ENL DedicatedOAEquipmentOD

Agenda and Objectives

Trane Engineers Newsletter Live Li ve Series

Dedicated Outdoor Air Equipment Previous ENLs have discussed system design and control considerations for dedicated outdoor‐air systems. This ENL will shift the discussion to the various types of equipment used for dedicated OA conditioning, from packaged DX units to split DX systems to air handlers and water chillers. By attending this ENL you will be able to: Summarize the definition of a dedicated OA unit 2. Identify what leaving‐air dew point is required 3. Summarize what the difference between cold versus neutral‐temperature air 4. Identify ASHRAE Standard 90.1 requirements related to dedicated OA systems 5. Identify specific dedicated OA equipment configurations 1.

Agenda 1) Opening (welcome, agenda, introductions) 2) Overview a) What is a dedicated OA unit? b) Review content from previous broadcasts c) Review of ASHRAE 90.1 requirements relates to DOAS 3) Specific dedicated OA equipment configurations a) Identify the goal(s)/purpose of the dedicated OA unit ( b) Goals = Dehumidify Ventilation Only + Meet ASHRAE 90.1 c) Goals = Dehumidify to Offset Space Latent Loads + Meet ASHRAE 90.1 d) Goals = Dehumidify Ventilation Only + Exceed 90.1 (Higher Efficiency) e) Goals = Dehumidify to Offset Space Latent Loads + Exceed 90.1 (Higher Efficiency) a) Cooling/heating sources (list advantages and drawbacks of each) 4) Summary

Presenters

Trane T rane Engineers Newsletter Live Series

Dedicated Outdoor Air Equipment (2011)

Ronnie Moffitt | applications engineer | Trane Trane Ronnie joined Trane Trane in 1996 and currently is an airside applications engineer whose responsibility is to aid design engineers and Trane Trane sales personnel in the proper design and application of HVA HVAC C systems. His primary focus has been dehumidification and air ‐to‐air energy recovery design. This includes the development, design and control optimization of desiccants in commercial HVAC HVAC systems. He has several patents pa tents related to this subject and serves ser ves on related AHRI and ASHRAE engineering committees. Ronnie led the development de velopment of the Trane Trane CDQ system, a winner of the R&D 100 Award for The Most Technologically Significant New Products of 2005. He is a certified Energy Manager (CEM) by Association of Energy Engineers and received his B.S. in Aerospace Engineering from Syracuse University. University. John Murphy | applications engineer | Trane John has been with Trane Trane since 1993. His primary responsibility as an applications engineer is to aid a id design engineers and Trane Trane sales personnel in the proper design and application of HVA HVAC C systems. As a LEED Accredited Professional, he has helped our customers and local offices on a wide range of LEED projects. His main areas of expertise include energy efficiency, dehumidification, dedicated outdoor‐air systems, air‐to‐air energy recovery recovery,, psychrometry,, and ventilation. psychrometry John is the author of numerous Trane Trane application manuals and Engineers Newsletters, and is a frequent presenter on Trane’s Trane’s Engineers Newsletter Live series of broadcasts. He also is a member of ASHRAE, has authored several articles for the ASHRAE Journal, and is a member of ASHRAE’s “Moisture Management in Buildings” and “Mechanical Dehumidifiers” technical committees. He was a contributing author of the Advanced E nergy Design Guide for K‐12 Schools and the Advanced Energy Design Guide for Small Hospitals and Health Care Facilities, and technical reviewer for The ASHRAE Guide for Buildings in Hot and Humid Climates. Paul Solberg | applications engineer | Trane A mechanical engineer from the University of Wisconsin at Platteville, Paul is a 35‐year veteran of Trane. Trane. He specializes in compressor and refrigeration systems, and has authored numerous Trane Trane publications on these subjects, including application manuals, engineering bulletins, and Engineers Newsletters. Paul served in the technical service and applications engineering areas at various var ious manufacturing locations, where he developed particular expertise supporting split systems, small packaged chillers, rooftop air conditioners, and other unitary products.

Engineers Engineers Newsletter Newsletter L ive

Dedic De dicate ated d Outdoor -Air Equipment Equipm ent

Ingersoll Rand

Dedicated Outdoor-Air Equipment

1.5 2

© 2011 Trane, a business of Ingersoll-Rand

Dedicated Dedicated Outdoor-Air Equipment © 201 2 011 1 Tra T rane ne,, a bus busines inessof Inge I ngerrsoll-Ra oll -Rand nd

1

Engineers Newsletter L ive

“Trane” is

a Registered Provider with The American Institute of Architects Continuing Education Systems. Credit earned on completion of this program will be . Completion for n on-AIA members available on request.

This program is r egistered with the AIA/CES for continuing professional education. As such, it does not includ e content that may be deemed or constru ed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of t his presentation.

3


Copyrighted Materials Thispresentation isprotected by U.S. and international copyr g t aws. epro uct on, str ut on, sp ay, an use o the presentation without written permission of Trane is prohibited. © 2011 Trane, a business of Ingersoll-Rand. All rights reserved.

4


Dedicated Outdoor-Air Equipment © 2011 Trane, a businessof Ingersoll-Rand

2


Learnin g Objectives 

Summarize the definition of a dedicated OA unit



Identify what leaving-air dew point isrequired







5

Summarize what the difference between cold versus neutral-temperature air Identify ASHRAE Standard 90.1 requirementsrelated to dedicated OA systems Identif s ecific dedicated OA e ui ment confi urations


Dedicated Outdoor -Air Equipment

Today’s Topics 

Definition of a dedicated OA unit • What leaving-air dew point s i required? • Cold versusneutral-temperature air?





