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HomeMy WebLinkAboutAttachment 4 - 2014 WWTP HVAC evaluation DOCUMENT 1 T E C H N I C A L M E M O R A N D U M City and Borough of Sitka Wastewater Treatment Plant, Heating and Ventilation Systems Upgrade - FINAL City and Borough of Sitka Alaska, Department of Public Works David Longtin, Senior Engineer/CBS Chris Wilbur Facility Manager/CBS Mark Buggins, Env. Super./CBS Stephen Weatherman, Muni Eng/CBS Kim Ervin, Proj Mgr/CH2M HILL Patrick Rausch, P.E./CH2M HILL Carl Shank, QCR/CH2M HILL Nick Cavalleri, Cost Est/CH2M HILL PREPARED BY: Jim Sackinger/CH2M HILL REVIEWED BY: Carl Shank/CH2M HILL DATE: March 18, 2014, Revised June 19, 2014 PROJECT NUMBER: 487617 Introduction This memo provides recommendations and a cost estimate for upgrading and replacement of the heating and ventilation equipment and controls at the City and Borough of Sitka Municipal Wastewater Treatment Plant. Recommendations include: 1. Conversion from an oil fired boiler hydronic system to a water source heat pump hydronic system. 2. Replacement of the heating and ventilation equipment which has reached the end of its useful life. 3. Replacement of the HVAC controls system. 4. Upgrades to the ventilation system deemed necessary for health and safety and compliance with current best practice standards. This memo includes four appendices: A. Drawing Mark-ups B. Calculations and Code Review C. Equipment Vendor Information D. Cost Estimate Background This memo summarizes the results of 2 days of site investigations and review of construction documents, applicable codes and standards, shop drawings and manufacturer’s data for the City and Borough of Sitka Wastewater Treatment Plant. It also includes recommendations and costs for upgrades to current building codes and National Fire Protection Association Standards for the equipment and systems being replaced. Other than repairs, most of the mechanical and process systems and equipment are original to the 1980 design. For the heat pump conversion, the State has provided an energy conservation grant to remove the oil fired hydronic heating system and install an effluent heat pump based system. This will reduce energy consumption and allow use of locally generated energy rather than expensive fuel oil. The conversion will require replacement of the existing unit heaters, heating coils, distribution system, and controls. The heat pump conversion operates at a lower 120F hydronic water temperature and requires 3 to 4 times larger capacity air heating coils with more rows that result in a higher air pressure drop. This means it will be difficult to use the existing air handlers as they are optimized for a different pressure, temperature rise, and flow. PREPARED FOR: COPY TO: HEATING AND VENTILATION SYSTEMS UPGRADE - FINAL 2 DOCUMENT The effluent temperature graph in Appendix B shows that in the winter, the effluent temperature gets down to about 47 degrees F, from as high as 57 F in the summer. Excursions below 47F are brief and would result in reduced capacity. A heat pump would be sized for 80% load, so the boiler would supplement in months of November thru March. As shown by the Heat Pump Selections in Appendix C, this is adequate for heat pump use. The pneumatic control system requires frequent calibration and is obsolete and in disrepair. Parts and expertise for pneumatic systems are getting harder to find. The proposed heat pump system is not designed to operate with pneumatic controls and would require a custom controls interface that would be expensive and unreliable. Much of the other equipment, including air handlers, fans, return grilles, louvers, dampers, and some return and exhaust ductwork is corroded from foul air. Rather than replace these intertwined systems separately, there will be cost and efficiency savings by replacing them all at once. Standards Compliance Design changes per the 2012 edition of the National Fire Protection Association (NFPA) 820 “Standard for Fire Protection in Wastewater Treatment Plants and Collection Facilities”, are recommended to increase Plant safety, improve the odor capture, reduce corrosion, and improve indoor air quality. These changes are summarized below. 1. Eliminate recirculation of process air. Change air flow pattern to provide fresh air to the occupied, non- process, and non-odorous equipment spaces, and transfer it to the odor generating spaces before exhausting. 2. Due to the processes on the Grit Mezzanine, that area should be electrically classified per the Electrical Code and NFPA 820. NFPA 820 does not allow recirculation of air in electrically classified spaces. Nor does it allow transfer of air from classified spaces to unclassified spaces. 