Raised Access Floor - (AE Breadth Area)

Raised Access Floor - (AE Breadth Area) Currently, the Plaza has a raised access flooring system on both the 7 th and 8 th floors. The 8 th floor is designed with an independent HVAC system utilizing an underfloor distribution system. The 7 th floor, however, uses a conventional distribution HVAC system which is tied to the building HVAC. The suggestion to use a raised access flooring system was made by the architect, Kendall Heaton, primarily due to the sophisticated and rapidly changing technical needs of the communication system on those floors. Benefits Utilizing raised access flooring throughout an office has proven to be a beneficial choice for a variety of building owners and occupants. Pennsylvania s Department of Environmental Protection found that by using a raised access flooring system coupled with an underfloor air distribution system they could reduce life cycle and energy costs while increasing occupant productivity. Also, ASHRAE has found that underfloor air can provide increased indoor air quality and occupant comfort. The primary benefits addressed in this analysis are the ease of initial installation of the systems, the quicker renovation Investigated Benefits Ease of initial installation Quicker renovation times Reduced churn costs Additional Benefits Improved Indoor Air Quality (IAQ) Improved occupant comfort durations and the decreased churn costs. Currently, the Plaza is designed with a complex system of ductwork. This presents not only an MEP coordination challenge, but also adds to the overall cost of the systems. Basic Design Components The raised access flooring system is a 12 inch high system, 24 x24 flooring tiles. It is covered by modular carpeting tiles, allowing for ease of access to the flooring system. The underfloor HVAC system utilizes the space below the flooring as the supply air plenum, with specialized ducted designs for zones which have more specific climate control needs. Air terminals supply air through the floor into the occupied space. These terminals, also called MIT s (Modular Integrated Terminal), can be used either with or without ductwork, and function as either a simple diffuser or also as a VAV box. The system uses the ceiling plenum as the return air plenum. HVAC control, power, data and voice are all supplied through specialized modular components. These include control boxes, utility boxes, and quick connect cables. Because these systems share an integrated supply system, are modular, and have plug connections, installation is greatly simplified, reducing installation time and labor cost. 15

Concerns Floor to floor height considerations One obvious concern with raised access flooring is the idea that it will require additional floor to floor height, thus adding to the overall cost of the structure. On the Plaza, the additional floor to floor height between floors seven and eight, however, is a result of the overhead HVAC and fifteen foot ceilings. A raised access floor can be implemented on floors two through six with no increase in floor to floor height. There are a few beams which, under the modified system, would protrude six inches below the bottom of the ceiling. This can be solved, however, with minimal modification by constructing small bulkheads around these beams. Cold Feet On early implementations of underfloor air distribution, occupants complained of having cold feet and legs. This problem is correctable, however, by utilizing air terminals which offer both air volume control as well as directional control, and by locating these terminals between occupant workspaces. HVAC System Design Airflow Design The underfloor air system is a displacement system. In contrast to a traditional HVAC system, a displacement system is designed to supply air at only a few degrees cooler than the desired room temperature. Diffusers in the floor supply this cool air at a low velocity, displacing the warmer air already in the room. The warmer air, rising naturally, is exhausted through returns located at ceiling level. Because air supplied at a warmer temperature and at a lower velocity this system is less drafty than a conventional overhead air supply system. Also, because the air is moving from the floor to the ceiling, the heat and contaminants produced in the space are carried away from the occupants rather than forced toward them. Base Building System The system currently designed for the Plaza is a traditional overhead supply system, supplying air at 55 degrees and at a higher velocity. For a displacement distribution system, which supplies air at 65 degrees, the cooling loads are lessened. Also, the elimination of ductwork reduces the fan load on the system. This allows for the current chillers and air handling units to be retained. A common concern of displacement systems is humidity control. Because the supply air is warmer than a traditional system, it is more difficult to ensure that the air is sufficiently dehumidified as it passes through the chiller system. This concern is addressed, however, by retaining the current chilled air temperature. 16

Because the air supplied by the chiller is at a cooler temperature than the required supply air temperature, VAV boxes with reheat coils are required on each of the floors. Also, underfloor supply plenum systems generally incorporate individual air handling units for each floor. This is emulated by the VAV boxes, however, by allowing each floor to individually mix and control the air being supplied. The underfloor system also allows for the elimination of some of the base building ductwork. The main vertical supplies and returns must be retained. The main supply and return trunks on each floor, however, are no longer necessary. HVAC Zones To help with individual control of building zones with differing climate control needs, a rectangular office building such as the Plaza, is divided up into no less than 9 zones. These zones include a central zone, four perimeter zones and four corner zones. These are further divided for areas such as conference rooms and individual offices. In order to separately control the individual zones, plenum barriers, VAV air terminals and underfloor ductwork are utilized. Each of these zones utilizes the space above the ceiling as the return air plenum. Central Zones The central zone is the most basic of the various zones. Because the heating and cooling loads are consistent across the entire space, the air can be supplied at a constant volume throughout the zone. The air terminals used in this space do not need to be automatically controlled, although accessible manual controls are often viewed as a benefit by the occupants. The floor plenum in the Plaza is obstructed by the underfloor ductwork needed to supply air to enclosed spaces, such as conference rooms. Also, the ceiling return plenum is obstructed by a few deep girders. Therefore, these are used as natural zone barriers, which separate the central zone into four smaller zones. Therefore, each of these smaller zones has its own supply and return ducting to compensate. Perimeter Zones Because of the additional heating and cooling loads which are incurred around the perimeter of the building, additional thermal control is required. In order to compensate for this, perimeter zones are created using a semi-ducted distribution system. Air terminals are placed both along the perimeter wall as well as along the central zone. The terminals are connected through ductwork, and a fan powered heating terminal. During cooling mode, all of the air terminals act as simple, independent VAV boxes, regulating the supply from the underfloor plenum. During heating mode, the central air terminals act as intakes, from which the fan draws air from the occupied space, through the heating terminal, and is supplied back to the occupied space through the perimeter air terminals. 17

