Urbana Free Library HVAC Analysis
Prepared for the Urbana Free Library
Prepared by Paul Boland, P.E., and Nathan Alderman, E.I.T.
Report Dated August 8, 2016
1. Introduction
The Urbana Free Library is a three-story building, and its loads are served by two large air handling units, one packaged air-cooled chiller, and one boiler in the basement. The building was expanded to the west in 2002, in an expansion project that nearly doubled the size of the library and its footprint. Cooling is provided to the original portion of the building by two direct- expansion air-cooled condensing units mounted on the roof and a main air handling unit in the east penthouse, while cooling is provided to the 2002 addition by a packaged air-cooled chiller serving chilled water to a main air handling unit in the west penthouse. Neither air handling unit has a heating coil installed in its enclosure; heating is distributed to the space by means of reheat coils at each variable air volume box throughout the library, and the hot water that serves these boxes is produced by the boiler in the basement.
The Urbana Free Library has requested an analysis of these heating, cooling, and air conditioning (HVAC) systems, including their performance, construction, controls, and potential repairs needed. In addition to the analysis, the Library staff has requested that HEI provide an analysis of the HVAC systems that serve the Archives on the second floor and a schematic design of a new independent HVAC system that only serves the Archives.
2. Existing Boiler
Hot water is provided to the building as it is generated by a Cleaver-Brooks model 3 packaged condensing boiler. The boiler’s catalog number is WTW-7A-1500, serial number is 635, and unit number is G-05525-M3. The faceplate input and output capacities are 1,500,000 BTUH input and 1,400,000 BTUH output, indicating that this boiler is operating at 93% efficiency. This type of boiler uses low return water temperatures to recover heat from the combustion air stream; typically a steam or hot water boiler cannot exceed 83% efficiency as heat is exhausted through the combustion air stream.
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The boiler’s faceplate indicates that it was installed in 1974. Hot water boilers typically have an expected life of 30 years; this boiler is past its life expectancy, and will need to be repaired or replaced soon. HEI contacted Cleaver-Brooks to ascertain the availability of parts to replace inside the boiler in lieu of a more expensive boiler replacement; unfortunately, due to the age of the boiler, parts are no longer available for this model. When the parts begin to fail the boiler will need to be replaced in its entirety. HEI’s correspondence with Cleaver-Brooks was conducted through Michelle Frye on May 24, 2016, who can be reached at (309)-944-3149 or by email at [email protected].
The current boiler is having no trouble managing the heating loads in the building, and if it is to be replaced the heating capacity should remain the same. HEI would recommend that two separate boilers sized for half the load (700,000 BTUH output) be installed for better turndown at part-load conditions and as insurance in case one boiler fails or needs to be taken offline for maintenance. The new boilers should also be the modular condensing type as is currently installed, to maintain the increased efficiency that this type of boiler offers. A preliminary estimate of probable construction cost for the replacement of the boiler in this manner would fall around $93,150, which includes a 15% markup for contingencies and the contractor’s overhead and profit.
3. Existing Air Handling Units
The library is served by two air handling units located in separate penthouses on the roof. Both units are variable air volume cooling-only units with economizers to take advantage of free cooling, and heat is provided to the spaces through reheat coils in the terminal boxes on each system.
The east half of the library is served by a Trane type M-63 air handling unit, serial number K2L228866, which is original to the building. Cooling is provided to this air handling unit by two air cooled condensing units placed on the roof directly west of the east penthouse, each with a cooling capacity of 40 tons, with four fans and two compressors in each unit. At the time of investigation, one condensing unit was in operation with three of the four fans running, and the other condensing unit was not operating. Outdoor air is drawn in through a 10’x6’ louver on the west face of the penthouse, and building air is relieved through a second 10’x6’ louver on the east face of the penthouse. This unit has an economizer to make use of free cooling when the outdoor air temperature falls between 50°F and 60°F.
The supply fan motor in the east penthouse air handling unit was rattling during operation, suggesting that a fan bearing must be nearing the end of its life. This is a common maintenance item, and should be addressed as soon as possible.
The west half of the library is a new addition to the building that was constructed in 2002, and is served by a new air handling unit in the west penthouse. This unit is a York model AP660, serial number CGMM18527D, sales order 03-242845-0101 and is tagged AHU-1. Cooling is provided to this unit through a chilled water coil, and chilled water is provided by a packaged air-cooled chiller located directly east of the west penthouse. The chiller is tagged C-1 and is a
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York model YCAS, serial number RFMM006037. Chilled water is circulated through the chiller and AHU-1 cooling coil by an Armstrong model 4030 pump with 287 gallons per minute (GPM) capacity at 70 feet of head, with a 10 horsepower motor. The air handling unit AHU-1 has an economizer to make use of free cooling when the outdoor air temperature falls below 60°F.
The chiller tag indicates that it uses R-22 refrigerant, which is under phase-out at the moment and will be expensive to replace. It is recommended to upgrade the chiller to R-410a as soon as possible. In addition to the refrigerant, HEI notes that the insulation on the chilled water supply and return piping and the condensing unit refrigerant piping has deteriorated significantly and is cracking, which will allow moisture to gather in the insulation. HEI recommends that this insulation be replaced to maintain the vapor barrier around the piping and to improve the efficiency of the chilled water system.
