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4.5. SR 04-20-1998y of iver MEMORANDUM Item #4.5. TO: FROM: DATE: SUBJECT: Mayor & City Council Pat Klaers, City Ad~trator April 20, 1998 Dehumidification Feasibility Study Attached for your review is the Ice Arena Dehumidification Feasibility Study as prepared by Nelson-Rudie & Associates, Inc. On March 16, the City Council authorized this study and in April the Council identified funding sources for this capital expenditure. The conclusions of the feasibility study are identified in the Executive Summary on Page 1. The Ice Arena Commission unanimously recommended approval of the feasibility study at its meeting on April 14, 1998. Arena Manager Rich Czech and Building Official Cliff Skogstad are scheduled to meet with Michael Woehrle of Nelson-Rudie to get more information about the project. References have been checked and Rich is comfortable working with this firm based on the feedback he has received. We are still exploring issues with this firm including some heating improvements to the old arena, planning for additional bleachers in the future and needing heat in these areas, having this firm help identify the market and help us sell the old Dextron units, putting together a project/construction timetable, and clearly identifying the Nelson-Rudie fees for this project. If the feasibility study is accepted, and Nelson-Rudie hired to do the project, then they will design the system, put together the bid specifications for the project, guide the city in going out for bids, and supervise the installation of the new desiccant based dehumidification system. Please be aware that the figures in the study are estimates and that the actual bids could be higher than estimated, but it does look like we can accomplish our goals for less than originally estimated and somewhere in the neighborhood of the $110,000 amount identified by the Council in April. Recommendation It is recommended that the City Council accept the feasibility study and hire Nelson-Rudie & Associates, Inc. as the engineers for the project. 13065 Orono Parkway · P.O. Box 490 · Elk River, MN 55330 · TDD & Phone: (612) 441-7420 · Fax: (612) 441-7425 Elk River Ice Arena Elk River, Minnesota DEHUMIDIFICATION FEASABILITY STUDY PREPARED FOR CITY OF ELK RIVER APRIL 8, 1998 By Nelson-Rudie & Associates. Inc. 2575 University Avenue, Suite 140 St. Paul, Minnesota 55114 Nelson-Rudie & Associates, Inc. Consulting Engineers 2575 University Ave. West, Suite 140, St. Paul, MN 55114 Dennis A. Nelson, P.E. Scott F. Rudie, P.E. Andrew N. Erdmann, P.E. Joseph M. Pearce, P.E. Michael D. Woehfle April 9, 1998 Mr. Rich Czech Elk River Arena 1000 School Street P.O. Box 720 Elk River, Minnesota 55330 Re.' Dehumidification Feasibility Study Elk River Arena NRA Comm. No. 98-056 Dear Rich: We have enclosed the dehumidification feasibility report for the Elk River Arena. Our review of the existing mechanical systems concurs with your experience at the arena. The existing dehumidification system is not adequate to prevent condensation and fogging during summer operation of the facility. We have indicated in our study that a desiccant based dehumidification system is recommended for the building. We have previously discussed the numerous advantages of using a desiccant based system instead of the conventional refrigerant based system currently installed in the arena. Please let us know if any additional information is needed on the systems. We appreciate your input into the operation of the existing systems and the time spent with us touting the facility. We would very much like to help with the design of a new dehumidification system for the arena when the decision is made to upgrade the systems. We recommend that the problems be addressed before significant damage occurs to the building. Please let us know if you have any questions or if you need further information. Thanks again for contacting us. Yours~~/very truly, . .... '~,- Michael D. Woehrle Enclosure F:XFEEPROPXLTS0409.DOC 612/644-2400 Fax: 6121647-4120 E-Mail: nelsonrudie@ibrn.net Modern: 612/6474139 ELK RIVER ARENA ELK RIVER, MINNESOTA APRIL 8, 1998 FEASABILITY STUDY EXECUTICE SUMMARY: The City of Elk River recently constructed a second ice sheet addition to the Elk River Ice Arena. The new arena has experienced problems with the operation of the facility due to high moisture levels in the arena. The high moisture levels result in condensation on the building surfaces. The condensation creates both long and short term problems for the facility. Short term problems appear in form of condensation dripping on the ice and floor Surfaces. Fog can also be an issue on humid days. Long term problems take the form of rust which quickly forms on exposed metal surfaces, deteriorating the roof deck and other structural components of the building. Rust is visible on many of the exposed metal surfaces after just one year of operation. The moisture problems that the facility has been experiencing are the result of insufficient dehumidification capacity. The amount of moisture being introduced into the building in the summer months far exceeds the capacity of the existing dehumidification units. We recommend that a new desiccant based dehumidification system be considered for the facility. The desiccant based systems are ideally suited for ice arena applications. They have the capability to provide a much