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Integrated Sustainable Design for Research Laboratoriesby Joseph J. Ferraro, AIA, Bruce Haxton, AIA, and Robert Lord B.E. 4. Engineering Design Considerations General: The building envelope’s design incorporates excellent shading provisions to minimize entrance of solar heat. Fenestration is single-glazed since exterior-to-interior temperature difference will not exceed 9°C, and will average less than 2°C, year around. The glass shading coefficient is 0.41. Upper portions of vertical glazing on each story are for daylighting with a shelf also shading the window below.
Available energy sources at the site include adequate electric utility power and piped synthetic natural gas. Diesel oil is readily available, but fuel costs are high. Engine- driven refrigeration would have a far higher energy cost than electric motor driven vapor-compression equipment. Waste heat is recovered and solar energy is used in the design to a significant extent. To optimize HVAC systems efficiency, the concept separates HVAC functions of cooling, ventilation and dehumidification. Decoupling of these functions, which are normally interdependent, allows the optimum process for each to be used. This design concept leads to a far more specialized approach to each function without the requirements of one function driving the efficiency of another. (e.g. in most HVAC systems for tropical climates, chilled water is cooled to a temperature needed for dehumidification which is lower than that are required for cooling). Dehumidification: All of the air introduced into the building will be pre-conditioned, both cooled and dehumidified, to the extent that the entering air dew point does not exceed desired room dew point. The pre-conditioning system is roof-mounted and uses a liquid desiccant dehumidification process for the outdoor air. This process uses a lithium-chloride liquid desiccant system permitting one regenerator to serve dehumidifiers in two outdoor air pre-conditioning units. A roof mounted evacuated- tube solar collector array heats water to a maximum of 82°C for regeneration of the desiccant. The liquid desiccant process also kills 98% of airborne bacteria. Ventilation: Ventilation is designed to comply with ASHRAE Standard 62-1999 requirements. Outdoor design conditions are 31°C dry bulb, 23°C wet bulb for cooling; with 24°C wet bulb and mean coincident dry bulb 30°C representing peak moisture-load weather. No space heating is required; lowest local dry bulb ever encountered is 12°C. The 99 percent annual cumulative frequency of occurrence of cold temperature is 17.2°C. The air conditioning systems are designed to minimize the size and extent of ducts and piping while providing sufficient zoning and proper controllability. The preconditioned outdoor air is ducted to space-conditioning air handling units. Each wing has one air-handling unit per floor, with variable-speed drive fan, which supplies all-outdoor air to the offices and laboratories. The air handling units for the building have to handle only about one-fourth the air flow rate of a conventional all-air system, with significant power saving. Chilled water coils in the building’s air handling units have two-way chilled water control valves to minimize pumping power by reducing system flow when any control valve is throttled at reduced load. Cooling: Each office is a separately controlled zone. Principal means of cooling is by radiant chilled water ceiling panels. The interior load is kept low by the daylighting, lighting controls, and the pre-conditioned ventilating air. The panels are supplied with chilled water at 14°C, leaving at 16°C under full load with an average panel surface temperature of 17°C. The chilled water flow rate is controlled by a two-way valve and room temperature sensor with occupancy monitor. A ceiling diffuser in the office supplies a small amount of conditioned air at about 16°C, about one and one half air changes per hour, sufficient to ventilate and pick up a little load, sensible and latent. This satisfies the ventilation requirements, and maintains the office at positive pressure relative to the corridors and outdoors. A damper closes the air supply if the office is unoccupied. The air is transferred by ducts to corridors, storage areas and toilets, and exhausted. Exhausted air runs through air to air heat exchanges to recover energy & cool incoming outside air. To accomplish the efficient controlled operation of a zone, a digital thermostat is wall-mounted in the conditioned space. It controls a chilled water valve supplying the radiant ceiling panels. It receives input for the after-hours shut down of the building and contains a motion detector which shuts off the supply air damper and chilled water control valve when the room is unoccupied. It also overrides the ambient lightning’s sensor to shut off the lights when the room is unoccupied. When the zone is occupied, the light fixtures’ own ambient light sensor permits operation of the artificial lighting as needed. The building’s air handling systems generally shut down outside normal working hours, but any occupied zone can manually override the shutdown of its respective air handling unit. Laboratories are conditioned by a system similar to the offices. The supply air is not recirculated but is exhausted, together with exhaust from variable-flow fume hoods, in a general exhaust system, sized to keep laboratories at negative pressure relative to their surroundings. A separate “snorkel” exhaust system with flexible branch ducts and inlet hoods permits local exhaust at higher negative pressure from any specimen when required. A radiant ceiling panel is the principal means to cool the space. Directly in front of fume hoods, conditioned air at 22°C and 50 % relative humidity is supplied. Typical clothing in Honolulu offices and laboratories is 0.5 clo insulating value or less. With a metabolic rate of 1.2 met or less, and a minimum air velocity of 0.40 mis, a predicted mean vote of 5 percent dissatisfied, the optimum possible, can be achieved with an air temperature of 26°C and 50% relative humidity. An all-air system’s air