*4.2.1 Energy saving potential*

The energy saving potential of using a passive ventilation system was carried out in comparison to using mechanical ventilation system, which is given as follows:

### *4.2.2 Mechanical ventilation system's cost analysis*

Installation Cost: The installation cost consists of the purchase cost and the fixing cost of the system i.e. fans. The average cost of purchase was found to be ₦5000 per fans and fixing cost was ₦200 per fans. For nine fans present in the room, we have:

**DC (₦) IC (₦) OC (₦) MC (₦) TT (₦)**

Mechanical System (Fans) 46,000 16,420 4500 66,920 Passive System (Solar Chimney) 25,000 10,000 5000 40,000

*Computational Analysis of a Lecture Room Ventilation System*

*DOI: http://dx.doi.org/10.5772/intechopen.92725*

**Years MVS (₦) PVS (₦) Increase (₦) % Increase** 66,920 40,000 26,920 40.23 87,840 45,000 42,840 48.77 108,760 50,000 58,760 54.03 129,680 55,000 74,680 57.59 150,600 60,000 90,600 60.16 171,520 65,000 106,520 62.10 192,440 70,000 122,440 63.63 213,360 75,000 138,360 64.85 234,280 80,000 154,280 65.85 255,200 85,000 170,200 66.69

**Table 10.**

**Table 11.**

**Figure 16.**

**Figure 17.**

**95**

*Cumulative cost and percentage increase.*

*Graph of the cost of solar chimney and fans against number of years.*

*Graph of percentage increase against number of years.*

*Total cost of ventilation systems.*

**Figure 15.**

*Effect of solar chimney size on the air change per hour of the lecture room.*


#### **Table 8.**

*Energy demand information of a unit of the ventilation device.*


#### **Table 9.**

*Annual energy cost for the mechanical ventilation system.*

Installation Cost = (₦5000 \* 9) + (₦200 \* 9) = ₦ (45,000 + 1800) = ₦46,800. Operation Cost: This is the average cost for the day to day running of the system. **Tables 8** and **9** shows the operational cost of running the fans.

Maintenance Cost: This is the cost of maintaining the system. It includes repair and basic cleaning. The average charge for maintenance was found to be at ₦500 per year.

Maintenance Cost = ₦500 \* 9 = ₦4,500.

#### *4.2.3 Passive ventilation system's (solar chimney) cost analysis*

Design Cost: This entails the cost of materials used for the design e.g. wood, glass, pvc piping, washers, eye hook, grease, nozzle etc. and overall fabrication of the chimney. Using an exchange rate of ₦250 = \$1.

Design Cost = ₦25,000.

Installation Cost: This includes cost of installing the design to the lecture room. Installation cost was found to be between ₦5000 and ₦15000. The average from this was obtained as ₦10,000.

Installation Cost = ₦10,000.

Maintenance Cost: It is referred to as the expense of using the solar chimney daily. The average maintenance cost was found to be ₦5000 yearly.

## *Computational Analysis of a Lecture Room Ventilation System DOI: http://dx.doi.org/10.5772/intechopen.92725*


### **Table 10.**

*Total cost of ventilation systems.*


#### **Table 11.**

Installation Cost = (₦5000 \* 9) + (₦200 \* 9) = ₦ (45,000 + 1800) = ₦46,800. Operation Cost: This is the average cost for the day to day running of the system.

**Energy demand (9 fans) (kW)**

Fan 25 9 0.225 8 1.8 657

**System Cost (₦) per kWh Cost/day (₦) Cost/month (₦) Cost/year (₦)** 1 fan 25 5 150 1825 9 fans 225 45 1350 16,425

**Hours/day (8 h)**

**kWh/ day**

**kWh/ year**

Maintenance Cost: This is the cost of maintaining the system. It includes repair and basic cleaning. The average charge for maintenance was found to be at ₦500

Design Cost: This entails the cost of materials used for the design e.g. wood, glass, pvc piping, washers, eye hook, grease, nozzle etc. and overall fabrication of

Installation Cost: This includes cost of installing the design to the lecture room. Installation cost was found to be between ₦5000 and ₦15000. The average from

Maintenance Cost: It is referred to as the expense of using the solar chimney

daily. The average maintenance cost was found to be ₦5000 yearly.