dryer environment in the arena than conventional dehumidification systems. They also operate on natural gas instead of electricity which reduces the overall electrical demand charges on the facility. The estimated cost to install a new desiccant based system including the desiccant unit, ductwork, electrical connections, structural openings in the building, and engineering fees is $108,00.00. The Gas Company offers a rebate for the installation of desiccant based dehumidification systems. We have estimated the rebate to be approximately $22,000.00. The total cost of the dehumidification system after rebates is estimated to be $86,000.00. We have also been requested to review the costs associated with adding heat to the arena. We recommend incorporating the heating system into the design of the new dehumidification/ventilation system. The costs associated with the building heating system are estimated to be $10,000.00. The total project costs including dehumidification and building heat will be approximately $96,000.00 after rebates. We have designed desiccant dehumidification systems for numerous arenas in the Twin City area and around the country. The systems allow the arenas to operate without condensation or fog on even the most humid days. We are confident that the City will see a dramatic change in the arena conditions once an adequately sized dehumidification system is installed in the facility. NELSON-RUDIE & ASSOCIATES, INC. Page 1 ELK RIVER ARENA ELK RIVER, MINNESOTA APRIL 8, 1998 FEASABILITY STUDY REVIE~V OF THE EXISTING ARENA MOISTURE PROBLEMS: We recently visited the site and discussed some of the moisture problems with the arena manager, Mr. Rich Czech. The following items were discussed during our visit: 1. Condensation forms on the roof deck above the ice sheet. Water droplets form on the metal deck and drip down onto the ice sheet. This creates several problems. a. The water droplets collect on the ice sheet where they are frozen by the ice sheet refrigeration system. During unoccupied periods of operation the condensation builds up and forms stalagmites on the ice surface. Rich stated that this occurs very frequently during the summer months. The arena operators need to scrape the stalagmites off the ice surface and resurface the ice before the arena can be used. This adds a considerable amount of maintenance time to the operation of · the arena. b. The water vapor that collects on the metal deck creates rust that will quickly deteriorate the roof deck. The rust is clearly visible from the ground and is especially visible on the metal surfaces near the outside air intakes into the arena. c. The condensation that is frozen on the ice surface forms a layer of frost on the ice surface. The process of freezing the condensation into frost places increased load on the ice plant, increasing the operational costs of the system. As the frost builds up on the ice surface, the thickness of the ice grows. This reduces the efficiency of the refrigeration system increasing the operational costs of the facility. 2. Condensation will form on any surfaces that are below the dew point temperature of the air. Many of the surfaces may not be visible. We are concerned that condensation may be occurring in sheet rock walls, on the building structure, on the concrete floors, on the metal bleachers and on the building electrical components. The condensation will continue to form and deteriorate the building systems and may cause serious problems. NELSON-RUDIE & ASSOCIATES, INC. Page 2 ELK RIVER ARENA ELK RIVER, MINNESOTA APRIL 8, 1998 FEASABILITY STUDY ESTIMATE OF THE EXISTING BUILDING HUMIDITY LOAD: The moisture problems that occur in the arena are directly related to the amount of moisture in the air and the temperature of the building surfaces in the arena. The ice sheet acts as a giant refrigerator that cools the building structure during even the warmest summer days. Common structural beam temperatures in arenas range from 50°F to 55°F. Condensation will form on the surface of the structure anytime the dew point temperature of the air is above the temperature of the structure. This is the same principle that causes water to condense on the outside of a cold glass of water on a humid summer day. When the dewpoint temperature of the air is higher than the surface temperature of the glass of water or structural beam, water condenses on the surface. There are several major sources of moisture that need to be evaluated during the design of an ice arena: (1) the moisture load from outside air used for ventilation purposes; (2) the moisture load from outside air due to infiltration; and (3) the moisture load from the building occupants. The moisture load from the outside air is by far the largest source of moisture into the building. We have summarized the moisture load on the new arena in the following paragraphs. The amount of moisture being added or removed from a building is commonly estimated in pounds of moisture per hour, (lbs/hr). 