6

ASHRAE 90.1 requirementsrelated to dedicated OA systems Specific dedicated OA equipment configurations



3


Today’s Presenters

John Murphy Ap plic ation s Engineer 7

Ronnie Moffitt Ap plic ation s Engineer

Paul Solberg Appl icati on s Engineer



Definition of a Dedic ated OA Unit


4


What is a Dedic ated OA Unit ? AHRI St and ard 920 (cu rr ent ly in developm ent ) “ separate sensible cooling system to satisfy th e entire building humidity load . The system issized to maintain a prescribed ventilation rate under any load condition. The ventilation rate can be constant or varied based on the building operation or occupancy schedule or in response to the actual occupancy. It may pre-conditio n outdoor air by containing an enthalpy wheel, sensible wheel, desiccant wheel, plate heat exchanger, heat pipesor other heat or masstransfer apparatus. It may reheat the ventilation air by containing a reheat refrigerant circuit, sensible wheel, heat pipe, or other heat or masstransfer apparatus.”

9


Satisfies entire building humidity (latent) load

May pre-condition outdoor air using air-to-air energy recovery

May reheat dehumidif ied ventilation air

dedicated OA unit

OA

Delivers prescribed (typically minimum) ventilation rate

EA

CA

CA

CA

SA

Operates in combination with a separate sensible cooling/heating system

10

SA

RA

RA



5


Dedicated OA Systems 

What leaving-air dew point isrequired? • Cooled, but not dehumidified • Cooled and dehumidified

11


example: k itchen

Cooled But Not Dehumi difi ed 180

OA

95°F DB 78°F WB

160

space 80°F DB 60% RH 65°F DPT CA 70°F DB 67°F DPT

140

OA

120

70

60

100

CA space

80 60

50

40

40 30

20

30

40

50

60

70

80

90

100

h u m i d i t y r a t i o , g r a i n s / l b o f d r y i r

75 70 65 60 55

d e w p o i n t t e m p e r a t u r e , ° F

50 40 30

110

dry-bulb temperature, °F

12



6


example: f an-coils , VAV, WSHPs, VRF

Cooled and Dehumidi fied

180

OA

95°F DB 78°F WB

160

space 75°F DB 60% RH 61°F DPT CA 52°F DB 52°F DPT

140

worst-case upper limit 70

OA

100 60

80

space

dry enough to remove space

50 40

120

CA

60 40


30 20

30

40

50

60

70

80

90

100

75 70 65 60 55


50 40 30

110


13


What Leaving -Air Dew Point is Requir ed? 









14

“Dedicated Outdoor-Air Ventilation Systems” Engineers Newsletter Live , "Designing Dedicated Outdoor-Air Systems," Trane application guide SYS-APG001-EN (2003) "Dedicated Ventilation Systems," Engineers Newsletter 30-3 (2001) Morris, W. 2003. “The ABCsof DOAS: Dedicated Outdoor Air Systems.” ASHRAE Journal (May) Murphy, J. 2006. “Smart Dedicated Outdoor Air Systems.” ASHRAE Journal (July)



7


example: chil led beams, radiant co oling

Cooled and Over-Dehumidified 180

OA

95°F DB 78°F WB

160 140

s pac e 75°F DB 50% RH 55°F DPT CA 55°F DB 45°F DPT

40

120 100 80

60

space

50

30

OA

to pr event 70 condensation

dry enough to remove space latent load

CA

60 40 20

30

40

50

60

70

80

90

100


75 70 65 60 55


50 40 30

110


15



What leaving-air dew point isrequired?



Cold versusneutral-temperature air?

16



8


dedicated OA system

OA

95°F DB 78°F WB

CA

71°F DB 52°F DPT

(“neutral” air) 180 160

(450 cfm)

RA

SA

140

74°F DB 50% RH 55°F DPT 55°F DB (1380 cfm)

OA

100 80

60

SA

local unit

50

RA

CA

40

40

50

60

60 40

1380 cfm 2.4 tons

30

30

120

70

70

80

90


70 65 60 55


50 40 30

20

100

75

110


17


dedicated OA system (“neutral” air) 180 160

sensible cooling

140

d

OA e

h u m i d i f i c a t i o n

70

60

CA

50

space

40 30

30

wasted cooling energy 40

50

60

70

120 100 80 60 40 20

80

90

100


75 70 65 60 55


50 40 30

110


18



9


dedicated OA system

OA

95°F DB 78°F WB

CA

52°F DB 52°F DPT

(“cold” air) 180 160

(450 cfm)

RA

SA

140

74°F DB 50% RH 55°F DPT 55°F DB

OA

100

(930 cfm)

80

60 local unit 50

40

RA

CA

40

50

60 40

930 cfm 1.6 ton s

30

30

120

70

60

70

80

90

20

100


75 70 65 60 55


50 40 30

110


19


CA 450 cfm at 52°F

cold-air system

930 cfm at 55°F

CA

SA

1380 cfm

RA

CA 450 cfm at 71°F 1380 cfm at 55°F

CA

SA

1830 cfm

20

neutral-air system

RA



10


Cold versus Neutral 

Lessoverall cooling capacity • Sensible cooling provided by cold conditioned OA reducesrequired cooling capacity of local HVAC units • Cooling (dehumidification) capacity of the dedicated OA unit isthe same in either case



Lessoverall cooling energy • Sensible cooling provided by cold conditioned OA re ucescoo ng requ re rom oca un s

21


Cold versus Neutral neutral to space/unit dedicated OA unit cooling capacity, tons reheat capacity, MBh fan airflow, cfm

local HVAC unit cooling capacity, tons fan airflow, cfm

22

cold to space

cold to local unit

3.4

3.4

3.4

9.3

0

0

450

450

450

2.4

1.6

1.6

1380

930

1380



11


Cold versus Neutral 

Lessoverall fan energy, if OA isdelivered cold or coo rec y o spaces • Cold conditioned OA removessome of the space sensible cooling load, which reducesthe airflow needed from local HVAC units • Airflow delivered by the dedicated OA unit si the same in either case

23


Won’t Delivering OA Cold Overcool the Space? Qs ,s

ace

Qs,ca

= 29,750 Btu/h (design load) = 1.085  450 cfm



(74°F – 52°F)

= 10,740 Btu/h

Space sensible cool ing l oad mus e o es gn before overcooling wil l occur!

