Understanding Chilled Beam and VAV Systems John Murphy, LEED® AP BD+C Applications Engineer Trane Ingersoll Rand La Crosse, Wisconsin

Chilled Beams • Brief overview of chilled beams • Assess marketed advantages of chilled beam systems versus VAV • Discuss challenges of applying chilled beam systems • Review some common applications

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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Passive Chilled Beam

ceiling

water pipes coil

perforated metal casing

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Active Chilled Beam primary air

nozzles coils

ceiling induced air

induced air + primary air

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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Active Chilled Beams

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Source of images: Halton

active chilled beams

Primary Air System

primary air handler

OA RA

EA

PA

RA

PA

RA

active chilled beam

RA

Primary air must be sufficiently drier than space: • to offset space latent load, and • to keep space DP below chilled beam surface temp

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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window

Induction of Mid-20th Century Active Chilled Beams • Installed on ceiling rather than under windows – More coil surface area – Lower air pressure required induced room air

• Warmer water temperature – No condensation – More coil surface area – Lower air pressure required

nozzles

• Larger ducts floor primary air

condensate drain connection

– Lower air pressure required – Less noise

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Chilled Beams • Brief overview of chilled beams • Assess marketed advantages of chilled beam systems versus VAV • Discuss challenges of applying chilled beam systems • Review some common applications

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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active chilled beams

Claimed Advantage #1 • “An ACB system typically allows for smaller ductwork and d smaller ll air-handling i h dli units it than th a VAV system.” t ” – Primary airflow < supply airflow due to induction – Shorter floor-to-floor height required? – Less mechanical room floor space?

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active chilled beams

Determining Primary Airflow Rate • Primary airflow (PA) is

PA

b based d on llargestt of: f – Minimum outdoor airflow required (ASHRAE 62.1) – Airflow required to offset space latent load (depends on dew point of PA) – Airflow needed to induce sufficient room air (RA) to offset the space sensible cooling load

RA SA

SA

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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active chilled beams

Determining Primary Airflow Rate Minimum OA per ASHRAE 62.1 (to achieve LEED IEQc2) ACB C system Airflow required to offset space latent load

Airflow needed to induce sufficient room air to offset space sensible ibl cooling li lload d VAV system Airflow needed to offset space sensible cooling load

Example: office space 0.085 cfm/ft2 (0.085 × 1.3 = 0.11 cfm/ft2) 0.085 cfm/ft2 0.11 cfm/ft2 0.36 cfm/ft2

(DPTPA = 47°F) (DPTPA = 49°F) (DPTPA = 53°F)

0.36 cfm/ft2 (55°F primary air) (four, 6-ft long beams)

0.90 cfm/ft2 (55°F supply air)

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active chilled beams

Determining Primary Airflow Rate Minimum OA per ASHRAE 62.1 (to achieve LEED IEQc2) ACB C system Airflow required to offset space latent load

Airflow needed to induce sufficient room air to offset space sensible ibl cooling li lload d VAV system Airflow needed to offset space sensible cooling load

Example: K-12 classroom 0.47 cfm/ft2 (0.47 × 1.3 = 0.61 cfm/ft2) 0.47 cfm/ft2 0.61 cfm/ft2 1.20 cfm/ft2

(DPTPA = 44°F) (DPTPA = 47°F) (DPTPA = 51°F)

0.47 cfm/ft2 (55°F primary air) (eight, 4-ft long beams)

1.20 cfm/ft2 (55°F supply air)

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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Minimum Outdoor Airflow Required by ASHRAE 62.1 typical ACB primary airflow (0.30 to 0.70 cfm/ft2) Barracks sleeping area example (0.47 cfm/ft2)

Classroom (age 9 plus) Conference/meeting room Corridor Courtroom Hotel bedroom/living room Laboratory Lecture classroom Library Lobby (hotel, dormitory)

example (0.36 cfm/ft2)

Office space Reception area Retail sales floor 0.10

0.20

0.30

0.40

0.50

0.60

0.70

minimum outdoor airflow required,

0.80

0.90

1.0

cfm/ft2

(based on default occupant densities)

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active chilled beams

Claimed Advantage #2 • “An ACB system can typically achieve relatively low sound d llevels.” l ” – No fans or compressors in or near occupied spaces – Constant primary airflow = constant sound – Depends on air pressure

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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active chilled beams

Claimed Advantage #3 • “An ACB system uses significantly less energy than a VAV system, t due d to: t 1. Significant fan energy savings (because of the reduced primary airflow), and 2. Higher chiller efficiency (because of the warmer water temperature delivered to the chilled beams), and 3. Avoiding reheat (because of zone-level cooling coils).”