3. Remove scrubbers from the Mechanical room. Having odorous air scrubbers in the Mechanical room makes that space electrically classified, and triggers a 6 air change per hour NFPA 820 ventilation requirement. The Mechanical room equipment does not meet electrical classification requirements. Removing the scrubbers would eliminate the requirement from that room. 4. Increase outside air ventilation rates to 12 air changes per hour per NFPA 820 to the Grit Mezzanine and the Upper Sludge room to reduce electrical classification from Class 1 Div 1 to Class 1 Div 2. 5. Provide NFPA 820 specified differential pressures between the main Office space and the Process Spaces. Also between classified and unclassified spaces, where possible. 6. Spaces such as Grit and Upper Sludge Thickener cannot be completely declassified by ventilation, and electrical equipment may not meet the NEC requirements for classification. However a complete electrical review is outside the scope of this study. Compliance for Existing Facilities The National Fire Protection Association Standard 820 - 2012, “Fire Protection in Wastewater Treatment and Collection Facilities” can be interpreted in different ways, but in every interpretation, the standard recommends higher ventilation rates and more electrical classification than are currently provided. Achieving full compliance with NFPA 820 is beyond the scope of this report. The Sitka facility has a 30 year record of operation. Extended field measurements have shown that even though ventilation rates do not meet the standard, air in the plant does not reach explosive concentrations, and that OSHA limits for hydrogen sulfide are not exceeded. The NFPA 820 standard does make concessions for existing Plants. Strict compliance for existing plants is not always practical. Judgment may be used, but improvements are still recommended. HEATING AND VENTILATION SYSTEMS UPGRADE - FINAL CITY AND BOROUGH OF SITKA, ALASKA 3 Non combustible and limited combustible construction is called for in the standard, and the existence of wood studs and wood siding may not comply. Compliance is not determined in this evaluation for non-combustible construction. Electrical compliance with design standards is not in this scope except that new installed electrical components will comply. If an electrical classification upgrade is desired, an electrical engineer should be consulted. NFPA 820 Recommended ventilation changes: 1. Provide capability for 12 air changes per hour (ACH) of air with no recirculation in the Grit Mezzanine which includes the Headworks and Screening, and also in Sludge Thickening, and Primary Clarification rooms. 2. Ventilation rate will be at least 6 air changes per hour in these spaces when the space is unoccupied and the supply air temperature is at or below 50 degrees F. 3. The ventilation rate will be manually increased when occupied, and it must be increased automatically to the higher rate when a combustible gas detector detects combustible gas in excess of 10% of the lower explosive limit. 4. Ventilation failure in these spaces shall alarm to a constantly attended location. 5. Provide an air pressure differential, where possible, of 0.1” water column between electrically classified and unclassified areas, and also a differential of 0.1” water column between classified areas and outdoors. 6. The following spaces will have an NEC Electrical Classification of Class 1 Division 2 and shall have Combustible Gas Detectors: a. Grit Mezzanine including Screening and Headworks, b. Sludge Thickener Room, and c. Clarifier Room. Maintainability Improvements: The equipment in the main mechanical room is tightly packed and stacked to the ceiling. Maintenance access does not meet OSHA or the Mechanical Code. Process equipment such as scrubbers and process exhaust shares space with clean equipment such as supply fans, controls and electrical systems, and office area HVAC. Other air handlers also have maintenance access issues, such as the air handler SF-4 over the clarifier basins, and the recirculating air handler SF-3 for the offices. There is no safe way to reach this equipment for maintenance without bringing in scaffolding, which is rarely done. SF-4 over the Clarifier will be removed and replaced with an exhaust fan as described below. SF-2 in the office space will be replaced with a similar, but more maintainable unit further from the wall. There will be less equipment in the