HEI’s preliminary cost estimates indicate a total cost of $468,082 including 15% markup to replace the chiller, two air handling units, and two condensing units, not counting the cost of the controls upgrade from pneumatic to direct digital controls discussed in the next section. This cost may be broken down into the replacement cost based on system. The following is a list of HEI’s estimates of probable construction cost for each piece of equipment on this system, each line including the 15% markup:
Chiller C-1 Insulation Repairs: $1,196 Chiller C-1 Replacement: $144,578 Air Handling Unit AHU-1 Replacement: $122,668 Air Handling Unit Trane M-63 and Condensing Units replacement: $199,640
4. Controls
The building is served by two separate controls systems, divided between the original section of the building and the addition. The control panels serving each section are located in the penthouse mechanical spaces, mounted near the coil connection side of each air handling unit. The controls system serving the original section of the building is a pneumatic system tied to the Trane M-63 air handling unit and its associated air-cooled condensing units. The controls system serving the addition is a direct digital control (DDC) system tied to AHU-1, chiller C-1, and associated equipment throughout the building.
The equipment controllers serving the building addition are mounted at the west end of the west mechanical penthouse. The controllers are Invensys model PXP-100 controllers, used to control equipment on the system other than AHU-1. The controls diagrams are present on the inside of the controls box. These controllers serve the variable air volume boxes, reheat coils, pumps, and unit heaters throughout the addition.
During observation, HEI observed that the control panel serving AHU-1 indicated a mixed air temperature of 73.0°F and a leaving air temperature of 53.6°F; however, it also indicated that the chilled water valve was 0% open. The control panel is showing that the air passing through the chilled water coil is being cooled somehow, but it also shows that the cooling coil is shut
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down. Since the building return, mixed, and supply air temperatures are in line with how the unit would be expected to operate at the outdoor air temperature observed at the time of the walkthrough, it is likely that the reading from the chilled water coil valve position may be inaccurate.
The controls systems serving both portions of the building are in good working order. The DDC system serving AHU-1 is anticipated to last at least another 10 years before replacement will be necessary, and the pneumatic system serving the original building is anticipated to last another 5 years. When the pneumatic control system begins to fail and need to be replaced, a full replacement of the pneumatic system with matching DDC system would be estimated to cost roughly $159,045 including the 15% markup discussed above.
5. Archive Storage
During our initial site visit and investigation, HEI interviewed the Director of Champaign County Historical Archives Anke Voss. Anke reported that the library archives are used to store several fragile artifacts on paper, microfilm, cassette tapes, photographs, and print negatives. Currently, 1500 linear feet of artifacts are stored in the space. The Society of American Archivists Standards state that the environment in which these artifacts are stored shall be held to the median temperature and humidity required to preserve all the different types of artifacts; in this case, the environment will need to be held at 70°F dry bulb and 40% relative humidity.
The library archives are currently heated, cooled, and ventilated by air handler AHU-1, which also serves the rest of the west addition to the library. Due to this, when the air handling unit is set to shutdown mode every night when the library closes, the archives are not adequately conditioned to maintain the required temperature and humidity. In order to maintain the required conditions in the archives, a separate unit will need to be installed that only serves the archives, and is indexed to maintain 70°F and 40% relative humidity at all times with no night setback.
The library archives consist of three separate rooms. Room 204 Archives is the main section of the archive storage, measures 2,200 square feet, and has desk and table space in the center and east ends as well as shelf storage on the west end. Room 205 Archives Office measures 450 square feet, and holds office space for the archive employees. Room 206 Archive Storage measures 600 square feet, and contains high-density storage shelves for the majority of the artifacts stored. Per ASHRAE 62.1, this space will need to be provided with 560 cubic feet per minute (CFM) of outdoor air to meet the ventilation requirements. Preliminary load calculations show that to maintain this amount of outdoor air and condition the space to the required set point, a new 2,600 CFM unit with cooling capacity of 7 tons and heating capacity of 115 MBH will need to be added to serve the archive space alone. This unit should be direct expansion cooled with a new dedicated condensing unit on the roof of the library rather than making use of the chilled water system, as the chiller will be deactivated when the outdoor air temperature drops below a certain point. This new cooling coil shall also be provided with digital scroll compressors for capacity control, which will allow the system to continue to cool and dehumidify at part load.
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Humidity controls will be required with this new unit as well. Dehumidification will be provided by the cooling coil during normal operation, but due to the relatively low relative humidity setpoint a reheat coil will be required as well to prevent space over-cooling. Humidification may be provided through a small infrared pan humidifier inside the unit itself, and in order to maintain 40% relative humidity at 70°F this humidifier will need to have a rated capacity of 16.25 pounds per hour. An electric humidifier may also be used, but since steam, softened water, or reverse osmosis water are not available on site the infrared humidifier will operate more reliably and responsively than an electric humidifier.
While HEI would recommend that an airside economizer be provided with this new unit to take advantage of energy savings in cooler weather, an economizer is not strictly required by International Energy Conservation Code (IECC, 2015 edition) for this unit. Exception 3 in section C403.3 states that economizers are not required “[w]here more than 25 percent of the air designed to be supplied by the system is to spaces that are designed to be humidified above 35°F (1.7°C) dewpoint temperature to satisfy process needs.” This unit supplies all of its air to the Archives, which need to be held at 44.6°F dewpoint; therefore, an economizer will not be required.
The unit will need to have a new mechanical room or other location set aside where it may be located. Since the archives are on the top floor of the library, the unit may be located on the roof directly above; however, if the unit is to be installed exposed to outdoors the infrared humidifier may not be used due to freezing concerns. An electric steam-generating humidifier will need to be mounted inside the building to provide humidity in the winter. If part of the Archives can be sectioned off as a new mechanical room for the air handling unit, the infrared humidifier may be used. The small section of the Archives just south of the Office 205 would be the best location for the unit, as it allows a portion of the archives to be set aside with minimal impact on the floor plans.
Based on the requirements of the new system, HEI’s opinion of probable cost for this installation would be $46,827. This is based on installation of a new direct-expansion cooled furnace with reheat coil and infrared humidifier, along with associated ductwork, grilles, electrical connections, and unitary controls.
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