Seasonal Free Cooling for University Data Center

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Sponsor
Team Name Free Breeze Brothers
Duration Summer - Fall 2017
Faculty Adviser Dr. Steve Beyerlein
Client Scott Smith
Team Members
  • Kevin Marwan
  • Justin Hinrichs
  • Alex Leppek
  • Frank Guo

The design and implementation of a free cooling system to chill water for the UI campus, during the winter months, is the main goal of this project. By considering system economics, environmental impact, and overall optimization, among other factors, the designed system will provide an efficient, cost-saving method of cooling water through the use of cold ambient air.

Problem Definition[edit]

Currently, to chill water for campus, the University uses vapor-compression chillers throughout the entire year. While this process is able to handle the load, this type of system experiences problems during the winter time. The main issue is with the evaporative cooling towers, which are prone to ice build-up. The reason for this is that the cooling water is directly exposed to the freezing conditions. When this build-up happens, damage may occur to the system, so ice must be manually removed from the cooling towers. There are a few methods for ice removal, but none of them are very efficient and all require human intervention into an otherwise automated system. Other than freezing, which interrupts system operation and is hard on equipment, other issues include working fluids freezing within pipes and flash freezing of humid exhaust air.

Background[edit]

Free cooling, also known as enterprise cooling, involves utilizing relatively low temperature ambient air to cool a working fluid within a system. Conversely, a conventional method for completing the same task would be to use refrigeration cycle chiller. However, free cooling is enticing for a few reasons. First, air is a working fluid within the system that does not have an associated monetary cost, hence the name "free" cooling. Secondly, operational costs for a free cooling system are generally lower, due to the fact that pumps and fans are the only main components that must be powered. In a conventional system, compressors and cooling towers, along with pumps, produce a much higher power demand while operating. Finally, a free cooling system can be a completely enclosed system, protecting it from the environment and eliminating the need for make-up water and continuous chemical treatment of the system.

Deliverables[edit]

For this project, the final product will be a complete design and analysis, with supporting calculations, of a free cooling system to chill water for the UI campus during the winter season. Once our design has been approved, the University will purchase and install the components outlined in our design to create a full scale, operational free cooling system.

Specifications[edit]

2017 FreeBreezeBrothers Specs.JPG

Project Design[edit]

Potential Heat Exchangers for System
Heat Exchanger Comparison
Decision table
Decision Selection Justification
Conventional Cooling Tower vs Dry Cooler Dry Cooler The dry cooler meets all of the specifications for this project. These include: 1) Keeping the coolant from freezing. 2) Keeping the coolant from being exposed to the environment. 3) Utilizes cold ambient air or “Free Cooling” to chill coolant instead of refrigeration cycle.
Shell and Tube vs Plate and Frame Heat Exchanger Plate and Frame The plate and frame heat exchanger is a much better fit for our project due to its efficiency, space requirement, and ability to be easily modified, by adding or removing plates, for different cooling loads. Also, it is much easier to clean and maintain opposed to a shell and tube.
Conventional Pump vs VFD Pump for Coolant Loop VFD Pump Due to the fact that our systems uses ambient air, which has a large temperature range, our system will require a VFD pump to vary the flow through the coolant loop i.e. less flow when ambient temps are lower and more flow when ambient temps are higher.
Water vs Ethylene Glycol in Coolant Loop Ethylene Glycol Since our system will be operating in sub-freezing temperatures, it is important that our coolant fluid does not freeze. An ethylene glycol solution has a lower freezing point than water, so this added safety factor against freezing makes sense for our system.
Free vs Forced Convection in Dry Cooler Forced Convection Based on our calculations, forced convention is much more feasible for the system. With free convection, the size of dry cooler necessary is very large and expensive. Additionally, forced convection gives us much greater control of system efficiency and performance.
Top vs Bottom Mounting of Dry Cooler Fans Top Mounting For our system, it makes more sense to have the bottom side of the heat exchanger open and have the fans draw air through the system. All we will have to add is a method for protecting the fans from ice and snow. Lastly, most manufacturers produce the dry coolers with top mounted fans, and it would likely be an added cost, if even possible, for underside mounting of the fans.
New PFHX vs Repurposing Old PFHX Repurpose Old PFHX Because we have access to a PFHX in good condition that we can reuse, it was a simple decision to go this route instead of buying new.
System Schematic