Enhancement of HVAC Load, Energy Consumption and Energy Cost for a Proposed Residential Building, Bhaisepati, Lalitpur, Nepal

Abstract

HVAC has become the most important infrastructure for ensuring human comfort in workplace, residencies and commercial hubs. However large energy consumption by HVAC system is the major factor limiting its usage. Proper material selection in building construction not only ensures physical comfort but also ensures low operational cost of HVAC system throughout the year. But deciding the proper material of construction for low HVAC operational cost needs knowledge about the HVAC load resulted by each of the materials available. The same gap has been intended to be filled by comparing the energy consumption resulted due to usage of different types of materials and equipment in constructing building. A case study of a proposed residential building has been performed. The building model has been generated in Autodesk Revit and HVAC load has been determined by using Radiant Transfer Function Method, a HVAC load calculation method defined by ASHRAE. Similarly, the gbxml file of this model was extracted and it was run for energy simulation using Green Building Studio. The equipment like laptop, freezer, television and microwave have been considered for calculation process. Heat produced by light and energy consumed by them have also been considered for the calculation and simulation process. The HVAC heating load was found to be 5.96 TOR, HVAC cooling load was 5.36 TOR, EUI was 40 kWh/sq ft.yr. The annual energy consumption was 55244 units of electricity and annual energy cost was NRs. 710191. The simulation was run for operating the AC for 24/7 schedule. The above processes were repeated by varying alternative options for walls, roofs, windows, equipment and sensors. Total of 1240 energy simulations were run and Energy Use Intensity (EUI) were compared for different materials. Walls described by ASHRAE edition 19 and 18 along with common walls used in Nepal were used for running simulations. Similarly, roofs were varied. Variation in windows, equipment and sensors option was made based upon the previous literatures. After running all simulations and comparing the results, it was found out that wooden wall resulted in least EUI of 198kBTU/sqft.yr. However due to construction trend, it was not used and prefab that resulted in least EUI of 231 kBTU/sq.ft.yr among commonly used construction material in Nepal, was selected. In case of roof, R60 roof resulted in least EUI, but casted concrete roof was selected based upon the availability. Window with 0.3 wall window ratio, 2/3 window height shading and triple pane low-E v glass resulted in least EUI. It was possible to make in aluminum frame. So, it was finalized. Among different types of HVAC equipment for residential purpose, package terminal heat pump resulted in least energy consumption with EUI 122 kBTU/sq. ft.yr. Use of occupancy sensor and lighting sensor was also done. After finalizing all these parameters, model was regenerated using all these parameters and HVAC load, energy consumption and energy cost were calculated. The final building was found to have HVAC peak heating load of 2.88 TOR, peak cooling load of 3.8 TOR, energy consumption of 37420kWh and energy cost of NRs. 478486. The EUI was decreased from 40 to 29 by this work. By simple alteration of building parameters without modifying any layout, rooms and outlook, HVAC load was seen to have decreased by large portion. Energy saving by almost 32% and energy cost saving by 33% was possible by this simple work. However, the cost involved in construction of enhanced building is higher than proposed building. But the cost is balanced by energy cost in 38 months.