If you are planning to build a new commercial building, you should carefully select the air conditioning system because this system consume around 40% of total building energy consumption and over its expected 20 years of service life, its running cost will be substantial. Therefore, you need to select the most efficient system to reduce your energy bills and in the same time get the best return on investment.

To discuss this subject and spread the benefit, we will share with you one of our projects that we completed. In this project, one of our clients engaged us to conduct an energy efficiency design review to one of their aged care facilities in Canberra and they sent us the design drawings and the specifications for this project. We reviewed the design for this facility and we recommended to them many energy conservation measures to include them in the design and modify it accordingly. The annual cost savings from our recommendations was $52,164 with annual energy savings of 1,015 GJ and 234 tonnes CO2 emissions avoidance.  The major recommendation was changing of the air conditioning system from 4-pipe heat recovery chiller to VRV system with heat recovery.

To find out and advise our client on the most efficient air conditioning system for this facility, we analysed three options as listed below. All these systems provide simultaneous cooling and heating:

• Constant Speed 4-Pipe Heat Recovery Chiller System.
• Chiller/boiler System.
• Variable Refrigerant Volume (VRV) System with heat recovery.

We have assumed that the cost of the fan coil units, pipes, valves, controls and the installation labour are the same for all the three options because they are very similar. We considered the cost of the followings in our calculations for each system:

• For the heat recovery chiller, we have considered the cost of the chiller itself only because the chiller has built-in pumps and pumps VSD.
• For the chiller/boiler system, we have considered the cost of the chiller, the boiler and the chilled water and hot water pumps and their VSD.
• For the VRV System, we have considered the cost of the outdoor units and the heat recovery boxes.

The best way to analyse and compare the efficiency of these three options is by using energy simulation software, however, this is was beyond the scope of this project. We used instead the manual calculations with reasonable assumptions and estimations such as the heating and cooling degree days method to give indication about which system is the most efficient to allow our client decide on which system to use for this facility.

The required air conditioning system cooling capacity for this facility was 500 kW and the heating capacity was 560 kW. The table below compares the three options and their annual running cost:

From the above table, we can note the followings:

• VRV system has the lowest running cost. The running cost of the VRV system is around 62% of the running cost of the heat recovery chiller and 48% of the running cost of the chiller/boiler system
• VRV system has the lowest capital cost. The capital cost of the VRV system is around 65% of the capital cost of the heat recovery chiller and around 78% of the capital cost of the chiller/boiler system
• VRV system has the lowest GHG emissions. Although, the chiller/boiler has lower GHG missions than the heat recovery chiller but its running cost is higher. Note that this is true for Canberra because the gas tariff is high but if the project is located in Melbourne for example where the gas tariff is almost half the tariff in Canberra, then the running cost of the chiller/boiler system would be less than the running cost of the recovery chiller.
• Chiller/boiler system has higher annual energy consumption than the heat recovery chiller but less GHG emissions. The reason for that is the natural gas produces less GHG emissions per MJ compared to the electricity.

Therefore, the total savings in the first year if VRV system is used instead of 4-pipe heat recovery chiller will be $149,698.90.

We further carried out life cycle cost analysis to estimate the present value of the total cost of each option over 20 years, which is the expected service life of all the three options. Our analysis showed that the heat recovery chiller will cost $1,783,908 over 20 year service life, while the chiller/boiler system will cost $2,132,393 and the VRV System will cost only $1,121,026. If the VRV system is used, it will save $662,881 over its entire 20 years service life compared to the specified 4-pipe heat recovery chiller.

Based on the above savings of the VRV system, we recommended to our client reconsidering this system for their facility. We have roughly examined the dimensions of the VRV outdoor units and found that 20 outdoor units with 28 kW nominal cooling capacity each, will fit in the plantroom apace available on the roof. These 20 VRV Units give much better redundancy than only two heat recovery chillers. For example, if one of the heat recovery chillers is faulty or shut down for maintenance, the air conditioning system will lose 50% of its cooling and heating capacities, while if one of the VRV units is faulty, then the air conditioning system will lose only 5% of its capacity.

If you have a building or a facility under design and you need to make sure the design is efficient, then please contact AESS for an energy efficiency design review to make sure your design does not miss any energy conservation opportunity. Obviously, changing the system design on paper is more sense and more cost effective that changing it after the system is installed.

To save energy when we use the systems and equipment in the building, we need to know how these systems operate and how they waste energy. Whether the system is an air conditioning system, hot water system or any other type of system, it should be run efficiently by knowing its principal of operation and how it is controlled.

In most of small to medium buildings there is no facility/building manager resident in the building who should have the technical knowledge and expertise and can understand the operation of these systems and run them efficiently and therefore, this responsibility lay on the building owner and the tenants. We conducted energy audits for a lot of small to medium buildings and in many cases; we found that the users waste energy without knowing they do that. In other cases, we found that some systems and equipment have energy saving functions in their controls but the users did not know about them and they did not use them.

We appreciate that most of the users don’t have that technical knowledge to understand how all the systems in the building operate but the operation principals of these systems can be explained to them in a simple language by an experienced person to help them save energy and reduce their energy bills.

Therefore, what should the building owners and tenants do to better know their building systems and run them more efficiently?

• Engage a qualified energy auditing company to conduct a comprehensive review for all the systems and equipment in the building and to explain to you how these systems operate and how to use them efficiently. In addition, the energy auditing company will provide you with recommendations for energy conservation measures.
• Ask your service agent who services your building systems regularly to sit with you for a cup of coffee and explain to you how these systems operate and how you can run them more efficiently.
• Read the operation manual of these systems when you have time. These manuals usually provide description for the operation of these systems and how to control them. In many cases during our energy audits, we found energy saving functions built-in in the controls of these systems, which can be activated through the user interface but the users did not know about them.

For a comprehensive review and energy audit to your building systems, please contact AESS.

As a building owner or a tenant, it is important for you to reduce your expenses to increase your profit. Energy prices (gas & electricity) continue climbing every year and became substantial expenses for the building owner and tenants. In addition to reducing the energy bills, reducing the energy consumption reduces the emissions of the greenhouse gases that lead to global warming and climate change and thus preserve the environment for the coming generations.

Replacing an old water chiller for the air conditioning system with a brand new chiller will definitely save energy but how to maximize the energy savings and money savings by this measure? Replacing a chiller is a big investment for the building owner and they need to make sure they get the best return on investment from this measure.