24



12


When Should I Reheat Dehumi dif ied OA? 



Applicationswherespacesensible cooling loads differ grea y a any g ven me e.g., o es, orm or es To avoid overcooling at part-load conditions • Implement demand-controlled ventilation to reduce outdoor airflow aspopulation changes • Activate heat in the local HVAC unit (few zones, WSHP) • Reheat dehumidified air in dedicated OA unit (consider using recovery energy)

25


Reheating Dehumidified OA BAS

dedicated OA unit

OA EA

CA

CA

CA T

T

SA

local HVAC unit s

26

SA

RA

RA



13


When Should I Reheat Dehumi dif ied OA? 



Applicationswherespacesensible cooling loads differ grea y a any g ven me e.g., o es, orm or es To avoid overcooling at part-load conditions • Implement demand-controlled ventilation • Activate heat in the local HVAC unit • Reheat dehumidified air in dedicated OA unit





27

A

lications re uirin lower-than-normal dew oints

To avoid condensation when conditioned OA is delivered to the ceiling plenum



What leaving-air dew point isrequired?



Cold versusneutral-temperature air?



How will conditioned OA be delivered to spaces? • Directly to each space • To intake of each local unit • To supply-side of each local unit • To ceilin

28

lenum near each local unit



14



ASHRA E 90.1-2010 Requirements

ASHRA E 90.1 and Dedicated OA Systems 

Minimum equipment efficiencies



Fan power limitation



Economizer



Exhaust-air energy recovery



30

Limitation on simultaneous heating and cooling



15


Section 6.4.1, mandatory requirements

Minimum Equipment Efficiencies 

Currently there isno rating or certification standard or e ca e equ pmen , so . not list a minimum efficiency requirement

oes

“ 6.4.1.3 Equipm ent Not List ed. Equipment not listed in the tables referenced in Sections 6.4.1.1 and 6.4.1.2 may be used.” 

31

AHRI Standard 920 is under develo ment


Section 6.5.3.1, prescriptive requirements

Fan Power Lim itation 

What is a “ fan system” ? “fan system bhp: the sum of the fan brake horsepower (bhp) of all fans that are required to operate at fan system design conditions to supply air from the heating or cooling source to the conditioned space(s) and return it to the source or exhaust it to the outdoors” (Section 3.2)

32



16


example 6-DDD

User’s Manual f or 90.1-2010 QUESTION: A wing of an elementary school building si served by , single classroom. Ventilation air si supplied directly to each classroom by a dedicated outdoor-airsystem. Each classroom requires500 cfm of outdoor air, so the DOAS deliversthe total of 4000 cfm of conditioned outdoor air using a 5-hp fan. Doesthissystem need to comply with section 6.5.3.1?

ANSWER: Each WSHP is a se arate fan s s tem because each hasa separate cooling and heating source. The power of the DOAS fan must b e allocated to each heat pump on a cfm-weighted bassi.

33


example 6-DDD

User’s Manual f or 90.1-2010 

34



17



Fan Power Lim itation 

Only applies to fan systems> 5 hp



Each fan system shall not exceed: • Option 1: fan system motor nameplate hp • Option 2: fan system bhp



Exceptions: a. Health and safety (systemsmaintaining space-to-space pressure differences) b. Individual exhaust fans≤ 1 hp

35


Section 6.5.1, prescriptive requirements

Economizers

“ 6.5.1 Econo mizers. Each cooling system that has a fan the requirements of Sections 6.5.1.1 through 6.5.1.4.” 

Most notable exceptions: a. Cooling capacity < 54,000 Btu/hr (4.5 tons) b. Systemsthat use non-particulate air treatment d. Systemswith condenser heat recovery e. Residential with cooling capacity < 270,000 Btu/hr

36



18


If an Econo mizer is Required… 





Oversize the dedicated OA system to “provide up to o esgn supp y a r quan y a r or coo ng ” Include a second OA intake (path) for airside economizing Waterside economizing • Fan-coils, radiant cooling



37

Com l usin Ener Cost Bud et Section 10 method, rather than prescriptive requirements



Exhaust-Air Energy Recovery 

38

For dedicated (100%) OA systems, exhaust-air energy recovery srequ re on more sma er sysems or many climate zones.



19



Exhaust-Air Energy Recovery “…at least 50% energy recovery effectiveness. change in the enthalpy of the outdoor air supply equal to 50% of the difference between the outdoor air and return air enthalpies at design conditions.”

Be careful of this term!

RA

75°F DB 63°F WB 28.5 Btu/lb

OA 95°F DB 78°F WB 41.3 Btu/lb

39

h leaving ≤ 34.9

Btu/lb


ASHRAE Stan dar d 84 and AHRI Stand ard 1060

Effectiveness T

ṁOA

(h1 –

h2)

“total energy exchange rate”

ṁmin

(h1 –

h3)

“maximum energy exchange rate”

ṁEA h 4

h 3

h 1

h 2

ṁOA

40



20


different definitions o f effectiveness

Example of Unbalanced Airf lows 50% =

10,000 cfm

(41.3 –

h2)



8,000 cfm

(41.3 – 28.5)

h 1

h 3

= 41.3 Btu/lb

= 36.2 Btu lb

Does not meet ASHRAE 90.1

8,000 cfm

h 4

h

(ṁEA < ṁOA)

