Consulting-Specifying Engineer - December 2007 - (Page 27) • For receptacles actual: 19,200 sq. ft x 8,760 h x 0.29 W/sq. ft = 48,776 kWh. The actual number of hours increased because they had to start up the unit two hours earlier every day, used the unit during the lunch hour, and used it for two additional hours every day in the afternoon, which lead to the difference between design and actual electricity use for the air conditioning system. The number of hours used in the design model is 2,496, but the actual number of hours is 4,400: 4,400/2,496 x 51,885 kWh = 91,464 kWh Mechanical integration The air conditioning system consists of an air-handling unit (AHU) with a VAV adjustable-pitch vane axial fan with variable volume boxes to maintain static pressure and variable volume diffusers in every location. The AHU has a DX cooling coil that is vertically split intertwined and has a double circuit, top and bottom. The AHU is a draw-through type, and each coil section closest to the fan has an individual 5 TR (tons of refrigeration) condensing unit connected to it that runs continuously while the fan is operating. Each of the other coil sections of the split coil is connected to a variable speed 5 TR condensing unit and responds to leaving air temperature (set at 53 F). The variable speed condensing units are not allowed to cycle more than six times per hour. If the building temperature drops below 73 F, the VAV reheat water pump operates to raise the building return air temperature through the reheat coil. This combination of sequences allows the A/C system to maintain 72 F +/-1 F and 50% +/-5% relative humidity. Outside air is forced into the AHU return plenum by a VAV energy recovery unit that is capable of 125% of the required air for ventilation. The AHU has (MERV 14) 85% efficient permanent filters and 40% throw away pre-filters. It also has UV-C lights in the return air plenum using the intensity recommendations from “Immune Building Systems Technology” (Wladyslaw Jan Kowalski, McGraw-Hill, 2002). All ductwork in the building is galvanized sheet metal double-wall with solid interior Table 3 - Energy management system data Use Lighting Receptacles A/C Design (kWh) 29,823 19,740 51,885 Actual (kWh) 23,000 48,000 83,500 Design uniqueness “The positive environmental impacts that result from the design of our new building are significant and many,” Quintana said, “including condensing units that use R-410A refrigerant; electrical savings of 70% that substantially reduce carbon dioxide generation; and recycling of materials such as glass, paper, aluminum, cardboard, electrical lamps, printer cartridges, car batteries, oil, cellular phones, sheet metal, car tires, wood pallets, and grass.” In addition, light pollution is eliminated by keeping the illumination within the site; all storm water is strained for removal of oil residue and some phosphorus; rain water is used for toilets and urinals; and the facility’s own sewage treatment plant operates on evapotranspiration, which does not impact acquifer recharging. Storm water is retained in an underground rechargeable tank that slowly releases water during a 72 h timeframe so that water will not affect the level of the creek close to our site. “We feel that our building is really unique,” Quintana said. “It is located in Puerto Rico without the benefits of using cold outside air for air conditioning at any time during the year. Yet still, we have achieved 750 sq. ft/ton. “The greatest reward was that project goals were accomplished, and that the owner obtained substancial savings from energy and water measures that were implemented during the design process,” he said. “The coordination between the owner, which in this case was the contractor, and the rest of the design team was a great plus for implementing all the energy savings into the project.” Because the owners of the facility are in the MEP business themselves, they began this project with a strong notion of what could be achieved, and challenged their design team with the task of far surpassing their existing building in energy use reduction. And the design team did a “platinum” job of meeting the challenge. liner and fiberglass insulation sandwiched between duct walls. Additionally, the inner duct liner is covered with a technology that liberates silver ions and prevents bacterial growth inside the ducts. All VAV diffusers (thermafusers) were placed so as to achieve an air diffusion performance index of 90 or greater. Areas with more than one occupant have a thermostat that can bypass the VAV serving the area and convert the VAV to temperature-controlled for a period of 3 hours. A Web-based monitoring system samples seven different areas of the building for temperature, relative humidity, carbon monoxide, carbon dioxide, VOCs, and particulate. This continuous sampling process also reports to the energy management system. In order to verify the particulate reported by the monitoring system, the engineers brought in a particle counter and the area sampled at random reported as ISO class 8 clean room. The ratio is maintained at a maximum of 1.0 cfm/sq. ft and a minimum of 0.7 cfm/sq. ft by the VAV system. The ratio of exhaust air to intake air is controlled using VAV units in both supply and exhaust fans to achieve positive building pressurization, adequate exhaust control, and minimum ventilation requirements at all times. Only if the carbon monoxide in the building exceeds 800 parts per million will the minimum ventilation rate be exceeded while always maintaining building pressurization. Not only did the design team create a high-performance facility in terms of energy efficiency, but they also maximized efficiencies with respect to operation and maintenance. The AHU, energy recovery unit, condensing units, desuperheaters, reheat water tank, reheat pump and domestic solar hot water collectors all are located on a single pad outside the building for ease of maintenance. And the commissioning process verified each and every item of the HVAC and plumbing system. Consulting-Specifying Engineer • DECEMBER 2007 27
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