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Fan Energy Use: ACB vs. VAV •

A zone served by ACB’s may require 60% to 70% less primary airflow, at design cooling conditions… …but the difference in annual fan energy use will be much closer because the VAV system benefits from: 1. Reduced zone airflow at part load 2. System load diversity 3. U 3 Unloading oad g o of tthe e supp supply y fan a at pa partt load oad

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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example

Zone Primary Airflow at Part Load zone e primary airflow, cfm m/ft2

1.0

1.0

conventional VAV system

0.8

0.8

0.6

0.6

0.4

0.4

30% minimum i i airflow i fl setting tti

0.2

0

cold-air VAV system

active chilled beam system

design heating load

space load

0.2

design cooling load

0

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System Load Diversity variable-volume fan 0.72 cfm/ft2

OA

multiple-zone VAV system central VAV fan sized for “block” airflow

RA

EA

PA

PA

fan airflow = diversity × Σ zone primary airflows

RA

RA

RA

0.90 cfm/ft2

0.90 cfm/ft2

0.90 cfm/ft2

constant-volume fan 0.36 cfm/ft2

OA

active chilled beam system central CV fan sized for “sum-of-peaks” sum of peaks airflow

RA

EA

For this example: system load diversity = 80% fan airflow = 80% × 0.90 cfm/ft2 = 0.72 cfm/ft2

PA

RA

0.36 cfm/ft2

PA

RA

0.36 cfm/ft2

RA

0.36 cfm/ft2

fan airflow = Σ zone primary airflows For this example: fan airflow = 0.36 cfm/ft2

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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typical VAV system supply fan

Part-Load Performance fan input power, % of de esign

100

80

60

40

VAV supply l fan f with VFD

20

0

0

20

40

60

80

100

supply fan airflow, % of design 19

supply fan energy use

ACB vs. Conventional VAV fan in nput power, bhp/100 00 ft2

1.0

0.8

conventional VAV

design cooling conditions

0.6

active chilled beam

0.4

VAV uses more fan energy

ACB uses more fan energy

0.2

68% of VAV supply fan design airflow

0

0

0.2

0.4

0.6

0.8

1.0

supply fan airflow, cfm/ft2 20

© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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supply fan energy use

ACB vs. Cold-Air VAV fan in nput power, bhp/100 00 ft2

1.0

0.8

0.6

cold-air VAV

active chilled beam

0.4

design cooling conditions VAV uses more fan energy

ACB uses more fan energy

0.2

80% of VAV supply fan design airflow

0

0

0.2

0.4

0.6

0.8

1.0

supply fan airflow, cfm/ft2 21

Chiller Energy Use: ACB vs. VAV •

Chilled water delivered to the chilled beams must be warmer to avoid condensation… …but the chilled water delivered to the primary AHU’s still must be cold to dehumidify the building.

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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Dedicated Chilled-Water Plants chillers

57°F

42°F

63°F

58°F

variable-flow pumps

bypass for minimum flow primary air handlers

chilled beams

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Shared Chilled-Water Plant

42°F

57°F

mixing valve primary air handlers

42°F

T

chilled beams

58°F

54°F 63°F

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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Chiller Energy Use ACB system • Warm water delivered to chilled beams • Still needs cold water delivered to the primary AHU’s for dehumidification • Typically no DCV • No (or minimal) capacity for airside economizing • Waterside economizing (more effective due to warmer water temp)

VAV system Cold water delivered to central VAV air-handling units

•

• • •

Commonly implement DCV 100% capacity for airside economizing Can use waterside economizing, but airside economizing is more efficient

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Waterside Economizer chillers

57°F

42°F variable-flow pumps

bypass for minimum flow primary air handlers

mixing valve 42°F

T

variable-flow pump

58°F

54°F 63°F from cooling tower

chilled beams

waterside economizer heat exchanger

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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Pumping Energy: ACB vs. VAV ACB system • Higher pumping energy use • Warm water temperatures (58°F to 60°F) • Small waterside ΔT (5°F to 6°F) • Water pumped to chilled beams in every space

VAV system Lower pumping energy use • Cold water temperatures (40°F to 44°F) • Large waterside ΔT (12°F to 14°F) • Water pumped only to centralized mechanical rooms

•

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Impact of Reheat Energy VAV terminal with 40% minimum airflow setting primary airflow at design conditions = 0.90 cfm/ft2 primary airflow when reheat is activated: = 40% × 0.90 cfm/ft2 = 0.36 0 36 cfm/ft f /f 2 cooling provided when primary airflow is at minimum: = 0.36 cfm/ft2 of 55°F primary air

PA 0.36 cfm/ft2 55°F

Reheat is needed to avoid overcooling the space when the space sensible cooling load < 40% of design load.

