ENERGY EFFICIENT BUILDING DESIGN : ENERGY MODELING & ANALYSIS
Energy efficiency of buildings, more particularly for the commercial establishments, is a very important aspect of facility-design. Energy cost is a major contributor to the operational expenditure of a building. Hence, any step to improve the energy efficiency, pays back as huge energy cost saving, also reducing the carbon foot-print. Energy modeling is a tool, which helps to simulate the energy expenditure of the facility. With the help of energy simulation various alternatives can be tested before installation, and can be selected by assessing their life-time cost/ benefit. This can also be very useful for taking the retrofit decisions.
As, HVAC systems (Heating, Ventilation & Air-conditioning) are responsible for a significant part of energy bill, naturally there is lot of scope for energy saving by taking appropriate measures. In this case study, Variable Air Volume (VAV) air-conditioning system, and the approach to energy modeling is discussed.
Variable Air Volume (VAV) is a type of heating, ventilating, and/or air-conditioning system, which supply a constant airflow at a variable temperature. VAV systems vary the airflow at a constant temperature. The advantages of VAV systems is it has more precise temperature control, reduced compressor wear, lower energy consumption by system fans, less fan noise, and additional passive dehumidification. For this case study, the energy consumed by a hotel due to various demands of the load, is analyzed.
A 3d model of the hotel was created using a building modeling tool and their respective zones for the room are created, and the thermal data of the construction materials are given as inputs. There are many HVAC systems like variable refrigeration system, constant air volume system,etc. VAV system is used for this simulation. Inside the building everything contribute to heat production for example people, lighting, electrical equipment, infiltration, glass conduction of sunlight, These things are considered as heat loads, depending on this system the zone type control is set.
The heating load and the cooling loads are calculated analytically along with the fenestration details is also considered. The solar heat gain from the window material is also considered with the minute details of what gas is used in between two glass plane.
The temperature of the zone is found by setting a thermostat fixing the minimum temperature such that when the temperature goes below it, heating starts by allowing outdoor filtered air at controlled rate, and the other thermostat is fixed so that if that zone reaches the value above the set point cooling begins to happen at a specified rate.
Chilled Water Coil:
Chilled water coil are heat exchangers, typically consisting of rows of tubes. Most chilled water-coils have air entering the system at a temperature ranging from 23 ◦ C to 35 ◦ C, while chilled water enters the coil at a temperature around 45 ◦ C. As warm air passes across the coil and contacts the cold surface, heat transfers from the water flowing through the tubes to the air entering the coil. Chilled water coils are suitable for air cooling and dehumidifying. In the VAV system the fan supply pressure and its efficiency is calculated along with the cooling coil efficiency and the type of cooling system used for the building.
System’s fan capacity is an important parameter in the VAV system. In the cooling mode of operation, as the temperature in the zone is satisfied, a VAV box closes to reduce the flow of the cool air into the zone. As the temperature increase the box opens up to increase the cool air flow, The fan runs at constant static pressure.
Result and Conclusion:
The cooling required for the entire year for the 44 zones of the building was found and the detailed report of the zone by zone heating and cooling load was found the its corresponding energy consumption, and the electricity used by the hvac system was also found.
A graph has been plotted for the amount of electricity used in all the zone on monthly basis for an entire year. A separate graph for the amount of electricity consumed by the HVAC system to cool the entire zone on a monthly basis.