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Multipurpose Facility

 

AZ DEMA – WAATS Administration/Flight Training/Dorms – L4500, Marana, AZ.

Building Description

L4500 is a critical 24/7 Flight Simulator Training Facility with one supporting Data Room, Administrative Offices, Training and Conference areas and Dorm Rooms to house the troops being flight trained. As would be expected of such a facility, the HVAC requirements of the various areas differ significantly.
The HVAC system consists of:

  • The central plant included two water chillers with associated pumps and cooling towers, and is primary-secondary pumped and piped. All pumps were constant volume, and the cooling tower fans were equipped with variable frequency drives.
  • 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.
  • 8 central station air handling units, one of which is constant volume, the VAV air handling units serves the VAV boxes in the office/training areas. All air handling units used inlet guide vanes for capacity control, and all were equipped with 100% outside air economizers.
  • 75 room fan coil units located in each Dorm room.
  • 4 chilled water/hot water computer room a/c (CRAC) units serving the Data Rooms
  • Incomplete direct digitally controlled EMS.

Project Problems/Issues

  • 30 year old central plant, no automation or energy conservation capabilities, lack of redundancy and excessive maintenance costs
  • Dilapidated air handling units, most equipped with inlet guide vanes. Most control valve, damper and inlet guide vane actuators were inoperable
  • 2-pipe system serving the Dorm Rooms resulted in constant comfort complaints
  • General lack of energy management capabilities
  • Inability to provide accurate and repeatable temperature and humidity control to the newly installed Data Room serving the newly installed Simulator

Project Overview

Energy-Environment-Economics provided a detailed engineering study and report of 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 $1,000,000 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 modernization and automation of the chilled water central plant and the air distribution system. Also, project coordination and test & balance services were provided in addition to the commissioning and optimization services provided.

Solutions Provided

The study quantified in great detail the extent of deterioration of the HVAC system, identified existing maintenance deficiencies and generated schematic designs with cost estimates to repair and modernize the system. These estimates were used to provide the economic justification to move the project forward, as energy conservation potential, reliability concerns, and avoided maintenance costs made modernizing the HVAC system fiscally responsible. However, the critical nature of the facility and the required scope of work to implement the recommendations mandated precise scheduling and provision of temporary utilities.

So in addition to providing the final construction documents, Energy-Environment-Economics also provided project coordination services, eliminating the need and additional cost for a general contractor. Preparation of the construction documents was critical to meeting the project’s energy conservation goals, maintaining the schedule and meeting budget requirements, so Energy-Environment-Economics worked closely with equipment suppliers to generate precise pre-purchase specifications for the new central plant equipment and air handling units. To reduce construction costs, the new air handling units were designed to utilize the existing roof curbs, eliminating any roofing costs or potential risks.

Because the facility’s loads had increased significantly over 30 years, and the central plant was going to incorporate a hydronic economizer capability, the air handling units were increased in airflow and coil size and capacity. Larger coils result in lower pressure drops and required fan HP, but also result in lower velocities and closer approach temperatures that extend the potential for operating in hydronic economizer mode. The air handling units were equipped with factory installed variable frequency drives, and new pressure independent control valves were installed inside the air handling units’ pipe vestibules to protect them from the weather.

These specific control valves were part of the overall central plant modernization plan, and were important to final chilled water coil selection criteria. Because low chilled water system temperature differentials (DT) result in capacity loss and increased energy costs, and because redundancy was critical to the uninterrupted operations of the facility, the valves and chilled water coils were carefully selected to compliment the new central plant design. The design intent was to provide 100% redundant capacity in the chillers, pumps and cooling towers, and the design day load was calculated exactly and did not contain any typical safety factors, so the chilled water system’s correct operation – at a minimum maintaining the design (12degrees) DT - was of the utmost importance.

Demolition of the central plant began after a temporary air-cooled chiller, with power provided from abandoned circuits, was installed to provide temporary cooling to critical areas. Once demolished, construction of the new state of the art variable flow primary only chilled water central plant began. Three new chiller modules were provided, and a dual circuited fluid cooler was installed to serve the dual purpose of heat rejection during chiller mode as well as act as the hydronic economizer. Eight new automated control valves were added, as was a flow measuring station and bypass valve intended to ensure a minimum flow rate to the chiller during low load periods if needed.

Because each of the fluid cooler’s circuits were sized for a design day, and that the entire tube bundle was to be used during hydronic economizer( heat exchanger) mode, a chiller low flow condition was unlikely. In addition to the large surface area of the fluid cooler’s tube bundle, the condenser water pumps were equipped with variable frequency drives that would modulate to provide and maintain the chilled water system’s differential pressure setpoint during heat exchanger mode, as the chilled water/condenser water system is now one closed loop. During heat exchanger mode only the condenser water pump operates, variably, reducing flow rates and velocities thru the tube bundle. The extended surface and reduced velocities create conditions where we have achieved 2-degree approaches between ambient wet-bulb (WB) temperatures and leaving “chilled” (in heat exchanger mode) water temperatures. In a typical open cooling tower/plate/frame heat exchanger/constant volume condenser water pumping system a 10-degree approach would be more common.

Obviously this capability greatly extends the hours when economizer mode is available to be used, even considering the sensitive nature of the Data Room’s temperature and humidity requirements. It also allowed us to stage – if needed – one of the two air handling units dedicated to the Simulator Bay on or off according to need. Prior to OptimissioningSM both existing air handling units operated 24/7 in a constant volume mode. Our analysis and carefully selected air handling units now cycle as needed, and were converted into a single zone VAV configuration to save even more energy.

To complement the new HVAC system’s capabilities, new EMS algorithms were written and all vital system setpoints were optimized for maximum energy efficiency. Innovative reset schedules for chiller and heat exchanger modes of operations were devised and implemented, and Energy-Environment-Economics Test & Balance services were used to optimize the control setpoints and reset schedules of the air handling units. While not the prime focus of the project, the hot water system was outfitted with reset schedules to save energy but also to reduce the constant complaints of the Dorm occupants due to the either cooling or heating capability of the 2-pipe system serving that area of the facility.

Results

Results of the project reflected an approximate 30% reduction in HVAC related energy costs with improved reliability and space conditions. After commencing in November of 2006 and being released to full control March of 2007, the project has had an immediate impact on energy consumption and utility costs. Space comfort has improved, including the Data Rooms’ ability to maintain temperature and humidity within specified limits.

Considering that only the HVAC system was OptimissionedSM, and that lighting and approximately 100 HP of hydraulic pumping (serving the flight simulator) capability was left untouched, these results are exceptional. Due to the concerted efforts of the OptimissioningSM team, including Mr. Jeff Seaton (Energy Manager, State of AZ., NGB), the HVAC system was made much more efficient and reliable. The following charts were created from actual utility data provided by Mr. Seaton, and generated by his Utility Manager software. The new Flight Simulator and Computer Room was added in 2006, note the increase in energy consumption. The OptimissioningSM project was completed in 2007.

kWhChart

 

 

 

 

      Copyright Energy Environment Economics - 2003