PA 0.36 cfm/ft2 55°F

RA

active chilled beam primary airflow at design conditions = 0.36 cfm/ft2 primary airflow when CHW valve is fully closed = 0.36 cfm/ft2 cooling provided when CHW valve is fully closed: = 0.36 cfm/ft2 of 55°F primary air

Heat is needed to avoid overcooling the space when the space sensible cooling load < 40% of design load. 28

© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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example office space

Cold vs. Neutral Primary Air “Cold” (55°F) primary-air temperature

PA 0.36 cfm/ft2 55°F

RA

• four ((4)) ACBs,, each 6-ft long g x 2-ft wide • primary airflow at design conditions = 0.36 cfm/ft2 • total water flow = 6.0 gpm

“Neutral” (70°F) primary-air temperature

PA 0.50 0 50 cfm/ft f /ft2 70°F

RA

• six (6) ACBs, each 6-ft long x 2-ft wide • primary i airflow i fl att design d i conditions diti = 0.50 0 50 cfm/ft f /ft2 • total water flow = 9.0 gpm

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Heating Energy: ACB vs. VAV ACB system • Heat added when CHW valve closes and primary airflow begins to overcool the space • Typically no DCV

VAV system Heat added when damper closes to minimum and primary airflow begins to overcool space • Commonly implement DCV • Parallel fan-powered VAV terminals can draw warm air from ceiling plenum

•

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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office building

Example Energy Analysis • “Baseline” chilled-water VAV system – ASHRAE 90.1-2007, Appendix G (55°F supply air)

• Active chilled beam system – Four-pipe active chilled beams – Separate primary AHUs for perimeter and interior areas (with SAT reset and economizers) – Separate water-cooled chiller plants (low-flow plant supplying primary AHUs)

• “High-performance” chilled-water VAV system – 48°F supply l air i (d (ductwork t k nott downsized) d i d) – Optimized VAV system controls (ventilation optimization, SAT reset) – Parallel fan-powered VAV terminals – Low-flow, water-cooled chiller plant 31

Example Energy Analysis Annual Building Energy U Use, kBtu/yr

12,000,000

10,000,000

Houston

Los Angeles

Philadelphia

St. Louis

Pumps Fans Heating

8,000,000

Cooling Plug Loads Lighting

6,000,000

4,000,000

2,000,000

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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Chilled Beams • Brief overview of chilled beams • Assess marketed advantages of chilled beam systems versus VAV • Discuss challenges of applying chilled beam systems • Review some common applications

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ACB challenges

High Installed Cost • Limited cooling capacity = lots of ceiling space – Warmer water temperature requires more coil surface area – Induction with low static pressures requires more coil surface area to keep airside pressure drop low

eight i h (8) active i chilled hill d beams, b each 4-ft long x 2-ft wide four (4) active chilled beams, each 6-ft long x 2-ft wide

Example: 1000-ft2 office space

Example: 1000-ft2 classroom

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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System design variable

Impact on installed cost of the chilled beams

Impact on performance of the overall system

2-pipe versus 4-pipe chilled beams

A 2-pipe beam provides more cooling capacity than a 4-pipe beam because more coil surface is available

Using 2-pipe beams requires a separate heating system, otherwise it can result in poorer comfort control because either cold water or warm water is delivered to all zones

Primary airflow rate (cfm)

Increasing the primary airflow rate through the nozzles results in more air being induced from the space space, which increased the capacity of the chilled beam coils

Increasing the primary airflow rate increases primary AHU fan energy use, increases noise in the space space, and requires a larger primary AHU and larger ductwork

Inlet static pressure of the primary air

Increasing the static pressure at the inlet to the nozzles results in more air being induced from the space, which increased the capacity of the chilled beam coils

Increasing the inlet pressure increases primary AHU fan energy use, and increases noise in the space

Dry-bulb temperature of the primary air

Delivering the primary air at a colder temperature means that less of the space sensible cooling load needs to be offset by the chilled beams

