Airflow Analysis of a Custom Green Air Handling Unit Without a - - PowerPoint PPT Presentation

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Airflow Analysis of a Custom Green Air Handling Unit Without a - - PowerPoint PPT Presentation

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Airflow Analysis of a Custom Green Air Handling Unit Without a Pre-heater Performed by M/E Engineering The CAES Group 22 June 2010 Background Two years ago, a pharmaceutical client finished construction on a new LEED certified

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SLIDE 1

Airflow Analysis of a Custom “Green” Air Handling Unit Without a Pre-heater

Performed by M/E Engineering The CAES Group

22 June 2010

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SLIDE 2

Background

  • Two years ago, a pharmaceutical client finished construction on a new

LEED certified building in New England.

  • The facility’s air handlers were custom-fabricated and employed

economizers without pre-heaters upstream of the water-based coils.

  • Without pre-heaters, the air handlers were much more energy efficient.
  • The air handler manufacturer believed that their design was capable of

adequately mixing warm RETURN air with 30% cold OUTSIDE air effectively enough to prevent coil freezing.

  • During the first year of operation, freezestat alarms shut most of the

units down during several cold winter days.

  • The client asked that we model their air handlers to:

– Understand the issues with the current design, and – Provide them with a redesign that would be immune to cold climatic conditions.

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Case 1: Parameters

  • Star CCM+ software was used to model an Economizer/Air Handling

Unit installed on a LEED silver certified building in the pharmaceutical industry.

  • Given Values:

– Air Flow CFM = 51,100 CFM – 30% Outside Air and Temperature = 0ºF – Supply Air Temperature Target = 55ºF

  • Assumptions:

– Return Air Temperature = 70ºF

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SLIDE 4

Custom Air Handler without Pre-Heating Geometric Elevation View

(Visualization Only) Return Fan Supply Fan Actual CFD Model Humidifier Spray Nozzles Pre-Filters Cooling Coils Blenders Return Air Enters Outside Air Enters Case 1

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SLIDE 5

Custom Air Handler without Pre-Heating Geometric Plan View

Supply Fan Humidifier Spray Nozzles Pre-Filters Cooling Coils Blenders Outside Air Enters Supply Fan Motor Case 1

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SLIDE 6

Custom Air Handler without Pre-Heating Geometric Elevation View

Supply Fan Humidifier Spray Nozzles Pre-Filters Cooling Coils Blenders Outside Air Enters Return Air Enters Case 1

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SLIDE 7

Custom Air Handler without Pre-Heating Geometric Isometric View

Supply Fan Humidifier Spray Nozzles Pre-Filters Cooling Coils Blenders Outside Air Enters Return Air Enters Case 1

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SLIDE 8

Custom Air Handler without Pre-Heating Pathlines Isometric View

Case 1

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Custom Air Handler without Pre-Heating Pathlines Plan View

Pre-Filters Cooling Coils Blenders Humidifier Spray Nozzles Case 1

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Custom Air Handler without Pre-Heating Pathlines Elevation View

Pre-Filters Cooling Coils Blenders Humidifier Spray Nozzles Case 1

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SLIDE 11

Custom Air Handler without Pre-Heating Temperature Contour – Isometric View

Cut Plane approx. thru center of AHU Case 1

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SLIDE 12

Custom Air Handler without Pre-Heating Temperature Contour – Side Elevation View

Cooling Coils Case 1

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Custom Air Handler without Pre-Heating Relative Pressure Contour – Side Elevation View

∆P =0.23 in WG ∆P =0.48 in WG P ≈ 0 in WG Case 1

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SLIDE 14

Custom Air Handler without Pre-Heating Velocity Vectors – Side Elevation View

Pre-Filters Cooling Coils Blenders Humidifier Spray Nozzles Case 1

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Custom Air Handler without Pre-Heating Velocity Vectors – Close up Side Elevation View

