Indirect Evaporative Cooling for Clean Data Center Air Control
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Solution Overview
Problem
Current cooling systems for enclosed spaces, such as data centers, face challenges including high energy consumption, dust accumulation, contaminant transfer, and limited climate suitability due to existing evaporative and adiabatic cooling methods, which often require maintenance and backup equipment.
Innovation Solution
A combination of a direct evaporative cooler (DEC) in a scavenger air stream and an air-to-air heat exchanger (AAHX) is used to indirectly and sensibly cool process air, with a pre-cooler coil and a direct expansion (DX) cooling system for enhanced performance in hot and humid climates, reducing the need for backup chillers and improving humidity control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by stationary object
If conventional direct evaporative coolers are used to cool enclosed spaces, then energy consumption is reduced compared to vapor compression systems, but the supply air temperature becomes difficult to control and may be excessively humid
Solution Approach 1:
The cooling system is segmented into two independent streams: a process air stream that is recirculated and cooled to supply air, and a scavenger air stream that is evaporatively cooled and used to cool the process air stream through a heat exchanger. This segmentation allows independent control of each stream's temperature and humidity, solving the temperature control problem while maintaining energy efficiency.
Solution Approach 2:
A heat exchanger acts as an intermediary between the scavenger air stream and the process air stream. The scavenger air stream indirectly cools the process air stream without direct contact, allowing temperature control while preventing humidity transfer from the evaporative cooler to the supply air.
2Use of energy by stationary object
If direct evaporative coolers are used, then energy efficiency is improved, but contaminants including bacteria, algae, fungi can proliferate in the water system and transfer into the supply air stream
Solution Approach 1:
The heat exchanger serves as a physical barrier and intermediary that prevents direct contact between the scavenger air stream (which contacts the evaporative water system) and the process air stream (which becomes supply air). This eliminates the contamination pathway while preserving the energy efficiency of evaporative cooling.
Solution Approach 2:
The air handling system is divided into separate contaminated and clean zones. The scavenger air stream that contacts the evaporative cooler is completely separated from the process air stream that supplies conditioned air to the enclosed space, preventing contaminant transfer while maintaining energy efficiency.
3Adaptability or versatility
If evaporative coolers operate in hot and humid climates, then cooling capacity is sufficient, but the system is limited to temperatures no lower than the wet bulb temperature of the air stream
Solution Approach 1:
The system separates the evaporative cooling function (applied to scavenger air) from the supply air cooling function (applied to process air). This allows the evaporative cooler to operate at its optimal wet-bulb temperature while the heat exchanger transfers cooling to the process air stream, enabling temperatures below the wet bulb limit.
Solution Approach 2:
The heat exchanger mediates the cooling process by transferring thermal energy from the cooled scavenger air stream to the process air stream. This indirect heat transfer mechanism enables the process air to be cooled to temperatures lower than the wet bulb temperature of the incoming air, expanding climate adaptability.
4Use of energy by stationary object
If air-side economizers are used to reject heat from the data center, then energy consumption is reduced, but dust accumulation and air contaminants increase inside the space
Solution Approach 1:
The heat exchanger acts as an intermediary that allows heat rejection using outdoor air (scavenger air) without direct mixing with the indoor process air. Outdoor air can be used for cooling when conditions are suitable, reducing energy consumption, while the physical barrier prevents dust and contaminants from entering the enclosed space.
Solution Approach 2:
The system segments outdoor air handling from indoor air handling. Outdoor scavenger air is cooled evaporatively and used only to cool the recirculated process air through the heat exchanger, never directly entering the enclosed space. This eliminates contaminant introduction while maintaining the energy-saving benefits of economizer operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution reduces energy consumption, minimizes dust and contaminant transfer, and expands the cooling system's climate suitability, providing efficient and flexible cooling with reduced maintenance needs, while maintaining indoor air quality.
Implementation Method 1
a direct evaporative cooler (DEC) in a scavenger air stream... used to indirectly and sensibly cool process air
Implementation Method 2
conventional evaporative/adiabatic coolers, including indirect/hybrid designs for space cooling
Implementation Method 3
an air-to-air heat exchanger (AAHX) exchanging heat between the scavenger air stream and a process air stream
Implementation Method 4
exchanging heat between the scavenger air stream and a process air stream
Implementation Method 5
a pre-cooler coil and a direct expansion (DX) cooling system for enhanced performance in hot and humid climates
Data Source
AI summary
Systems and methods for controlling temperature in an enclosed space can include an air-to-air heat exchanger (AAHX) and a direct evaporative cooler (DEC). The DEC can be located in a scavenger or outdoor air stream such that the DEC cools the outdoor air, which is then used to cool or reject heat from a process air stream passing through the AAHX. In an example, the AAHX can be a sensible wheel. In another example, the AAHX can be a counter-flow flat plate. The system can operate in various modes, including an economizer mode and an evaporation mode, depending, in part, on the outdoor air conditions and a load on the system. In some examples, the system can include a DX coil to provide additional cooling to the process air in another operating mode.