firm profile
contact us



Name of Project:
Arizona Heart Hospital

MedCath Inc.
1072 Sikes Place, Suite 300
Charlotte, NC 28277


Building Description:
The Arizona Heart Hospital focuses on the diagnosis and treatment of heart disease. By focusing on the nation's number one killer, the heart hospital offers patients the benefits of advanced technology, associated services and a state of the art facility designed to meet their individual needs. The facility is a 54-bed heart hospital with four operating theaters; Cath and diagnostic labs, ICU, CCU, and an around the clock emergency room serviced by air and ground transportation. The facility is approximately 160,000 square feet multi-story (basement and two floors above grade) building. The heating, ventilating and air conditioning (HVAC) system consists of:
• Constant flow chilled water/hot water systems
• 2 Parallel piped water cooled water chillers, approximately 320 tons each
• 8 central station air-handling units, all of which equipped for variable volume (VAV) using either variable frequency drives or inlet guide vanes, all having both supply and return fans
• Approximately 240 constant and variable volume boxes, most with reheat coils

Project Problems – Issues:
Severe variations in space pressures, and an inability to consistently maintain temperature and humidity control to critical spaces, with all HVAC equipment operating at 100% capacity, and at much lower than design air and water temperatures. A detailed system analysis revealed numerous design and installation deficiencies including:
• Egregious pressure drops throughout the air distribution systems, including at the in-stream style fire/smoke dampers (FSD), equipment duct connections (causing system effect pressure loss), high initial duct velocity design (2500 fpm) and the routine use of 90-degree elbows. Forensic test data also showed that the supply and return fans were not tracking, creating more work for the supply fans that were already at maximum capacity. Our team also assumed a high-pressure drop to be associated with the inlet guide vanes.
• Complete inability to control outside air delivery. The outside air duct was passive, and each air-handling unit was tapped into this “plenum”. Because all air-handling units were VAV outside air quantities varied widely, and there were no provisions for monitoring or controlling the amount of outside air delivered to each unit. Test data showed return air entering the outside air system, creating a worst-case patient care and risk management scenario.

These issues resulted in a general inability to consistently and reliably maintain temperature, humidity, and ventilation requirements throughout the facility. Excessive utility costs were also a consequence of the deficiencies, and combined with the hospital’s primary concern for patient care resulted in the remediation efforts.

Solutions provided by Energy-Environment-Economics:
It was obvious that the air handling units’ system curves needed to be shifted back to design, so an intense analysis of system components began, focusing on the FSD’s and ductwork in the fan room (air handling unit room). Our ability to make changes was largely predicated on space limitations, as this is a fully functional hospital with all the associated infrastructure.

A new pressure drop vs. airflow rating system for the FSD’s was invaluable in evaluating the impact on system pressures, and Energy-Environment-Economics site construction experts were able to identify locations where FSD change-outs were possible. Considering that disruptions in hospital operations were unacceptable, highly accurate construction documentation was required, and produced, to permit major duct modifications during very limited windows of opportunity.

Our calculations determined that substantial modifications to the ductwork and associated components – FSD change-outs and optimissioningSM of all VAV boxes that were previously not commissioned – in addition to:
• a complete system re-balance
• adding airflow measuring stations (AFMS) to all outside air drops (including downsizing of the outside air drops to the (3) air handling units with 100%outside air capability to have sufficient velocity for the AFMS)
• replacing all inlet guide vanes with variable frequency drives on the fan motors
• rewriting the control algorithms to ensure proper supply/return fan tracking were required to alleviate the excessive pressure drops. Additionally, there was extreme duct leakage causing a shortage of airflow to the spaces, a waste of energy, and a drop in system capacity. A duct-sealing program was also established and executed.

Optimization opportunities
Because of the original system design and installation, there were numerous energy conservation opportunities – what our team would call optimization – that could be implemented in concert with the requisite repairs noted above. Our evaluation of utility consumption allowed us to present these opportunities to the owner for consideration. In the end, all measures were accepted and implemented, once again without interruption to the facility's HVAC needs. They included:

Cooling tower:
A new and larger cooling tower was provided, and included a variable frequency drive on the lead cell. The tower was selected to have the ability to isolate one cell from the other and as such was air and water baffled. During this phase of construction, a temporary cooling tower was brought in and connected with flexible pipe, through the pre-existing head pressure control bypass line, to the water chillers. Also, because it was determined at the time that one chiller was sufficient to handle the building load, each chiller was removed from service – swapping the emergency power to ensure reliability – and an epoxy of the end bells and eddy current of the tubes was performed.