Pre-Filters Cooling Coils Blenders Humidifier Spray Nozzles Case 1

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SLIDE 16

Custom Air Handler without Pre-Heating Speed Contour & Velocity Vectors – Side Elevation View

Pre-Filters Cooling Coils Blenders Humidifier Spray Nozzles Case 1

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SLIDE 17

Custom Air Handler without Pre-Heating Cooling Coil Face Temperature – Isometric View

Pre-Filters Cooling Coils Blenders Humidifier Spray Nozzles Case 1

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Custom Air Handler without Pre-Heating Cooling Coil Face Temperature – Front Elevation View

Cooling Coils (min & max values) Case 1

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SLIDE 19

Cooling Coils (cold spots below 35°F)

Custom Air Handler without Pre-Heating Cooling Coil Face Temperature – Front Elevation View

Case 1

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Custom Air Handler without Pre-Heating Cooling Coil Face Temperatures at Various Heights

Bottom Coil Middle Coil Top Coil Case 1

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Custom Air Handler without Pre-Heating Pre-Filter Face Air Speed – Isometric View

Pre-Filters Cooling Coils Blenders Humidifier Spray Nozzles Case 1

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SLIDE 22

Pre-Filters

Custom Air Handler without Pre-Heating Pre-Filter Face Air Speed – Front Elevation View

Case 1

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SLIDE 23

Estimated Supply Temperature with perfect mixing

70% Return & 30% Outside Air

Case 1

Estimated supply discharge temperature

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Conclusions

  • The model shows that there’s still a probability of the top cooling coil

to freeze compared to a design without blenders. – The temperatures in the supply chamber range from 65ºF down to 26ºF, with an average discharge temperature of 44ºF. – A simple mixing model calculates the discharge temperature at 49.2°F. (assuming perfect mixing)

Case 1

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Case 2: Parameters

  • Star CCM+ software was used to model the Economizer.
  • Given Values:

– Air Flow CFM = 51,100 CFM – 30% Outside Air and Temperature = 0ºF – Supply Air Temperature Target = 55ºF

  • Assumptions:

– Return Air Temperature = 70ºF

  • Modified Blender location and interior wall.
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SLIDE 26

Custom Air Handler without Pre-Heating Geometric Elevation View

Supply Fan Humidifier Spray Nozzles Pre-Filters Cooling Coils New Location for Blenders Outside Air Enters Return Air Enters Modified interior wall Case 2

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SLIDE 27

Custom Air Handler without Pre-Heating Geometric Isometric View

Supply Fan Humidifier Spray Nozzles Pre-Filters Cooling Coils Outside Air Enters Return Air Enters New Location for Blenders Modified interior wall Case 2

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SLIDE 28

Custom Air Handler without Pre-Heating Temperature Contour – Side Elevation View

Cooling Coils Case 2

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SLIDE 29

Custom Air Handler without Pre-Heating Cooling Coil Face Temperature – Front Elevation View

Cooling Coils (min & max values) Case 2

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Cooling Coils (cold spots below 35°F)

Custom Air Handler without Pre-Heating Cooling Coil Face Temperature – Front Elevation View

Case 2

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Custom Air Handler without Pre-Heating Cooling Coil Face Temperatures at Various Heights

Bottom Coil Middle Coil Top Coil 35° Case 2

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SLIDE 32

Estimated Supply Temperature with perfect mixing

Case 2

70% Return & 30% Outside Air Estimated supply discharge temperature

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SLIDE 33

Conclusions – Case 2

  • This Economizer model shows that there’s still a probability of the

cooling coils to freeze. – The temperatures in the supply chamber range from 63ºF down to 26ºF, with an average discharge temperature of 43ºF. – Temperature distribution at coil faces was shifted to slightly higher temperatures.

