# Water or Air: Better Cooling Medium?

##### Subject

Building Services

,Climatology

,##### Academic Year

3'rd Year

,##### Complexity Level

Intermediate

,##### Content tags

Active Cooling

,Air Conditioning

,Space Cooling

,##### Activity Type

Numerical Exercise

,##### Activity duration

1-2 hours

,##### Objective

To compare the effectiveness of air vs water as a cooling medium.

##### Outcome

Students will realize that water is a much better cooling medium than air. Students will realize that air conditioning is an inefficient method to cool buildings.

##### Requirements

None

##### Prerequisites

** **A conceptual knowledge of the following:

- Density
- Specific Heat Capacity
- Volumetric Heat Capacity
- Thermal Conductivity
- Functioning of Airconditioning and Water coolers

##### Procedure

** Step 1: **Find out the thermal conductivity (in W/m-K) of

- air
- water

** Step 2:** Estimate the thermal conductivity multiplier for water and air by dividing the higher thermal conductivity value with the lower one.

** Step 3: **Find out the density (in kg/m

^{3}). of

- air
- water

** Step 4: **Find out the specific heat capacity (in kW/kg-K) of

- air
- water

** Step 5:** Estimate the volumetric heat capacity (i.e multiplier of density and specific heat capacity) (in kW/m

^{3}-K) of

- air
- water

** Step 6:** Estimate the volumetric heat capacity multiplier for water and air by dividing the higher volumetric heat capacity value with the lower one.

** Step 7:** Ask the students: ‘Which one of water and air can be a better medium for cooling spaces?’

##### Calculations

##### Table

Thermal Conductivity (K) (W/m-K) | Specific Heat Capacity (C_{p}) (kW/kg-K) | Density (⍴) (kg/m^{3}) | Volumetric Heat Capacity (C_{p}x⍴) (V_{P}) (kW/m^{3}-K) | |

Air | 0.03 | 1.004 | 1.225 | 1.23 |

Water | 0.6 | 4.186 | 1000 | 4186 |

** Step 1: **Thermal Conductivity Multiplier =

^{KWater(W⁄m-K)}⁄

_{KAir(W⁄m-K)}

= 0.60.03

= 20 times

Hence, Thermal Conductivity of water is 20 times that of air.

** Step 2: **Volumetric Heat Capacity Multiplier =

^{VP-Water(kW⁄m3-K)}⁄

_{VP-Air(kW⁄m3-K)}

= 41861.23

= 3403 times

Hence, Volumetric Heat Capacity of water is approximately 3400 times that of air.

**Step 8: **Discuss the following questions to students:

- As the calculations infer that Water is a better conductor of heat, with more density and Volumetric Heat Capacity, why do we use ‘air’ to cool our buildings and why are water coolers used less?
- How did an entire industry get established using this inefficient medium?

##### References

- Fairconditioning: Radiant Cooling Animation https://www.youtube.com/watch?v=dYjMBfORftk
- https://www.theatlantic.com/technology/archive/2017/08/the-moral-history-of-air-conditioning/536364/