Air Conditioner’s Water Generation
Subject
Building Services
,Climatology
,Academic Year
2'nd Year
,Complexity Level
Advanced
,Intermediate
,Content tags
Air Conditioning
,Cooling Load
,Energy Efficiency
,Psychrometry
,Activity Type
Numerical Exercise
,Activity duration
< 30 mins
,Objective
To estimate the water generated from the dehumidification of fresh-air cooling load in a bedroom.
Outcome
Students will realize that water generated from dehumidification of air while cooling a room by Airconditioning, can be used for handy purposes (like gardening)
Requirements
Psychrometric chart
Prerequisites
- Conceptual knowledge of psychrometry and psychrometric chart
- Understanding of the phenomenon of Enthalpy and Humidity ratio.
Given Data:
Design Conditions (peak summer)
- Ambient : DB = 40°C, RH = 60%
- Desired : DB = 24°C, RH = 50%
- Cooling Load : 0.8 TR (calculated in the last activity)
- Density of air : 1.12 kg/m3
- AC Operation hours (daily average) : 2 hours
DB – Dry Bulb temperature, RH – Relative Humidity
Conversion Factors:
- 1 kW = 1 kJ/s
- 1 hr = 3,600 s
- 1 TR = 3.517 kW of cooling
Procedure
Step 1: Estimate the Enthalpies and Specific Humidity Ratios (⍵) of Ambient and Desired Air Conditions (g H2O/kg air) and ∆⍵.
Step 2: Estimate the required volumetric air flow rate (m3 air/hr); convert to mass flow rate (kg air/hr).
Step 3: Estimate cooling required (kg air/hr x g H2O/kg air).
Step 4: Determine annual water generation by multiplying with hours of AC operation per year.
Step 5: Reflect on ways to capture the water generated from Air conditioners.
Calculations:
Step 1: Enthalpy and Humidity Ratio values
| Unit | Ambient | Desired | Difference | |
| Enthalpy (H) | kJkg | 48.5 | 114 | 65.5 |
| Humidity Ratio (w) | g H2Okg air | 29 | 9 | 20 |
Step 2: Mass flow rate of air (ma) (kghr) = (Heat Load (TR) 3.517) (kJs) 3600 (shr)ΔH (kghr)
= 0.8 3.517 360065.5
= 154.64 kghr
Step 3: Water generated (kghr) (Wg) = mass flow rate of air (kg airhr) x Δ⍵ (g H20kg air)1000 g H2Okg H2O
= 154.64 22.51000
= 3.48 kghr
Step 4: Annual water generation (kgyr) = Wg (kghr) x average daily operation x 365 (no.
of days in a year)
= 3.48 x 2 x 365
= 2,540 kgyr
Reference image:
Enthalpies & Humidity Ratios for different air conditions
References
None