Case 2

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SLIDE 34

Case 3: Parameters

  • Star CCM+ software was used to model the Economizer.
  • Given Values:

– Air Flow CFM = 51,100 CFM – 30% Outside Air and Temperature = 0ºF – Supply Air Temperature Target = 55ºF

  • Assumptions:

– Return Air Temperature = 70ºF

  • Moved the Blender down 5” from the floor.
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SLIDE 35

Custom Air Handler without Pre-Heating Geometric Elevation View

Supply Fan Humidifier Spray Nozzles Pre-Filters Cooling Coils New Location for Blenders

(5” from floor)

Outside Air Enters Return Air Enters Case 3

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SLIDE 36

Custom Air Handler without Pre-Heating Geometric Isometric View

Supply Fan Humidifier Spray Nozzles Pre-Filters Cooling Coils Outside Air Enters Return Air Enters New Location for Blenders

(5” from floor)

Case 3

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SLIDE 37

Custom Air Handler without Pre-Heating Temperature Contour – Side Elevation View

Cooling Coils Case 3

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SLIDE 38

Custom Air Handler without Pre-Heating Cooling Coil Face Temperature – Front Elevation View

Cooling Coils (min & max values) Case 3

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SLIDE 39

Cooling Coils (cold spots below 35°F)

Custom Air Handler without Pre-Heating Cooling Coil Face Temperature – Front Elevation View

Case 3

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SLIDE 40

Custom Air Handler without Pre-Heating Cooling Coil Face Temperatures at Various Heights

Bottom Coil Middle Coil Top Coil 35° Case 3

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SLIDE 41

Case 3 Case 2 Case 1

Custom Air Handler without Pre-Heating Cooling Coil Face Temperature – Front Elevation View Comparison of Surface Areas below 35°F

Case 3

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SLIDE 42

Estimated Supply Temperature with perfect mixing

Case 3

70% Return & 30% Outside Air Estimated supply discharge temperature

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Conclusions

  • This Economizer model shows that there’s still a probability of the

cooling coils to freeze. – The temperatures in the supply chamber range from 58ºF down to 28ºF, with an average discharge temperature of 43ºF.

  • SUGGESTED DESIGN CHANGE

– Place vanes beneath the outside air damper to skew the cold air flow rightward.

Case 3

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SLIDE 44

Case 4: Parameters

  • Star CCM+ software was used to model the Economizer.
  • Given Values:

– Air Flow CFM = 51,100 CFM – 30% Outside Air and Temperature = 0ºF – Supply Air Temperature Target = 55ºF

  • Assumptions:

– Return Air Temperature = 70ºF

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SLIDE 45
  • Kept the Blender 5” from the floor
  • Added 9” deep vanes below the outside air damper. (6” gap between

damper and top of vanes, half of the vanes are at 45º to the outside side walls with the middle vane placed vertically. All vanes are evenly spaced 1ft apart under the Outside Damper.

  • Added a perturbation airfoil that starts 6” above the opening of the

blenders, protrudes 10 inches upstream and angles back at a 45º to the

  • wall. This perturbation airfoil extends laterally wall to wall above the
  • penings of the blenders.

Case 4: Parameters

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SLIDE 46

Custom Air Handler without Pre-Heating Geometric Side Elevation View

Pre-Filters Cooling Coils Outside Air Enters Return Air Enters Case 4 Blenders Added Vanes Perturbation Airfoil

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Custom Air Handler without Pre-Heating Geometric Front Elevation View

Outside Air Damper Return Air Damper Case 4 Added 9” Vanes @ 45 º

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Custom Air Handler without Pre-Heating Geometric Isometric View

Supply Fan Humidifier Spray Nozzles Blenders Cooling Coils Outside Air Enters Return Air Enters Case 4 Added Vanes Pre-Filters Perturbation Airfoil

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Custom Air Handler without Pre-Heating Temperature Contour – Side Elevation View

Cooling Coils Case 4

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Custom Air Handler without Pre-Heating Cooling Coil Face Temperature – Front Elevation View

Cooling Coils (min & max values) Case 4

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Custom Air Handler without Pre-Heating Cooling Coil Face Temperatures at Various Heights

Bottom Coil Middle Coil Top Coil 35° Case 4

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Custom Air Handler without Pre-Heating Relative Pressure Contour – Side Elevation View

∆P =0.26 in WG ∆P =0.48 in WG Case 4 ∆P =0.33 in WG P ≈ 0 in WG

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SLIDE 53

Estimated Supply Temperature with perfect mixing

Case 4

70% Return & 30% Outside Air Estimated supply discharge temperature

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SLIDE 54

Conclusions

  • With the added vanes before the Blenders increases the cooling coil

face temperature up to 35ºF.

