Commissioning of Hospitals for Occupant Health and Energy Reduction

Transcription

1 Commissioning of Hospitals for Occupant Health and Energy Reduction Jean O Brien Gibbons #1, John D Villani #2 # Grumman/Butkus Associates 820 Davis Street, Evanston, IL, 60201, USA 1 jgibbons@grummanbutkus.com 2 jvillani@grummanbutkus.com Abstract In addition to providing for occupant comfort, the heating, ventilating, and airconditioning (HVAC) systems serving hospitals aim to provide an indoor environment that enhances patient health. To this end codes and standards define many aspects of hospitals' HVAC systems: temperature and humidity requirements, filtration levels, minimum airflows, air pressure relationships between adjacent spaces, etc. These stringent HVAC requirements contribute to hospitals high energy use as compared to other types of facilities. Reducing the energy consumed without sacrificing patient safety and health has resulted in more complex HVAC and control systems, making the likelihood of all the systems working as-intended, without commissioning, less likely. Many hospitals management teams are, however, reluctant to spend the money on commissioning. This presentation highlights some real-world patient health and energy reduction benefits of problems that were identified and corrected as part of commissioning and describes the value of these benefits is a way that hospital management teams can understand. 1. Introduction Grumman/Butkus Associates (G/BA), a consulting firm in Evanston, Illinois just outside of Chicago, has numerous examples of healthcare HVAC systems that would not have worked as-intended if commissioning had not taken place. In addition, many engineering and construction-related associations such as the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) and U.S. Green Building Council (USGBC) encourage commissioning as a means to a successful project. Even so, many facility Owners remain reluctant to spend the perceived extra money required for commissioning. From their point of view, if the design documents are good and the construction team successfully completes their contractual duties, including providing a fully functioning temperature control system, why should commissioning be necessary? The American Society for Healthcare Engineering of the American Hospital Association (ASHE) states in their Health Facility Commissioning Guidelines[1], that this reluctance to provide adequate funding for commissioning frequently comes from the C-level, the leadership team

2 commonly consisting of a chief executive officer, chief operating officer, chief financial officer, chief nursing officer, and others with similar titles. Facilities management professionals often lack the skills to effectively communicate the benefits of commissioning to the C-level, resulting in an uninformed decision by the C-level to remove the funds needed to support commissioning from a project budget. This paper describes a major hospital commissioning effort. The identified problems, their solutions, and benefits of the corrections described. In addition, a monetary value of the benefits is calculated. Benefits fit into one of two categories; energy use reduction or improved patient environment. The benefit of energy use reduction is easily documented by lower energy use costs. The benefits of the improved indoor environment are more difficult to quantify. The indoor environment can enhance or detract from patient health and recovery outcomes; however, measurement of these benefits is difficult. For the purpose of this paper, it is assumed that patients outcomes are not jeopardized and may be enhanced if the HVAC systems are performing as intended and satisfy all applicable codes. 2. Case Study Overview A Chicago area hospital finished the construction of a 5,200 m 2 surgery addition at a construction cost of $35,000,000. The new addition houses 15 operating rooms (ORs); six general ORs and nine cardiac ORs. The original construction project did not include commissioning. After 18 months of operation, increased patient infection rates after surgeries performed in the new ORs were documented. An investigation of items affecting infection rates, such as OR staff processes and procedure and cleanliness and performance of the HVAC system found that at times the OR temperature and humidity levels were outside of the code-required ranges. The hospital infection control personnel were particularly concerned about the high humidity levels, so a project to determine the cause and subsequent correction of the temperature and humidity fluctuation was initiated. 3. HVAC System Description Two 23,600 l/s air handling units (AHUs) serve the 15 ORs. Each AHU consists of, in the order of airflow, maximum outside air (OA) dampers in parallel with a minimum OA damper and an airflow measuring station, prefilters, secondary-filters, integral face and bypass vertical (IFB) steam preheat coil, humidifier, chilled water cooling coil, glycol/water secondary cooling coil, single supply fan with variable frequency drive (VFD), hot water reheat coil, HEPA final filters, isolation dampers and dual return fans with VFDs. During normal operation the AHUs operate in parallel at 50% of full airflow. If either unit fails, cross-connect dampers shut and the airflow in the other AHU increases to provide 100% airflow to all ORs. In addition, the

