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Data Center

 

AZ DEMA – WAATS CMSB – L4525, Marana, AZ


Building Description

The building is a Mission Critical 24/7 Flight Simulator Training Facility with three full-motion Simulators and two supporting Data (Computer) Rooms. The devices provide flight training to the military of the U.S. and numerous allied countries. Training, office and conference areas make up the balance of the facility.
The HVAC system consists of:

  • The central plant includes three water chillers with associated pumps and cooling towers, and is primary-secondary pumped and piped. The secondary pumps and the cooling tower fans are all equipped with variable frequency drives.
  • There is a hydronic plate/frame heat exchanger to provide “free” cooling during the appropriate ambient conditions.
  • The hot water system is comprised of one boiler and associated pumps and provides space heating used for Data Rooms’ humidity control (reheat) and zone heating.
  • 4 central station air handling units, one of which is VAV and serves the VAV boxes in the office/training areas.
  • 10 chilled water/hot water computer room a/c (CRAC) units serving the Data Rooms
  • Complete direct digitally controlled EMS.

Project Problems/Issues

  • Inability to maintain temperature and humidity control in the Data Rooms
  • Central plant was suffering from reverse decoupling due to original design
  • All three 110-ton chillers had 30,000+ hours of operation, building peaks at 110 tons
  • Inability to utilize the existing waterside economizer
  • Outrageous (approximately 6 $/s.f./year) utility costs

Project Overview

Energy-Environment-Economics provided a detailed engineering study and report on the HVAC System’s current (existing) condition and operation including: HVAC system design and DDC system deficiencies, potential energy conservation opportunities with budgeted project costs and economic analysis, and maintenance related operational and efficiency analysis. The result of this study became an approximately $500,000 Energy Conservation Project, including Retro-Commissioning and OptimissioningSM - a combination of HVAC system commissioning and optimization - of the facility. The project included the engineering required for the repair, modernization and automation of the chilled water central plant, the air distribution system, and the critical Data Rooms’ HVAC components.

Solutions Provided

The study identified that the central plant was incorrectly piped and as a result was suffering from “reverse” decoupling. This condition is actually quite common in primary-secondary systems, and under various operating conditions elevates the supply chilled water temperature above what is required. The elevated water temperatures prevented the Data Rooms from maintaining temperature and humidity setpoints that were critical to operations. To compensate, additional chiller systems must be started and operated.

This central plant, intentionally or not, was equipped with 200% redundant capabilities. The Data Rooms were equipped with approximately 200% redundancy as well, yet not even this massive amount of available capacity could overcome the poor design and lacking EMS practices and setpoints. Naturally, HVAC related energy costs were extreme as a result. During OptimissioningSM the central plant was re-piped to eliminate this reverse decoupling, and valves were added to allow the secondary pumps alone to provide the necessary chilled water to the facility during heat exchanger mode of operation.

An inability to ever use the heat exchanger was cited by one consultant as a root cause of the excessive utility costs, and a recommendation to add an additional air-cooled water chiller dedicated to the CRAC units so as to enable the heat exchanger to serve the balance of the facility – and thereby save energy – was provided to the client. Our study and the subsequent OptimissioningSM now allows the chilled water system to operate in heat exchanger mode approximately 4 months of the year, sans any additional chiller, saving energy and wear and tear on the chiller systems.

The study proposed using the available excess capacity of the CRAC units to satisfy the Data Rooms cooling needs during heat exchanger mode, as the warmer than design chilled water temperature delivered during this mode results in elevated supply air temperatures. Ambient conditions suitable for heat exchanger operation are low humidity, making humidity control of the Data Rooms a non-issue at these times. Iterations of the chilled water coils and load analysis of the Data Rooms showed that up to 62-degree supply air temperatures were sufficient to satisfy cooling demands, so the CRAC’s were equipped with staging (on-off) controls that enable units to be cycled as needed to meet need, saving significant energy without affecting temperature/humidity requirements. The analysis also allowed the chiller-heat exchanger wet-bulb (WB) temperature changeover setpoint to be established and optimized for maximum energy efficiency.

All critical EMS setpoints were similarly established and optimized, and all central plant algorithms were revised. Notably, the differential pressure setpoint used to control the speed of the secondary pumps’ variable frequency drives, was eventually lowered from 12.5 PSI to 4 PSI. A combination of factors enabled this dramatic reduction, including an engineering innovation devised to force the CRAC units’ chilled water control valves closed when the unit was off. This capability did not exist previously, and manufacturing engineers had stated that it was impossible to accomplish without a control valve replacement.

To maintain 4 PSI one secondary pump easily satisfies the demand of the facility. At 12.5 PSI both secondary pumps (one is intentionally redundant) operated – usually at 60 Hz – in an attempt to meet the setpoint. All of the electrical loads that were shed as a result of this OptimissioningSM project, chillers, pumps, cooling tower fans, and CRAC units, resulted in outstanding energy savings and corrected all existing deficiencies. The OptimissioningSM project consisted of the study, the engineering, the commissioning, the Test & Balance and the optimization of the facility. Also, project coordination services were provided by Energy-Environment-Economics in addition to the HVAC commissioning and optimization services provided.

Results

Results of the project reflected a 70% reduction in HVAC related energy costs with improved reliability and space conditions. After commencing in November of 2004 and being released to full control March of 2005, the project has had an immediate and staggering impact on energy consumption and utility costs. Space comfort has improved, including the Data Rooms’ ability to maintain temperature and humidity within specified limits. The project has conserved approximately 1.5 million KwH every year in fully automatic operation. The Kw demand has almost been cut in ½, from approximately 620 Kw to 350 Kw.

Considering that only the HVAC system was OptimissionedSM, and that lighting and approximately 400 HP of hydraulic pumping (serving the simulators) capability was left untouched, these results are nothing short of spectacular. Due to the concerted efforts of the OptimissioningSM team, including Mr. Jeff Seaton (Energy Manager, State of AZ., NGB), approximately 2/3 of all major HVAC equipment was turned off, thereby generating these savings, extending the life expectancy of the existing equipment, and reducing their associated maintenance requirements and costs. The following charts were created from actual utility data provided by Mr. Seaton, and generated by his Utility Manager software: Click here to read more.

kWhChart CMSB Demand Chart

 

 

 

 

      Copyright Energy Environment Economics - 2003