= 28.5 Btu/lb

h 2 ≤ 34.9

Btu/lb to meet ASHRAE 90.1

10,000 cfm

41


“As-Applied” vs. “Rated” Effectiveness 



Be careful not to confuse “as-applied” effectiveness requ re y . w “ra e ” e ec veness per AHRI 1060 Strive for balanced airflows • Bring back asmuch exhaust air aspossible

42



21


exhaust-air energy recovery

Using Restroom Exhaust

43


ASHRAE 62.1-2010

Recirculation of Restroom Exhaust “ 5.16.3.2.5. Class 2 air [which includes restrooms] shall not be . Exception: When using an energy recovery device, recirculation from leakage, carryover, or transfer from the exhaust side of the energy recovery device is permitted. Recirculated Class 2 air shall not exceed 10% of the outdoor air intake flow.” V4

V3

V3-to-2 OA V1

44

V2

EATR ≤ 10% Exhaust Air Transfer Ratio s i defined by ASHRAE Standard 84 and certified by AHRI Standard 1060



22


Section 6.5.2, prescriptive requirements

Simultaneous Heating and Cooling “ 6.5.2.3 Dehumidi ficati on. Where humidistatic controls , , mixing of hot and cold airstreams, or other means of simultaneous heating and cooling of the same airstream.” 

Exception A: “The system is capable of reducing supp ly air volume to 50% or less of the design airflow rate or the minimum outdoor air ventil ation rate spec ified in ASHRAE Standard 62.1 … whichever is larger, before simultaneous heating and cooling takes place.”



45

See example 6-TT, User’s Manual f or 90.1-2010



Specific Dedicated OA Equipment Configurations


23


dedicated outdoor-air equipment

Which Configuration is Best?

1) Dehumidification Duty

47

3) Efficiency Target


1

What is the Dehumidific ation Duty? infiltration

people ventilation

permeance space (indoor) latent loads

typical latent loads for a school classroom

48



source: Humidity Control Design Guide, ASHRAE © 2001, p. 278

24


what is the dehumidif ication duty?

Dehumidify Ventilation Air Only dedicated OA unit

OA EA

latent loads ventilation latent load

CA

• Dedicated OA unit r emoves latent

load due to ventilation CA

• Space latent loads mu st be

CA

removed by local unit s (any space SA

SA

RA

RA

49

local HVAC unit


Dehumidify Ventilation Air Only 180 160

80

140 120 70 100

60% RH = 60° 60°F DPT

60 50

30

30

Dedicated OA unit d elivers air at a 40 dew point close to desired space condition (does not remove any space latent loads) 40

50

60

70

50% RH = 55° 55°F DPT

80 60 40 20

80

90

100

h u m i d i t y r a t i o , g r a i n s / l b o f d r y a i r

75 70 65 60 55 50

d e w p o i n t t e m p e r a t u r e , °

40 30

110


50



25



Dehumi dify the Space (for Comfor t) dedicated OA unit

OA EA


CA

• Dedicated OA unit removes both CA

CA

SA

SA

RA

RA

51

ventilation and space latent loads (controls space humidity) • Local HVAC units need only

local HVAC unit


dehumidify the space (for comfo rt)

What Leaving-Air Dew Point is Requir ed? 55 F ° , t n i o p w e d r i a g n i v a l

Assumptions: • 200 Btu/h/person latent load • °

50 45 40 35 30 25 6

52

8

10 12 14 outdoor airflow, cfm/person

16

18



26


dehumidify the space (for comfo rt)

What Leaving-Air Dew Point is Requir ed? Assumptions: • 200 Btu/h/person latent load • °

55 F ° , t n i o p w e d r i a g n i v a e l

50 45 40 35

office

30 lecture hall

25 6

53

8

K-12 classroom

10 12 14 outdoor airflow, cfm/person

16

18


Dehumi dify to Space (for Comfort) 180 160

80

140 120 70 100

desired space condition

60

60

50 40

point drier than desired space condition (removes all space latent loads)

30

30

40

80

50

60

70

80

90

100

40 20


75 70 65 60 55 50


40 30

110


54



27



Dehumi dify the Space (for Condensation) dedicated OA unit

OA EA


CA

• Dedicated OA unit removes both CA

55

radiant cooling panels

ventilation and space latent loads (leaving-air DPT low enough to prevent condensation on local units)

CA

space sensible loads


Dehumi dify the Space (for Condensation) 180 160

80

140 120 70 100 80

60

desired space condition 50 40

low enough to prevent condensation on local cooling equipment

30

30

40

50

60

70

80

90

100

60 40 20


75 70 65 60 55 50


40 30

110


56



28



What is the Dehumidification Duty?

1

1) Dehumidification Duty • Dehumidify ventilation only • Dehumidifyspace (comfort) • Dehumidify space (condensation)

57


2 

What is the Cooli ng Duty?

Neutr al air • Remove the sensible ventilation load only



Cool air • Trim some of the space sensible cooling load



Cold air • Remove asmuch of the space sensible cooling load aspossible

58



29


what is the cooling duty?

Neutral A ir

dedicated OA unit



OA EA

CA

Dedicated OA unit delivers close to desired space condition • Doesnot remove any space sensible loads

CA

CA

SA

SA

SA

local HVAC uni t

SA

Space sensible loadsmust be removed b local coolin equipment

RARA

RARA

59





Cold A ir

dedicated OA unit



OA EA

Dedicated OA unit delivers cooler than the space • Removessome of the space sensible loads

CA



CA

CA

SA

Remainder of space sensible loadsremoved b local coolin e ui ment

SA

local HVAC unit RA

60

RA



30



Cool A ir

dedicated OA unit



OA EA

RA

SA

• Air s i reheated some before delivery

CA CA

local HVAC unit

Dedicated OA unit delivers cooler than the space

CA

• Removessome of the space sensible loads

RA

SA 

loadsremoved by local cooling equipment

61



2

What is the Cooli ng Duty?