3 system has a smoke exhaust mode in which all return air is exhausted to outside and the AHU operates with 100% OA. The AHU components are, therefore, sized to operate at 100% OA on a Chicago winter design day of C and summer design of 35 C dry bulb with 23.8 C wet bulb, so the capacities of the preheat and cooling coil are over twice the capacity required for normal operation at 11,800 l/s or 22% outside air. The space temperatures for the general ORs can vary between 20 C and 22.7 C, but the cardiac ORs can operate with space temperature as low as 15.5 C. Space temperature and humidity design criterion is summarized in Table 1. Table 1. OR Temperature and Humidity Design Criteria Cardiac ORs General ORs Space Temperature 15.5 C to 25.5 C 20 C to 22.7 C Space Humidity 40% rh to 60% rh 40% rh to 60% rh Each of the cardiac ORs is served by a supply variable air volume (VAV) terminal unit with hot water reheat coils followed by a booster steam humidifier. Return air has a modulating damper and a duct-mounted return air relative humidity sensor. Each of the general ORs have supply VAV terminal units with reheat. Return air has a modulating damper and a duct-mounted return air relative humidity sensor. There are no individual booster humidifiers serving the general ORs. 4. OR Space Humidity Problem At the beginning of the commissioning effort, the humidifier valves at the two main AHUs were controlled from the single common return air relative humidity based on the following reset schedule: as the common return air humidity rises from 42% to 58%, the common return air humidity setpoint linearly varies from 58% rh to 42% rh, and the cardiac OR booster humidifiers were not being used. Conceptually, this reset schedule will maintain the common return air relative humidity near the middle range (about 50% rh). The problem with this approach is that both the cardiac and general ORs are served from the same AHUs and the cardiac ORs space temperatures can be set as low as 15.5 C. If the majority of ORs are at 21 C/50% rh, any cardiac OR with a temperature below about 19 C will have an unacceptable humidity level above 60% rh. Figure 1 is a psychometric chart that illustrates this OR humidity control problem. The RED line connects the supply air conditions delivered to the ORs to the common return air condition, depicting the range of air conditions that may occur within the ORs. The YELLOW highlighted area shows a room temperature range of 15.5 C to 16.6 C, illustrating a cardiac OR

4 operating at the low end of its temperature range. The 60% rh curve is illustrated in green. This graph shows that any cardiac OR in which a temperature at or below about 16.5 C will have humidity levels above the maximum allowable 60% rh. Fig. 1 ORs Relative Humidity Chart The original OR humidity control sequence was based on a slight misinterpretation of the code. The Illinois Department of Public Health requires a minimum winter humidity of 40% rh, and a summer maximum of 60% rh. In other words, in the winter when humidification is required, a humidity level of 40% is acceptable. Humidifying to 50% is unnecessary and will result in higher energy consumption. A revised sequence of operation for humidity control was developed: Monitor all individual ORs return air relative humidity levels. Modulate the AHU humidifier valves to maintain the OR with the lowest relative humidity at 40% rh. If one or more general OR is less than 40% rh, modulate the AHU OR valve open until all general ORs are at 40% rh, or any given Cardiac OR is at 58% rh. Modulate any given Cardiac Cath OR s individual humidifier valve to maintain that OR return air relative humidity at 45%. Because only the cardiac ORs have booster humidifiers, it is not always possible to maintain the general ORs at a minimum of 40% rh without overhumidifying a low temperature cardiac OR. Per the direction of the hospitals

5 infection control personal, elimination of high humidity levels was to take precedent over low humidity levels. Implementation of this revised sequence will result in supply and return conditions along the orange line in Figure 1, so the highest humidity level obtained in a 15 C OR will be about 50% rh. Commissioning functional performance testing after the corrective action was taken confirmed these result. 5. OR Pressurization Problem The ORs have a high air change rate (30 ach), so to reduce energy use each OR has a reduced-airflow unoccupied mode (15 ach). During commissioning testing, it was found that the ORs were, at most times, positively pressurized as required by codes and for infection control. When the ORs switched from occupied to unoccupied mode, however, they became negatively pressurized for a period of time. Figure 2 summarizes data for one of the ORs that illustrate this problem. Fig. 2 OR Pressurization This was caused by the VAV box damper position adjusting immediately upon implementation of unoccupied mode. The return damper, however, responded slower so for a time the return airflow was greater than the supply airflow, resulting in the OR negative pressurization. To correct this problem, the speed of the supply and return airflow changes was slowed to more closely match the rate at which the supply VAV box responds. This allows time for the room pressure sensor and return