  • Still a small possibility that the cooling coils might freeze on the lower

right cooling coil.

  • Recommend mirroring the blade rotation of the right blender to create

a more even temperature distribution on the cooling coils.

Case 4

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SLIDE 55

Case 5: Parameters

  • Star CCM+ software was used to model the Economizer.
  • Given Values:

– Air Flow CFM = 51,100 CFM – 30% Outside Air and Temperature = 0ºF – Supply Air Temperature Target = 55ºF

  • Assumptions:

– Return Air Temperature = 70ºF

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SLIDE 56

Case 5: Parameters

  • Kept the Blender 5” from the floor
  • Kept the vanes below the outside air damper.
  • Kept the perturbation airfoil.
  • Mirrored the right blender (when looking downstream towards the

supply fan in the air handling unit.)

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SLIDE 57

Custom Air Handler without Pre-Heating Geometric Side Elevation View

Pre-Filters Cooling Coils Outside Air Enters Return Air Enters Case 5 Blenders Vanes Perturbation Airfoil

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Custom Air Handler without Pre-Heating Geometric Isometric View

Supply Fan Humidifier Spray Nozzles Blenders Cooling Coils Outside Air Enters Return Air Enters Case 5 Vanes Pre-Filters Mirrored Blender Perturbation Airfoil

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Custom Air Handler without Pre-Heating Geometric Isometric View

Blenders Outside Air Enters Return Air Enters Case 5 Vanes Pre-Filters Mirrored Blender Perturbation Airfoil

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Custom Air Handler without Pre-Heating Temperature Contour – Side Elevation View

Cooling Coils Case 5

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Custom Air Handler without Pre-Heating Cooling Coil Face Temperature – Front Elevation View

Cooling Coils (35º - max value) Case 5

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Bottom Coil Middle Coil Top Coil Case 5

Custom Air Handler without Pre-Heating Cooling Coil Face Temperatures at Various Heights

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Custom Air Handler without Pre-Heating Relative Pressure Contour – Side Elevation View

∆P =0.22 in WG ∆P =0.41 in WG Case 5 ∆P =0.40 in WG P ≈ 0 in WG

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SLIDE 64

Estimated Supply Temperature with perfect mixing

Case 5

70% Return & 30% Outside Air Estimated supply discharge temperature

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Conclusions

  • With the added vanes below the outside air damper, a perturbation

airfoil and mirrored rotation of one blender, this model shows that the minimum temperature across the cooling coil is calculated to be 42ºF.

  • The average supply temperature discharge is calculated to be 46ºF

whereas the theoretical perfect mixing case would be 49.24°F.

  • An added bonus to this design shows that the mirrored blender

enhances the temperature distribution on the cooling coils to be more symmetrical left to right.

Case 5

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Case 6: Parameters

  • Star CCM+ software was used to model the Economizer.
  • Given Values:

– Air Flow CFM = 51,100 CFM – 20% Outside Air and Temperature = 0ºF – Supply Air Temperature Target = 55ºF

  • Assumptions:

– Return Air Temperature = 70ºF

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SLIDE 67

Case 6: Parameters

  • Kept the Blender 5” from the floor
  • Kept the vanes below the outside air damper.
  • Kept the perturbation airfoil.
  • Kept the mirrored right blender (when looking down towards the

supply fan in the air handling unit.)

