Greenhouse Gas  Inventories

Etotal,t = Econtainers,t + ECharge,t + Elifetime,t + Eendoflife,t

Where,

Econtainers,t = emissions from all refrigerant containers in year in kg

ECharge,t =emission during system manufacture/assembly in year in kg

Elifetime,t = emission during system operations in year in kg

Eendoflife,t = emission at system disposal in kg

Refrigerant Life cycle emission factors (considering all the above mentioned emissions stages) for developing countries = 149.76 kg Co2e/Kw cooling/year

Hence Scope 1 emissions (Refrigerant leakage) = 149.76 kg/Co2e/Kw cooling/year x cooling output (electrical) 

I.e. 149.76×295.4 = 44.2 MT Co2e/year

Scope 1 emissions (Refrigerant leakage) = 44.2 MT Co2e/year

Step 5: Determine Annual operating (Energy) cost: 

• Energy use cost = 302487 (Annual energy consumption) x 13.25 (Energy cost)

Energy use cost = 40.08 Lakh INR/year

• Energy penalty cost = Energy penalty x Apparent power x 12 (months/year)

Where, Energy penalty – 300 INR/KvA/Month

Apparent power – Electrical input/Power factor = 100.8/0.9 = 112 KvA

Therefore, 300 x 112 x 12 = 4.03 Lakh INR/year

Energy penalty cost = 4.03 Lakh INR/year

• Total Energy cost (Operating cost) = 40.08 + 4.03 = 44.11 Lakh INR/year

1. Natural AC

Refrigerant: R290 

Global Warming Potential: 3.3

Calculations:

Step1: 

• Derive power consumption for the required tonnage – Tonnage to Kw

1 TR = 3.517 Kw 

84 TR = 295.4 Kw cooling output

• EER = 2.93 = 53 TR compressor output x 3.517 KW/ X KW input

Therefore X = 186.4 KW compressor output/ 2.93 = 63.6 KW input (electrical)

Effective EER = Cooling output/Input electrical energy (W) = 295.4/63.6

Effective EER = 4.64 

Step 2: Determine annual energy consumption for calculated electrical input 

63.6 Kw x 3000 hours/year = 190800 KwH/year

Step 3: Calculate annual GHG emissions for energy consumption

• Scope 2 emission i.e. Indirect electricity emissions

0.96 kg CO2 emissions/KwH (Avg. India Grid electricity emission factor)

0.96 x 190800 = 183.2 MT CO2/year

• Scope 3 emissions (AT&C loss emissions)

0.29 kg CO2 emissions/KwH (Avg. India Grid AT&C losses emission factor)

0.29 x 190800 = 55.3 MT CO2/year

Step 4: Determine Non-energy emissions for Refrigerant use life-cycle (Scope 1 emissions)

REFRIGERATION AND AIR CONDITIONING, Volume 3: Industrial Processes and Product Use, Chapter 7: Emissions of  Fluorinated Substitutes for Ozone Depleting Substances, 2006 IPCC Guidelines for National Greenhouse Gas  Inventories

Etotal,t = Econtainers,t + ECharge,t + Elifetime,t + Eendoflife,t

Where,

Econtainers,t = emissions from all refrigerant containers in year in kg

ECharge,t =emission during system manufacture/assembly in year in kg

Elifetime,t = emission during system operations in year in kg

Eendoflife,t = emission at system disposal in kg

Refrigerant Life cycle emission factors (considering all the above mentioned emissions stages) for developing countries = 0.08 kg Co2e/Kw cooling/year

Hence Scope 1 emissions (Refrigerant leakage) = 149.76 kg/Co2e/Kw cooling/year x cooling output (electrical) 

I.e. 0.08 x 186.4 = 0.015 MT Co2e/year

Scope 1 emissions (Refrigerant leakage) = 0.015 MT Co2e/year

Step 5: Determine Annual operating (Energy) cost: 

• Energy use cost = 190800 (Annual energy consumption) x 13.25 (Energy cost)

Energy use cost = 25.28 Lakh INR/year

• Energy penalty cost = Energy penalty x Apparent power x 12 (months/year)

Where, Energy penalty – 300 INR/KvA/Month

Apparent power – Electrical input/Power factor = 63.6/0.9 = 70.7 KvA

Therefore, 300 x 70.7 x 12 = 4.03 Lakh INR/year

Energy penalty cost = 2.54 Lakh INR/year

• Total Energy cost (Operating cost) = 25.28 + 2.54 = 27.82 Lakh INR/year

Analogy: Comparison of Conventional vs Natural Refrigerant use AC

Parameter	Conventional (R22) Values	Natural (R290) values	Units
Scope 1 Emissions	44.2	0.015	MT Co2e/year
Scope 2 Emissions	290.4	183.2	MT Co2e/year
Scope 3 Emissions	87.7	55.3	MT Co2e/year
Total GHG Emissions	422.3	238.65	MT Co2e/year
Capital Cost	16.20	54	INR Lakh/year
Annual operating cost	44.11	27.82	INR Lakh/year

References:

None