**Tables 8** and **9** shows the operational cost of running the fans.

*Effect of solar chimney size on the air change per hour of the lecture room.*

*Zero-Energy Buildings - New Approaches and Technologies*

**Number of fans**

*Energy demand information of a unit of the ventilation device.*

*4.2.3 Passive ventilation system's (solar chimney) cost analysis*

Maintenance Cost = ₦500 \* 9 = ₦4,500.

*Annual energy cost for the mechanical ventilation system.*

the chimney. Using an exchange rate of ₦250 = \$1.

Design Cost = ₦25,000.

this was obtained as ₦10,000. Installation Cost = ₦10,000.

per year.

**94**

**Figure 15.**

**Table 8.**

**Table 9.**

**System Unit Watt (W)**

*Cumulative cost and percentage increase.*

**Figure 16.** *Graph of the cost of solar chimney and fans against number of years.*

**Figure 17.** *Graph of percentage increase against number of years.*

The total cost implications are presented in **Table 10**. The cumulative costs and respective percentage increases are presented in **Table 11**.

**Nomenclature**

ACH air change per hour

BC before Christ Btu British thermal unit

engineers

*DOI: http://dx.doi.org/10.5772/intechopen.92725*

cfm cubic feet per minute C*mech* mechanical ventilation cost

C*sc* solar chimney cost

CO2 carbon dioxide

IAQ indoor air quality kg/m<sup>3</sup> kilogram per cubic metre kg/s kilogram per second

mm millimetre m<sup>3</sup> cubic metre

SC solar chimney TC thermal comfort

C degree celsius ZE zero energy

o

**97**

CFD computational fluid dynamics

HSE health and safety executive

RANS Reynolds average Navier stokes

CIBSE chartered institute of building services engineers

NASA national aeronautics and space administration

UNCHS United Nations centre for human settlements

HVAC heating, ventilation and air conditioning

*Computational Analysis of a Lecture Room Ventilation System*

ASHRAE American society of heating, refrigerating, and air-conditioning

**Figure 16** depicts the relationship between the cost of solar chimney and fans against number of years. It can be observed that the cumulative cost of running the mechanical ventilation system (fans) kept increasing continuously by over 30% each year and that of passive ventilation was lesser with about 12.5%. This indeed tells that the use of the solar chimney for ventilation is less costly, and invariably, energy efficient.

**Figure 17** shows a relative increase in cost over number of years with the use of fans. It can be deduced that there was a 66.69% increase in cost due to the use of fans compared to the use of solar chimney in the lecture room for over 10 years. Therefore, with this percentage increase it can be understood that there is more energy and cost saving potential for the use of passive ventilated systems than mechanical ventilated systems.

### **5. Conclusion**

Passive ventilation systems are a natural ventilation technique that has the potential of saving energy as well as maintaining good air quality in a building as compared to mechanical ventilated systems. This research was carried out with the aim of improving the ventilation performance (thermal comfort and indoor air quality) of a lecture hall. In this project, a detailed and systematic assessment of a lecture hall using CFD simulations was performed for determining the air flow caused by wind velocity stratification (0.05–2.0 m/s), solar radiation (200– 1000 W/m<sup>2</sup> ) and pressure outlet of 1 atm within a space with seven ventilation openings. The air change per hour was deduced using different boundary conditions in the lecture room. The research revealed the airflow and temperature pattern within the room. It was obtained that a solar chimney of size between 1 and 100 m<sup>3</sup> , improved the natural ventilation in the room. Also, from an energy and cost analysis carried out, cost-saving potential of the passive system (solar chimney) was established and found to be both energy and cost-effective in comparison to mechanical systems for better indoor air quality and thermal comfort. There was a 66.69% increase after 10 years in the saving of energy and cost using Solar Chimney (SC) as compared to fans. It is therefore acceptable to state that objectives were achieved and in turn a contribution to knowledge.

The knowledge of temperature stratification and mass flow rate is essential so as to aid the thermal comfort of occupants in indoor environments, especially in public buildings like lecture rooms, conference halls, etc.

#### **Acknowledgements**

The inputs and critique of members of the research team are acknowledged and appreciated. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

#### **Conflict of interest**

The authors declare no conflict of interest.

*Computational Analysis of a Lecture Room Ventilation System DOI: http://dx.doi.org/10.5772/intechopen.92725*