Mechanical room. The return fans and scrubbers, and Purafil box will be removed, making space for the new water source heat pump, hydronic pumps, and controls. Energy Conservation: Previous energy conservation measures have resulted in increased corrosion of electrical and electronic equipment in both the offices and the process spaces. Reductions in ventilation air flow have also inadvertently reversed the recommended pressurization relationships between process and non-process spaces. Computers and circuit boards in the Control room and Sample Lab have reduced life expectancy. In the Process spaces, increased recirculation of air has saved energy, but it has also increases consumption of Purafil deodorant media. Current costs for Purafil are $6,000 per year according to staff. HEATING AND VENTILATION SYSTEMS UPGRADE - FINAL 4 DOCUMENT Increasing ventilation as recommended by NFPA 820 increases heating costs. However that can be more than offset if the process space temperature is reduced from 65F to 50F. This by itself results in a 2/3 reduction in heating costs based on Sitka weather data. But limiting the supply air temperature to 50F also allows a 50% reduction in unoccupied ventilation rate per NFPA 820. Combining the 2 this results in up to an 83% reduction in heating costs compared to compliance with NFPA 820 at the current 65F temperature setpoint. Existing Equipment Assessment: Boiler Room Equipment (B-1/B-2/CP-1/CP-2/WH-1/WH-2): Boiler 2 is new and can be reused, but Boiler 1 leaks and should be removed. These cast iron boilers develop leaks after being shut-off for the summer so the remaining operational boiler is kept in hot stand-by and not shut down. The building heating pumps are old but appear serviceable. For Domestic hot water, the 2 each 120 gallon oil fired water heaters are oversized now that they are no longer used for process wash-down. One water heater is leaking and out of service. The other is used for the Sample Lab and a couple of showers, not safety showers, so is still oversized. Hydronic Heating: The distribution piping is copper and all of it should be removed. It is corroded from hydrogen sulfide, including in the office spaces where one wouldn’t expect corrosion. The hydronic distribution piping develops 1 or 2 leaks per year according to the maintenance staff, usually at joints, unions, valves, or at equipment. Unit heaters last about 6 years before requiring replacement due to corrosion. About 1/3 of the 16 unit heaters have been disconnected and have not been replaced. Many of the unit heaters are not required. The process facility is still warm on cold days. South side Load-out unit heaters for example were operational but turned off. A few of the remaining unit heaters were operating, keeping the facility above 60 degrees at an outside temperature of about 25F. Process Area HV (RF-1/SF-1/HC-1/Purafil): This equipment is in fair condition, although dirty, with obsolete controls, and with corroded ductwork. Return Fan RF-1 returns air from the process space above the Grit Screening Area, back to the Mechanical room. After RF-1 there are discharge diversion dampers and about ¾ of the air is diverted to an adsorbant media filter box (Purafil) before it is recycled. After odors are removed in the Purafil media, the return air is blended with outside air in the supply air handler SF-1. Inside the air handler it goes through heating coil HC-1 and supply fan SF-1 before being directed back in to the process space. The other 1/4 of the air from RF-1 goes through the scrubber SC-2 before being exhausted out the roof. The RF-1 fan wheel is dirty but in good shape, but the bearings are making a grinding noise and may be about to fail. The air handler including supply fan SF-1 and heating coil HC-1 are also in relatively good shape, with some dirt and corrosion. The dampers in general are corroded, but operational. Thickening Area Exhaust (EF-1/EF-2/SC-1): Exhaust fans EF-1 and EF-2 return air to scrubber SC-1 before exhausting. EF-2 is operational, but EF-1 was not operational at the time of the visit and alarm light for it was burned out. Maintenance access to the fans is poor. EF-2 draws air from the from the Lower Thickener room, which is not ideal because that area has no odor generation. Air for EF-2 is drawn from other odorous spaces such as grit, sludge, and clarifier areas. This spreads odors over the entire process area. When exhaust fan 1 was operational it drew air from the Upper Thickener room, which has significant odor and mist generation, particularly when the (open top) thickener tank