6 damper to adjust, so now positive OR pressure is maintained at all times. After the adjustments were made, maintenance of positive pressure during changeover was confirmed via commissioning testing. 6. Economizer Cycle and Integral Face and Bypass Coil Problem Figure 3 is a partial diagram of the AHU and a snap shot of the positions in which the economizer and integral face and bypass (IFB) steam preheat coil were found on a -1.0 C day: Outside air temperature: C Mixed air temperature: -1.0 C Max and min outside air dampers: 100% open Return air dampers: closed Preheat steam valve: 100% open IFB dampers: 0% open Mixed air temperature: -1.0 C Humidifier valve: 40% open Supply airflow: 9,310 l/s Cooling coil discharge air temperature: 11.8 C AHU discharge air temperature: 14.0 C Fig. 3 AHU Diagram This data shows the AHU operating at 100% OA. The fixed minimum OA requirement is 2,560 l/s, so with a supply airflow of 9,310 l/s, the mixed air temperature is about 15.8 C. Based on the OA temperature, the maximum OA damper should, therefore, open to allow just enough additional OA to maintain the 11.7 C cooling coil discharge air temperature. In this correct scenario, no active heating would be required. So what is driving the OA

7 dampers open, thus requiring heat and more humidification than would be required if the economizer was operating correctly? The following items were identified: The IFB steam preheat coil valve is programmed to be 100% open whenever the outside air temperature is 4.4 C and below. The IFB damper goes fully closed to the coil unless additional heat is required, at which point the damper will modulate. With the steam valve open 100% and the integral bypass dampers closed the steam coil increases the supply air temperature by 12.8 C. In summary, the sequence is energizing the IFB steam preheat coil at an outside air temperature of 4.4 C and below and increases the discharge air temperature higher than required. Since no chilled water is available in the winter, the only way to cool the air is to bring in more outside air. To determine how to proceed with adjustments and revisions to the IFB coil sequence, the design intent of the coil selection and sequence of operation must be understood. The design engineer reported that the IFB coil manufacturer requires the steam valve be 100% open whenever the outside air temperature is 4.4 C or less or the warranty would be invalid. This proved to be a misinterpretation of the manufacturer s requirements. The statement applies to IFB coils used in 100% OA system. If fact, the manufacturer required that the steam valve be 100% open whenever the air entering the coil in 4.4 C or less, and in this system the air entering the preheat coil in the warmer mixed air. In addition, the IFB coil was sized to handle the worst case condition, 100% outside air for smoke evacuation mode, so the coil and its steam valve are oversized. As a result, with the IFB bypass dampers closed the supply air temperature increased across the IFB coil. Figure 4 summarizes some critical temperatures that illustrate the problems with the system. These temperatures correspond to a unit operating at the same airflow as shown in Figure 3; 9,310 l/s total airflow with 2,562 l/s our outside air assuming a return air temperature of 22.2 C. Figure 4 reveals that if the steam valve remains closed, no heat is required until the OA temperature is below C; secondly, with the steam valve open and no chilled water available, the maximum OA dampers must open to cool the overheated air. The following changes were made to the economizer cycle and IFB steam preheat coil control logic. The IFB coil steam valve was changed to open whenever the mixed air temperature entering the coil was 4.4 C or less. Above 4.4 C, the steam preheat valve modulates to maintain the cooling coil discharge air temperature of 11.7 C. These changes resulted in the AHU operating with minimum outside air and maximum recirculating air at most times.