Using a colder primary-air temperature may cause the space to overcool and low sensible cooling loads, thus requiring the chilled beam (or separate heating system) to add heat to prevent overcooling space

Entering water temperature

Supplying colder water to the chilled beam increases the cooling capacity of the beam

Using a colder water temperature requires the space dew point to be lower to avoid condensation, which means the primary air needs to be dehumidified to a lower dew point

Water flow rate (gpm)

Increasing the water flow rate increases the cooling capacity of the beam

Increasing the water flow rate increases pump energy use and requires larger pipes and pumps 35

ACB challenges

Need to Prevent Condensation • Primary air system used to limit indoor dew point (typically (t i ll below b l 55°F) • Warm chilled-water temperatures delivered to beams (typically between 58°F and 60°F) • Start primary air system (chilled beams off) to reduce indoor humidity following shutdown • Tight g building g envelope and g good building g pressure control to minimize infiltration – Use caution if the building has operable windows or natural ventilation

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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ACB challenges

Risk of Water Leaks • Lots of water piping, pipe connections, and valves above b every space iin th the b building ildi – Four-pipe systems have twice as much piping and twice as many connections

Example: 1000-ft2 office space

Example: 1000-ft2 classroom

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ACB challenges

No Filtration of Local Recirc Air • Chilled beams typically not equipped with a filter – Coils intended to operate dry (no condensation), lessening concern about preventing wet coil surfaces from getting dirty – Still concern about removing particles generated indoors or brought indoors

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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ACB challenges

Limited Heating Capability • Active chilled beams have limited heating capacity • Chilled beam systems often use a separate heating system (baseboard convectors, radiant floor heat)

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Chilled Beams • Brief overview of chilled beams • Assess marketed advantages of chilled beam systems versus VAV • Discuss challenges of applying chilled beam systems • Review some common applications

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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Office Buildings Why ACB might be a good fit:

Why ACB might not be a good fit:

• Low sensible cooling loads • Low ventilation rates resultlt in i primary i AHU • Low latent loads using mixed air • Not friendly for re-configuring spaces

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Schools Why ACB might be a good fit:

Why ACB might not be a good fit:

• High ventilation rates

• High latent loads require

resultlt in i primary i AHU with 100% OA • Low sound levels

llow d dew point i t primary i air i • Lack of economizing capacity

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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Hospital Patient Rooms Why ACB might be a good fit:

Why ACB might not be a good fit:

• High minimum air change

• No local filtration

rates t (6 ACH) • Low latent loads

( d requirement?) (code i t?)

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Patient Room: All-Air System VAV terminal with reheat coil

230 cfm supply airflow 200 cfm (6 ACH) minimum 67 cfm (2 ACH) outdoor air

return airflow 200 ft2 with 10-ft ceiling height

Design space sensible cooling load = 5000 Btu/hr Design supply airflow (55°F) = 230 cfm Minimum outdoor airflow (ASHRAE 170) = 67 cfm (2 ACH) Minimum supply airflow (ASHRAE 170) = 200 cfm (6 ACH) Airflow turndown before activating reheat = 12%

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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Patient Room: ACB System active chilled beam (qty 1, 10 ft long, 4-pipe)

67 cfm (2 ACH) primary airflow 100% outdoor air

268 cfm (>6 ACH) total airflow primary air + induced room air (3:1 induction ratio)

exhaust airflow 200 ft2 with 10-ft ceiling height

Design space sensible cooling load Design primary airflow (55°F) Minimum outdoor airflow (ASHRAE 170) Total room airflow Capacity turndown before activating heat

= 5000 Btu/hr = 67 cfm = 67 cfm (2 ACH) = 268 cfm (8 ACH, 3:1 induction ratio) = 70%

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active chilled beam systems compared to VAV systems

Summary Potential advantages • Smaller ductwork and smaller air handlers – Primary airflow < supply airflow, but likely > outdoor airflow

• Low sound levels • Impact on overall system energy? – Primary airflow < supply airflow, but constant airflow – Warm water for beams, but cold water primary AHU – Increased pumping energy – No DCV, limited airside economizing

Challenges • High installed cost • Need to prevent condensation • Risk of water leaks • No filtration of local recirculated air • Limited heating capability

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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Additional Resources •

“Understanding Chilled Beam Systems,” Trane Engineers Newsletter ADM-APN034-EN (2009) www.trane.com/engineersnewsletter

•

Chilled-Water VAV Systems, Trane application manual SYS-APM008-EN (2009)

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© 2010 Trane, a business of Ingersoll-Rand Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.

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