is aerated with compressed air for about 20 minutes out of each hour. The room is not cold, even though the unit heaters have been removed due to corrosion. It appears to be heated by the open tank. Plastic sheeting had been place over the exhaust grille in an attempt to keep the corrosive mist, and washdown water away from the already highly corroded grille. Odor Control Scrubbers (SC-1. SC-2): The scrubbers SC-1 and SC-2 are operational, but are obsolete, poorly located, and have corroded the ductwork and drainage systems. The scrubbers are designed to operate as follows. They use compressed air to aspirate about 2 gpm of about 0.2% aqueous chlorine dioxide solution in to the air as it enters the scrubber which swirls around in the scrubber box with the exhaust air before exiting HEATING AND VENTILATION SYSTEMS UPGRADE - FINAL CITY AND BOROUGH OF SITKA, ALASKA 5 through mist eliminators. The chlorine dioxide used in the scrubbers is effective in removing hydrogen sulfide, but less effective in removing other, more complex odorous chemicals compared to more current technology such as biofilters. The scrubbers and fans are installed in a room with no active ventilation. The scrubbers are under positive air pressure in a room full of equipment, including the HVAC control system, and the office air handler. The only exit is through the main Control and Electrical room, with the offices beyond. If there is a leak, odorous air will reach and corrode sensitive equipment, as well as contaminate the offices and Lab. Because of its simple construction the scrubbers could last indefinitely, but the ductwork needs replacement, and maintenance access is poor. The ducts are visibly rusted through in spots. Also there is concern about potential rust of a roof beam which is inaccessible. Clarifier HV (SF-4): The Primary Clarifier building is fully enclosed and was originally designed as a heated, positively pressurized space. However the space should be negatively pressurized per NFPA. Since the supply fan SF-4 and its heating coil HC-3 broke down years ago, the clarifier has been operated as an enclosed, unheated space, with no mechanical ventilation, and manually operated vents which are opened in mild weather. Based on observed conditions, the space does not really require heat, but the humidity is a concern. During the site visit the vents were closed, and the atmosphere was warm but humid, in spite of freezing weather outside. The space was not particularly odorous, but it sometimes becomes odorous in the summer. There was significant condensation at door frames and other thermal bridges. The non-functional air handler SF-4 is suspended over the middle pool with poor maintenance access. SF-4 was designed to take air from a roof vent overhead and blend it with recirculated air, heat it, and supply it over the pool surfaces. There is no safe way to maintain the unit since it is suspended over the open water. Boiler Room HV (SF-5): This ventilation unit is set for about 50% outside air when it runs. It appears operational, but is designed to cool the boiler room with outside air. The unit is rarely used and considered unnecessary. Existing Ventilation Rates Assessment Process Spaces: The original design called for up to 12,000 CFM of scrubbed exhaust, variable down to 4,000 cfm with the rest recirculated through a Purafil type potassium permanganate media before being returned to SF-1. The outside air/return air ratio is no longer variable, and has been set at about 5,250 CFM when all exhaust fans are operating. During the site visit, EF-2 was no longer operational, so the the scrubbed exhaust has been reduced to 2,700 CFM. About 75% of the air in the supply air stream from the return air RF-1 fan after being cleansed using Purafil type potassium permanganate media. If the cleansed return air is counted with the outside air and design flows are assumed, the total air flow to the space is 10,500 CFM. The current outside air ventilation to the process spaces is 2,700 CFM based on a recent Energy Audit. Based on the NFPA 820 Ventilation analysis in the Appendix, the recommended outside air ventilation rate during Occupied periods is 21,750 CFM, and 10,875 CFM during unoccupied periods. The original design is about 55% of NFPA-820 occupied recommendation. In the current operating condition, the ventilation is about 12% of the NFPA occupied recommendation. Additionally, there are issues with pressurization. Process spaces should be negatively pressurized relative to non-process, and odorous spaces negative relative to non-odorous. Having