1. Three 12,000 ft3/min exhaust fans are located above the ice sheet. All three of the fans are used during the ice resurfacing operation. This amounts to a total of 36,000 ft3/min of outside air used during the resurfacing operation. The make-up air drawn into the building by the exhaust fans adds approximately 2,000 lbs/hr of moisture to the building during a humid design day. The fans typically are run for 15 minutes per hour. The average moisture load due to the ventilation fans is therefore 500 lbs/hr on a summer design day. 2. When the air outside the arena contains more moisture than the air in the arena, moisture will infiltrate into the building. This infiltration occurs through cracks in the building construction, through doors and windows, through louvers and directly through the building structure. We have estimated that the moisture load due to infiltration for the arena is approximately 130 lbs/hr. 3. The spectators that are in the arena add moisture to the air. We have been informed that the arena was designed for 500 spectators during a summer event and 1500 spectators during a winter event. The spectators for a summer event add an estimated 50 lbs/hr of moisture load to the arena. 4. An additional 20 people are typically actively involved with the hockey game or skating competition on the ice. The people actively skating in the arena add an estimated 20 lbs/hr of moisture to the arena. 5. The total moisture load that the facility will experience will fluctuate with the amount of people in the arena and the conditions of the outdoor air. Ifa large event were held on a humid day, with 500 people watching the event, the total moisture load being added to the arena would be approximately 700 lbs/hour of water vapor. 6. A more typical moisture load for a practice with twenty skaters and one 15 minute ventilation period per hour would be 650 lbs/hr. The dehumidifiers installed in the arena have a total moisture removal capacity of 34 lbs/hr. The large difference between the amount of moisture being added to the arena and the amount being removed by the dehumidifiers accounts for the humidity problems being experienced at the facility. NELSON-RUDIE & ASSOCIATES, INC. Page 3 ELK RIVER ARENA ELK RIVER, MINNESOTA APRIL 8, 1998 FEASABILITY STUDY DETERMINE THE REQUIRED VENTILATION AIR FOR THE FACILITY: The State of Minnesota has adopted ASHRAE 62-1989 as the standard for determining the amount of ventilation air required for acceptable air quality in commercial buildings. The standard requires the following quantities of outdoor air for the arena: 1. The playing surface of an ice arena must be provided with 0.5 ft3/min of outdoor air per square foot of ice surface. The area of the ice surface is 17,172 ft2. The amount of ventilation air that is required for the ice surface is therefore 8,590 ft3/min. The occupants of the arena require 15 ft3/min of outdoor air per person. We have been informed that the summer spectator occupancy is 500 people and the winter occupancy is 1,500 people. The ventilation rate may be reduced if the occupant load is variable and the maximum fully loaded event is less than three hours long. We typically reduce the required ventilation rate by 50%. The amount of outdoor air that is required for a 500 occupant summer event is 3,750 ft3/min. The amount of outdoor air that is required for a 1,500 occupant winter event is 11,250 ft3/min. 3. The total amount of outdoor air required for the arena is 19,840 ft3/min. The ventilation air for the ice surface is typically run during resurfacing operations. The outdoor air for the occupants should be provided whenever the people are present in the facility. The facility currently has a total ventilation air quantity of 36,000 ft3/min. The total amount of ventilation air is in excess of the minimum code requirements. REVIEW OF THE EXISTING ARENA VENTILATION AND DEHUMIDIFICATION SYSTEM: The existing arena ventilation system consists of three exhaust fans that are located over the ice surface. The fans are interconnected to large intake louvers located near the ice on the north end of the arena, below the walking track. The dasher boards extend up above the top of the walking track creating an enclosed corridor on the north end of the arena in front of the intake louvers. We have several concerns pertaining to the present design: 1. The warm, humid intake air enters the arena directly adjacent to the ice surface where the temperature is the coldest. The surfaces near the louvers are frequently saturated with condensation. The condensation has resulted in visible surface rust on the majority of the exposed metal surfaces in the area. 2. The exhaust fans for the arena ventilation system are currently controlled with a manual switch with an override from the carbon monoxide detection system. The fans are typically set to run for ten minutes when the ice resurfacer is being used. The fans are then shut off after the resurfacing is completed. The carbon monoxide detection system will energize the fans if the carbon monoxide levels in the arena are above recommended concentrations. We have the following comments pertaining to the control system: NELSON-RUDIE & ASSOCIATES, INC. Page 4 ELK RIVER ARENA ELK RIVER, MINNESOTA APRIL 8, 1998 FEASABILITY STUDY a. The three 12,000 CFM fans are used to bring ventilation air into the facility. There are two primary uses for the ventilation air: (1) provide fresh air for the occupants of the building, and (2) provide ventilation air for the ice resurfacer. b. The three exhaust fans are typically all energized during an ice resurfacing operation. This is 4.2 times the minimum ventilation rate required by the governing codes. We have designed numerous ice arena facilities with code mandated ventilation rates and have not had any problems controlling the