Description:

Multi-tenant commercial office buildings often include small server rooms scattered throughout the building that house the tenants’ computer servers. These spaces are typically unoccupied, and are often cooled by a small dedicated DX cooling fan coil unit. For many large office buildings, these spaces are located near the core of the floor plate, making it difficult to locate a small dedicated condensing unit outside to reject the heat from the fan coils. For these spaces, heat is typically rejected to a building fluid cooler/condenser water loop dedicated for the server rooms. With this system, heat is ultimately rejected to the outdoors through the building’s cooling tower, or a dedicated fluid cooler. Fluid coolers are often used in cold climates, where the cooling tower is drained during the wintertime. They usually utilize a glycol/water mixture as the fluid, to prevent freezing during cold outside air conditions. Energy savings can be realized by replacing the server room fan coils with units that have higher-efficiency compressors and waterside economizer capability. These units would have two cooling coils: one using condenser/fluid cooler water to cool the air (first stage cooling), the other using refrigerant to cool the air (second stage cooling).

Special Considerations

• The reduced mechanical cooling energy usage due to the waterside economizer must be weighed against the increased energy usage of the fluid cooler/cooling tower to cool the water to a lower temperature and the added air pressure drop due to the second cooling coil. It may be more efficient to have a higher water loop temperature setpoint at warmer outside air conditions (for DX cooling at the server room units), and a colder water loop setpoint at cooler outside air conditions (to allow waterside economizer cooling at the server room units).
• Tenant server room HVAC equipment is often owned and operated by the tenants. Implementation of this measure would likely be driven more from the tenants than the building owner.

Estimates for this measure come from the Department of Energy's Advanced Energy Retrofit Guide.