proper airflow will increase the effectiveness of odor collection, and will reduce corrosion in both process and non-process spaces. Non-Process spaces: Other than for pressurization, non-process spaces do not have NFPA ventilation requirements. The outside air ventilation rate prescribed by the International Mechanical Code is about 1,050 HEATING AND VENTILATION SYSTEMS UPGRADE - FINAL 6 DOCUMENT CFM. Bathroom and shower exhausts ensure some ventilation, but much of that now comes from odorous process spaces. To satisfy both the Mechanical and the NFPA codes, additional outside air should be supplied to non-process spaces. Correction of these deficiencies will increase energy cost, but will reduce maintenance costs due to corrosion. Note: See NFPA 820 Ventilation Calculations in Appendix B for additional detail. Recommendations General The recommendations provided here address the following: 1. Conversion from an oil fired boiler hydronic system to a water source heat pump hydronic system. 2. Replace most of the heating and ventilation equipment, since it has reached the end of its useful life. 3. Replacement of the HVAC controls system. 4. Upgrades to the ventilation system deemed necessary for health and safety and compliance with current best practice standards. All existing unit heaters, scrubbers, air handlers, exhaust fans, dampers, louvers, and hoods should be replaced or eliminated where appropriate. The mechanical room should be gutted, with all items replaced. All hydronic distribution piping should be removed. More detailed descriptions of the recommended work are provided below. See attached Appendix A for Existing and Proposed Air Flow Schematics and Plan Mark-ups. The proposed airflow configuration will positively pressurize normally occupied, non-rated, and non-corrosion resistant spaces. These spaces including offices, storage rooms, Sample Lab, Blower room, Utilidor, and Boiler room should be pressurized to keep out process odors and reduce corrosion. Replace Ventilation 1. Remove existing RF-1, SF-1, Purafil box, scrubbers, dampers, and ductwork from the Mechanical room. Provide a new AHU-1 in the Mechanical room. Replace the scrubbers with a new bio-filter outside the building on the West side of the Grit Mezzanine. 2. Similarly, provide a new Process Make-Up air unit AHU-2 in the former Chlorine room, now the Hypochlorite room, to pressurize the isolated non-classified spaces. These areas include the Hypochlorite room and the offices above it, Electrical shop, Blower room, and Boiler room. This air keeps those spaces clean and is transferred to the Truck Bay, Sludge Pump room, and Utilidor, keeping those spaces clean as well. This keeps contaminated air from the Grit Mezzanine and the Upper Sludge room from migrating in to those spaces. 3. Replace the existing supply air handler SF-4 with a new exhaust fan EF-2. Remove the existing exhaust fan EF-1 in the Mechanical room and reverse the air flow to the lower Sludge Thickener room. The air from the Lower Thickener is transferred to the Utilidor, and then the Clarifier Pump Chamber, and then transferred to the Clarifier Building before exhausting. 4. Provide new office air handlers AHU-3, AHU-4. Adjust outside air flows so the recommended differential pressures between the main office space and the process spaces are maintained. This is an NFPA 820 requirement, but will also result in less office equipment corrosion, and more tenable working conditions. The principal means of doing this will be to increase the outside air flow to existing air handler SF-2 or its replacement. HEATING AND VENTILATION SYSTEMS UPGRADE - FINAL CITY AND BOROUGH OF SITKA, ALASKA 7 Convert Hydronic Heating System The previous report by Alaska Engineering discusses this at length. This is essentially the same equipment, except that pumps have been added. One of the 2 existing boilers will be retained and repiped for use as supplemental heat. New piping will include a primary/secondary loop to allow it to supply heat at the lower temperature. All existing piping, unit heaters, heating coils and accessories will be removed. On the treated effluent side, 2 low pressure pumps, about 220 gpm and 70 feet total dynamic head (TDH) each, will be provided in the Utilidor next to the Clarifier. These will pump to the plate-and-frame heat exchanger in the Boiler room. There another set of pumps will circulate a 25% glycol loop up to the Mechanical room where the new heat pumps will be located. In the Mechanical room, a new 80 ton nominal capacity heat pump will create 120F glycol solution which