Carbon Offset from AC’s

Objective

To estimate the number of trees required to offset GHG emissions of refrigerants from ACs installed in college buildings.

Outcome

Students will realise that offsetting carbon emissions from AC’s by planting trees is an impractical solution.

Requirements

Details of AC’s installed in their own college campus.

Prerequisites

A conceptual knowledge of 

1. Carbon Footprinting.
2. Global Warming Potential (GWP).

Given Data

1. 1 tree absorbs approximately 0.25 ton of CO₂ in its lifetime.
2. Life-cycle refrigerant charge (C) 1.5 kg of refrigerant/TR
3. 1 ton ~ 1000 kg

Procedure

Step 1: Students find out the total air conditioning load (TR) of the campus.

Step 2: Students find out the refrigerants used in the AC’s installed in college campus.

Step 3: Estimate the total amount of refrigerants used in AC’s in the college campus (kg of refrigerant).

Step 4: Estimate the carbon emissions from the refrigerants used in AC’s in the college building in CO₂ equivalent (t CO₂e).

Step 5: Estimate the number of trees to be planted to offset the emissions from refrigerant usage in the college building.

Sample Calculation

Step 1: Air conditioning load in college campus (TR) = 40 TR

Step 2-3-4: 

Refrigerant Name	R22	R134a	Total
Cooling Load in the Building (L) (TR)	20	20	40
Total Refrigerant used in building (CxL) (T) (kg of refrigerant)	30	30	60
GWP (kg of CO2 /kg of refrigerant)	1810	1430	–
Carbon Emissions from refrigerants (E) = T x GWP (kg of CO2 e)	54,300	42,900	97,200
Carbon Emissions from refrigerants (t CO2 e) = E/1000	54.3	42.9	97.2

Hence, Emissions from refrigerants used for AC’s in entire college building in t CO₂e = 97.2 t CO₂e 

Step 5: No. of Trees to be planted to offset GHG Emissions of refrigerants used in college building = $$\frac{\:\text{Carbon Emissions from refrigerants }}{\:\text{Lifetime Carbon Absorption Capacity of one tree }}$$

= $$\frac{\:\text{97.2}}{\:\text{0.25}}$$

~ 390 trees

References

To learn more about carbon footprint, refer Supplementary Notes Section