I am working on an underground building project aiming for LEED NC gold/platinum. Project design feasibility showed that 25% energy saving can be achieved with little effort as the HVAC design parameters were selected taking into account of sustainability and energy saving targets. Project considers district cooling plant chilled water as cooling source with no heating source in the design. District cooling is considered in the design to achieve the energy saving target as the project location pushed the client to not to go with water - cooled chillers due to limited water availability.
We opted for option 2; reasoning being the point cap when considering option 1 and our targeted point for EAC1.
Our project’s design parameters are quiet efficient in terms of envelope (don’t think it will affect the saving as the project building is almost 80% underground), efficient HVAC systems (ERU units with FCUs and with district chilled water system). Due to un-availability of DES details, we considered 4.4 as plant COP for proposed case as per the assumptions referenced in ‘Treatment of District or Campus Thermal Energy in LEED V2 and LEED 2009 – Design & Construction’. Baseline is done based on ASHRAE 90.1-2007 with System 8 and chiller of 6.1 COP. The results are not as expected showing a different pattern. I have some questions which are listed below.
1. Is there any way to model the proposed system to account for cost of the energy source i.e. to account for the impact of chilled water/energy cost alone?
2. Comparing a water cooled chiller with 6.1(COP) in Base with 4.4 plant COP for proposed doesn’t look fair. When we calculated the overall plant COP for Base case it comes around 5.5 a much higher COP than 4.4(proposed plant COP). But in actual cases, district chilled water plant is much more efficient than a standalone chiller. This questions the performance of the district chilled water systems and opting out from such options. Correct me if I am wrong.
3. In general, water cooled chillers are not a feasible option in very hot and humid condition. Projects will opt for air cooled chillers or district energy systems in these areas. A COP of 6.1 with water cooled centrifugal will prove both the options less efficient in terms of energy savings. Correct me if I am wrong.
4. I am modelling my project based on the document referenced above. Is there any other option or method which is accepted by USGBC to do simulation with district chilled water systems.
5. What are all the areas, I need to check in my energy model to make sure of the system and plant side parameters for this scenario?
I can understand my questions might take lot of your time. But you suggestions and comments will help me a lot.
Thanks a lot for your time.
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