will be piped to the new air handlers and fan coils around the facility. There will be a total of 3 sets of duplex pumps, 6 pumps total. Each pump will be sized for approx 220 gpm and 70 feet TDH. The new piping system could be CPVC, HDPE, polypropylene, or thin wall mechanically coupled stainless steel piping. The stainless will cost more for material, but there will be labor savings, and only about half as many supports required. It should also last longer. Examples of polypropylene, and thin wall stainless are in Appendix C. For the cost estimate, 316 stainless steel with Victaulic Pressfit fittings is assumed. New piping will have 1” of fiberglass insulation with a PVC jacket. Replace Office HVAC The existing design of the office HVAC is acceptable, but worn and obsolete. The air handlers are incompatible with the Low temperature heating fluid, and must be replaced. There should be an attempt to improve maintenance access for the new air handlers. For this cost estimate, a 1 for 1 change-out of the office HVAC, but with larger, chilled water type coils, and new controls is assumed. Existing non-process area radiators will be replaced with fan-coils. Supply and return grilles and some ductwork can be reused. Eliminate Most Unit Heaters Unit heaters are generally not required in the process spaces. Many of the unit heaters have been removed and not replaced, including several on the most exterior of zones. Yet those spaces are not getting cold because of the required air flow in the spaces. It has been calculated that with the prescribed ventilation rates, exhaust air temperature will be a maximum of about 5.5F lower than the supply air temperature. Installing unit heaters for 120F heating water would be a custom item, expensive bulky, and unneeded. Therefore there will only be a few unit heaters installed in the process space, as shown in the attached mark-up. This will also save on piping cost. Scrubbed Exhaust The existing scrubbers will be removed from the Mechanical room and replaced with a new 6,200 CFM Biofilter or equivalent outside on the West side of the Grit Mezzanine and South of the Upper Sludge Thickener room, or possibly on the North side of the Sludge Thickener room next to the water. This will replace the 2 existing scrubbers. See Plan Mark-up in Appendix A. Another 5,000 CFM Biofilter for outside the Clarifier building is seen as less necessary because at the time of the site inspection at least, there was no significant odor coming from it. Each Biofilter for odor control adds approx. $435,000 including mark-ups and installation to the cost estimate. Therefore recommended options for odor control should be examined before final design. A dispersion model may determine that odor control is not needed if proper odor dispersion methods are used. Process Air Handlers Two new Process Area air handlers are recommended similar to existing, but with larger, chilled water type coils. A new AHU-1, 8,700 CFM capacity is recommended in the Mechanical room to provide 50 degree F air and replace HEATING AND VENTILATION SYSTEMS UPGRADE - FINAL 8 DOCUMENT existing SF-1/HC-1. It will connect to existing supply ductwork. A new Non-Process pressurization air handler AHU-2, 2,500 CFM capacity is recommended in or near the former Chlorine room. AHU-2 will provide 70F air to non-process spaces isolated out in the main process space. Process Exhaust fans There will be five main process exhaust fans per the attached schematic. One is associated with the scrubber described above. The scrubber exhaust fan and a Clarifier exhaust fan will operate continuously. Another 3 exhaust fans are for intermittent use during the summer when heat is off, during occupied periods such as during the weekly sludge load-out, and during alarm situations when excessive hydrogen sulfide or combustible gas is detected. During alarm situations, the fans will go on automatically. Occupied Process Make-up Air When the high ventilation rate is activated, make-up air is brought in through new louvers in to the process space with backdraft dampers. This air will be untempered, so a unit heater will be provided near each make-up louver to prevent freezing conditions. Cost Estimate This estimate is for the recommended construction costs only. It does not include cost for engineering, design, owner costs, or engineering services during construction. This is considered a Class 4 Estimate with an accuracy range of -30% to +50%. The detailed cost estimate is provided in Appendix D. Estimate Total $2,040,000 High Range (+50%) $3,060,000 Low Range (-30%) $1,430,000