Chilled water pumping system:
The system was converted from constant flow to variable primary flow and was not decoupled. Variable frequency drives were added to each chilled water pump, and the control valves at all air handling units were changed from 3-way to 2-way pressure independent type. These valves are extremely rugged and have a variable Cv, assuring accurate flow control regardless of system differential pressures. The system has since approximately doubled it’s Delta Temperature (DT), even though approximately 1/3 of full flow of one chiller is still pumped thru 3-way valves remaining at various locations using fan coil units for spot cooling.

The challenges of varying water flow thru chillers comprise of two main issues. First, the rate of change of the flow must not be too high, and a minimum flow must be maintained at all times. Our chillers were originally selected at a 12-degree DT, and this original selection was the limiting factor for minimum flow rates. The rate of change challenge was difficult to overcome considering the type of chilled water isolation valves selected. Our team eventually solved the issue with control strategies that started pumps prior to traveling the valves, among other things. The chilled water pump variable frequency drives are controlled to maintain a remote differential pressure.

Plate/frame heat exchanger:
The hospital had a pre-existing heat exchanger. It was never used because of a multitude of factors, including the original selection – the tower at 76 degree wet bulb, heat exchanger with a 3-degree approach - had too little capacity and an erroneous control strategy that was based upon return air temperature of a critical air handling unit. Replacing the heat exchanger with one nearly twice as large (in capacity) and using a 1-degree approach, coupled with the new larger cooling tower, will result in “free” cooling for many hours of the year

Direct Digital Control (DDC) system:
A major overhaul of the existing control sequences was required for the remediation measures and the optimization measures. Space pressure and differential pressure sensors were added, relocated static pressure sensors, the AFMS’s, the cooling tower variable frequency drive, the chilled water pump(s) variable frequency drives, and modulating condenser water isolation valves for head pressure control were new hardware items that had to be controlled.

The positioning of dampers serving the air handling units, and controlling the speed of the return fans in relation to the supply fans, was critical in our ability to maintain space pressure control, including making the operating rooms positive to the surrounding Cath areas. The new air handling unit sequences also enabled us to maintain a fixed, constant outside airflow to each air-handling unit. New supply air reset schedules reduce chilled water flow rates and hot water reheat requirements.

New algorithms for wet-bulb calculation and chiller/heat exchanger change-over were added, and our team modified the central plant sequences to incorporate the variable pumping scheme. Control sequences were developed for the cooling tower variable frequency drive for both plate/frame conditions and chilled water conditions, for both one and two chiller operation.

Probably the most important aspect of any of the early analysis, forensic data collection, site space limitation evaluation, ductwork and FSD impact study, and preparation of extremely accurate construction documents was the optimissioning
SM of all air and water systems, and the control sequences serving them. We cannot stress enough how important the optimissioningSM process was to the overall success of the project. The optimissioningSM process was extremely time consuming and could only be accomplished after "normal" operating hours, usually late at night and on weekends when surgeries were sporadic.

The optimissioningSM process was made even more complex because the controls sequences were not developed from scratch, and the fact that many of the critical care areas fail to emergency generators in the event of a power loss. Our professionals were able to successfully commission these systems only because of extensive experience in the controls application field and an excellent understanding of HVAC system dynamics.

The mechanical upgrades project was extremely successful considering all deficiencies that had to be identified and remedied, that the hospital’s normal operations could not be interrupted, that there were onerous space limitations and time constraints, that indoor air quality could not deteriorate, and that heating and air conditioning functions had to be maintained at all times. The team assembled worked at a very high level to achieve the projected and expected results.

Although this project was necessitated by management’s concern for patient care quality and the well being and comfort of the staff, they are currently realizing very substantial savings generated by the application of the optimizing technologies. They are doing so in lieu of the fact that after the remedial work was completed an additional cooling requirement of approximately 75 tons, previously unsatisfied due to pre-existing conditions, was effectively connected to the HVAC system. Utility costs prior to the start of work were approximately $550,000/year, and at last report the hospital was projecting a savings of approximately $150,000/year.

These savings would not have been remotely possible by the application of optimizing technologies alone, it was and is always imperative to remedy existing performance issues prior to application of any energy conservation measures. Eliminating performance deficiencies in any HVAC system will save energy as a byproduct and will improve space conditions and indoor air quality.




"With the combined backgrounds and experience, E3 provides a team that understands the complexities of the entire HVAC system and the Building Automated Control System that runs it."

Rick L. Cox, TBE


      Copyright Energy Environment Economics - 2003