Energy conservation in Building

A huge amount of energy is spent by building. Lighting, motors, electronic equipment, etc are needed and found in building. Moreover HVAC system is the highest energy consumption for commercial building. Energy conservation in building becomes great interest and causes energy audit needed especially for old building.

There are several actions which can be applied to conserve energy for building. Building envelope, Electrical System, and HVAC System are the most common part of it.

Building envelope

Building envelope is related to cooling or heating system because when cooling or heating system is being designed, one of the important thing is material selection for wall, roof, windows, etc. When outdoor and inside temperature are different, heat transfer will occur and add heat gain for the building. Therefore building envelope material selection is very important.

If the building is already built, several actions to improve thermal performance are:

• Thermal insulation attachment for building surface without thermal insulation
• Replace windows with more efficient windows which has high R value, low emisivity glazing, etc
• Reduction of air leakage. Air leakage causes outdoor air enter the inside the building and add heat gain which has sensible and latent heat.

Electrical System

Electrical system involves Lighting, office equipment and motors. In Lighting, the conservation energy actions which can be applied are use energy efficient lamp and ballast. Now, LED technology has begun to replace conventional lighting such incandescent. Besides that, optimize day light is also can be applied.

Office equipment includes computer, printer, fax, copier, etc. Motors can be found in many equipments such as fan, washing machine, etc. For office equipments and motors, the actions which can be applied are choose the energy efficient equipment. Set computers automatically switch to low power also can be applied for it

HVAC

HVAC is the highest energy consumption in building. About 40% of the total energy is consumed in commercial building for HVAC system. Some actions for this are:

•         Set the temperature set point in thermal comfort zone. Turn on the HVAC system only when it is needed.
•        Retrofit of constant air volume system
•              Heat recovery system installation
•              Central cooling plants retrofit.

Source: Hand Book of Thermal Engineering.

Cooling Load Estimation

Design and selection HVAC System based on determination cooling load and heating load. There are several methods to determine cooling load and heating load. The most common method is cooling load temperature differences/Solar cooling load/Cooling load factor (CLTD/SCL/CLF) method. This method developed by ASHRAE along ago.

Cooling load is heat that must be removed from space or room or zone want to be cooled. There are several components must be considered.

1. Conduction from building envelope. Heat is transferred from higher temperature to lower temperature. If outside temperature is higher than inside, so spontaneously heat enter inside space. Heat can enter the space through wall, roof, skylight, or windows.
2. Radiation from sun through window and sky light
3. Conduction through ceiling, partition walls and floor.
4. Internal heat gain such as people, light, and equipment in the room.
5.  Heat gain from infiltrating from outside through door, window, etc. 
6. Cooling load calculation also needs to consider the ventilation heat gain and heat generated by fans in system.

There are latent heat and sensible. Sensible heat is heat which causes changes temperature. Besides that, Latent heat is heat which is not makes temperature difference. This heat cannot be measured by thermometer because no difference temperature occurs. This heat only causes phase change. The simple explanation about latent heat is when water is being heated and boiled, its temperature is stay at 100 ^oC although it is still being heated. This heat is used to change phase not to increase temperature.  Inside surrounding air contains moisture, latent in this case is related to phase change of the moisture.

Conduction from building envelope, radiation from sun, are the example of sensible heat and internal heat from people, infiltration is the example of both sensible and latent heat because moisture is involved.