Corner Zones Corner zones are separate from perimeter zones, but are treated similarly. Two air terminals are placed along the central zone as air intakes, while another two air terminals are placed along the perimeter wall as supply air. These units are connected in the same fashion as with the perimeter system, with ductwork and a fan powered heating terminal. Perimeter Enclosed Offices Perimeter enclosed offices utilize the same system as perimeter zones. Because the air terminals are individual VAV boxes, each terminal can be separately controlled, thereby independently regulating office temperatures. Non-perimeter Enclosed Offices These office spaces can be regulated using constant volume air terminals, treated in the same way as the central zone. If the space is expected to receive unusually high cooling loads, it can be treated instead as a conference room and supplied with ducted cooling. Conference Rooms Because of the higher and more varied loads experienced by conference rooms, a ducted system is preferable to the underfoor plenum. The air is then supplied through VAV air terminals, which combined with individual thermostats, allows for temperature control of individual rooms. 18

Construction Although there is the added task of installing the raised access floor, the installation of the mechanical, electrical and communication infrastructure is simplified. By utilizing a fully modular system, installation and connection of these components is made significantly simpler. Because power, data and voice can all utilize a shared cable, only one cable needs to be run between each box. The HVAC controls utilize a similar system, even further simplifying the overall installation. Renovation Because of the modular nature of these systems, renovation is simplified. Components can be reused, virtually eliminating additional materials costs. This includes nearly all of the components, from the mechanical system VAV boxes to the modular carpet tiles. The modular nature of the system also allows for convenient renovation of individual work spaces, which permits spaces to be configured to meet the needs of specific employees. Impact to Initial Cost The base building costs are increased for a raised floor system due to the additional costs of the floor and of the need to raise the core area. For the Plaza redesign, there was no change to the base building HVAC systems. The tenant fitout costs are also slightly more for the raised floor system. This is due to the increased cost of materials for the specialized distribution systems. The HVAC costs are significantly reduced, however, due to the elimination of large quantities and complexities of ductwork. Also, because of the modular nature and integration of the electrical and communication distribution systems, installation labor costs are reduced. The additional first cost, therefore, is only $800,000, or about $3.67/SF. First Costs Conventional Overhead Systems Raised Floor Systems Base Building Raised Access Floor $0 $1,104,831 Raised Core Area $0 $231,192 HVAC $2,015,000 $2,015,000 Tenant Fitout HVAC $1,873,182 $1,011,893 Electrical Power $982,091 $1,146,100 Data/Comm. $1,081,364 $1,259,032 TOTAL $5,951,636 $6,768,048 Cost/SF $26.77 $30.45 Additional First Cost Per SF $0.00 $3.67 Total $0 $816,411 Churn Cost Analysis The average office churn rate for utilities is nearly 50%, while typical general office buildings are around 40% (International Facilities Management Association). Because 19

this building is not exclusively leased by PPL Resources, the more conservative general office churn rate of 40% is Distributed Churn Costs used in the cost savings analysis. For a typical overhead system the churn costs for the Plaza would be $1.2 million per year. For a raised access system, however, the yearly churn cost is only $270,000, an 80% reduction in cost. Therefore, the payback period for the system is less than a year. Impact to Schedule The schedule is impacted in a variety of ways through the use of Conventional Overhead Systems Raised Access Systems Churn Cost /SF $14.89 $3.08 Churn Cost Total $3,309,694 $684,066 Churn Rate (%) 40% 40% Churn Cost /Year $1,323,878 $273,626 Churn Cost Savings /Year $0 $1,050,251 First Costs /SF $27 $30 First Costs Total $5,951,636 $6,768,048 Additional First Cost $0 $816,411 Payback Period (Years) 0 0.8 raised access flooring, an underfloor air distribution system and a modular utility distribution system. The raised access floor itself increases the duration of the schedule. For the Plaza, 70 days are necessary to install the flooring system. This is done simultaneously to the installation of MEP rough-ins, however, and is offset by the decrease in time required to install the MEP systems. The significant simplification and reduction in ductwork will decrease MEP coordination times, and overall cause the project to progress more smoothly. 20