2) Coolin g Duty • Neutral air • Cool air • Cold air

62



31


3 

What is the Efficiency Target?

Code or ASHRAE 90.1 mini mum • Meet the minimum requirementsof the local energy code or ASHRAE Standard 90.1



Higher level of efficiency • More efficient than the minimum requirements

63


4 

What is the Cooling Source?

Shared chil ler plant • Chiller plant that servesboth the dedicated outdoor-air equipment and the local cooling equipment



Dedicated chiller

air-cooled chiller

• Chiller that servesonly the dedicated outdoor-air equipment 

rec expans on

un

• Packaged or split • Air-cooled or water-cooled

64

packaged DX dedicated OA unit



32


many combinations … no silver bullet!

Financial Constraints? 1) Dehumidification Duty

3) Efficiency Target

• Dehumidify ventilation only • Dehumidifyspace (comfort) • Dehumidify space (condensation)

• Code / ASHRAE 90.1 minimum • Higher efficiency

$ 2) Coolin g Duty • Neutral air • Cool air • Cold air

65

• Shared chiller lant • Dedicated chiller • Direct expansion (DX)




66

4) Cooling Source

3 Efficienc Tar et • Code / ASHRAE 90.1 minimum • Higher efficiency

4) Cooling Source • Shared chiller plant • Dedicated chiller • Direct expansion (DX)



33


energy wheel + cooling coil

Dehumi dify Ventilation Only (Cold Air)

CC

OA'

EA'

57 F

EA 75 F DB 55% RH

67

OA OA' CC CA EA

coolin coil

CA

total-ener wheel

OA

59 F DB 57 F DPT

95 F DB 78 F WB 72 F DPT


95°F DB 72°F DPT 81°F DB 63°F DPT 57°F DB 57°F DPT 59°F DB 57°F DPT 75°F DB 55% RH 57°F DPT 50


Dehumidify Ventilation Only (Cold Air) 180 160

80

140

OA 70

100

CC

OA'

60

80

not dry enough EA to remove space a en oa

CA

40 30

30

120

60 40 20

40

50

60

70

80

90

100


80

75 70 65 60 55


50 40 30

110


68



34


OA OA' CC CA EA

95°F DB 72°F DPT 81°F DB 67°F DPT 57°F DB 57°F DPT 59°F DB 57°F DPT 75°F DB 71% RH 65°F DPT


Dehumidify Ventilation Only (Cold Air) 180 160

80

140

OA 70

CC

50

OA'

100

space latent load

EA

60

120

80 60

CA

40

40 30


20

30

40

50

60

70

80

90

100

80

75 70 65 60 55


50 40 30

110


69




70





35



Dehumi dify Space (Cold Air)

CC

OA'

EA'

46 F

EA

OA OA' CC CA EA

OA 95 F DB 78 F WB 72 F DPT


95°F DB 72°F DPT 81°F DB 63°F DPT 46°F DB 46°F DPT 48°F DB 46°F DPT 75°F DB 55% RH 57°F DPT CC 40

30

30

total-ener wheel

48 F DB 46 F DPT

75 F DB 55% RH

71

coolin coil

CA


Dehumidify Space (Cold Air ) 180 160

80

140

OA

120

70 100

OA'

60

space latent load

EA

50

80 60 40

CA 20

40

50

60

70

80

90

100


80

75 70 65 60 55


50 40 30

110


72



36



Dehumidify Space (Cool Air)

CC

OA'

EA'

46 F

EA

CA

OA OA' CC CA EA

coolin coil

total-ener wheel

OA

58 F DB 46 F DPT

75 F DB 55% RH

73

heatin coil



95°F DB 72°F DPT 81°F DB 63°F DPT 46°F DB 46°F DPT 58°F DB 46°F DPT 75°F DB 55% RH 57°F DPT CC


Dehumidify Space (Cool Air) 180 160

80

140

OA 70

100

OA'

60

40

80

space latent load

EA

50

20

reheat 40

50

60

60 40

CA

30

30

120

70

80

90

100


80

75 70 65 60 55


50 40 30

110


74



37


Consider Unoccupied Humidity Control “In humid climatesseriousl consider rovidin dehumidification during the summer, even if school isunoccupied, to prevent mold and mildew.” Chapter 7 (p. 7.3), 2011 ASHRAE Handbook—HVAC Applications

75



Dehumidify Space (Unoccup ied Mode)

CC

RA

76

reheat coil

coolin coil

total-ener wheel

OA dam ers closed

CA



38


OA

95°F DB 72°F DPT 81°F DB 63°F DPT 46°F DB 46°F DPT 58°F DB 46°F DPT 75°F DB 55% RH 57°F DPT

OA' CC CA EA


Dehumidify Space (Cool Air) 180

140

OA

100

OA'

60

40

80

space latent load

EA

reheat = co oling energy w asted 40

50

60 40

CA

30

30

120

70

50

CC

160

80

60

70

80

90

100

20


80

75 70 65 60 55


50 40 30

110


77


series air-to-air HX (with bypass) + coo ling coil

Dehumidify Space (Cool Air)

46 F air-to-air HX


CA

CA

heating co

OA'

CC cooling co

58 F DB 46 F DPT

78



39


OA OA' CC CA

95°F DB 72°F DPT 88°F DB 70°F DPT 46°F DB 46°F DPT 58°F DB 46°F DPT

series air-to-air HX + cooling coil


80

ypasses around HX

OA

100

pre-cooling

25% passes through HX

60

40

40

50

60

70

80

90

o f d r y a i r

20

recovered reheat energy 40

80 60

50

30

30

120

70

OA'