temperature would have to be at least 2°C lower for equivalent comfort. Storage rooms are generally in the building interior, with very low cooling load. They are conditioned by transfer air at about 2 air changes per hour, exhausted to the general exhaust system. The entrance foyer is conditioned with a displacement ventilation supply system. Assembly and conference rooms are conditioned as for offices, but with a greater maximum supply rate of conditioned air. The parking garage is arranged for sufficient wall opening to permit natural ventilation. The building includes a kitchen and food service facility. Kitchen exhaust from cooking hoods conforms to NFPA 96. Water Chilling Plant: The air conditioning design results in a very efficient chilled water system. The chilled water piping system is a primary-secondary system with a constant-speed primary pump for each chiller, and two variable-speed secondary pumps. This permits flexibility of chilled water distribution without extra complication in control of the chiller plant. The chillers are selected for excellent part-load efficiency, with consideration that the available entering condenser water temperature can almost never be below about 25°C in Hawaii’s climate. Dual-compressor centrifugal chillers offer the best performance at the roughly 200 ton/ 800 kw water chiller load. A chiller selected to deliver 13°C chilled water has a coefficient of performance (COP) of 7 from full load to below one-fourth full load. With two chillers, the COP is above 8 nearly all of the time. Refrigerant is chlorine-free, low global-warming-potential HFC 1 34a. The chiller plant is controlled by the manufacturer’s microprocessor-based system. Heat rejection from the refrigerant compressors is handled by roof-mounted cooling towers. Chillers are mounted near the center of the roof to shorten chilled water piping and condenser water piping. The cooling towers also have to cool the water which removes heat of absorption, sensible heat from air cooling, and residual heat from the warm concentrated liquid desiccant returning from the regenerator. Pumps for liquid desiccant system cooling water have variable speed drives. Condenser water pumps are constant speed to ensure sufficient flow for centrifugal compressors at light loads. Water, Waste and Drainage: The solar thermal collector system used for regeneration of the liquid desiccant has sufficient storage to provide full capacity over a period of several cloudy, rainy days. Domestic service hot water is also provided by the solar collectors. Back-up for the system is provided by a reciprocating water source heat pump using R-1 34a refrigerant, which can provide 71°C water, providing reasonable dehumidifier performance. A gas-fired hot water boiler is also being considered at lower first cost to provide the regeneration hot water, as well as the service hot water, but will have much higher operating cost. Plumbing design includes low-flow water closets and urinals, with flow-controlled faucets on lavatories. Size of the facility and site mitigate against use of gray water, but site irrigation is supplemented from rain water storage tanks. Potable water, from the Honolulu municipal system, is supplied at sufficient pressure that no service water pumps are needed. Drainage sump pumps are provided at the basement level, discharging to a city storm sewer. Waste piping is discharged to a city sanitary sewer. Laboratories’ waste piping is chemical resistant, and provision is made for a dilution tank prior to discharge into the sanitary sewer. Compressed air, gas, and vacuum systems are provided to the laboratories. Fire Protection: The building is completely protected by a wet-pipe automatic fire sprinkler system conforming to NFPA-13, and the building is completely protected by a fire alarm system conforming to NFPA. Lighting and Electrical: Day-lighting is the principal source of illumination, supplemented by artificial ambient lighting by direct-indirect fluorescent lighting fixtures suspended from the ceilings and task lighting mounted on office furniture. Lighting intensity generally conforms to recommendations of the IESNA for the applications involved, with a low level of ambient lighting. Exterior lighting is minimal, but sufficient for security. Light fixtures contain their own ambient light sensor to turn off when day lighting levels are sufficient. A manual override can be operated by the occupant using an infra red link to the light fixture. This results in an installation which is very flexible and economical on cabling. Each light fixture (8 feet long using 2 x 39 watt T5 lamps) is virtually self-contained requiring only a single power feed cable. No switching or control cabling is needed. Future relocations will be easier and will cause minimal wastage in cabling, switch drops etc. Electric power is supplied at utility voltage, three-phase four-wire 208/120 volt, 60 hertz. The entire building works on 208/120 volt only thereby eliminating, energy losses & heat loads from step down tranferences. A diesel electric emergency generator is provided for essential services, life safety and egress systems, with a 48-hour supply tank. Construction of the facility will include a modular wiring system for all receptacles & communication cabling in a readily removable and accessible raised floor system. Telecommunications, data and intrusion access systems will be included. The Government will provide computers and networking components. The building’s structural wiring system will conform to TIAIEIA 568-A-5. 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The building’s arrangement, essentially three east-west oriented wings, minimizes solar load and makes daylighting of offices more efficient, since there is very little west fenestration, with office windows generally north and south. Most of the office area is in the South Wing and laboratories in the North Wing. Mechanical and electrical systems are designed to meet the project’s objective: functional, sustainable and energy-efficient, contractible within budget. At this writing the design is schematically complete but details are still under development.