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Description

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Task/ambient conditioning (TAC) systems

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“… the occupant can control the perceived temperature … [with a] … higher degree of personal comfort control provided by the localized supply outlets.”

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Fig 1.3

“TAC systems use active diffusers … as part of the furniture or partitions.”

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“… zero-pressure plenums pose no risk of uncontrolled air leakage to the conditioned space, adjacent zones, or the outside.”

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“Fan-driven TAC diffusers can more directly influence local thermal comfort by using increased air movement to provide occupant cooling.”

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“Tenants’ ability to control the temperature … is the only feature to show up on both the list of most important features (96%) and the list of items where tenants are least satisfied (65%).”

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“TAC system concept approaches the optimal solution … under the control of … a ‘human’ thermostat.”

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“(Most of the cost of access flooring, if not all of it, is amortized by the savings in wiring for electric, power, telephone, and computers, as well as reduced ductwork.)”

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Reference Levy, 2002, “Individual Control by Individual VAV.”

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Reference Argon literature 2002.

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“… fan-driven supply outlets (airflow directed at the occupant) provide personal control of an occupant’s microclimate over a sizeable range … total cooling (including latent effects) would be even higher … more than enough to allow the full range of individual thermal preferences …”

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“… desk-mounted TAC diffusers can provide significantly improved ventilation effectiveness over mixing systems.”

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“In-house maintenance personnel can carry out … reconfigurations at significantly reduced expense using simple tools and modular hardware.”

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“… improvements in productivity in the range of 0.5% to 5% may be possible …”

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“TAC systems [have] strong potential for improved thermal comfort and ventilation performance over other system configurations.”

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“By allowing personal control … TAC systems satisfy the requirements for higher allowable air velocities contained in [ASHRAE] Standard 55 and have the potential to satisfy all occupants.”

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“One of the greatest potential advantages of TAC systems [is that] individual preferences can be accommodated.”

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Fig 3.3

Underdesk active (fan-powered} diffusers

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“… personal cooling control of equivalent whole-body temperature … up to 7°F(4C) of sensible cooling for underdesk outlets.”

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Fig 3.5

Sensible whole-body cooling rates (ΔEHT) for underdesk jet diffuser.

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“… occupants who have no individual control capabilities are twice as sensitive to changes in the temperature of their environment …”

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“Faulkner found that air change effectiveness … produced by an underdesk diffuser … ranged from 1.4 to 2.7”

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“Kroner … concluded that [a] desktop TAC system was responsible for a 2.8% increase in worker productivity.”

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“Wyon estimates that … the provision of individual control of local cooling and heating +/- 5°F(+/-3°C) can improve group work performance by 2.7% [to] 8.6%.”

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“Fan-powered outlets provide improved control …”

“Zero-pressure plenums pose no risk of uncontrolled air leakage …”

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“… designers can expect to encounter leakage losses from 10-30% …”

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“The most effective TAC diffusers are local fan-driven, jet-type diffusers and are located on the furniture in close proximity to the occupant.”

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Fig 5.1

TAC diffusers

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“… active underdesk TAC diffuser … permits a true task/ambient control strategy to be employed.”

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Fig 5.13

Underdesk TAC supply unit (Argon 2002)

Fig 5.14

Alternative TAC supply outlet configurations (Argon 2002)

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“… offset carpet tiles provide an improved seal for air leakage between floor panels from a pressurized plenum.”

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Control problems with interior zone CAV pressurized plenums require supply air temp reset

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Return air face and bypass for humidity control

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“Another task/ambient control strategy … allows individuals to choose the amount of air from an underdesk diffuser for personal comfort without influencing the total amount of air being delivered to the space [Levy 2002].”

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Individual control utilization

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Underfloor plenum cleaning

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“Both increased SAT and increased RAT extend economizer operation.”

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Active fan-driven diffusers to control conference rooms

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Cost considerations

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ASHRAE Std 62-2001

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Increased ventilation effectiveness for displacement ventilation and UFAD

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NFPA 90A – Dirt collection and grille spacing standards

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Return air configuration with bypass for humidity and SAT control

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Levy, 2002. “Individual Control by Individual VAV.”