contaminant level in the buildings. The excessive ventilation rate is one of the biggest moisture sources for the arena. c. The control of the ventilation air for the occupants of the arena is also a concern. One 12,000 CFM fan closely matches the amount of ventilation air required for a 1,500 occupant wintertime event. We recommend that one of the fans be run continuously when the arena is fully loaded. d. The maximum building occupancy occurs very infrequently during the use of the facility. During all other periods of operation a reduced ventilation rate could be used. The current ventilation system allows the choice of running one, two or three of the 12,000 CFM exhaust fans. One of the fans will accommodate the maximum occupancy of the facility. We recommend that a method of providing fresh air for the occupants of the arena be included in future design revisions. The arena dehumidification system consists of two 17 lb/hour refrigerant style dehumidifiers. The units are installed in opposing comers of the arena. We have the following comments pertaining to the design of the system: 1. The units were sized to remove only a small portion of the total moisture load in the building. We have estimated that the typical moisture load on the building on a warm humid day would be approximately 600 lbs/hour. The installed dehumidifiers remove approximately 6% of the moisture introduced into the building on a design day. This accounts for the moisture problems experienced in the facility. 2. The existing dehumidifiers are located in the arena. The moisture enters the building through the ventilation air and people loads. The dehumidifiers then attempt to remove the moisture fi.om the building and dry the air back out. We recommend that as much of the moisture be removed from the ventilation air before it ever enters the building. This is accomplished by dehumidifying the ventilation air prior to introducing it into the building. 3. The existing dehumidification units use refrigeration to remove the moisture from the air. The units cool the arena air down below the dewpoint temperature of the air. The moisture then condenses on the cooling coil, is collected in the drain pan and disposed of in the sewer system. The units are effective when the temperature of the air in the arena is fairly warm, say 70 °F. As the temperature in the arena drops the efficiency of the units drop and they remove less moisture from the air. NELSON-RUDIE & ASSOCIATES, INC. Page 5 ELK RIVER ARENA ELK RIVER, MINNESOTA APRIL 8, 1998 FEASABILITY STUDY SYSTEM RECOMMENDATIONS We recommend that significant changes be considered for the design of the ventilation system. The existing system is creating problems that will greatly reduce the life of the building. Continued use of the facility during warm summer months will result in deterioration of the roof deck and other exposed metal surfaces, deterioration of the building electrical components, possible deterioration of sheet rock walls and increased liability due to the wet floor surfaces. We strongly recommend that a desiccant based dehumidification system be considered for the facility. Desiccant based dehumidification systems use a material that has a high affinity for water to absorb the moisture from the air. Systems typically consist of a large air handler with a desiccant wheel installed in the air stream. The moist ai~ is forced through the desiccant wheel. Moisture is removed from the air stream and collected by the desiccant wheel. The wheel continually rotates with a portion of the wheel moving out of the arena air stream. The moisture is then forced off of the wheel into the atmosphere by a heating process. The dry portion of the wheel then rotates back into the moist air stream to continue the dehumidification process. The units are particularly suited for ice arena applications. We have installed desiccant based dehumidification systems in numerous facilities in the Twin City area and around the country with great success. The systems have the following advantages: 1. The desiccant based dehumidification systems are capable of drying the air to a much lower moisture content than refrigeration based systems. 2. The ventilation air is typically dehumidified before it is introduced into the arena. This removes the single largest source of moisture from the facility. 3. The amount of ventilation air introduced into the facility can be varied with the occupant load in the building. This reduces the overall dehumidification load and energy consumption of the facility. 4. The systems use natural gas or other sources of heat to regenerate the wheel. This reduces the electrical demand on the facility. The need for dehumidification normally is coincident with the highest energy demand on the ice plant. Switching from an electrically driven, refrigeration based dehumidification system, to a desiccant based system which uses natural gas as it's energy source will remove a portion of the electrical demand charges from the facility. 