8 Fig. 4 AHU Mixed Air Temperatures 7. AHU Humidifier Control Problem The picture at the right shows the humidifier dispersion tubes in operation on a -1.1 C day. The large quantity of steam introduced into the supply air could not be absorbed. Unabsorbed steam travelled through the chilled water coil, glycol coil, and supply fan, reheat coil into the final HEPA filters. Wetting of the final HEPA filters is an infection control Fig. 5 Humidifier Photo concern due to the potential for causing mold growth in the filters. Functional performance testing revealed that on a call for humidity, the humidifier steam control valve opens to 100% almost immediately, resulting in over-humidification. Then the valve quickly closed. The PID loop for the humidifier valve was slowed, which partially helped. Evaluation of the design revealed that the AHU humidifiers and their single steam control valves were sized for backup mode. Thus in normal lower airflow mode, more steam than can be absorbed is added to the airstream. A normal mode humidifier valve limit of 60% open was programmed. This adjustment coupled with the slower control valve response, allows for steam absorption prior to HEPA filters and reduces humidification steam usage.

9 8. Simultaneous Humidification and Cooling Facilities operations personal reported that the AHUs had problems with water collecting on the floor of the AHU. On a mild 17.8 C day, large amounts of water were observed on the floor of the AHU on the discharge side of the cooling coil. It appeared that cooling coil carryover missed the drain pans and collected in the floor of the AHU. On the same day the following conditions were documented: Outside air temperature: 17.6 C Outside air relative humidity: 56.1% RH Outside air enthalpy: 53,265 J/kg Return air enthalpy: 58,615 J/kg Humidifier steam valve: 92% open Mixed air temperature: 17.8 C Cooling coil valve: 37% open This data shows that the AHU was in economizer mode with cooling active, as it should be given the outside air temperature. The humidifier steam valve was, however, 92% open. This deviated from the specified sequence of operations in which the humidifier was to be inactivated above a 10 C wet bulb. The excess humidity in the air was causing cooling coil carry over, and wasting energy by humidifying air that was later cooled and dehumidified. The specified lock-out of the humidifier when the AHU is in cooling mode was implemented, eliminating condensate collection problems and reducing humidification steam consumption. 9. Static Pressure Setpoint too High The supply fan speed for these VAV AHUs is controlled via a duct static pressure. A starting point for this setpoint was defined in the design documents with the intention that the setpoint would be field-adjusted, The specified balancing called for the duct static pressure to be set to a value that just satisfies the inlet static pressure requirement of the most remote VAV terminal units. Many times, as with this project, this final tuning does not take place. These two AHUs had 100 hp fan motors, so lowering the static pressure setpoint from 1.5 w.g. to 1.0 w.g. saved significant fan electrical energy. 10. Conclusion The cost to the Owner for this commissioning effort was $181,000; $121,000 for the commissioning agent s fee and $60,000 in control hardware and software. The energy reduction and patient health benefits are summarized in Table 2.

10 Problem Corrected OR Space Humidity Control Table 2. Summary of Commissioning Benefits Energy Cost Reduction $3,710 OR Pressurization $0 Economizer and IFB AHU Humidifier Control Simultaneous Humidification & Cooling Static Pressure Setpoint $32,920 Included in OR Space Humidity Control $50,370 $13,690 Patient Health Benefits Elimination of high, (>60% rh) humidity levels Positive pressure at all times as required by OR codes/standards Elimination of AHU HEPA filter wetting/pooling of water in AHU, both risks for microbial growth. The following summarizes the benefits of this case study: The commissioning cost of $180,000 is recovered in 1.8 years based only on the annual energy savings of $100,690. Better OR humidity and space pressure control and consistently satisfying HVAC code requirements may benefit patient health, but definitely limits the risks to the hospital should there be a poor patient outcome. The cost of this project would be dwarfed by a single lawsuit settlement. Hospital HVAC systems are complicated. The design and construction team had 18 months to resolve the humidity control problems. Only through the systematic commissioning efforts were solutions developed. In addition, other problems that would not have been otherwise found were identified. Experience shows that these types of findings during commissioning are typical, and support the claim that commissioning is usually well worth the money spent. Using this benefit versus costs language may be helpful to hospital facilities personnel in explaining the value of commissioning to the C-level management personal. 11. References [1] The American Society for Healthcare Engineering of the American Hospital Association. Health Facility Commissioning Guidelines. Chicago, Illinois, ASHE.