CC

140

h u m i d i t y r a t i o , g r a i n s / l b

100

80

75 70 65 60 55


50 40 30

110


79


Series Air-to-Air Devices (Cool Air) sensible effectiveness

pressure drop (per pass)

OA temp below which reheat is required*

heat pi pe

40%

0.5 in. H2O

76°F

coil loop

50%

0.5 in. H2O

70°F

fixed-plate HX

65%

0.5 in. H2O

64°F

* to achieve 58°F leaving dry-bulb temperature with 46°F dew point

80



40


OA 58 F

CA

46 F

CA

58 F DB 46 F DPT

cooling c oil + reheat (cool air) • Delivering conditioned OA at same dew point and dry bulb


58 F DB 46 F DPT

series HX + cooling coil • Dedicated OA unit • 13% lesscoolin ca acit • 12°F lessreheat • Local HVAC equipment • 13% more cooling capacity • 13% more airflow

82

OA

58 F DB 46 F DPT

series HX + cooling coil • 13% lesscooling capacity • 12 F lessreheat

81

58 F 46 F

48 F DB 46 F DPT

cooling co il + reheat (cold air) • Dedicated OA unit • 13% more coolin ca acit •

Local HVAC equipment • 13% lesscooling capacity • 13% lessairflow



41



2) Coolin g Duty


4) Cooling Source

• Neutral air • Cool air • Cold air

83

3 Efficienc Tar et

• Shared chiller plant • Dedicated chiller • Direct expansion (DX)


series air-to-air HX (without bypass) + coolin g coil

Dehumidify Space (Neutral Air) 46 F air-to-air HX


CA

CA

80 F heating co

OA'

CC cooling co

80 F DB 46 F DPT

84



42


OA OA' CC CA


series air-to-air HX + cooling coil

Dehumidify Space (Neutral Air) 180 160

80

140

OA

120

70 100 60

CC

pre-cooling

OA'

80 60

50

40

40 30

recovered reheat energy 30

40

50

60

70

80

90

100


20

80

75 70 65 60 55


50 40 30

110


85


Series Air-to-Air Devices (Neutral Air) sensible effectiveness

pressure drop (per pass)

OA temp below which reheat is required*

heat pi pe

40%

0.5 in. H2O

118°F

coil loop

50%

0.5 in. H2O

100°F

fixed-plate HX

65%

0.5 in. H2O

90°F

* to achieve 75°F leaving dry-bulb temperature with 46°F dew point

86



43


Parallel or Series?

energy wheel + cooling c oil (parallel) • Exhaust air si available for recovery • Deliver air at a cool or cold temperature • Recoverable reheat (if needed) energy s i available

87




88

series HX + cooling coil (series) • Exhaust air NOT available for recovery • Deliver air at a neutral temperature • Recoverable reheat energy s i NOT available





44


series desiccant wheel + cooling coil

Dehumi dify Space (Cool Air) heating coil

OA'

OA

CC

52 F


series es ccan wheel

CA

cooling co

58 F DB 46 F DPT

89

OA OA' CC CA





80

OA'

140

OA

120

70 100 80

60

CC

60

50

40

40

coolin g energy saved

30

20


80

75 70 65 60 55


50 40 30

reheat energy saved 30

40

50

60

70

80

90

100

110


90



45



2) Coolin g Duty


4) Cooling Source

• Neutral air • Cool air • Cold air

91

3 Efficienc Tar et

• Shared chiller plant • Dedicated chiller • Direct expansion (DX)



Dehumidify Space (Neutral Air) heating coil

OA'

OA

CC


reheat co

CA

series es ccan wheel

cooling co

75 F DB 46 F DPT

92



46


Parallel Pa rallel or o r Series?

energy wheel + cooling c oil (parallel) • Exha Exhau ust air air savailable si available for recovery • Deli Delive verr air air at a cool cool (or (or col cold) d) temperature • Reco Recove vera rabl ble e rehea reheatt (if nee neede ded) d) energy savailable s i available

93


1) Dehumidification Duty • Dehu Dehumidify midify vent ventilatio ilation n only • Dehumidifyspace (comfort) • Dehumidi Dehumidify fy space (conden (con densation)

2) Coolin g Duty • Ne Neut utra rall air • Co Cool ol ai air r • Co Cold ld ai air r

94

series desiccant desiccant + cooling co il (series) • Requ Requir ired ed lea leavi ving ng-a -air ir DPT < CHW temp temp + 5 F • Deli Delive verr air air at a coo cooll temperature • Reco Recove vera rabl ble e rehe reheat at energy sNOT s i NOT available

3 Ef f i c i en c Tar et • Code / ASHR ASHRAE AE 90.1 90.1 minimum minimum • Highe Higherr effi efficienc ciency y

4) Cooling Cooling Source • Shared Shared chille chillerr plant plant • Ded Dedica icated ted chille chiller r • Direct expansion (DX)



47


total-energy total-e nergy wheel + cooling coil + coil l oop

Dehumi De humi dify Spa Space ce (Cool (Cool Air) Ai r)

EA'

EA''

OA'

CC 46 F coil l o op

EA

OA OA ' CC CA EA

EA '

OA 95 F DB DB 78 F WB WB 72 F DPT DPT

58 F DB DB 46 F DPT DPT


95°F DB 72°F DPT 75°F DB 62°F DPT 46°F DB 46°F DPT 58°F DB 46°F DPT 75°F DB 55% RH 57°F DPT 63°F DB 57°F DPT CC

energy wheel wheel + cooling coil + coil loop


80

140

OA

120

70 100

OA'

60

EA'

50

40

80 60

EA

40

CA

30

30

t o t al -en er g y w h eel

CA

75 F DB DB 55% RH

95

cooling coil

20

40

50

60

70

80

90

100


80

75 70 65 60 55


50 40 30

110


96



48


total-energy total-e nergy wheel + coolin g co il + fixed-plate HX HX

Dehumi De humi dify Spa Space ce (Cool (Cool Air) Ai r) 68 F

EA'

fixed-plate HX

cooling coil

CA 70 F DB DB 46 F DPT DPT

97

EA''

