This report presents a summary of the findings and activities of Stage 2 of the LCL-CRC research project RP 1033 “High Performance Commercial Building HVAC”.
This research examined the HVAC design of a high performance commercial office building (hereafter referred to as the case study building) and compared its electricity consumption to that of a standard BCA compliant HVAC design for the same building. The main HVAC system designed and installed in the case study building as a low temperature VAV, air-water HVAC system, which is one of the most common designs currently utilised for commercial buildings. The case study building is based on a project completed by AECOM where they were engaged as both the Mechanical Services and ESD consultant.
This study was used to gain a better understanding of HVAC design used in high performance buildings verses that required for minimum code compliance. This work is part of a broader CRC project - Mainstreaming High Performance HVAC, which is looking at factors associated with facilitating increased industry uptake of high performance HVAC design. The focus of this study is to examine the potential energy savings from improved duct and pipe system design.
A validated IES model for the case study building and its associated high efficiency HVAC design (the case study HVAC design) was utilised in this work. The following two scenarios were modelled and compared:
- A HVAC design that met the minimum BCA HVAC requirements (BCA compliant HVAC design)
- The case study HVAC design
The simulation results showed that the annual electricity consumption of the case study HVAC system was 13% less than the consumption for the BCA compliant HVAC system. This was mainly due to energy usage reductions in the air handling units (AHU’s) and return air (RA) fans (24% reduction), the chillers (25% reduction) and the chilled water pumps (28% reduction) for the case study HVAC design compared to the BCA compliant HVAC design.
The energy reduction for the AHU’s fans for the case study HVAC design was achieved by using larger ducts (around 10% larger hydraulic diameter), more efficient duct fittings as well as reducing the number of duct fittings. Further, the energy reduction in the chillers and their associated chilled water pumps for the case study HVAC design was achieved by selecting more efficient chillers and utilizing larger pipes for the chilled water pipe network (around 7% larger hydraulic diameter).
Other aspects of the case study HVAC design did not achieve as great an energy reduction as the three components described previously. As such, for all elements of the case study HVAC design, the overall reduction in electricity consumption achieved was 13% in comparison to the BCA compliant HVAC system. Note that this reduction in the electricity consumption for the case study building leads to an approximate 171 tons reduction in annual CO2 emissions.
Additionally, an economic analysis was performed to determine the cost-benefit of the case study HVAC design compared to the BCA compliant HVAC design. The results showed that the initial cost of the case study HVAC design is only 1% greater than the capital cost of the BCA compliant HVAC design. Further, a discounted payback period of 4 years was calculated for the additional cost invested on the case study HVAC design instead of the BCA compliant HVAC design.
The widespread adoption of the design criteria utilised for the case study HVAC design is recommended for other low temperature VAV, air-water HVAC systems. If adopted by HVAC designers, this approach would lead to significant reductions in the energy usage and greenhouse gas emissions of these systems.