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SLIDE 68

Custom Air Handler without Pre-Heating Geometric Side Elevation View

Pre-Filters Cooling Coils 20% Outside Air Enters Return Air Enters Case 6 Blenders Vanes Perturbation Airfoil

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Custom Air Handler without Pre-Heating Geometric Isometric View

Supply Fan Humidifier Spray Nozzles Blenders Cooling Coils 20 % Outside Air Enters Return Air Enters Case 6 Vanes Pre-Filters Mirrored Blender Perturbation Airfoil

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Custom Air Handler without Pre-Heating Temperature Contour – Side Elevation View

Cooling Coils Case 6

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Custom Air Handler without Pre-Heating Cooling Coil Face Temperature – Front Elevation View

Cooling Coils (35º - max value) Case 6

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Bottom Coil Middle Coil Top Coil Case 6

Custom Air Handler without Pre-Heating Cooling Coil Face Temperatures at Various Heights

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Custom Air Handler without Pre-Heating Relative Pressure Contour – Side Elevation View

∆P =0.22 in WG ∆P =0.40in WG Case 6 ∆P =0.38 in WG P ≈ 0 in WG

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SLIDE 74

Estimated Supply Temperature with perfect mixing

Case 6

80% Return & 20% Outside Air Estimated supply discharge temperature

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SLIDE 75

Conclusions

  • With the added vanes below the outside air damper, a perturbation

airfoil and mirrored rotation of one blender, this model shows that the minimum temperature across the cooling coil is calculated to be 47ºF.

  • The average supply temperature discharge is calculated to be 55ºF.

Case 6

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SLIDE 76

Case 7: Parameters

  • Star CCM+ software was used to model the Economizer.
  • Given Values:

– Air Flow CFM = 51,100 CFM – 50% Outside Air and Temperature = 35ºF – Supply Air Temperature Target = 55ºF

  • Assumptions:

– Return Air Temperature = 70ºF

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SLIDE 77

Case 7: Parameters

  • Kept the Blender 5” from the floor
  • Kept the vanes below the outside air damper.
  • Kept the perturbation airfoil.
  • Kept the mirrored right blender (when looking down towards the

supply fan in the air handling unit.)

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SLIDE 78

Custom Air Handler without Pre-Heating Geometric Side Elevation View

Pre-Filters Cooling Coils 50% Outside Air Enters @ 35ºF Return Air Enters Case 7 Blenders (5” above floor) Vanes Perturbation Airfoil

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SLIDE 79

Custom Air Handler without Pre-Heating Geometric Isometric View

Supply Fan Humidifier Spray Nozzles Blenders Cooling Coils 50 % Outside Air Enters @ 35ºF Return Air Enters Case 7 Vanes Pre-Filters Mirrored Blender Perturbation Airfoil

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SLIDE 80

Custom Air Handler without Pre-Heating Temperature Contour – Side Elevation View

Cooling Coils Case 7

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Custom Air Handler without Pre-Heating Cooling Coil Face Temperature – Front Elevation View

Cooling Coils (35º - max value) Case 7

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SLIDE 82

Bottom Coil Middle Coil Top Coil Case 7

Custom Air Handler without Pre-Heating Cooling Coil Face Temperatures at Various Heights

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SLIDE 83

Estimated Supply Temperature with perfect mixing

Case 7

50% Return & 50% Outside Air Estimated supply discharge temperature

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Conclusions

  • With the added vanes below the outside air damper, a perturbation

airfoil and mirrored rotation of one blender, this model shows that the minimum temperature across the cooling coil is calculated to be 52ºF.

  • The average supply temperature discharge is calculated to be 52ºF.

Case 7

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Summary

  • Four air handler design variations were evaluated for their resistance to

coil freezing.

  • The proportion of outside air was also evaluated at 20%, 30% and 50%

at two temperatures.

  • The final design variation shows very good resistance to freezing down

to temperatures of 0 °F (-18°C) and below.

  • The new design was implemented on all but one air handler at the

facility.

  • Last winter’s operation saw no freeze-stat alerts for the retrofitted

equipment, but several shutdowns for the unaltered unit.