OA'

CC

total-energy w h eel

OA 95 F DB DB 78 F WB WB 72 F DPT DPT

EA 75 F DB DB 55% RH


total-energy total-e nergy wheel + coolin g coil + parallel parallel desiccant wheel

Dehumi De humi dify Spa Space ce (Cool (Cool Air) Ai r) 95 F DB 78 F WB WB 72 F DPT DPT

cooling coil

OA

reheat coil

CC

OA'

CA

51 F

55 F DB DB 46 F DPT DPT

EA' 70 F DB DB 72% RH total-energy wheel

EA''

desiccant wheel

EA 75 F DB 55% RH

98



49


OA OA' CC CA EA

EA'

95°F DB 72°F DPT 78°F DB 65°F DPT 51°F DB 51°F DPT 55°F DB 46°F DPT 75°F DB 55% RH 57°F DPT 70°F DB 61°F DPT

energy wheel + cooling coil + parallel desiccant wheel


140

OA

120

70 100

OA'

60

EA'

50 40

160

80

80 60

EA

CC

40

30

30


50

60

70

80

90

100

75 70 65 60 55


50 40 30

20

40

80

110


99

OA OA' CC CA EA

EA'


72°F DB 68°F DPT 71°F DB 62°F DPT 51°F DB 51°F DPT 55°F DB 46°F DPT 75°F DB 55% RH 57°F DPT 70°F DB 61°F DPT

energy wheel + cooling coil + parallel desiccant wheel


140 120 70

OA 100

OA'


60

EA'

50 40

160

80

80 60

EA

CC

40


30

20


80

75 70 65 60 55


50 40 30


40

50

60

70

80

90

100

110


100



50


total-energy wheel + coolin g coil + parallel desiccant wheel

Dehumi dify Space (Cool Air) 95 F DB 78 F WB 72 F DPT

cooling coil

OA

reheat coil

CC

OA'

CA

51 F

55 F DB 46 F DPT

EA' 70 F DB 72% RH

101

desiccant wheel para e

total-energy wheel

EA''

EA 75 F DB 55% RH


total-energy wheel + coolin g coil + series desiccant wheel

Dehumi dify Space (Cool Air) 95 F DB 78 F WB

desiccant wheel (series)

OA OA'

OA'' CC

total-energy wheel

EA'

EA 75 F DB 55% RH

102

CA

reheat coil

cooling coil

57 F DB 46 F DPT



51


OA

95°F DB 72°F DPT OA' 81°F DB 63°F DPT OA'' 77°F DB 67°F DPT CC 52°F DB 52°F DPT CA 57°F DB 46°F DPT EA 75°F DB 55% RH 57°F DPT

energy wheel + cooling coil + series desiccant wheel


140

OA 70

120

OA''

100

OA'

60

80 60

EA

50 40

160

80

CC

40

30

30


50

60

70

80

90

100

75 70 65 60 55


50 40 30

20

40

80

110


103


OA

72°F DB 68°F DPT OA' 74°F DB 62°F DPT OA'' 70°F DB 64°F DPT CC 51°F DB 51°F DPT CA 55°F DB 46°F DPT EA 75°F DB 55% RH 57°F DPT

energy wheel + cooling coil + series desiccant wheel


140 120 70

OA coolin g energy saved

OA'' 60

100 80

OA'

60

EA

50 40

160

80

CC

40


30

20


80

75 70 65 60 55


50 40 30


40

50

60

70

80

90

100

110


104



52


energy wheel + coolin g coil + downstream desiccant wheel

Parallel vs. Series

180 160

80

parallel series

140

OA 70

120

OA'' OA'

OA'

60

100 80 60

50

CC

40 30

40


CA 20

30

40

50

60

70

80

90

100

80

75 70 65 60 55


50 40 30

110


105



Parallel vs. Series

parallel

series

cooling coil load

leaving-air conditions

outdoor air conditions

52 tons

55°F DB 46°F DPT

95°F DB 48% RH

46°F DPT

88% RH

55°F DB 46°F DPT

60°F DB 95% RH

ons 23 tons

106

cooling coil load

leaving-air conditions

49 tons

57°F DB 46°F DPT

ons 46°F DPT 32 tons

55°F DB 46°F DPT



53



Parallel vs. Series

desiccant w heel in parallel • Better on mild, humid days • Horizontal duct connections

107




108

desiccant wheel in s eries • Better on hot and warm days • Ratio of EA/OA flows< 0.9 • High external static pressures





54


Dedicated OA Cooli ng Sources Dew Point of Condition ed Outdoor Air (CA) °

°

°

°

°

°

Dew point required 60% space RH 50% space RH Dew point capability packaged DX

chill er + AHU specialty dehumidifier

109


considerations for

Packaged DX Dedicated OA Equipm ent 



Air-cooled or water-cooled condensing Required leaving-air dew point • Reheat only asmuch asnecessary • Cool or cold air reducescapacity of local equipment


110



55


Packaged vs. Split DX Packaged DX Unit 

-



Laboratory tested



Smaller footprint



111

Split DX System

Integral reheat and hot gasbypass

specific application 

Potentially long line lengths (and more refrigerant)



Difficult reheat design



Indoor or outdoor location



HGBP line length



Oil management


DX Compressor Unloading 

Single, on/off compressor



Single, unloading compressor (including pulsed)



Single, variable-speed compressor



Manifolded, on/off compressors



Manifolded compressors, one unloading



Manifolded compressors, one variable speed

112



56


ASHRAE Stan dar d 90.1-2010

Hot Gas B ypass

“ 6.5.9 Hot Gas Byp ass Limit ation. Cooling systems pressure control systems unless the system is designed with multiple steps of unloading or continuous capacity modulation. The capacity of the hot gas bypass shall be limited as indicated in Table 6.5.9.”

