BLACKSTONE (2006) – Each area of the building has one or more two-pipe valance units, with a condensate drain riser adjacent to each unit. Blackstone's valance units are part of a system in which the heating and cooling is decoupled from the ventilation, which reduces the fan load.

 

Valance systems are induction units that provide cooling or heating. In cooling mode, chilled water is circulated through finned coils in the unit. As warm air rises, it passes over the coils, is cooled, and sinks to the floor, creating a constant convective loop. By eliminating the need for forced air, the cooling load is reduced. In heating mode, hot water passes through the finned tubes. As air passes over the coils, a layer of radiative warmth is formed across the ceiling and is radiated back down into the space. These units eliminate the need for an electric-driven fan to push air, saving money and energy, while reducing draft and eliminating noise.

 

ASHRAE Standard 62-2001 Ventilation for Acceptable Indoor Air Quality

Building Air Quality, US Environmental Protection Agency, Indoor Air Division

SMACNA IAQ Guideline for Occupied Buildings Under Construction

ANSI/ASHRAE Standard 55-1992 Thermal Environmental Conditions for Human Occupancy

 

ALDRICH HALL, HBS (2006) – Supplemental cooling in the lecture rooms is provided by active chilled beams (Trox DID300) installed in the ceiling of each lecture room. Chilled water for the beams is provided via a plate and frame heat exchanger connected to the return line of the campus chilled water system.

Chilled beams are linear ceiling-mounted units with coils that cool space by moving the air in a convective loop. There are two types: passive and active. Passive chilled beams are convective units located in the ceiling. As warm air rises, it passes over the beams and cools the air, which then sinks downward. They can be used in conjunction with raised access floors. Active chilled beams are coupled with nozzles to provide ventilation. Click here for an animation of chilled beams. These systems can result in significant energy reductions. See the November 2005 Building Design and Construction article for more information. Affiliated Engineers also compared the economic benefits of chilled beams versus a VAV system.

 

 

WYSS HALL (2006) – The HANSA smart panel system is a ceiling-mounted induction system. The system is expected to save over $4,000 in annual energy costs, with a 9.75 year payback period. Michael Willamson of Cosentini Associates wrote a description of the panels: "The system takes primary air from a central air handling unit and ducts it to each unit.  The primary air induces room air through a cooling coil and back into the room.  The cooling capacity of each unit is directly related to the volume of primary air.  Although no fan energy is required at the units, there is a significant pressure drop at each unit, shifting the fan energy from the terminal units to the main air-handling unit.  All dehumidification is done at the central air handling unit.  If untreated outdoor air is introduced into the space directly, the potential for condensation at the unit exists.  The system at Wyss Hall takes return air to the air handling unit and has a larger air supply (and duct size) to each unit. The advantage to the Hansa Smart system is that it is quiet.  The disadvantage is that it shifts part of the cooling load to a central air handling unit which requires larger ductwork and air volumes to each space, and requires a return air system." See the Hansa website for more information.

 

60 OXFORD STREET (2004) – At the 60 Oxford data center, the servers area is arranged so that cold air enters through the raised access floor, blowing directly onto the computers, where cool air is most needed.  This design solution saves energy by reducing the cooling load. This variable air volume system has a one year warranty for parts and labor after start-up or 18 months from date of shipment from the factory, whichever occurs first. The contractor and/or vendor shall maintain availability of replacement parts compatible with the terminals for no less than ten years after acceptance. The system is a York Flexsys Underfloor System with variable air volume.

 

LANDMARK CENTER (2001)

MAKE AND MODEL	PAYBACK	CHILLER REDUCTION
Tate Access Floor		$307,000 (35,000 sq.ft) = $9/sq. ft., energy savings of 20% or more Savings of $14,000 per year

 

 

With displacement ventilation, supply air is provided at the floor. Return vents are placed at the ceiling, so that air from the floor constantly pushes old air out. This can significantly improve indoor air quality and increase worker productivity. Raised access flooring, or underfloor air distribution, is an energy-efficient and healthy means of circulating air. In typical office construction, cold air is diffused through the ceiling.  Since warm air rises, this system can often be inefficient. See the Tate Access Floor brochure for detailed environmental benefits of these systems.

 

Underfloor air distribution systems improve both energy efficiency and air quality. Network and computer equipment is often a source of continuous upward convection as the integral fans reject heat from the device to the room. Warm air rejected from these devices rises rapidly relative to the convection of typical office space heat sources. This more pronounced convection, found in areas with a high density of electrically powered heat sources, would impede delivery of cool air to where it is typically needed most in computer rooms – at the floor where the equipment resides. Thus, the coolest air never reaches the equipment, since it is "warmed" on its way to being directed downward to the warm equipment. With an underfloor system, the coolest air is delivered to the space at the zone where the most heat is being generated, providing the benefit of delivering the coolest air directly to where it is needed.

 

When compared to traditional overhead air delivery systems, underfloor systems provide inherent savings, as well as indoor environmental benefits. HVAC fan energy is reduced since convection in the spaces now assists, rather than impedes, the HVAC system fans. Fan energy consumption is further decreased due to the elimination of much of the ductwork associated with overhead HVAC systems. Also, air can be delivered to spaces at a warmer temperature, since it is being delivered to those points where it is most needed before being warmed by other space loads, such as ceiling lights. The natural convection assisting underfloor air systems also helps to sweep the dust by-products from fax and copy machines up and away from the breathing zone. Since clean, filtered supply air doesn't have to mix with unfiltered room air, the air that flows through the breathing zone is new, and cleaner. The health improvements associated with underfloor air systems are essential to occupant productivity, comfort, health, and safety.

 

(image from Tate Access Floor - click top image for larger views)

 

(image from Danny Beaudoin, 2006 Landmark Center presentation)

 

The Landmark Center HVAC system is a variable air volume raised access floor displacement ventilation system, which is the largest raised access floor in New England. This design incorporates three York variable frequency drive air handler units capable of delivering a maximum of 15,500 CFM of mixed air each through the under-floor plenum area and York VAV boxes to the occupied space. The VFD operates within a range of 24 to 54 hertz to ensure 20 CFM of outdoor air per occupant is available year round in all occupied office areas. The outdoor air is provided pre-conditioned to 55 0F DB at a fixed value of 1,850 CFM per AHU. The outdoor air supply duct is outfitted with an airflow station, which modulates the damper actuators via direct digital control (DDC) program logic to maintain a constant 1,850 CFM of outdoor air to the AHU. Differential pressure sensors shall maintain the plenum at 0.05 in water closets by controlling the AHU VFD’s. Field-testing was performed to establish the leakage rate through the raised access floor system by closing all VAV boxes completely and monitoring the VFD signal required to maintain plenum pressure (description from Landmark LEED submission).

 

According to Danny Beaudoin, HSPH Manager of Facilities, Energy, and Utilities, energy reduction with a displacement ventilation VAV system is typically 20 to 30%. With HVAC energy costs at $5 per square foot, then: $5 x 35,000 square feet = $175,000 x 20% = $35,000 annually.