5. The Gas Company providing gas to the facility is very interested in the use of desiccant based systems. The systems consume natural gas during the summer when the gas companies have a small total demand, and they typically do not operate on cold winter days when the gas companies have their highest demand. The gas companies offer rebates to offset the first cost of the system. They also offer rebates to offset the engineering costs for the design of the system. We recommend that a desiccant based dehumidifier with a total air flow capacity of 12,000 f¢/hr be provided for the arena. The system should have the capacity to remove approximately 420 lbs/hr of moisture from the air. This system would be capable of introducing enough outside air into the facility to ventilate the arena during a resurfacing operation and also provide adequate ventilation for the occupants of the building during a summer time event. The proposed ventilation rate is less than the existing system which will lower the dehumidification requirements for the building. 600 lbs/hr are required for the existing ventilation system. NELSON-RUDIE & ASSOCIATES, INC. Page 6 ELK RIVER ARENA ELK RIVER, MINNESOTA APRIL 8, 1998 FEASABILITY STUDY The desiccant unit is typically installed outside the arena, either on the ground or on the roof of the building. The units can be located inside the building if space is available. The location of the unit will need to be determined during the design of the system. We recommend installing distribution ductwork above the bleacher side of the arena to distribute the dry air throughout the building. The following factors will be considered when determining the location of the unit: 1. The location of the unit with respect to residential buildings. We will need consider the noise impact on the neighbors, especially on the north side of the arena. 2. The location of the existing gas meter and piping. 3. The structural capacity of the existing building. 4. The proximity of the unit to the ductwork distribution system. We prefer to distribute the supply air along the bleacher side of the arena. COST ESTIMATE: The cost estimate to complete the installation will vary significantly depending on the final design of the system. To prepare our cost estimate we have assumed that a new desiccant unit could be located on grade, or on the roof near the resurfacer room of the new arena. Ductwork has been extended the length of the arena over the bleachers. We have a preliminary estimate of $108,000.00 to complete the installation of the dehumidification system. The estimate includes engineering fees to complete the design of the system. MINNEGASCO REBATES: Minnegaso offers rebates for the installation and design of desiccant based dehumidification systems. The following rebate programs are available: A rebate of $90.00 per offset ton of refrigerant based dehumidification is offered for the installation of desiccant based dehumidification. A rebate of $20.00 per offset ton of refrigerant based dehumidification is offered for the engineering of desiccant based dehumidification. The rebates are both based on offset tons of refrigerant based dehumidification systems. We have estimated a moisture removal requirement of approximately 400 lbs/hr. A typical 10 ton refrigerant based dehumidification unit similar to the units installed at the facility will remove 17 lbs/hr of water vapor from the arena. We have estimated the total offset tonnage for the arena to be approximately 200 tons. The preliminary rebate estimate based on the installation of a 400 lb/kr desiccant dehumidification system will amount to an $18,000.00 rebate for the equipment installation, plus a $4,000.00 rebate for the engineering rebate. The total estimated rebate for the system would be $22,000.00. This is a preliminary estimate that will need to be confirmed with the final equipment selection. The entire rebate goes to the owner to help offset the costs associated with the engineering and installation of the desiccant dehumidification system. NELSON-RUDIE & ASSOCIATES, INC. Page 7 ELK RIVER ARENA ELK RIVER, MINNESOTA APRIL 8, 1998 FEASABILITY STUDY BUILDING HEATING SYSTEM: We have also been requested to review the costs associated with adding heat to the arena. The arena is currently heated with infra-red heat installed over the bleacher area. Additional heat can be added into the building through the dehumidification/ventilation system. We recommend installing a gas fired duct furnace in the dehumidification system ductwork. The duct furnace would be sized to maintain an arena temperature of 60 °F on a winter day. We estimate the cost associated with adding the duct furnace to the building to be approximately $10,000.00. Some of the desiccant dehumidification units can also be designed to incorporate the heating system into the design of the dehumidification unit. The costs are comparable with the duct furnace discussed above. CONCLUSION: The Elk River Arena is beautiful facility that has been in operation only a few short years. The effects of operating the arena during the humid summer months without adequate dehumidification are clearly evident. Exposed metal surfaces have visible surface rust, frost forms on the ice surface quickly after a resurfacing operation, and condensation drips fi-om the building structure. The use of a desiccant based dehumidification system is a clear and logical choice for the facility. We have specified the units for numerous ice arena applications and have had excel, lent results. We look forward to completing the design of the system. We are confident that the City will see a dramatic change in the arena conditions once an adequately sized dehumidification system is installed in the facility. END OF REPORT NELSON-RUDIE & ASSOCIATES, INC. Page 8