113


hot gas reheat

Refrigerant Heat Recovery 

Prudent to use recovered heat for reheat



Deliver conditioned outdoor cold, if possible



For a split DX system: • Design reheat coil for little reheat • Actively control head pressure • Pay particular attention to oil management

114



57


Split DX System Selection Assumptions: • 200 Btu/h/person latent load • °

18 16 14 12 10 8 6

35

115

40 45 saturated suction temperature, °F

50


Chilled-Water DOAS 





116

Standalone or shared chiller Air-cooled or water-cooled Indoor or outdoor equipment



58


Benefits of Chilled-Water DOAS 

Can achieve lower dew points



Wider operating envelope •

spec a y w en usng var a e a r ow

• DX equipment often requires hot gasbypass(energy waste) 

Greater flexibility and efficiency • Fans, air cleaning, energy recovery, desiccant wheel, airflow measurement, ice storage, potential to eliminate HGBP



Certified performance • AHRI, UL, ETL • No AHRI certification for DX dedicated OA units (EER’stypically not published)



117

Reduced refrigerant charge


air-handling un it OA CA Vreheat

n r u t e r p o l

y l p p u s p o o l

w a er- o -w a er heat pump Psource

118

Pload source-side heat exchanger

load-side heat exchanger



59


air-handling un it OA CA

n r u t e r p o l

y l p p u s p o o l

a r-coo e chiller Psource

119


120



evaporator

60



Summary


Which Configuration is Best? e um

ca on

uy

• Dehumidify ventilation only • Dehumidifyspace (comfort) • Dehumidify space (condensation)

2) Coolin g Duty • Neutral air • Cool air •

122

3) Efficiency Target • Code / ASHRAE 90.1 minimum • Higher efficiency

4) Cooling Source • Shared chiller plant • Dedicated chiller •



61



Which Configuration is Best? 1

+

2 +

3

+

4

= no silver bullet!


indoor air-handling u nit

outdoor air-handling un it 123


references for this broadcast

Where to L earn More

www.trane.com/EN

124



62


LEED Continuing Education Cours es on-demand, no charg e, 1.5 CE credits 

ASHRAE Standards62.1 and 90.1 an ysems



ASHRAE standard 62.1: Ventilation Rate Procedure



ASHRAE 90.1-2010





Energy Saving Strategiesfor Rooftop VAV Systems Air-Handing Systems, Energy and IAQ





Ice Storage Design and Control

www.trane.com/Continuin gEducation 125


watch past broadcasts

ENL Archiv es

Insightful topicson HVAC system design: • Chilled-water plants • Air distribution • Refrigerant-to-air systems • Control strategies • Industry standardsand LEED • Energy and the environment • Acoustics • Ventilation • Dehumidification

www.trane.com/ENL

126



63


2012 ENL Programs 

March g er ormance reen u ngs: ASHRAE Standard 189.1-2011



e mpac o

June Heat Pump Systems



October Air-to-Air Energy Recovery

127



Supplemental Slides


64


Dedicated OA System Configurations Conditioned OA delivered… 1. Directly to each zone 2. To intake of each local unit 3. To supply-side of each local unit 4. To ceiling plenum, near each local unit

129


condit ioned OA delivered

Directly to Each Zone OA

OA unit CA

CA

CA

SA

SA

RA

130

• fan-coil • WSHP • PTAC • passive chilled beams • radiant cooling panels

RA



65


conditi oned OA delivered

Directly to Each Zone Advan tag es 







131

Drawbacks

Easier to ensure required outdoor airflow reacheseach zone (separate diffusers) Opportunity to cycle off local fan because OA isnot distributed through it





Allowsdedicated OA system to operate during unoccupied periodswithout needing to operate local fans

Requiresinstallation of additional ductwork and separate diffusers May require multiple diffusers to ensure that outdoor air is adequately dispersed throughout the zone

Opportunity to downsize local equipment (if OA delivered cold)



To Intake of Local HVAC Equipment OA

OA unit CA

SA

132

RA

RA

SA

• fan-coil • WSHP • small RTU • VRF



66



To Intake of Local HVAC Equip ment Advan tag es 





133

Drawbacks

Helpsensure required OA reacheseach zone ducted directly to each unit)



Avoidscost andspace to install additional ductwork and separate diffusers



Easier to ensure that OA is adequately dispersed throughout zone because it si distributed by local fan





Measurement and balancing s i more difficult than if OA delivered directly to zone Typically requiresfieldfabricated plenum to connect OA duct to mix with RA Local fan must operate continuously to provide OA during scheduled occupancy Local fan must operate if dedicated OA system operates during unoccupied period



To Supply-Side of Local HVAC Equipment OA

OA unit CA CA

• fan-coil • WSHP • small RTU RA

SA

SA

RA

direct to spaces

134



67



To Supply-Side of L ocal HVAC Equipment Advan tag es 







135

Drawbacks

Helpsensure required OA reacheseach zone ducted directly to each unit)



Avoidscost andspace to install additional ductwork and separate diffusers



Easier to ensure that OA is adequately dispersed throughout zone because it si distributed by local fan

Measurement and balancing s i more difficult than if OA delivered directly to zone Local fan typically must operate continuously to provide OA during scheduled occupancy (unlesspressureindependent VAV terminal)

Opportunity to downsize local equipment (if OA delivered cold)



To Plenum, Near Loc al HVAC Equipment OA

OA unit CA

• fan-coil • WSHP • VRF SA

136

RA

RA

SA



68

ENL DedicatedOAEquipmentOD

Recommend Documents